Implementation of vertex form factors in grid-oriented version of CompHEP

A.Kryukov

(kryukov@theory.sinp.msu.ru)

Skobeltsyn Institute of Nuclear Physics
Moscow State University

A.Kryukov

ACAT 2005, Berlin, DESY-Zeuthen	23-27/05/2005

Outline

Introduction

CompHEP features

N(N)LO correction in CompHEP

User interface

Implementation

Conclusion

Using FORM

A.Kryukov

ACAT 2005, Berlin, DESY-Zeuthen	23-27/05/2005

Introduction

CompHEP (http://theory.sinp.msu.ru/comphep) is a program for calculation of differential cross sections and MC generation of events flow.

Last version is 4.4.3

CompHEP Collaboration: E.Boos, V.Bunichev, M.Dubinin, L.Dudko, V.Edneral, V.Ilyin, A.Kryukov, V.Savrin, A.Semenov, A.Sherstnev

A.Kryukov

ACAT 2005, Berlin, DESY-Zeuthen	23-27/05/2005

Introduction (cont.)

User friendly interface

Predefined main particle physics models

New models defined by users

Automatic generation of Feynman rules from Lagrangian by LanHEP.

Symbolic (exact) calculation of differential cross sections (uses the squared matrix element technique)

MC integration (VEGAS)

Event flow generator

Histogramming

A.Kryukov

ACAT 2005, Berlin, DESY-Zeuthen	23-27/05/2005

N(N)LO correction in CompHEP

Initial and final state radiation

Next order of tree calculation

No loop corrections

A.Kryukov

ACAT 2005, Berlin, DESY-Zeuthen	23-27/05/2005

Scalar formfactor

We call scalar formfactor - the function depends on scalar product of incoming momenta:

where T is tensor (Lorentz part).

A.Kryukov

ACAT 2005, Berlin, DESY-Zeuthen	23-27/05/2005

User interface

In the CompHEP model (lagrangian table) the scalar factor designate by special prefix @.

A.Kryukov

ACAT 2005, Berlin, DESY-Zeuthen	23-27/05/2005

User interface (cont.)

User should realized the numeric procedure on C language for calculation of formfactor by using the following template:
and save it in file with ff.c name in directory $WDIR/ffactor

double ff(double p11,double p22,double p33,
double p12,double p13,double p23)

/* here pij is a scalar product (pi.pj) */

{

double res=0;	/* return value */

/* here the numerical calculation of formfactor */

return res;

}

A.Kryukov

ACAT 2005, Berlin, DESY-Zeuthen	23-27/05/2005

User interface (cont.)

All C-program in directory ffactor will be compiled and linked with numerical part of CompHEP automatically.

During numeric (Monte-Carlo) calculation of cross section and/or event generation the formfactor functions will be call with proper set of arguments.

A.Kryukov

ACAT 2005, Berlin, DESY-Zeuthen	23-27/05/2005

Implementation

Program flow in CopHEP

squared
diagram

symbolic calculation
(traces, tensor alg.,...)

c-program
generation

compilation
and linking

c-program

n_comphep

A.Kryukov

ACAT 2005, Berlin, DESY-Zeuthen	23-27/05/2005

Implementation

Modified program flow in CopHEP

squared
diagram

symbolic calculation
(traces, tensor alg.,...)

c-program
generation

compilation
and linking

formfactor
c-program

c-program

n_comphep

A.Kryukov

ACAT 2005, Berlin, DESY-Zeuthen	23-27/05/2005

Implementation

Modified program flow in CopHEP

squared
diagram

symbolic calculation
(traces, tensor alg.,...)

c-program
generation

compilation
and linking

formfactor
c-program

c-program

n_comphep

fill ff_arr

A.Kryukov

ACAT 2005, Berlin, DESY-Zeuthen	23-27/05/2005

Implementation

Modified program flow in CopHEP

squared
diagram

symbolic calculation
(traces, tensor alg.,...)

c-program
generation

compilation
and linking

formfactor
c-program

c-program

n_comphep

fill ff_arr

substitute
@ff->ffnmom_set

A.Kryukov

ACAT 2005, Berlin, DESY-Zeuthen	23-27/05/2005

Implementation

Modified program flow in CopHEP

squared
diagram

symbolic calculation
(traces, tensor alg.,...)

c-program
generation

compilation
and linking

formfactor
c-program

c-program

n_comphep

fill ff_arr

substitute
@ff->ffnmom_set

generate ff calls:
ffnmom_set=ff(p11,p22,...)

A.Kryukov

ACAT 2005, Berlin, DESY-Zeuthen	23-27/05/2005

Implementation

Mark of squared diagram. Index of set momenta is assigned to each vertex. This information is stored into additional C-structute:

structure ff_struct{

int vnum; /* number of vertex */

int pset; /* number of momenta set */

} ff_struct;

struct ff_struct ff_arr[MAXVERT];

A.Kryukov

ACAT 2005, Berlin, DESY-Zeuthen	23-27/05/2005

Implementation (cont.)

Generation C-code for squared matrix element. Special call if formfactor function is generated in fnn.c file:

Here DP[i] – scalar product of momenta defined in n_comphep.

...

HAA1=HAA(0,0,DP[4],0);

HAA2=HAA(DP[1],DP[2],DP[3],0);

RNUM=+HAA1*DP[3]*DP[2]+HAA2*DP[4]*DP[1];

...

A.Kryukov

ACAT 2005, Berlin, DESY-Zeuthen	23-27/05/2005

Conclusions

Implementation of scalar formfactor in CompHEP improve

taking into account of N(N)LO correction;

simplify realization SUSY models;

open new area of application like J/Psi production;

and so on.

The similar approach will use in future version of CompHEP that should be based on FORM symbolic calculation program by J.Vermaseren.

A.Kryukov

ACAT 2005, Berlin, DESY-Zeuthen	23-27/05/2005

Conclusion

A.Kryukov

ACAT 2005, Berlin, DESY-Zeuthen	23-27/05/2005

CompHEP collaboration (incomplete list)

Alexander Kryukov

2005-05-24T23:24:50