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

\[\frac{\sigma_L(Q^2)}{\sigma_T(Q^2)}=\frac{\xi Q^2/m^2}{1+\xi\chi Q^2/m^2}.\]

Note

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

Warning

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