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Vineet KumarNPD BARC

Measurement of +- ,e+e- in Ultra peripheral PbPb collisions at 5.5 TeV in

CMSStatus Report

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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 γe+e-,µ+ µ-)

reconstruction with trigger in CMS

Low Pt electron reconstruction using Particle Flow technique in CMS Results Future Plans

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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.

(a) 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.

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Ultra Peripheral Collisions

Experimental Characteristics of UPCsExperimental Characteristics of UPCsLow central multiplicities

“cleaner” than hadronic collisionsZero net chargeNarrow dN/dy peaked at mid-rapidity

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Physics Motivations in UPC +AVM+A (VM=J/, ) sensitive to gluon density squared

Test QED at very high energies

ℓℓ

Pb Pb

Pb

Pb

Unexplored (x,Q2) regime of nPDFs: Kinematical range covered

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Predicted cross sections

STARLIGHT Generator[J.Nystrand,S.KleinNPA752(2005)470]

Signal• PbPb Pb+X µ+ µ- ,e+e-

BR % No. for ʃ L 0.5(nb)-1

(1s) 78 µ b 2.4% 936

(2s) 33 µ b 1.9% 313

(3s) 23 µ b 2.2% 253

Dilepton continum µ+ µ- e+e-

(mass>6Gev) No. for ʃ L 0.5(nb)-1

0.6 mb 3x105

1.4 mb 7x105

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Muon reconstruction with trigger Simulated data from starlight StarlightHepMcGenSim.cfgSim.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)

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Trigger efficiency for HLT_DoubleMu3 and HLT_Mu3

+-

TrigReport ---------- Event Summary ------------TrigReport Events total = 10000 passed = 4279 failed = 5721TrigReport ---------- Path Summary ------------TrigReport Trig Bit# Run Passed Failed Error NameTrigReport 1 0 10000 4579 5421 0 HLTMu3HLTMu3 Eff 42 %TrigReport ---------- Event Summary ------------TrigReport Events total = 10000 passed = 1786 failed = 8214TrigReport ---------- Path Summary ------------TrigReport Trig Bit# Run Passed Failed Error NameTrigReport 1 0 10000 1786 8214 0 HLTDoubleMu3HLTDoubleMu3 Eff 17% +-TrigReport ---------- Event Summary ------------ TrigReport Events total = 50000 passed = 1126 failed = 48874TrigReport ---------- Path Summary ------------ TrigReport Trig Bit# Run Passed Failed Error Name TrigReport 1 0 50000 1126 48874 0 HLT_DoubleMu3HLT_DoubleMu3 2%

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Full reconstruction with HLT

dielectron cont (Gev/C2 )

__Gen__OfflineReco__TriggeredEvents__Triggered+Reco

Total events 500000Triggerd 26661Reconstructed 21541Trigger eff 5.3%Reco eff 4.24%

Total events 80570Triggerd 36672Reconstructed 31009Trigger eff 45%Reco eff 37%

+-

+-

M+- (Gev/C2)

Without trigger Reco eff

+- 8.3% (4.2%)+- 52% (37%)

Reconstruction Sequence GenHlt + Select only those event which pass HLT Path +OfflineRecoHLT Path Used HLT_Mu3

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Family Pt and Y distributions

rapidity

reco::muon

__triggered__reco

+-

__triggered__reco

+-

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and dimuon cont scaled for L=0.5 nb-1

M+- (Gev/C2)M+- (Gev/C2)

Upsilon+Dimuoncont Poll4+3GaussDimuonCont Poll4

+-+

(1s) 9.45 GeV/C2

(2s) 9.99 GeV/C2

(3s) 10.3 GeV/C2 gauss ~ 95 MeV

’’’

PbPb UPC 5.5 TeV__ Pb(+-)__+-

PbPb UPC 5.5 TeVFull CMS Sim+Reco__ Pb(+-)

’’’

Bkg subtracted

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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.

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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

Electron

__ Gen electrons__PF electrons __GSF electrons

__ Gen electrons__PF electrons __GSF electrons

Electron Pt (GeV)

no (|| <1.0) eff

gen 8082 ---PF 5101 63.1%gsf 2126 26.3%

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Electron reconstruction using PF In full kinematical range. __ Gen electrons

__PF electrons __GSF electrons

__ Gen electrons__PF electrons __GSF electrons

Electron

Electron Pt (GeV)

no efficiency

gen 20,000 ---PF 7944 39.7%gsf 4403 22.0%

Clearly method works best for || <1.0

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PFlow reconstruction of electrons

Dielctron cont reco effPF=1.49%GSF=0.6%

Up(1s) reco effPF=19%GSF=10%

__PF__GSF

__PF__GSF

Inv mass (Gev/C2 ) dielectron cont (Gev/C2 )

Mass resolution is better for GSF electron collection Increase is more prominent for dielctron continuum

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e+e- continuum (QED Test)

Pair pT Minv

- - -Lowest order

__Higher order

- - -Lowest order __Higher order

S T A R

A. J. Baltz, Phys. Rev. Lett. 100, 062302 466 (2008).

2-photon interactionHigher order diagrams are required to explain STAR data.

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inv masse+e- (Gev/C2 )

__e+e-

__e+e-

and dielectron cont scaled for L=0.5 nb-1

inv masse+e- (Gev/C2 )

+ dielectron continuum

Large cross section of dieletron continuum preventsus 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.

PbPb UPC 5.5 TeVFull CMS Sim+Reco

__e+e-__e+e-

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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

Summary and future plans

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Back up slides

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(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

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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

flowcd RecoParticleFlow/Configuration/testcmsRun fullSimForParticleFlow_cfg.py

Access to particle flow output1.PAT run PF2PAT+PAT to get pattuples.2.Access the PFCandidates directly from an ED Analyzer in full

framework3.Acsess the PFCandidates from ROOT+FWLitecd RecoParticleFlow/Configuration/testcmsRun analyzePFCandidates_cfg.py

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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

Particle Flow :as a user’s point of view

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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 variablesA multivariate approch is followd .the so called Boosted Decision Trees

(BDT) method was chosen.Journal of physics:Conference Series 120(2008)032039

electron reco in Particle Flow :as a user’s point of view

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e,e, measurement in CMS measurement in CMS

Tracking + ECAL + muon-chambers

electronsTracker+EMCAL

muonsTracker+muchambers

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+e+ e- and Pt distributions

____ gen_____rec

____ gen_____rec

Single e eta Single e pt

Electrons are peaking outside CMS acceptanceAlmost all electrons are concentrated at very low Pt

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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

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Weizsacker -Williams formula for flux radiated by a ion with charge Z at distance r

Here ω=k r/ γL and 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

Ultra Peripheral Collisions at LHC

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)

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➢ Input MC: STARLIGHT [J. Nystrand, S.Klein, NPA752(2005)470]

ℓℓ

Signal Background

PbPb

PbPb

Signal + Bkg cross sections