Status report on the showering of Alpgen events with Herwig++ for ATLAS

Transcription

1 Status report on the showering of Alpgen events with Herwig++ for ATLAS University of Oslo December 202

2 Introduction We want to set up and validate the processing of Alpgen events with Herwig++ in ATLAS, as Herwig++ is expected to gradually take over all the responsibilities of Fortran Herwig The processing of Alpgen events with Herwig++ has been possible since release Initial validation of this setup was performed by Andreas Papaefstathiou (one of the authors) by comparing Herwig++ showered samples with corresponding Fortran Herwig showered samples without underlying event simulation

3 Validation strategy For validation of the Alpgen+Herwig++ setup, I use existing parton level Alpgen events from the grid, and compare the showered events to the corresponding samples using Rivet From Andreas study, we know what kind of agreement to expect between Herwig++ and Fortran Herwig when underlying event simulation is not included I regenerated the ATLAS samples for W +jets production at 8 TeV without underlying event simulation in order to be able to make the same kind of comparison as Andreas (setting msflag=0) Some plots will also be shown with comparison to data, in which case we use samples with underlying event simulation included

4 Standalone running The standalone running of Herwig++ for processing Alpgen events is done in two steps: One first runs the small standalone program AlpGenToLH, which Converts the Alpgen unweighted events file (.unw) to the modern LHE file format Produces a steering file for Herwig++ for setting it up to process Alpgen events Then, one runs Herwig++ with the steering file from AlpGenToLH, editing possibly some merging parameters and setting whether the sample should be exclusive or inclusive For my Herwig++ runs, I merged the steering file from AlpGenToLH with a corresponding one from an infiledump of the JO for Herwig++ LHEF reading in ATLAS in order to get any ATLAS-specific settings into the steering file This did not make much difference when underlying event was turned off, though

5 Systematic differences reported by Andreas W boson p in peak region Mass of first jet dσ/dp W [pb/gev] dσ/dm(jet ) [pb/gev] p W [GeV] m(jet ) Systematic differences observed in W p T and jet mass distributions These were however shown to be present also when using native matrix elements, and are thus not related to the handling of Alpgen inputs I will not show these distributions, but you can note that these disagreements are present also in my plots

6 Some of Andreas plots for W +jets at 7 TeV dσ/dη(jet ) [pb] Pseudorapidity of leading jet dσ/dη(jet 2) [pb] Pseudorapidity of second jet η(jet ) η(jet 2) Pseudorapidity of third jet Pseudorapidity of fourth jet dσ/dη(jet 3) [pb] dσ/dη(jet 4) [pb] η(jet 3) η(jet 4)

7 Some of Andreas plots for W +jets at 7 TeV Transverse momentum of leading jet Transverse momentum of second jet dσ/dp (jet ) [pb/gev] dσ/dp (jet 2) [pb/gev] dσ/dp (jet 3) [pb/gev] p (jet ) [GeV] Transverse momentum of third jet dσ/dp (jet 4) [pb/gev] p (jet 2) [GeV] Transverse momentum of fourth jet p (jet 3) [GeV] p (jet 4) [GeV]

8 Some of my plots for W +jets at 8 TeV Pseudorapidity of leading jet Pseudorapidity of second jet dσ/dη(jet )[pb] dσ/dη(jet 2)[pb] dσ/dη(jet 3)[pb].4.2 η(jet ) Pseudorapidity of third jet dσ/dη(jet 4)[pb].4.2 η(jet 2) Pseudorapidityoffourthjet η(jet 3) η(jet 4)

9 Some of my plots for W +jets at 8 TeV dσ/dp (jet 3)[pb/GeV] dσ/dp (jet )[pb/gev] Transversemomentumofleadingjet p (jet )[GeV] Transversemomentumofthirdjet p (jet 3)[GeV] dσ/dp (jet 4)[pb/GeV] dσ/dp (jet 2)[pb/GeV] Transverse momentum of second jet p (jet 2)[GeV] Transverse momentum of fourth jet p (jet 4)[GeV]

10 The disagreement in my plots were clearly larger than in Andreas, so some further investigation was necessary The first thing I did, was to generate some Alpgen+Herwig++ samples at 7 TeV, in order to compare my Herwig++ samples directly to Andreas Fortran Herwig samples (for which the Rivet files were available on the web)

11 My H++ samples at 7 TeV compared to Andreas FHw Transverse momentum of leading jet Transverse momentum of second jet dσ/dp (jet )[pb/gev] Andreas FHw MyH++ dσ/dp (jet 2)[pb/GeV] Andreas FHw MyH p (jet )[GeV] 0 3 p (jet 2)[GeV] dσ/dp (jet 3)[pb/GeV] Transversemomentumofthirdjet Andreas FHw 0 4 MyH dσ/dp (jet 4)[pb/GeV] Transverse momentum of fourth jet Andreas FHw MyH p (jet 3)[GeV] p (jet 4)[GeV]

