Measurement of ϒ+ϒ- and e+e- in Ultra Peripheral PbPb Collisions at 5.5 TeV in CMS

1. Summary of measurement of +- ,e+e- in Ultra peripheral PbPb collisions at 5.5 TeV in CMS Vineet Kumar LHC CMS Meeting 31 August 2009

2. Plan of presentation • Introduction: • Fields of relativistic moving charged particles. • Weizsacker-Williams method of virtual quanta • UPC PbPb(γPb)  Pb* in CMS • Motivation for  measurement in CMS • Theoretical cross section for  family and dilepton continuum (γ γe+e-,µ+ µ-) • Total reconstruction efficiencies for  family and dilepton continuum in CMS • Expected  yields for one month LHC running. • Summary

3. Field of moving charges x2 X’2 S β S b b q X’1 K’ K x1 q x1 β x3 X’3 E’1(t)= - q  v t (b2 +2v2 t2) -3/2 E1(t)= - q  v t (b2 +2v2 t2) -3/2 E’2(t) = q b (b2 +2v2 t2) -3/2 E2(t)= q  b (b2 +2v2 t2) -3/2 E’3(t) = 0 B’1(t) = 0 B’2(t) = 0 B’3(t) = 0 B3(t)= β q  b (b2 +2v2 t2) -3/2 = β E2(t)

4. Shape of fields E1 (t) β ~ 1 E2 (t)=β-1 B3(t) t β ~ 1 • Magnetic Field B3(t) • Duration of appreciable field strength at point S decrease as β1 • Observer at S sees nearly equal transverse and mutually perpendicular electric and magnetic fields. • These are indistingusible from the fields of a plane polarized pulse propagating in x1 direction. • Extra longitudinal field gives zero time integral β ~ 0 t

5. Weizsacker-Williams method of virtual quanta • This equivalence of fields of relativistic charged particles • And those of a pulse of radiation is basis of Weizsacker • Williams formula. • For pulse P1 the frequency spectrum {energy / area-freq} • Is given by • dI1(,b) = C/2 | E2() |2 • dI2(,b) = C/2 | E1() |2 x2 P1 P2 x1 E2 () and E1 () are the Fourier transform of E2 (t) and E1 (t). P1 ~ E2 B3 P2 ~ E1 X

6. 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.

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

8. Theoretically predicted cross sections • STARLIGHT Generator explain PHENIX UPC data • Cross section is given with one neutron emission probability. • dilepton continuum production cross section is much larger than  • [J.Nystrand,S.KleinNPA752(2005)470]

9. STARLIGHT distributions for photo-produced  in UPC Pb Pb at 5.5 TeV

10. STARLIGHT distributions for photo-produced dileptons in UPC PbPb at 5.5 TeV

11. Reconstruction efficiency for  family and dimuon continuum

12. Trigger efficiency for HLT_DoubleMu3 and HLT_Mu3 __Gen __OfflineReco __TriggeredEvents __Triggered+Reco • Reconstruction Sequence • GenHlt + Select only those event which pass HLT Path +OfflineReco • HLT Path Used HLT_Mu3

13. Reconstructed  pt and rapidity distributions

14. Total Reconstruction efficiency as a function of  pt and rapidity

15.  and dimuon cont scaled for L=0.5 nb-1

16. 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

17. Electron reconstruction efficiency __ Gen electrons __PF electrons __GSF electrons __ Gen electrons __PF electrons __GSF electrons

18. Reconstructed  pt and rapidity distributions

19. Total Reconstruction efficiency as a function of  pt and rapidity

20.  and dimuon cont scaled for L=0.5 nb-1 PbPb UPC 5.5 TeV Full CMS Sim+Reco __e+e- __e+e- • Large cross section of dieletron continuum almost prevents us to extract  from continuum. • e+e- continum can be used as signal (QED Test)

21. 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

22. Summary • In PbPb→( Pb)→  Pb* at 5.5 TeV with →µ+µ-whole  family can be reconstructed with good resolution. • A detailed study for geometrical acceptance and reconstruction efficiency is done. It is found that reconstruction efficiency increases 50% to 57% for (1s) to (3s). • Total reconstruction efficiency (geometrical acceptance ×Trigger efficiency × reconstruction efficiency) is found nearly 35 % for  family and 4% for dimuon continuum. • 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.

23. Back up slides

24. (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

25. 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

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

27.  +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

28. 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

29. 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)

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