PYTHIA/pythia/pystfu.F

   1
   2 C*********************************************************************
   3
   4       SUBROUTINE PYSTFU(KF,X,Q2,XPQ)
   5
   6 C...Gives electron, photon, pi+, neutron, proton and hyperon
   7 C...structure functions according to a few different parametrizations.
   8 C...Note that what is coded is x times the probability distribution,
   9 C...i.e. xq(x,Q2) etc.
  10       COMMON/LUDAT1/MSTU(200),PARU(200),MSTJ(200),PARJ(200)
  11       COMMON/LUDAT2/KCHG(500,3),PMAS(500,4),PARF(2000),VCKM(4,4)
  12       COMMON/PYPARS/MSTP(200),PARP(200),MSTI(200),PARI(200)
  13       COMMON/PYINT1/MINT(400),VINT(400)
  14       COMMON/PYINT8/XPVMD(-6:6),XPANL(-6:6),XPANH(-6:6),XPBEH(-6:6),
  15      &XPDIR(-6:6)
  16       SAVE /LUDAT1/,/LUDAT2/
  17       SAVE /PYPARS/,/PYINT1/,/PYINT8/
  18       DIMENSION XPQ(-25:25),XPEL(-25:25),XPGA(-6:6),XPPI(-6:6),
  19      &XPPR(-6:6)
  20
  21 C...Interface to PDFLIB.
  22       COMMON/W50513/XMIN,XMAX,Q2MIN,Q2MAX
  23       SAVE /W50513/
  24       DOUBLE PRECISION XX,QQ,UPV,DNV,USEA,DSEA,STR,CHM,BOT,TOP,GLU,
  25      &VALUE(20),XMIN,XMAX,Q2MIN,Q2MAX
  26       CHARACTER*20 PARM(20)
  27       DATA VALUE/20*0D0/,PARM/20*' '/
  28
  29 C...Data related to Schuler-Sjostrand photon distributions.
  30       DATA ALAMGA/0.2/, PMCGA/1.3/, PMBGA/4.6/
  31
  32 C...Reset structure functions.
  33       MINT(92)=0
  34       DO 100 KFL=-25,25
  35       XPQ(KFL)=0.
  36   100 CONTINUE
  37
  38 C...Check x and particle species.
  39       IF(X.LE.0..OR.X.GE.1.) THEN
  40         WRITE(MSTU(11),5000) X
  41         RETURN
  42       ENDIF
  43       KFA=IABS(KF)
  44       IF(KFA.NE.11.AND.KFA.NE.22.AND.KFA.NE.211.AND.KFA.NE.2112.AND.
  45      &KFA.NE.2212.AND.KFA.NE.3122.AND.KFA.NE.3112.AND.KFA.NE.3212
  46      &.AND.KFA.NE.3222.AND.KFA.NE.3312.AND.KFA.NE.3322.AND.
