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0001 ---
0002 title: PEPSI
0003 name: pepsi
0004 category: pepsi
0005 layout: default
0006 ---
0007 {% include layouts/title.md %}
0008
0009 **Note: By now it is better to use DJANGOH for polarized studies as it is the more complete generator**
0010
0011 * TOC
0012 {:toc}
0013
0014 PEPSI (Polarized Electron Proton Scattering Interactions) is a Monte Carlo generator for polarized deep inelastic scattering (pDIS). It is based on the LEPTO 6.5 Monte Carlo for unpolarized DIS.
0015
0016 See L. Mankiewicz, A. Schäfer and M. Veltri, Comp. Phys. Comm. 71, 305-318 (1992),
0017 {% include navigation/findlink.md name='pepsi_paper' tag='PEPSI.paper.pdf' %}
0018
0019 #### Parton distribution functions
0020
0021 The distribution function to use in polarized leptoproduction is set via the variable <tt>LST(15)</tt> in the LEPTO <tt>COMMON</tt> block <tt>/LEPTOU/</tt>.
0022 [Table 1](#table-1-polarized-parton-distributions) and [Table 2](#table-2-unpolarized-parton-distributions) list internal allowed values of <tt>LST(15)</tt> for polarized and unpolarized distributions respectively.
0023
0024 Pepsi is linked with the pdflib such that all PDFs included in there can be used by setting <tt>LST(15)</tt> to the respective PDF-ID
0025
0026 ##### PEPSI processes important in ep
0027
0028 | Subprocess | \# | Description |
0029 |:---:|:---:|:---:|
0030 | DIRECT |||
0031 | γ<sup>*</sup>q → q | 1 | LO DIS |
0032 | γ<sup>*</sup>q → qg | 2| QCDC |
0033 | γ<sup>*</sup>g → q qbar | 3| PGF |
0034 {:.table-bordered}
0035 {:.table-striped}
0036
0037 <br />
0038 *QCDC*: QCD-Compton, radiation of a gluon from incoming or outgoing quark lines
0039 <br />
0040 *PGF*: Photon Gluon Fusion
0041
0042 #### Running PEPSI
0043 In the standard setup in the singularity cvmfs environment or at BNL, the code can be found in
0044 ```bash
0045 $EICDIRECTORY/PACKAGES/pepsi
0046 ```
0047
0048 The executables are in the same directory and called `pepsieRHICnoRAD` and `pepsieRHICwithRAD`, respectively. There are several steer files (named `input.data.XXXXX.eic`) provided in this directory to run PEPSI and get reasonable output.
0049
0050 PEPSI has to be run twice if polarized asymmetries should be generated, once for parallel, lepton and proton beam spin direction, and once antiparallel.
0051 Charge Current events can only be generated in the unpolarized mode.
0052 The <tt>LST(8)</tt> can only be different from 0 or 1 in the unpolarized mode.
0053
0054 Note that the executables expect the `pdf/` directory in the directory of execution. Easiest way to achieve this is a softlink (adapt to your location)
0055 ```bash
0056 ln -s $EICDIRECTORY/PACKAGES/PEPSI/pdf
0057 ```
0058
0059 ##### Without radiative corrections
0060 Choose or create a steering file. Some that are provided in `$EICDIRECTORY/PACKAGES/pepsi/STEER-FILES`:
0061 * `input.data_noradcor.eic.pol.anti` is an example to run PEPSI with settings tuned for Hermes, and/or H1 and ZEUS for the antiparallel polarized cross-section
0062 * `input.data_noradcor.eic.pol.par`: for the parallel polarized cross-section
0063 * `input.data_noradcor.eic.unpol`: for the unpolarized cross-section
0064
0065 You can then run:
0066 ```bash
0067 ./pepsieRHICnoRAD < STEER-FILES/input.EW_noradcor.eic.posi.test > XXX.log
0068 ```
0069 where the output redirect to `XXX.log` is optional.
