Difference between revisions of "PEPSI"

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==== By now it is better to use DJANGOH for polarised studies as it is the more complete generator ====
This page is now maintained at [https://eic.github.io/software/pepsi.html https://eic.github.io/software/pepsi.html].
PEPSI (Polarised Electron Proton Scattering Interactions) [[#Ref1|[1]]] is a Monte Carlo generator for polarised deep inelastic scattering (pDIS). It is based on the [http://www.isv.uu.se/thep/lepto/ LEPTO] 6.5 Monte Carlo for unpolarised DIS.
== PEPSI References ==
<span id="Ref1">(1)</span> ''"PEPSI - a Monte Carlo generator for polarized leptoproduction"'', L. Mankiewicz, A. Schäfer and M. Veltri, Comp. Phys. Comm. '''71''', 305-318 (1992) [https://wiki.bnl.gov/eic/upload/PEPSI.paper.pdf PEPSI.paper.pdf].
== Parton distribution functions ==
The distribution function to use in polarised leptoproduction is set via the variable <tt>LST(15)</tt> in the LEPTO <tt>COMMON</tt> block <tt>/LEPTOU/</tt>. [[PEPSI-pdf|Tables 1 and 2]] list internal allowed values of <tt>LST(15)</tt> for polarised and unpolarised distributions respectively.
Pepsi is linked with the pdflib such all PDFs included in there can be used by setting <tt>LST(15)</tt> to the respective PDF-ID
==== PEPSI processes important in ep ====
{| class="wikitable" style="text-align:left" border="1" cellpadding="3" cellspacing="0"
! style="background:#ffdead;" | Subprocess
! style="background:#ffdead;" | #
! style="background:#ffdead;" | Description
| colspan="3" align="center" | DIRECT
! γ∗q → q
! 1
! γ∗ q → qg
! 2
! γ∗ g → q qbar
! 3
QCDC: QCD-Compton, radiation of a gluon from incoming or outgoing quark lines<br/>PGF: Photon Gluon Fusion
== Running PEPSI ==
In the standard setup in the singularity cvmfs environment or at BNL, the code can be found in
This code is based on PEPSI/LEPTO and was modified to include radiative corrections using [[#Documentation_on_Radiative_Corrections:|RadGen]].<br/>The main program is in the same directory and called pepsiMaineRHIC_noradcorr.f / pepsiMaineRHIC_radcorr.f, several other routines are needed, which are in the same directory.<br/>The executable is in the same directory and called pepsieRHICnoRAD / pepsieRHICwithRAD<br/>There are several steer files (named: input.data. XXXXX.eic) provided in this directory to run PEPSI and get reasonable output.
=== How to Run the Code ===
==== Features ====
PEPSI has to be run twice if polarized asymmetries should be generated, once for parallel, lepton and proton beam spin direction, and once antiparallel.<br/>Charge Current events can only be generated in the unpolarized mode.<br/>The LST(8) can only be used different from 0 or 1 in the unpolarised mode.
==== without radiative corrections ====
  pepsieRHICwithRAD < input.data_noradcor.eic.pol.anti > XXX.log 
input.data_noradcor.eic.pol.anti is one of the steer file examples in the directory to run PEPSI with settings tuned for Hermes, and/or H1 and ZEUS for the antiparallel polarized cross-section<br/>input.data_noradcor.eic.pol.par: for the parallel polarized cross-section<br/>input.data_noradcor.eic.unpol: for the unpolarised cross-section
==== with radiative corrections ====
*create a directory called radgen in the area you want to run the code
*you either need to generate the lookup table for your cuts and beam energy settings first
    pepsieRHICwithRAD < input.data_make-radcor.eic.unpol
*or you can use one of the files already generated
the files are in the directory
and called xytab1unp.04.050.dat or xytab1ant.04.050.dat or xytab1par.04.050.dat
*to run the code than with radiative corrections simply change the steer file to either
input.data_radcor.eic.unpol or input.data_radcor.eic.pol.par or .... and
  type pepsieRHICwithRAD < input.data_radcor.eic.unpol > XXX.log
=== Output file structure ===
the output file is in a text format which has the following structure.
*2nd line: "============================================"
*3rd line: Information on event wise variables stored in the file
{| class="wikitable" style="text-align:left" border="1" cellpadding="2" cellspacing="0"