  47      &KFA.NE.3334.AND.KFA.NE.111) THEN
  48         WRITE(MSTU(11),5100) KF
  49         RETURN
  50       ENDIF
  51
  52 C...Electron structure function call.
  53       IF(KFA.EQ.11) THEN
  54         CALL PYSTEL(X,Q2,XPEL)
  55         DO 110 KFL=-25,25
  56         XPQ(KFL)=XPEL(KFL)
  57   110   CONTINUE
  58
  59 C...Photon structure function call (VDM+anomalous).
  60       ELSEIF(KFA.EQ.22.AND.MINT(109).LE.1) THEN
  61         IF(MSTP(56).EQ.1.AND.MSTP(55).EQ.1) THEN
  62           CALL PYSTGA(X,Q2,XPGA)
  63           DO 120 KFL=-6,6
  64           XPQ(KFL)=XPGA(KFL)
  65   120     CONTINUE
  66         ELSEIF(MSTP(56).EQ.1.AND.MSTP(55).GE.5.AND.MSTP(55).LE.8) THEN
  67           Q2MX=Q2
  68           P2MX=0.36
  69           IF(MSTP(55).GE.7) P2MX=4.0
  70           IF(MSTP(57).EQ.0) Q2MX=P2MX
  71           CALL PYGGAM(MSTP(55)-4,X,Q2MX,0.,F2GAM,XPGA)
  72           DO 130 KFL=-6,6
  73           XPQ(KFL)=XPGA(KFL)
  74   130     CONTINUE
  75           VINT(231)=P2MX
  76         ELSEIF(MSTP(56).EQ.1.AND.MSTP(55).GE.9.AND.MSTP(55).LE.12) THEN
  77           Q2MX=Q2
  78           P2MX=0.36
  79           IF(MSTP(55).GE.11) P2MX=4.0
  80           IF(MSTP(57).EQ.0) Q2MX=P2MX
  81           CALL PYGGAM(MSTP(55)-8,X,Q2MX,0.,F2GAM,XPGA)
  82           DO 140 KFL=-6,6
  83           XPQ(KFL)=XPVMD(KFL)+XPANL(KFL)+XPBEH(KFL)+XPDIR(KFL)
  84   140     CONTINUE
  85           VINT(231)=P2MX
  86         ELSEIF(MSTP(56).EQ.2) THEN
  87 C...Call PDFLIB structure functions.
  88           PARM(1)='NPTYPE'
  89           VALUE(1)=3
  90           PARM(2)='NGROUP'
  91           VALUE(2)=MSTP(55)/1000
  92           PARM(3)='NSET'
  93           VALUE(3)=MOD(MSTP(55),1000)
  94           IF(MINT(93).NE.3000000+MSTP(55)) THEN
  95             CALL PDFSET(PARM,VALUE)
  96             MINT(93)=3000000+MSTP(55)
  97           ENDIF
  98           XX=X
  99           QQ=SQRT(MAX(0.,SNGL(Q2MIN),Q2))
 100           IF(MSTP(57).EQ.0) QQ=SQRT(Q2MIN)
 101           CALL STRUCTM(XX,QQ,UPV,DNV,USEA,DSEA,STR,CHM,BOT,TOP,GLU)
 102           VINT(231)=Q2MIN
 103           XPQ(0)=GLU
 104           XPQ(1)=DNV
 105           XPQ(-1)=DNV
 106           XPQ(2)=UPV
 107           XPQ(-2)=UPV
 108           XPQ(3)=STR
 109           XPQ(-3)=STR
 110           XPQ(4)=CHM
 111           XPQ(-4)=CHM
 112           XPQ(5)=BOT
 113           XPQ(-5)=BOT
 114           XPQ(6)=TOP
 115           XPQ(-6)=TOP
 116         ELSE
 117           WRITE(MSTU(11),5200) KF,MSTP(56),MSTP(55)
 118         ENDIF
 119
 120 C...Pion/gammaVDM structure function call.
 121       ELSEIF(KFA.EQ.211.OR.KFA.EQ.111.OR.(KFA.EQ.22.AND.
 122      &MINT(109).EQ.2)) THEN
 123         IF(KFA.EQ.22.AND.MSTP(56).EQ.1.AND.MSTP(55).GE.5.AND.
 124      &  MSTP(55).LE.12) THEN
 125           ISET=1+MOD(MSTP(55)-1,4)
 126           Q2MX=Q2
 127           P2MX=0.36
 128           IF(ISET.GE.3) P2MX=4.0
 129           IF(MSTP(57).EQ.0) Q2MX=P2MX
 130           CALL PYGVMD(ISET,2,X,Q2MX,P2MX,ALAMGA,XPGA)
