PYTHIA/pythia/pyklim.F

   1
   2 C***********************************************************************
   3
   4       SUBROUTINE PYKLIM(ILIM)
   5
   6 C...Checks generated variables against pre-set kinematical limits;
   7 C...also calculates limits on variables used in generation.
   8       COMMON/LUJETS/N,K(4000,5),P(4000,5),V(4000,5)
   9       COMMON/LUDAT1/MSTU(200),PARU(200),MSTJ(200),PARJ(200)
  10       COMMON/LUDAT2/KCHG(500,3),PMAS(500,4),PARF(2000),VCKM(4,4)
  11       COMMON/LUDAT3/MDCY(500,3),MDME(2000,2),BRAT(2000),KFDP(2000,5)
  12       COMMON/PYSUBS/MSEL,MSUB(200),KFIN(2,-40:40),CKIN(200)
  13       COMMON/PYPARS/MSTP(200),PARP(200),MSTI(200),PARI(200)
  14       COMMON/PYINT1/MINT(400),VINT(400)
  15       COMMON/PYINT2/ISET(200),KFPR(200,2),COEF(200,20),ICOL(40,4,2)
  16       SAVE /LUJETS/,/LUDAT1/,/LUDAT2/,/LUDAT3/
  17       SAVE /PYSUBS/,/PYPARS/,/PYINT1/,/PYINT2/
  18
  19 C...Common kinematical expressions.
  20       MINT(51)=0
  21       ISUB=MINT(1)
  22       ISTSB=ISET(ISUB)
  23       IF(ISUB.EQ.96) GOTO 110
  24       SQM3=VINT(63)
  25       SQM4=VINT(64)
  26       IF(ILIM.NE.0) THEN
  27         IF(ABS(SQM3).LT.1E-4.AND.ABS(SQM4).LT.1E-4) THEN
  28           CKIN09=MAX(CKIN(9),CKIN(13))
  29           CKIN10=MIN(CKIN(10),CKIN(14))
  30           CKIN11=MAX(CKIN(11),CKIN(15))
  31           CKIN12=MIN(CKIN(12),CKIN(16))
  32         ELSE
  33           CKIN09=MAX(CKIN(9),MIN(0.,CKIN(13)))
  34           CKIN10=MIN(CKIN(10),MAX(0.,CKIN(14)))
  35           CKIN11=MAX(CKIN(11),MIN(0.,CKIN(15)))
  36           CKIN12=MIN(CKIN(12),MAX(0.,CKIN(16)))
  37         ENDIF
  38       ENDIF
  39       IF(ILIM.NE.1) THEN
  40         TAU=VINT(21)
  41         RM3=SQM3/(TAU*VINT(2))
  42         RM4=SQM4/(TAU*VINT(2))
  43         BE34=SQRT(MAX(1E-20,(1.-RM3-RM4)**2-4.*RM3*RM4))
  44       ENDIF
  45       PTHMIN=CKIN(3)
  46       IF(MIN(SQM3,SQM4).LT.CKIN(6)**2.AND.ISTSB.NE.1.AND.ISTSB.NE.3)
  47      &PTHMIN=MAX(CKIN(3),CKIN(5))
