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New version of MUON from M.Bondila & A.Morsch
[u/mrichter/AliRoot.git] / PYTHIA / pythia / pystpi.F
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fe4da5cc 1
2C*********************************************************************
3
4 SUBROUTINE PYSTPI(X,Q2,XPPI)
5
6C...Gives pi+ structure function according to two different
7C...parametrizations.
8 COMMON/LUDAT1/MSTU(200),PARU(200),MSTJ(200),PARJ(200)
9 COMMON/PYPARS/MSTP(200),PARP(200),MSTI(200),PARI(200)
10 COMMON/PYINT1/MINT(400),VINT(400)
11 SAVE /LUDAT1/
12 SAVE /PYPARS/,/PYINT1/
13 DIMENSION XPPI(-6:6),COW(3,5,4,2),XQ(9),TS(6)
14
15C...The following data lines are coefficients needed in the
16C...Owens pion structure function parametrizations, see below.
17C...Expansion coefficients for up and down valence quark distributions.
18 DATA ((COW(IP,IS,1,1),IS=1,5),IP=1,3)/
19 1 4.0000E-01, 7.0000E-01, 0.0000E+00, 0.0000E+00, 0.0000E+00,
20 2 -6.2120E-02, 6.4780E-01, 0.0000E+00, 0.0000E+00, 0.0000E+00,
21 3 -7.1090E-03, 1.3350E-02, 0.0000E+00, 0.0000E+00, 0.0000E+00/
22 DATA ((COW(IP,IS,1,2),IS=1,5),IP=1,3)/
23 1 4.0000E-01, 6.2800E-01, 0.0000E+00, 0.0000E+00, 0.0000E+00,
24 2 -5.9090E-02, 6.4360E-01, 0.0000E+00, 0.0000E+00, 0.0000E+00,
25 3 -6.5240E-03, 1.4510E-02, 0.0000E+00, 0.0000E+00, 0.0000E+00/
26C...Expansion coefficients for gluon distribution.
27 DATA ((COW(IP,IS,2,1),IS=1,5),IP=1,3)/
28 1 8.8800E-01, 0.0000E+00, 3.1100E+00, 6.0000E+00, 0.0000E+00,
29 2 -1.8020E+00, -1.5760E+00, -1.3170E-01, 2.8010E+00, -1.7280E+01,
30 3 1.8120E+00, 1.2000E+00, 5.0680E-01, -1.2160E+01, 2.0490E+01/
31 DATA ((COW(IP,IS,2,2),IS=1,5),IP=1,3)/
32 1 7.9400E-01, 0.0000E+00, 2.8900E+00, 6.0000E+00, 0.0000E+00,
33 2 -9.1440E-01, -1.2370E+00, 5.9660E-01, -3.6710E+00, -8.1910E+00,
34 3 5.9660E-01, 6.5820E-01, -2.5500E-01, -2.3040E+00, 7.7580E+00/
35C...Expansion coefficients for (up+down+strange) quark sea distribution.
36 DATA ((COW(IP,IS,3,1),IS=1,5),IP=1,3)/
37 1 9.0000E-01, 0.0000E+00, 5.0000E+00, 0.0000E+00, 0.0000E+00,
38 2 -2.4280E-01, -2.1200E-01, 8.6730E-01, 1.2660E+00, 2.3820E+00,
39 3 1.3860E-01, 3.6710E-03, 4.7470E-02, -2.2150E+00, 3.4820E-01/
40 DATA ((COW(IP,IS,3,2),IS=1,5),IP=1,3)/
41 1 9.0000E-01, 0.0000E+00, 5.0000E+00, 0.0000E+00, 0.0000E+00,
42 2 -1.4170E-01, -1.6970E-01, -2.4740E+00, -2.5340E+00, 5.6210E-01,
43 3 -1.7400E-01, -9.6230E-02, 1.5750E+00, 1.3780E+00, -2.7010E-01/
44C...Expansion coefficients for charm quark sea distribution.
45 DATA ((COW(IP,IS,4,1),IS=1,5),IP=1,3)/
46 1 0.0000E+00, -2.2120E-02, 2.8940E+00, 0.0000E+00, 0.0000E+00,
47 2 7.9280E-02, -3.7850E-01, 9.4330E+00, 5.2480E+00, 8.3880E+00,
48 3 -6.1340E-02, -1.0880E-01, -1.0852E+01, -7.1870E+00, -1.1610E+01/
49 DATA ((COW(IP,IS,4,2),IS=1,5),IP=1,3)/
50 1 0.0000E+00, -8.8200E-02, 1.9240E+00, 0.0000E+00, 0.0000E+00,
51 2 6.2290E-02, -2.8920E-01, 2.4240E-01, -4.4630E+00, -8.3670E-01,
52 3 -4.0990E-02, -1.0820E-01, 2.0360E+00, 5.2090E+00, -4.8400E-02/
53
54C...Euler's beta function, requires ordinary Gamma function
55 EULBET(X,Y)=PYGAMM(X)*PYGAMM(Y)/PYGAMM(X+Y)
56
57C...Reset output array.
