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655b45b0 | 1 | \documentclass[11pt]{article} |
9e3855d0 | 2 | \renewcommand{\rmdefault}{ptm} |
3 | \usepackage{mathptmx} | |
655b45b0 | 4 | \usepackage[margin=2cm,twoside,a4paper]{geometry} |
5 | \usepackage{amstext} | |
6 | \usepackage{amsmath} | |
7 | \usepackage[ruled,vlined,linesnumbered]{algorithm2e} | |
ffa07380 | 8 | \usepackage{graphicx} |
9 | \usepackage{color} | |
10 | \usepackage{units} | |
11 | \usepackage{listings} | |
56bd6baf | 12 | \usepackage[colorlinks,urlcolor=black,hyperindex,% |
dc64f2ea | 13 | linktocpage,a4paper,bookmarks=true,% |
14 | bookmarksopen=true,bookmarksopenlevel=2,% | |
15 | bookmarksnumbered=true]{hyperref} | |
16 | %% \usepackage{bookmark} | |
ffa07380 | 17 | \def\AlwaysText#1{\ifmmode\relax\text{#1}\else #1\fi} |
18 | \newcommand{\AbbrName}[1]{\AlwaysText{{\scshape #1}}} | |
56bd6baf | 19 | \newcommand{\CERN}{\AbbrName{cern}} |
20 | \newcommand{\ALICE}{\AbbrName{alice}} | |
655b45b0 | 21 | \newcommand{\SPD}{\AbbrName{spd}} |
22 | \newcommand{\ESD}{\AbbrName{esd}} | |
23 | \newcommand{\AOD}{\AbbrName{aod}} | |
24 | \newcommand{\INEL}{\AbbrName{inel}} | |
25 | \newcommand{\INELONE}{$\AbbrName{inel}>0$} | |
26 | \newcommand{\NSD}{\AbbrName{nsd}} | |
8c548214 | 27 | \newcommand{\FMD}[1][]{\AbbrName{fmd\ifx|#1|\else#1\fi}} |
56bd6baf | 28 | \newcommand{\OCDB}{\AbbrName{ocdb}} |
29 | \newcommand{\mult}[1][]{\ensuremath N_{\text{ch}#1}} | |
655b45b0 | 30 | \newcommand{\dndetadphi}[1][]{{\ensuremath% |
31 | \ifx|#1|\else\left.\fi% | |
56bd6baf | 32 | \frac{d^2\mult{}}{d\eta\,d\varphi}% |
655b45b0 | 33 | \ifx|#1|\else\right|_{#1}\fi% |
34 | }} | |
35 | \newcommand{\landau}[1]{{\ensuremath% | |
36 | \text{landau}\left(#1\right)}} | |
37 | \newcommand{\dndeta}[1][]{{\ensuremath% | |
38 | \ifx|#1|\else\left.\fi% | |
56bd6baf | 39 | \frac{1}{N}\frac{d\mult{}}{d\eta}% |
655b45b0 | 40 | \ifx|#1|\else\right|_{#1}\fi% |
41 | }} | |
ffa07380 | 42 | \newcommand{\MC}{\AlwaysText{MC}} |
fc6a90cc | 43 | \newcommand{\N}[2]{{\ensuremath N_{#1#2}}} |
44 | \newcommand{\NV}[1][]{\N{\text{V}}{#1}} | |
45 | \newcommand{\NnotV}{\N{\not{\text{V}}}} | |
46 | \newcommand{\NT}{\N{\text{T}}{}} | |
47 | \newcommand{\NA}{\N{\text{A}}{}} | |
56bd6baf | 48 | \newcommand{\Ngood}{{\ensuremath N_{\text{good}}}} |
ffa07380 | 49 | \newcommand{\GeV}[1]{\unit[#1]{\AlwaysText{GeV}}} |
549a0be3 | 50 | \newcommand{\TeV}[1]{\unit[#1]{\AlwaysText{TeV}}} |
ffa07380 | 51 | \newcommand{\cm}[1]{\unit[#1]{\AlwaysText{cm}}} |
56bd6baf | 52 | \newcommand{\secref}[1]{Section~\ref{#1}} |
53 | \newcommand{\figref}[1]{Figure~\ref{#1}} | |
54 | \newcommand{\etaphi}{\ensuremath(\eta,\varphi)} | |
dc64f2ea | 55 | % Azimuthal acceptance |
56 | \newcommand{\Corners}{\ensuremath A^{\varphi}_{t}} | |
57 | % Acceptance due to dead strips | |
58 | \newcommand{\DeadCh}{\ensuremath A^{\eta}_{v,i}\etaphi} | |
59 | \newcommand{\SecMap}{\ensuremath S_v\etaphi} | |
655b45b0 | 60 | \setlength{\parskip}{1ex} |
61 | \setlength{\parindent}{0em} | |
9e3855d0 | 62 | \title{% |
63 | {\LARGE EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH}\\% | |
64 | {\Large European Organization for Particle Physics}\\[2ex]% | |
65 | {\normalsize% | |
66 | \begin{tabular}[t]{@{}p{.25\textwidth}@{\hspace{.05\textwidth}}% | |
67 | p{.4\textwidth}@{\hspace{.05\textwidth}}% | |
68 | p{.25\textwidth}@{}}% | |
69 | % \vfil% | |
70 | \vfil | |
71 | \includegraphics[keepaspectratio,width=.12\textwidth]{alice_logo_v3}% | |
72 | \vfil% | |
73 | &% | |
74 | \vfil | |
75 | \begin{center}% | |
76 | {\LARGE\bf Analysing the FMD data for $\dndeta$}% | |
77 | \end{center}% | |
78 | \vfil | |
79 | &% | |
80 | % \vfil% | |
81 | \vfil | |
82 | \begin{tabular}[t]{@{}p{.25\textwidth}@{}} | |
83 | \hfill\includegraphics[keepaspectratio,width=.12\textwidth]{% | |
84 | cernlogo}\\ | |
85 | \hfill ALICE-INT-2012-040 v1\\ | |
86 | \hfill \today | |
87 | \end{tabular}% | |
88 | \vfil% | |
89 | \end{tabular}}} | |
655b45b0 | 90 | \author{Christian Holm |
ffa07380 | 91 | Christensen\thanks{\texttt{$\langle$cholm@nbi.dk$\rangle$}}\quad\&\quad |
92 | Hans Hjersing Dalsgaard\thanks{\texttt{$\langle$canute@nbi.dk$\rangle$}}\\ | |
655b45b0 | 93 | Niels Bohr Institute\\ |
94 | University of Copenhagen} | |
9e3855d0 | 95 | \date{} |
655b45b0 | 96 | \begin{document} |
dc64f2ea | 97 | \pdfbookmark{Analysing the FMD data for dN/deta}{top} |
655b45b0 | 98 | \maketitle |
99 | ||
ffa07380 | 100 | \tableofcontents |
101 | \section{Introduction} | |
655b45b0 | 102 | |
103 | This document describes the steps performed in the analysis of the | |
104 | charged particle multiplicity in the forward pseudo--rapidity | |
56bd6baf | 105 | regions. The primary detector used for this is the \FMD{} |
dc64f2ea | 106 | \cite{FWD:2004mz,cholm:2009}. |
107 | ||
108 | The \FMD{} is | |
109 | organised in 3 \emph{sub--detectors} \FMD{1}, \FMD{2}, and \FMD{3}, each | |
110 | consisting of 1 (\FMD{1}) or 2 (\FMD{2} and~3) \emph{rings}. | |
111 | The rings fall into two types: \emph{Inner} or \emph{outer} rings. | |
112 | Each ring is in turn azimuthally divided into \emph{sectors}, and each | |
113 | sector is radially divided into \emph{strips}. How many sectors, | |
114 | strips, as well as the $\eta$ coverage is given in | |
115 | \tablename~\ref{tab:fmd:overview}. | |
116 | ||
117 | \begin{table}[htbp] | |
118 | \begin{center} | |
119 | \caption{Physical dimensions of Si segments and strips.} | |
120 | \label{tab:fmd:overview} | |
121 | \vglue0.2cm | |
122 | \begin{tabular}{|c|cc|cr@{\space--\space}l|r@{\space--\space}l|} | |
123 | \hline | |
124 | \textbf{Sub--detector/} & | |
125 | \textbf{Azimuthal}& | |
126 | \textbf{Radial} & | |
127 | $z$ & | |
128 | \multicolumn{2}{c|}{\textbf{$r$}} & | |
129 | \multicolumn{2}{c|}{\textbf{$\eta$}} \\ | |
130 | \textbf{Ring}& | |
131 | \textbf{sectors} & | |
132 | \textbf{strips} & | |
133 | \textbf{[cm]} & | |
134 | \multicolumn{2}{c|}{\textbf{range [cm]}} & | |
135 | \multicolumn{2}{c|}{\textbf{coverage}} \\ | |
136 | \hline | |
137 | FMD1i & 20& 512& 320 & 4.2& 17.2& 3.68& 5.03\\ | |
138 | FMD2i & 20& 512& 83.4& 4.2& 17.2& 2.28& 3.68\\ | |
139 | FMD2o & 40& 256& 75.2& 15.4& 28.4& 1.70& 2.29\\ | |
140 | FMD3i & 20& 512& -75.2& 4.2& 17.2&-2.29& -1.70\\ | |
141 | FMD3o & 40& 256& -83.4& 15.4& 28.4&-3.40& -2.01\\ | |
142 | \hline | |
143 | \end{tabular} | |
144 | \end{center} | |
145 | \end{table} | |
146 | ||
b9bd46b7 | 147 | The \FMD{} \ESD{} object contains the scaled energy deposited $\Delta |
148 | E/\Delta E_{mip}$ for each of the 51,200 strips. This is determined | |
149 | in the reconstruction pass. The scaling to $\Delta E_{mip}$ is done | |
150 | using calibration factors extracted in designated pulser runs. In | |
151 | these runs, the front-end electronics is pulsed with an increasing | |
