Skip to content

processes-diffvm.md

Latest commit

 

History

History
68 lines (47 loc) · 2.02 KB

processes-diffvm.md

File metadata and controls

68 lines (47 loc) · 2.02 KB
orphan true

Diffractive vector meson production

The $ep$-induced $\gamma^{(\ast)}\Pom\rightarrow$ vector meson production process may be selected from the diffvm label. It was designed for HERA physics cases, hence the asymmetric electron-proton initial beam kinematics.

Process-specific options

  • vmFlavour: PDG id of the VM produced

  • vmMode: vector meson production mode, protonMode: proton side emission type

    • BeamMode.GluonFragmentation := -1
    • BeamMode.Elastic := 0
    • BeamMode.StandardFragmentation := 1
    • BeamMode.NucleonPionsDecay := 2

  • photonMode: photon emission type

    • PhotonMode.Fixed := -1
    • PhotonMode.InvK := 0
    • PhotonMode.WWA := 1
    • PhotonMode.ABTSmith = 2
    • PhotonMode.AandS := 3

Furthermore, the following parameters can be steered in this process:

slopeParameters

  • wb0 is the $w _ {\gamma p}$ centre-of-mass energy (in GeV) at which b0 $=b_0$ was measured
  • amxb0 is the mass $M_X$ of the diffractively dissociating hadronic system $X$ for which $b_0$ was measured
  • anexp is a power-law exponent

pomeronParameters

  • epsilonW and epsilonM are controlling the intercept of the pomeron trajectory (minus 1). The first one steers the rise of $\sigma _ {\gamma p}$ with $W$, while the second controls the $M_X$ spectrum
  • alpha1 and alpha1m control the pomerons trajectory’s $\alpha'$ (therefore, expressed in GeV¯²)

vmParameters

  • lambda and eprop control the $Q^2$-dependence of the total production cross section, through
\sigma(Q^2) = \sigma_0\left(1 + Q^2/\Lambda^2\right)^{-\epsilon _ {\rm prop}}
  • xi and chi control the behaviour of the longitudinal-to-transverse cross section ratio through
\frac{\sigma_L(Q^2)}{\sigma_T(Q^2)}=\frac{\xi Q^2/m^2}{1+\xi\chi Q^2/m^2}.

In this scheme, $\sigma_L/\sigma_T\to\xi Q^2/m^2$ for low-$Q^2$, and $1/\chi$ for high-$Q^2$.