0070
0071 ##### With radiative corrections
0072
0073 **Note: DO NOT USE radiative corrections. Currently this is no longer supported. See [Known Issues](#known-issues)**
0074
0075 ##### Output file structure
0076
0077 The output file is in a text format which has the following structure:
0078 * 1st line: <tt> PEPSI EVENT FILE</tt>
0079 * 2nd line: <tt>============================================</tt>
0080 * 3rd line: Information on event wise variables stored in the file:
0081
0082 | I: | 0 (line index) |
0083 | ---------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------ |
0084 | ievent: | eventnumber running from 1 to XXX |
0085 | genevent: | trials to generate this event |
0086 | process: | pepsi subprocess (LST(23)), for details see table above |
0087 | subprocess: | pythia subprocess (LST(24)), for details see table above |
0088 | nucleon: | hadron beam type (LST(22)) |
0089 | struckparton: | parton hit in the target (LST(25)) |
0090 | partontrack: | \# or parton track (LST(26)) |
0091 | truey, trueQ2, truex, trueW2, trueNu: | are the kinematic variables of the event. |
0092 | | If radiative corrections are turned **on** they are **different** from what is calculated from the scattered lepton. |
0093 | | If radiative corrections are turned **off** they are **the same** as what is calculated from the scattered lepton |
0094 | mcfixedweight | weight calculated from generation limits |
0095 | weight | total weight including everything |
0096 | dxsec | cross section included in the weight |
0097 | mcextraweight | Pepsi total cross section in pb from numerical integration parl(23) |
0098 | dilut, F1, F2, A1, A2, R, Depol, d, eta, eps, chi | true variables needed to calculate g1 |
0099 | gendilut, genF1, genF2, genA1, genA2, genR, genDepol, gend, geneta, geneps, genchi | variables needed to calculate g1 |
0100 | SigRadCor: | information used and needed in the radiative correction code |
0101 | EBrems: | energy of the radiative photon in the nuclear rest frame |
0102 | nrTracks: | number of tracks in this event, includes also virtual particles<br><br> |
0103 {:.table-bordered}
0104 {:.table-striped}
0105
0106 * 4th line: <tt>============================================</tt>
0107 * 5th line: Information on track-wise variables stored in the file:
0108
0109 | I: | line index, runs from 1 to nrTracks |
0110 | ------- | -------------------------------------------------------------------------------------------------------- |
0111 | K(I,1): | status code KS (1: stable particles 11: particles which decay 55; radiative photon) |
0112 | K(I,2): | particle KF code (211: pion, 2112:n, ....) |
0113 | K(I,3): | line number of parent particle |
0114 | K(I,4): | normally the line number of the first daughter; it is 0 for an undecayed particle or unfragmented parton |
0115 | K(I,5): | normally the line number of the last daughter; it is 0 for an undecayed particle or unfragmented parton. |
0116 | P(I,1): | px of particle |
0117 | P(I,2): | py of particle |
0118 | P(I,3): | pz of particle |
0119 | P(I,4): | Energy of particle |
0120 | P(I,5): | mass of particle |
0121 | V(I,1): | x vertex information |
0122 | V(I,2): | y vertex information |
0123 | V(I,3): | z vertex information |
0124 {:.table-bordered}
0125 {:.table-striped}
0126 <br />
0127
0128 * 6th line: <tt>============================================</tt>
0129 * 7th line: event information for first event
0130 * 8th line: <tt>============================================</tt>
0131 * 9th to X-1 line: track-wise info of 1st event
0132 * Xth line <tt>============================================</tt>
0133
0134 **For each subsequent event, lines 7 through X repeat analogously .**
0135
0136 ##### How to analyze events
0137
0138 The recommended way is to create and use a ROOT tree with the `BuildTree` function and other tools provided by [eic-smear](eicsmear.html).
0139 Some guidelines regarding Monte Carlo normalization can be found [here](https://wiki.bnl.gov/eic/index.php/Simulations#MC_Analysis_Techniques).
0140
0141 <br />
0142 <br />
0143 <br />
0144
0145 #### Installation
0146
0147 It is recommended to take advantage of the pre-installed versions on the lab farms or
0148 the available stand-alone [singularity](eicsmear_generators_singularity.html) or [escalate](escalate_singularity_1.html) containers.