152 | known pulse size, and the conversion factor from ADC counts to $\Delta | |
153 | E_{mip}$ is determined \cite{cholm:2009}. | |
154 | ||
dc64f2ea | 155 | The \SPD{} is used for determination of the position of the primary |
156 | interaction point. | |
655b45b0 | 157 | |
158 | The analysis is performed as a two--step process. | |
159 | \begin{enumerate} | |
160 | \item The Event--Summary--Data (\ESD{}) is processed event--by--event | |
161 | and passed through a number of algorithms, and | |
162 | $\dndetadphi$ for each event is output to an Analysis--Object--Data | |
dc64f2ea | 163 | (\AOD{}) tree (see \secref{sec:gen_aod}). |
655b45b0 | 164 | \item The \AOD{} data is read in and the sub--sample of the data under |
165 | investigation is selected (e.g., \INEL{}, \INELONE{}, \NSD{}, or | |
166 | some centrality class) and the $\dndetadphi$ histogram read in for | |
dc64f2ea | 167 | those events to build up $\dndeta$ (see \secref{sec:ana_aod}). |
655b45b0 | 168 | \end{enumerate} |
169 | The details of each step above will be expanded upon in the | |
170 | following. | |
171 | ||
dc64f2ea | 172 | In Appendix~\ref{app:nomen} is an overview of the nomenclature used in |
173 | this document. | |
174 | ||
175 | ||
176 | ||
ffa07380 | 177 | \section{Generating $\dndetadphi[i]$ event--by--event} |
dc64f2ea | 178 | \label{sec:gen_aod} |
655b45b0 | 179 | |
180 | When reading in the \ESD{}s and generating the $\dndetadphi$ | |
181 | event--by--event the following steps are taken (in order) for each | |
182 | event $i$ | |
183 | \begin{description} | |
184 | \item[Event inspection] The global properties of the event is | |
56bd6baf | 185 | determined, including the trigger type and primary interaction |
186 | point\footnote{`Vertex' and `primary interaction point' will be used | |
187 | interchangeably in the text, since there is no ambiguity with | |
188 | particle production vertex in this analysis.} $z$ coordinate (see | |
189 | \secref{sec:sub:event_inspection}). | |
655b45b0 | 190 | \item[Sharing filter] The \ESD{} object is read in and corrected for |
56bd6baf | 191 | sharing. The result is a new \ESD{} object (see |
192 | \secref{sec:sub:sharing_filter}). | |
655b45b0 | 193 | \item[Density calculator] The (possibly un--corrected) \ESD{} object |
56bd6baf | 194 | is then inspected and an inclusive (primary \emph{and} secondary |
195 | particles), per--ring charged particle density | |
196 | $\dndetadphi[incl,r,v,i]$ is made. This calculation depends in | |
197 | general upon the interaction vertex position along the $z$ axis | |
198 | $v_z$ (see \secref{sec:sub:density_calculator}). | |
199 | \item[Corrections] The 5 $\dndetadphi[incl,r,v,i]$ are corrected for | |
200 | secondary production and acceptance. The correction for the | |
201 | secondary particle production is highly dependent on the vertex $z$ | |
202 | coordinate. The result is a per--ring, charged primary particle | |
203 | density $\dndetadphi[r,v,i]$ (see \secref{sec:sub:corrector}). | |
655b45b0 | 204 | \item[Histogram collector] Finally, the 5 $\dndetadphi[r,v,i]$ are |
205 | summed into a single $\dndetadphi[v,i]$ histogram, taking care of | |
206 | the overlaps between the detector rings. In principle, this | |
207 | histogram is independent of the vertex, except that the | |
208 | pseudo--rapidity range, and possible holes in that range, depends on | |
56bd6baf | 209 | $v_z$ --- or rather the bin in which the $v_z$ falls (see |
210 | \secref{sec:sub:hist_collector}). | |
655b45b0 | 211 | \end{description} |
212 | ||
213 | Each of these steps will be detailed in the following. | |
214 | ||
ffa07380 | 215 | \subsection{Event inspection} |
56bd6baf | 216 | \label{sec:sub:event_inspection} |
655b45b0 | 217 | |
218 | The first thing to do, is to inspect the event for triggers. A number | |
549a0be3 | 219 | of trigger bits, like \INEL{} (Minimum Bias for Pb+Pb), \INELONE{}, \NSD{}, and so on is then |
655b45b0 | 220 | propagated to the \AOD{} output. |
221 | ||
b9bd46b7 | 222 | Just after the sharing filter (described below) but before any further |
655b45b0 | 223 | processing, the vertex information is queried. If there is no vertex |
224 | information, or if the vertex $z$ coordinate is outside the | |
56bd6baf | 225 | pre--defined range, then no further processing of that event takes place. |
655b45b0 | 226 | |
549a0be3 | 227 | \subsubsection{Displaced Vertices} |
228 | \label{sec:sub:sub:dispvtx} | |
229 | ||
230 | The analysis can be set up to run on the `displaced vertices' that | |
231 | occur during LHC Pb+Pb running. Details on the displaced vertices, and | |
232 | their selection can be found in the VZERO analysis note \cite{maxime}. | |
ffa07380 | 233 | \subsection{Sharing filter} |
56bd6baf | 234 | \label{sec:sub:sharing_filter} |
655b45b0 | 235 | |
dc64f2ea | 236 | A particle originating from the vertex can, because of its incident |
56bd6baf | 237 | angle on the \FMD{} sensors traverse more than one strip (see |
238 | \figref{fig:share_fraction}). This means that the energy loss of the | |
239 | particle is distributed over 1 or more strips. The signal in each | |
b9bd46b7 | 240 | strip should therefore possibly be merged with its neighboring strip |
56bd6baf | 241 | signals to properly reconstruct the energy loss of a single particle. |
655b45b0 | 242 | |
56bd6baf | 243 | \begin{figure}[htbp] |
244 | \centering | |
245 | \includegraphics[keepaspectratio,height=3cm]{share_fraction} | |
246 | \caption{A particle traversing 2 strips and depositing energy in | |
247 | each strip. } | |
248 | \label{fig:share_fraction} | |
249 | \end{figure} | |
250 | ||
251 | The effect is most pronounced in low--flux\footnote{Events with a low | |
252 | hit density.} events, like proton--proton collisions or peripheral | |
253 | Pb--Pb collisions, while in high--flux events the hit density is so | |
254 | high that most likely each and every strip will be hit and the effect | |
255 | cancel out on average. | |
655b45b0 | 256 | |
257 | Since the particles travel more or less in straight lines toward the | |
dc64f2ea | 258 | \FMD{} sensors, the sharing effect is predominantly in the $r$ or |
259 | \emph{strip} direction. Only neighbouring strips in a given sector is | |
655b45b0 | 260 | therefor investigated for this effect. |
261 | ||
262 | Algorithm~\ref{algo:sharing} is applied to the signals in a given | |
263 | sector. | |
264 | ||
265 | \begin{algorithm}[htpb] | |
dc64f2ea | 266 | \belowpdfbookmark{Algorithm 1}{algo:sharing} |
655b45b0 | 267 | \SetKwData{usedThis}{current strip used} |
268 | \SetKwData{usedPrev}{previous strip used} | |
269 | \SetKwData{Output}{output} | |
270 | \SetKwData{Input}{input} | |
271 | \SetKwData{Nstr}{\# strips} | |
272 | \SetKwData{Signal}{current} | |
