1 <chapter name="Particle Properties">
3 <h2>Particle Properties</h2>
5 A <code>Particle</code> corresponds to one entry/slot in the
6 event record. Its properties therefore is a mix of ones belonging
7 to a particle-as-such, like its identity code or four-momentum,
8 and ones related to the event-as-a-whole, like which mother it has.
11 What is stored for each particle is
13 <li>the identity code,</li>
14 <li>the status code,</li>
15 <li>two mother indices,</li>
16 <li>two daughter indices,</li>
17 <li>a colour and an anticolour index,</li>
18 <li>the four-momentum and mass,</li>
19 <li>the scale at which the particle was produced (optional),</li>
20 <li>the polarization/spin/helicity of the particle (optional),</li>
21 <li>the production vertex and proper lifetime (optional),</li>
22 <li>a pointer to the particle kind in the particle data table, and</li>
23 <li>a pointer to the whole particle data table.</li>
25 From these, a number of further quantities may be derived.
27 <h3>Basic output methods</h3>
29 The following member functions can be used to extract the most important
32 <method name="int Particle::id()">
33 the identity of a particle, according to the PDG particle codes
37 <method name="int Particle::status()">
38 status code. The status code includes information on how a particle was
39 produced, i.e. where in the program execution it was inserted into the
40 event record, and why. It also tells whether the particle is still present
41 or not. It does not tell how a particle disappeared, whether by a decay,
42 a shower branching, a hadronization process, or whatever, but this is
43 implicit in the status code of its daughter(s). The basic scheme is:
45 <li>status = +- (10 * i + j)</li>
46 <li> + : still remaining particles</li>
47 <li> - : decayed/branched/fragmented/... and not remaining</li>
48 <li> i = 1 - 9 : stage of event generation inside PYTHIA</li>
49 <li> i = 10 -19 : reserved for future expansion</li>
50 <li> i >= 20 : free for add-on programs</li>
51 <li> j = 1 - 9 : further specification</li>
53 In detail, the list of used or foreseen status codes is:
55 <li>11 - 19 : beam particles</li>
57 <li>11 : the event as a whole</li>
58 <li>12 : incoming beam</li>
59 <li>13 : incoming beam-inside-beam (e.g. <ei>gamma</ei>
60 inside <ei>e</ei>)</li>
61 <li>14 : outgoing elastically scattered</li>
62 <li>15 : outgoing diffractively scattered</li>
64 <li>21 - 29 : particles of the hardest subprocess</li>
66 <li>21 : incoming</li>
67 <li>22 : intermediate (intended to have preserved mass)</li>
68 <li>23 : outgoing</li>
70 <li>31 - 39 : particles of subsequent subprocesses</li>
72 <li>31 : incoming</li>
73 <li>32 : intermediate (intended to have preserved mass)</li>
74 <li>33 : outgoing</li>
75 <li>34 : incoming that has already scattered</li>
77 <li>41 - 49 : particles produced by initial-state-showers</li>
79 <li>41 : incoming on spacelike main branch</li>
80 <li>42 : incoming copy of recoiler</li>
81 <li>43 : outgoing produced by a branching</li>
82 <li>44 : outgoing shifted by a branching</li>
83 <li>45 : incoming rescattered parton, with changed kinematics
84 owing to ISR in the mother system (cf. status 34)</li>
85 <li>46 : incoming copy of recoiler when this is a rescattered
86 parton (cf. status 42)</li>
88 <li>51 - 59 : particles produced by final-state-showers</li>
90 <li>51 : outgoing produced by parton branching</li>
91 <li>52 : outgoing copy of recoiler, with changed momentum</li>
92 <li>53 : copy of recoiler when this is incoming parton,
93 with changed momentum</li>
94 <li>54 : copy of a recoiler, when in the initial state of a
95 different system from the radiator</li>
96 <li>55 : copy of a recoiler, when in the final state of a
97 different system from the radiator</li>
99 <li>61 - 69 : particles produced by beam-remnant treatment</li>
101 <li>61 : incoming subprocess particle with primordial <ei>kT</ei>
103 <li>62 : outgoing subprocess particle with primordial <ei>kT</ei>
105 <li>63 : outgoing beam remnant</li>
107 <li>71 - 79 : partons in preparation of hadronization process</li>
109 <li>71 : copied partons to collect into contiguous colour singlet</li>
110 <li>72 : copied recoiling singlet when ministring collapses to
111 one hadron and momentum has to be reshuffled</li>
112 <li>73 : combination of very nearby partons into one</li>
113 <li>74 : combination of two junction quarks (+ nearby gluons)
