BMBF Forschungsschwerpunkt BMBF Forschungsschwerpunkt 202 ALICE Experiment � ALICE Experiment � Stochastic Identification of Jet particles in pPb and PbPb Martin Schmidt Physikalisches Institut, University of Tübingen Jet Meeting Tübingen - July 14th, 2017 M. Schmidt (PI Tübingen) Jet PID in pPb/PbPb 14.07.2017 1 / 19
Outline Motivation The Experiment: ALICE@LHC Method: The M ulti- T emplate F it Challenges Current status Outlook M. Schmidt (PI Tübingen) Jet PID in pPb/PbPb 14.07.2017 2 / 19
Why Jet Analysis? What are jets? Why study jets? M. Schmidt (PI Tübingen) Jet PID in pPb/PbPb 14.07.2017 3 / 19
Why Jet Analysis? What are jets? Why study jets? ◮ pp collisions: QCD, reference M. Schmidt (PI Tübingen) Jet PID in pPb/PbPb 14.07.2017 3 / 19
Why Jet Analysis? What are jets? Why study jets? ◮ pp collisions: QCD, reference ◮ p–Pb collisions: Cold nuclear matter effects M. Schmidt (PI Tübingen) Jet PID in pPb/PbPb 14.07.2017 3 / 19
Why Jet Analysis? What are jets? Why study jets? ◮ pp collisions: QCD, reference ◮ p–Pb collisions: Cold nuclear matter effects ◮ Pb–Pb collisions: Medium properties M. Schmidt (PI Tübingen) Jet PID in pPb/PbPb 14.07.2017 3 / 19
Use of (identified) fragmentation functions pp collisions ◮ Extract information about the non-perturbative fragmentation process ◮ Reference for more complex systems p–Pb collisions ◮ No medium formed ◮ Study influence of a nucleus (= cold nuclear matter) Pb–Pb collisions ◮ Presence of a medium changes the jet ◮ Mechanism: e.g. jet quenching ◮ Theory predicts higher baryon and strangeness production in the presence of a medium M. Schmidt (PI Tübingen) Jet PID in pPb/PbPb 14.07.2017 4 / 19
Jet Reconstruction This analysis: charged jets Input: charged tracks ◮ p T > 0 . 15 GeV/ c ◮ | η | < 0 . 9 Jet reconstruction done with anti-k T -algorithm with resolution parameter R = 0.4 → gives jets with circular cones of radius R Only jets fully contained in acceptance: | η jet | < 0.9 - R M. Schmidt (PI Tübingen) Jet PID in pPb/PbPb 14.07.2017 5 / 19
The L arge H adron C ollider Most powerful hadron collider at present: pp: √ s = 13 TeV p–Pb: √ s NN = 8 TeV Pb–Pb: √ s NN = 5 TeV This talk: p–Pb at √ s NN = 5.023 TeV (75M MB events), recorded in 2013 M. Schmidt (PI Tübingen) Jet PID in pPb/PbPb 14.07.2017 6 / 19
The Experiment: ALICE@LHC - The detector Central barrel: Solenoid with B = 0.5 T ITS ITS ◮ tracking ◮ vertexing TPC ◮ (PID) VO TPC TOF ◮ tracking ◮ PID TOF ◮ (PID) Trigger: V0 Multiplicity Estimator: VOA M. Schmidt (PI Tübingen) Jet PID in pPb/PbPb 14.07.2017 7 / 19
The Multi-Template-Fit* Track-by-Track PID for low p T Stochastic Particle Identification for high p T 2013/10/13 ALI-PERF-60751 * PhD-Thesis of B.Hess M. Schmidt (PI Tübingen) Jet PID in pPb/PbPb 14.07.2017 8 / 19
The Multi-Template-Fit* Track-by-Track PID for low p T Stochastic Particle Identification for high p T 2013/10/13 Parametrize the 1 TPC response ALI-PERF-60751 * PhD-Thesis of B.Hess M. Schmidt (PI Tübingen) Jet PID in pPb/PbPb 14.07.2017 8 / 19
The Multi-Template-Fit* Track-by-Track PID for low p T Stochastic Particle Identification for high p T 2013/10/13 Parametrize the 1 TPC response Produce 2 templates for species using data ALI-PERF-60751 * PhD-Thesis of B.Hess M. Schmidt (PI Tübingen) Jet PID in pPb/PbPb 14.07.2017 8 / 19
The Multi-Template-Fit* Track-by-Track PID for low p T Stochastic Particle Identification for high p T 2013/10/13 Parametrize the 1 TPC response Produce 2 templates for species using data Fit templates to 3 data in p T /z-slices ALI-PERF-60751 * PhD-Thesis of B.Hess M. Schmidt (PI Tübingen) Jet PID in pPb/PbPb 14.07.2017 8 / 19
The Multi-Template-Fit Entries ch ch pp s =7 TeV, p 10-15 GeV/ c , z 0.6-0.65 ALICE Preliminary T, jet anti- k R =0.4 T 3 Measured 10 | Multi-template fit + - π + π , template 2 10 - + K +K , template p+ p , template + - e +e , template 10 1 (Data - Fit) / Data 0.4 0.2 0 -0.2 -0.4 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 ’ = dE/dx / <dE/dx> ∆ ALI−PREL−70018 π π M. Schmidt (PI Tübingen) Jet PID in pPb/PbPb 14.07.2017 9 / 19