273 | \SetKwData{Eta}{$\eta$} | |
274 | \SetKwData{prevE}{previous strip signal} | |
275 | \SetKwData{nextE}{next strip signal} | |
276 | \SetKwData{lowFlux}{low flux flag} | |
277 | \SetKwFunction{SignalInStrip}{SignalInStrip} | |
278 | \SetKwFunction{MultiplicityOfStrip}{MultiplicityOfStrip} | |
279 | \usedThis $\leftarrow$ false\; | |
280 | \usedPrev $\leftarrow$ false\; | |
281 | \For{$t\leftarrow1$ \KwTo \Nstr}{ | |
282 | \Output${}_t\leftarrow 0$\; | |
283 | \Signal $\leftarrow$ \SignalInStrip($t$)\; | |
284 | ||
285 | \uIf{\Signal is not valid}{ | |
286 | \Output${}_t \leftarrow$ invalid\; | |
287 | } | |
288 | \uElseIf{\Signal is 0}{ | |
289 | \Output${}_t \leftarrow$ 0\; | |
290 | } | |
291 | \Else{ | |
292 | \Eta$\leftarrow$ $\eta$ of \Input${}_t$\; | |
293 | \prevE$\leftarrow$ 0\; | |
294 | \nextE$\leftarrow$ 0\; | |
295 | \lIf{$t \ne 1$}{ | |
296 | \prevE$\leftarrow$ \SignalInStrip($t-1$)\; | |
297 | } | |
298 | \lIf{$t \ne $\Nstr}{ | |
299 | \nextE$\leftarrow$ \SignalInStrip($t+1$)\; | |
300 | } | |
301 | \Output${}_t\leftarrow$ | |
302 | \MultiplicityOfStrip(\Signal,\Eta,\prevE,\nextE,\\ | |
303 | \hfill\lowFlux,$t$,\usedPrev,\usedThis)\; | |
304 | } | |
305 | } | |
306 | \caption{Sharing correction} | |
307 | \label{algo:sharing} | |
308 | \end{algorithm} | |
309 | ||
310 | Here the function \FuncSty{SignalInStrip}($t$) returns the properly | |
311 | path--length corrected signal in strip $t$. The function | |
56bd6baf | 312 | \FuncSty{MultiplicityOfStrip} is where the real processing takes |
313 | place (see page \pageref{func:MultiplicityOfStrip}). | |
655b45b0 | 314 | |
315 | \begin{function}[htbp] | |
dc64f2ea | 316 | \belowpdfbookmark{MultiplicityOfStrip}{func:MultiplicityOfStrip} |
56bd6baf | 317 | \caption{MultiplicityOfStrip(\DataSty{current},$\eta$,\DataSty{previous},\DataSty{next},\DataSty{low |
655b45b0 | 318 | flux flag},\DataSty{previous signal used},\DataSty{this signal |
319 | used})} | |
56bd6baf | 320 | \label{func:MultiplicityOfStrip} |
655b45b0 | 321 | \SetKwData{Current}{current} |
322 | \SetKwData{Next}{next} | |
323 | \SetKwData{Previous}{previous} | |
324 | \SetKwData{lowFlux}{low flux flag} | |
325 | \SetKwData{usedPrev}{previous signal used} | |
326 | \SetKwData{usedThis}{this signal used} | |
327 | \SetKwData{lowCut}{low cut} | |
328 | \SetKwData{total}{Total} | |
329 | \SetKwData{highCut}{high cut} | |
330 | \SetKwData{Eta}{$\eta$} | |
331 | \SetKwFunction{GetHighCut}{GetHighCut} | |
332 | \If{\Current is very large or \Current $<$ \lowCut} { | |
333 | \usedThis $\leftarrow$ false\; | |
334 | \usedPrev $\leftarrow$ false\; | |
335 | \Return{0} | |
336 | } | |
337 | \If{\usedThis}{ | |
338 | \usedThis $\leftarrow$ false\; | |
339 | \usedPrev $\leftarrow$ true\; | |
340 | \Return{0} | |
341 | } | |
342 | \highCut $\leftarrow$ \GetHighCut($t$,\Eta)\; | |
dc64f2ea | 343 | %\If{\Current $<$ \Next and \Next $>$ \highCut and \lowFlux set}{ |
344 | % \usedThis $\leftarrow$ false\; | |
345 | % \usedPrev $\leftarrow$ false\; | |
346 | % \Return{0} | |
347 | %} | |
655b45b0 | 348 | \total $\leftarrow$ \Current\; |
349 | \lIf{\lowCut $<$ \Previous $<$ \highCut and not \usedPrev}{ | |
350 | \total $\leftarrow$ \total + \Previous\; | |
351 | } | |
352 | \If{\lowCut $<$ \Next $<$ \highCut}{ | |
353 | \total $\leftarrow$ \total + \Next\; | |
354 | \usedThis $\leftarrow$ true\; | |
355 | } | |
356 | \eIf{\total $>$ 0}{ | |
357 | \usedPrev $\leftarrow$ true\; | |
358 | \Return{\total} | |
359 | }{ | |
360 | \usedPrev $\leftarrow$ false\; | |
361 | \usedThis $\leftarrow$ false\; | |
362 | \Return{0} | |
363 | } | |
364 | \end{function} | |
56bd6baf | 365 | Here, the function \FuncSty{GetHighCut} evaluates a fit to the energy |
366 | distribution in the specified $\eta$ bin (see also | |
367 | \secref{sec:sub:density_calculator}). It returns | |
655b45b0 | 368 | $$ |
369 | \Delta_{mp} - 2 w | |
370 | $$ | |
371 | where $\Delta_{mp}$ is the most probable energy loss, and $w$ is the | |
372 | width of the Landau distribution. | |
373 | ||
374 | The \KwSty{if} in line 5, says that if the previous strip was merged | |
375 | with current one, and the signal of the current strip was added to | |
56bd6baf | 376 | that, then the current signal is set to 0, and we mark it as used for |
377 | the next iteration (\DataSty{previous signal used}$\leftarrow$true). | |
655b45b0 | 378 | |
dc64f2ea | 379 | % The \KwSty{if} in line 10 checks if the current signal is smaller than |
380 | % the next signal, if the next signal is larger than the upper cut | |
381 | % defined above, and if we have a low--flux event\footnote{Note, that in | |
382 | % the current implementation there are never any low--flux events.}. | |
383 | % If that condition is met, then the current signal is the smaller of | |
384 | % two possible candidates for merging, and it should be merged into the | |
385 | % next signal. Note, that this \emph{only} applies in low--flux events. | |
56bd6baf | 386 | |
dc64f2ea | 387 | In line 11, % 15, |
388 | we test if the previous signal lies between our low and | |
655b45b0 | 389 | high cuts, and if it has not been marked as being used. If so, we add |
390 | it to our current signal. | |
391 | ||
dc64f2ea | 392 | The next \KwSty{if} on line 12 % 16 |
393 | checks if the next signal is within our | |
655b45b0 | 394 | cut bounds. If so, we add that signal to the current signal and mark |
395 | it as used for the next iteration (\DataSty{this signal | |
396 | used}$\leftarrow$true). It will then be zero'ed on the next | |
397 | iteration by the condition on line 6. | |
398 | ||
399 | Finally, if our signal is still larger than 0, we return the signal | |
400 | and mark this signal as used (\DataSty{previous signal | |
401 | used}$\leftarrow$true) so that it will not be used in the next | |
402 | iteration. Otherwise, we mark the current signal and the next signal | |
403 | as unused and return a 0. | |
404 | ||
405 | ||
ffa07380 | 406 | \subsection{Density calculator} |
56bd6baf | 407 | \label{sec:sub:density_calculator} |
655b45b0 | 408 | |
dc64f2ea | 409 | The density calculator loops over all the strip signals in the sharing |
410 | corrected\footnote{The sharing correction can be disabled, in which | |
411 | case the density calculator used the input \ESD{} signals.} \ESD{} | |
56bd6baf | 412 | and calculates the inclusive (primary + secondary) charged particle |
413 | density in pre--defined $\etaphi$ bins. | |
655b45b0 | 414 | |
549a0be3 | 415 | \subsubsection{Inclusive number of charged particles: Energy Fits} |
dc64f2ea | 416 | \label{sec:sub:sub:eloss_fits} |
ffa07380 | 417 | |
b9bd46b7 | 418 | The number charged particles in a strip $\mult[,t]$ is calculated |
419 | using multiple Landau-like distributions fitted to the energy loss | |
