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Syntax problems on HP-UX corrected
[u/mrichter/AliRoot.git] / PHOS / shaker / lushow.f
CommitLineData
fe4da5cc 1*CMZ : 17/07/98 15.44.33 by Federico Carminati
2*-- Author :
3C*********************************************************************
4
5 SUBROUTINE LUSHOW(IP1,IP2,QMAX)
6
7C...Purpose: to generate timelike parton showers from given partons.
8 IMPLICIT DOUBLE PRECISION(D)
9*KEEP,LUJETS.
10 COMMON /LUJETS/ N,K(200000,5),P(200000,5),V(200000,5)
11 SAVE /LUJETS/
12*KEEP,LUDAT1.
13 COMMON /LUDAT1/ MSTU(200),PARU(200),MSTJ(200),PARJ(200)
14 SAVE /LUDAT1/
15*KEEP,LUDAT2.
16 COMMON /LUDAT2/ KCHG(500,3),PMAS(500,4),PARF(2000),VCKM(4,4)
17 SAVE /LUDAT2/
18*KEND.
19 DIMENSION PMTH(5,40),PS(5),PMA(4),PMSD(4),IEP(4),IPA(4),
20 &KFLA(4),KFLD(4),KFL(4),ITRY(4),ISI(4),ISL(4),DP(4),DPT(5,4)
21
22C...Initialization of cutoff masses etc.
23 IF(MSTJ(41).LE.0.OR.(MSTJ(41).EQ.1.AND.QMAX.LE.PARJ(82)).OR.
24 &QMAX.LE.MIN(PARJ(82),PARJ(83)).OR.MSTJ(41).GE.3) RETURN
25 PMTH(1,21)=ULMASS(21)
26 PMTH(2,21)=SQRT(PMTH(1,21)**2+0.25*PARJ(82)**2)
27 PMTH(3,21)=2.*PMTH(2,21)
28 PMTH(4,21)=PMTH(3,21)
29 PMTH(5,21)=PMTH(3,21)
30 PMTH(1,22)=ULMASS(22)
31 PMTH(2,22)=SQRT(PMTH(1,22)**2+0.25*PARJ(83)**2)
32 PMTH(3,22)=2.*PMTH(2,22)
33 PMTH(4,22)=PMTH(3,22)
34 PMTH(5,22)=PMTH(3,22)
35 PMQTH1=PARJ(82)
36 IF(MSTJ(41).EQ.2) PMQTH1=MIN(PARJ(82),PARJ(83))
37 PMQTH2=PMTH(2,21)
38 IF(MSTJ(41).EQ.2) PMQTH2=MIN(PMTH(2,21),PMTH(2,22))
39 DO 100 IF=1,8
40 PMTH(1,IF)=ULMASS(IF)
41 PMTH(2,IF)=SQRT(PMTH(1,IF)**2+0.25*PMQTH1**2)
42 PMTH(3,IF)=PMTH(2,IF)+PMQTH2
43 PMTH(4,IF)=SQRT(PMTH(1,IF)**2+0.25*PARJ(82)**2)+PMTH(2,21)
44 100 PMTH(5,IF)=SQRT(PMTH(1,IF)**2+0.25*PARJ(83)**2)+PMTH(2,22)
45 PT2MIN=MAX(0.5*PARJ(82),1.1*PARJ(81))**2
46 ALAMS=PARJ(81)**2
47 ALFM=LOG(PT2MIN/ALAMS)
48
49C...Store positions of shower initiating partons.
50 M3JC=0
51 IF(IP1.GT.0.AND.IP1.LE.MIN(N,MSTU(4)-MSTU(32)).AND.IP2.EQ.0) THEN
52 NPA=1
53 IPA(1)=IP1
54 ELSEIF(MIN(IP1,IP2).GT.0.AND.MAX(IP1,IP2).LE.MIN(N,MSTU(4)-
55 &MSTU(32))) THEN
56 NPA=2
57 IPA(1)=IP1
58 IPA(2)=IP2
59 ELSEIF(IP1.GT.0.AND.IP1.LE.MIN(N,MSTU(4)-MSTU(32)).AND.IP2.LT.0.
60 &AND.IP2.GE.-3) THEN
61 NPA=IABS(IP2)
62 DO 110 I=1,NPA
63 110 IPA(I)=IP1+I-1
64 ELSE
65 CALL LUERRM(12,
66 & '(LUSHOW:) failed to reconstruct showering system')
67 IF(MSTU(21).GE.1) RETURN
68 ENDIF
69
70C...Check on phase space available for emission.
71 IREJ=0
72 DO 120 J=1,5
73 120 PS(J)=0.
74 PM=0.
75 DO 130 I=1,NPA
76 KFLA(I)=IABS(K(IPA(I),2))
77 PMA(I)=P(IPA(I),5)
78 IF(KFLA(I).NE.0.AND.(KFLA(I).LE.8.OR.KFLA(I).EQ.21))
79 &PMA(I)=PMTH(3,KFLA(I))
80 PM=PM+PMA(I)
81 IF(KFLA(I).EQ.0.OR.(KFLA(I).GT.8.AND.KFLA(I).NE.21).OR.
82 &PMA(I).GT.QMAX) IREJ=IREJ+1
83 DO 130 J=1,4
84 130 PS(J)=PS(J)+P(IPA(I),J)
85 IF(IREJ.EQ.NPA) RETURN
86 PS(5)=SQRT(MAX(0.,PS(4)**2-PS(1)**2-PS(2)**2-PS(3)**2))
87 IF(NPA.EQ.1) PS(5)=PS(4)
88 IF(PS(5).LE.PM+PMQTH1) RETURN
89 IF(NPA.EQ.2.AND.MSTJ(47).GE.1) THEN
90 IF(KFLA(1).GE.1.AND.KFLA(1).LE.8.AND.KFLA(2).GE.1.AND.
91 & KFLA(2).LE.8) M3JC=1
92 IF(MSTJ(47).GE.2) M3JC=1
93 ENDIF
94
95C...Define imagined single initiator of shower for parton system.