  48
  49       IF(ILIM.EQ.0) THEN
  50 C...Check generated values of tau, y*, cos(theta-hat), and tau' against
  51 C...pre-set kinematical limits.
  52         YST=VINT(22)
  53         CTH=VINT(23)
  54         TAUP=VINT(26)
  55         TAUE=TAU
  56         IF(ISTSB.GE.3.AND.ISTSB.LE.5) TAUE=TAUP
  57         X1=SQRT(TAUE)*EXP(YST)
  58         X2=SQRT(TAUE)*EXP(-YST)
  59         XF=X1-X2
  60         IF(MINT(47).NE.1) THEN
  61           IF(TAU*VINT(2).LT.CKIN(1)**2) MINT(51)=1
  62           IF(CKIN(2).GE.0..AND.TAU*VINT(2).GT.CKIN(2)**2) MINT(51)=1
  63           IF(YST.LT.CKIN(7).OR.YST.GT.CKIN(8)) MINT(51)=1
  64           IF(XF.LT.CKIN(25).OR.XF.GT.CKIN(26)) MINT(51)=1
  65         ENDIF
  66         IF(MINT(45).NE.1) THEN
  67           IF(X1.LT.CKIN(21).OR.X1.GT.CKIN(22)) MINT(51)=1
  68         ENDIF
  69         IF(MINT(46).NE.1) THEN
  70           IF(X2.LT.CKIN(23).OR.X2.GT.CKIN(24)) MINT(51)=1
  71         ENDIF
  72         IF(ISTSB.EQ.2.OR.ISTSB.EQ.4.OR.ISTSB.EQ.6) THEN
  73           PTH=0.5*BE34*SQRT(TAU*VINT(2)*MAX(0.,1.-CTH**2))
  74           EXPY3=MAX(1.E-10,(1.+RM3-RM4+BE34*CTH)/
  75      &    MAX(1.E-10,(1.+RM3-RM4-BE34*CTH)))
  76           EXPY4=MAX(1.E-10,(1.-RM3+RM4-BE34*CTH)/
  77      &    MAX(1.E-10,(1.-RM3+RM4+BE34*CTH)))
  78           Y3=YST+0.5*LOG(EXPY3)
  79           Y4=YST+0.5*LOG(EXPY4)
  80           YLARGE=MAX(Y3,Y4)
  81           YSMALL=MIN(Y3,Y4)
  82           ETALAR=10.
  83           ETASMA=-10.
  84           STH=SQRT(MAX(0.,1.-CTH**2))
  85           EXSQ3=SQRT(MAX(1E-20,((1.+RM3-RM4)*COSH(YST)+BE34*SINH(YST)*
  86      &    CTH)**2-4.*RM3))
  87           EXSQ4=SQRT(MAX(1E-20,((1.-RM3+RM4)*COSH(YST)-BE34*SINH(YST)*
  88      &    CTH)**2-4.*RM4))
  89           IF(STH.GE.1.E-6) THEN
  90             EXPET3=((1.+RM3-RM4)*SINH(YST)+BE34*COSH(YST)*CTH+EXSQ3)/
  91      &      (BE34*STH)
  92             EXPET4=((1.-RM3+RM4)*SINH(YST)-BE34*COSH(YST)*CTH+EXSQ4)/
  93      &      (BE34*STH)
  94             ETA3=LOG(MIN(1.E10,MAX(1.E-10,EXPET3)))
  95             ETA4=LOG(MIN(1.E10,MAX(1.E-10,EXPET4)))
  96             ETALAR=MAX(ETA3,ETA4)
  97             ETASMA=MIN(ETA3,ETA4)
  98           ENDIF
  99           CTS3=((1.+RM3-RM4)*SINH(YST)+BE34*COSH(YST)*CTH)/EXSQ3
 100           CTS4=((1.-RM3+RM4)*SINH(YST)-BE34*COSH(YST)*CTH)/EXSQ4
 101           CTSLAR=MIN(1.,MAX(CTS3,CTS4))
 102           CTSSMA=MAX(-1.,MIN(CTS3,CTS4))
 103           SH=TAU*VINT(2)
 104           RPTS=4.*VINT(71)**2/SH
 105           BE34L=SQRT(MAX(0.,(1.-RM3-RM4)**2-4.*RM3*RM4-RPTS))
