| fe4da5cc |
1 | |
| 2 | C********************************************************************* |
| 3 | |
| 4 | SUBROUTINE PYGVMD(ISET,KF,X,Q2,P2,ALAM,XPGA) |
| 5 | C...Purpose: to evaluate the VMD parton distributions of a photon, |
| 6 | C...evolved homogeneously from an initial scale P2 to Q2. |
| 7 | C...Does not include dipole suppression factor. |
| 8 | C...ISET is parton distribution set, see above; |
| 9 | C...additionally ISET=0 is used for the evolution of an anomalous photon |
| 10 | C...which branched at a scale P2 and then evolved homogeneously to Q2. |
| 11 | C...ALAM is the 4-flavour Lambda, which is automatically converted |
| 12 | C...to 3- and 5-flavour equivalents as needed. |
| 13 | DIMENSION XPGA(-6:6) |
| 14 | DATA PMC/1.3/, PMB/4.6/, AEM/0.007297/, AEM2PI/0.0011614/ |
| 15 | |
| 16 | C...Reset output. |
| 17 | DO 100 KFL=-6,6 |
| 18 | XPGA(KFL)=0. |
| 19 | 100 CONTINUE |
| 20 | KFA=IABS(KF) |
| 21 | |
| 22 | C...Calculate Lambda; protect against unphysical Q2 and P2 input. |
| 23 | ALAM3=ALAM*(PMC/ALAM)**(2./27.) |
| 24 | ALAM5=ALAM*(ALAM/PMB)**(2./23.) |
| 25 | P2EFF=MAX(P2,1.2*ALAM3**2) |
| 26 | IF(KFA.EQ.4) P2EFF=MAX(P2EFF,PMC**2) |
| 27 | IF(KFA.EQ.5) P2EFF=MAX(P2EFF,PMB**2) |
| 28 | Q2EFF=MAX(Q2,P2EFF) |
| 29 | |
| 30 | C...Find number of flavours at lower and upper scale. |
| 31 | NFP=4 |
| 32 | IF(P2EFF.LT.PMC**2) NFP=3 |
| 33 | IF(P2EFF.GT.PMB**2) NFP=5 |
| 34 | NFQ=4 |
| 35 | IF(Q2EFF.LT.PMC**2) NFQ=3 |
| 36 | IF(Q2EFF.GT.PMB**2) NFQ=5 |
| 37 | |
| 38 | C...Find s as sum of 3-, 4- and 5-flavour parts. |
| 39 | S=0. |
| 40 | IF(NFP.EQ.3) THEN |
| 41 | Q2DIV=PMC**2 |
| 42 | IF(NFQ.EQ.3) Q2DIV=Q2EFF |
| 43 | S=S+(6./27.)*LOG(LOG(Q2DIV/ALAM3**2)/LOG(P2EFF/ALAM3**2)) |
| 44 | ENDIF |
| 45 | IF(NFP.LE.4.AND.NFQ.GE.4) THEN |
| 46 | P2DIV=P2EFF |
| 47 | IF(NFP.EQ.3) P2DIV=PMC**2 |
| 48 | Q2DIV=Q2EFF |
| 49 | IF(NFQ.EQ.5) Q2DIV=PMB**2 |
| 50 | S=S+(6./25.)*LOG(LOG(Q2DIV/ALAM**2)/LOG(P2DIV/ALAM**2)) |
| 51 | ENDIF |
| 52 | IF(NFQ.EQ.5) THEN |
| 53 | P2DIV=PMB**2 |
| 54 | IF(NFP.EQ.5) P2DIV=P2EFF |
| 55 | S=S+(6./23.)*LOG(LOG(Q2EFF/ALAM5**2)/LOG(P2DIV/ALAM5**2)) |
| 56 | ENDIF |
| 57 | |
| 58 | C...Calculate frequent combinations of x and s. |
| 59 | X1=1.-X |
| 60 | XL=-LOG(X) |
| 61 | S2=S**2 |
| 62 | S3=S**3 |
| 63 | S4=S**4 |
| 64 | |
| 65 | C...Evaluate homogeneous anomalous parton distributions below or |
| 66 | C...above threshold. |
| 67 | IF(ISET.EQ.0) THEN |
| 68 | IF(Q2.LE.P2.OR.(KFA.EQ.4.AND.Q2.LT.PMC**2).OR. |
| 69 | &(KFA.EQ.5.AND.Q2.LT.PMB**2)) THEN |
| 70 | XVAL = X * 1.5 * (X**2+X1**2) |
| 71 | XGLU = 0. |
| 72 | XSEA = 0. |
| 73 | ELSE |
