Talk on Sherpa - IPNL

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Talk on Sherpa - IPNL

Sherpa, Event Generatorfor the LHCStefan HöcheDresden University of Technology


Outline_________________________________IntroductionMatrix Elements in SherpaMerging ME’s with the Parton ShowerSimulation results vs. DataConclusion and Outlook_________________________________Stefan Höche, SM Workshop, Lyon 13.10.2005


Why Event Generators ?_________________________________High-flying expectations coupled tonext generation collider experiments:Will we see SUSY ?Extra dimensions ?Unexpected new physics ?Facts so far ...Tremendous event rates atfuture colliders, e.g. LHCMust understandSM issues first !The Higgsboson ?Final StateEvents / sJet, E T > 100GeV 10 3Jet, E T > 1TeV 1.5 · 10 2W → lν 20W W → lνlν 6 · 10 −3b¯b-pair 5 · 10 5t¯t-pair 1QCD radiation patternsMultiple partoninteractionsParton Distributions_________________________________Stefan Höche, SM Workshop, Lyon 13.10.2005


Sherpa - Status of developmement_________________________________Sherpa: T. Fischer, T. Gleisberg, S.H., F. Krauss, T. Laubrich,A. Schälicke1, S. Schumann and J. Winter ( JHEP 0402 (2004) 056 )Intention: Provide a multi-purpose tool, capable ofsimulating SM backgrounds as well asnew physics scenarios (e.g. MSSM, ADD)at ee, γγ and hadron collidersKey featuresAutomatic cross section calculationvia AMEGIC++ ( JHEP 0202:044,2002 )Generation of QCD/QED Bremsstrahlungvia APACIC++ ( hep-ph/0503087 )Merging of ME and PS ( hep-ph/0205283 )Simulation of Multiple Interactionsacc. to ( T. Sjöstrand et. al Phys. Rev. D36 (1987) )Lund string fragmentation via PYTHIAOwn model in preparation ( hep-ph/0311085 )_________________________________1 DESY ZeuthenStefan Höche, SM Workshop, Lyon 13.10.2005


AMEGIC++ - Automatic ME Generator_________________________________Fully automated calculation of (polarised) cross sectionsin the SM, the MSSM and the ADD modelPerformance comparable to that of dedicated codesAllows to study signal and backgrounds in one frameworkEasy to extend (feel free to implement your own model ...)_________________________________Tested e.g. in e + e − → 6fmutual deviations inabout 100 processesOngoing comparisonof arbitrary 2 2 SUSY processesvs. WHIZARD and MADGRAPHagainst HELAC/PHEGAS_________________________________Stefan Höche, SM Workshop, Lyon 13.10.2005


µ H∆ g (Q cut ,Q 1 )AMEGIC++ - Automatic ME Generator∆¯q (Q cut ,µ H )_________________________________ME Domain PS DomainEmploy helicity methods to decompose amplitudes intoQ cutcomplex numbers reduce to basic building blocksZ(1, 2; 3, 4) = [ u(p 1 )γ µ u(p 2 ) ] [ u(p 3 )γ µ u(p 4 ) ]X(1, 2; 3) = [ u(p 1 )ˆp 3 u(p 2 ) ]Y (1, 2) = [ u(p 1 )u(p 2 ) ]Generate corresponding phase space mappingfor each amplitudeD iso (23, 45) ⊗ P 0 (23) ⊗ P 0 (45) ⊗ D iso (2, 3) ⊗ D iso (4, 5)2µ H∆q(Q cut ,µ H )∆q (Q cut ,Q 1 )∆ q (Q cut ,Q 1 )∆¯q (Q cut ,µ H )∆ g (Q cut ,Q 1 )αs(Q 1 )αs(Q cut )3 4 5Factorize out common parts of different amplitudesSuperamplitudes10_________________________________Stefan Höche, SM Workshop, Lyon 13.10.2005