420 | spectrum of all strips in a given at a given $\eta$ bin. | |
655b45b0 | 421 | \begin{align} |
0a89eed1 | 422 | \Delta_{i,mp} &= i (\Delta_{1,mp}+ \xi_1 \log(i))\nonumber\\ |
423 | \xi_i &= i\xi_1\nonumber\\ | |
424 | \sigma_i &= \sqrt{i}\sigma_1\nonumber\\ | |
56bd6baf | 425 | \mult[,t] &= \frac{\sum_i^{N_{max}} |
0a89eed1 | 426 | i\,a_i\,F(\Delta_t;\Delta_{i,mp},\xi_i,\sigma_i)}{ |
427 | \sum_i^{N_{max}}\,a_i\,F(\Delta_t;\Delta_{i,mp},\xi_i,\sigma_i)}\quad, | |
655b45b0 | 428 | \end{align} |
0a89eed1 | 429 | where $F(x;\Delta_{mp},\xi,\sigma)$ is the evaluation of the Landau |
430 | distribution $f_L$ with most probable value $\Delta_{mp}$ and width | |
56bd6baf | 431 | $\xi$, folded with a Gaussian distribution with spread $\sigma$ at the |
432 | energy loss $x$ \cite{nim:b1:16,phyrev:a28:615}. | |
433 | \begin{align} | |
434 | \label{eq:energy_response} | |
435 | F(x;\Delta_{mp},\xi,\sigma) = \frac{1}{\sigma \sqrt{2 \pi}} | |
436 | \int_{-\infty}^{+\infty} d\Delta' f_{L}(x;\Delta',\xi) | |
437 | \exp{-\frac{(\Delta_{mp}-\Delta')^2}{2\sigma^2}}\quad, | |
438 | \end{align} | |
439 | where $\Delta_{1,mp}$, $\xi_1$, and $\sigma_1$ are the parameters for | |
440 | the first MIP peak, $a_1=1$, and $a_i$ is the relative weight of the | |
dc64f2ea | 441 | $i$-fold MIP peak. The parameters $\Delta_{1,mp}, \xi_1, |
442 | \sigma_1, \mathbf{a} = \left(a_2, \ldots a_{N_{max}}\right)$ are | |
443 | obtained by fitting | |
0a89eed1 | 444 | $$ |
dc64f2ea | 445 | F_j(x;C,\Delta_{mp},\xi,\sigma,\mathbf{a}) = C |
446 | \sum_{i=1}^{j} a_i F(x;\Delta_{i,mp},\xi_{i},\sigma_i) | |
0a89eed1 | 447 | $$ |
56bd6baf | 448 | for increasing $j$ to the energy loss spectra in separate $\eta$ bins. |
b9bd46b7 | 449 | The fit procedure is stopped when one for $j+1$ |
450 | \begin{itemize} | |
451 | \item the reduced $\chi^2$ exceeds a certain threshold, or | |
452 | \item the relative error $\delta p/p$ of any parameter of the fit | |
453 | exceeds a certain threshold, or | |
454 | \item when the weight $a_j+1$ is smaller than some number (typically | |
455 | $10^{-5}$). | |
456 | \end{itemize} | |
457 | $N_{max}$ is then set to $j$. Examples of the result of these fits | |
458 | are given in \figref{fig:eloss_fits} in Appendix~\ref{app:eloss_fits}. | |
549a0be3 | 459 | \subsubsection{Inclusive number of charged particles: Poisson Approach} |
460 | \label{sec:sub:sub:poisson} | |
461 | Another approach to the calculation of the number of charged particles | |
462 | is using Poisson statistics. | |
463 | Assume that in a region of the FMD % where | |
464 | $\mult$ | |
465 | %is azimuthally uniform in $\eta$ intervals it | |
466 | is | |
467 | distributed according to a Poisson distribution. This means that the | |
468 | probability of $\mult=n$ becomes: | |
469 | \begin{equation} | |
470 | P(n) = \frac{\mu^n e^{-\mu}}{n!} \label{eq:PoissonDef} | |
471 | \end{equation} | |
472 | In particular the measured occupancy, $\mu_{meas}$, is the probability | |
473 | of any number of hits, thus using \eqref{eq:PoissonDef} : | |
474 | \begin{equation} | |
475 | \mu_{meas} = 1 - P(0) = 1 - e^{-\mu } | |
476 | %\Rightarrow \mu = \ln | |
477 | %(1 - \mu_{meas})^{-1} \label{eq:PoissonDef2} | |
478 | \end{equation} | |
479 | which implies: | |
480 | \begin{equation} | |
481 | \mu = \ln | |
482 | (1 - \mu_{meas})^{-1} \label{eq:PoissonDef2} | |
483 | \end{equation} | |
484 | The mean number of particles in a hit strip becomes: | |
485 | \begin{eqnarray} | |
486 | C &=& \frac{\sum_{n>0} n P(n>0)}{\sum_{n>0} P(n>0)} \nonumber \\ | |
487 | &=& \frac{e^{-\mu}}{1-e^{-\mu}} \mu \sum \frac{\mu^n}{n!} | |
488 | \nonumber \\ | |
489 | &=& \frac{e^{-\mu}}{1-e^{-\mu}} \mu e^{\mu} \nonumber \\ | |
490 | &=& \frac{\mu}{1-e^{-\mu}} | |
491 | \end{eqnarray} | |
492 | %While $\mu$ can be calculated analytically for practical purposes we | |
493 | With $\mu$ defined in \eqref{eq:PoissonDef2} this calculation is | |
494 | carried out per event in | |
495 | regions of the FMD each containing 256 strips. %Defining | |
496 | %$\mu_{meas}^{region}$ to be the measured occupancy | |
497 | In such a region, | |
498 | $\mult$ for a hit strip ($N_{hits} \equiv 1$) in that region becomes: | |
499 | \begin{equation} | |
500 | \mult = N_{hits} \times C = 1 \times C = C | |
501 | \end{equation} | |
502 | Where C is calculated using $\mu_{meas}^{region}$. | |
655b45b0 | 503 | |
56bd6baf | 504 | \subsubsection{Azimuthal Acceptance} |
ffa07380 | 505 | |
56bd6baf | 506 | Before the signal $\mult[,t]$ can be added to the $\etaphi$ |
655b45b0 | 507 | bin in one of the 5 per--ring histograms, it needs to be corrected for |
56bd6baf | 508 | the $\varphi$ acceptance of the strip. |
655b45b0 | 509 | |
b9bd46b7 | 510 | The sensors of the \FMD{} are not perfect arc--segments --- the two |
511 | top corners are cut off to allow the largest possible sensor on a 6'' | |
512 | Si-wafer. This means, however, that the strips in these outer | |
513 | regions do not fully cover $2\pi$ in azimuth, and there is therefore a | |
514 | need to correct for this limited acceptance. | |
515 | ||
655b45b0 | 516 | The acceptance correction is only applicable where the strip length |
517 | does not cover the full sector. This is the case for the outer strips | |
518 | in both the inner and outer type rings. The acceptance correction is | |
519 | then simply | |
520 | \begin{align} | |
521 | \label{eq:acc_corr} | |
dc64f2ea | 522 | \Corners{} &= \frac{l_t}{\Delta\varphi}\quad |
655b45b0 | 523 | \end{align} |
524 | where $l_t$ is the strip length in radians at constant $r$, and | |
525 | $\Delta\varphi$ is $2\pi$ divided by the number of sectors in the | |
526 | ring (20 for inner type rings, and 40 for outer type rings). | |
527 | ||
b9bd46b7 | 528 | Note, that this correction is a hardware--related correction, and does |
529 | not depend on the properties of the collision (e.g., primary vertex | |
530 | location). | |
531 | ||
56bd6baf | 532 | The final $\etaphi$ content of the 5 output vertex dependent, |
655b45b0 | 533 | per--ring histograms of the inclusive charged particle density is then |
534 | given by | |
535 | \begin{align} | |
8c548214 | 536 | \label{eq:density} |
56bd6baf | 537 | \dndetadphi[incl,r,v,i\etaphi] &= \sum_t^{t\in\etaphi} |
dc64f2ea | 538 | \mult[,t]\,\Corners{} |
655b45b0 | 539 | \end{align} |
56bd6baf | 540 | where $t$ runs over the strips in the $\etaphi$ bin. |
655b45b0 | 541 | |
ffa07380 | 542 | \subsection{Corrections} |
56bd6baf | 543 | \label{sec:sub:corrector} |
655b45b0 | 544 | |
545 | The corrections code receives the five vertex dependent, | |
546 | per--ring histograms of the inclusive charged particle density | |
547 | $\dndetadphi[incl,r,v,i]$ from the density calculator and applies | |
56bd6baf | 548 | two corrections |
ffa07380 | 549 | |
550 | \subsubsection{Secondary correction} | |
551 | %% | |
552 | %% hHits_FMD<d><r>_vtx<v> | |
553 | %% hCorrection = ----------------------- | |
554 | %% hPrimary_FMD_<r>_vtx<v> | |
555 | %% | |
556 | %% where | |
557 | %% - hPrimary_FMD_<r>_vtx<vtx> is 2D of eta,phi for all primary ch | |
558 | %% particles | |
559 | %% - hHits_FMD<d><r>_vtx<v> is 2D of eta,phi for all track-refs that | |
560 | %% hit the FMD - The 2D version of hMCHits_nocuts_FMD<d><r>_vtx<v> | |
561 | %% used below. | |
56bd6baf | 562 | This is a 2 dimensional histogram generated from simulations, as the |
563 | ratio of primary particles to the total number of particles that fall | |
564 | within an $\etaphi$ bin for a given vertex bin | |
565 | ||
566 | \begin{align} | |
567 | \label{eq:secondary} | |
dc64f2ea | 568 | \SecMap{} &= |
fc6a90cc | 569 | \frac{\sum_i^{\NV[,v]}\mult[,\text{primary},i]\etaphi}{ |
570 | \sum_i^{\NV[,v]}\mult[,\text{\FMD{}},i]\etaphi}\quad, | |
56bd6baf | 571 | \end{align} |
fc6a90cc | 572 | where $\NV[,v]$ is the number of events with a valid trigger and a |
56bd6baf | 573 | vertex in bin $v$, and $\mult[,\FMD{},i]$ is the total number of |
574 | charged particles that hit the \FMD{} in event $i$ in the specified | |
575 | $\etaphi$ bin and $\mult[,\text{primary},i]$ is number of | |
576 | primary charged particles in event $i$ within the specified | |
577 | $\etaphi$ bin. | |
578 | ||
579 | $\mult[,\text{primary}]\etaphi$ is given by summing over the | |
580 | charged particles labelled as primaries \emph{at the time of the | |
581 | collision} as defined in the simulation code. That is, it is the | |
582 | number of primaries within the $\etaphi$ bin at the collision | |
583 | point --- not at the \FMD{}. | |
584 | ||
b9bd46b7 | 585 | $\SecMap$ is varies from $\approx 1.5$ for the most forward bins to |
586 | $\approx 3$ for the more central bins. For pp, different event | |
587 | generators were used and found to give compatible results within | |
588 | 3--5\%. For pp, at least some millions of events must be | |
589 | accumulated to reach satisfactory statistics. For Pb--Pb where the | |
590 | general hit density is larger, reasonable statistics can be achieved | |
591 | with less data. | |
592 | ||
56bd6baf | 593 | \subsubsection{Acceptance due to dead channels} |
594 | ||
595 | Some of the strips in the \FMD{} have been marked up as \emph{dead}, | |
596 | meaning that they are not used in the reconstruction or analysis. | |
597 | This leaves holes in the acceptance of each defined $\etaphi$ | |
598 | which need to be corrected for. | |
599 | ||
600 | Dead channels are marked specially in the \ESD{}s with the flag | |
601 | \textit{Invalid Multiplicity}. This is used in the analysis to build | |
602 | up and event--by--event acceptance correction in each $\etaphi$ | |
603 | bin by calculating the ratio | |
ffa07380 | 604 | \begin{align} |
56bd6baf | 605 | \label{eq:dead_channels} |
dc64f2ea | 606 | \DeadCh{} &= |
56bd6baf | 607 | \frac{\sum_t^{t\in\etaphi}\left\{\begin{array}{cl} |
608 | 1 & \text{if not dead}\\ | |
609 | 0 & \text{otherwise} | |
610 | \end{array}\right.}{\sum_t^{t\in\etaphi} 1}\quad, | |
ffa07380 | 611 | \end{align} |
dc64f2ea | 612 | where $t$ runs over the strips in the $\etaphi$ bin. This correction |
613 | is obviously $v_z$ dependent since which $\etaphi$ bin a strip $t$ | |
614 | corresponds to depends on its relative position to the primary vertex. | |
56bd6baf | 615 | |
616 | Alternatively, pre--made acceptance factors can be used. These are | |
617 | made from the off-line conditions database (\OCDB{}). | |
655b45b0 | 618 | |
619 | The 5 output vertex dependent, per--ring histograms of the primary | |
620 | charged particle density is then given by | |
621 | \begin{align} | |
56bd6baf | 622 | \dndetadphi[r,v,i\etaphi] &= |
dc64f2ea | 623 | \SecMap{} \frac{1}{\DeadCh{}}\dndetadphi[incl,r,v,i\etaphi] |
655b45b0 | 624 | \end{align} |
625 | ||
ffa07380 | 626 | \subsection{Histogram collector} |
56bd6baf | 627 | \label{sec:sub:hist_collector} |
655b45b0 | 628 | |
629 | The histogram collector collects the information from the 5 vertex | |
630 | dependent, per--ring histograms of the primary charged particle | |
631 | density $\dndetadphi[r,v,i]$ into a single vertex dependent histogram | |
632 | of the charged particle density $\dndetadphi[v,i]$. | |
633 | ||
634 | To do this, it first calculates, for each vertex bin, the $\eta$ bin | |
635 | range to use for each ring. It investigates the secondary correction | |
dc64f2ea | 636 | maps $\SecMap{}$ to find the edges of each map. The edges are given |
637 | by the $\eta$ range where $\SecMap{}$ is larger than some | |
638 | threshold\footnote{Typically $t_s\approx 0.1$.} $t_s$. The code | |
8c548214 | 639 | applies safety margin of a $N_{cut}$ bins\footnote{Typically |
640 | $N_{cut}=1$.}, to ensure that the data selected does not have too | |
641 | large corrections associated with it. | |
655b45b0 | 642 | |
643 | It then loops over the bins in the defined $\eta$ range and sums the | |
8c548214 | 644 | contributions from each of the 5 histograms. In the $\eta$ ranges |
645 | where two rings overlap, the collector calculates the average and adds | |
b9bd46b7 | 646 | the errors in quadrature\footnote{While not explicitly checked, it was |
647 | found that the histograms agrees within error bars in the | |
648 | overlapping region}. | |
655b45b0 | 649 | |
650 | The output vertex dependent histogram of the primary | |
651 | charged particle density is then given by | |
652 | \begin{align} | |
ffa07380 | 653 | \label{eq:superhist} |
56bd6baf | 654 | \dndetadphi[v,i\etaphi] &= |
655 | \frac{1}{N_{r\in\etaphi}}\sum_{r}^{r\in\etaphi} | |
656 | \dndetadphi[r,v,i\etaphi]\\ | |
657 | \delta\left[\dndetadphi[v,i\etaphi]\right] &= | |
658 | \frac{1}{N_{r\in\etaphi}}\sqrt{\sum_{r}^{r\in\etaphi} | |
659 | \delta\left[\dndetadphi[r,v,i\etaphi]\right]^2} | |
655b45b0 | 660 | \quad, |
661 | \end{align} | |
56bd6baf | 662 | where $N_{r\in\etaphi}$ is the number of overlapping histograms |
663 | in the given $\etaphi$ bin. | |
655b45b0 | 664 | |
ffa07380 | 665 | The histogram collector stores the found $\eta$ ranges in the |
666 | underflow bin of the histogram produced. The content of the overflow | |
667 | bins are | |
668 | \begin{align} | |
669 | \label{eq:overflow} | |
670 | I_{v,i}(\eta) &= | |
671 | \frac{1}{N_{r\in(\eta)}} | |
672 | \sum_{r}^{r\in(\eta)} \left\{\begin{array}{cl} | |
673 | 0 & \eta \text{\ bin not selected}\\ | |
674 | 1 & \eta \text{\ bin selected} | |
675 | \end{array}\right.\quad, | |
676 | \end{align} | |
677 | where $N_{r\in(\eta)}$ is the number of overlapping histograms in the | |
678 | given $\eta$ bin. The subscript $v$ indicates that the content | |
679 | depends on the current vertex bin of event $i$. | |