| 74 | XVAL = (1.5/(1.-0.197*S+4.33*S2)*X**2 + (1.5+2.10*S)/ |
| 75 | & (1.+3.29*S)*X1**2 + 5.23*S/(1.+1.17*S+19.9*S3)*X*X1) * |
| 76 | & X**(1./(1.+1.5*S)) * (1.-X**2)**(2.667*S) |
| 77 | XGLU = 4.*S/(1.+4.76*S+15.2*S2+29.3*S4) * |
| 78 | & X**(-2.03*S/(1.+2.44*S)) * (X1*XL)**(1.333*S) * |
| 79 | & ((4.*X**2+7.*X+4.)*X1/3. - 2.*X*(1.+X)*XL) |
| 80 | XSEA = S2/(1.+4.54*S+8.19*S2+8.05*S3) * |
| 81 | & X**(-1.54*S/(1.+1.29*S)) * X1**(2.667*S) * |
| 82 | & ((8.-73.*X+62.*X**2)*X1/9. + (3.-8.*X**2/3.)*X*XL + |
| 83 | & (2.*X-1.)*X*XL**2) |
| 84 | ENDIF |
| 85 | |
| 86 | C...Evaluate set 1D parton distributions below or above threshold. |
| 87 | ELSEIF(ISET.EQ.1) THEN |
| 88 | IF(Q2.LE.P2.OR.(KFA.EQ.4.AND.Q2.LT.PMC**2).OR. |
| 89 | &(KFA.EQ.5.AND.Q2.LT.PMB**2)) THEN |
| 90 | XVAL = 1.294 * X**0.80 * X1**0.76 |
| 91 | XGLU = 1.273 * X**0.40 * X1**1.76 |
| 92 | XSEA = 0.100 * X1**3.76 |
| 93 | ELSE |
| 94 | XVAL = 1.294/(1.+0.252*S+3.079*S2) * X**(0.80-0.13*S) * |
| 95 | & X1**(0.76+0.667*S) * XL**(2.*S) |
| 96 | XGLU = 7.90*S/(1.+5.50*S) * EXP(-5.16*S) * |
| 97 | & X**(-1.90*S/(1.+3.60*S)) * X1**1.30 * XL**(0.50+3.*S) + |
| 98 | & 1.273 * EXP(-10.*S) * X**0.40 * X1**(1.76+3.*S) |
| 99 | XSEA = (0.1-0.397*S2+1.121*S3)/(1.+5.61*S2+5.26*S3) * |
| 100 | & X**(-7.32*S2/(1.+10.3*S2)) * |
| 101 | & X1**((3.76+15.*S+12.*S2)/(1.+4.*S)) |
| 102 | XSEA0 = 0.100 * X1**3.76 |
| 103 | ENDIF |
| 104 | |
| 105 | C...Evaluate set 1M parton distributions below or above threshold. |
| 106 | ELSEIF(ISET.EQ.2) THEN |
| 107 | IF(Q2.LE.P2.OR.(KFA.EQ.4.AND.Q2.LT.PMC**2).OR. |
| 108 | &(KFA.EQ.5.AND.Q2.LT.PMB**2)) THEN |
| 109 | XVAL = 0.8477 * X**0.51 * X1**1.37 |
| 110 | XGLU = 3.42 * X**0.255 * X1**2.37 |
| 111 | XSEA = 0. |
| 112 | ELSE |
| 113 | XVAL = 0.8477/(1.+1.37*S+2.18*S2+3.73*S3) * X**(0.51+0.21*S) |
| 114 | & * X1**1.37 * XL**(2.667*S) |
| 115 | XGLU = 24.*S/(1.+9.6*S+0.92*S2+14.34*S3) * EXP(-5.94*S) * |
| 116 | & X**((-0.013-1.80*S)/(1.+3.14*S)) * X1**(2.37+0.4*S) * |
| 117 | & XL**(0.32+3.6*S) + 3.42 * EXP(-12.*S) * X**0.255 * |
| 118 | & X1**(2.37+3.*S) |
| 119 | XSEA = 0.842*S/(1.+21.3*S-33.2*S2+229.*S3) * |
| 120 | & X**((0.13-2.90*S)/(1.+5.44*S)) * X1**(3.45+0.5*S) * |
| 121 | & XL**(2.8*S) |
| 122 | XSEA0 = 0. |
| 123 | ENDIF |
| 124 | |
| 125 | C...Evaluate set 2D parton distributions below or above threshold. |
| 126 | ELSEIF(ISET.EQ.3) THEN |
| 127 | IF(Q2.LE.P2.OR.(KFA.EQ.4.AND.Q2.LT.PMC**2).OR. |
| 128 | &(KFA.EQ.5.AND.Q2.LT.PMB**2)) THEN |
| 129 | XVAL = X**0.46 * X1**0.64 + 0.76 * X |
| 130 | XGLU = 1.925 * X1**2 |
| 131 | XSEA = 0.242 * X1**4 |
| 132 | ELSE |
| 133 | XVAL = (1.+0.186*S)/(1.-0.209*S+1.495*S2) * X**(0.46+0.25*S) |
