Heavy Ion Physics with CMS LHC Dipak Kumar

Heavy Ion Physics with CMS @ LHC Dipak Kumar Mishra Nuclear Physics Division BARC, Mumbai 24/10/2009 Dipak Mishra, BARC

Outline • Introduction • Detectors at LHC • Physics interests in Heavy Ion Physics • Soft probes: Multiplicity q ET q • Hard probes: Heavy Flavor q Quarkonia q Jet Physics q • Physics in Ultra peripheral collision • Summary & Outlook 24/10/2009 Dipak Mishra, BARC

Motivation Lattice QCD predicts→ at high temp and energy density, hadronic matter undergoes a phase transition to a system of deconfined partonic matter (Quark-Gluon-Plasma). • beleived to have existed ten millionths of second after the Big Bang. Characterize: • early stage → hard probes (heavy flavor, jets, quakonia) • later stage→ soft probes (multiplicity, low p. T spectra, flow) 24/10/2009 Dipak Mishra, BARC

Introduction Investigating the QCD prediction of a deconfined (chiral symmetry restored) high-energy-density phase of nuclear matter Pre-equilibrium Initial state Heavy-Flavor, g QGP Hydrodynamic expansion S, W, f Hadronic phase Freeze-out , Λ* , Σ* hadronization/ Chemical freeze-out Tch = 160 -170 Me. V p, K, p Tfo = 100 Me. V 1) Initial condition: 2) System evolves: 3) Bulk freeze-out: - baryon transfer - parton/hadron expansion - hadronic dof - ET production - interaction cease - Partonic dof 24/10/2009 Tth, <b. T> Dipak Mishra, BARC

How does the event look like? p+p @ s = 200 Ge. V Au+Au @ s. NN = 200 Ge. V STAR Expt At RHIC 24/10/2009 Dipak Mishra, BARC

Some evidence from RHIC Local equilibrium in Freeze-out stage? Color Glass Condensate? Flow & NQ scaling: quark recombination NPA 757(2005)28 -101 Jet quenching: strong interaction of high-p. T hadrons with the medium PRL 98, 162301(2007) Similar J/y suppression at SPS and RHIC Regeneration? 24/10/2009 Dipak Mishra, BARC 6

LHC: New Energy Frontier AGS SPS RHIC LHC (Si, Au) (S, Pb) (Au, Cu) (Pb) 5 20 200 5500 Energy increase x 4 x 10 x 28 Lifetime < 2 fm 2 -4 fm > 10 fm ± 3. 0 ± 5. 3 ± 8. 6 √s. NN [Ge. V] Y- range ± 1. 6 • LHC energies are much higher than the previous heavy-ion accelerators q Extended kinematic reach for pp, p. A, AA q New properties of the initial state, possible gluon saturation at mid-rapidity q A hotter and longer lived partonic phase q Increased cross sections and availability of new hard probes • LHC will significantly increase energy density 24/10/2009 Dipak Mishra, BARC 7

LHC with higher energy density ~ ~ PRC 71 034908 (2005) Can we get Net Baryon free region at LHC? RHIC (130 Ge. V) pbar/p ~ 0. 65 (200 Ge. V) pbar/p ~ 0. 77 ! STAR, PRL 86, 4778 (2001) ! BRAHMS, NPA 734 , 13 (2004) LHC (5. 5 Te. V) pbar/p ~ 1 (? ) 24/10/2009 Dipak Mishra, BARC

New Era at LHC d. Nch/d /<Npart>/2 LHC? d. N/d ~1400 RHIC shows simple energy dependence How about LHC? NPA 757(2005)28 -101 Copious production of high p. T and high-mass particles I. Vitev, hep-ph/0212109 24/10/2009 Dipak Mishra, BARC

Access to wider range of Q 2 and x LHC energy 30 -45 times larger RHIC 30 -45 times lower Bjorken x x values probed< 10 -5 Z 0 Large Gluon density J/ Gross properties of the matter can be described in terms of classical colour fields 24/10/2009 Saturation R. Vogt NPA 752 (2005)447 -456 Dipak Mishra, BARC