 131           DO 150 KFL=-6,6
 132           XPQ(KFL)=XPGA(KFL)
 133   150     CONTINUE
 134           VINT(231)=P2MX
 135         ELSEIF(MSTP(54).EQ.1.AND.MSTP(53).GE.1.AND.MSTP(53).LE.3) THEN
 136           CALL PYSTPI(X,Q2,XPPI)
 137           DO 160 KFL=-6,6
 138           XPQ(KFL)=XPPI(KFL)
 139   160     CONTINUE
 140         ELSEIF(MSTP(54).EQ.2) THEN
 141 C...Call PDFLIB structure functions.
 142           PARM(1)='NPTYPE'
 143           VALUE(1)=2
 144           PARM(2)='NGROUP'
 145           VALUE(2)=MSTP(53)/1000
 146           PARM(3)='NSET'
 147           VALUE(3)=MOD(MSTP(53),1000)
 148           IF(MINT(93).NE.2000000+MSTP(53)) THEN
 149             CALL PDFSET(PARM,VALUE)
 150             MINT(93)=2000000+MSTP(53)
 151           ENDIF
 152           XX=X
 153           QQ=SQRT(MAX(0.,SNGL(Q2MIN),Q2))
 154           IF(MSTP(57).EQ.0) QQ=SQRT(Q2MIN)
 155           CALL STRUCTM(XX,QQ,UPV,DNV,USEA,DSEA,STR,CHM,BOT,TOP,GLU)
 156           VINT(231)=Q2MIN
 157           XPQ(0)=GLU
 158           XPQ(1)=DSEA
 159           XPQ(-1)=UPV+DSEA
 160           XPQ(2)=UPV+USEA
 161           XPQ(-2)=USEA
 162           XPQ(3)=STR
 163           XPQ(-3)=STR
 164           XPQ(4)=CHM
 165           XPQ(-4)=CHM
 166           XPQ(5)=BOT
 167           XPQ(-5)=BOT
 168           XPQ(6)=TOP
 169           XPQ(-6)=TOP
 170         ELSE
 171           WRITE(MSTU(11),5200) KF,MSTP(54),MSTP(53)
 172         ENDIF
 173
 174 C...Anomalous photon structure function call.
 175       ELSEIF(KFA.EQ.22.AND.MINT(109).EQ.3) THEN
 176         Q2MX=Q2
 177         P2MX=PARP(15)**2
 178         IF(MSTP(56).EQ.1.AND.MSTP(55).LE.8) THEN
 179           IF(MSTP(55).EQ.5.OR.MSTP(55).EQ.6) P2MX=0.36
 180           IF(MSTP(55).EQ.7.OR.MSTP(55).EQ.8) P2MX=4.0
 181           IF(MSTP(57).EQ.0) Q2MX=P2MX
 182           CALL PYGANO(0,X,Q2MX,P2MX,ALAMGA,XPGA)
 183           DO 170 KFL=-6,6
 184           XPQ(KFL)=XPGA(KFL)
 185   170     CONTINUE
 186           VINT(231)=P2MX
 187         ELSEIF(MSTP(56).EQ.1) THEN
 188           IF(MSTP(55).EQ.9.OR.MSTP(55).EQ.10) P2MX=0.36
 189           IF(MSTP(55).EQ.11.OR.MSTP(55).EQ.12) P2MX=4.0
 190           IF(MSTP(57).EQ.0) Q2MX=P2MX
 191           CALL PYGGAM(MSTP(55)-8,X,Q2MX,0.,F2GM,XPGA)
 192           DO 180 KFL=-6,6
 193           XPQ(KFL)=MAX(0.,XPANL(KFL)+XPBEH(KFL)+XPDIR(KFL))
 194   180     CONTINUE
 195           VINT(231)=P2MX
 196         ELSEIF(MSTP(56).EQ.2) THEN
 197           IF(MSTP(57).EQ.0) Q2MX=P2MX
 198           CALL PYGANO(0,X,Q2MX,P2MX,ALAMGA,XPGA)
 199           DO 185 KFL=-6,6
 200           XPQ(KFL)=XPGA(KFL)
 201   185     CONTINUE
 202           VINT(231)=P2MX
 203         ELSEIF(MSTP(55).GE.1.AND.MSTP(55).LE.5) THEN
 204           IF(MSTP(57).EQ.0) Q2MX=P2MX
 205           CALL PYGVMD(0,MSTP(55),X,Q2MX,P2MX,PARP(1),XPGA)
 206           DO 190 KFL=-6,6
 207           XPQ(KFL)=XPGA(KFL)
 208   190     CONTINUE
 209           VINT(231)=P2MX
 210         ELSE
 211   200     RKF=11.*RLU(0)
