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Measurement of    +  - ,e + e - in Ultra peripheral PbPb collisions at 5.5 TeV in CMS

Measurement of    +  - ,e + e - in Ultra peripheral PbPb collisions at 5.5 TeV in CMS. Status Report. Vineet Kumar NPD BARC. Plan of presentation. Introduction: Brief introduction of Ultra peripheral collisions (UPC) Physics motivation UPC PbPb ( γ Pb)  ¡ Pb* in CMS

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Measurement of    +  - ,e + e - in Ultra peripheral PbPb collisions at 5.5 TeV in CMS

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  1. Measurement of +- ,e+e- in Ultra peripheral PbPb collisions at 5.5 TeV in CMS Status Report Vineet Kumar NPD BARC

  2. Plan of presentation • Introduction: • Brief introduction of Ultra peripheral collisions (UPC) • Physics motivation • UPC PbPb(γPb)¡Pb* in CMS • Theoretical cross section for signal ¡ (1s), ¡ (2s), ¡ (3s) • Theoretical cross section for dileptons continuum (γ γe+e-,µ+ µ-) • ¡reconstruction with trigger in CMS • Low Pt electron reconstruction using Particle Flow technique in CMS • Results • Future Plans

  3. Ultra Peripheral Collisions • Ultra Relativistic Heavy ions produce very high electromagnetic fields due to coherent action of all protons • UPC are those reactions in which ions interact via their cloud of virtual photons. • An electromagnetic interaction where photons • emitted by ions interact with each other • (b) A photon-nuclear reaction in which a photon • emitted by an ion interacts with other nucleus.

  4. Ultra Peripheral Collisions Experimental Characteristics of UPCs • Low central multiplicities • “cleaner” than hadronic collisions • Zero net charge • Narrow dN/dy peaked at mid-rapidity

  5. Physics Motivations in UPC ℓ ℓ • +AVM+A (VM=J/, ) sensitive to • gluon density squared • TestQEDat veryhigh energies Pb Pb Pb Pb • Unexplored (x,Q2)regime of nPDFs: • Kinematical range covered

  6. Predicted cross sections STARLIGHT Generator [J.Nystrand,S.KleinNPA752(2005)470] Signal • PbPb Pb+X • µ+ µ- ,e+e- Dilepton continum • µ+ µ- •  e+e-

  7. Muon reconstruction with trigger • Simulated data from starlight StarlightHepMcGenSim.cfgSim.root • Raw data is made using configuration file HLTrigger/Configuration/test/RelVal_Digi_Digi2Raw_cfg.py • Selected HLT Paths for muons ‘HLT_DoubleMu3’ ‘HLT_Mu3’ • Partial HLT path from confDB by* edmConfigFromDB --configName /dev/CMSSW_2_1_X/HLT --format Python --paths HLT_ DoubleMu3> HLTDoubleMu3Config.py • HLTrigger/Configuration/test/RelVal_HLTFromRaw_2E30_cfg.py Having all the trigger path of trigger table (CMSSW_2_1_X)

  8.   +- TrigReport ---------- Event Summary ------------ TrigReport Events total = 10000 passed = 4279 failed = 5721 TrigReport ---------- Path Summary ------------ TrigReport Trig Bit# Run Passed Failed Error Name TrigReport 1 0 10000 4579 5421 0 HLTMu3 HLTMu3 Eff  42 % TrigReport ---------- Event Summary ------------ TrigReport Events total = 10000 passed = 1786 failed = 8214 TrigReport ---------- Path Summary ------------ TrigReport Trig Bit# Run Passed Failed Error Name TrigReport 1 0 10000 1786 8214 0 HLTDoubleMu3 HLTDoubleMu3 Eff 17%   +- TrigReport ---------- Event Summary ------------ TrigReport Events total = 50000 passed = 1126 failed = 48874 TrigReport ---------- Path Summary ------------ TrigReport Trig Bit# Run Passed Failed Error Name TrigReport 1 0 50000 1126 48874 0 HLT_DoubleMu3 HLT_DoubleMu3  2% Trigger efficiency for HLT_DoubleMu3 and HLT_Mu3

