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e74335a4 | 1 | * $Id$ |
2 | ||
3 | C********************************************************************* | |
4 | ||
5 | SUBROUTINE LUXJET_HIJING(ECM,NJET,CUT) | |
6 | ||
7 | C...Purpose: to select number of jets in matrix element approach. | |
8 | #include "ludat1_hijing.inc" | |
9 | DIMENSION ZHUT(5) | |
10 | ||
11 | C...Relative three-jet rate in Zhu second order parametrization. | |
12 | DATA ZHUT/3.0922, 6.2291, 7.4782, 7.8440, 8.2560/ | |
13 | ||
14 | C...Trivial result for two-jets only, including parton shower. | |
15 | IF(MSTJ(101).EQ.0.OR.MSTJ(101).EQ.5) THEN | |
16 | CUT=0. | |
17 | ||
18 | C...QCD and Abelian vector gluon theory: Q^2 for jet rate and R. | |
19 | ELSEIF(MSTJ(109).EQ.0.OR.MSTJ(109).EQ.2) THEN | |
20 | CF=4./3. | |
21 | IF(MSTJ(109).EQ.2) CF=1. | |
22 | IF(MSTJ(111).EQ.0) THEN | |
23 | Q2=ECM**2 | |
24 | Q2R=ECM**2 | |
25 | ELSEIF(MSTU(111).EQ.0) THEN | |
26 | PARJ(169)=MIN(1.,PARJ(129)) | |
27 | Q2=PARJ(169)*ECM**2 | |
28 | PARJ(168)=MIN(1.,MAX(PARJ(128),EXP(-12.*PARU(1)/ | |
29 | & ((33.-2.*MSTU(112))*PARU(111))))) | |
30 | Q2R=PARJ(168)*ECM**2 | |
31 | ELSE | |
32 | PARJ(169)=MIN(1.,MAX(PARJ(129),(2.*PARU(112)/ECM)**2)) | |
33 | Q2=PARJ(169)*ECM**2 | |
34 | PARJ(168)=MIN(1.,MAX(PARJ(128),PARU(112)/ECM, | |
35 | & (2.*PARU(112)/ECM)**2)) | |
36 | Q2R=PARJ(168)*ECM**2 | |
37 | ENDIF | |
38 | ||
39 | C...alpha_strong for R and R itself. | |
40 | ALSPI=(3./4.)*CF*ULALPS_HIJING(Q2R)/PARU(1) | |
41 | IF(IABS(MSTJ(101)).EQ.1) THEN | |
42 | RQCD=1.+ALSPI | |
43 | ELSEIF(MSTJ(109).EQ.0) THEN | |
44 | RQCD=1.+ALSPI+(1.986-0.115*MSTU(118))*ALSPI**2 | |
45 | IF(MSTJ(111).EQ.1) RQCD=MAX(1.,RQCD+(33.-2.*MSTU(112))/12.* | |
46 | & LOG(PARJ(168))*ALSPI**2) | |
47 | ELSE | |
48 | RQCD=1.+ALSPI-(3./32.+0.519*MSTU(118))*(4.*ALSPI/3.)**2 | |
49 | ENDIF | |
50 | ||
51 | C...alpha_strong for jet rate. Initial value for y cut. | |
52 | ALSPI=(3./4.)*CF*ULALPS_HIJING(Q2)/PARU(1) | |
53 | CUT=MAX(0.001,PARJ(125),(PARJ(126)/ECM)**2) | |
54 | IF(IABS(MSTJ(101)).LE.1.OR.(MSTJ(109).EQ.0.AND.MSTJ(111).EQ.0)) | |
55 | & CUT=MAX(CUT,EXP(-SQRT(0.75/ALSPI))/2.) | |
56 | IF(MSTJ(110).EQ.2) CUT=MAX(0.01,MIN(0.05,CUT)) | |