680 | ||
681 | \section{Building the final $\dndeta$} | |
dc64f2ea | 682 | \label{sec:ana_aod} |
ffa07380 | 683 | |
684 | To build the final $\dndeta$ distribution it is enough to sum | |
685 | \eqref{eq:superhist} and \eqref{eq:overflow} over all interesting | |
fc6a90cc | 686 | events and correct for the acceptance $I(\eta)$ |
56bd6baf | 687 | \begin{align} |
fc6a90cc | 688 | \dndetadphi[\etaphi] &= \sum_i^{\NA}\dndetadphi[i,v\etaphi]\\ |
689 | I(\eta) &= \sum_i^{\NA}I_{i,v}(\eta)\quad. | |
56bd6baf | 690 | \end{align} |
fc6a90cc | 691 | Note, that $I(\eta)\le\NA$. |
56bd6baf | 692 | |
fc6a90cc | 693 | We then need to normalise to the total number of events $N_X$, given |
694 | by | |
ffa07380 | 695 | \begin{align} |
fc6a90cc | 696 | \N{X}{} &= \frac{1}{\epsilon_X}\left[\NA + \alpha(\NnotV - |
697 | \beta)\right] \label{eq:fulleventnorm}\\ | |
698 | & = \frac{1}{\epsilon_X}\left[\NA + \frac{\NA}{\NV}(\NT-\NV{} - | |
699 | \beta)\right]\nonumber \\ | |
700 | & =\frac{1}{\epsilon_X}\NA\left[1+\frac{1}{\epsilon_V}-1- | |
701 | \frac{\beta}{\NV}\right]\nonumber\\ | |
702 | & = \frac{1}{\epsilon_X}\frac{1}{\epsilon_V}\NA | |
703 | \left(1-\frac{\beta}{\NT{}}\right)\nonumber | |
704 | \end{align} | |
705 | where | |
706 | \begin{description} | |
707 | \item[$\epsilon_X$] is the trigger efficiency for type | |
708 | $X\in[\text{\INEL},\text{\INELONE},\text{\NSD},...]$ | |
709 | \item[$\epsilon_V=\frac{\NV{}}{\NT{}}$] is the vertex efficiency | |
710 | evaluated over the data. | |
711 | \item[$\NA$] is the number of events with a trigger \emph{and} a valid | |
712 | vertex in the selected range | |
713 | \item[$\NV{}$] is the number of events with a trigger \emph{and} a valid | |
714 | vertex. | |
715 | \item[$\NT$] is the number of events with a trigger. | |
716 | \item[$\NnotV{}=\NT-\NV{}$] is the number of events with a trigger | |
717 | \emph{but no} valid vertex | |
718 | \item[$\alpha=\frac{\NA}{\NV}$] is the fraction of accepted events of | |
719 | the total number of events with a trigger and valid vertex. | |
720 | \item[$\beta=\N{a}{}+\N{b}{}-\N{e}{}$] is the number of background | |
721 | events \emph{with} a valid off-line trigger. | |
722 | \end{description} | |
723 | The two terms under the parenthesis in \eqref{eq:fulleventnorm} refers | |
724 | to the observed number of event $\NA$, and the events missed because | |
725 | of no vertex reconstruction. Note, for $\beta\ll\NT{}$ | |
726 | \eqref{eq:fulleventnorm} reduces to the simpler expression | |
727 | $$ | |
728 | \N{X}{} = \frac1{\epsilon_X}\frac1{\epsilon_V}\NA{} | |
729 | $$ | |
730 | The trigger efficiency $\epsilon_X$ for a given trigger type $X$ is | |
731 | evaluated from simulations as | |
732 | \begin{align} | |
733 | \epsilon_X = \frac{\N{X\wedge \text{T}}{}}{\N{X}{}}\quad, | |
734 | \end{align} | |
735 | that is, the ratio of number of events of type $X$ with a | |
736 | corresponding trigger to the number of events of type $X$. | |
737 | ||
738 | The final event--normalised charged particle density then becomes | |
739 | \begin{align} | |
740 | \frac{1}{N}\frac{dN_{\text{ch}}}{d\eta} &= | |
741 | \frac{1}{\N{X}{}} \int_0^{2\pi} d\varphi | |
742 | \frac{\dndetadphi[\etaphi]}{I(\eta)} | |
743 | \label{eq:eventnormdndeta} | |
744 | \end{align} | |
745 | ||
746 | If the trigger $X$ introduces a bias on the measured number of events, | |
747 | then \eqref{eq:eventnormdndeta} need to be modified to | |
748 | \begin{align} | |
749 | \frac{1}{N}\frac{dN_{\text{ch}}}{d\eta} &= | |
750 | \frac{1}{\N{X}{}} \int_0^{2\pi} d\varphi | |
751 | \frac{\frac{1}{B\etaphi}\dndetadphi[\etaphi]}{I(\eta)} | |
752 | \label{eq:eventnormdndeta2}\quad, | |
753 | \end{align} | |
754 | where $B\etaphi$ is the bias correction. This is typically | |
755 | calculated from simulations using the expression | |
756 | \begin{align} | |
757 | B\etaphi = \frac{\frac{1}{\N{X\wedge | |
758 | \text{T}}{}}\sum_i^{\N{X\wedge \text{T}}{}} | |
759 | \mult[,\text{primary}]\etaphi}{\frac{1}{\N{X}{}}\sum_i^{\N{X}{}} | |
760 | \mult[,\text{primary}]\etaphi} | |
ffa07380 | 761 | \end{align} |
fc6a90cc | 762 | |
655b45b0 | 763 | |
ffa07380 | 764 | \section{Using the per--event $\dndetadphi[i,v]$ histogram for other |
765 | analysis} | |
655b45b0 | 766 | |
ffa07380 | 767 | \subsection{Multiplicity distribution} |
655b45b0 | 768 | |
ffa07380 | 769 | To build the multiplicity distribution for a given $\eta$ range |
770 | $[\eta_1,\eta_2]$, one needs to find the total multiplicity in that | |
771 | $\eta$ range for each event. To do so, one should sum the | |
772 | $\dndetadphi[i,v]$ histogram over all $\varphi$ and in the selected | |
773 | $\eta$ range. | |
774 | \begin{align} | |
775 | n'_{i[\eta_1,\eta_2]}, &= \int_{\eta_1}^{\eta_2}d\eta\int_0^{2\pi}d\varphi | |
776 | \dndetadphi[i,v]\quad.\nonumber | |
777 | \end{align} | |
778 | However, $n'_i$ is not corrected for the coverage in $\eta$ for the | |
779 | particular vertex range $v$. One therefor needs to correct for the | |
780 | number of missing bins in the range $[\eta_1,\eta_2]$. Suppose | |
781 | $[\eta_1,\eta_2]$ covers $N_{[\eta_1,\eta_2]}$ $\eta$ bins, then the acceptance | |
782 | correction is given by | |
783 | \begin{align} | |
784 | A_{i,[\eta_1,\eta_2]} = \frac{N_{[\eta_1,\eta_2]}}{\int_{\eta_1}^{\eta_2}d\eta\, | |
785 | I_{i,v}(\eta)}\quad.\nonumber | |
786 | \end{align} | |
787 | The per--event multiplicity is then given by | |
788 | \begin{align} | |
789 | n_{i,[\eta_1,\eta_2]} &= A_{i,[\eta_1,\eta_2]}\,n'_{i,[\eta_1,\eta_2]}\nonumber\\ | |
790 | &= \frac{N_{[\eta_1,\eta_2]}}{\int_{\eta_1}^{\eta_2}\eta | |
791 | I_{i,v}(\eta)} \int_{\eta_1}^{\eta_2}d\eta\int_0^{2\pi}d\varphi | |
792 | \dndetadphi[i,v] | |
793 | \label{eq:event_n} | |
794 | \end{align} | |
795 | ||
796 | \subsection{Forward--Backward correlations} | |
797 | ||
798 | To do forward--backward correlations, one need to calculate | |
799 | $n_{i,[\eta_1,\eta_2]}$ as shown in \eqref{eq:event_n} in two bins | |
800 | $n_{i,[\eta_1,\eta_2]}$ and $n_{i,[-\eta_2,-\eta_1]}$ \textit{e.g.}, | |
801 | $n_{i,f}=n_{i,[-3,-1]}$ and $n_{i,b}=n_{i,[1,3]}$. | |
802 | ||
dc64f2ea | 803 | \clearpage |
ffa07380 | 804 | \section{Some results} |
805 | ||
dc64f2ea | 806 | %% \figurename{}s \ref{fig:1} to \ref{fig:3} shows some results. |
549a0be3 | 807 | Figures below show some examples \cite{hhd:2009}. Note these are not finalised |
dc64f2ea | 808 | plots. |
549a0be3 | 809 | \begin{figure}[hbp] |
810 | \centering | |
811 | \includegraphics[keepaspectratio,width=\textwidth]{% | |
812 | results_ppdndeta} | |
813 | \caption{$\dndeta$ for pp for \INEL{} events at | |
814 | $\sqrt{s}=\GeV{900}$, $\sqrt{s}=\TeV{2.76}$, and $\sqrt{s}=\TeV{7}$ | |
815 | $\cm{-10}\le v_z\le\cm{10}$, rebinned by a factor 5 \cite{hhd:2009}. | |
816 | % Middle panel | |