Matrix Element vs. Parton Shower_________________________________Matrix Elementst+ uExact to fixed orderin running coupling +tuInclude all quantuminterferencesCalculable only for lowFS multiplicity ( n≤6-8 )_______________22 2dσ n+1 = dσ n ⊗ ∑+ uResum (next-to) leadinglogarithms to all orders in Interference effects e.g.through angular ordering_________________________________tParton Showersta∈n,b+Stefan Höche, SM Workshop, Lyon 13.10.2005u22 2dttdzzα s (t, z)2πDesirable to combine both approaches to haveGood description of hard/wide-angle emissions (ME)Correct intrajet evolution (PS)Must prevent double counting e.g. through CKKWP a→b (z)_________________________________


µ HCombining ME & PS à la CKKW∆¯q (Q cut ,µ H )< ñ(b) >_________________________________Define phase space cut Q cutSelect jet multiplicity and kinematicsaccording to differential cross sectionKTcluster backwards andidentify core processAdd αSweight (ME taken at Qcut)Add Sudakov weightStart PS at scale Qhardp(p ⊥ , b) = f c f(b) 1 dσME Domainσ ND∆ q (Q cut ,Q 1 )ME DomainQ cutME Domain∆¯q (Q cutPS Domainq Γ(q, µ hard) + . . .,µ H )µ H∆ g (Q cut ,Q 1 )µ HQ cutQ cutαs(Q 1 )∆q(Q cut ,µ H )αs(Q cut )∆q(Q cut ,Q 1 )µ H∆¯q (Q cut ,µ H )∆ q (Q cut ,Q 1 ), reject emissions above Q∆ g (Q cut ,Q 1 )Q cutαs(Q 1 )∆q(Q cut ,µ H ) cut∆q(Q cut ,Q 1 µ )αs(Q cut )HPS Domain_________________________________µ H∆∆q(Q g (Qcut ,µ cut ,QH )1 )Yields correct jet rates, e.g. 2-jet rate at scale q through∆q(Q cut ,Q 1 ){ ∫ ∆¯q (Q cut ,µ∆ H q (Q )µhardcut ,Q 1 ) }√R2 (q 2 ) =∆(Q cut , µ hard ) ∆(q, µ hard )=∆(Q cut , µ hard )∆(q, µ hard )∆(Q cut , µ hard )Q cut∆ g (Q cut ,Q 1 )∆ q (Q cut ,Q 1 )Qαs(Q cut αs(Q 1 ) 1 )∆q(Q cut ,µ H αs(Q ) αs(Q cut ) cut )∆q(Q cut ,Q 1 )µ H_________________________________1 +Q cutdqStefan Höche, SM Workshop, ∆Lyon g (Q cut 13.10.2005 ,Q 1 )∆q(Q cut ,µ H )∆q(Q cut ,Q )


Tests of the Merging Procedure_________________________________W+jets production at Tevatron Run IIStability tests of the procedure( F. Krauss et. al hep-ph/0409106 )104 5 Applications – ResultsVariation of phase space separation cut QcutW / GeVd!/dp10210Q cut=10 GeVW + XW + 0jetW + 1jetW + 2jetW + 3jetreferenceW / GeVd!/dp10210Q cut=30 GeVW + XW + 0jetW + 1jetW + 2jetW + 3jetreferenceW / GeVd!/dp10210Q cut=50 GeVW + XW + 0jetW + 1jetW + 2jetW + 3jetreference111-110-110-110-2100.40.20-0.2-0.4SHERPA0 20 40 60 80 100 120 140 160 180p / GeV200W-2100.40.20-0.2-0.4SHERPA-210SHERPA0.40.20-0.2-0.40 20 40 60 80 100 120 140 160 180 / GeV200 0 20 40 60 80 100 120 140 160 180p / GeV200pW We / GeVe / GeV_________________________________101010111d!/dp1/!102-110Q cut=10 GeVGlobal K-factord!/dp1/!102-110Q cut=30 GeVe / GeVd!/dp1/!10102-1Q cut=50 GeVStefan Höche, SM Workshop, Lyon 13.10.2005