LHC @ CERN CMS Geneva Lake LHCb ALICE ATLAS CERN 24/10/2009 Dipak Mishra, BARC

CMS Detector Designed for precision measurements in high luminosity p+p collisions chambers Si Tracker including Pixels ECAL HCAL In Heavy Ion Collisions: Functional at highest expected multiplicities Detailed studies at ~d. Nch/dh ~3000 cross-checks up to 7000 -8000 24/10/2009 Dipak Mishra, BARC

CMS as a Heavy Ion Experiment Calorimeters: high resolution and segmentation Hermetic coverage up to | |<5 | |<6. 6 with CASTOR Zero Degree Calorimeter Muon tracking: from Z 0, J/ , Wide rapidity coverage: | |<2. 4 σm 50 Me. V at the mass in the barrel Silicon Tracker Good efficiency and purity for p. T>1 Ge. V Pixel occupancy: <2% at d. Nch/d 3500 p/p 1 -2% for p. T <100 Ge. V Good low p. T reach using pixels DAQ and Trigger High rate capability for A+A, p+p High Level Trigger: real time HI event reconstruction CMS is a Superb and Versatile Detector for Heavy Ion Physics Excellent performance in high p. T (ET) region and for muon pairs 24/10/2009 Dipak Mishra, BARC

CMS Capabilities for HI • Larger coverage than ALICE near midrapidity • detection of charged & neutral hadrons, muons, electrons, photons over a large p. T • Very good dimuon mass resolution clear separation of many Quarkonia states ( , J/ ) • Full e-m and hadronic calorimetry for complete jet triggering and reconstruction. • Very good forward physics capabilities 24/10/2009 Dipak Mishra, BARC

Soft Probes 24/10/2009 Dipak Mishra, BARC

Charged particle multiplicity ? d. Nch/d /(<Npart>/2) Charged Particle Multiplicities • Predictions vary by a factor of 4! • d. N/dy ~ 2000 – 8000 (RHIC extrapolation vs. HIJING) d. N/d Energy of Collision • One Event • Reconstructed + MC Input -- Systematic Error -2 24/10/2009 -1 0 1 2 • • Three methods are used to evaluate multiplicity: • Pixel Tracklets (2 layers) • Pixel Cluster Shape (1 layer) • Tracks Needs few events O(1000) Few seconds of data taking Dipak Mishra, BARC 16

Event Characterization Centrality: Forward ET measurements (CASTOR and Had. Cal. ) 24/10/2009 Dipak Mishra, BARC

Low p. T PID with tracker, d. E/dx Solid lines: reconstructed, dotted lines: generated Inclusive yield can be extracted up to p. T ≈ 1 Ge. V/c for π± and K±, and up to p. T ≈ 2 Ge. V/c for p± Can study 24/10/2009 Collective radial flow, hadron ratios, thermalization time, medium equation of state constraints Dipak Mishra, BARC

Hard Probes Quarkonia 24/10/2009 Dipak Mishra, BARC

Why is Quarkonia interesting? • In a deconfined phase the QCD binding potential is Debye screened and the heavy quarkonia states are “dissolved”. • Different heavy quarkonium states have different binding energies • dissolved at successive thresholds in energy density / temperature of the medium. • Their suppression pattern thermometer of the produced QCD matter. 1. 10 0. 74 0. 15 2. 31 1. 13 0. 93 0. 83 0. 74 Feed-down from higher states leads to step-wise suppression patterns. Important to measure the heavy quarkonium yields produced in HI collisions at LHC as a function of p. T and centrality H. Satz, hep-ph/0512217 24/10/2009 Dipak Mishra, BARC

