hijing/src/ulmass.f

0001
0002 C*********************************************************************
0003
0004       FUNCTION ULMASS(KF)
0005
0006 C...Purpose: to give the mass of a particle/parton.
0007       COMMON/LUDAT1/MSTU(200),PARU(200),MSTJ(200),PARJ(200)
0008       SAVE /LUDAT1/
0009       COMMON/LUDAT2/KCHG(500,3),PMAS(500,4),PARF(2000),VCKM(4,4)
0010       SAVE /LUDAT2/
0011
0012 C...Reset variables. Compressed code.
0013       ULMASS=0.
0014       KFA=IABS(KF)
0015       KC=LUCOMP(KF)
0016       IF(KC.EQ.0) RETURN
0017       PARF(106)=PMAS(6,1)
0018       PARF(107)=PMAS(7,1)
0019       PARF(108)=PMAS(8,1)
0020
0021 C...Guarantee use of constituent masses for internal checks.
0022       IF((MSTJ(93).EQ.1.OR.MSTJ(93).EQ.2).AND.KFA.LE.10) THEN
0023         ULMASS=PARF(100+KFA)
0024         IF(MSTJ(93).EQ.2) ULMASS=MAX(0.,ULMASS-PARF(121))
0025
0026 C...Masses that can be read directly off table.
0027       ELSEIF(KFA.LE.100.OR.KC.LE.80.OR.KC.GT.100) THEN
0028         ULMASS=PMAS(KC,1)
0029
0030 C...Find constituent partons and their masses.
0031       ELSE
0032         KFLA=MOD(KFA/1000,10)
0033         KFLB=MOD(KFA/100,10)
0034         KFLC=MOD(KFA/10,10)
0035         KFLS=MOD(KFA,10)
0036         KFLR=MOD(KFA/10000,10)
0037         PMA=PARF(100+KFLA)
0038         PMB=PARF(100+KFLB)
0039         PMC=PARF(100+KFLC)
0040
0041 C...Construct masses for various meson, diquark and baryon cases.
0042         IF(KFLA.EQ.0.AND.KFLR.EQ.0.AND.KFLS.LE.3) THEN
0043           IF(KFLS.EQ.1) PMSPL=-3./(PMB*PMC)
0044           IF(KFLS.GE.3) PMSPL=1./(PMB*PMC)
0045           ULMASS=PARF(111)+PMB+PMC+PARF(113)*PARF(101)**2*PMSPL
0046         ELSEIF(KFLA.EQ.0) THEN
0047           KMUL=2
0048           IF(KFLS.EQ.1) KMUL=3
0049           IF(KFLR.EQ.2) KMUL=4
0050           IF(KFLS.EQ.5) KMUL=5
0051           ULMASS=PARF(113+KMUL)+PMB+PMC
0052         ELSEIF(KFLC.EQ.0) THEN
0053           IF(KFLS.EQ.1) PMSPL=-3./(PMA*PMB)
0054           IF(KFLS.EQ.3) PMSPL=1./(PMA*PMB)
0055           ULMASS=2.*PARF(112)/3.+PMA+PMB+PARF(114)*PARF(101)**2*PMSPL
0056           IF(MSTJ(93).EQ.1) ULMASS=PMA+PMB
0057           IF(MSTJ(93).EQ.2) ULMASS=MAX(0.,ULMASS-PARF(122)-
0058      &    2.*PARF(112)/3.)
0059         ELSE
0060           IF(KFLS.EQ.2.AND.KFLA.EQ.KFLB) THEN
0061             PMSPL=1./(PMA*PMB)-2./(PMA*PMC)-2./(PMB*PMC)
0062           ELSEIF(KFLS.EQ.2.AND.KFLB.GE.KFLC) THEN
0063             PMSPL=-2./(PMA*PMB)-2./(PMA*PMC)+1./(PMB*PMC)
0064           ELSEIF(KFLS.EQ.2) THEN
0065             PMSPL=-3./(PMB*PMC)
0066           ELSE
0067             PMSPL=1./(PMA*PMB)+1./(PMA*PMC)+1./(PMB*PMC)
0068           ENDIF
0069           ULMASS=PARF(112)+PMA+PMB+PMC+PARF(114)*PARF(101)**2*PMSPL
0070         ENDIF
0071       ENDIF
0072
0073 C...Optional mass broadening according to truncated Breit-Wigner
0074 C...(either in m or in m^2).
0075       IF(MSTJ(24).GE.1.AND.PMAS(KC,2).GT.1E-4) THEN
0076         IF(MSTJ(24).EQ.1.OR.(MSTJ(24).EQ.2.AND.KFA.GT.100)) THEN
0077           ULMASS=ULMASS+0.5*PMAS(KC,2)*TAN((2.*RLU(0)-1.)*
0078      &    ATAN(2.*PMAS(KC,3)/PMAS(KC,2)))
0079         ELSE
0080           PM0=ULMASS
0081           PMLOW=ATAN((MAX(0.,PM0-PMAS(KC,3))**2-PM0**2)/
0082      &    (PM0*PMAS(KC,2)))
0083           PMUPP=ATAN((PM0+PMAS(KC,3))**2-PM0**2)/(PM0*PMAS(KC,2))
0084           ULMASS=SQRT(MAX(0.,PM0**2+PM0*PMAS(KC,2)*TAN(PMLOW+
0085      &    (PMUPP-PMLOW)*RLU(0))))
0086         ENDIF
0087       ENDIF
0088       MSTJ(93)=0
0089
0090       RETURN
0091       END