0149
0150 However, the package can also be built using "make".
0151 The Makefile should be customized to your environment before using,
0152 specifically you need to adapt the "install" target and point to a compatible CERNLIB installation.
0153
0154 Ignore warnings of the form:
0155 ```
0156 Warning: $ should be the last specifier in format
0157 ```
0158 Which should be okay (it is a g77 extension allowed by gfortran).
0159 As well as:
0160 ```
0161 Warning: Deleted feature: PAUSE statement at (1)
0162 ```
0163 This feature is deleted in F95; here, it should eventually be replaced by write() + read().
0164
0165 ##### Changes made for more recent fortran versions
0166 Multiple warnings like this:
0167 ```pepsi/setctq5.F:9.10:
0168 > './pdf/cteq5hj.tbl',
0169 1
0170 Warning: Initialization string starting at (1) was truncated to fit the variable (16/17)
0171 ```
0172
0173 indicate a too short variable length. Changed to
0174 ```fortran
0175 Character Flnm(Isetmax)*100
0176 ```
0177 in line 6 (of setctq5.F).
0178
0179 #### Known Issues
0180 **Note: DO NOT USE radiative corrections. Currently does not work.**
0181
0182 If radiative corrections are restored, this would be the procedure to use them:
0183
0184 * Create a directory called `radgen` in the area you want to run the code.
0185 * You either need to generate the lookup table for your cuts and beam energy settings first
0186 ```
0187 pepsieRHICwithRAD < input.data_make-radcor.eic.unpol
0188 ```
0189 or you can use one of the files already generated in the directory
0190 `$EICDIRECTORY/PACKAGES/pepsi/radgen`
0191 and called `xytab1unp.04.050.dat` or `xytab1ant.04.050.dat` or `xytab1par.04.050.dat`.
0192 * 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 run
0193 ```
0194 pepsieRHICwithRAD < input.data_radcor.eic.unpol > XXX.log
0195 ```
0196
0197 However, as noted above, they cannot currently be used.
0198 ```
0199 ./pepsieRHICwithRAD < STEER-FILES/input.data_radcor.eic.pol.anti
0200
0201 At line 514 of file pepsiMaineRHIC_radcorr.v2.F (unit = 29, file =
0202 'pepsi.ep.4x100.1Mevents.pol-anti.RadCor=1.txt')
0203 Fortran runtime error: Expected REAL for item 42 in formatted
0204 transfer, got INTEGER
0205 ```
0206
0207 Details about radiative corrections can be found [here](pythia6.html/#radiative-corrections).
0208
0209 <br />
0210
0211 #### Table 1: Polarized parton distributions
0212
0213 | LST(15) | Polarized parton distribution function |
0214 | ------- | ------------------------------------------------------------------------------------------------------------------------ |
0215 | 101 | Schaefer, Phys. Lett. B 208,2 (1988) 175 for comparison with older PEPSI versions |
0216 | 102 | free |
0217 | 103 | free |
0218 | 104 | Schaefer et al hep-ph/9505306 using Glueck et al. Z. Phys. C 53 (1992) 127 |
0219 | 105 | Bartelski et al hep-ph/9502271 Set II(p,n) |
0220 | 106 | Bartelski et al hep-ph/9502271 Set II(P,n) |
0221 | 107 | Gehrmann hep-ph/9512406 Gluon A (NLO) + DGLAP |
0222 | 108 | Gehrmann hep-ph/9512406 Gluon A (NLO) + DGLAP |
0223 | 109 | Gehrmann hep-ph/9512406 Gluon A (NLO) + DGLAP |
