Sherpa, Event Generator for the LHC. Stefan Höche Dresden University of Technology

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1 Sherpa, Event Generator for the LHC Stefan Höche Dresden University of Technology

2 Outline Introduction Matrix Elements in Sherpa Merging ME s with the Parton Shower Simulation results vs. Data Conclusion and Outlook Stefan Höche, SM Workshop, Lyon 3..5

3 Why Event Generators? High-flying expectations coupled to next generation collider experiments: Will we see SUSY? Extra dimensions? Unexpected new physics? Facts so far... Tremendous event rates at future colliders, e.g. LHC Must understand SM issues first! The Higgs boson? Final State Events / s Jet, E T > GeV 3 Jet, E T > TeV.5 W lν W W lνlν 6 3 b b-pair 5 5 t t-pair QCD radiation patterns Multiple parton interactions Parton Distributions Stefan Höche, SM Workshop, Lyon 3..5

4 Sherpa - Status of developmement Sherpa: T. Fischer, T. Gleisberg, S.H., F. Krauss, T. Laubrich, A. Schälicke, S. Schumann and J. Winter ( JHEP 4 (4) 56 ) Intention: Provide a multi-purpose tool, capable of simulating SM backgrounds as well as new physics scenarios (e.g. MSSM, ADD) at ee, γγ and hadron colliders Key features Automatic cross section calculation via AMEGIC++ ( JHEP :44, ) Generation of QCD/QED Bremsstrahlung via APACIC++ ( hep-ph/5387 ) Merging of ME and PS ( hep-ph/583 ) Simulation of Multiple Interactions acc. to ( T. Sjöstrand et. al Phys. Rev. D36 (987) ) Lund string fragmentation via PYTHIA Own model in preparation ( hep-ph/385 ) DESY Zeuthen Stefan Höche, SM Workshop, Lyon 3..5

5 AMEGIC++ - Automatic ME Generator Fully automated calculation of (polarised) cross sections in the SM, the MSSM and the ADD model Performance comparable to that of dedicated codes Allows to study signal and backgrounds in one framework Easy to extend (feel free to implement your own model...) Tested e.g. in e + e 6f mutual deviations in about processes Ongoing comparison of arbitrary SUSY processes vs. WHIZARD and MADGRAPH against HELAC/PHEGAS Stefan Höche, SM Workshop, Lyon 3..5

6 AMEGIC++ - Automatic ME Generator Employ helicity methods to decompose amplitudes into complex numbers reduce to basic building blocks Z(, ; 3, 4) = [ u(p )γ µ u(p ) ] [ u(p 3 )γ µ u(p 4 ) ] X(, ; 3) = [ u(p )ˆp 3 u(p ) ] Y (, ) = [ u(p )u(p ) ] Generate corresponding phase space mapping for each amplitude cut D iso (3, 45) P (3) P (45) D iso (, 3) D iso (4, 5) Factorize out common parts of different amplitudes Superamplitudes Stefan Höche, SM Workshop, Lyon 3..5

7 Matrix Element vs. Parton Shower Matrix Elements t + u Exact to fixed order in running coupling Include all quantum interferences Calculable only for low FS multiplicity ( n 6-8 ) dσ n+ = dσ n Parton Showers Resum (next-to) leading logarithms to all orders in Interference effects e.g. through angular ordering t a n,b + dt t dz z Stefan Höche, SM Workshop, Lyon 3..5 u α s (t, z) π Desirable to combine both approaches to have Good description of hard/wide-angle emissions (ME) Correct intrajet evolution (PS) Must prevent double counting e.g. through CKKW P a b (z)

8 Combining ME & PS à la CKKW ME Domain Define phase space cut Q cut Select jet multiplicity and kinematics according to differential cross section K T cluster backwards and identify core process Add α S weight (ME taken at Q cut ) Add Sudakov weight Start PS at scale Q hard q (Q cut,q ) q(q cut,µ H ) q(q cut,q ) µ H q (Q cut,µ H ) ME Domain, reject emissions above Q Q cut αs(q ) αs(q cut ) g (Q cut,q ) cut PS Domain Yields correct jet rates, e.g. -jet rate at scale q through R (q ) = (Q cut, µ hard ) (q, µ hard ) = (Q cut, µ hard ) { (q, µ hard ) (Q cut, µ hard ) + µhard Q cut } dq q Γ(q, µ hard) +... Stefan Höche, SM Workshop, Lyon 3..5