817 | % shows the ratio of ALICE data to UA5, and the bottom panel shows | |
818 | % the ratio of the right (positive) side to the left (negative) side | |
819 | % of the forward $\dndeta$. | |
820 | } | |
821 | \label{fig:1} | |
822 | \end{figure} | |
823 | \begin{figure}[hbp] | |
824 | \centering | |
825 | \includegraphics[keepaspectratio,width=\textwidth]{% | |
826 | results_PbPbdndeta} | |
827 | \caption{$\dndeta$ for Pb+Pb for Minimum Bias events at | |
828 | $\sqrt{s_{NN}}=\TeV{2.76}$ $\cm{-10}\le v_z\le\cm{10}$, rebinned by a | |
829 | factor 5 in 10 centrality intervals \cite{hhd:2009}. | |
830 | % Middle panel | |
831 | % shows the ratio of ALICE data to UA5, and the bottom panel shows | |
832 | % the ratio of the right (positive) side to the left (negative) side | |
833 | % of the forward $\dndeta$. | |
834 | } | |
835 | \label{fig:2} | |
836 | \end{figure} | |
ffa07380 | 837 | |
549a0be3 | 838 | |
839 | \iffalse | |
dc64f2ea | 840 | \begin{figure}[hbp] |
ffa07380 | 841 | \centering |
842 | \includegraphics[keepaspectratio,width=\textwidth]{% | |
b9bd46b7 | 843 | dndeta_pp_0900GeV_INEL_m10p10cm} |
ffa07380 | 844 | \caption{$\dndeta$ for pp for \INEL{} events at $\sqrt{s}=\GeV{900}$, |
b9bd46b7 | 845 | $\cm{-10}\le v_z\le\cm{10}$, rebinned by a factor 5. Middle panel |
846 | shows the ratio of ALICE data to UA5, and the bottom panel shows | |
847 | the ratio of the right (positive) side to the left (negative) side | |
848 | of the forward $\dndeta$.} | |
ffa07380 | 849 | \label{fig:1} |
850 | \end{figure} | |
dc64f2ea | 851 | |
549a0be3 | 852 | |
ffa07380 | 853 | \begin{figure}[tbp] |
854 | \centering | |
855 | \includegraphics[keepaspectratio,width=\textwidth]{% | |
856 | dndeta_0900GeV_m10-p10cm_rb05_inelgt0} | |
857 | \caption{$\dndeta$ for pp for \INELONE{} events at | |
858 | $\sqrt{s}=\GeV{900}$, $\cm{-10}\le v_z\le\cm{10}$, rebinned by a | |
859 | factor 5. Comparisons to other measurements shown where | |
860 | applicable} | |
861 | \label{fig:2} | |
862 | \end{figure} | |
863 | \begin{figure}[tbp] | |
864 | \centering | |
865 | \includegraphics[keepaspectratio,width=\textwidth]{% | |
866 | dndeta_0900GeV_m10-p10cm_rb05_nsd} | |
867 | \caption{$\dndeta$ for pp for \NSD{} events at $\sqrt{s}=\GeV{900}$, | |
868 | $\cm{-10}\le v_z\le\cm{10}$, rebinned by a factor 5. Comparisons | |
869 | to other measurements shown where applicable} | |
870 | \label{fig:3} | |
871 | \end{figure} | |
dc64f2ea | 872 | \fi |
ffa07380 | 873 | |
874 | \clearpage | |
dc64f2ea | 875 | %% \currentpdfbookmark{Appendices}{Appendices} |
ffa07380 | 876 | \appendix |
56bd6baf | 877 | \section{Nomenclature} |
dc64f2ea | 878 | \label{app:nomen} |
56bd6baf | 879 | |
880 | \begin{table}[hbp] | |
881 | \centering | |
882 | \begin{tabular}[t]{|lp{.8\textwidth}|} | |
883 | \hline | |
884 | \textbf{Symbol}&\textbf{Description}\\ | |
885 | \hline | |
886 | \INEL & In--elastic event\\ | |
887 | \INELONE & In--elastic event with at least one tracklet in the | |
888 | \SPD{} in the region $-1\le\eta\le1$\\ | |
889 | \NSD{} & Non--single--diffractive event. Single diffractive | |
890 | events are events where one of the incident collision systems | |
891 | (proton or nucleus) is excited and radiates particles, but there | |
892 | is no other processes taking place\\ | |
893 | \hline | |
fc6a90cc | 894 | $\NT{}$ & Number of events with a valid trigger\\ |
895 | $\NV{}$ & Number of events with a valid trigger \emph{and} a valid | |
896 | vertex.\\ | |
897 | $\NA{}$ & Number of events with a valid trigger | |
898 | \emph{and} a valid vertex \emph{within} the selected vertex range.\\ | |
899 | $\N{a,c,ac,e}{}$ & Number of events with background triggers $A$, | |
900 | $B$, $AC$, or $E$, \emph{and} a valid off-line trigger of the | |
901 | considered type. Background triggers are typically flagged with | |
902 | the trigger words \texttt{CINT1-A}, \texttt{CINT1-C}, | |
903 | \texttt{CINT1-AC}, \texttt{CINT1-E}, or similar.\\ | |
56bd6baf | 904 | \hline |
905 | $\mult{}$ & Charged particle multiplicity\\ | |
906 | $\mult[,\text{primary}]$ & Primary charged particle multiplicity | |
907 | as given by simulations\\ | |
908 | $\mult[,\text{\FMD{}}]$ & Number of charged particles that hit the | |
909 | \FMD{} as given by simulations\\ | |
910 | $\mult[,t]$ & Number of charged particles in an \FMD{} strip as | |
911 | given by evaluating the energy response functions $F$\\ | |
912 | \hline | |
913 | $F$ & Energy response function (see \eqref{eq:energy_response})\\ | |
914 | $\Delta_{mp}$ & Most probably energy loss\\ | |
915 | $\xi$ & `Width' parameter of a Landau distribution\\ | |
916 | $\sigma$ & Variance of a Gaussian distribution\\ | |
dc64f2ea | 917 | $a_i$ & Relative weight of the $i$--fold MIP peak in the energy |
56bd6baf | 918 | loss spectra.\\ |
919 | \hline | |
dc64f2ea | 920 | $\Corners{}$ & Azimuthal acceptance of strip $t$\\ |
921 | $\SecMap{}$ & Secondary particle correction factor in $\etaphi$ | |
922 | for a given vertex bin $v$\\ | |
923 | $\DeadCh{}$ & Acceptance in $\etaphi$ for a given vertex bin $v$\\ | |
56bd6baf | 924 | \hline |
925 | $\dndetadphi[incl,r,v,i]$ & Inclusive (primary \emph{and} | |
926 | secondary) charge particle density in event $i$ with vertex $v$, | |
927 | for \FMD{} ring $r$.\\ | |
928 | $\dndetadphi[r,v,i]$ & Primary charged particle | |
929 | density in event $i$ with vertex $v$ for \FMD{} ring $r$. \\ | |
930 | $\dndetadphi[v,i]$ & Primary charged particle density in event $i$ | |
931 | with vertex $v$\\ | |
932 | $I_{v,i}(\eta)$ & $\eta$ acceptance of event $i$ with vertex $v$\\ | |
fc6a90cc | 933 | $I(\eta)$ & Integrated $\eta$ acceptance over $\NA$ events. |
934 | Note, that this has a value of $\NA$ for $(\eta)$ bins where we | |
56bd6baf | 935 | have full coverage\\ |
936 | \hline | |
b9bd46b7 | 937 | $X_t$ & Value $X$ for strip number $t$ (0-511 for inner rings, |
938 | 0-255 for outer rings)\\ | |
939 | $X_r$ & Value $X$ for ring $r$ (where rings are \FMD{1i}, | |
940 | \FMD{2i}, \FMD{2o}, \FMD{3o}, and \FMD{3i} in decreasing $\eta$ | |
941 | coverage).\\ | |
942 | $X_v$ & Value $X$ for vertex bin $v$ (typically 10 bins from -10cm | |
943 | to +10cm)\\ | |
944 | $X_i$ & Value $X$ for event $i$\\ | |
945 | \hline | |
56bd6baf | 946 | \end{tabular} |
947 | \caption{Nomenclature used in this document} | |
948 | \label{tab:nomenclature} | |
949 | \end{table} | |
950 | \clearpage | |
951 | ||
952 | ||
ffa07380 | 953 | \section{Second pass example code} |
56bd6baf | 954 | \label{app:exa_pass2} |
ffa07380 | 955 | \lstset{basicstyle=\small\ttfamily,% |
956 | keywordstyle=\color[rgb]{0.627,0.125,0.941}\bfseries,% | |
957 | identifierstyle=\color[rgb]{0.133,0.545,0.133}\itshape,% | |
958 | commentstyle=\color[rgb]{0.698,0.133,0.133},% | |
