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CMS Heavy Ion Physics. Pablo Yepes Rice University. Hadronic Collisions Quarkonia Production Jet Collisions Coherent Interactions. Why HI at LHC Jurgen Shukraft, Quark Matter 2001. Before. Pb. Pb. Pb+Pb, central collisions (b=0). After. J/ Y Melting. p -. J / Y. c c. Hadron
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CMS Heavy Ion Physics Pablo Yepes Rice University • Hadronic Collisions • Quarkonia Production • Jet Collisions • Coherent Interactions
Why HI at LHCJurgen Shukraft, Quark Matter 2001 Before Pb Pb Pb+Pb, central collisions (b=0) After
J/Y Melting p- J/Y c c Hadron gas K p+ u,d u,d c c d QGP d u u,d u,d NA50 Collaboration, CERN J/Y Yield L(fm): Average distance travel by the J/Y inside tNuclear Matter.
Quarkonia Acceptance in CMS m-Chambers J/Y at CMS • CMS: J/Y mainly pT>5 GeV with barrel, due to m cutoff. • ALICE: h>2.5 with m • ATLAS (if they do HI) lower acceptance due to higher m pT cutoff. Full Detector 10% Acceptance Barrel Pt(GeV) Upsilon at CMS 20% Full Detector Barrel
Quarkonia Reconstruction • Essential sub-detectors: • Tracking devices • Muon system • Pessimistic assumptions for background estimates: • dNch/dy=8000 (most generators < 5500) • <pt>p=0.48 GeV/c (HIJING 0.39 GeV/c) • <pt>k=0.67 GeV/c Special Heavy Ion Tracking Algorithm Significant Muon background from p and K decays
J/Y Signal 1 month running at top Luminosity: J/Y’s detected and reconstructed in the Barrel: Min bias collisions - 1 month run - barrel only muons with P > 3.5 GeV/c 4 10 Pb-Pb L= 1027 cm2 s-1 Y/cont.= 1.0 # events/25 MeV/c2 3 10 2 2.25 2.5 2.75 3 3.25 3.5 3.75 4 4.25 4.5 5 Ca-Ca L= 2.5 1029 cm2 s-1 10 Y/cont.= 9.7 ALICE: ~2K events with ms # events/25 MeV/c2 4 10 2 2.25 2.5 2.75 3 3.25 3.5 3.75 4 4.25 4.5 Opposite-sign di-muon invariant mass (GeV/c2)
Upsilon in Pb-Pb L= 1027 cm-2 s-1 Upsilon/cont.= 1.6 104 7000 Total Combinatorial background subtracted after reconstruction # Events/25 MeV/c2 6000 Decay-Decay Decay-b 3 103 5000 b-b 4000 Decay-c 3000 2 102 2000 c-c 1000 0 8.5 8.75 9 9.25 9.5 9.75 10 10.25 10.5 10.75 11 8.5 8.75 9 9.25 9.5 9.75 10 10.25 10.5 10.75 11 Di-muon Invariant Mass (GeV/c2) 1 month: 22000 and 7500 ’ detected in the barrel # Events/25 MeV/c2 Opposite-sign di-muon Invariant Mass (GeV/c2) Background contributions
Upsilon in Ca-Ca L= 2.5 1029 cm-2s-1 Upsilon/cont.= 9.4 # Events/25 MeV/c2 105 Total 104 b-b Decay-Decay Decay-b 103 Decay-c 8.5 8.75 9 9.25 9.5 9.75 10 10.25 10.5 10.75 11 Opposite-sign di-muon invariant mass (GeV/c2) • 1 month: • 340000 • 115000 ’ • Only barrel used.