12 Strong coupling Browsing through Andreas H++ steering files and comparing to my own, I discovered one difference While the AlpGenToLH generated steering file automatically sets the strong coupling (both the value at the Z mass and the number of loops for evolution) to be consistent with the PDF used in Alpgen, it seemed Andreas had overwritten these settings This was in order to use the same strong coupling in Herwig++ as in Fortran Herwig, given by Λ QCD = 80 MeV and 2 loop running I then enforced this setting for the strong coupling in Herwig++, and compared once again to Andreas Fortran Herwig samples

13 My H++ samples at 7 TeV compared to Andreas FHw Transverse momentum of leading jet Transverse momentum of second jet dσ/dp (jet )[pb/gev] Andreas FHw MyH++ dσ/dp (jet 2)[pb/GeV] Andreas FHw MyH p (jet )[GeV] 0 3 p (jet 2)[GeV] dσ/dp (jet 3)[pb/GeV] Transversemomentumofthirdjet Andreas FHw MyH dσ/dp (jet 4)[pb/GeV] Transverse momentum of fourth jet Andreas FHw 0 4 MyH p (jet 3)[GeV] p (jet 4)[GeV]

14 Strong coupling As it seems clear that the choice of strong coupling makes a significant difference, I then tried introducing the Fortran Herwig compatible strong coupling into Herwig++ for my 8 TeV ATLAS comparison It should be noted that I have not been able to verify definitively that this is the setting used in the ATLAS samples, but in the Fortran Herwig manual, this setting is listed as the default As seen in the next slides, enforcing the Fortran Herwig compatible strong coupling definitely improves the agreement, but the discrepancy between my 8 TeV samples are still greater than Andreas discrepancies

15 8 TeV comparison side by side with Andreas 7 TeV Pseudorapidity of leading jet Pseudorapidity of leading jet dσ/dη(jet )[pb] dσ/dη(jet ) [pb] dσ/dη(jet 2)[pb].4.2 η(jet ) Pseudorapidity of second jet dσ/dη(jet 2) [pb].4.2 η(jet ) Pseudorapidity of second jet η(jet 2) η(jet 2)

16 8 TeV comparison side by side with Andreas 7 TeV Pseudorapidity of third jet Pseudorapidity of third jet dσ/dη(jet 3)[pb] dσ/dη(jet 3) [pb] 0 dσ/dη(jet 4)[pb].4.2 η(jet 3) Pseudorapidityoffourthjet dσ/dη(jet 4) [pb].4.2 η(jet 3) Pseudorapidity of fourth jet η(jet 4) η(jet 4)

17 8 TeV comparison side by side with Andreas 7 TeV dσ/dp (jet )[pb/gev] Transversemomentumofleadingjet dσ/dp (jet ) [pb/gev] Transverse momentum of leading jet p (jet )[GeV] 0 3 p (jet ) [GeV] Transverse momentum of second jet Transverse momentum of second jet dσ/dp (jet 2)[pb/GeV] dσ/dp (jet 2) [pb/gev] p (jet 2)[GeV] 0 3 p (jet 2) [GeV]

18 8 TeV comparison side by side with Andreas 7 TeV dσ/dp (jet 3)[pb/GeV] Transversemomentumofthirdjet p (jet 3)[GeV] dσ/dp (jet 3) [pb/gev] Transverse momentum of third jet p (jet 3) [GeV] Transverse momentum of fourth jet Transverse momentum of fourth jet dσ/dp (jet 4)[pb/GeV] dσ/dp (jet 4) [pb/gev] p (jet 4)[GeV] p (jet 4) [GeV]

19 8 TeV comparison side by side with Andreas 7 TeV Separation between W boson and leading jet Separation between W boson and leading jet dσ/d R(W, st jet)[pb] 0 3 dσ/d R(W, st jet) [pb] R(W, st jet) R(W, st jet) My 8 TeV comparisons between Alpgen+Herwig++ and are still showing a bit more disagreement than that in Andreas study This might be due to some settings for Fortran Herwig in the Athena job options scripts which differ from the settings used in Andreas Fortran Herwig setup Would be good to understand exactly where this extra disagreement is coming from

20 8 TeV comparison WenuNp sample dσ/dη(jet )[pb] Pseudorapidity of leading jet dσ/dη(jet 2)[pb] Pseudorapidityofsecondjet 0 dσ/dp (jet )[pb/gev].4.2 η(jet ) Transverse momentum of leading jet dσ/dp (jet 2)[pb/GeV].4.2 η(jet 2) Transversemomentumofsecondjet p (jet )[GeV] 0 3 p (jet 2)[GeV]

21 7 TeV comparison WenuNp sample to Andreas FHw Pseudorapidity of leading jet Pseudorapidity of second jet dσ/dη(jet )[pb] dσ/dη(jet 2)[pb] AndreasFHw 0 AndreasFHw η(jet ) η(jet 2) Transverse momentum of leading jet Transverse momentum of second jet dσ/dp (jet )[pb/gev] AndreasFHw dσ/dp (jet 2)[pb/GeV] AndreasFHw p (jet )[GeV] 0 3 p (jet 2)[GeV]