| I:
| 0 (line index)
| ievent:
| eventnumber running from 1 to XXX
| genevent:
| trials to generate this event
| process:
| pepsi subprocess (LST(23)), for details see table above
| subprocess:
| pythia subprocess (LST(24)), for details see table above
| nucleon:
| hadron beam type (LST(22))
| struckparton:
| parton hit in the target (LST(25))
| partontrack:
| # or parton track (LST(26))
| truey, trueQ2, truex, trueW2, trueNu:
| are the kinematic variables of the event.
| If radiative corrections are turned on they are different from what is calculated from the scattered lepton.
| If radiative corrections are turned off they are the same as what is calculated from the scattered lepton
| mcfixedweight
| weight calculated from generation limits
| weight
| total weight including everything
| dxsec
| cross section included in the weight
| mcextraweight
| Pepsi total cross section in pb from numerical integration parl(23)
| dilut, F1, F2, A1, A2, R, Depol, d, eta, eps, chi
| true variables needed to calculate g1
| gendilut, genF1, genF2, genA1, genA2, genR, genDepol, gend, geneta, geneps, genchi
| variables needed to calculate g1
| SigRadCor:
| information used and needed in the radiative correction code
| EBrems:
| energy of the radiative photon in the nuclear rest frame
| nrTracks:
| number of tracks in this event, includes also virtual particles
*4th line: "============================================"
*5th line: Information on track wise variables stored in the file
{| class="wikitable" style="text-align:left" border="1" cellpadding="2" cellspacing="0"
| I:
| line index, runs from 1 to nrTracks
| K(I,1):
| status code KS (1: stable particles 11: particles which decay 55; radiative photon)
| K(I,2):
| particle KF code (211: pion, 2112:n, ....)
| K(I,3):
| line number of parent particle
| K(I,4):
| normally the line number of the first daughter; it is 0 for an undecayed particle or unfragmented parton
| K(I,5):
| normally the line number of the last daughter; it is 0 for an undecayed particle or unfragmented parton.
| P(I,1):
| px of particle
| P(I,2):
| py of particle
| P(I,3):
| pz of particle
| P(I,4):
| Energy of particle
| P(I,5):
| mass of particle
| V(I,1):
| x vertex information
| V(I,2):
| y vertex information
| V(I,3):
| z vertex information
*6th line: "============================================"
*7th line: event information for first event
*8th line: "============================================"
*9th to X-1 line: trackwise info of 1st event
*Xth line "=============== Event finished ==============="
'''the information from line 7 to X repeats for each event.'''
=== How to analyze events ===
*create a root tree
there are root macros available to convert the output txt-files into root trees.<br/>Details how to run the macros can be found [https://wiki.bnl.gov/eic/index.php/ROOT [here]]
===== MC normalization (still under construction) =====
to normalize your counts to cross section you need two informations
*the total number of trials (NGEN(0,3)), it is printed to the screen/logfile if PYTHIA finishes
*the total integrated cross section (PARI(1)), the unit is microbarn (10^-6), it is printed to the screen/logfile if PYTHIA finishes
==> count * total integrated cross section /total number of trials
to calculate the corresponding luminosity
==> total number of trials/ total integrated cross section
== Documentation on Radiative Corrections: ==
the code implemented in PTHIA to calculate radiative corrections is called RADGEN<br/>The writeup on it can be found here [http://arXiv.org/pdf/hep-ph/9906408 [hep-ph/9906408]]<br/>The following steps have been done to implement it in PYTHIA:
*change the subroutine pygaga.f so it calls radgen after you have thrown y and Q2
*get the true y and Q2 from radgen and the radiated photon
*Pythia will continue to now generate an event based on this y and Q2
*Pythia still operates under accept reject, the extra weigt from the radiative corrections is absorbed in the flux factor
[[Category:Event Generators]]

Latest revision as of 13:42, 9 June 2020

This page is now maintained at https://eic.github.io/software/pepsi.html.