  9. Full reconstruction with HLT Reconstruction Sequence GenHlt + Select only those event which pass HLT Path +OfflineReco HLT Path Used HLT_Mu3 +- Total events 500000 Triggerd 26661 Reconstructed 21541 Trigger eff 5.3% Reco eff 4.24% __Gen __OfflineReco __TriggeredEvents __Triggered+Reco +- Total events 80570 Triggerd 36672 Reconstructed 31009 Trigger eff 45% Reco eff 37% dielectron cont (Gev/C2 ) Without trigger Reco eff +- 8.3% (4.2%) +- 52% (37%) M+- (Gev/C2)

  10.  Family Pt and Y distributions +- +- __triggered __reco __triggered __reco  rapidity reco::muon

  11.  and dimuon cont scaled for L=0.5 nb-1 Bkg subtracted   PbPb UPC 5.5 TeV Full CMS Sim+Reco __ Pb(+-) PbPb UPC 5.5 TeV __ Pb(+-) __+- + +- ’ ’ ’’ ’’ M+- (Gev/C2) M+- (Gev/C2) Upsilon+Dimuoncont Poll4+3Gauss DimuonCont Poll4 (1s) 9.45 GeV/C2 (2s) 9.99 GeV/C2 (3s) 10.3 GeV/C2  gauss ~ 95 MeV

  12. Low Pt electron reconstruction using PF technique in CMS • I tried low Pt electron reconstruction using ParticleFlow Tools. https://twiki.cern.ch/twiki/bin/view/CMS/SWGuideParticleFlowDevelopers#CMSSW_2_1_11 • They claim an increase in electron reconstruction efficiency from 15% to ~ 80% at Pt=4GeV. http://indico.cern.ch/getFile.py/access?contribId=2&sessionId=14&resId=0&materialId=slides&confId=35611 • These tools are under development and not fully integrated in CMSSW.

  13. PF in ||<1.0 • This technique was tested in || < 1.0 • I start with 10,000 e+ e- and reconstruct them using particle flow patches. • Technique seems to work efficiency goes up __ Gen electrons __PF electrons __GSF electrons Electron  __ Gen electrons __PF electrons __GSF electrons Electron Pt (GeV)

  14. Electron reconstruction using PF • In full kinematical range. __ Gen electrons __PF electrons __GSF electrons Electron  __ Gen electrons __PF electrons __GSF electrons • Clearly method works best for || <1.0 Electron Pt (GeV)

  15. PFlow reconstruction of electrons __PF __GSF __PF __GSF  Inv mass (Gev/C2 ) dielectron cont (Gev/C2 ) Dielctron cont reco eff PF=1.49% GSF=0.6% Up(1s) reco eff PF=19% GSF=10% • Mass resolution is better for GSF electron collection • Increase is more prominent for dielctron continuum

  16. STAR Pair pT Minv e+e- continuum (QED Test) • 2-photon interaction • Higher order diagrams are required to explain STAR data. A. J. Baltz, Phys. Rev. Lett. 100, 062302 466 (2008). - - -Lowest order __Higher order - - -Lowest order __Higher order

  17.  and dielectron cont scaled for L=0.5 nb-1 + dielectron continuum PbPb UPC 5.5 TeV Full CMS Sim+Reco __e+e- __e+e- __e+e-__e+e- inv masse+e- (Gev/C2 ) inv masse+e- (Gev/C2 ) • Large cross section of dieletron continuum prevents • us to extract  from continuum. • e+e- continum can be used as signal (QED Test) • We purpose reconstruction of electron continuum to test QED at more energy.

