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2\section{Changes in Recent Versions}
3
4 This section contains a record of changes in recently released
5versions of ISAJET, taken from the memoranda distributed to users.
6Note that the released version numbers are not necessarily consecutive.
7
8\subsection{Version~7.51, May 2000}
9
10 Several improvements in the SUSY RGE's have been made. All
11two-loop terms including both gauge and Yukawa couplings and the
12contributions from right-handed neutrinos are now included. There is a
13new keyword \verb|SSBCSC| to specify a scale other than the GUT scale
14for the RGE boundary conditions.
15
16 The process $Z+\gamma$ is now included in \verb|WPAIR|. (This
17was omitted because it has no contribution from triple gauge boson
18couplings.)
19
20 An incorrect type declaration produced unphysical results for
21beamsstrahlung on some computers. This has been fixed. While the bug is
22serious for $e^+e^-$ with the \verb|EEBEAM| option, it has no effect on
23other processes. Some other minor bugs have also been fixed.
24
25\subsection{Version~7.47, December 1999}
26
27 There are several improvements in the treatment of
28supersymmetry. The Anomaly Mediated SUSY Breaking model of of Randall
29and Sundrum and of Gherghetta, Giudice, and Wells (hep-ph/9904378) has
30been added. The parameters of the model are a universal scalar mass
31$m_0$ at the GUT scale, a gravitino mass $m_{3/2}$, and the usual
32$\tan\beta$ and $\sgn\mu$. These are set by the \verb|AMSB| keyword. The
33renormalization group equations have been extended to include two-loop
34Yukawa terms and right-handed sneutrinos (with default masses above the
35Planck scale). The $\tilde\nu_R$ play a role in the evolution for the
36inverted hierarchy models of Bagger, Feng, and Polonsky, hep-ph/9905292.
37SUSY loop corrections to Yukawa couplings have been incorporated in the
38SUSY mass calculations.
39
40 The Helas library of Murayama, Watanabe, and Hagiwara has been
41incorporated together with a simple multi-body phase space generator.
42This makes it possible to use code generated by MadGraph to produce
43multi-body hard scattering processes. As a first example, a \verb|ZJJ|
44process that generates $Z + \hbox{2 jets}$ has been added, with the $Z$
45treated as a narrow resonance. Additional processes may be added in
46future releases.
47
48 A new \verb|EXTRADIM| process has been added to generate
49Kaluza-Klein graviton production in association with a jet or photon in
50models with extra dimensions at the TeV scale. The cross sections are
51from G.F.Giudice et al., hep-ph/9811291. We thank I. Hinchliffe and L.
52Vacavant for providing this.
53
54 A number of bugs have been fixed, including in particular one in
55the decay $\widetilde W_i \to \widetilde Z_j \tau \nu$.
56
57\subsection{Version~7.44, April 1999}
58
59 A serious bug introduced in Version~7.42 that could lead to
60matrix elements being stored for the wrong mode has been corrected.
61Some sign errors in the matrix elements for gaugino decays have also
62been corrected.
63
64\subsection{Version~7.42, January 1999}
65
66 Beginning with this version, matrix elements are taken into
67account in the event generator as well as in the calculation of decay
68widths for MSSM three-body decays of the form $\tilde A \to \tilde B f
69\bar f$, where $\tilde A$ and $\tilde B$ are gluinos, charginos, or
70neutralinos. This is implemented by having ISASUSY save the poles and
71their couplings when calculating the decay width and then using these
72to reconstruct the matrix element. Other three-body decays may be
73included in the future. Decays selected with \verb|FORCE| use the
74appropriate matrix elements.
75
76 As part of the changes to implement these matrix elements, the
77format of the decay table has changed. It now starts with a header
78line; if this does not match the internal version, then a warning is
79printed. The decay table now includes an index MELEM that specifies the
80matrix element to be used for all processes. This is also used for
81\verb|FORCE| decays and is printed on the run listing for them. SUSY
823-body decays have internally generated negative values of MELEM.