 106           RM34=MAX(1E-20,2.*RM3*RM4)
 107           IF(2.*VINT(71)**2/(VINT(21)*VINT(2)).LT.0.0001)
 108      &    RM34=MAX(RM34,2.*VINT(71)**2/(VINT(21)*VINT(2)))
 109           RTHM=(4.*RM3*RM4+RPTS)/(1.-RM3-RM4+BE34L)
 110           THA=0.5*SH*MAX(RTHM,1.-RM3-RM4-BE34*CTH)
 111           UHA=0.5*SH*MAX(RTHM,1.-RM3-RM4+BE34*CTH)
 112           IF(PTH.LT.PTHMIN) MINT(51)=1
 113           IF(CKIN(4).GE.0..AND.PTH.GT.CKIN(4)) MINT(51)=1
 114           IF(YLARGE.LT.CKIN(9).OR.YLARGE.GT.CKIN(10)) MINT(51)=1
 115           IF(YSMALL.LT.CKIN(11).OR.YSMALL.GT.CKIN(12)) MINT(51)=1
 116           IF(ETALAR.LT.CKIN(13).OR.ETALAR.GT.CKIN(14)) MINT(51)=1
 117           IF(ETASMA.LT.CKIN(15).OR.ETASMA.GT.CKIN(16)) MINT(51)=1
 118           IF(CTSLAR.LT.CKIN(17).OR.CTSLAR.GT.CKIN(18)) MINT(51)=1
 119           IF(CTSSMA.LT.CKIN(19).OR.CTSSMA.GT.CKIN(20)) MINT(51)=1
 120           IF(CTH.LT.CKIN(27).OR.CTH.GT.CKIN(28)) MINT(51)=1
 121           IF(THA.LT.CKIN(35)) MINT(51)=1
 122           IF(CKIN(36).GE.0..AND.THA.GT.CKIN(36)) MINT(51)=1
 123           IF(UHA.LT.CKIN(37)) MINT(51)=1
 124           IF(CKIN(38).GE.0..AND.UHA.GT.CKIN(38)) MINT(51)=1
 125         ENDIF
 126         IF(ISTSB.GE.3.AND.ISTSB.LE.5) THEN
 127           IF(TAUP*VINT(2).LT.CKIN(31)**2) MINT(51)=1
 128           IF(CKIN(32).GE.0..AND.TAUP*VINT(2).GT.CKIN(32)**2) MINT(51)=1
 129         ENDIF
 130
 131 C...Additional cuts on W2 (approximately) in DIS.
 132         IF(ISUB.EQ.10) THEN
 133           XBJ=X2
 134           IF(IABS(MINT(12)).LT.20) XBJ=X1
 135           Q2BJ=THA
 136           W2BJ=Q2BJ*(1.-XBJ)/XBJ
 137           IF(W2BJ.LT.CKIN(39)) MINT(51)=1
 138           IF(CKIN(40).GT.0..AND.W2BJ.GT.CKIN(40)) MINT(51)=1
 139         ENDIF
 140
 141 C...Additional p_T cuts on 2 -> 3 process.
 142         IF(ISTSB.EQ.6) THEN
 143           KFQ=KFPR(131,2)
 144           PMQQ=SQRT(VINT(64))
 145           PMQ=PMAS(KFQ,1)
 146           PZQ=SQRT(MAX(0.,(0.5*PMQQ)**2-PMQ**2))
 147           DO 100 I=MINT(84)+1,MINT(84)+2
 148           K(I,1)=1
 149           P(I,1)=0.
 150           P(I,2)=0.
 151           P(I,3)=PZQ*(-1.)**(I-1)
 152           P(I,4)=0.5*PMQQ
 153           P(I,5)=PMQ
 154   100     CONTINUE
 155           PEQQ=0.5*SQRT(TAU*VINT(2))*(1.+(VINT(64)-VINT(63))/
 156      &    (TAU*VINT(2)))
 157           PZQQ=SQRT(MAX(0.,PEQQ**2-VINT(64)))
 158           CALL LUDBRB(MINT(84)+1,MINT(84)+2,ACOS(VINT(83)),VINT(84),
 159      &    0D0,0D0,-DBLE(PZQQ/PEQQ))
 160           CALL LUDBRB(MINT(84)+1,MINT(84)+2,ACOS(VINT(23)),VINT(24),
 161      &    0D0,0D0,0D0)
 162           PTQ2=SQRT(P(MINT(84)+1,1)**2+P(MINT(84)+1,2)**2)
 163           PTQ3=SQRT(P(MINT(84)+2,1)**2+P(MINT(84)+2,2)**2)
 164           PTMNQ=MIN(PTQ2,PTQ3)
 165           PTMXQ=MAX(PTQ2,PTQ3)
 166           IF(PTMNQ.LT.CKIN(51)) MINT(51)=1
 167           IF(CKIN(52).GE.0..AND.PTMNQ.GT.CKIN(52)) MINT(51)=1
 168           IF(PTMXQ.LT.CKIN(53)) MINT(51)=1
 169           IF(CKIN(54).GE.0..AND.PTMXQ.GT.CKIN(54)) MINT(51)=1
 170           VINT(85)=PTMNQ
 171           VINT(86)=PTMXQ
 172         ENDIF
 173
 174       ELSEIF(ILIM.EQ.1) THEN
 175 C...Calculate limits on tau
 176 C...0) due to definition
 177         TAUMN0=0.
 178         TAUMX0=1.
 179 C...1) due to limits on subsystem mass
 180         TAUMN1=CKIN(1)**2/VINT(2)
 181         TAUMX1=1.
 182         IF(CKIN(2).GE.0.) TAUMX1=CKIN(2)**2/VINT(2)
 183 C...2) due to limits on pT-hat (and non-overlapping rapidity intervals)
 184         TM3=SQRT(SQM3+PTHMIN**2)
 185         TM4=SQRT(SQM4+PTHMIN**2)
 186         YDCOSH=1.
 187         IF(CKIN09.GT.CKIN12) YDCOSH=COSH(CKIN09-CKIN12)
 188         TAUMN2=(TM3**2+2.*TM3*TM4*YDCOSH+TM4**2)/VINT(2)
 189         TAUMX2=1.
 190 C...3) due to limits on pT-hat and cos(theta-hat)
 191         CTH2MN=MIN(CKIN(27)**2,CKIN(28)**2)
 192         CTH2MX=MAX(CKIN(27)**2,CKIN(28)**2)
 193         TAUMN3=0.
 194         IF(CKIN(27)*CKIN(28).GT.0.) TAUMN3=
 195      &  (SQRT(SQM3+PTHMIN**2/(1.-CTH2MN))+
 196      &  SQRT(SQM4+PTHMIN**2/(1.-CTH2MN)))**2/VINT(2)
 197         TAUMX3=1.
 198         IF(CKIN(4).GE.0..AND.CTH2MX.LT.1.) TAUMX3=
 199      &  (SQRT(SQM3+CKIN(4)**2/(1.-CTH2MX))+
 200      &  SQRT(SQM4+CKIN(4)**2/(1.-CTH2MX)))**2/VINT(2)
 201 C...4) due to limits on x1 and x2
 202         TAUMN4=CKIN(21)*CKIN(23)
 203         TAUMX4=CKIN(22)*CKIN(24)
 204 C...5) due to limits on xF
 205         TAUMN5=0.
 206         TAUMX5=MAX(1.-CKIN(25),1.+CKIN(26))
 207 C...6) due to limits on that and uhat
 208         TAUMN6=(SQM3+SQM4+CKIN(35)+CKIN(37))/VINT(2)
 209         TAUMX6=1.
 210         IF(CKIN(36).GT.0..AND.CKIN(38).GT.0.) TAUMX6=
 211      &  (SQM3+SQM4+CKIN(36)+CKIN(38))/VINT(2)
