Underlying Event Studies Using Calorimeter Jets with the ALAS Detector at LHC Sebastian Wahrmund supervised by Deepak Kar, Arno Straessner DPG Frühjahrstagung Karlsruhe
Introduction Motivation 2 / 2
Introduction Motivation Analyze event structure in pp-collisions Complex collision landscape due to the complex proton structure dominated by (soft) QCD Background for many interesting physical processes 2 / 2
Introduction Quantum Chromodynamics - QCD Concentrate on QCD Physics at low energy scale (soft QCD) Effective strong coupling is increasing for decreasing energy scale Q 0.5 0.3 Introduction of phenomenological models 0.2 Goal: Analyze the soft QCD behavior and provide data for tuning Deep Inelastic Scattering e+e Annihilation Heavy Quarkonia 0.4 Soft QCD physics can t be calculated via perturbation theory Implemented in various Monte Carlo generators model dependent parameter (tune) July 09 α s(q) 0. QCD α s (Μ Z) = 4 ± 0.0007 0 Q [GeV] 00 3 / 2
Introduction Underlying Event hard scattered parton final state radiation beam beam remnants initial state radiation multiple parton interaction hard scattered parton Hard process: hard scattered partons, initial/final state radiation Underlying event: multiple parton interaction, beam beam remnants, inital/final state radiation,... 4 / 2
Analysis General Idea def. object corresponding to hard scattered part calorimeter jet (anti-k, R = 0.4) with highest p Leading Jet Δϕ using tracks to describe the underlying event split φ-space into 3 region according to φ = φleadjet φtrack toward φ < transverse < φ < away φ > toward Δϕ < transverse transverse < Δϕ < < Δϕ < away Δϕ > toward/away contains mostly particles from hard process transverse regions is sensitive for underlying events 5 / 2
Analysis Measured Quantities Charged particle multiplicity density D d2 ch dηdφ E evt vs. plead Jet Scalar transverse momentum sum density D E P d2 p dηdφ evt vs. plead Jet Mean transverse momentum hp i = DP p ch E evt vs. ch 6 / 2
Results <d2ch/dηdφ> ransverse ch - Detector Level MC/Data.4 s = 7 ev - Calibrated Level Data 0 prk > 0.5 GeV and ηrk < 2.5 PYHIA ALAS MC09.3.2. 0.9 0.7 ransverse Region 0.6 ALAS Work in Progress 90 00 plead Jet [GeV]. 0.9 90 00 7 / 2
Results Correction Factors p Detector Level Data: p p MC Simu: p Particle Level Detector Simulation Detector Level 8 / 2
Results Correction Factors p Corrected Level Data: p Corrections p MC Simu: p Particle Level Detector Simulation Detector Level Detector Level Corrections: rigger- and vertex efficiency rack reconstruction efficiency Additional contribution from fakes and secondaries Migrations 8 / 2
Results <d2ch/dηdφ> ransverse ch - Corrected Level.8.6 s = 7 ev - Corrected Level Data 0 PYHIA ALAS MC09 PYHIA AMB PYHIA DW Herwig++ ALAS MC09 prk > 0.5 GeV and ηrk < 2.5.4.2 ransverse Region MC/Data 0.6 ALAS Work in Progress 90 00 90 00 plead Jet [GeV].2 9 / 2
Results MC/Data <d2 p/dηdφ> [GeV] ransverse P pch - Corrected Level 2.6 Data 0 s = 7 ev - Corrected Level PYHIA ALAS MC09 2.4 prk > 0.5 GeV and ηrk < 2.5 PYHIA AMB PYHIA DW 2.2 Herwig++ ALAS MC09 2.8.6.4.2 ransverse Region ALAS Work in Progress.2. 0.9 90 00 90 00 plead Jet [GeV] 0 / 2
Results MC/Data <p > [GeV] ransverse p - Corrected Level 2.4 Data 0 s = 7 ev - Corrected Level PYHIA ALAS MC09 2.2 prk > 0.5 GeV and ηrk < 2.5 PYHIA AMB 2 PYHIA DW Herwig++ ALAS MC09.8.6.4.2 ransverse Region 0.6 0.4 ALAS Work in Progress 0.2 5 0 5 25 35.2 5 0 5 25 35 ch / 2