83
84 This version also includes both initial state radiation and
85beamstrahlung for $e^+e^-$ interactions. For initial state radiation
86(bremsstrahlung), if the \verb|EEBREM| keyword is selected, an electron
87structure function will be used. For a convolution of both
88bremsstrahlung and beamstrahlung, the keyword \verb|EEBEAM| must be
89used, with appropriate inputs (see documentation).
90
91\subsection{Version~7.40, October 1998}
92
93 A new process WHIGGS generates $W^\pm+H$ and $Z+H$ events for
94both the Standard Model and SUSY models and also Higgs pair production
95for SUSY models. The types and $W$ decay modes are selected with
96JETTYPE and WMODE as for WPAIR events. This process is of particular
97interest for producing fairly light Higgs bosons at the Tevatron. See
98the documentation for more details.
99
100 Some non-minimal GMSB models can be generated using a new
101keyword GMSB2. The optional parameters are an extra factor between the
102gaugino and scalar masses, shifts in the Higgs masses, a $D$-term
103proportional to hypercharge, and independent numbers of messenger
104fields for the three gauge groups. The documentation gives more
105details and references.
106
107 The default for SUGRA models has been changed to use
108$\alpha_s(M_Z)=0.118$, the experimental value. This means that the
109couplings do not exactly unify at the GUT scale, presumably because of
110the effects of heavy particles. The keyword AL3UNI can be used to
111select exact unification, which produces too large a value for
112$\alpha_s(M_Z)$.
113
114 A number of three-body slepton decays that occur through
115left-right mixing are now included. These are obviously small but
116might compete with gravitino decays. In particular, a decay like
117$\tilde\mu_R \to \tilde\tau_1 \nu\bar\nu$ might lead to a wrong
118momentum measurement in the muon system. So far we have found no case
119in which this is probable.
120
121 The new release also includes a separate Unix tar file
122\verb|mcpp.tar| containing C++ code to read a standard ISAJET output
123file and copy all the information into C++ classes. The tar file
124contains makefiles for Software Release Tools, documentation, and
125examples as well as the code.
126
127\subsection{Version~7.37, April 1998}
128
129 Version~7.37 incorporates Gauge Mediated SUSY Breaking models
130for the first time. In these models, SUSY is broken in a hidden sector
131at a relatively low scale, and the masses of the MSSM fields are then
132produced through ordinary gauge interactions with messenger fields.
133The parameters of the GMSB model in ISAJET are $M_m$, the messenger
134mass scale; $\Lambda_m = F_m/M_m$, where $F_m$ is the SUSY breaking
135scale in the messenger sector; $N_5$, the number of messenger fields;
136the usual $\tan\beta$ and $\sgn\mu$; and $C_{\rm grav} \ge 1$, a
137factor which scales the gravitino mass and hence the lifetime for the
138lightest MSSM particle to decay into it.
139
140 GMSB models have a light gravitino $\tilde G$ as the lightest
141SUSY particle. The phenomenology of the model depends mainly on the
142nature of the next lightest SUSY particle, a $\tilde\chi_1^0$ or a
143$\tilde\tau_1$, which changes with the number $N_5$ of messengers. The
144phenomenology also depends on the lifetime for the $\tilde\chi_1^0 \to
145\tilde G \gamma$ or $\tilde\tau_1 \to \tilde G \tau$ decay; this
146lifetime can be short or very long. All the relevant decays are
147included except for $\tilde\mu \to \nu \nu \tilde\tau_1$, which is very
148suppressed.
149
150 The keyword MGVTNO allows the user to independently input a
151gravitino gravitino mass for the MSSM option. This allows studies of
152SUGRA (or other types) of models where the gravitino is the LSP.
153
154 Version~7.37 also contains an extension of the SUGRA model
155with a variety of non-universal gaugino and sfermion masses and $A$
156terms at the GUT scale. This makes it possible to study, for example,
157how well the SUGRA assumptions can be tested.
158
159 Two significant bugs have also been corrected. The decay modes
160for $B^*$ mesons were missing from the decay table since Version~7.29
161and have been restored. A sign error in the interference term for
162chargino production has been corrected, leading to a larger chargino
163pair cross section at the Tevatron.