Quarkonia Reference • At SPS, J/Y is compared to Drell-Yan. • At LHC Drell-Yan contribution is negligible. • Z0 proposed as reference to production. • MZ>M • Different production mechanisms: • Z0: antiquark-quark, quark-gluon and antiquark-gluon. • : gluon-gluon. • Cross check di-muon reconstruction algorithm
Jet Quenching • Large pT quarks affected by hot hadronic media • Jets at RHIC buried in low pT background • Look at particle pt spectrum
Jets at LHC are Easy for High Multiplicity PbPb Jet quenching • monojet/dijet enhancement • jet-Z0mm or jet-g dNch/dy=8000 Jet Finding 100 GeV ET - e~100% - s(ET)/ET=11.6%. Total Calorimeter Energy f h
Balancing Photons and Jets <E>=0 GeV <E>=4 GeV Background <E>=8 GeV • Etjet, g>120GeV in the barrel • 1 month: • 900 events for Pb-Pb • 104 events for Ca-Ca 2 weeks at L=1027 cm-2s-1 # Events/4 GeV ETg//p0-ETJet (GeV)
Ultra Peripheral Collisions(Coherent Interactions) A g orP g orP A • Low pT pT < 1/R 50 MeV • Low Energy ECMMax < g/R • CERN SPS ECMMax =0.5 GeV • RHIC ECMMax =6 GeV Detected • CERN LHC ECMMax =160 GeV
STAR Ultra-Peripheral Event(DNP 2000) End view Side view ZDC ZDC AuAu gP (gAu) r pp Trigger: Low multiplicity and zero energy at Zero Degree Calorimeter (ZDC)
gg Physics e+e- Cross Sections • Mainly studied at e+e- colliders.Typically p0<mgg<hc. stot up to 70 GeV by LEP. • Non perturbative QED, coupling Z2. • New Physics: • Standard Model H production marginal for HI • Any exotic particle coupling to gg. • Supersymmetric Higgs for some areas of parameters space.
Ultra-Peripheral Collisionsgg Cross Sections A g g A A 100 102 Meson or lepton/quark pair 107 h p0 f 2 h a 10-2 10 2 h 105 f ' c 2 c A cc0 10-4 10-2 cc2 103 1 102 (barn) e+e- H' 10-6 10-4 107 h b events/sec events/year 102 - 1 m+ m- 10 AA hadrons 105 t+ t- h0b 10-8 10-6 s h2b 104 10-2 cc 103 (M) (barn/GeV) 10-1 events/year/GeV events/sec/GeV 106 10-4 10-10 10-8 10 H 108 10-6 10-3 SM AA bb 10-1 s 10-12 10-10 1010 10-8 10-3 10-5 1012 10-10 10-14 10-12 10-5 -1 0 2 10 10 10 10 1014 10-12 1 10 102 M (GeV) M (GeV)
gg Physics, Hadron Spectroscopy • Light quark: Difficult at CMS because of low pT, challenge for triggering, unless a multiplicity trigger is used. • Heavy quark spectroscopy. Very large numbers expected
Photon Nucleus (gA) • gp studied in HERA: Wgp<200 GeV • gA at LHC: Wgp<900 GeV • Vector meson production: gp(A) Vp(A), V=r,w,f,J/Y • Very large rates, for example >104 Hz f in Ca-Ca • Interface QCD and hadronic physics • LHC will be a meson factory. Competitive with other meson factories like f factory at Frascatti (CP, QM tests, etc). • Can CMS trigger on these events. Clean events with only a few tracks.
Conclusions • CMS is provides unique tools to study Heavy Ion Collisions at LHC. • Some physics topics: • Quarkonium production: and J/ families. • Jet quenching. • Ultra-Peripheral collisions.
Addendum: Tracking 60 • Developed for dNch/dy=8000 and dN0/dy=4000. • Track only particles with tracks in m detector. • Use m-chambers tracks as seeds. • Use only tracking detector providing 3D space points. Detector Pitch mm MSGC 200 50 MSGC 240 Silicon 147 40 Occupancy (%) 30 20 10 0 60 70 80 90 100 110 120 Radius of MSGC layer (cm)
Interference • Nuclei can emit or scatter pair • two indistinguishable possibilities • Amplitudes add • Vector meson has negative parity • s ~ |A1 - A2eip·b|2 • Destructive interference when pT << 1/b