96 NS=N
97 IF(N.GT.MSTU(4)-MSTU(32)-5) THEN
98 CALL LUERRM(11,'(LUSHOW:) no more memory left in LUJETS')
99 IF(MSTU(21).GE.1) RETURN
100 ENDIF
101 IF(NPA.GE.2) THEN
102 K(N+1,1)=11
103 K(N+1,2)=21
104 K(N+1,3)=0
105 K(N+1,4)=0
106 K(N+1,5)=0
107 P(N+1,1)=0.
108 P(N+1,2)=0.
109 P(N+1,3)=0.
110 P(N+1,4)=PS(5)
111 P(N+1,5)=PS(5)
112 V(N+1,5)=PS(5)**2
113 N=N+1
114 ENDIF
115
116C...Loop over partons that may branch.
117 NEP=NPA
118 IM=NS
119 IF(NPA.EQ.1) IM=NS-1
120 140 IM=IM+1
121 IF(N.GT.NS) THEN
122 IF(IM.GT.N) GOTO 380
123 KFLM=IABS(K(IM,2))
124 IF(KFLM.EQ.0.OR.(KFLM.GT.8.AND.KFLM.NE.21)) GOTO 140
125 IF(P(IM,5).LT.PMTH(2,KFLM)) GOTO 140
126 IGM=K(IM,3)
127 ELSE
128 IGM=-1
129 ENDIF
130 IF(N+NEP.GT.MSTU(4)-MSTU(32)-5) THEN
131 CALL LUERRM(11,'(LUSHOW:) no more memory left in LUJETS')
132 IF(MSTU(21).GE.1) RETURN
133 ENDIF
134
135C...Position of aunt (sister to branching parton).
136C...Origin and flavour of daughters.
137 IAU=0
138 IF(IGM.GT.0) THEN
139 IF(K(IM-1,3).EQ.IGM) IAU=IM-1
140 IF(N.GE.IM+1.AND.K(IM+1,3).EQ.IGM) IAU=IM+1
141 ENDIF
142 IF(IGM.GE.0) THEN
143 K(IM,4)=N+1
144 DO 150 I=1,NEP
145 150 K(N+I,3)=IM
146 ELSE
147 K(N+1,3)=IPA(1)
148 ENDIF
149 IF(IGM.LE.0) THEN
150 DO 160 I=1,NEP
151 160 K(N+I,2)=K(IPA(I),2)
152 ELSEIF(KFLM.NE.21) THEN
153 K(N+1,2)=K(IM,2)
154 K(N+2,2)=K(IM,5)
155 ELSEIF(K(IM,5).EQ.21) THEN
156 K(N+1,2)=21
157 K(N+2,2)=21
158 ELSE
159 K(N+1,2)=K(IM,5)
160 K(N+2,2)=-K(IM,5)
161 ENDIF
162
163C...Reset flags on daughers and tries made.
164 DO 170 IP=1,NEP
165 K(N+IP,1)=3
166 K(N+IP,4)=0
167 K(N+IP,5)=0
168 KFLD(IP)=IABS(K(N+IP,2))
169 ITRY(IP)=0
170 ISL(IP)=0
171 ISI(IP)=0
172 170 IF(KFLD(IP).GT.0.AND.(KFLD(IP).LE.8.OR.KFLD(IP).EQ.21)) ISI(IP)=1
173 ISLM=0
174
175C...Maximum virtuality of daughters.
176 IF(IGM.LE.0) THEN
177 DO 180 I=1,NPA
178 IF(NPA.GE.3) P(N+I,4)=(PS(4)*P(IPA(I),4)-PS(1)*P(IPA(I),1)-
179 & PS(2)*P(IPA(I),2)-PS(3)*P(IPA(I),3))/PS(5)
180 P(N+I,5)=MIN(QMAX,PS(5))
181 IF(NPA.GE.3) P(N+I,5)=MIN(P(N+I,5),P(N+I,4))
182 180 IF(ISI(I).EQ.0) P(N+I,5)=P(IPA(I),5)
183 ELSE
184 IF(MSTJ(43).LE.2) PEM=V(IM,2)
185 IF(MSTJ(43).GE.3) PEM=P(IM,4)
186 P(N+1,5)=MIN(P(IM,5),V(IM,1)*PEM)
187 P(N+2,5)=MIN(P(IM,5),(1.-V(IM,1))*PEM)
188 IF(K(N+2,2).EQ.22) P(N+2,5)=PMTH(1,22)
189 ENDIF
190 DO 190 I=1,NEP
191 PMSD(I)=P(N+I,5)
192 IF(ISI(I).EQ.1) THEN
193 IF(P(N+I,5).LE.PMTH(3,KFLD(I))) P(N+I,5)=PMTH(1,KFLD(I))
194 ENDIF
195 190 V(N+I,5)=P(N+I,5)**2
196
197C...Choose one of the daughters for evolution.
198 200 INUM=0
199 IF(NEP.EQ.1) INUM=1
200 DO 210 I=1,NEP
201 210 IF(INUM.EQ.0.AND.ISL(I).EQ.1) INUM=I
202 DO 220 I=1,NEP
203 IF(INUM.EQ.0.AND.ITRY(I).EQ.0.AND.ISI(I).EQ.1) THEN
204 IF(P(N+I,5).GE.PMTH(2,KFLD(I))) INUM=I
205 ENDIF
206 220 CONTINUE
207 IF(INUM.EQ.0) THEN
208 RMAX=0.
209 DO 230 I=1,NEP
210 IF(ISI(I).EQ.1.AND.PMSD(I).GE.PMQTH2) THEN
211 RPM=P(N+I,5)/PMSD(I)
212 IF(RPM.GT.RMAX.AND.P(N+I,5).GE.PMTH(2,KFLD(I))) THEN
213 RMAX=RPM
214 INUM=I
215 ENDIF
216 ENDIF
217 230 CONTINUE
218 ENDIF
219
220C...Store information on choice of evolving daughter.
221 INUM=MAX(1,INUM)
222 IEP(1)=N+INUM
223 DO 240 I=2,NEP
224 IEP(I)=IEP(I-1)+1
225 240 IF(IEP(I).GT.N+NEP) IEP(I)=N+1
226 DO 250 I=1,NEP
227 250 KFL(I)=IABS(K(IEP(I),2))
228 ITRY(INUM)=ITRY(INUM)+1
229 IF(ITRY(INUM).GT.200) THEN
230 CALL LUERRM(14,'(LUSHOW:) caught in infinite loop')
231 IF(MSTU(21).GE.1) RETURN
232 ENDIF
233 Z=0.5
234 IF(KFL(1).EQ.0.OR.(KFL(1).GT.8.AND.KFL(1).NE.21)) GOTO 300
235 IF(P(IEP(1),5).LT.PMTH(2,KFL(1))) GOTO 300
236
237C...Calculate allowed z range.