164
165\subsection{Version 7.32, November 1997}
166
167 This version makes several corrections in various chargino and
168neutralino widths, thus changing the branching ratios for large
169$\tan\beta$. For $\tilde\chi_2^0$, for example, the $\tilde\chi_1^0
170b\bar b$ branching ratio is decreased significantly, while the
171$\tilde\chi_1^0 \tau^+ \tau^-$ one is increased. Thus the SUGRA
172phenomenology for $\tan\beta \sim 30$ is modified substantially.
173
174 The new version also fixes a few bugs, including a possible
175numerical precision problem in the Drell-Yan process at high mass and
176$q_T$. It also includes a missing routine for the Zebra interface.
177
178\subsection{Version 7.31, August 1997}
179
180 Version fixes a couple of bugs in Version~7.29. In
181particular, the JETTYPE selection did not work correctly for
182supersymmetric Higgs bosons, and there was an error in the interactive
183interface for MSSM input. Since these could lead to incorrect results,
184users should replace the old version. We thank Art Kreymer for finding
185these problems.
186
187 Since top quarks decay before they have time to hadronize,
188they are now put directly onto the particle list. Top hadrons ($t\bar
189u$, $t\bar d$, etc.) no longer appear, and FORCE should be used
190directly for the top quark, i.e.
191\begin{verbatim}
192FORCE
1936,11,-12,5/
194\end{verbatim}
195
196 The documentation has been converted to LaTeX. Run either
197LaTeX~2.09 or LaTeX~2e three times to resolve all the forward
198references. Either US (8.5x11 inch) or A4 size paper can be used.
199
200\subsection{Version 7.30, July 1997}
201
202 This version fixes a couple of bugs in the previous version.
203In particular, the JETTYPE selection did not work correctly for
204supersymmetric Higgs bosons, and there was an error in the interactive
205interface for MSSM input. Since these could lead to incorrect results,
206users should replace the old version. We thank Art Kreymer for finding
207these problems.
208
209 Since top quarks decay before they have time to hadronize,
210they are now put directly onto the particle list. Top hadrons ($t\bar
211u$, $tud$, etc.) no longer appear, and FORCE should be used directly
212for the top quark, i.e.
213\begin{verbatim}
214FORCE
2156,11,-12,5/
216\end{verbatim}
217
218 The documentation has been converted to \LaTeX. Run either
219\LaTeX~2.09 or \LaTeX~2e three times to resolve all the forward
220references. Either US ($8.5\times11$~inch) or A4 size paper can be
221used.
222
223\subsection{Version 7.29, May 1997}
224
225 While the previous version was applicable for large as well as
226small $\tan\beta$, it did contain approximations for the 3-body decays
227$\tilde g \to t \bar b \tilde W_i$, $\tilde Z_i \to b \bar b \tilde
228Z_j, \tau \tau \tilde Z_j$, and $\tilde W_i \to \tau \nu \tilde Z_j$.
229The complete tree-level calculations for three body decays of the
230gluino, chargino and neutralino, with all Yukawa couplings and
231mixings, have now been included (thanks mainly to M. Drees). We have
232compared our branching ratios with those calculated by A.~Bartl and
233collaborators; the agreement is generally good.
234
235 The decay patterns of gluinos, charginos and neutralinos may
236differ from previous expectations if $\tan\beta$ is large. In
237particular, decays into $\tau$'s and $b$'s are often enhanced, while
238decays into $e$'s and $\mu$'s are reduced. It could be important for
239experiments to study new types of signatures, since the cross sections
240for conventional signatures may be considerably reduced.
241
242 We have also corrected several bugs, including a fairly
243serious one in the selection of jet types for SUSY Higgs. We thank
244A.~Kreymer for pointing this out to us.
245
246\subsection{Version 7.27, January 1997}
247
248 The new version contains substantial improvements in the
249treatment of the Minimal Supersymmetric Standard Model (MSSM) and the
250SUGRA model. The squarks of the first two generations are no longer
251assumed to be degenerate. The mass splittings and all the two-body
252decay modes are now correctly calculated for large $\tan\beta$. While
253there are still some approximations for three-body modes, ISAJET is
254now usable for the whole range $1 \simle \tan\beta \simle M_t/M_b$. The
255most interesting new feature for large $\tan\beta$ is that third
256generation modes can be strongly enhanced or even completely dominant.
257
258 To accomodate these changes it was necessary to change the
259MSSM input parameters. To avoid confusion, the MSSM keywords have
260been renamed MSSM[A-C] instead of MSSM[1-3], and the order of the
261parameters has been changed. See the input section of the manual for
262details.
263
264 Treatment of the MSSM Higgs sector has also been improved. In
265the renormalization group equations the Higgs couplings are frozen at
266a higher scale, $Q = \sqrt{M(\tilde t_L)M(\tilde t_R)}$. Running
267$t$, $b$ and $\tau$ masses evaluated at that scale are used to
268reproduce the dominant 2-loop effects. There is some sensitivity to
269the choice of $Q$; our choice seems to give fairly stable results over
270a wide range of parameters and reasonable agreement with other
271calculations. In particular, the resulting light Higgs masses are
272significantly lower than those from Version~7.22.
273
274 The default parton distributions have been updated to CTEQ3L.
275A bug in the PDFLIB interface and other minor bugs have been fixed.
276
277\subsection{Version 7.22, July 1996}
278
279 The new version fixes errors in $\tilde b \to \tilde W t$ and in
280some $\tilde t$ decays and Higgs decays. It also contains a new decay
281table with updated $\tau$, $c$, and $b$ decays, based loosely on the
282QQ decay package from CLEO. The updated decays are less detailed than
283the full CLEO QQ program but an improvement over what existed before.
284The new decays involve a number of additional resonances, including
285$f_0(980)$, $a_1(1260)$, $f_2(1270)$, $K_1(1270)$, $K_1^*(1400)$,
286$K_2^*(1430)$, $\chi_{c1,2,3}$, and $\psi(2S)$, so users may have to
287change their interface routines.
288
289 A number of other small bugs have been corrected.
290
291\subsection{Version 7.20, June 1996}
292
293 The new version corrects both errors introduced in Version~7.19
294and longstanding errors in the final state QCD shower algorithm. It
295also includes the top mass in the cross sections for $g b \to W t$ and
296$g t \to Z t$. When the $t$ mass is taken into account, the process $g
297t \to W b$ can have a pole in the physical region, so it has been
298removed; see the documentation for more discussion.
299
300 Steve Tether recently pointed out to us that the anomalous
301dimension for the $q \to q g$ branching used in the final state QCD
302branching algorithm was incorrect. In investigating this we found an
303additional error, a missing factor of $1/3$ in the $g \to q \bar q$
304branching. The first error produces a small but non-negligible
305underestimate of gluon radiation from quarks. The second overestimates
306quark pair production from gluons by about a factor of 3. In
307particular, this means that backgrounds from heavy quarks $Q$ coming
308from $g \to Q \bar Q$ have been overestimated.
309
310 The new version also allows the user to set arbitrary masses
311for the $U(1)$ and $SU(2)$ gaugino mases in the MSSM rather than
312deriving these from the gluino mass using grand unification. This
313could be useful in studying one of the SUSY interpretations of a CDF
314$ee\gamma\gamma\etmiss$ event recently suggested by Ambrosanio, Kane,
315Kribs, Martin and Mrenna. Note, however, that radiative decay are
316{\it not} included, although the user can force them and multiply by
317the appropriate branching ratios calculated by Haber and Wyler,
318Nucl.{} Phys.{} B323, 267 (1989). No explicit provision for the decay
319$\tilde Z_1 \to \tilde G \gamma$ of the lightest zino into a gravitino
320or goldstino and a photon has been made, but forcing the decay $\tilde
321Z_1 \to \nu\gamma$ has the same effect for any collider detector.
322
323 A number of other minor bugs have also been corrected.
324
325\subsection{Version 7.16, October 1995}
326
327 The new version includes $e^+e^-$ cross sections for both SUSY
328and Standard Model particles with polarized beams. The $e^-$ and $e^+$
329polarizations are specified with a new keyword EPOL. Polarization
330appears to be quite useful in studying SUSY particles at an $e^+e^-$
331collider.