Tests of the Merging Procedure_________________________________W+jets production at Tevatron Run IIStability tests of the procedure( F. Krauss et. al hep-ph/0409106 )5.3 W/Z + jets production at the Fermilab Tevatron 107Variation of maximum jet multiplicityW [ pb/GeV ]d!/dp210101W [ pb/GeV ]W + XW + 0jetW + 1jet 10referenced!/dp2101W [ pb/GeV ]d!/dp210W + XW + 0jetW + 1jet 10W + 2jetreference1W + XW + 0jetW + 1jetW + 2jetW + 3jetreference-110-110-110-210-210-210SHERPASHERPASHERPA20 40 60 80 100 120 140 160 180p / GeVW20 40 60 80 100 120 140 160 180p / GeVW20 40 60 80 100 120 140 160 180p / GeVWGlobal K-factor_________________________________Figure 5.13: p ⊥ (W − ) for Q cut = 15 GeV and different maximal numbers of ME jets included.The dashed line corresponds to a maximal numbers Stefan of ME Höche, jetsSM n maxWorkshop, = 2. Lyon 13.10.2005


V+jets production @ Tevatron_________________________________Jet p T in W- and Z+1jet eventsSherpa vs. MCFM110 5 Applications – Results&" 3&B+)C)(,DA-@EF)&" 3&X+)C)(,DA-@EF)&6!)7!67' ()/&60,12&" 3!&" 35&" 3#89:8);?,@'A


&" 34!" #" $" %" &"" &!" &#" &$" &%"V+jets production' ()*+,-.)/0,12@ Tevatron_________________________________Figure 5.18: Jet p ⊥ distribution of Z + 1jet events at the Tevatron where for the NLO andLO calculation the renormalisation and factorisation scales have been chosen to be µ R = µ F =160.838 GeV.Jet p T in W- and Z+2jet eventsSherpa vs. MCFMZ++)E)(,FC-BGHD++)E)(,FC-BGH&6!)7!67' ())/&60,12&" 3&&" 3!&" 3589:8);


V+jets production @ Tevatron_________________________________Jet p T in inclusive W productionSherpa vs. PYTHIA & MC@NLO5.3 W/Z + jets production at the Fermilab Tevatron 115[ 1/GeV ]1/! d!/dp T-110-210SherpaPYTHIAMC@NLO[ 1/GeV ]1/! d!/dp T-110-210SherpaPYTHIAMC@NLO-310-310-410-410-510SHERPA20 40 60 80 100 120 140 160 180(first jet) [ GeV ]p TSHERPA20 40 60 80 100 120 140 160(second jet) [ GeV ]p T[ 1/GeV ]Global K-factor1/! d!/dp T-110SherpaPYTHIAMC@NLO_________________________________10-2-310Stefan Höche, SM Workshop, Lyon 13.10.2005


[ 1/GeV ]V+jets production @ Tevatron-2_________________________________10101/! d!/dp T-110SherpaPYTHIAMC@NLO[ 1/GeV ]1/! d!/dp T10-1-2SherpaPYTHIAMC@NLO-310-410-310Jet p T in inclusive W production-4Sherpa vs. PYTHIA & MC@NLO10-510SHERPA20 40 60 80 100 120 140 160 180(first jet) [ GeV ]p TSHERPA20 40 60 80 100 120 140 160(second jet) [ GeV ]p T[ 1/GeV ]1/! d!/dp T-110-210SherpaPYTHIAMC@NLO-310-410SHERPA20 40 60 80 100 120(third jet) [ GeV ]p TFigure 5.24: Jet p ⊥ distribution of the three hardest jets in inclusive W production at theTevatron, Run II. Compared are the hadron level results of SHERPA (black), PYTHIA (green)and MC@NLO (red) after 2.5 million events.Global K-factor_________________________________Stefan Höche, SM Workshop, Lyon 13.10.2005be taken as some kind of theoretical uncertainty. For higher jet configurations, however, the


V+jets production @ Tevatron_________________________________( F. Krauss et. al hep-ph/0409106 )78 4 Merging matrix elements and parton showersInclusive jet cross sections,CDF ( hep-ex/0405067 )/ pb410CDF Run II Preliminary" incl.310W $ e # + ! n jetsCDF DataSHERPA210101JetClu R=0.4 (E T> 15 GeV, | %|