J/ suppression: SPS RHIC LHC? regeneration ? SPS RHIC LHC suppression ? Energy Density • J/ψ suppression: RHIC comparable to SPS • Regeneration compensate screening The yield of J/ mesons per DY dimuon is “slightly smaller” in p-Pb collisions than in p-Be collisions; and is “strongly suppressed” in central Pb-Pb collisions • J/ not screened at RHIC (TD~2 Tc)? Suppression via feed down • LHC: recombination or suppression? Interpretation: strongly bound ccbar pairs are “anomalously dissolved” by the deconfined medium created in central Pb-Pb collisions at SPS energies 24/10/2009 Dipak Mishra, BARC

Quarkonia from SPS RHIC LHC RHIC J/ψ Vogt. hep-ph/0205330 • Large production cross-section for J/ and family. • Availability of new probes , ‘, “ 24/10/2009 LHC Dipak Mishra, BARC

CMS: Signal and Background simulation Signal sources: Yellow Report, CERN-2004 -009, hep-ph/0311048: CEM, NLO-pp, shadowing effect (CTEQ 5 M+EKS 98 PDF) Main background sources; • hadron Bkg: uncorrelated muon pairs from p/K decays. • Charm, bottom bkg: muons from ccbar and bbar pairs. 24/10/2009 Dipak Mishra, BARC

J/ , + - (signal+bkg) with fast MC For Pb+Pb, d. Nch/d = 2500, L = 0. 5 nb-1 (one month LHC run) barrel + endcaps O. Kodolova, M. Bedjidian, CMS note 2006/089 S/B J/ 24/10/2009 1. 2 0. 12 N 180000 25000 Dipak Mishra, BARC

After background subtraction J/ ’ ’’ • Best J/ , mass resolution at LHC. Mass resolution: • Unique separation of (1 S), (2 S), (3 S) s. J/ ~ 35 Me. V/c 2 at | |<2. 5 s ~ 54 Me. V/c 2 (barrel), | | < 0. 8 ~ 90 Me. V/c 2 (plus endcap), | | < 2. 4 24/10/2009 Dipak Mishra, BARC

Jet Physics 24/10/2009 Dipak Mishra, BARC

Why Jet physics intersting? In heavy-ion collisions: The suppression of the jets or of the quarkonia states gives the density profile and the state (hadronic or partonic) of the matter they travel. The produced hard partons lose energy by multiple gluon radiation while traversing the dense medium Observe parton energy loss → derive medium properties Flavor-dependent energy loss: DEloss(g) > DEloss(q) (color factor) > DEloss(Q) (mass effect) Suppression of high p. T leading hadrons → seen at RHIC Disappearance of “away-side” jets → indirectly seen at RHIC Modified energy / particle flow within jet (fragmentation function) → not yet seen 24/10/2009 Dipak Mishra, BARC

How Jets gets quenched? In pp, expect two back-to-back jets In the QGP. . . expect mono jets The away-side jet gets “absorbed” by the dense QCD medium p+p @ s = 200 Ge. V It’s not easy to find jet in HI case. Leading particle was considered as the Jet signal at RHIC 24/10/2009 Dipak Mishra, BARC STAR Au+Au @ s. NN = 200 Ge. V

Jet suppression in HI collisions @ RHIC Two-particle azimuthal correlations show back-to-back jets in pp and d-Au collisions; the jet opposite to the high-p. T trigger particle “disappears” in central Au-Au collisions The photons are not affected by the dense medium they cross Interpretation: the produced hard partons (our probe) are “anomalously absorbed” by the dense colored medium created in central Au+Au collisions at RHIC energies 24/10/2009 Dipak Mishra, BARC

Jet study @ LHC Jet ET ~100 Ge. V, Pb+Pb background d. Nch/dy ~ 5000 Jet in p+p after pileup subtraction Binary scaling Jet superimposed on Pb+Pb background p+p reference Will be measured at CMS: • jets up to ET ≈ 500 Ge. V • charged hadrons up to p. T ≈ 300 Ge. V/c 24/10/2009 Dipak Mishra, BARC Jet in Pb+Pb after pileup subtraction

Heavy Flavor 24/10/2009 Dipak Mishra, BARC

Heavy Flavor study @ RHIC Interaction of heavy quarks with the medium experimentally can be studied through measuring the p. T spectra of the heavy flavor. Clear evidence for heavy quark medium modification at high p. T suppression is like p 0 24/10/2009 Dipak Mishra, BARC