0224 | 110 | Gehrmann et al hep-ph/9512406 Gluon A (LO) |
0225 | 111 | Gehrmann et al hep-ph/9512406 Gluon B (LO) |
0226 | 112 | Gehrmann et al hep-ph/9512406 Gluon C (LO) |
0227 | 113 | Gehrmann et al hep-ph/9512406 Gluon A (LO) + (DGLAP) |
0228 | 114 | Gehrmann et al hep-ph/9512406 Gluon B (LO) + (DGLAP) |
0229 | 115 | Gehrmann et al hep-ph/9512406 Gluon C (LO) + (DGLAP) |
0230 | 116 | M. Glueck, E. Reya, M. Stratmann and W. Vogelsang, DO-TH 95/13, RAL-TR-95-042 'standard' scenario, next-to-leading order |
0231 | 117 | M. Glueck, E. Reya, M. Stratmann and W. Vogelsang, DO-TH 95/13, RAL-TR-95-042 'valence' scenario, next-to-leading order |
0232 | 118 | M. Glueck, E. Reya, M. Stratmann and W. Vogelsang, DO-TH 95/13, RAL-TR-95-042 'standard' scenario, leading order |
0233 | 119 | M. Glueck, E. Reya, M. Stratmann and W. Vogelsang, DO-TH 95/13, RAL-TR-95-042 'valence' scenario, leading order |
0234 | 120 | Stanley J.Brodsky Nucl.Phys. B441(1995) |
0235 | 121 | S.Keler & J.F.Owens Phys.Lett. B266(1991) & Phys.Rev. D19(1994)1199 |
0236 | 124 | D. de Florian et al., hep-ph/9711440 LO set 1 |
0237 | 125 | D. de Florian et al., hep-ph/9711440 LO set 2 |
0238 | 126 | D. de Florian et al., hep-ph/9711440 LO set 3 |
0239 | 127 | D. de Florian et al., hep-ph/9711440 NLO set 1 |
0240 | 128 | D. de Florian et al., hep-ph/9711440 NLO set 2 |
0241 | 129 | D. de Florian et al., hep-ph/9711440 NLO set 3 |
0242 | 130 | Fake sample: unpolarized Gehrmann et al hep-ph/9512406 with Delta u(x) = 0.5 \* u(x) and Delta d(x) = 0. |
0243 | 131 | Fake sample: unpolarized Gehrmann et al hep-ph/9512406 with Delta d(x) = 0.5 \* d(x) and Delta u(x) = 0. |
0244 | 132 | fit routine. (Is outside the official code.) |
0245 | 133 | CTEQ4LQ . UNPOL: Low Q2 parametrization is the only one used here. POL: BOGUS, du=0.5\* u(x) dd=-0.3\*d(x) 0.0 all else |
0246 | 137 | MRS low Q2 |
0247 | 144 | grsv2000 hep-ph/0011215 LO standard scenario |
0248 | 145 | grsv2000 hep-ph/0011215 LO valence scenario |
0249 | 146 | grsv2000 hep-ph/0011215 NLO standard scenario |
0250 | 147 | grsv2000 hep-ph/0011215 NLO valence scenario |
0251 {:.table-bordered}
0252 {:.table-striped}
0253
0254 <br />
0255
0256 #### Table 2: Unpolarized parton distributions
0257
0258 | LST(15) | Unpolarized parton distribution function |
0259 | ------- | ------------------------------------------------------------------------------------------------------------------------ |
0260 | 150 | cteq5l LO |
0261 | 151 | cteq5m NLO MSBAR |
0262 | 152 | cteq5m1 NLO MSBAR (update) |
0263 | 161 | mrs99 cor01 central gluon, a\_s |
0264 | 162 | mrs99 cor02 higher gluon |
0265 | 163 | mrs99 cor03 lower gluon |
0266 | 164 | mrs99 cor04 lower a\_s |
0267 | 165 | mrs99 cor05 higher a\_s |
0268 | 166 | mrs99 cor06 quarks up |
0269 | 167 | mrs99 cor07 quarks down |
0270 | 168 | mrs99 cor08 strange up |
0271 | 169 | mrs99 cor09 strange down |
0272 | 170 | mrs99 cor10 charm up |
0273 | 171 | mrs99 cor11 charm down |
0274 | 172 | mrs99 cor12 larger d/u |
0275 | 173 | cteq6l LO |
0276 | 174 | cteq6d DIS NLO |
0277 | 175 | cteq6m NLO MSBAR |
0278 {:.table-bordered}
0279 {:.table-striped}