22 Rivet ATLAS 202 I TeV comparison to data with underlying event on Finally, we look at some comparisons to data with underlying event on This is done using the Rivet analysis ATLAS 202 I08338: W+jets production at 7 TeV The ATLAS tune is used for the underlying event in Herwig++ The Fortran Herwig ( ) samples are taken directly from the grid

23 Rivet ATLAS 202 I TeV comparison to data with underlying event on dσ/dp [pb/gev] FirstJetp ATLAS data dσ/dp [pb/gev] SecondJetp ATLAS data 0 0 MC/data p [GeV] MC/data p [GeV] ThirdJetp First Jet Rapidity dσ/dp [pb/gev] 0 ATLAS data dσ/dy[pb] ATLAS data MC/data p [GeV] MC/data y

24 Rivet ATLAS 202 I TeV comparison to data with underlying event on Inclusive Jet Multiplicity Inclusive Jet Multiplicity σ(w + Njetjets)[pb] 0 3 ATLAS data σ(w + Njetjets)[pb] 0 3 ATLAS data p jet >20GeV 2 2 MC/data MC/data Njet Njet The results from are closer to data

25 This just in Andreas suggested trying out an improvement to the Herwig++ shower based on a paper by Schofield and Seymour The following lines are added to the Herwig++ commands: cd /Herwig/Shower set Evolver:ColourEvolutionMethod set PartnerFinder:PartnerMethod set GtoGGSplitFn:SplittingColourMethod I just looked at the results with these settings today, and agreement with data is somewhat improved, though still not as good as with

26 Old results (left) and improved results (right) FirstJetp FirstJetp dσ/dp [pb/gev] ATLAS data dσ/dp [pb/gev] ATLAS data MC/data p [GeV] MC/data p [GeV] dσ/dp [pb/gev] SecondJetp ATLAS data dσ/dp [pb/gev] SecondJetp ATLAS data MC/data p [GeV] MC/data p [GeV]

27 Old results (left) and improved results (right) First Jet Rapidity First Jet Rapidity dσ/dy[pb] ATLAS data dσ/dy[pb] ATLAS data MC/data y MC/data y Inclusive Jet Multiplicity Inclusive Jet Multiplicity σ(w + Njetjets)[pb] 0 3 ATLAS data σ(w + Njetjets)[pb] 0 3 ATLAS data 2 2 MC/data MC/data Njet Njet

28 Athena implementation I have started working on an Athena implementation My approach has been to copy/paste the code from the AlpGenToLH standalone program into Athena code, making adaptations where I see fit (for example, I remove the underlying event related stuff, since we want the ATLAS tune for the underlying event, not some numbers hard coded in the AlpGenToLH program) This saves the user the trouble of running this code separately, and makes the Athena implementation 00% compatible with existing input datasets on the grid (I make sure that the extra lines in the parameters files with the merging parameters are read by the interface and set correctly)

29 Athena implementation However, I have been made aware that a new version of Alpgen (2.2) will soon make the conversion step unnecessary, so I will also make a simpler implementation where some Alpgen specific commands are simply put into config.py In this case, the user must first run AlpGenToLH separately when the current Alpgen version is used, or inputs from the grid are used The library files AlpGenHandler.so and BasicLesHouchesFileReader.so are not compiled and available through Athena release which I use for testing The relevant code and makefiles are under Contrib/ and Contrib/AlpGen/ in the Herwig++ source tree For testing, I have just put these library files in the run directory

30 Conclusions Alpgen events can be showered with Herwig++ since version 2.6 I have compared Herwig++ showered events to Fortran Herwig showered events for validation of my Herwig++ setup This is done mainly with underlying event off to eliminate this source of discrepancy and so that we know from a previous study what level of agreement to expect When comparing to ATLAS Fortran Herwig showered samples some additional discrepancy is observed Even when setting the strong coupling constant to match the Fortran Herwig one, we see some additional discrepancy - could be due to some specific settings in Fortran Herwig for ATLAS Would be good to understand this fully

31 Conclusions An Athena implementation is underway, and will soon be documented so that anyone interested can start looking at their favourite Alpgen samples using Herwig++ One implementation will be compatible with existing input event samples on the grid, but this will be replaced by a simpler implementation due to the fact that future Alpgen versions will make modern LHE files automatically, so no AlpGenToLH conversion will be necessary

32 Additional information Grid datasets for 8 TeV inputs: group.physgener.alpgen x.wenunpx CTEQ6L 8TeV.TXT.mc2* Grid datasets for 7 TeV inputs: group0.phys-gener.alpgen.0768x.wenunpx pt20 7tev.TXT.* Grid datasets for with UE at 7 TeV: mc 7TeV.0768X.AlpgenJimmyWenuNpX pt20.evgen.evnt.e825* Job options for regeneration of 8 TeV Jimmy samples without UE: MC2.0768X.AlpgenJimmy AUET2CTEQ6L WenuNpX.py with additional lines: # Turn UE off in Herwig topalg.herwig.herwigcommand += [ "msflag 0" ]

33 Additional information Web address to Andreas plots: andreasp/val/wjet/plots Herwig version: Athena version for production without underlying event: