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[u/mrichter/AliRoot.git] / PYTHIA / jetset / ulmass.F

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+ 
+C********************************************************************* 
+ 
+      FUNCTION ULMASS(KF) 
+ 
+C...Purpose: to give the mass of a particle/parton. 
+      COMMON/LUDAT1/MSTU(200),PARU(200),MSTJ(200),PARJ(200) 
+      COMMON/LUDAT2/KCHG(500,3),PMAS(500,4),PARF(2000),VCKM(4,4) 
+      SAVE /LUDAT1/,/LUDAT2/ 
+ 
+C...Reset variables. Compressed code. 
+      ULMASS=0. 
+      KFA=IABS(KF) 
+      KC=LUCOMP(KF) 
+      IF(KC.EQ.0) RETURN 
+      PARF(106)=PMAS(6,1) 
+      PARF(107)=PMAS(7,1) 
+      PARF(108)=PMAS(8,1) 
+ 
+C...Guarantee use of constituent masses for internal checks. 
+      IF((MSTJ(93).EQ.1.OR.MSTJ(93).EQ.2).AND.KFA.LE.10) THEN 
+        ULMASS=PARF(100+KFA) 
+        IF(MSTJ(93).EQ.2) ULMASS=MAX(0.,ULMASS-PARF(121)) 
+ 
+C...Masses that can be read directly off table. 
+      ELSEIF(KFA.LE.100.OR.KC.LE.80.OR.KC.GT.100) THEN 
+        ULMASS=PMAS(KC,1) 
+ 
+C...Find constituent partons and their masses. 
+      ELSE 
+        KFLA=MOD(KFA/1000,10) 
+        KFLB=MOD(KFA/100,10) 
+        KFLC=MOD(KFA/10,10) 
+        KFLS=MOD(KFA,10) 
+        KFLR=MOD(KFA/10000,10) 
+        PMA=PARF(100+KFLA) 
+        PMB=PARF(100+KFLB) 
+        PMC=PARF(100+KFLC) 
+ 
+C...Construct masses for various meson, diquark and baryon cases. 
+        IF(KFLA.EQ.0.AND.KFLR.EQ.0.AND.KFLS.LE.3) THEN 
+          IF(KFLS.EQ.1) PMSPL=-3./(PMB*PMC) 
+          IF(KFLS.GE.3) PMSPL=1./(PMB*PMC) 
+          ULMASS=PARF(111)+PMB+PMC+PARF(113)*PARF(101)**2*PMSPL 
+        ELSEIF(KFLA.EQ.0) THEN 
+          KMUL=2 
+          IF(KFLS.EQ.1) KMUL=3 
+          IF(KFLR.EQ.2) KMUL=4 
+          IF(KFLS.EQ.5) KMUL=5 
+          ULMASS=PARF(113+KMUL)+PMB+PMC 
+        ELSEIF(KFLC.EQ.0) THEN 
+          IF(KFLS.EQ.1) PMSPL=-3./(PMA*PMB) 
+          IF(KFLS.EQ.3) PMSPL=1./(PMA*PMB) 
+          ULMASS=2.*PARF(112)/3.+PMA+PMB+PARF(114)*PARF(101)**2*PMSPL 
+          IF(MSTJ(93).EQ.1) ULMASS=PMA+PMB 
+          IF(MSTJ(93).EQ.2) ULMASS=MAX(0.,ULMASS-PARF(122)- 
+     &    2.*PARF(112)/3.) 
+        ELSE 
+          IF(KFLS.EQ.2.AND.KFLA.EQ.KFLB) THEN 
+            PMSPL=1./(PMA*PMB)-2./(PMA*PMC)-2./(PMB*PMC) 
+          ELSEIF(KFLS.EQ.2.AND.KFLB.GE.KFLC) THEN 
+            PMSPL=-2./(PMA*PMB)-2./(PMA*PMC)+1./(PMB*PMC) 
+          ELSEIF(KFLS.EQ.2) THEN 
+            PMSPL=-3./(PMB*PMC) 
+          ELSE 
+            PMSPL=1./(PMA*PMB)+1./(PMA*PMC)+1./(PMB*PMC) 
+          ENDIF 
+          ULMASS=PARF(112)+PMA+PMB+PMC+PARF(114)*PARF(101)**2*PMSPL 
+        ENDIF 
+      ENDIF 
+ 
+C...Optional mass broadening according to truncated Breit-Wigner 
+C...(either in m or in m^2). 
+      IF(MSTJ(24).GE.1.AND.PMAS(KC,2).GT.1E-4) THEN 
+        IF(MSTJ(24).EQ.1.OR.(MSTJ(24).EQ.2.AND.KFA.GT.100)) THEN 
+          ULMASS=ULMASS+0.5*PMAS(KC,2)*TAN((2.*RLU(0)-1.)* 
+     &    ATAN(2.*PMAS(KC,3)/PMAS(KC,2))) 
+        ELSE 
+          PM0=ULMASS 
+          PMLOW=ATAN((MAX(0.,PM0-PMAS(KC,3))**2-PM0**2)/ 
+     &    (PM0*PMAS(KC,2))) 
+          PMUPP=ATAN(((PM0+PMAS(KC,3))**2-PM0**2)/(PM0*PMAS(KC,2))) 
+          ULMASS=SQRT(MAX(0.,PM0**2+PM0*PMAS(KC,2)*TAN(PMLOW+ 
+     &    (PMUPP-PMLOW)*RLU(0)))) 
+        ENDIF 
+      ENDIF 
+      MSTJ(93)=0 
+ 
+      RETURN 
+      END