58 DO 100 KFL=-6,6
59 XPPI(KFL)=0.
60 100 CONTINUE
61
62 IF(MSTP(53).LE.2) THEN
63C...Pion structure functions from Owens.
64C...Allowed variable range: 4 GeV^2 < Q^2 < approx 2000 GeV^2.
65
66C...Determine set, Lambda and s expansion variable.
67 NSET=MSTP(53)
68 IF(NSET.EQ.1) ALAM=0.2
69 IF(NSET.EQ.2) ALAM=0.4
70 VINT(231)=4.
71 IF(MSTP(57).LE.0) THEN
72 SD=0.
73 ELSE
74 Q2IN=MIN(2E3,MAX(4.,Q2))
75 SD=LOG(LOG(Q2IN/ALAM**2)/LOG(4./ALAM**2))
76 ENDIF
77
78C...Calculate structure functions.
79 DO 120 KFL=1,4
80 DO 110 IS=1,5
81 TS(IS)=COW(1,IS,KFL,NSET)+COW(2,IS,KFL,NSET)*SD+
82 & COW(3,IS,KFL,NSET)*SD**2
83 110 CONTINUE
84 IF(KFL.EQ.1) THEN
85 XQ(KFL)=X**TS(1)*(1.-X)**TS(2)/EULBET(TS(1),TS(2)+1.)
86 ELSE
87 XQ(KFL)=TS(1)*X**TS(2)*(1.-X)**TS(3)*(1.+TS(4)*X+TS(5)*X**2)
88 ENDIF
89 120 CONTINUE
90
91C...Put into output array.
92 XPPI(0)=XQ(2)
93 XPPI(1)=XQ(3)/6.
94 XPPI(2)=XQ(1)+XQ(3)/6.
95 XPPI(3)=XQ(3)/6.
96 XPPI(4)=XQ(4)
97 XPPI(-1)=XQ(1)+XQ(3)/6.
98 XPPI(-2)=XQ(3)/6.
99 XPPI(-3)=XQ(3)/6.
100 XPPI(-4)=XQ(4)
101
102C...Leading order pion structure functions from Gluck, Reya and Vogt.
103C...Allowed variable range: 0.25 GeV^2 < Q^2 < 10^8 GeV^2 and
104C...10^-5 < x < 1.
105 ELSE
106
107C...Determine s expansion variable and some x expressions.
108 VINT(231)=0.25
109 IF(MSTP(57).LE.0) THEN
110 SD=0.
111 ELSE
112 Q2IN=MIN(1E8,MAX(0.25,Q2))
113 SD=LOG(LOG(Q2IN/0.232**2)/LOG(0.25/0.232**2))
114 ENDIF
115 SD2=SD**2
116 XL=-LOG(X)
117 XS=SQRT(X)
118
119C...Evaluate valence, gluon and sea distributions.
120 XFVAL=(0.519+0.180*SD-0.011*SD2)*X**(0.499-0.027*SD)*
121 & (1.+(0.381-0.419*SD)*XS)*(1.-X)**(0.367+0.563*SD)
122 XFGLU=(X**(0.482+0.341*SQRT(SD))*((0.678+0.877*SD-0.175*SD2)+
123 & (0.338-1.597*SD)*XS+(-0.233*SD+0.406*SD2)*X)+
124 & SD**0.599*EXP(-(0.618+2.070*SD)+SQRT(3.676*SD**1.263*XL)))*
125 & (1.-X)**(0.390+1.053*SD)
126 XFSEA=SD**0.55*(1.-0.748*XS+(0.313+0.935*SD)*X)*(1.-X)**3.359*
127 & EXP(-(4.433+1.301*SD)+SQRT((9.30-0.887*SD)*SD**0.56*XL))/
128 & XL**(2.538-0.763*SD)
129 IF(SD.LE.0.888) THEN
130 XFCHM=0.
131 ELSE
132 XFCHM=(SD-0.888)**1.02*(1.+1.008*X)*(1.-X)**(1.208+0.771*SD)*
133 & EXP(-(4.40+1.493*SD)+SQRT((2.032+1.901*SD)*SD**0.39*XL))
134 ENDIF
135 IF(SD.LE.1.351) THEN
136 XFBOT=0.
137 ELSE
138 XFBOT=(SD-1.351)**1.03*(1.-X)**(0.697+0.855*SD)*
139 & EXP(-(4.51+1.490*SD)+SQRT((3.056+1.694*SD)*SD**0.39*XL))
140 ENDIF
141
142C...Put into output array.
143 XPPI(0)=XFGLU
144 XPPI(1)=XFSEA
145 XPPI(2)=XFSEA
146 XPPI(3)=XFSEA
147 XPPI(4)=XFCHM
148 XPPI(5)=XFBOT
149 DO 130 KFL=1,5
150 XPPI(-KFL)=XPPI(KFL)
151 130 CONTINUE
152 XPPI(2)=XPPI(2)+XFVAL
153 XPPI(-1)=XPPI(-1)+XFVAL
154 ENDIF
155
156 RETURN
157 END