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/VecMesWinkel [ Modules ]

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NAME

module VecMesWinkel

PURPOSE

Incorporates the functions used for angular distributions of final states in gamma N -> V N and gamma N -> V Delta.

VecMesWinkel/vecmesa [ Subroutines ]

[ Top ] [ VecMesWinkel ] [ Subroutines ]

NAME

subroutine vecmesa(sqrts,idM,massM,massIn2,cost,iParam,successflag)

PURPOSE

determines scattering angle for gamma N --> V N

INPUTS

  • real :: sqrts -- sqrt(s)
  • integer :: idM -- ID of vector meson
  • real :: massM -- mass of outgoing vector meson
  • real :: massIn2 -- mass squared of incoming gamma (negative: Q^2!)
  • integer :: iParam -- select the distribution (see below)

OUTPUT

  • real :: cost -- cos(theta) of scattering angle
  • logical, OPTIONAL :: successflag -- false, if problems with in-medium masses

NOTES

  • massIn2 may be negative: Q^2 !
  • The slope parameter B and the total cross section should be consistent!

The parameter 'iParam' selects the used distribution:

  • =0: 'old' parametrisation for gammaN->VN (cf. Effenberger PhD): Slope paremeter B according ABBHHM collab, PR 175, 1669 (1968)
  • =1: Pythia parametrisation: Slope parameter B=2*b_p+2*b_V+4*s**eps-4.2
  • =2: 'Donnachie, Landshoff' Select t according dsig/dt as given by VecMesWinkel/dsigdt, not by a given slope parameter
  • =3: as 1, but for rho and W<~6GeV slope parameter adjusted according CLAS experimental data [Morrow et al, EPJ A39, 5 (2009)]
  • =4: old Muehlich routines
  • =5: as 1, but modified for low W (used in rho0 Toy Init)
  • =6: W and Q2 dependent slope as fitted to VMD distribution of PYTHIA. Only valid for W<3.3GeV. (used in rho0 Toy Init)

The default value for iParam is 3 (until Jan 2010 the default was 2)

VecMesWinkel/dsigdt [ Functions ]

[ Top ] [ VecMesWinkel ] [ Functions ]

NAME

real function dsigdt(sqrts,t,iv)

PURPOSE

Calculate the cross section dsigma/dt for gamma N -> V N according a parametrization of scattering amplitude from Donnachie and Landshoff

INPUTS

  • real :: sqrts -- sqrt(s)
  • real :: t -- Mandelstam-t ( <0!)
  • integer :: iv -- ID of vector meson

OUTPUT

function value: dsig/dt in mub/GeV^2

NOTES

Reference:

  • A. Donnachie and P. V. Landshoff, ``Exclusive vector photoproduction: Confirmation of Regge theory,'' Phys. Lett. B 478, 146 (2000).

The parametrization is for photoproduction.

Range of validity: sqrt(s)=6.9...200 GeV.

Maybe one should upgrade to the newest work of the authors:

  • A.~Donnachie and P.~V.~Landshoff, ``Successful description of exclusive vector meson electroproduction,'' arXiv:0803.0686 [hep-ph].

VecMesWinkel/vecdelta [ Subroutines ]

[ Top ] [ VecMesWinkel ] [ Subroutines ]

NAME

subroutine vecdelta(sqrts,idM,massD,massM,massIn2,cost,successflag)

PURPOSE

determines scattering angle for gamma N --> V Delta

INPUTS

  • real :: sqrts -- sqrt(s)
  • integer :: idM -- ID of vector meson
  • real :: massD -- mass of outgoing baryon (Delta)
  • real :: massM -- mass of outgoing vector meson
  • real :: massIn2 -- mass squared of incoming gamma (negative: Q^2!)

OUTPUT

  • real :: cost -- cos(theta) of scattering angle
  • logical, OPTIONAL :: successflag -- false, if problems with in-medium masses

NOTES

  • massIn2 may be negative: Q^2 !