115 <li>75 : gluons split to decouple a junction-antijunction pair</li>
116 <li>76 : partons with momentum shuffled to decouple a
117 junction-antijunction pair </li>
118 <li>77 : temporary opposing parton when fragmenting first two
119 strings in to junction (should disappear again)</li>
120 <li>78 : temporary combined diquark end when fragmenting last
121 string in to junction (should disappear again)</li>
123 <li>81 - 89 : primary hadrons produced by hadronization process</li>
125 <li>81 : from ministring into one hadron</li>
126 <li>82 : from ministring into two hadrons</li>
127 <li>83, 84 : from normal string (the difference between the two
128 is technical, whether fragmented off from the top of the
129 string system or from the bottom, useful for debug only)</li>
130 <li>85, 86 : primary produced hadrons in junction fragmentation of
131 the first two string legs in to the junction,
132 in order of treatment</li>
134 <li>91 - 99 : particles produced in decay process, or by Bose-Einstein
137 <li>91 : normal decay products</li>
138 <li>92 : decay products after oscillation <ei>B0 <-> B0bar</ei> or
139 <ei>B_s0 <-> B_s0bar</ei></li>
140 <li>93, 94 : decay handled by external program, normally
141 or with oscillation</li>
142 <li>99 : particles with momenta shifted by Bose-Einstein effects
143 (not a proper decay, but bookkept as an <ei>1 -> 1</ei> such,
144 happening after decays of short-lived resonances but before
145 decays of longer-lived particles)</li>
147 <li>101 - 109 : particles in the handling of R-hadron production and
148 decay, i.e. long-lived (or stable) particles containing a very heavy
151 <li>101 : when a string system contains two such long-lived particles,
152 the system is split up by the production of a new q-qbar
153 pair (bookkept as decay chains that seemingly need not conserve
154 flavour etc., but do when considered together)</li>
155 <li>102 : partons rearranged from the long-lived particle end to prepare
156 for fragmentation from this end</li>
157 <li>103 : intermediate "half-R-hadron" formed when a colour octet particle
158 (like the gluino) has been fragmented on one side, but not yet on
160 <li>104 : an R-hadron</li>
161 <li>105 : partons or particles formed together with the R-hadron during
162 the fragmentation treatment</li>
163 <li>106 : subdivision of an R-hadron into its flavour content, with
164 momentum split accordingly, in preparation of the decay of
165 the heavy new particle, if it is unstable</li>
166 <li>107 : two temporary leftover gluons joined into one in the formation
167 of a gluino-gluon R-hadron.</li>
169 <li>111 - 199 : reserved for future expansion</li>
170 <li>201 - : free to be used by anybody</li>
174 <method name="int Particle::mother1()">
176 <methodmore name="int Particle::mother2()">
177 the indices in the event record where the first and last mothers are
178 stored, if any. There are five allowed combinations of <code>mother1</code>
179 and <code>mother2</code>:
181 <li><code>mother1 = mother2 = 0</code>: for lines 0 - 2, where line 0
182 represents the event as a whole, and 1 and 2 the two incoming
183 beam particles; </li>
184 <li><code>mother1 = mother2 > 0</code>: the particle is a "carbon copy"
185 of its mother, but with changed momentum as a "recoil" effect,
186 e.g. in a shower;</li>
187 <li><code>mother1 > 0, mother2 = 0</code>: the "normal" mother case, where
188 it is meaningful to speak of one single mother to several products,
189 in a shower or decay;</li>
190 <li><code>mother1 < mother2</code>, both > 0, for
191 <code>abs(status) = 81 - 86</code>: primary hadrons produced from the
192 fragmentation of a string spanning the range from <code>mother1</code>
193 to <code>mother2</code>, so that all partons in this range should be
194 considered mothers; and analogously for
195 <code>abs(status) = 101 - 106</code>, the formation of R-hadrons;</li>
196 <li><code>mother1 < mother2</code>, both > 0, except case 4: particles
197 with two truly different mothers, in particular the particles emerging
198 from a hard <ei>2 -> n</ei> interaction.</li>
200 <note>Note 1:</note> in backwards evolution of initial-state showers,
201 the mother may well appear below the daughter in the event record.
202 <note>Note 2:</note> the <code>motherList(i)</code> method of the
203 <code>Event</code> class returns a vector of all the mothers,
204 providing a uniform representation for all five cases.