 212
 213 C...Net effect of all separate limits.
 214         VINT(11)=MAX(TAUMN0,TAUMN1,TAUMN2,TAUMN3,TAUMN4,TAUMN5,TAUMN6)
 215         VINT(31)=MIN(TAUMX0,TAUMX1,TAUMX2,TAUMX3,TAUMX4,TAUMX5,TAUMX6)
 216         IF(MINT(47).EQ.1.AND.(ISTSB.EQ.1.OR.ISTSB.EQ.2.OR.ISTSB.EQ.6))
 217      &  THEN
 218           VINT(11)=0.99999
 219           VINT(31)=1.00001
 220         ELSEIF(MINT(47).EQ.5) THEN
 221           VINT(31)=MIN(VINT(31),0.999998)
 222         ENDIF
 223         IF(VINT(31).LE.VINT(11)) MINT(51)=1
 224
 225       ELSEIF(ILIM.EQ.2) THEN
 226 C...Calculate limits on y*
 227         TAUE=TAU
 228         IF(ISTSB.GE.3.AND.ISTSB.LE.5) TAUE=VINT(26)
 229         TAURT=SQRT(TAUE)
 230 C...0) due to kinematics
 231         YSTMN0=LOG(TAURT)
 232         YSTMX0=-YSTMN0
 233 C...1) due to explicit limits
 234         YSTMN1=CKIN(7)
 235         YSTMX1=CKIN(8)
 236 C...2) due to limits on x1
 237         YSTMN2=LOG(MAX(TAUE,CKIN(21))/TAURT)
 238         YSTMX2=LOG(MAX(TAUE,CKIN(22))/TAURT)
 239 C...3) due to limits on x2
 240         YSTMN3=-LOG(MAX(TAUE,CKIN(24))/TAURT)
 241         YSTMX3=-LOG(MAX(TAUE,CKIN(23))/TAURT)
 242 C...4) due to limits on xF
 243         YEPMN4=0.5*ABS(CKIN(25))/TAURT
 244         YSTMN4=SIGN(LOG(MAX(1E-20,SQRT(1.+YEPMN4**2)+YEPMN4)),CKIN(25))
 245         YEPMX4=0.5*ABS(CKIN(26))/TAURT
 246         YSTMX4=SIGN(LOG(MAX(1E-20,SQRT(1.+YEPMX4**2)+YEPMX4)),CKIN(26))
 247 C...5) due to simultaneous limits on y-large and y-small
 248         YEPSMN=(RM3-RM4)*SINH(CKIN09-CKIN11)
 249         YEPSMX=(RM3-RM4)*SINH(CKIN10-CKIN12)
 250         YDIFMN=ABS(LOG(MAX(1E-20,SQRT(1.+YEPSMN**2)-YEPSMN)))
 251         YDIFMX=ABS(LOG(MAX(1E-20,SQRT(1.+YEPSMX**2)-YEPSMX)))
 252         YSTMN5=0.5*(CKIN09+CKIN11-YDIFMN)
 253         YSTMX5=0.5*(CKIN10+CKIN12+YDIFMX)
 254 C...6) due to simultaneous limits on cos(theta-hat) and y-large or
 255 C...   y-small
 256         CTHLIM=SQRT(MAX(0.,1.-4.*PTHMIN**2/(BE34**2*TAUE*VINT(2))))
 257         RZMN=BE34*MAX(CKIN(27),-CTHLIM)
 258         RZMX=BE34*MIN(CKIN(28),CTHLIM)
 259         YEX3MX=(1.+RM3-RM4+RZMX)/MAX(1E-10,1.+RM3-RM4-RZMX)
 260         YEX4MX=(1.+RM4-RM3-RZMN)/MAX(1E-10,1.+RM4-RM3+RZMN)
 261         YEX3MN=MAX(1E-10,1.+RM3-RM4+RZMN)/(1.+RM3-RM4-RZMN)