 212           KFR=1
 213           IF(RKF.GT.1.) KFR=2
 214           IF(RKF.GT.5.) KFR=3
 215           IF(RKF.GT.6.) KFR=4
 216           IF(RKF.GT.10.) KFR=5
 217           IF(KFR.EQ.4.AND.Q2.LT.PMCGA**2) GOTO 200
 218           IF(KFR.EQ.5.AND.Q2.LT.PMBGA**2) GOTO 200
 219           IF(MSTP(57).EQ.0) Q2MX=P2MX
 220           CALL PYGVMD(0,KFR,X,Q2MX,P2MX,PARP(1),XPGA)
 221           DO 210 KFL=-6,6
 222           XPQ(KFL)=XPGA(KFL)
 223   210     CONTINUE
 224           VINT(231)=P2MX
 225         ENDIF
 226
 227 C...Proton structure function call.
 228       ELSE
 229         IF(MSTP(52).EQ.1.AND.MSTP(51).GE.1.AND.MSTP(51).LE.11) THEN
 230           CALL PYSTPR(X,Q2,XPPR)
 231           DO 220 KFL=-6,6
 232           XPQ(KFL)=XPPR(KFL)
 233   220     CONTINUE
 234         ELSEIF(MSTP(52).EQ.2) THEN
 235 C...Call PDFLIB structure functions.
 236           PARM(1)='NPTYPE'
 237           VALUE(1)=1
 238           PARM(2)='NGROUP'
 239           VALUE(2)=MSTP(51)/1000
 240           PARM(3)='NSET'
 241           VALUE(3)=MOD(MSTP(51),1000)
 242           IF(MINT(93).NE.1000000+MSTP(51)) THEN
 243             CALL PDFSET(PARM,VALUE)
 244             MINT(93)=1000000+MSTP(51)
 245           ENDIF
 246           XX=X
 247           QQ=SQRT(MAX(0.,SNGL(Q2MIN),Q2))
 248           IF(MSTP(57).EQ.0) QQ=SQRT(Q2MIN)
 249           CALL STRUCTM(XX,QQ,UPV,DNV,USEA,DSEA,STR,CHM,BOT,TOP,GLU)
 250           VINT(231)=Q2MIN
 251           XPQ(0)=GLU
 252           XPQ(1)=DNV+DSEA
 253           XPQ(-1)=DSEA
 254           XPQ(2)=UPV+USEA
 255           XPQ(-2)=USEA
 256           XPQ(3)=STR
 257           XPQ(-3)=STR
 258           XPQ(4)=CHM
 259           XPQ(-4)=CHM
 260           XPQ(5)=BOT
 261           XPQ(-5)=BOT
 262           XPQ(6)=TOP
 263           XPQ(-6)=TOP
 264         ELSE
 265           WRITE(MSTU(11),5200) KF,MSTP(52),MSTP(51)
 266         ENDIF
 267       ENDIF
 268
 269 C...Isospin average for pi0/gammaVDM.
 270       IF(KFA.EQ.111.OR.(KFA.EQ.22.AND.MINT(109).EQ.2)) THEN
 271         IF(KFA.EQ.22.AND.MSTP(55).GE.5.AND.MSTP(55).LE.12) THEN
 272           XPV=XPQ(2)-XPQ(1)
 273           XPQ(2)=XPQ(1)
 274           XPQ(-2)=XPQ(-1)
 275         ELSE
 276           XPS=0.5*(XPQ(1)+XPQ(-2))
 277           XPV=0.5*(XPQ(2)+XPQ(-1))-XPS
 278           XPQ(2)=XPS
 279           XPQ(-1)=XPS
 280         ENDIF
 281         IF(KFA.EQ.22.AND.MINT(105).LE.223) THEN
 282           XPQ(1)=XPQ(1)+0.2*XPV
 283           XPQ(-1)=XPQ(-1)+0.2*XPV
 284           XPQ(2)=XPQ(2)+0.8*XPV
 285           XPQ(-2)=XPQ(-2)+0.8*XPV
 286         ELSEIF(KFA.EQ.22.AND.MINT(105).EQ.333) THEN