9 Tests of the Merging Procedure W+jets production at Tevatron Run II Stability tests of the procedure ( F. Krauss et. al hep-ph/496 ) Variation of phase space separation cut Q cut W / GeV d!/dp Q cut = GeV W + X W + jet W + jet W + jet W + 3jet reference W / GeV d!/dp Q cut =3 GeV W + X W + jet W + jet W + jet W + 3jet reference W / GeV d!/dp Q cut =5 GeV W + X W + jet W + jet W + jet W + 3jet reference p / GeV W / GeV p / GeV p W W Global K-factor Stefan Höche, SM Workshop, Lyon 3..5

10 Tests of the Merging Procedure W+jets production at Tevatron Run II Stability tests of the procedure ( F. Krauss et. al hep-ph/496 ) Variation of maximum jet multiplicity W [ pb/gev ] d!/dp W [ pb/gev ] W + X W + jet W + jet reference d!/dp W [ pb/gev ] d!/dp W + X W + jet W + jet W + jet reference W + X W + jet W + jet W + jet W + 3jet reference p / GeV W p / GeV W p / GeV W Global K-factor Stefan Höche, SM Workshop, Lyon 3..5

11 V+jets Tevatron Jet p T in W- and Z+jet events Sherpa vs. MCFM &" 3& B+)C)(,DA-@EF) &" 3& X+)C)(,DA-@EF) &6!)7!67' ( )/&6, &" 3! &" 35 &" 3# 89:8);<= >?,@'A <= GH:I)J-,K$L 9M-NI)' ( L,'O)!"),P)Q" L,' QR& ' ( +,-O)&4),P)Q" +,- QR! ' ( STNNO)!"), #U ++ O)"VW &6!)7!67' ( )/&6, &" 3! &" 35 &" 3# 89:8);<= >?,@'A <= GH:I)J-,K$L 9M-NI)' ( L,'O)!"),P)Q" L,' QR& ' ( +,-O)&4),P)Q" +,- QR! S LL O)&4), #U ++ O)"VW &" 34!" #" $" %" &"" &!" &#" &$" &%" ' ( )*+,-.)/, &" 34!" #" $" %" &"" &!" &#" &$" &%" ' ( )*+,-.)/, Global K-factor Stefan Höche, SM Workshop, Lyon 3..5

12 V+jets Tevatron Jet p T in W- and Z+jet events Sherpa vs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lobal K-factor Stefan Höche, SM Workshop, Lyon 3..5

13 V+jets Tevatron Jet p T in inclusive W production Sherpa vs. PYTHIA & MC@NLO [ /GeV ] /! d!/dp T - - Sherpa PYTHIA MC@NLO [ /GeV ] /! d!/dp T - - Sherpa PYTHIA MC@NLO (first jet) [ GeV ] p T (second jet) [ GeV ] p T Global K-factor Stefan Höche, SM Workshop, Lyon 3..5

14 V+jets Tevatron Jet p T in inclusive W production Sherpa vs. PYTHIA & MC@NLO [ /GeV ] /! d!/dp T - - Sherpa PYTHIA MC@NLO (third jet) [ GeV ] p T Global K-factor Stefan Höche, SM Workshop, Lyon 3..5

15 V+jets Tevatron ( F. Krauss et. al hep-ph/496 ) Inclusive jet cross sections, CDF ( hep-ex/4567 ) / pb 4 CDF Run II Preliminary " incl. 3 W $ e # +! n jets CDF Data JetClu R=.4 (E T > 5 GeV, % <.4) jet multiplicity (! n jets) Global K-factor Stefan Höche, SM Workshop, Lyon 3..5

16 V+jets Tevatron ( F. Krauss et. al hep-ph/496 ) jet-p T, measured at CDF ( hep-ex/4567 ) 4 3 CDF Run II Preliminary W $ e # +! n jets Sherpa CDF data R =.4 (E T > 5 GeV & % <.4 ) jet E T / GeV Global K-factor Stefan Höche, SM Workshop, Lyon 3..5

17 V+jets Tevatron ( F. Krauss et. al hep-ph/496 ) p T, Z measured at CDF ( Phys. Lett. B53 () 9 ) pb GeV / d! dp pt Z Z + jet Z + jet Z + jet Z + 3 jet CDF pb GeV / d! dp pt Z Z + jet Z + jet Z + jet Z + 3 jet CDF P / GeV Z P / GeV Z Global K-factor Stefan Höche, SM Workshop, Lyon 3..5

18 V+jets Tevatron ( F. Krauss et. al hep-ph/496 ) p measured at D T, W / ( Phys. Rev. Lett. 84 () 845 ) W [ pb/gev ] d!/dp p W W + jet W + jet W + jet W + 3jet W + 4jet D Data p / GeV W Global K-factor Stefan Höche, SM Workshop, Lyon 3..5