57 | ||
58 | C...Parametrization of first order three-jet cross-section. | |
59 | 100 IF(MSTJ(101).EQ.0.OR.CUT.GE.0.25) THEN | |
60 | PARJ(152)=0. | |
61 | ELSE | |
62 | PARJ(152)=(2.*ALSPI/3.)*((3.-6.*CUT+2.*LOG(CUT))* | |
63 | & LOG(CUT/(1.-2.*CUT))+(2.5+1.5*CUT-6.571)*(1.-3.*CUT)+ | |
64 | & 5.833*(1.-3.*CUT)**2-3.894*(1.-3.*CUT)**3+ | |
65 | & 1.342*(1.-3.*CUT)**4)/RQCD | |
66 | IF(MSTJ(109).EQ.2.AND.(MSTJ(101).EQ.2.OR.MSTJ(101).LE.-2)) | |
67 | & PARJ(152)=0. | |
68 | ENDIF | |
69 | ||
70 | C...Parametrization of second order three-jet cross-section. | |
71 | IF(IABS(MSTJ(101)).LE.1.OR.MSTJ(101).EQ.3.OR.MSTJ(109).EQ.2.OR. | |
72 | & CUT.GE.0.25) THEN | |
73 | PARJ(153)=0. | |
74 | ELSEIF(MSTJ(110).LE.1) THEN | |
75 | CT=LOG(1./CUT-2.) | |
76 | PARJ(153)=ALSPI**2*CT**2*(2.419+0.5989*CT+0.6782*CT**2- | |
77 | & 0.2661*CT**3+0.01159*CT**4)/RQCD | |
78 | ||
79 | C...Interpolation in second/first order ratio for Zhu parametrization. | |
80 | ELSEIF(MSTJ(110).EQ.2) THEN | |
81 | IZA=0 | |
82 | DO 110 IY=1,5 | |
83 | 110 IF(ABS(CUT-0.01*IY).LT.0.0001) IZA=IY | |
84 | IF(IZA.NE.0) THEN | |
85 | ZHURAT=ZHUT(IZA) | |
86 | ELSE | |
87 | IZ=100.*CUT | |
88 | ZHURAT=ZHUT(IZ)+(100.*CUT-IZ)*(ZHUT(IZ+1)-ZHUT(IZ)) | |
89 | ENDIF | |
90 | PARJ(153)=ALSPI*PARJ(152)*ZHURAT | |
91 | ENDIF | |
92 | ||
93 | C...Shift in second order three-jet cross-section with optimized Q^2. | |
94 | IF(MSTJ(111).EQ.1.AND.IABS(MSTJ(101)).GE.2.AND.MSTJ(101).NE.3. | |
95 | & AND.CUT.LT.0.25) PARJ(153)=PARJ(153)+(33.-2.*MSTU(112))/12.* | |
96 | & LOG(PARJ(169))*ALSPI*PARJ(152) | |
97 | ||
98 | C...Parametrization of second order four-jet cross-section. | |
99 | IF(IABS(MSTJ(101)).LE.1.OR.CUT.GE.0.125) THEN | |
100 | PARJ(154)=0. | |
101 | ELSE | |
102 | CT=LOG(1./CUT-5.) | |
103 | IF(CUT.LE.0.018) THEN | |
104 | XQQGG=6.349-4.330*CT+0.8304*CT**2 | |
105 | IF(MSTJ(109).EQ.2) XQQGG=(4./3.)**2*(3.035-2.091*CT+ | |
106 | & 0.4059*CT**2) | |
107 | XQQQQ=1.25*(-0.1080+0.01486*CT+0.009364*CT**2) | |
108 | IF(MSTJ(109).EQ.2) XQQQQ=8.*XQQQQ | |
109 | ELSE | |
110 | XQQGG=-0.09773+0.2959*CT-0.2764*CT**2+0.08832*CT**3 | |
111 | IF(MSTJ(109).EQ.2) XQQGG=(4./3.)**2*(-0.04079+0.1340*CT- | |