V+jets production @ TevatronFigure 4.14: Inclusive cross sections for the process p¯p → W + njets. The SHERPA prediction_________________________________is contrasted with the measurement by CDF [125]( F. Krauss et. al hep-ph/0409106 )jet-p T, measured at CDF( hep-ex/0405067 )410310210CDF Run II PreliminaryW $ e # + ! n jetsSherpaCDF dataR = 0.4 (E T> 15 GeV & |%|


5.3 W/Z + jets production at the Fermilab Tevatron 117V+jets production @ Tevatron_________________________________( F. Krauss et. al hep-ph/0409106 )pT, Zmeasured at CDF( Phys. Lett. B513 (2001) 292 )pbGeV/d!dP101pt ZZ + 0 jetZ + 1 jetZ + 2 jetZ + 3 jetCDFpbGeV/d!dP10pt ZZ + 0 jetZ + 1 jetZ + 2 jetZ + 3 jetCDF10 -110 -2110 -30 20 40 60 80 100 120 140 160 180 200P / GeV Z0 5 10 15 20 25 30 35 40 45 50P / GeV ZGlobal K-factorFigure 5.26: The p ⊥ distribution of the Z-boson in comparison with data from CDF at theTevatron, Run I [123]. The total result is indicated by the black line. The coloured linesshow the contributions of the different multiplicity processes. The applied separation cut isQ cut = 20 GeV. The right plot focuses on the low momentum region of the left one._________________________________Stefan Höche, SM Workshop, Lyon 13.10.2005


Similarly, in Fig. 5.26, the (inclusive) p ⊥ distribution of the Z is compared with data,this time taken by CDF at Run I of Tevatron [123]. Again the overall agreement is excellent.This time the result has been multiplied by a constant K-factor of 1.6 to match the data.The result is perfectly smooth around the merging scale of Q cut = 20 GeV. This is especiallyV+jets production @ Tevatron_________________________________highlighted in the right plot of Fig. 5.26, which concentrates on the low momentum region. Itis interesting to note that the description of the data for momenta smaller than the mergingscale is almost only covered by the Z+0jet contribution and is therefore very sensitive tothe details of the parton showers and the treatment of beam remnants. A parameter ofspecific impact on the very low momentum region therefore is the primordial (or intrinsic)k ⊥ used for the interacting partons. This is modelled through a Gaussian distribution with( F. Krauss et. al hep-ph/0409106 )pmeasured at D0T, W/( Phys. Rev. Lett. 84 (2000) 845 )a central value of 0.8 GeV. Nevertheless, the shower performance of SHERPA has not beenespecially tuned; the low momentum behaviour may therefore still be improved once adetailed parameter tune is available.W [ pb/GeV ]d!/dp21010pWW + 0jetW + 1jetW + 2jetW + 3jetW + 4jetD0 Data1-110-210SHERPA0 20 40 60 80 100 120 140 160 180 200p / GeVWFigure 5.25: The p ⊥ distribution of the W -boson in comparison with data from D0 at theTevatron, Run I [156]. The total result is indicated by the black line. The coloured lines showGlobal K-factor_________________________________the contributions of the different multiplicity processes. Here matrix elements with up to fourextra jets have been considered. The applied separation cut is Q cut = 20 GeV.Stefan Höche, SM Workshop, Lyon 13.10.2005


Jet production @ Tevatron_________________________________Azimuthal dijetdecorrelation in pT, maxbinsd$ dijet/d#" dijet510410103maxp T> 180 GeV (x8000)max130 < p T< 180 GeV (x400)max100 < p < 130 GeV (x20)max T75 < p T< 100 GeVSherpa1/$ dijet102101-110-210SHERPA-310! /23/4 !!#" dijet_________________________________Stefan Höche, SM Workshop, Lyon 13.10.2005


Jet production @ Tevatron_________________________________Jet rate ratioR32 = R 3R 2R 320.90.80.7D0 Data E T>40SHERPASHERPA with MI0.60.50.40.30.20.10100 200 300 400 500 600[GeV]H T_________________________________Stefan Höche, SM Workshop, Lyon 13.10.2005