238 IF(NEP.EQ.1) THEN
239 PMED=PS(4)
240 ELSEIF(IGM.EQ.0.OR.MSTJ(43).LE.2) THEN
241 PMED=P(IM,5)
242 ELSE
243 IF(INUM.EQ.1) PMED=V(IM,1)*PEM
244 IF(INUM.EQ.2) PMED=(1.-V(IM,1))*PEM
245 ENDIF
246 IF(MOD(MSTJ(43),2).EQ.1) THEN
247 ZC=PMTH(2,21)/PMED
248 ZCE=PMTH(2,22)/PMED
249 ELSE
250 ZC=0.5*(1.-SQRT(MAX(0.,1.-(2.*PMTH(2,21)/PMED)**2)))
251 IF(ZC.LT.1E-4) ZC=(PMTH(2,21)/PMED)**2
252 ZCE=0.5*(1.-SQRT(MAX(0.,1.-(2.*PMTH(2,22)/PMED)**2)))
253 IF(ZCE.LT.1E-4) ZCE=(PMTH(2,22)/PMED)**2
254 ENDIF
255 ZC=MIN(ZC,0.491)
256 ZCE=MIN(ZCE,0.491)
257 IF((MSTJ(41).EQ.1.AND.ZC.GT.0.49).OR.(MSTJ(41).EQ.2.AND.
258 &MIN(ZC,ZCE).GT.0.49)) THEN
259 P(IEP(1),5)=PMTH(1,KFL(1))
260 V(IEP(1),5)=P(IEP(1),5)**2
261 GOTO 300
262 ENDIF
263
264C...Integral of Altarelli-Parisi z kernel for QCD.
265 IF(MSTJ(49).EQ.0.AND.KFL(1).EQ.21) THEN
266 FBR=6.*LOG((1.-ZC)/ZC)+MSTJ(45)*(0.5-ZC)
267 ELSEIF(MSTJ(49).EQ.0) THEN
268 FBR=(8./3.)*LOG((1.-ZC)/ZC)
269
270C...Integral of Altarelli-Parisi z kernel for scalar gluon.
271 ELSEIF(MSTJ(49).EQ.1.AND.KFL(1).EQ.21) THEN
272 FBR=(PARJ(87)+MSTJ(45)*PARJ(88))*(1.-2.*ZC)
273 ELSEIF(MSTJ(49).EQ.1) THEN
274 FBR=(1.-2.*ZC)/3.
275 IF(IGM.EQ.0.AND.M3JC.EQ.1) FBR=4.*FBR
276
277C...Integral of Altarelli-Parisi z kernel for Abelian vector gluon.
278 ELSEIF(KFL(1).EQ.21) THEN
279 FBR=6.*MSTJ(45)*(0.5-ZC)
280 ELSE
281 FBR=2.*LOG((1.-ZC)/ZC)
282 ENDIF
283
284C...Integral of Altarelli-Parisi kernel for photon emission.
285 IF(MSTJ(41).EQ.2.AND.KFL(1).GE.1.AND.KFL(1).LE.8)
286 &FBRE=(KCHG(KFL(1),1)/3.)**2*2.*LOG((1.-ZCE)/ZCE)
287
288C...Inner veto algorithm starts. Find maximum mass for evolution.
289 260 PMS=V(IEP(1),5)
290 IF(IGM.GE.0) THEN
291 PM2=0.
292 DO 270 I=2,NEP
293 PM=P(IEP(I),5)
294 IF(KFL(I).GT.0.AND.(KFL(I).LE.8.OR.KFL(I).EQ.21)) PM=
295 & PMTH(2,KFL(I))
296 270 PM2=PM2+PM
297 PMS=MIN(PMS,(P(IM,5)-PM2)**2)
298 ENDIF
299
300C...Select mass for daughter in QCD evolution.
301 B0=27./6.
302 DO 280 IF=4,MSTJ(45)
303 280 IF(PMS.GT.4.*PMTH(2,IF)**2) B0=(33.-2.*IF)/6.
304 IF(MSTJ(44).LE.0) THEN
305 PMSQCD=PMS*EXP(MAX(-80.,LOG(RLU(0))*PARU(2)/(PARU(111)*FBR)))
306 ELSEIF(MSTJ(44).EQ.1) THEN
307 PMSQCD=4.*ALAMS*(0.25*PMS/ALAMS)**(RLU(0)**(B0/FBR))
308 ELSE
309 PMSQCD=PMS*RLU(0)**(ALFM*B0/FBR)
310 ENDIF
311 IF(ZC.GT.0.49.OR.PMSQCD.LE.PMTH(4,KFL(1))**2) PMSQCD=
312 &PMTH(2,KFL(1))**2
313 V(IEP(1),5)=PMSQCD
314 MCE=1
315
316C...Select mass for daughter in QED evolution.
317 IF(MSTJ(41).EQ.2.AND.KFL(1).GE.1.AND.KFL(1).LE.8) THEN
318 PMSQED=PMS*EXP(MAX(-80.,LOG(RLU(0))*PARU(2)/(PARU(101)*FBRE)))
319 IF(ZCE.GT.0.49.OR.PMSQED.LE.PMTH(5,KFL(1))**2) PMSQED=
320 & PMTH(2,KFL(1))**2
321 IF(PMSQED.GT.PMSQCD) THEN
322 V(IEP(1),5)=PMSQED
323 MCE=2
324 ENDIF
325 ENDIF
326
327C...Check whether daughter mass below cutoff.
328 P(IEP(1),5)=SQRT(V(IEP(1),5))
329 IF(P(IEP(1),5).LE.PMTH(3,KFL(1))) THEN
330 P(IEP(1),5)=PMTH(1,KFL(1))
331 V(IEP(1),5)=P(IEP(1),5)**2
332 GOTO 300
333 ENDIF
334
335C...Select z value of branching: q -> qgamma.
336 IF(MCE.EQ.2) THEN
337 Z=1.-(1.-ZCE)*(ZCE/(1.-ZCE))**RLU(0)
338 IF(1.+Z**2.LT.2.*RLU(0)) GOTO 260
339 K(IEP(1),5)=22
340
341C...Select z value of branching: q -> qg, g -> gg, g -> qqbar.
