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Exploring Heavy Ion Physics with CMS: Insights from LHC and CMS Detector Capabilities

Join Pablo Yepes from Rice University as he discusses the advancements in heavy ion physics anticipated at the LHC. This presentation covers the expected heavy ion collisions at 7 TeV per charge and the unique capabilities of the CMS detector, designed primarily for proton-proton collisions but adaptable for heavy ion studies. Key topics include event characterization, quarkonium production (Upsilon and J/ψ), jet production, and ultra-peripheral collisions. Discover how CMS provides essential tools for investigating the complex phenomena of heavy ion collisions.

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Exploring Heavy Ion Physics with CMS: Insights from LHC and CMS Detector Capabilities

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  1. Heavy Ion Physics with CMS Pablo Yepes, Rice University for the CMS Collaboration Quark Matter Jan 16, 2001

  2. What To Expect from LHC • LHC (Large Heavy ion Collider) is expected to provide pA and AA collisions. • Energy: 7 TeV/charge Luminosity

  3. What to Expect From CMS

  4. Stretching CMS Detector designed for pp. However due to flexible design offers unique capabilities for AA mm A minimum bias Pb-Pb event in CMS

  5. Some CMS Assets • CMS has excellent muon detection capabilities: • |h|<1.3 for barrel and |h|<2.4 with endcaps. • Good mass resolution: 46 MeV for the Upsilon. • Efficient suppression of background from p/K decays: • Electromagnetic calorimeter at 1.3 m from beam axis. • PT threshold at 3.5 GeV/c for a single muon to reach the m-chambers. • Large calorimeter coverage with good jet reconstruction capabilities.

  6. Physics Topics • Event Characterization • Quarkonium Production: Upsilon and J/Y • Zmm • Jet Production: • Single/Double jet ratios. • Z and g tagged jets • Ultra-Peripheral Collisions: gg and g-Pomeron

  7. Event Characterization In spite of very strong magnetic field (4 Tesla) there is a good correlation between centrality and transverse energy.

  8. Quarkonia Cross Sections Production Cross Sections for our studies • A scaling law: sAA= A2a spp • spp from CDF @ 1.8 TeV extrapolated to 5.5(7) TeV. • a=0.9(0.95) for J/Y (Upsilon).

  9. Quarkonia Acceptance in m-Chambers J/Y • J/Y with • pT>5 GeV • in Barrel • Upsilon down to low transverse momentum Full Detector 10% Acceptance Barrel Pt(GeV) Upsilon 20% Full Detector Barrel

  10. 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

  11. J/Y Signal Min bias collisions - 1 month run - barrel only muons with P > 3.5 GeV/c 1 month running at top Luminosity: J/Y’s detected and reconstructed in the Barrel: 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 # 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)

  12. 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

  13. 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.

  14. 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

  15. Jets are Easy Jet quenching • monojet/dijet enhancement • jet-Z0mm or jet-g dNch/dy=8000 Jet Finding 100 GeV ET - e~100% - s(ET)/ET=11.6%. Total Calorimeter Energy f h

  16. 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)

  17. Ultra-Peripheral Collisions 2 100 10 2 1 10 7 10 h e+e- ' p f 2 7 0 h 10 a 10-2 10 2 -2 5 10 - 1 h m+ m- 10 f ' c 2 c 5 hadrons -2 cc0 10 t+ t- 10-4 10 cc2 -4 -2 3 10 10 10 (barn) -4 3 H' 10-6 10 cc 10 h (M) (barn/GeV) b events/sec events/year -6 -4 events/year/GeV 10 events/sec/GeV 10 10 AA -6 h0b s 10 10 h2b 10 -1 10 -8 -6 10 10 -10 -8 10 10 -1 bb 10 AA -3 H 10 s SM -10 -8 10 10 -12 -10 10 10 -3 10 -5 10 -12 -10 10 10 -14 -12 10 10 -1 0 2 -5 10 10 10 10 10 -14 -12 M (GeV) 10 10 2 1 10 10 M (GeV) A A g orP Meson or lepton/quark pair g orP A A

  18. Conclusions • CMS is provides unique tools to study Heavy Ion Collisions at LHC. • Physics considered: • Event characterization with large rapidity coverage. • Quarkonium production:  and J/ families. • Jet quenching. • Ultra-Peripheral collisions.

  19. 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)

  20. LHC Parameters (Addendum) • Bunches 7.5 cm long every 125 ns.

  21. Addendum: Upsilon Acceptance T dN /dp ¡ 3000 2000 1000 0 0 1 2 3 4 5 6 7 8 9 10 p (GeV/c) T 6000 dN /dy ¡ 4000 2000 0 -10 -8 -6 -4 -2 0 2 4 6 8 10 y h dN /d ¡ 4000 2000 0 -10 -8 -6 -4 -2 0 2 4 6 8 10 h 69

  22. STAR First Ultra-Peripheral Collisions

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