| 134 | & * X1**((0.64+0.14*S+5.*S2)/(1.+S)) * XL**(1.9*S) + |
| 135 | & (0.76+0.4*S) * X * X1**(2.667*S) |
| 136 | XGLU = (1.925+5.55*S+147.*S2)/(1.-3.59*S+3.32*S2) * |
| 137 | & EXP(-18.67*S) * X**((-5.81*S-5.34*S2)/(1.+29.*S-4.26*S2)) |
| 138 | & * X1**((2.-5.9*S)/(1.+1.7*S)) * XL**(9.3*S/(1.+1.7*S)) |
| 139 | XSEA = (0.242-0.252*S+1.19*S2)/(1.-0.607*S+21.95*S2) * |
| 140 | & X**(-12.1*S2/(1.+2.62*S+16.7*S2)) * X1**4 * XL**S |
| 141 | XSEA0 = 0.242 * X1**4 |
| 142 | ENDIF |
| 143 | |
| 144 | C...Evaluate set 2M parton distributions below or above threshold. |
| 145 | ELSEIF(ISET.EQ.4) THEN |
| 146 | IF(Q2.LE.P2.OR.(KFA.EQ.4.AND.Q2.LT.PMC**2).OR. |
| 147 | &(KFA.EQ.5.AND.Q2.LT.PMB**2)) THEN |
| 148 | XVAL = 1.168 * X**0.50 * X1**2.60 + 0.965 * X |
| 149 | XGLU = 1.808 * X1**2 |
| 150 | XSEA = 0.209 * X1**4 |
| 151 | ELSE |
| 152 | XVAL = (1.168+1.771*S+29.35*S2) * EXP(-5.776*S) * |
| 153 | & X**((0.5+0.208*S)/(1.-0.794*S+1.516*S2)) * |
| 154 | & X1**((2.6+7.6*S)/(1.+5.*S)) * XL**(5.15*S/(1.+2.*S)) + |
| 155 | & (0.965+22.35*S)/(1.+18.4*S) * X * X1**(2.667*S) |
| 156 | XGLU = (1.808+29.9*S)/(1.+26.4*S) * EXP(-5.28*S) * |
| 157 | & X**((-5.35*S-10.11*S2)/(1.+31.71*S)) * |
| 158 | & X1**((2.-7.3*S+4.*S2)/(1.+2.5*S)) * |
| 159 | & XL**(10.9*S/(1.+2.5*S)) |
| 160 | XSEA = (0.209+0.644*S2)/(1.+0.319*S+17.6*S2) * |
| 161 | & X**((-0.373*S-7.71*S2)/(1.+0.815*S+11.0*S2)) * |
| 162 | & X1**(4.+S) * XL**(0.45*S) |
| 163 | XSEA0 = 0.209 * X1**4 |
| 164 | ENDIF |
| 165 | ENDIF |
| 166 | |
| 167 | C...Threshold factors for c and b sea. |
| 168 | SLL=LOG(LOG(Q2EFF/ALAM**2)/LOG(P2EFF/ALAM**2)) |
| 169 | XCHM=0. |
| 170 | IF(Q2.GT.PMC**2.AND.Q2.GT.1.001*P2EFF) THEN |
| 171 | SCH=MAX(0.,LOG(LOG(PMC**2/ALAM**2)/LOG(P2EFF/ALAM**2))) |
| 172 | IF(ISET.EQ.0) THEN |
| 173 | XCHM=XSEA*(1.-(SCH/SLL)**2) |
| 174 | ELSE |
| 175 | XCHM=MAX(0.,XSEA-XSEA0*X1**(2.667*S))*(1.-SCH/SLL) |
| 176 | ENDIF |
| 177 | ENDIF |
| 178 | XBOT=0. |
| 179 | IF(Q2.GT.PMB**2.AND.Q2.GT.1.001*P2EFF) THEN |
| 180 | SBT=MAX(0.,LOG(LOG(PMB**2/ALAM**2)/LOG(P2EFF/ALAM**2))) |
| 181 | IF(ISET.EQ.0) THEN |
| 182 | XBOT=XSEA*(1.-(SBT/SLL)**2) |
| 183 | ELSE |
| 184 | XBOT=MAX(0.,XSEA-XSEA0*X1**(2.667*S))*(1.-SBT/SLL) |
| 185 | ENDIF |
| 186 | ENDIF |
| 187 | |
| 188 | C...Fill parton distributions. |
| 189 | XPGA(0)=XGLU |
| 190 | XPGA(1)=XSEA |
| 191 | XPGA(2)=XSEA |
| 192 | XPGA(3)=XSEA |
| 193 | XPGA(4)=XCHM |
| 194 | XPGA(5)=XBOT |
| 195 | XPGA(KFA)=XPGA(KFA)+XVAL |
| 196 | DO 110 KFL=1,5 |
| 197 | XPGA(-KFL)=XPGA(KFL) |
| 198 | 110 CONTINUE |
| 199 | |
| 200 | RETURN |
| 201 | END |
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