342 ELSEIF(MSTJ(49).NE.1.AND.KFL(1).NE.21) THEN
343 Z=1.-(1.-ZC)*(ZC/(1.-ZC))**RLU(0)
344 IF(1.+Z**2.LT.2.*RLU(0)) GOTO 260
345 K(IEP(1),5)=21
346 ELSEIF(MSTJ(49).EQ.0.AND.MSTJ(45)*(0.5-ZC).LT.RLU(0)*FBR) THEN
347 Z=(1.-ZC)*(ZC/(1.-ZC))**RLU(0)
348 IF(RLU(0).GT.0.5) Z=1.-Z
349 IF((1.-Z*(1.-Z))**2.LT.RLU(0)) GOTO 260
350 K(IEP(1),5)=21
351 ELSEIF(MSTJ(49).NE.1) THEN
352 Z=ZC+(1.-2.*ZC)*RLU(0)
353 IF(Z**2+(1.-Z)**2.LT.RLU(0)) GOTO 260
354 KFLB=1+INT(MSTJ(45)*RLU(0))
355 PMQ=4.*PMTH(2,KFLB)**2/V(IEP(1),5)
356 IF(PMQ.GE.1.) GOTO 260
357 PMQ0=4.*PMTH(2,21)**2/V(IEP(1),5)
358 IF(MOD(MSTJ(43),2).EQ.0.AND.(1.+0.5*PMQ)*SQRT(1.-PMQ).LT.
359 & RLU(0)*(1.+0.5*PMQ0)*SQRT(1.-PMQ0)) GOTO 260
360 K(IEP(1),5)=KFLB
361
362C...Ditto for scalar gluon model.
363 ELSEIF(KFL(1).NE.21) THEN
364 Z=1.-SQRT(ZC**2+RLU(0)*(1.-2.*ZC))
365 K(IEP(1),5)=21
366 ELSEIF(RLU(0)*(PARJ(87)+MSTJ(45)*PARJ(88)).LE.PARJ(87)) THEN
367 Z=ZC+(1.-2.*ZC)*RLU(0)
368 K(IEP(1),5)=21
369 ELSE
370 Z=ZC+(1.-2.*ZC)*RLU(0)
371 KFLB=1+INT(MSTJ(45)*RLU(0))
372 PMQ=4.*PMTH(2,KFLB)**2/V(IEP(1),5)
373 IF(PMQ.GE.1.) GOTO 260
374 K(IEP(1),5)=KFLB
375 ENDIF
376 IF(MCE.EQ.1.AND.MSTJ(44).GE.2) THEN
377 IF(Z*(1.-Z)*V(IEP(1),5).LT.PT2MIN) GOTO 260
378 IF(ALFM/LOG(V(IEP(1),5)*Z*(1.-Z)/ALAMS).LT.RLU(0)) GOTO 260
379 ENDIF
380
381C...Check if z consistent with chosen m.
382 IF(KFL(1).EQ.21) THEN
383 KFLGD1=IABS(K(IEP(1),5))
384 KFLGD2=KFLGD1
385 ELSE
386 KFLGD1=KFL(1)
387 KFLGD2=IABS(K(IEP(1),5))
388 ENDIF
389 IF(NEP.EQ.1) THEN
390 PED=PS(4)
391 ELSEIF(NEP.GE.3) THEN
392 PED=P(IEP(1),4)
393 ELSEIF(IGM.EQ.0.OR.MSTJ(43).LE.2) THEN
394 PED=0.5*(V(IM,5)+V(IEP(1),5)-PM2**2)/P(IM,5)
395 ELSE
396 IF(IEP(1).EQ.N+1) PED=V(IM,1)*PEM
397 IF(IEP(1).EQ.N+2) PED=(1.-V(IM,1))*PEM
398 ENDIF
399 IF(MOD(MSTJ(43),2).EQ.1) THEN
400 PMQTH3=0.5*PARJ(82)
401 IF(KFLGD2.EQ.22) PMQTH3=0.5*PARJ(83)
402 PMQ1=(PMTH(1,KFLGD1)**2+PMQTH3**2)/V(IEP(1),5)
403 PMQ2=(PMTH(1,KFLGD2)**2+PMQTH3**2)/V(IEP(1),5)
404 ZD=SQRT(MAX(0.,(1.-V(IEP(1),5)/PED**2)*((1.-PMQ1-PMQ2)**2-
405 & 4.*PMQ1*PMQ2)))
406 ZH=1.+PMQ1-PMQ2
407 ELSE
408 ZD=SQRT(MAX(0.,1.-V(IEP(1),5)/PED**2))
409 ZH=1.
410 ENDIF
411 ZL=0.5*(ZH-ZD)
412 ZU=0.5*(ZH+ZD)
413 IF(Z.LT.ZL.OR.Z.GT.ZU) GOTO 260
414 IF(KFL(1).EQ.21) V(IEP(1),3)=LOG(ZU*(1.-ZL)/MAX(1E-20,ZL*
415 &(1.-ZU)))
416 IF(KFL(1).NE.21) V(IEP(1),3)=LOG((1.-ZL)/MAX(1E-10,1.-ZU))
417
418C...Three-jet matrix element correction.
419 IF(IGM.EQ.0.AND.M3JC.EQ.1) THEN
420 X1=Z*(1.+V(IEP(1),5)/V(NS+1,5))
421 X2=1.-V(IEP(1),5)/V(NS+1,5)
422 X3=(1.-X1)+(1.-X2)
423 IF(MCE.EQ.2) THEN
424 KI1=K(IPA(INUM),2)
425 KI2=K(IPA(3-INUM),2)
426 QF1=KCHG(IABS(KI1),1)*ISIGN(1,KI1)/3.
427 QF2=KCHG(IABS(KI2),1)*ISIGN(1,KI2)/3.
428 WSHOW=QF1**2*(1.-X1)/X3*(1.+(X1/(2.-X2))**2)+
429 & QF2**2*(1.-X2)/X3*(1.+(X2/(2.-X1))**2)
430 WME=(QF1*(1.-X1)/X3-QF2*(1.-X2)/X3)**2*(X1**2+X2**2)
431 ELSEIF(MSTJ(49).NE.1) THEN
432 WSHOW=1.+(1.-X1)/X3*(X1/(2.-X2))**2+
433 & (1.-X2)/X3*(X2/(2.-X1))**2
434 WME=X1**2+X2**2
435 ELSE
436 WSHOW=4.*X3*((1.-X1)/(2.-X2)**2+(1.-X2)/(2.-X1)**2)
437 WME=X3**2
438 ENDIF
439 IF(WME.LT.RLU(0)*WSHOW) GOTO 260
440
441C...Impose angular ordering by rejection of nonordered emission.
442 ELSEIF(MCE.EQ.1.AND.IGM.GT.0.AND.MSTJ(42).GE.2) THEN
443 MAOM=1
444 ZM=V(IM,1)
445 IF(IEP(1).EQ.N+2) ZM=1.-V(IM,1)
446 THE2ID=Z*(1.-Z)*(ZM*P(IM,4))**2/V(IEP(1),5)
447 IAOM=IM
448 290 IF(K(IAOM,5).EQ.22) THEN
449 IAOM=K(IAOM,3)
450 IF(K(IAOM,3).LE.NS) MAOM=0
451 IF(MAOM.EQ.1) GOTO 290
452 ENDIF
453 IF(MAOM.EQ.1) THEN
454 THE2IM=V(IAOM,1)*(1.-V(IAOM,1))*P(IAOM,4)**2/V(IAOM,5)
455 IF(THE2ID.LT.THE2IM) GOTO 260
456 ENDIF
457 ENDIF
458
459C...Impose user-defined maximum angle at first branching.
460 IF(MSTJ(48).EQ.1) THEN
461 IF(NEP.EQ.1.AND.IM.EQ.NS) THEN
462 THE2ID=Z*(1.-Z)*PS(4)**2/V(IEP(1),5)
463 IF(THE2ID.LT.1./PARJ(85)**2) GOTO 260
464 ELSEIF(NEP.EQ.2.AND.IEP(1).EQ.NS+2) THEN
465 THE2ID=Z*(1.-Z)*(0.5*P(IM,4))**2/V(IEP(1),5)
466 IF(THE2ID.LT.1./PARJ(85)**2) GOTO 260
467 ELSEIF(NEP.EQ.2.AND.IEP(1).EQ.NS+3) THEN
468 THE2ID=Z*(1.-Z)*(0.5*P(IM,4))**2/V(IEP(1),5)
469 IF(THE2ID.LT.1./PARJ(86)**2) GOTO 260
470 ENDIF
471 ENDIF
472
473C...End of inner veto algorithm. Check if only one leg evolved so far.
474 300 V(IEP(1),1)=Z
475 ISL(1)=0
476 ISL(2)=0
477 IF(NEP.EQ.1) GOTO 330
478 IF(NEP.EQ.2.AND.P(IEP(1),5)+P(IEP(2),5).GE.P(IM,5)) GOTO 200
479 DO 310 I=1,NEP
480 IF(ITRY(I).EQ.0.AND.KFLD(I).GT.0.AND.(KFLD(I).LE.8.OR.KFLD(I).EQ.
481 &21)) THEN
482 IF(P(N+I,5).GE.PMTH(2,KFLD(I))) GOTO 200
483 ENDIF
484 310 CONTINUE
485
486C...Check if chosen multiplet m1,m2,z1,z2 is physical.
487 IF(NEP.EQ.3) THEN
488 PA1S=(P(N+1,4)+P(N+1,5))*(P(N+1,4)-P(N+1,5))
489 PA2S=(P(N+2,4)+P(N+2,5))*(P(N+2,4)-P(N+2,5))
490 PA3S=(P(N+3,4)+P(N+3,5))*(P(N+3,4)-P(N+3,5))
491 PTS=0.25*(2.*PA1S*PA2S+2.*PA1S*PA3S+2.*PA2S*PA3S-
492 & PA1S**2-PA2S**2-PA3S**2)/PA1S
493 IF(PTS.LE.0.) GOTO 200
494 ELSEIF(IGM.EQ.0.OR.MSTJ(43).LE.2.OR.MOD(MSTJ(43),2).EQ.0) THEN
495 DO 320 I1=N+1,N+2
496 KFLDA=IABS(K(I1,2))
497 IF(KFLDA.EQ.0.OR.(KFLDA.GT.8.AND.KFLDA.NE.21)) GOTO 320
498 IF(P(I1,5).LT.PMTH(2,KFLDA)) GOTO 320
499 IF(KFLDA.EQ.21) THEN
500 KFLGD1=IABS(K(I1,5))
501 KFLGD2=KFLGD1
502 ELSE
503 KFLGD1=KFLDA
504 KFLGD2=IABS(K(I1,5))
505 ENDIF
506 I2=2*N+3-I1
507 IF(IGM.EQ.0.OR.MSTJ(43).LE.2) THEN
508 PED=0.5*(V(IM,5)+V(I1,5)-V(I2,5))/P(IM,5)
509 ELSE
510 IF(I1.EQ.N+1) ZM=V(IM,1)
511 IF(I1.EQ.N+2) ZM=1.-V(IM,1)
512 PML=SQRT((V(IM,5)-V(N+1,5)-V(N+2,5))**2-
513 & 4.*V(N+1,5)*V(N+2,5))
514 PED=PEM*(0.5*(V(IM,5)-PML+V(I1,5)-V(I2,5))+PML*ZM)/V(IM,5)
515 ENDIF
516 IF(MOD(MSTJ(43),2).EQ.1) THEN
517 PMQTH3=0.5*PARJ(82)
518 IF(KFLGD2.EQ.22) PMQTH3=0.5*PARJ(83)
519 PMQ1=(PMTH(1,KFLGD1)**2+PMQTH3**2)/V(I1,5)
520 PMQ2=(PMTH(1,KFLGD2)**2+PMQTH3**2)/V(I1,5)
521 ZD=SQRT(MAX(0.,(1.-V(I1,5)/PED**2)*((1.-PMQ1-PMQ2)**2-
522 & 4.*PMQ1*PMQ2)))