959 | stringstyle=\color[rgb]{0.737,0.561,0.561}, | |
fc6a90cc | 960 | emph={TH2D,TH1D,TFile,TTree,AliAODForwardMult},emphstyle=\color{blue},% |
ffa07380 | 961 | emph={[2]dndeta,sum,norm},emphstyle={[2]\bfseries\underbar},% |
fc6a90cc | 962 | emph={[3]file,tree,mult,nV,nBg,nA,nT,i,gSystem},emphstyle={[3]},% |
ffa07380 | 963 | language=c++,% |
964 | } | |
965 | \begin{lstlisting}[caption={Example 2\textsuperscript{nd} pass code to | |
966 | do $\dndeta$},label={lst:example},frame=single,captionpos=b] | |
fc6a90cc | 967 | void Analyse(int mask=AliAODForwardMult::kInel, |
968 | float vzLow=-10, float vzHigh=10, float trigEff=1) | |
ffa07380 | 969 | { |
970 | gSystem->Load("libANALYSIS.so"); // Load analysis libraries | |
971 | gSystem->Load("libANALYSISalice.so"); // General ALICE stuff | |
bd6f5206 | 972 | gSystem->Load("libPWGLFforward2.so"); // Forward analysis code |
ffa07380 | 973 | |
fc6a90cc | 974 | int nT = 0; // # of ev. w/trigger |
975 | int nV = 0; // # of ev. w/trigger&vertex | |
976 | int nA = 0; // # of accepted ev. | |
977 | int nBg = 0; // # of background ev | |
978 | TH2D* sum = 0; // Summed hist | |
979 | AliAODForwardMult* mult = 0; // AOD object | |
980 | TFile* file = TFile::Open("AliAODs.root","READ"); | |
981 | TTree* tree = static_cast<TTree*>(file->Get("aodTree")); | |
982 | tree->SetBranchAddress("Forward", &forward); // Set the address | |
ffa07380 | 983 | |
56bd6baf | 984 | for (int i = 0; i < tree->GetEntries(); i++) { |
ffa07380 | 985 | // Read the i'th event |
986 | tree->GetEntry(i); | |
987 | ||
988 | // Create sum histogram on first event - to match binning to input | |
0a89eed1 | 989 | if (!sum) |
990 | sum = static_cast<TH2D*>(mult->GetHistogram()->Clone("d2ndetadphi")); | |
ffa07380 | 991 | |
fc6a90cc | 992 | // Calculate beta=A+C-E |
993 | if (mult->IsTriggerBits(mask|AliAODForwardMult::kA)) nBg++; | |
994 | if (mult->IsTriggerBits(mask|AliAODForwardMult::kC)) nBg++; | |
995 | if (mult->IsTriggerBits(mask|AliAODForwardMult::kE)) nBg--; | |
56bd6baf | 996 | |
ffa07380 | 997 | // Other trigger/event requirements could be defined |
998 | if (!mult->IsTriggerBits(mask)) continue; | |
fc6a90cc | 999 | nT++; |
ffa07380 | 1000 | |
56bd6baf | 1001 | // Check if we have vertex and select vertex range (in centimeters) |
fc6a90cc | 1002 | if (!mult->HasIpZ()) continue; |
1003 | nV++; | |
1004 | ||
1005 | if (!mult->InRange(vzLow, vzHigh) continue; | |
1006 | nA++; | |
ffa07380 | 1007 | |
1008 | // Add contribution from this event | |
1009 | sum->Add(&(mult->GetHistogram())); | |
1010 | } | |
655b45b0 | 1011 | |
ffa07380 | 1012 | // Get acceptance normalisation from underflow bins |
fc6a90cc | 1013 | TH1D* norm = sum->ProjectionX("norm", 0, 0, ""); |
ffa07380 | 1014 | // Project onto eta axis - _ignoring_underflow_bins_! |
fc6a90cc | 1015 | TH1D* dndeta = sum->ProjectionX("dndeta", 1, -1, "e"); |
ffa07380 | 1016 | // Normalize to the acceptance, and scale by the vertex efficiency |
1017 | dndeta->Divide(norm); | |
fc6a90cc | 1018 | dndeta->Scale(trigEff * nT/nV / (1 - nBg/nT), "width"); |
ffa07380 | 1019 | // And draw the result |
1020 | dndeta->Draw(); | |
1021 | } | |
1022 | \end{lstlisting} | |
0a89eed1 | 1023 | |
56bd6baf | 1024 | \section{$\Delta E$ fits} |
1025 | \label{app:eloss_fits} | |
1026 | ||
1027 | \begin{figure}[htbp] | |
1028 | \centering | |
dc64f2ea | 1029 | \includegraphics[keepaspectratio,width=\textwidth]{eloss_fits} |
1030 | \caption{Summary of energy loss fits in each $\eta$ bin (see also | |
1031 | \secref{sec:sub:sub:eloss_fits}). | |
1032 | \newline | |
1033 | On the left side: Top panel shows the | |
1034 | reduced $\chi^2$, second from the top shows the found | |
1035 | scaling constant, 3\textsuperscript{rd} from the top is | |
1036 | the most probable energy loss $\Delta_{mp}$, 4\textsuperscript{th} | |
1037 | shows the width parameter $\xi$ of the Landau, and the | |
1038 | 5\textsuperscript{th} is the Gaussian width $\sigma$. | |
b9bd46b7 | 1039 | $\Delta_{mp}$, $\xi$, and $\sigma$ have units of $\Delta E/\Delta |
1040 | E_{mip}$. | |
dc64f2ea | 1041 | \newline |
1042 | On the right: The top panel shows the maximum number of | |
1043 | multi--particle signals that where fitted, and the 4 bottom panels | |
1044 | shows the weights $a_2,a_3,a_4,$ and $a_5$ for 2, 3, 4, and 5 | |
1045 | particle responses.} | |
56bd6baf | 1046 | \label{fig:eloss_fits} |
1047 | \end{figure} | |
1048 | ||
dc64f2ea | 1049 | \clearpage |
1050 | \currentpdfbookmark{References}{References} | |
0a89eed1 | 1051 | \begin{thebibliography}{99} |
56bd6baf | 1052 | \bibitem{FWD:2004mz} \ALICE{} Collaboration, Bearden, I.~G.\ \textit{et al} |
1053 | \textit{ALICE technical design report on forward detectors: FMD, T0 | |
1054 | and V0}, \CERN{}, 2004, CERN-LHCC-2004-025 | |
1055 | \bibitem{cholm:2009} Christensen, C.~H., \textit{The ALICE Forward | |
1056 | Multiplicity Detector --- From Design to Installation}, | |
1057 | Ph.D.~thesis, University of Copenhagen, 2009, | |
1058 | \url{http://www.nbi.dk/~cholm/}. | |
549a0be3 | 1059 | \bibitem{maxime} Guilbaud, M. \textit{et al}, \textit{Measurement of the charged-particle |
1060 | multiplicity density at forward rapidity | |
1061 | with ALICE VZERO detector in central | |
1062 | Pb-Pb collision at $\sqrt{s_{NN}}=\TeV{2.76}$}, | |
1063 | ALICE internal note, 2012, | |
1064 | \url{https://aliceinfo.cern.ch/Notes/node/17/}. | |
dc64f2ea | 1065 | \bibitem{nim:b1:16} |
1066 | %% \bibitem{Hancock:1983ry} | |
1067 | S.~Hancock, F.~James, J.~Movchet {\it et al.}, | |
1068 | ``Energy Loss Distributions For Single Particles And Several | |
1069 | Particles In A Thin Silicon Absorber,'' Nucl.\ Instrum.\ Meth.\ | |
b9bd46b7 | 1070 | \textbf{B1} (1984) 16, \url{http://cdsweb.cern.ch/record/147286/files/cer-000058451.pdf}. |
dc64f2ea | 1071 | \bibitem{phyrev:a28:615} |
1072 | %% \bibitem{Hancock:1983fp} | |
1073 | S.~Hancock, F.~James, J.~Movchet {\it et al.}, ``Energy Loss And | |
1074 | Energy Straggling Of Protons And Pions In The Momentum Range | |
b9bd46b7 | 1075 | 0.7-gev/c To 115-gev/c,'' Phys.\ Rev.\ \textbf{A28} (1983) 615, |
1076 | \url{http://cdsweb.cern.ch/record/145395/files/PhysRevA.28.615.pdf}. | |
549a0be3 | 1077 | \bibitem{hhd:2009} Dalsgaard, H.~H., \textit{Pseudorapidity Densities in p+p and Pb+Pb collisions at |
1078 | LHC measured with the ALICE experiment}, | |
1079 | Ph.D.~thesis, University of Copenhagen, 2011, | |
1080 | \url{http://www.nbi.dk/~canute/thesis.pdf}. | |
0a89eed1 | 1081 | \end{thebibliography} |
655b45b0 | 1082 | \end{document} |
56bd6baf | 1083 | |
1084 | % Local Variables: | |
1085 | % ispell-local-dictionary: "british" | |
9e3855d0 | 1086 | % TeX-PDF-mode: t |
56bd6baf | 1087 | % End: |
1088 | % | |
fc6a90cc | 1089 | % LocalWords: tracklet diffractive IsTriggerBits AliAODForwardMult ProjectionX |