 262         YEX4MN=MAX(1E-10,1.+RM4-RM3-RZMX)/(1.+RM4-RM3+RZMX)
 263         YSTMN6=CKIN09-0.5*LOG(MAX(YEX3MX,YEX4MX))
 264         YSTMX6=CKIN12-0.5*LOG(MIN(YEX3MN,YEX4MN))
 265
 266 C...Net effect of all separate limits.
 267         VINT(12)=MAX(YSTMN0,YSTMN1,YSTMN2,YSTMN3,YSTMN4,YSTMN5,YSTMN6)
 268         VINT(32)=MIN(YSTMX0,YSTMX1,YSTMX2,YSTMX3,YSTMX4,YSTMX5,YSTMX6)
 269         IF(MINT(47).EQ.1) THEN
 270           VINT(12)=-0.00001
 271           VINT(32)=0.00001
 272         ELSEIF(MINT(47).EQ.2) THEN
 273           VINT(12)=0.99999*YSTMX0
 274           VINT(32)=1.00001*YSTMX0
 275         ELSEIF(MINT(47).EQ.3) THEN
 276           VINT(12)=-1.00001*YSTMX0
 277           VINT(32)=-0.99999*YSTMX0
 278         ELSEIF(MINT(47).EQ.5) THEN
 279           YSTEE=LOG(0.999999/TAURT)
 280           VINT(12)=MAX(VINT(12),-YSTEE)
 281           VINT(32)=MIN(VINT(32),YSTEE)
 282         ENDIF
 283         IF(VINT(32).LE.VINT(12)) MINT(51)=1
 284
 285       ELSEIF(ILIM.EQ.3) THEN
 286 C...Calculate limits on cos(theta-hat)
 287         YST=VINT(22)
 288 C...0) due to definition
 289         CTNMN0=-1.
 290         CTNMX0=0.
 291         CTPMN0=0.
 292         CTPMX0=1.
 293 C...1) due to explicit limits
 294         CTNMN1=MIN(0.,CKIN(27))
 295         CTNMX1=MIN(0.,CKIN(28))
 296         CTPMN1=MAX(0.,CKIN(27))
 297         CTPMX1=MAX(0.,CKIN(28))
 298 C...2) due to limits on pT-hat
 299         CTNMN2=-SQRT(MAX(0.,1.-4.*PTHMIN**2/(BE34**2*TAU*VINT(2))))
 300         CTPMX2=-CTNMN2
 301         CTNMX2=0.
 302         CTPMN2=0.
 303         IF(CKIN(4).GE.0.) THEN
 304           CTNMX2=-SQRT(MAX(0.,1.-4.*CKIN(4)**2/(BE34**2*TAU*VINT(2))))
 305           CTPMN2=-CTNMX2
 306         ENDIF
 307 C...3) due to limits on y-large and y-small
 308         CTNMN3=MIN(0.,MAX((1.+RM3-RM4)/BE34*TANH(CKIN11-YST),
 309      &  -(1.-RM3+RM4)/BE34*TANH(CKIN10-YST)))
 310         CTNMX3=MIN(0.,(1.+RM3-RM4)/BE34*TANH(CKIN12-YST),
 311      &  -(1.-RM3+RM4)/BE34*TANH(CKIN09-YST))
 312         CTPMN3=MAX(0.,(1.+RM3-RM4)/BE34*TANH(CKIN09-YST),
 313      &  -(1.-RM3+RM4)/BE34*TANH(CKIN12-YST))
 314         CTPMX3=MAX(0.,MIN((1.+RM3-RM4)/BE34*TANH(CKIN10-YST),
 315      &  -(1.-RM3+RM4)/BE34*TANH(CKIN11-YST)))
