Diffractive Vector Meson Correction for SIDIS

Page maintainer: Achim

This page is considered done. It been reviewed by Elke. There may be missing elements, but they are all flagged and the text has no errors.

Intro

Fraction of hadrons from diffractive events

In the kinematic region of SIDIS, hadrons can also be produced by competing processes. One contribution is hadrons from the decay of diffractively produced vector mesons (VM), which subsecuently decay. The main reactions are

$ep\rightarrow ep\rho ^{0}\rightarrow ep+2\pi$
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Especially for pions the fraction of hadrons from this source can be quite large (>40% at large z > 0.8), while for kaons the fraction is usually < 10% (see plot on the right).

Essentials

There are two ways to check for the influence of decaying VM on the SIDIS analysis.

Calculation of correction factors to the hadron sample using Pythia MC

Pythia simulates both SIDIS events as well as the diffractive vector meson production. Thus the fraction of hadrons coming from diffractive processes in every bin can be obtained by performing the analysis on Pythia data and recording the fraction of hadrons coming from diffractive VM production.

The process type of an event is available in the bit pattern variable g1MEvent.bProcess. There it is stored as bits 4 to 11. This value can be copied into an integer variable eg by

process = (int)(g1MEvent.bProcess >> 4 &  0xFF);

The relevant process IDs signifying a diffractive event are:

91 (elastic scattering)
92 (single diffraction A+B -> X+B)
93 (single diffraction A+B -> A+X)
94 (double diffraction A+B -> X+Y)

Study of influence using Q2 cuts

While the DIS cross section depends on Fehler beim Parsen (MathML mit SVG- oder PNG-Rückgriff (empfohlen für moderne Browser und Barrierefreiheitswerkzeuge): Ungültige Antwort („Math extension cannot connect to Restbase.“) von Server „https://wikimedia.org/api/rest_v1/“:): {\displaystyle Q^{-4}} , the diffractive cross section is ~Fehler beim Parsen (MathML mit SVG- oder PNG-Rückgriff (empfohlen für moderne Browser und Barrierefreiheitswerkzeuge): Ungültige Antwort („Math extension cannot connect to Restbase.“) von Server „https://wikimedia.org/api/rest_v1/“:): {\displaystyle Q^{-6}} . Thus the influence of diffractive events can be minimized by requiring a higher Fehler beim Parsen (MathML mit SVG- oder PNG-Rückgriff (empfohlen für moderne Browser und Barrierefreiheitswerkzeuge): Ungültige Antwort („Math extension cannot connect to Restbase.“) von Server „https://wikimedia.org/api/rest_v1/“:): {\displaystyle Q^2} value.

More Info

Diffractive correction for multiplicities:
- Thesis by Achim Hillenbrand, pages 70-73
- Thesis by Bino Maiheu, pages 97-102

Code Repository