112 | & 0.1326*CT**2+0.04365*CT**3) | |
113 | XQQQQ=1.25*(0.003661-0.004888*CT-0.001081*CT**2+0.002093* | |
114 | & CT**3) | |
115 | IF(MSTJ(109).EQ.2) XQQQQ=8.*XQQQQ | |
116 | ENDIF | |
117 | PARJ(154)=ALSPI**2*CT**2*(XQQGG+XQQQQ)/RQCD | |
118 | PARJ(155)=XQQQQ/(XQQGG+XQQQQ) | |
119 | ENDIF | |
120 | ||
121 | C...If negative three-jet rate, change y' optimization parameter. | |
122 | IF(MSTJ(111).EQ.1.AND.PARJ(152)+PARJ(153).LT.0..AND. | |
123 | & PARJ(169).LT.0.99) THEN | |
124 | PARJ(169)=MIN(1.,1.2*PARJ(169)) | |
125 | Q2=PARJ(169)*ECM**2 | |
126 | ALSPI=(3./4.)*CF*ULALPS_HIJING(Q2)/PARU(1) | |
127 | GOTO 100 | |
128 | ENDIF | |
129 | ||
130 | C...If too high cross-section, use harder cuts, or fail. | |
131 | IF(PARJ(152)+PARJ(153)+PARJ(154).GE.1) THEN | |
132 | IF(MSTJ(110).EQ.2.AND.CUT.GT.0.0499.AND.MSTJ(111).EQ.1.AND. | |
133 | & PARJ(169).LT.0.99) THEN | |
134 | PARJ(169)=MIN(1.,1.2*PARJ(169)) | |
135 | Q2=PARJ(169)*ECM**2 | |
136 | ALSPI=(3./4.)*CF*ULALPS_HIJING(Q2)/PARU(1) | |
137 | GOTO 100 | |
138 | ELSEIF(MSTJ(110).EQ.2.AND.CUT.GT.0.0499) THEN | |
139 | CALL LUERRM_HIJING(26, | |
140 | & '(LUXJET_HIJING:) no allowed y cut value for '/ | |
141 | $ /'Zhu parametrization') | |
142 | ENDIF | |
143 | CUT=0.26*(4.*CUT)**(PARJ(152)+PARJ(153)+PARJ(154))**(-1./3.) | |
144 | IF(MSTJ(110).EQ.2) CUT=MAX(0.01,MIN(0.05,CUT)) | |
145 | GOTO 100 | |
146 | ENDIF | |
147 | ||
148 | C...Scalar gluon (first order only). | |
149 | ELSE | |
150 | ALSPI=ULALPS_HIJING(ECM**2)/PARU(1) | |
151 | CUT=MAX(0.001,PARJ(125),(PARJ(126)/ECM)**2,EXP(-3./ALSPI)) | |
152 | PARJ(152)=0. | |
153 | IF(CUT.LT.0.25) PARJ(152)=(ALSPI/3.)*((1.-2.*CUT)* | |
154 | & LOG((1.-2.*CUT)/CUT)+0.5*(9.*CUT**2-1.)) | |
155 | PARJ(153)=0. | |
156 | PARJ(154)=0. | |
157 | ENDIF | |
158 | ||
159 | C...Select number of jets. | |
160 | PARJ(150)=CUT | |
161 | IF(MSTJ(101).EQ.0.OR.MSTJ(101).EQ.5) THEN | |
162 | NJET=2 | |
163 | ELSEIF(MSTJ(101).LE.0) THEN | |
164 | NJET=MIN(4,2-MSTJ(101)) | |
165 | ELSE | |
166 | RNJ=RLU_HIJING(0) | |
167 | NJET=2 | |
168 | IF(PARJ(152)+PARJ(153)+PARJ(154).GT.RNJ) NJET=3 | |
169 | IF(PARJ(154).GT.RNJ) NJET=4 | |
170 | ENDIF | |
171 | ||
172 | RETURN | |
173 | END |