  18. Summary and future plans • In PbPb→( Pb)→  Pb* at 5.5 TeV with →µ+µ-whole  family can be reconstructed with good resolution. • This Study in CMS can be used as a tool to study low-x gluon density & evolution in the nucleus. • e+e- continuum can be reconstructed to extend STAR study. • CMS Note

  19. Back up slides

  20. (1s) or  bbbar 9.460 Gev 52.5 KeV • (2s) or ’ bbbar 10.023 Gev 44 KeV • (3s) or ’’ bbbar 10.355 Gev 26.5 KeV

  21. Particle Flow :as a user’s point of view How to run • Install recommended version of Particle Flow. https://twiki.cern.ch/twiki/bin/view/CMS/SWGuideParticleFlowInstall • Then run the following cfg file,which will replay the tracking and the particle flow cd RecoParticleFlow/Configuration/test cmsRun fullSimForParticleFlow_cfg.py Access to particle flow output 1.PAT run PF2PAT+PAT to get pattuples. 2.Access the PFCandidates directly from an ED Analyzer in full framework 3.Acsess the PFCandidates from ROOT+FWLite cd RecoParticleFlow/Configuration/test cmsRun analyzePFCandidates_cfg.py

  22. Particle Flow :as a user’s point of view • The aim of the particle flow is to provide a single list of reconstructed particles which can be of type: • Photon • Charged hadron • Neutral hadron • Electron • Muon • This list will provide a complete description of the event and is as easy to use as the list of true particles from the simulation. • The PF Algorithm • Calorimeter clustering (ECAL,HCAL,PS) PF Clusters • Track reconstruction and extrapolation to the calorimeters (iterative tracking) • Reconstructing blocks of topologically connected elements (tracks, ECAL clusters, HCAL clusters, PreShower clusters) PF Blocks • Analyzing these blocks to reconstruct particles PF Candidates Particle Flow :as a user’s point of view

  23. electron reco in Particle Flow :as a user’s point of view • Reconstruction of track up to ECAL entrance • Associating this track with the electron cluster • Identifying the clusters of emitted photons. • Electron pre identification: Track cluster matching variables Tracker only based variables A multivariate approch is followd .the so called Boosted Decision Trees (BDT) method was chosen. Journal of physics:Conference Series 120(2008)032039

  24. e, measurement in CMS Tracking + ECAL + muon-chambers electrons Tracker+EMCAL muons Tracker+muchambers

  25.  +e+ e- and Pt distributions ____ gen _____rec ____ gen _____rec Single e eta Single e pt • Electrons are peaking outside CMS acceptance • Almost all electrons are concentrated at very low Pt

  26. Summary • UPC A+A collisions generate high-energy  beams for photo production studies:  +  ,  +A physics as done at LEP & HERA. • Unique access to nuclear xGA(x,Q2) at small-x [Gluon saturation, non-linear QCD] • Unexplored kinematics regime • Study of PbPb→( Pb)→  Pb* at 5.5 TeV with →µ+µ- ,e+e- in CMS can be used as a tool to study low-x gluon density & evolution in the nucleus

  27. Ultra Peripheral Collisionsat LHC • Weizsacker -Williams formula for flux radiated by a ion with charge Z at distance r Here ω=k r/ γLand K0 (ω) and K1 (ω) are modified Bessel functions. • The photo production cross section can be factorized in to the product of photonuclear cross section and the photon flux • Very high photo production cross sections !! • σ(γA)~ Z2 (~104 for Pb), σ(γγ) ~ Z4 (i.e. ~5·107) times larger than e± beams • Characteristics of photon flux in UPC at LHC • Max γ energies :ω< ωmax ~ γ/R ~80 GeV (Coherence condition) Pb-Pb LHC • γA: max. √s γA ≈ 1. TeV ≈ 3. - 4. × √s γp(HERA) • γ γ : max. √s γγ ≈ 160 GeV ≈ √s γγ(LEP)

  28. ℓ ℓ Signal + Bkg cross sections Signal Background • Input MC: STARLIGHT [J. Nystrand, S.Klein, NPA752(2005)470] Pb Pb Pb Pb

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