Jet production @ Tevatron_________________________________Jet rate ratioR32 = R 3R 2R 320.90.80.70.60.50.40.30.20.10SHERPAD0 Data E T>30 GeV, |!SHERPASHERPA with MI|


Jet production @ Tevatron_________________________________Jet rate ratioR32 = R 3R 2R 320.90.80.70.60.50.40.30.20.10SHERPAD0 Data E T>20 GeV, |!SHERPASHERPA with MI|


Underlying Events @ Tevatron_________________________________PreliminaryN chargedResultsvs. p T, jet1 in CTCin 1 GeV bin2520Min Bias Run IJet20 Run ISherpa w/ MISherpa w/o MIPYTHIA w/ MIMC results correctedfor track finding efficiencN Charged15105Sherpa producescorrect shapeTotal charged multiplicityagrees0.20.10-0.1-0.2SHERPATheory / Data - 1p >0.5|η|


Underlying Events @ Tevatron_________________________________N charged vs. p T, jet1 in CTCPreliminary in different Results regions w.r.t. leading jetin 1 GeV binN Charged121086in 1 GeV binN Charged109876541.54Min Bias Run IMin Bias Run IMin Bias Run IJet20 Run I3Jet20 Run IJet20 Run ISherpa w/ MISherpa w/ MI1Sherpa w/ MISherpa w/o MI2Sherpa w/o MISherpa w/o MI2PYTHIA w/ MIPYTHIA w/ MIPYTHIA w/ MI10.5SHERPASHERPASHERPA0.20.20.20.1Theory / Data - 1p >0.5|η|0.5|η|0.5|η|


Underlying Events @ Tevatron_________________________________N charged vs. Δφ jet1 in CTCPreliminary for different Results p T of leading jetin 3.6°N Charged101P T, jet1> 2 GeV Jet20 Run IP > 2 GeV Sherpa w/ MIT, jet1P > 2 GeV Sherpa w/o MIT, jet1P T, jet1> 2 GeV PYTHIA w/ MIin 3.6°N Charged101P T, jet1> 5 GeV Jet20 Run IP > 5 GeV Sherpa w/ MIT, jet1P > 5 GeV Sherpa w/o MIT, jet1P T, jet1> 5 GeV PYTHIA w/ MIin 3.6°N Charged101P T, jet1> 30 GeV Jet20 Run IP > 30 GeV Sherpa w/ MIT, jet1P > 30 GeV Sherpa w/o MIT, jet1P T, jet1> 30 GeV PYTHIA w/ MI-110-110-110←"Toward" →← "Transverse" →← "Away"→←"Toward" →← "Transverse" →← "Away"→←"Toward" →← "Transverse" →← "Away"→SHERPASHERPASHERPA0.20.20.20.1Theory / Data - 1p >0.5|η|0.5|η|0.5|η| 2GeV∆φ → jet1∆φ → jet1p T,jet1 > 5GeVp T,jet1 > 30GeV∆φ → jet1Charged multiplicity vs. ∆φ →jet1relative to leading charged particle jetfor different p T,jet11_________________________________1∆φ∆φ∆φ η ∆φ∆φ η∆φ∆φ ηStefan Höche, SM TeV4LHC, Workshop, CERN, April 29. Lyon 2005 – p.12 13.10.2005


Conclusions and Outlook_________________________________Sherpa is capable of simulating full eventsin ee, γγ and hadron-hadron collisionsThe CKKW prescription has been implementedin full generality, tested in ee and hadron collisionsMultiple parton interactions are simulatedaccording to an extended model by T. SjöstrandA modified cluster hadronisation modelis currently being implementedA new hadron decay package is on the wayR-parity violating SUSY in the MSSM is being testedA new multiple interaction model is in preparation_________________________________Stefan Höche, SM Workshop, Lyon 13.10.2005


Find us at http://www.sherpa-mc.de_________________________________My thanks go to IPN Lyonfor invitation and hospitalityand to my collaboratorsTimo Fischer, Tanju Gleisberg, Frank Krauss,Thomas Laubrich, Steffen Schumann and Jan Winterat DresdenAndreas Schälickeat DESY Zeuthen_________________________________Stefan Höche, SM Workshop, Lyon 13.10.2005

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