207 <method name="int Particle::daughter1()">
209 <methodmore name="int Particle::daughter2()">
210 the indices in the event record where the first and last daughters
211 are stored, if any. There are five allowed combinations of
212 <code>daughter1</code> and <code>daughter2</code>:
214 <li><code>daughter1 = daughter2 = 0</code>: there are no daughters
216 <li><code>daughter1 = daughter2 > 0</code>: the particle has a
217 "carbon copy" as its sole daughter, but with changed momentum
218 as a "recoil" effect, e.g. in a shower;</li>
219 <li><code>daughter1 > 0, daughter2 = 0</code>: each of the incoming beams
220 has only (at most) one daughter, namely the initiator parton of the
221 hardest interaction; further, in a <ei>2 -> 1</ei> hard interaction,
222 like <ei>q qbar -> Z^0</ei>, or in a clustering of two nearby partons,
223 the initial partons only have this one daughter;</li>
224 <li><code>daughter1 < daughter2</code>, both > 0: the particle has
225 a range of decay products from <code>daughter1</code> to
226 <code>daughter2</code>;</li> <li><code>daughter2 < daughter1</code>,
227 both > 0: the particle has two separately stored decay products (e.g.
228 in backwards evolution of initial-state showers).</li>
230 <note>Note 1:</note> in backwards evolution of initial-state showers, the
231 daughters may well appear below the mother in the event record.
232 <note>Note 2:</note> the mother-daughter relation normally is reciprocal,
233 but not always. An example is hadron beams (indices 1 and 2), where each
234 beam remnant and the initiator of each multiparton interaction has the
235 respective beam as mother, but the beam itself only has the initiator
236 of the hardest interaction as daughter.
237 <note>Note 3:</note> the <code>daughterList(i)</code> method of the
238 <code>Event</code> class returns a vector of all the daughters,
239 providing a uniform representation for all five cases. With this method,
240 also all the daughters of the beams are caught, with the initiators of
241 the basic process given first, while the rest are in no guaranteed order
242 (since they are found by a scanning of the event record for particles
243 with the beam as mother, with no further information).
246 <method name="int Particle::col()">
248 <methodmore name="int Particle::acol()">
249 the colour and anticolour tags, Les Houches Accord <ref>Boo01</ref>
250 style (starting from tag 101 by default, see below).
251 <note>Note:</note> in the preliminary implementation of colour sextets
252 (exotic BSM particles) that exists since PYTHIA 8.150, a negative
253 anticolour tag is interpreted as an additional positive colour tag,
257 <method name="double Particle::px()">
259 <methodmore name="double Particle::py()">
261 <methodmore name="double Particle::pz()">
263 <methodmore name="double Particle::e()">
264 the particle four-momentum components.
267 <method name="Vec4 Particle::p()">
268 the particle four-momentum vector, with components as above.
271 <method name="double Particle::m()">
272 the particle mass, stored with a minus sign (times the absolute value)
273 for spacelike virtual particles.
276 <method name="double Particle::scale()">
277 the scale at which a parton was produced, which can be used to restrict
278 its radiation to lower scales in subsequent steps of the shower evolution.
279 Note that scale is linear in momenta, not quadratic (i.e. <ei>Q</ei>,
283 <method name="double Particle::pol()">
284 the polarization/spin/helicity of a particle. Currently Pythia does not
285 use this variable for any internal operations, so its meaning is not
286 uniquely defined. The LHA standard sets <code>SPINUP</code> to be the
287 cosine of the angle between the spin vector and the 3-momentum of the
288 decaying particle in the lab frame, i.e. restricted to be between +1
289 and -1. A more convenient choice could be the same quantity in the rest
290 frame of the particle production, either the hard subprocess or the
291 mother particle of a decay. Unknown or unpolarized particles should
292 be assigned the value 9.
295 <method name="double Particle::xProd()">
297 <methodmore name="double Particle::yProd()">
299 <methodmore name="double Particle::zProd()">
301 <methodmore name="double Particle::tProd()">
302 the production vertex coordinates, in mm or mm/c.
305 <method name="Vec4 Particle::vProd()">
306 The production vertex four-vector. Note that the components of a
307 <code>Vec4</code> are named <code>px(), py(), pz() and e()</code>
308 which of course then should be reinterpreted as above.
311 <method name="double Particle::tau()">
312 the proper lifetime, in mm/c. It is assigned for all hadrons with
313 positive nominal <ei>tau</ei>, <ei>tau_0 > 0</ei>, because it can be used
314 by PYTHIA to decide whether a particle should or should not be allowed
315 to decay, e.g. based on the decay vertex distance to the primary interaction
319 <h3>Input methods</h3>
321 The same method names as above are also overloaded in versions that
322 set values. These have an input argument of the same type as the
323 respective output above, and are of type <code>void</code>.
326 There are also a few alternative methods for input:
328 <method name="void Particle::statusPos()">
330 <methodmore name="void Particle::statusNeg()">
331 sets the status sign positive or negative, without changing the absolute value.
334 <method name="void Particle::statusCode(int code)">
335 changes the absolute value but retains the original sign.
338 <method name="void Particle::mothers(int mother1, int mother2)">
339 sets both mothers in one go.
342 <method name="void Particle::daughters(int daughter1, int daughter2)">
343 sets both daughters in one go.
346 <method name="void Particle::cols(int col, int acol)">
347 sets both colour and anticolour in one go.
350 <method name="void Particle::p(double px, double py, double pz, double e)">
351 sets the four-momentum components in one go.
354 <method name="void Particle::vProd(double xProd, double yProd,
355 double zProd, double tProd)">
356 sets the production vertex components in one go.
359 <h3>Further output methods</h3>
362 In addition, a number of derived quantities can easily be obtained,
363 but cannot be set, such as:
365 <method name="int Particle::idAbs()">
366 the absolute value of the particle identity code.
369 <method name="int Particle::statusAbs()">
370 the absolute value of the status code.
373 <method name="bool Particle::isFinal()">
374 true for a remaining particle, i.e. one with positive status code,
375 else false. Thus, after an event has been fully generated, it
376 separates the final-state particles from intermediate-stage ones.
377 (If used earlier in the generation process, a particle then
378 considered final may well decay later.)
381 <method name="bool Particle::isRescatteredIncoming()">
382 true for particles with a status code -34, -45, -46 or -54, else false.
383 This singles out partons that have been created in a previous
384 scattering but here are bookkept as belonging to the incoming state
385 of another scattering.
388 <method name="bool Particle::hasVertex()">
389 production vertex has been set; if false then production at the origin
393 <method name="double Particle::m2()">
394 squared mass, which can be negative for spacelike partons.
397 <method name="double Particle::mCalc()">
399 <methodmore name="double Particle::m2Calc()">
400 (squared) mass calculated from the four-momentum; should agree
401 with <code>m(), m2()</code> up to roundoff. Negative for spacelike
405 <method name="double Particle::eCalc()">
406 energy calculated from the mass and three-momentum; should agree
407 with <code>e()</code> up to roundoff. For spacelike partons a
408 positive-energy solution is picked. This need not be the correct
409 one, so it is recommended not to use the method in such cases.
412 <method name="double Particle::pT()">
414 <methodmore name="double Particle::pT2()">
415 (squared) transverse momentum.
418 <method name="double Particle::mT()">
420 <methodmore name="double Particle::mT2()">
421 (squared) transverse mass. If <ei>m_T^2</ei> is negative, which can happen
422 for a spacelike parton, then <code>mT()</code> returns
423 <ei>-sqrt(-m_T^2)</ei>, by analogy with the negative sign used to store
427 <method name="double Particle::pAbs()">
429 <methodmore name="double Particle::pAbs2()">
430 (squared) three-momentum size.
433 <method name="double Particle::eT()">
435 <methodmore name="double Particle::eT2()">
436 (squared) transverse energy,
437 <ei>eT = e * sin(theta) = e * pT / pAbs</ei>.
440 <method name="double Particle::theta()">
442 <methodmore name="double Particle::phi()">
443 polar and azimuthal angle.
446 <method name="double Particle::thetaXZ()">
447 angle in the <ei>(p_x, p_z)</ei> plane, between <ei>-pi</ei> and
448 <ei>+pi</ei>, with 0 along the <ei>+z</ei> axis
451 <method name="double Particle::pPos()">
453 <methodmore name="double Particle::pNeg()">
457 <method name="double Particle::y()">
459 <methodmore name="double Particle::eta()">
460 rapidity and pseudorapidity.
463 <method name="double Particle::xDec()">
465 <methodmore name="double Particle::yDec()">
467 <methodmore name="double Particle::zDec()">
469 <methodmore name="double Particle::tDec()">
471 <methodmore name="Vec4 Particle::vDec()">
472 the decay vertex coordinates, in mm or mm/c. This decay vertex is
473 calculated from the production vertex, the proper lifetime and the
474 four-momentum assuming no magnetic field or other detector interference.
475 It can be used to decide whether a decay should be performed or not,
476 and thus is defined also for particles which PYTHIA did not let decay.
480 Each Particle contains a pointer to the respective
481 <code>ParticleDataEntry</code> object in the
482 <aloc href="ParticleDataScheme">particle data tables</aloc>.
483 This gives access to properties of the particle species as such. It is
484 there mainly for convenience, and should be thrown if an event is
485 written to disk, to avoid any problems of object persistency. Should
486 an event later be read back in, the pointer will be recreated from the
487 <code>id</code> code if the normal input methods are used. (Use the
488 <code><aloc href="EventRecord">Event::restorePtrs()</aloc></code> method
489 if your persistency scheme bypasses the normal methods.) This pointer is
490 used by the following member functions:
492 <method name="string Particle::name()">
493 the name of the particle.
496 <method name="string Particle::nameWithStatus()">
497 as above, but for negative-status particles the name is given in
498 brackets to emphasize that they are intermediaries.
501 <method name="int Particle::spinType()">
502 <ei>2 *spin + 1</ei> when defined, else 0.
505 <method name="double Particle::charge()">
507 <methodmore name="int Particle::chargeType()">
508 charge, and three times it to make an integer.
511 <method name="bool Particle::isCharged()">
513 <methodmore name="bool Particle::isNeutral()">
514 charge different from or equal to 0.
517 <method name="int Particle::colType()">
518 0 for colour singlets, 1 for triplets,
519 -1 for antitriplets and 2 for octets. (A preliminary implementation of
520 colour sextets also exists, using 3 for sextets and -3 for antisextets.)
523 <method name="double Particle::m0()">
524 the nominal mass of the particle, according to the data tables.
527 <method name="double Particle::mWidth()">
529 <methodmore name="double Particle::mMin()">
531 <methodmore name="double Particle::mMax()">
532 the width of the particle, and the minimum and maximum allowed mass value
533 for particles with a width, according to the data tables.
536 <method name="double Particle::mass()">
537 the mass of the particle, picked according to a Breit-Wigner
538 distribution for particles with width. It is different each time called,
539 and is therefore only used once per particle to set its mass
543 <method name="double Particle::constituentMass()">
544 will give the constituent masses for quarks and diquarks,
545 else the same masses as with <code>m0()</code>.
548 <method name="double Particle::tau0()">
549 the nominal lifetime <ei>tau_0 > 0</ei>, in mm/c, of the particle species.
550 It is used to assign the actual lifetime <ei>tau</ei>.
553 <method name="bool Particle::mayDecay()">
554 flag whether particle has been declared unstable or not, offering
555 the main user switch to select which particle species to decay.
558 <method name="bool Particle::canDecay()">
559 flag whether decay modes have been declared for a particle,
560 so that it could be decayed, should that be requested.
563 <method name="bool Particle::doExternalDecay()">
564 particles that are decayed by an external program.
567 <method name="bool Particle::isResonance()">
568 particles where the decay is to be treated as part of the hard process,
569 typically with nominal mass above 20 GeV (<ei>W^+-, Z^0, t, ...</ei>).
572 <method name="bool Particle::isVisible()">
573 particles with strong or electric charge, or composed of ones having it,
574 which thereby should be considered visible in a normal detector.
577 <method name="bool Particle::isLepton()">
578 true for a lepton or an antilepton (including neutrinos).
581 <method name="bool Particle::isQuark()">
582 true for a quark or an antiquark.
585 <method name="bool Particle::isGluon()">
589 <method name="bool Particle::isDiquark()">
590 true for a diquark or an antidiquark.
593 <method name="bool Particle::isParton()">
594 true for a gluon, a quark or antiquark up to the b (but excluding top),
595 and a diquark or antidiquark consisting of quarks up to the b.
598 <method name="bool Particle::isHadron()">
599 true for a hadron (made up out of normal quarks and gluons,
600 i.e. not for R-hadrons and other exotic states).
603 <method name="ParticleDataEntry& particleDataEntry()">
604 a reference to the ParticleDataEntry.
608 Not part of the <code>Particle</code> class proper, but obviously tightly
609 linked, are the two methods
611 <method name="double m(const Particle& pp1, const Particle& pp2)">
613 <methodmore name="double m2(const Particle& pp1, const Particle& pp2)">
614 the (squared) invariant mass of two particles.
617 <h3>Methods that perform operations</h3>
619 There are some further methods, some of them inherited from
620 <code>Vec4</code>, to modify the properties of a particle.
621 They are of little interest to the normal user.
623 <method name="void Particle::rescale3(double fac)">
624 multiply the three-momentum components by <code>fac</code>.
627 <method name="void Particle::rescale4(double fac)">
628 multiply the four-momentum components by <code>fac</code>.
631 <method name="void Particle::rescale5(double fac)">
632 multiply the four-momentum components and the mass by <code>fac</code>.
635 <method name="void Particle::rot(double theta, double phi)">
636 rotate three-momentum and production vertex by these polar and azimuthal
640 <method name="void Particle::bst(double betaX, double betaY, double betaZ)">
641 boost four-momentum and production vertex by this three-vector.
644 <method name="void Particle::bst(double betaX, double betaY, double betaZ,
646 as above, but also input the <ei>gamma</ei> value, to reduce roundoff errors.
649 <method name="void Particle::bst(const Vec4& pBst)">
650 boost four-momentum and production vertex by
651 <ei>beta = (px/e, py/e, pz/e)</ei>.
654 <method name="void Particle::bst(const Vec4& pBst, double mBst)">
655 as above, but also use <ei>gamma> = e/m</ei> to reduce roundoff errors.
658 <method name="void Particle::bstback(const Vec4& pBst)">
660 <methodmore name="void Particle::bstback(const Vec4& pBst, double mBst)">
661 as above, but with sign of boost flipped.
664 <method name="void Particle::rotbst(const RotBstMatrix& M)">
665 combined rotation and boost of the four-momentum and production vertex.
668 <method name="void Particle::offsetHistory( int minMother, int addMother,
669 int minDaughter, int addDaughter))">
670 add a positive offset to the mother and daughter indices, i.e.
671 if <code>mother1</code> is above <code>minMother</code> then
672 <code>addMother</code> is added to it, same with <code>mother2</code>,
673 if <code>daughter1</code> is above <code>minDaughter</code> then
674 <code>addDaughter</code> is added to it, same with <code>daughter2</code>.
677 <method name="void Particle::offsetCol( int addCol)">
678 add a positive offset to colour indices, i.e. if <code>col</code> is
679 positive then <code>addCol</code> is added to it, same with <code>acol</code>.
682 <h3>Constructors and operators</h3>
684 Normally a user would not need to create new particles. However, if
685 necessary, the following constructors and methods may be of interest.
687 <method name="Particle::Particle()">
688 constructs an empty particle, i.e. where all properties have been set 0
692 <method name="Particle::Particle(int id, int status = 0, int mother1 = 0,
693 int mother2 = 0, int daughter1 = 0, int daughter2 = 0, int col = 0,
694 int acol = 0, double px = 0., double py = 0., double pz = 0., double e = 0.,
695 double m = 0., double scale = 0., double pol = 9.)">
696 constructs a particle with the input properties provided, and non-provided
697 ones set 0 (9 for <code>pol</code>).
700 <method name="Particle::Particle(int id, int status, int mother1, int mother2,
701 int daughter1, int daughter2, int col, int acol, Vec4 p, double m = 0.,
702 double scale = 0., double pol = 9.)">
703 constructs a particle with the input properties provided, and non-provided
704 ones set 0 (9 for <code>pol</code>).
707 <method name="Particle::Particle(const Particle& pt)">
708 constructs an particle that is a copy of the input one.
711 <method name="Particle& Particle::operator=(const Particle& pt)">
712 copies the input particle.
715 <method name="void Particle::setPDTPtr()">
716 sets the pointer to the <code>ParticleData</code> objects,
717 i.e. to the full particle data table. Also calls <code>setPDEPtr</code>
721 <method name="void Particle::setPDEPtr()">
722 sets the pointer to the <code>ParticleDataEntry</code> object of the
723 particle, based on its current <code>id</code> code.
729 <code><aloc href="EventRecord">Event</aloc></code>
730 class also contains a few methods defined for individual particles,
731 but these may require some search in the event record and therefore
732 cannot be defined as <code>Particle</code> methods.
735 Currently there is no information on polarization states.
739 <!-- Copyright (C) 2013 Torbjorn Sjostrand -->