Summary Summary/Outlook Summary Compare underlying event measurements at 7 ev with Monte Carlo prediction All models shows significant difference to the observations, as observed in the underlying event analysis with leading track [arxiv:02.079] Outlook Include more data to increase the p -range for the leading jet (plead jet > 0 GeV) Vary the splitting of the φ-space Improve systematic uncertainties and the correction process 2 / 2
Backup
Backup 3 2.5 <d2 p/dηdφ> [GeV] <d2ch/dηdφ> Results oward s = 7 ev - Corrected Level Data 0 PYHIA ALAS MC09 PYHIA AMB PYHIA DW Herwig++ ALAS MC09 prk > 0.5 GeV and ηrk < 2.5 2.5 oward Region 90 00 MC/Data ALAS Work in Progress.2 90 00 plead Jet [GeV] oward Region.4.2 90 00 90 00 plead Jet [GeV].2 s = 7 ev - Corrected Level Data 0 PYHIA ALAS MC09 PYHIA AMB PYHIA DW Herwig++ ALAS MC09 4.5 4 3.5 3 2.5 2.5 0.5 prk > 0.5 GeV and ηrk < 2.5 ALAS Work in Progress <p > [GeV] MC/Data MC/Data s = 7 ev - Corrected Level Data 0 PYHIA ALAS MC09 PYHIA AMB PYHIA DW Herwig++ ALAS MC09 9 8 7 6 5 4 3 2 prk > 0.5 GeV and ηrk < 2.5 oward Region ALAS Work in Progress 5 0 5 25 35 5 0 5 25 35 ch
Backup <d2ch/dηdφ> 3.5 3 <d2 p/dηdφ> [GeV] Results Away 4 s = 7 ev - Corrected Level Data 0 PYHIA ALAS MC09 PYHIA AMB PYHIA DW Herwig++ ALAS MC09 prk > 0.5 GeV and ηrk < 2.5 2.5 2.5 Away Region ALAS Work in Progress 90 00 MC/Data.2 90 00 plead Jet [GeV] 6 5 4 3 2 Away Region 90 00 plead Jet [GeV] s = 7 ev - Corrected Level prk > 0.5 GeV and ηrk < 2.5 2 Away Region.2. 0.9 90 00.2.5 0.5 prk > 0.5 GeV and ηrk < 2.5 ALAS Work in Progress Data 0 PYHIA ALAS MC09 PYHIA AMB PYHIA DW Herwig++ ALAS MC09 2.5 s = 7 ev - Corrected Level Data 0 PYHIA ALAS MC09 PYHIA AMB PYHIA DW Herwig++ ALAS MC09 <p > [GeV] MC/Data MC/Data 9 8 7 ALAS Work in Progress 5 0 5 25 35 5 0 5 25 35 ch
Backup Jet <d2ch/dηdφ> vs plead unfolding factor.6 s = 7 ev Unfolding Factor.4.2.8 Jet <d2 p/dηdφ> vs plead.6 Unfolding Factor.2 ALAS Work in Progress ALAS Work in Progress ransverse Region 0.6 s = 7 ev.4 90 ransverse Region 0.6 00 plead Jet [GeV].6 s = 7 ev Unfolding Factor.4.2 ALAS Work in Progress ransverse Region 0 90 <p> vs ch 5 00 plead Jet [GeV] unfolding factor unfolding factor Unfolding Factors 5 25 35 ch
Backup εvtx εtrig Correction Factors ALAS ALAS 0.98 0.98 0.96 0.96 Data 0 0.94 Data 0 0.94 nbs sel 2, p > 00 MeV, η < 2.5 0.92 nbs sel 2, p > 00 MeV, η < 2.5 0.92 s = 7 ev 2 3 4 5 6 7 8 9 0.9 0 nbs sel 0.9 εtrk εtrk 0.9 s = 7 ev ALAS 2 3 4 5 6 7 8 9 0 nbs sel 0.9 ALAS 0.7 0.7 0.6 0.6 0.5 MC D MC D 0.4 0.5 0.3 nch 2, p > 00 MeV, η < 2.5 0.4 0.2 0. s = 7 ev 0.3-2 - 0 nch 2, p > 00 MeV, η < 2.5 s = 7 ev 0 2 η 0 p [GeV]
Backup Jets g g g Proton Parton Jet Fragmentation Proton p, n, π±, π0, K±,... Particle Jet rack Jet Calorimeter Jet Jets are reconstructed objects and defined by the reconstruction algorithm Separation of quarks leads to an increasing of the QCD field energy production of real qq pairs ew quarks recombine with existing ones create a bunch of particles (Fragmentation) Reconstructed as jet
Backup Jet/rack Selection Jet Selection Anti-k topocluster jets with R = 0.4 Recalibration to EM+JES scale (derived from MC) pem+jes > GeV, η < 2.5 racks Selection ppv > 0 MeV, η PV < 2.5 Pix, SC 6 d0pv <.5 mm, z0pv sin(θpv ) <.5 mm d0bs < 4 mm P(χ2 ) > 0.0 for p,track > 0 GeV (P(χ2 ): χ2 probability)
Backup Event Selection Event Selection Run 5266-528 (GRL), L_MBS_ trigger pmax -jet pass cuts, min 2 tracks pass cuts Jetcleaning: reject events with bad or ugly jets Min pri. vertex, no sec. vertex with tracks > 3 (Pileup Veto)