B J/ + - Study at LHC SPS RHIC LHC Suppression+regeneration dominant • About 30% J/ are from decays of B mesons ● B meson flies to a measurable distance before decaying, ● a Secondary Vertex is used to separate the above two processes Muons from B J/ Muons from direct J/ | | < 2. 4 24/10/2009 Dipak Mishra, BARC

Measure B production using displaced J/ B J/ + - P. Shukla A cut of 0. 4 mm : B J/ + - (63%) J/ + (6%) 24/10/2009 Dipak Mishra, BARC

Ultra Peripheral Collisions 24/10/2009 Dipak Mishra, BARC

Ultra peripheral collisions: UPC are those, which interacts via their cloud of virtual photons. • electromagnetic interaction photons emitted by ions interact with each other • photon-nuclear reaction a photon emitted by an ion interacts with other nucleus. photo-production Strong E&M fields due to the coherent action of 82 proton charges (E max~80 Ge. V) • Measure the gluon distribution function in the nucleus ( Pb) • – low background – simpler initial state Pb→ photo-production in CMS – Unexplored (x, Q 2) regime: – Pin down amount of low-x suppression in the Pb nuclear PDF (compared to the proton PDF) 24/10/2009 Dipak Mishra, BARC 36

Ultra peripheral collisions: photo-production Vineet Kumar Unexplored x. G(x, Q 2) region + - scaled for L = 0. 5 nb-1 24/10/2009 Dipak Mishra, BARC d. Au 37 e. A

e+e- reconstruction Pb. Pb UPC 5. 5 Te. V Full CMS Sim+Reco __ e+e__ e+e- • Large cross section of di-electron continuum almost prevents us to extract from continuum. • e+e- continuum can be used as signal (QED Test) 24/10/2009 Dipak Mishra, BARC

Fabrication activities at NPD (BARC) Fully assembled RPC with front end electronics, gas flow pipes, cooling pipes, HV and signal cables July 2008 • 10 RPCS have been delivered • Eff, leakage curr cluster size have been studied • Certified cosmic test OK @ 9. 4 k. V 24/10/2009 Dipak Mishra, BARC

QA study of the RPCs Leakage current vs. HV at Mumbai Eff & leakage current Vs. HV measured at CERN (ISR) > 95% Efficiency plots of RPCs (# 2, 4, 6, 8) tested at ISR Lab. 24/10/2009 Dipak Mishra, BARC Cluster size for RPCs (# 2, 4, 6, 8)

Upscope for end-cap RPCs Another 80 (40 back-to-back) RPCs will be delivered from India • 40 RPCs from NPD (BARC) • 40 from PU, Chandigarh Jan’ 10 May’ 10 We would be here Ordering and delivery of parts should be over Jun ’ 10 All gas-gaps delivered Dec ’ 10 Chambers Testing, assembled Comissioning & delivered & Complete to CERN Installation priorities for CMS may change after initial operation experience 2009 -2010 24/10/2009 2010 -2011 Dipak Mishra, BARC Jan ’ 11

Summary & Outlook • RHIC has produced many exciting results on Quark-Gluon matter at extreme conditions. • Many new and cleaner probes will be available with good statistics at LHC • Finer detailed properties of QGP • The CMS detector is a versatile not only for pp but also for Heavy Ion collisions. • It has excellent capabilities to study the dense QCD matter produced in very-high-energy heavy-ion collisions. • CMS has a broad and exciting heavy ion program, including: • Bulk Observables (Soft physics) • Jet physics • Quarkonia and heavy-quarks • Ultra peripheral collisions • Coming years will witness many exciting and some surprising results in Heavy ion collisions. Thank you 24/10/2009 Dipak Mishra, BARC

Discovery of Jet Quenching Jet 24/10/2009 Dipak Mishra, BARC

Limiting fragmentation region - ybeam 24/10/2009 Dipak Mishra, BARC 44