CalcHEP_MG

Matrix Element Method using CalcHEP in C code

1. There are two files at the end of this page.

2. "main_22.c" is an example program that calculate the process: e,E -> m, M and A, A -> m, M in the Standard Model.

   1. • • 1. main_22:main code

             1. • 1. //============================== MAIN =============================

                  2. int main(void)

                  3. { int err;

                  4. double pvec[16];

                  5. double *p1=pvec, *p2=pvec+4, *p3=pvec+8, *p4=pvec+12;

                  6. double m1,m2,m3,m4;

                  7. double Pin,Pout;

                  8. double totcoef, sqrt_S, S, lambda12, lambda34,ms,md;

                  9. double cos_fi, cos_step;

                  10. double sigmaTot=0;

                  11. int i;

                  12. char mess[20];

                  13. double GG;

                  14. numout*cc,*cc1;

                  15. // Specify model for work: Model directory and model number.

                  16. setModel("../models" , 2 );

                  17. /* assign variables */

                  18. err=assignVal("SW", 0.483);

                  19. // Calculation of public constraints

                  20. err=calcMainFunc();

                  21. if(err) { printf("Can not calculate constrained parameter %s\n",varNames[err]);return err;}

                  22. // SQME code generation

                  23. // extern numout*getMEcode(int twidth,int UnitaryGauge, char* Process,

                  24. // char * excludeVirtual,char*excludeOut,char*libraryName);

                  26. cc= getMEcode(0,0,"e,E->m,M","","","eemm");

                  28. cc1=getMEcode(0,0,"A,A->m,M","","","aamm");

                  30. for(i=1;i<=cc->interface->nvar;i++) if(cc->link[i]) cc->interface->va[i]=*(cc->link[i]);

                  31. err=cc->interface->calcFunc();

                  32. if(err) { printf("Can not calculate constrained parameter %s\n",cc->interface->varName[err]); return err;}

                  34. for(i=1 ;i<=cc->interface->nvar;i++)

                  35. printf("%s=%E\n",cc->interface->varName[i], cc->interface->va[i]);

                  36. /* Initial cms momentum */

                  37. Pin=100;

                  39. /* find masses */

                  40. cc->interface->pinf(1,1,&m1,NULL);

                  41. cc->interface->pinf(1,2,&m2,NULL);

                  42. cc->interface->pinf(1,3,&m3,NULL);

                  43. cc->interface->pinf(1,4,&m4,NULL);

                  44. /* 2-2 kinematics */

                  45. sqrt_S=sqrt(m1*m1+Pin*Pin) +sqrt(m2*m2+Pin*Pin);

                  46. S=sqrt_S*sqrt_S;

                  47. lambda12=2*sqrt_S*Pin;

                  48. ms = m3+m4; if (ms >= sqrt_S) return 1;

                  49. md = m3 -m4;

                  50. lambda34 = sqrt((S - ms*ms) * (S - md*md));

                  51. totcoef = 3.8937966E8 * lambda34 /(32.0 * M_PI * lambda12 * S);

                  52. Pout=lambda34/(2*sqrt_S);

                  53. /* fill momenta of particles */

                  55. for(i=0;i<16;i++) pvec[i]=0;

                  57. p1[0]= sqrt(Pin*Pin + m1*m1);

                  59. p1[3]= Pin;

                  60. p2[0]= sqrt(Pin*Pin + m2*m2);

                  61. p2[3]= -Pin;

                  62. p3[0]= sqrt(Pout*Pout + m3*m3);

                  63. p4[0]= sqrt(Pout*Pout + m4*m4);

                  65. /* Assign QCD coupling */

                  66. GG=1.238;

                  69. cos_step=0.1; /* step to calculate dsigma/dcos */

                  70. sigmaTot=0.; /* total cross section */

                  71. /* cycle */

                  72. for(cos_fi=1-cos_step/2; cos_fi>-1; cos_fi -= cos_step)

                  73. { double DsigmaDcos;

                  74. double sin_fi=sqrt((1-cos_fi)*(1+cos_fi));

                  75. int err=0;

                  76. p3[3]=Pout*cos_fi; p4[3]=-p3[3];

                  77. p3[2]=Pout*sin_fi; p4[2]=-p3[2];

                  78. DsigmaDcos=totcoef*cc->interface->sqme(1,GG,pvec,&err);

                  79. sigmaTot += DsigmaDcos*cos_step;

                  80. }

                  81. printf("sigmaTot=%E\n",sigmaTot);

                  82. return 0;

                  83. }

3. "make_main" is the makefile to compile main_22.c file: ./make_main main_22.c

• • You need to change the first line of this code into your calchep directory.

    • CALCHEP= ...

4. excute main_22 and let's see what will happen.

Matrix Element Method using CalcHEP with Mathematica

1. Good example is here (This is for 2->2 process since it used "sum_int.m" file )

   • You must change the original "sum_int.m" file in "$CALCHEP/utile" directory with the one that is provided at the end of the webpage

2. For the general usage, please look at

   • process1 process2 process3 process4 process5 process6

3. Example is attached at the end of this page.