 316 C...4) due to limits on that
 317         CTNMN4=-1.
 318         CTNMX4=0.
 319         CTPMN4=0.
 320         CTPMX4=1.
 321         SH=TAU*VINT(2)
 322         IF(CKIN(35).GT.0.) THEN
 323           CTLIM=(1.-RM3-RM4-2.*CKIN(35)/SH)/BE34
 324           IF(CTLIM.GT.0.) THEN
 325             CTPMX4=CTLIM
 326           ELSE
 327             CTPMX4=0.
 328             CTNMX4=CTLIM
 329           ENDIF
 330         ENDIF
 331         IF(CKIN(36).GT.0.) THEN
 332           CTLIM=(1.-RM3-RM4-2.*CKIN(36)/SH)/BE34
 333           IF(CTLIM.LT.0.) THEN
 334             CTNMN4=CTLIM
 335           ELSE
 336             CTNMN4=0.
 337             CTPMN4=CTLIM
 338           ENDIF
 339         ENDIF
 340 C...5) due to limits on uhat
 341         CTNMN5=-1.
 342         CTNMX5=0.
 343         CTPMN5=0.
 344         CTPMX5=1.
 345         IF(CKIN(37).GT.0.) THEN
 346           CTLIM=(2.*CKIN(37)/SH-(1.-RM3-RM4))/BE34
 347           IF(CTLIM.LT.0.) THEN
 348             CTNMN5=CTLIM
 349           ELSE
 350             CTNMN5=0.
 351             CTPMN5=CTLIM
 352           ENDIF
 353         ENDIF
 354         IF(CKIN(38).GT.0.) THEN
 355           CTLIM=(2.*CKIN(38)/SH-(1.-RM3-RM4))/BE34
 356           IF(CTLIM.GT.0.) THEN
 357             CTPMX5=CTLIM
 358           ELSE
 359             CTPMX5=0.
 360             CTNMX5=CTLIM
 361           ENDIF
 362         ENDIF
 363
 364 C...Net effect of all separate limits.
 365         VINT(13)=MAX(CTNMN0,CTNMN1,CTNMN2,CTNMN3,CTNMN4,CTNMN5)
 366         VINT(33)=MIN(CTNMX0,CTNMX1,CTNMX2,CTNMX3,CTNMX4,CTNMX5)
 367         VINT(14)=MAX(CTPMN0,CTPMN1,CTPMN2,CTPMN3,CTPMN4,CTPMN5)
 368         VINT(34)=MIN(CTPMX0,CTPMX1,CTPMX2,CTPMX3,CTPMX4,CTPMX5)
 369         IF(VINT(33).LE.VINT(13).AND.VINT(34).LE.VINT(14)) MINT(51)=1
 370
 371       ELSEIF(ILIM.EQ.4) THEN
 372 C...Calculate limits on tau'
 373 C...0) due to kinematics
 374         TAPMN0=TAU
 375         IF((ISTSB.EQ.5.OR.ISTSB.EQ.6).AND.KFPR(ISUB,2).GT.0) THEN
 376           PQRAT=2.*PMAS(KFPR(ISUB,2),1)/VINT(1)
 377           TAPMN0=(SQRT(TAU)+PQRAT)**2
 378         ENDIF
 379         TAPMX0=1.
 380 C...1) due to explicit limits
 381         TAPMN1=CKIN(31)**2/VINT(2)
 382         TAPMX1=1.
 383         IF(CKIN(32).GE.0.) TAPMX1=CKIN(32)**2/VINT(2)
 384
 385 C...Net effect of all separate limits.
 386         VINT(16)=MAX(TAPMN0,TAPMN1)
 387         VINT(36)=MIN(TAPMX0,TAPMX1)
 388         IF(MINT(47).EQ.1) THEN
 389           VINT(16)=0.99999
 390           VINT(36)=1.00001
 391         ENDIF
 392         IF(VINT(36).LE.VINT(16)) MINT(51)=1
 393
 394       ENDIF
 395       RETURN
 396
 397 C...Special case for low-pT and multiple interactions:
 398 C...effective kinematical limits for tau, y*, cos(theta-hat).
 399   110 IF(ILIM.EQ.0) THEN
 400       ELSEIF(ILIM.EQ.1) THEN
 401         IF(MSTP(82).LE.1) VINT(11)=4.*PARP(81)**2/VINT(2)
 402         IF(MSTP(82).GE.2) VINT(11)=PARP(82)**2/VINT(2)
 403         VINT(31)=1.
 404       ELSEIF(ILIM.EQ.2) THEN
 405         VINT(12)=0.5*LOG(VINT(21))
 406         VINT(32)=-VINT(12)
 407       ELSEIF(ILIM.EQ.3) THEN
 408         IF(MSTP(82).LE.1) ST2EFF=4.*PARP(81)**2/(VINT(21)*VINT(2))
 409         IF(MSTP(82).GE.2) ST2EFF=0.01*PARP(82)**2/(VINT(21)*VINT(2))
 410         VINT(13)=-SQRT(MAX(0.,1.-ST2EFF))
 411         VINT(33)=0.
 412         VINT(14)=0.
 413         VINT(34)=-VINT(13)
 414       ENDIF
 415
 416       RETURN
 417       END