523 ZH=1.+PMQ1-PMQ2
524 ELSE
525 ZD=SQRT(MAX(0.,1.-V(I1,5)/PED**2))
526 ZH=1.
527 ENDIF
528 ZL=0.5*(ZH-ZD)
529 ZU=0.5*(ZH+ZD)
530 IF(I1.EQ.N+1.AND.(V(I1,1).LT.ZL.OR.V(I1,1).GT.ZU)) ISL(1)=1
531 IF(I1.EQ.N+2.AND.(V(I1,1).LT.ZL.OR.V(I1,1).GT.ZU)) ISL(2)=1
532 IF(KFLDA.EQ.21) V(I1,4)=LOG(ZU*(1.-ZL)/MAX(1E-20,ZL*(1.-ZU)))
533 IF(KFLDA.NE.21) V(I1,4)=LOG((1.-ZL)/MAX(1E-10,1.-ZU))
534 320 CONTINUE
535 IF(ISL(1).EQ.1.AND.ISL(2).EQ.1.AND.ISLM.NE.0) THEN
536 ISL(3-ISLM)=0
537 ISLM=3-ISLM
538 ELSEIF(ISL(1).EQ.1.AND.ISL(2).EQ.1) THEN
539 ZDR1=MAX(0.,V(N+1,3)/V(N+1,4)-1.)
540 ZDR2=MAX(0.,V(N+2,3)/V(N+2,4)-1.)
541 IF(ZDR2.GT.RLU(0)*(ZDR1+ZDR2)) ISL(1)=0
542 IF(ISL(1).EQ.1) ISL(2)=0
543 IF(ISL(1).EQ.0) ISLM=1
544 IF(ISL(2).EQ.0) ISLM=2
545 ENDIF
546 IF(ISL(1).EQ.1.OR.ISL(2).EQ.1) GOTO 200
547 ENDIF
548 IF(IGM.GT.0.AND.MOD(MSTJ(43),2).EQ.1.AND.(P(N+1,5).GE.
549 &PMTH(2,KFLD(1)).OR.P(N+2,5).GE.PMTH(2,KFLD(2)))) THEN
550 PMQ1=V(N+1,5)/V(IM,5)
551 PMQ2=V(N+2,5)/V(IM,5)
552 ZD=SQRT(MAX(0.,(1.-V(IM,5)/PEM**2)*((1.-PMQ1-PMQ2)**2-
553 & 4.*PMQ1*PMQ2)))
554 ZH=1.+PMQ1-PMQ2
555 ZL=0.5*(ZH-ZD)
556 ZU=0.5*(ZH+ZD)
557 IF(V(IM,1).LT.ZL.OR.V(IM,1).GT.ZU) GOTO 200
558 ENDIF
559
560C...Accepted branch. Construct four-momentum for initial partons.
561 330 MAZIP=0
562 MAZIC=0
563 IF(NEP.EQ.1) THEN
564 P(N+1,1)=0.
565 P(N+1,2)=0.
566 P(N+1,3)=SQRT(MAX(0.,(P(IPA(1),4)+P(N+1,5))*(P(IPA(1),4)-
567 & P(N+1,5))))
568 P(N+1,4)=P(IPA(1),4)
569 V(N+1,2)=P(N+1,4)
570 ELSEIF(IGM.EQ.0.AND.NEP.EQ.2) THEN
571 PED1=0.5*(V(IM,5)+V(N+1,5)-V(N+2,5))/P(IM,5)
572 P(N+1,1)=0.
573 P(N+1,2)=0.
574 P(N+1,3)=SQRT(MAX(0.,(PED1+P(N+1,5))*(PED1-P(N+1,5))))
575 P(N+1,4)=PED1
576 P(N+2,1)=0.
577 P(N+2,2)=0.
578 P(N+2,3)=-P(N+1,3)
579 P(N+2,4)=P(IM,5)-PED1
580 V(N+1,2)=P(N+1,4)
581 V(N+2,2)=P(N+2,4)
582 ELSEIF(NEP.EQ.3) THEN
583 P(N+1,1)=0.
584 P(N+1,2)=0.
585 P(N+1,3)=SQRT(MAX(0.,PA1S))
586 P(N+2,1)=SQRT(PTS)
587 P(N+2,2)=0.
588 P(N+2,3)=0.5*(PA3S-PA2S-PA1S)/P(N+1,3)
589 P(N+3,1)=-P(N+2,1)
590 P(N+3,2)=0.
591 P(N+3,3)=-(P(N+1,3)+P(N+2,3))
592 V(N+1,2)=P(N+1,4)
593 V(N+2,2)=P(N+2,4)
594 V(N+3,2)=P(N+3,4)
595
596C...Construct transverse momentum for ordinary branching in shower.
597 ELSE
598 ZM=V(IM,1)
599 PZM=SQRT(MAX(0.,(PEM+P(IM,5))*(PEM-P(IM,5))))
600 PMLS=(V(IM,5)-V(N+1,5)-V(N+2,5))**2-4.*V(N+1,5)*V(N+2,5)
601 IF(PZM.LE.0.) THEN
602 PTS=0.
603 ELSEIF(MOD(MSTJ(43),2).EQ.1) THEN
604 PTS=(PEM**2*(ZM*(1.-ZM)*V(IM,5)-(1.-ZM)*V(N+1,5)-
605 & ZM*V(N+2,5))-0.25*PMLS)/PZM**2
606 ELSE
607 PTS=PMLS*(ZM*(1.-ZM)*PEM**2/V(IM,5)-0.25)/PZM**2
608 ENDIF
609 PT=SQRT(MAX(0.,PTS))
610
611C...Find coefficient of azimuthal asymmetry due to gluon polarization.
612 HAZIP=0.
613 IF(MSTJ(49).NE.1.AND.MOD(MSTJ(46),2).EQ.1.AND.K(IM,2).EQ.21.
614 & AND.IAU.NE.0) THEN
615 IF(K(IGM,3).NE.0) MAZIP=1
616 ZAU=V(IGM,1)
617 IF(IAU.EQ.IM+1) ZAU=1.-V(IGM,1)
618 IF(MAZIP.EQ.0) ZAU=0.
619 IF(K(IGM,2).NE.21) THEN
620 HAZIP=2.*ZAU/(1.+ZAU**2)
621 ELSE
622 HAZIP=(ZAU/(1.-ZAU*(1.-ZAU)))**2
623 ENDIF
624 IF(K(N+1,2).NE.21) THEN
625 HAZIP=HAZIP*(-2.*ZM*(1.-ZM))/(1.-2.*ZM*(1.-ZM))
626 ELSE
627 HAZIP=HAZIP*(ZM*(1.-ZM)/(1.-ZM*(1.-ZM)))**2
628 ENDIF
629 ENDIF
630
631C...Find coefficient of azimuthal asymmetry due to soft gluon
632C...interference.