19 Jet Tevatron Azimuthal dijet decorrelation in p T, max bins d$ dijet /d#" dijet max p T > 8 GeV (x8) max 3 < p T < 8 GeV (x4) max < p < 3 GeV (x) max T 75 < p T < GeV Sherpa /$ dijet ! / 3/4!! #" dijet Stefan Höche, SM Workshop, Lyon 3..5

20 Jet Tevatron Jet rate ratio R3 = R 3 R R D Data E T >4 with MI [GeV] H T Stefan Höche, SM Workshop, Lyon 3..5

21 Jet Tevatron Jet rate ratio R3 = R 3 R R D Data E T >3 GeV,! with MI <3 jet 4 6 [GeV] H T Stefan Höche, SM Workshop, Lyon 3..5

22 Jet Tevatron Jet rate ratio R3 = R 3 R R D Data E T > GeV,! with MI < jet 4 6 [GeV] H T Stefan Höche, SM Workshop, Lyon 3..5

23 Underlying Tevatron N charged vs. p T, jet in CTC in GeV bin 5 Min Bias Run I Jet Run I Sherpa w/ MI Sherpa w/o MI PYTHIA w/ MI N Charged Theory / Data - p >.5 η <. T Track Finding Efficiency: GeV Charged multiplicity vs. P T, jet Stefan Höche, SM Workshop, Lyon 3..5

24 Underlying Tevatron N charged vs. p T, jet in CTC in different regions w.r.t. leading jet in GeV bin N Charged 8 6 in GeV bin N Charged Min Bias Run I Min Bias Run I Min Bias Run I Jet Run I 3 Jet Run I Jet Run I Sherpa w/ MI Sherpa w/ MI Sherpa w/ MI Sherpa w/o MI Sherpa w/o MI Sherpa w/o MI PYTHIA w/ MI PYTHIA w/ MI PYTHIA w/ MI Theory / Data - p >.5 η <. T. Theory / Data - p >.5 η <. T. Theory / Data - p >.5 η <. T Track Finding Efficiency:.9 Track Finding Efficiency:.9 Track Finding Efficiency: GeV GeV GeV P T, jet P T, jet in GeV bin N Charged P T, jet Charged multiplicity vs. Stefan Höche, SM Workshop, Lyon 3..5

25 Underlying Tevatron N charged vs. Δφ jet in CTC for different p of leading jet T in 3.6 N Charged P T, jet > GeV Jet Run I P > GeV Sherpa w/ MI T, jet P > GeV Sherpa w/o MI T, jet P T, jet > GeV PYTHIA w/ MI in 3.6 N Charged P T, jet > 5 GeV Jet Run I P > 5 GeV Sherpa w/ MI T, jet P > 5 GeV Sherpa w/o MI T, jet P T, jet > 5 GeV PYTHIA w/ MI in 3.6 N Charged P T, jet > 3 GeV Jet Run I P > 3 GeV Sherpa w/ MI T, jet P > 3 GeV Sherpa w/o MI T, jet P T, jet > 3 GeV PYTHIA w/ MI "Toward" "Transverse" "Away" "Toward" "Transverse" "Away" "Toward" "Transverse" "Away".... Theory / Data - p >.5 η <. T. Theory / Data - p >.5 η <. T. Theory / Data - p >.5 η <. T Track Finding Efficiency:.9 Track Finding Efficiency:.9 Track Finding Efficiency: p T,jet > GeV φ jet φ jet p T,jet > 5GeV p T,jet > 3GeV φ jet Stefan Höche, SM Workshop, Lyon 3..5

26 Conclusions and Outlook Sherpa is capable of simulating full events in ee, γγ and hadron-hadron collisions The CKKW prescription has been implemented in full generality, tested in ee and hadron collisions Multiple parton interactions are simulated according to an extended model by T. Sjöstrand A modified cluster hadronisation model is currently being implemented A new hadron decay package is on the way R-parity violating SUSY in the MSSM is being tested A new multiple interaction model is in preparation Stefan Höche, SM Workshop, Lyon 3..5

27 Find us at My thanks go to IPN Lyon for invitation and hospitality and to my collaborators Timo Fischer, Tanju Gleisberg, Frank Krauss, Thomas Laubrich, Steffen Schumann and Jan Winter at Dresden Andreas Schälicke at DESY Zeuthen Stefan Höche, SM Workshop, Lyon 3..5