DVCS Monte-Carlo Page

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Intro

Different Monte Carlo generators are traditionally used in the Hermes DVCS analysis for data-MC comparisons (e.g. Fehler beim Parsen (Konvertierungsfehler. Der Server („https://wikimedia.org/api/rest_“) hat berichtet: „Cannot get mml. Server problem.“): {\displaystyle M_{x}^{2}} ) and the estimation of systematic uncertainties. The elastic Bethe-Heitler (BH) process, the BH-process associated with the excitation of the target proton to a resonant state (e.g., the Fehler beim Parsen (Konvertierungsfehler. Der Server („https://wikimedia.org/api/rest_“) hat berichtet: „Cannot get mml. Server problem.“): {\displaystyle \Delta ^{+}} ), the DVCS process and semi-inclusive (sidis) and exclusive background processes need to be simulated. Read also about MC Generators used at Hermes and the general Monte Carlo page.

This page is supposed to provide useful information for all people working with Monte-Carlos related to DVCS analysis. Please help to improve it.

Essentials

Monte-Carlo generators for DVCS analysis

disNG

General information about disNG
Relevant for DVCS: contains elastic BH and sidis processes
Resonance ("associated") production:
- DISng contains no model of the resonance region $W_{\mathrm {True} }^{2}<4$ $W_{\mathrm {True} }^{2}<4$ GeV $^{2}$ $^{2}$ , LEPTO fails
  - Those events are called lowE and a "quasi-elastic" proton is generated (the principle of duality is applied to correctly calculate the total cross section)
  - $\Rightarrow$ problem to generate correct final hadronic state: resonance region shows no peak structure in the 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 W^2} -distribution
For the estimation of sidis background correction (fraction) and elastic BH.

gmcDVCS

The default MC generator for DVCS.
- Used for the estimation of the associated BH fractional contribution in each kinematic bin
- Used for the estimation of smearing, bin width, misalignment and acceptance effects ("4-in-1") in DVCS
Detailled information about gmcDVCS

gmc_Dual

gmc_Dual is an alternative to VGG to estimate the "4-in-1" systematic uncertainty
Detailled information about gmc_Dual

gmc_exclpion

For the estimation of exclusive 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 \pi^0} background.
- For the final papers: use upper limit on the fractional contribution from Arne's analysis
More detailled description of gmc_exclpion

MC processes relevant to DVCS

After applying all traditional DVCS cuts to the data, the exclusive sample is still left with certain fractions of background processes, of which some are corrected for.

Squared missing mass distribution of single photon events. All cuts have been applied (except for Mx2). The solid green vertical lines indicate the standard exclusive DVCS window, which is defined for positron beam data (solid circles). The window for electron beam data (open circles) is slightly shifted, as indicated by the dashed lines. The histograms stem from Monte Carlo (DISng plus gmcDVCS) and show the different process contributions. The figure is taken from the 2008 TTSA publication.

The signal

DVCS and elastic Bethe Heitler: 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 p\gamma^*\rightarrow p\gamma}

Semi-inclusive (sidis) Neutral Meson Production

For example: 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 p\gamma^*\rightarrow p\pi^0} and $\pi ^{0}\rightarrow \gamma \gamma$ , of which only one 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 \left.\gamma\right.} is detected in the calorimeter
Average contribution in the exclusive region: 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 \left.f_{sidis}=4%\right.} , thereof 80% 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 \left.\pi^0\right.} and 15% 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 \left.\eta^0\right.}
The sidis contribution is corrected for, for all DVCS releases in 2008 by the two-photon analysis based on real data and the fraction taken from MC.

Resonance Production ("Associated Production")

For example: Fehler beim Parsen (Konvertierungsfehler. Der Server („https://wikimedia.org/api/rest_“) hat berichtet: „Cannot get mml. Server problem.“): {\displaystyle p\gamma ^{*}\rightarrow \Delta ^{+}\gamma }

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 \Delta^+\rightarrow p\pi^0\;\; (2/3) \;\;\mathrm{or}\;\; \rightarrow n\pi^+ \;\; (1/3)}

Nuclear targets: resonance production exists both for incoherent (nucleon is excited) and for coherent production (nucleus is excited)
Average contribution in the exclusive region: 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 f_{asso}\approx 12%} . The resonant contribution is not corrected for, it stays part of the signal (as long as no Recoil detector information is available).
MAID is a program to fit resonances at low energies
Alternative to gmcDVCS(MAID): DISng with "Set FStruct RESO" (default in DISng is ALLM)
- RESO = Bodek's 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 F_2} fit of the resonance region from SLAC (Hermes energies)
- Norik's/Moskov's RESO-code which was originally used for Hermes GDH analysis was sent to DVCS people in summer 2008
- Result of study in summer 2008: resonance fraction and t-dependence very similar in MAID and RESO.
- MAID was used for e.g. the TTSA publication; shows 30% resonance production at high values of t
Resonance asymmetry ("associated asymmetry")
- Only one prediction available presently: see [DVCS-theo-019] on DVCS Analysis Page
Literature/Discussion
- Summer 2008 study on associated production: summary and pdf-file
- Thread on DVCS-list in Dec. 2009

Exclusive pion production

Upper limit (from Arne's studies): 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 \left.f_{excl.}=0.6%\right.} . The Recoil detector will tell us the truth!

How to select a certain MC process

Histograms of the squared missing mass obtained from gmcDVCS.

Histograms of the squared missing mass obtained from disNG.

gmc_DISng
- Elastic BH:
  - uDST format: g1MEvent.bProcess == 3145728 (hex-bitpattern: 0x300000)
  - hrc format: event.RadCorType==3; event.RadCorType is obtained by:

if ( !strncmp(mcRadCor.cType,"elas",4) ) 
 event.RadCorType = 3;

- Associated BH (there is no generated Fehler beim Parsen (Konvertierungsfehler. Der Server („https://wikimedia.org/api/rest_“) hat berichtet: „Cannot get mml. Server problem.“): {\displaystyle \Delta ^{+}} in such events!!):
  - uDST format: g1MEvent.bProcess == 1048577 (hex-bitpattern: 0x100001)
  - hrc format: event.RadCorType==1 && mcEvent.nucleon==1; event.RadCorType is obtained by:

if ( !strncmp(mcRadCor.cType,"inel",4) ) 
 event.RadCorType = 1;

- Sidis:
  - uDST format: leptoprocess = (g1MEvent.bProcess >> 4 & 0xFF) = 1
  - hrc format: mcEvent.process==1
gmc_DVCS
- Elastic BH: xtrue==1
- Associated BH: xtrue<1 && w2true<4 (resonance region!)
- Coherent (for deuterium target): xtrue>1.999

In this language, sidis would be xtrue<1 && w2true>4.

DVCS Monte-Carlo productions

Please see MC Productions, e.g. [15]-[21]

More Info

Back to DVCS Analysis Page