633 HAZIC=0.
634 IF(MSTJ(49).NE.2.AND.MSTJ(46).GE.2.AND.(K(N+1,2).EQ.21.OR.
635 & K(N+2,2).EQ.21).AND.IAU.NE.0) THEN
636 IF(K(IGM,3).NE.0) MAZIC=N+1
637 IF(K(IGM,3).NE.0.AND.K(N+1,2).NE.21) MAZIC=N+2
638 IF(K(IGM,3).NE.0.AND.K(N+1,2).EQ.21.AND.K(N+2,2).EQ.21.AND.
639 & ZM.GT.0.5) MAZIC=N+2
640 IF(K(IAU,2).EQ.22) MAZIC=0
641 ZS=ZM
642 IF(MAZIC.EQ.N+2) ZS=1.-ZM
643 ZGM=V(IGM,1)
644 IF(IAU.EQ.IM-1) ZGM=1.-V(IGM,1)
645 IF(MAZIC.EQ.0) ZGM=1.
646 HAZIC=(P(IM,5)/P(IGM,5))*SQRT((1.-ZS)*(1.-ZGM)/(ZS*ZGM))
647 HAZIC=MIN(0.95,HAZIC)
648 ENDIF
649 ENDIF
650
651C...Construct kinematics for ordinary branching in shower.
652 340 IF(NEP.EQ.2.AND.IGM.GT.0) THEN
653 IF(MOD(MSTJ(43),2).EQ.1) THEN
654 P(N+1,4)=PEM*V(IM,1)
655 ELSE
656 P(N+1,4)=PEM*(0.5*(V(IM,5)-SQRT(PMLS)+V(N+1,5)-V(N+2,5))+
657 & SQRT(PMLS)*ZM)/V(IM,5)
658 ENDIF
659 PHI=PARU(2)*RLU(0)
660 P(N+1,1)=PT*COS(PHI)
661 P(N+1,2)=PT*SIN(PHI)
662 IF(PZM.GT.0.) THEN
663 P(N+1,3)=0.5*(V(N+2,5)-V(N+1,5)-V(IM,5)+2.*PEM*P(N+1,4))/PZM
664 ELSE
665 P(N+1,3)=0.
666 ENDIF
667 P(N+2,1)=-P(N+1,1)
668 P(N+2,2)=-P(N+1,2)
669 P(N+2,3)=PZM-P(N+1,3)
670 P(N+2,4)=PEM-P(N+1,4)
671 IF(MSTJ(43).LE.2) THEN
672 V(N+1,2)=(PEM*P(N+1,4)-PZM*P(N+1,3))/P(IM,5)
673 V(N+2,2)=(PEM*P(N+2,4)-PZM*P(N+2,3))/P(IM,5)
674 ENDIF
675 ENDIF
676
677C...Rotate and boost daughters.
678 IF(IGM.GT.0) THEN
679 IF(MSTJ(43).LE.2) THEN
680 BEX=P(IGM,1)/P(IGM,4)
681 BEY=P(IGM,2)/P(IGM,4)
682 BEZ=P(IGM,3)/P(IGM,4)
683 GA=P(IGM,4)/P(IGM,5)
684 GABEP=GA*(GA*(BEX*P(IM,1)+BEY*P(IM,2)+BEZ*P(IM,3))/(1.+GA)-
685 & P(IM,4))
686 ELSE
687 BEX=0.
688 BEY=0.
689 BEZ=0.
690 GA=1.
691 GABEP=0.
692 ENDIF
693 THE=ULANGL(P(IM,3)+GABEP*BEZ,SQRT((P(IM,1)+GABEP*BEX)**2+
694 & (P(IM,2)+GABEP*BEY)**2))
695 PHI=ULANGL(P(IM,1)+GABEP*BEX,P(IM,2)+GABEP*BEY)
696 DO 350 I=N+1,N+2
697 DP(1)=COS(THE)*COS(PHI)*P(I,1)-SIN(PHI)*P(I,2)+
698 & SIN(THE)*COS(PHI)*P(I,3)
699 DP(2)=COS(THE)*SIN(PHI)*P(I,1)+COS(PHI)*P(I,2)+
700 & SIN(THE)*SIN(PHI)*P(I,3)
701 DP(3)=-SIN(THE)*P(I,1)+COS(THE)*P(I,3)
702 DP(4)=P(I,4)
703 DBP=BEX*DP(1)+BEY*DP(2)+BEZ*DP(3)
704 DGABP=GA*(GA*DBP/(1D0+GA)+DP(4))
705 P(I,1)=DP(1)+DGABP*BEX
706 P(I,2)=DP(2)+DGABP*BEY
707 P(I,3)=DP(3)+DGABP*BEZ
708 350 P(I,4)=GA*(DP(4)+DBP)
709 ENDIF
710
711C...Weight with azimuthal distribution, if required.
712 IF(MAZIP.NE.0.OR.MAZIC.NE.0) THEN
713 DO 360 J=1,3
714 DPT(1,J)=P(IM,J)
715 DPT(2,J)=P(IAU,J)
716 360 DPT(3,J)=P(N+1,J)
717 DPMA=DPT(1,1)*DPT(2,1)+DPT(1,2)*DPT(2,2)+DPT(1,3)*DPT(2,3)
718 DPMD=DPT(1,1)*DPT(3,1)+DPT(1,2)*DPT(3,2)+DPT(1,3)*DPT(3,3)
719 DPMM=DPT(1,1)**2+DPT(1,2)**2+DPT(1,3)**2
720 DO 370 J=1,3
721 DPT(4,J)=DPT(2,J)-DPMA*DPT(1,J)/DPMM
722 370 DPT(5,J)=DPT(3,J)-DPMD*DPT(1,J)/DPMM
723 DPT(4,4)=SQRT(DPT(4,1)**2+DPT(4,2)**2+DPT(4,3)**2)
724 DPT(5,4)=SQRT(DPT(5,1)**2+DPT(5,2)**2+DPT(5,3)**2)
725 IF(MIN(DPT(4,4),DPT(5,4)).GT.0.1*PARJ(82)) THEN
726 CAD=(DPT(4,1)*DPT(5,1)+DPT(4,2)*DPT(5,2)+
727 & DPT(4,3)*DPT(5,3))/(DPT(4,4)*DPT(5,4))
728 IF(MAZIP.NE.0) THEN
729 IF(1.+HAZIP*(2.*CAD**2-1.).LT.RLU(0)*(1.+ABS(HAZIP)))
730 & GOTO 340
731 ENDIF
732 IF(MAZIC.NE.0) THEN
733 IF(MAZIC.EQ.N+2) CAD=-CAD
734 IF((1.-HAZIC)*(1.-HAZIC*CAD)/(1.+HAZIC**2-2.*HAZIC*CAD).
735 & LT.RLU(0)) GOTO 340
736 ENDIF
737 ENDIF
738 ENDIF
739
740C...Continue loop over partons that may branch, until none left.