332
333 The new release also includes some bug fixes for $pp$ reactions,
334so you should upgrade even if you do not plan to use the polarized
335$e^+e^-$ cross sections.
336
337\subsection{Version 7.13, September 1994}
338
339 Version 7.13 of ISAJET fixes a bug that we introduced in the
340recently released 7.11 and another bug in $\tilde g \to \tilde q \bar
341q$. We felt it was essential to fix these bugs despite the
342proliferation of versions.
343
344 The new version includes the cross sections for the $e^+e^-$
345production of squarks, sleptons, gauginos, and Higgs bosons in Minimal
346Supersymmetric Standard Model (MSSM) or the minimal supergravity
347(SUGRA) model, including the effects of cascade decays. To generate
348such events, select the \verb|E+E-| reaction type and either SUGRA or
349MSSM, e.g.,
350\begin{verbatim}
351SAMPLE E+E- JOB
352300.,50000,10,100/
353E+E-
354SUGRA
355100,100,0,2,-1/
356TMASS
357170,-1,1/
358END
359STOP
360\end{verbatim}
361The effects of spin correlations in the production and decay, e.g., in
362$e^+e^- \to \widetilde W_1^+ \widetilde W_1^-$, are not included.
363
364 It should be noted that the Standard Model $e^+e^-$ generator in
365ISAJET does not include Bhabba scattering or $W^+W^-$ and $Z^0Z^0$
366production. Also, its hadronization model is cruder than that
367available in some other generators.
368
369\subsection{Version 7.11, September 1994}
370
371 The new version includes the cross sections for the $e^+e^-$
372production of squarks, sleptons, gauginos, and Higgs bosons in Minimal
373Supersymmetric Standard Model (MSSM) or the minimal supergravity
374(SUGRA) model including the effects of cascade decays. To generate
375such events, select the \verb|E+E-| reaction type and either SUGRA or
376MSSM, e.g.,
377\begin{verbatim}
378SAMPLE E+E- JOB
379300.,50000,10,100/
380E+E-
381SUGRA
382100,100,0,2,-1/
383TMASS
384170,-1,1/
385END
386STOP
387\end{verbatim}
388The effects of spin correlations in the production and decay, e.g., in
389$e^+e^- \to \widetilde W_1^+ \widetilde W_1^-$, are not included.
390
391 It should be noted that the Standard Model $e^+e^-$ generator in
392ISAJET does not include Bhabba scattering or $W^+W^-$ and $Z^0Z^0$
393production. Also, its hadronization model is cruder than that
394available in some other generators.
395
396\subsection{Version 7.10, July 1994}
397
398 This version adds a new option that solves the renormalization group
399equations to calculate the Minimal Supersymmetric Standard Model (MSSM)
400parameters in the minimal supergravity (SUGRA) model, assuming only that the
401low energy theory has the minimal particle content, that electroweak
402symmetry is radiatively broken, and that R-parity is conserved. The minimal
403SUGRA model has just four parameters, which are taken to be the common
404scalar mass $m_0$, the common gaugino mass $m_{1/2}$, the common trilinear
405SUSY breaking term $A_0$, all defined at the GUT scale, and $\tan\beta$; the
406sign of $\mu$ must also be given. The renormalization group equations are
407solved iteratively using Runge-Kutta integration including the correct
408thresholds. This program can be used either alone or as part of the event
409generator. In the latter case, the parameters are specified using
410\begin{verse}
411SUGRA\\
412$m_0$, $m_{1/2}$, $A_0$, $\tan\beta$, $\sgn\mu$
413\end{verse}
414While the SUGRA option is less general than the MSSM, it is theoretically
415attractive and provides a much more managable parameter space.
416
417 In addition there have been a number of improvements and bug fixes. An
418occasional infinite loop in the minimum bias generator has been fixed. A few
419SUSY cross sections and decay modes and the JETTYPE flags for SUSY
420particles have been corrected. The treatment of $B$ baryons has been
421improved somewhat.
422
423\end{document}