 287           XPQ(3)=XPQ(3)+XPV
 288           XPQ(-3)=XPQ(-3)+XPV
 289         ELSEIF(KFA.EQ.22.AND.MINT(105).EQ.443) THEN
 290           XPQ(4)=XPQ(4)+XPV
 291           XPQ(-4)=XPQ(-4)+XPV
 292           IF(MSTP(55).GE.9) THEN
 293             DO 230 KFL=-6,6
 294             XPQ(KFL)=0.
 295   230       CONTINUE
 296           ENDIF
 297         ELSE
 298           XPQ(1)=XPQ(1)+0.5*XPV
 299           XPQ(-1)=XPQ(-1)+0.5*XPV
 300           XPQ(2)=XPQ(2)+0.5*XPV
 301           XPQ(-2)=XPQ(-2)+0.5*XPV
 302         ENDIF
 303
 304 C...Rescale for gammaVDM by effective gamma -> rho coupling.
 305         IF(KFA.EQ.22.AND.MINT(109).EQ.2) THEN
 306           DO 240 KFL=-6,6
 307           XPQ(KFL)=VINT(281)*XPQ(KFL)
 308   240     CONTINUE
 309           VINT(232)=VINT(281)*XPV
 310         ENDIF
 311
 312 C...Isospin conjugation for neutron.
 313       ELSEIF(KFA.EQ.2112) THEN
 314         XPS=XPQ(1)
 315         XPQ(1)=XPQ(2)
 316         XPQ(2)=XPS
 317         XPS=XPQ(-1)
 318         XPQ(-1)=XPQ(-2)
 319         XPQ(-2)=XPS
 320
 321 C...Simple recipes for hyperon (average valence structure function).
 322       ELSEIF(KFA.EQ.3122.OR.KFA.EQ.3112.OR.KFA.EQ.3212.OR.KFA.EQ.3222
 323      &.OR.KFA.EQ.3312.OR.KFA.EQ.3322.OR.KFA.EQ.3334) THEN
 324         XPVAL=(XPQ(1)+XPQ(2)-XPQ(-1)-XPQ(-2))/3.
 325         XPSEA=0.5*(XPQ(-1)+XPQ(-2))
 326         XPQ(1)=XPSEA
 327         XPQ(2)=XPSEA
 328         XPQ(-1)=XPSEA
 329         XPQ(-2)=XPSEA
 330         XPQ(KFA/1000)=XPQ(KFA/1000)+XPVAL
 331         XPQ(MOD(KFA/100,10))=XPQ(MOD(KFA/100,10))+XPVAL
 332         XPQ(MOD(KFA/10,10))=XPQ(MOD(KFA/10,10))+XPVAL
 333       ENDIF
 334
 335 C...Charge conjugation for antiparticle.
 336       IF(KF.LT.0) THEN
 337         DO 250 KFL=1,25
 338         IF(KFL.EQ.21.OR.KFL.EQ.22.OR.KFL.EQ.23.OR.KFL.EQ.25) GOTO 250
 339         XPS=XPQ(KFL)
 340         XPQ(KFL)=XPQ(-KFL)
 341         XPQ(-KFL)=XPS
 342   250   CONTINUE
 343       ENDIF
 344
 345 C...Allow gluon also in position 21.
 346       XPQ(21)=XPQ(0)
 347
 348 C...Check positivity and reset above maximum allowed flavour.
 349       DO 260 KFL=-25,25
 350       XPQ(KFL)=MAX(0.,XPQ(KFL))
 351       IF(IABS(KFL).GT.MSTP(58).AND.IABS(KFL).LE.8) XPQ(KFL)=0.
 352   260 CONTINUE
 353
 354 C...Formats for error printouts.
 355  5000 FORMAT(' Error: x value outside physical range; x =',1P,E12.3)
 356  5100 FORMAT(' Error: illegal particle code for structure function;',
 357      &' KF =',I5)
 358  5200 FORMAT(' Error: unknown structure function; KF, library, set =',
 359      &3I5)
 360
 361       RETURN
 362       END