741 IF(IGM.GE.0) K(IM,1)=14
742 N=N+NEP
743 NEP=2
744 IF(N.GT.MSTU(4)-MSTU(32)-5) THEN
745 CALL LUERRM(11,'(LUSHOW:) no more memory left in LUJETS')
746 IF(MSTU(21).GE.1) N=NS
747 IF(MSTU(21).GE.1) RETURN
748 ENDIF
749 GOTO 140
750
751C...Set information on imagined shower initiator.
752 380 IF(NPA.GE.2) THEN
753 K(NS+1,1)=11
754 K(NS+1,2)=94
755 K(NS+1,3)=IP1
756 IF(IP2.GT.0.AND.IP2.LT.IP1) K(NS+1,3)=IP2
757 K(NS+1,4)=NS+2
758 K(NS+1,5)=NS+1+NPA
759 IIM=1
760 ELSE
761 IIM=0
762 ENDIF
763
764C...Reconstruct string drawing information.
765 DO 390 I=NS+1+IIM,N
766 IF(K(I,1).LE.10.AND.K(I,2).EQ.22) THEN
767 K(I,1)=1
768 ELSEIF(K(I,1).LE.10) THEN
769 K(I,4)=MSTU(5)*(K(I,4)/MSTU(5))
770 K(I,5)=MSTU(5)*(K(I,5)/MSTU(5))
771 ELSEIF(K(MOD(K(I,4),MSTU(5))+1,2).NE.22) THEN
772 ID1=MOD(K(I,4),MSTU(5))
773 IF(K(I,2).GE.1.AND.K(I,2).LE.8) ID1=MOD(K(I,4),MSTU(5))+1
774 ID2=2*MOD(K(I,4),MSTU(5))+1-ID1
775 K(I,4)=MSTU(5)*(K(I,4)/MSTU(5))+ID1
776 K(I,5)=MSTU(5)*(K(I,5)/MSTU(5))+ID2
777 K(ID1,4)=K(ID1,4)+MSTU(5)*I
778 K(ID1,5)=K(ID1,5)+MSTU(5)*ID2
779 K(ID2,4)=K(ID2,4)+MSTU(5)*ID1
780 K(ID2,5)=K(ID2,5)+MSTU(5)*I
781 ELSE
782 ID1=MOD(K(I,4),MSTU(5))
783 ID2=ID1+1
784 K(I,4)=MSTU(5)*(K(I,4)/MSTU(5))+ID1
785 K(I,5)=MSTU(5)*(K(I,5)/MSTU(5))+ID1
786 K(ID1,4)=K(ID1,4)+MSTU(5)*I
787 K(ID1,5)=K(ID1,5)+MSTU(5)*I
788 K(ID2,4)=0
789 K(ID2,5)=0
790 ENDIF
791 390 CONTINUE
792
793C...Transformation from CM frame.
794 IF(NPA.GE.2) THEN
795 BEX=PS(1)/PS(4)
796 BEY=PS(2)/PS(4)
797 BEZ=PS(3)/PS(4)
798 GA=PS(4)/PS(5)
799 GABEP=GA*(GA*(BEX*P(IPA(1),1)+BEY*P(IPA(1),2)+BEZ*P(IPA(1),3))
800 & /(1.+GA)-P(IPA(1),4))
801 ELSE
802 BEX=0.
803 BEY=0.
804 BEZ=0.
805 GABEP=0.
806 ENDIF
807 THE=ULANGL(P(IPA(1),3)+GABEP*BEZ,SQRT((P(IPA(1),1)
808 &+GABEP*BEX)**2+(P(IPA(1),2)+GABEP*BEY)**2))
809 PHI=ULANGL(P(IPA(1),1)+GABEP*BEX,P(IPA(1),2)+GABEP*BEY)
810 IF(NPA.EQ.3) THEN
811 CHI=ULANGL(COS(THE)*COS(PHI)*(P(IPA(2),1)+GABEP*BEX)+COS(THE)*
812 & SIN(PHI)*(P(IPA(2),2)+GABEP*BEY)-SIN(THE)*(P(IPA(2),3)+GABEP*
813 & BEZ),-SIN(PHI)*(P(IPA(2),1)+GABEP*BEX)+COS(PHI)*(P(IPA(2),2)+
814 & GABEP*BEY))
815 MSTU(33)=1
816 CALL LUDBRB(NS+1,N,0.,CHI,0D0,0D0,0D0)
817 ENDIF
818 DBEX=DBLE(BEX)
819 DBEY=DBLE(BEY)
820 DBEZ=DBLE(BEZ)
821 MSTU(33)=1
822 CALL LUDBRB(NS+1,N,THE,PHI,DBEX,DBEY,DBEZ)
823
824C...Decay vertex of shower.
825 DO 400 I=NS+1,N
826 DO 400 J=1,5
827 400 V(I,J)=V(IP1,J)
828
829C...Delete trivial shower, else connect initiators.
830 IF(N.EQ.NS+NPA+IIM) THEN
831 N=NS
832 ELSE
833 DO 410 IP=1,NPA
834 K(IPA(IP),1)=14
835 K(IPA(IP),4)=K(IPA(IP),4)+NS+IIM+IP
836 K(IPA(IP),5)=K(IPA(IP),5)+NS+IIM+IP
837 K(NS+IIM+IP,3)=IPA(IP)
838 IF(IIM.EQ.1.AND.MSTU(16).NE.2) K(NS+IIM+IP,3)=NS+1
839 K(NS+IIM+IP,4)=MSTU(5)*IPA(IP)+K(NS+IIM+IP,4)
840 410 K(NS+IIM+IP,5)=MSTU(5)*IPA(IP)+K(NS+IIM+IP,5)
841 ENDIF
842
843 RETURN
844 END