Goal of Analysis Create parametrizations of the TPC response (as spin-off) Stochastic particle identification (inclusive/jets) ◮ pp → done by Benjamin ◮ pPb → in progress ◮ PbPb → ToDo (High multiplicity environment challenging) Extension to full jets included in framework Extension to jet structure parameters (distance to axis, momentum transverse to jet axis) included in framework M. Schmidt (PI Tübingen) Jet PID in pPb/PbPb 14.07.2017 10 / 19
Occupancy effects in the TPC Mean d E /d x changes due to occupancy effects in the TPC with the multiplicity ◮ Parametrized with linear fit ◮ Slope of parametrization depends on η and d E /d x - dependency is parametrized Challenges: ◮ The fit of the mean d E /d x is challenging ◮ Shape of detector response changes → not parametrized M. Schmidt (PI Tübingen) Jet PID in pPb/PbPb 14.07.2017 11 / 19
Underlying Event Underlying Event: Particles in the reconstructed jet not coming from the original parton Important in pPb and especially in PbPb p jet T must be corrected ◮ area of jet is measured with ghost particles ◮ UE momentum density measured using k T jet-algorithm -> median without the two leading jets gives the momentum density ◮ resulting UE momentum is subtracted jet-by-jet particle yield of the UE must be subtracted from jet particle yield → shown in the next slides M. Schmidt (PI Tübingen) Jet PID in pPb/PbPb 14.07.2017 12 / 19
Underlying Event Estimation Assume: Equally distributed in φ Event display of Pb-Pb collision M. Schmidt (PI Tübingen) Jet PID in pPb/PbPb 14.07.2017 13 / 19
Underlying Event Estimation Assume: Equally distributed in φ Clone each jet cone and place it in the event Event display of Pb-Pb collision M. Schmidt (PI Tübingen) Jet PID in pPb/PbPb 14.07.2017 13 / 19
Underlying Event Estimation Assume: Equally distributed in φ Clone each jet cone and place it in the event ◮ Random Cones (RC, systematics) η UEcone = η jet ϕ UEcone drawn randomly from [ 0 , 2 π ] , outside other jet cones Event display of Pb-Pb collision M. Schmidt (PI Tübingen) Jet PID in pPb/PbPb 14.07.2017 13 / 19
Underlying Event Estimation Assume: Equally distributed in φ 90 ◦ Clone each jet cone and place it in the event ◮ Random Cones (RC, systematics) η UEcone = η jet 90 ◦ ϕ UEcone drawn randomly from [ 0 , 2 π ] , outside other jet cones ◮ Perpendicular Cones (PC, standard) η UEcone = η jet ϕ ± UEcone = ϕ jet ± π/ 2 . 0 Event display of Pb-Pb collision M. Schmidt (PI Tübingen) Jet PID in pPb/PbPb 14.07.2017 13 / 19
Underlying Event Estimation Assume: Equally distributed in φ 90 ◦ Clone each jet cone and place it in the event ◮ Random Cones (RC, systematics) η UEcone = η jet 90 ◦ ϕ UEcone drawn randomly from [ 0 , 2 π ] , outside other jet cones ◮ Perpendicular Cones (PC, standard) η UEcone = η jet ϕ ± UEcone = ϕ jet ± π/ 2 . 0 Event display of Pb-Pb collision Estimate yield of particles in UE cones → UE yield M. Schmidt (PI Tübingen) Jet PID in pPb/PbPb 14.07.2017 13 / 19
Underlying Event Subtraction Subtracting the Underlying Event: M. Schmidt (PI Tübingen) Jet PID in pPb/PbPb 14.07.2017 14 / 19
Underlying Event Subtraction π -1 (GeV/c) T dN/dp Subtracting the Underlying Event: Jets 1/N Estimate jet cone particle 1 yield π Jet cone particles 0.2 1 2 3 4 5 6 10 20 p (GeV/c) T M. Schmidt (PI Tübingen) Jet PID in pPb/PbPb 14.07.2017 14 / 19
Underlying Event Subtraction π -1 (GeV/c) T dN/dp Subtracting the Underlying Event: Jets 1/N Estimate jet cone particle 1 yield Estimate UE particle yield 2 π Jet cone particles π UE particles 0.2 1 2 3 4 5 6 10 20 p (GeV/c) T M. Schmidt (PI Tübingen) Jet PID in pPb/PbPb 14.07.2017 14 / 19
Underlying Event Subtraction π -1 (GeV/c) T dN/dp Subtracting the Underlying Event: Jets 1/N Estimate jet cone particle 1 yield π Jet cone particles Estimate UE particle yield 2 Jet particle yield = Jet cones 3 π UE particles particle yield - UE particle π Jet particles yield 0.2 1 2 3 4 5 6 10 20 p (GeV/c) T M. Schmidt (PI Tübingen) Jet PID in pPb/PbPb 14.07.2017 14 / 19
Other issues in pPb/PbPb Jet reconstruction influenced by fluctuations in underlying event → examine using embedded jets? Hot to separate low p T -jets from background? ◮ Increase p jet T -cut ◮ Use further methods to eliminate combinatorial jets Corrections (for example energy resolution) done with a bin-by-bin correction → unfolding needed in PbPb? M. Schmidt (PI Tübingen) Jet PID in pPb/PbPb 14.07.2017 15 / 19
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