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Prospects for Studying Heavy Quarkonia with ATLAS at the LHC

Prospects for Studying Heavy Quarkonia with ATLAS at the LHC. Armin NAIRZ CERN on behalf of the ATLAS B-Physics Group. Heavy Quarkonium Workshop, FNAL, September 20-22, 2003. Outline. Heavy Quarkonia Production at the LHC Recent Developments in the ATLAS B-Physics Trigger

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Prospects for Studying Heavy Quarkonia with ATLAS at the LHC

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  1. Prospects for Studying Heavy Quarkonia with ATLAS at the LHC Armin NAIRZ CERN on behalf of the ATLAS B-Physics Group Heavy Quarkonium Workshop, FNAL, September 20-22, 2003

  2. Outline • Heavy Quarkonia Production at the LHC • Recent Developments in the ATLAS B-Physics Trigger • ATLAS Studies on J/ • Recent Developments • ATLAS Studies on Bc • Recent Developments Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, 2003 2

  3. Heavy Quarkonia Production at the LHC • The production rates for heavy quark flavours at the LHCwill be huge • total cross-sections • charm: 7.8 mb (7.81012 ev @ 1 fb-1) • bottom: 0.5 mb (0.51012 ev @ 1 fb-1) • top: 0.8 nb (0.8106ev @ 1 fb-1) • c,b cross-sections • equal for high pT in LO PQCD, differences expected from NLO (pT spectrum for c softer) • mass effects visible for low pT • Prediction of LHC rates by • tuningmodels withTevatron data • extrapolating to LHC energies Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, 2003 3

  4. Heavy Quarkonia Production at the LHC II LHC • The LHCwill produce heavy quarkonia withhigh pT in large numbers • assess importance of individual production mechanisms • e.g. colour-singlet vs. colour-octet, factorisation Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, 2003 4

  5. Heavy Quarkonia Production at the LHC III • allow for better discrimination between different models of heavy quarkonia polarisation • e.g. NRQCD vs. colour-evaporation model LHC Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, 2003 5

  6. B-Physics Trigger • The ATLAS Trigger will consist of three levels • Level-1 (40 MHz  O(20 kHz)) • muons, Regions-of-Interest (RoI’s) in the Calorimeters • B-physics (‘classical’ scenario): muon with pT > 6 GeV, || < 2.4 • Level-2 (O(20 kHz)  O(1-5 kHz)) • RoI-guided, running dedicated on-line algorithms • B-physics (‘classical’ scenario): muon confirmation, ID full scan • Event Filter (O(1-5 kHz)  O(200 Hz)) • offline algorithms, alignment and calibration data available • The B-physics trigger strategy had to be revised • changed LHC luminosity target (1  21033 cm-2s-1) • changes in detector geometry, possibly reduced detector at start-up • tight funding constraints Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, 2003 6

  7. B-Physics Trigger II • Alternatives to reduce resource requirements • require at LVL1, in addition to single-muon trigger, a second muon,a Jet or EM RoI,reconstruct at LVL2 and EF within RoI • re-analyse thresholds and use flexible trigger strategy • start with a di-muon trigger for higher luminosities • add further triggers (hadronic final states, final states with electrons and muons) in the beam-coast/for low-luminosity fills • B-physics trigger types (always single muon at LVL1) • di-muon trigger: additional muon at LVL1 • hadronic final states trigger: RoI-guided reconstruction in ID at LVL2, RoI from LVL1 Jet trigger • electron-muon final states trigger: RoI-guided reconstruction in TRT at LVL2, RoI from LVL1 EM trigger • ‘classical’ scenario as fall-back • Results are promising(but further studies necessary) Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, 2003 7

  8. B-Physics Trigger III • Di-muon trigger • effective selection ofchannelswith J/(+-), rare decays like B  +-(X), etc. • minimum possible thresholds: pT > 5 GeV (Muon Barrel) pT > 3 GeV (Muon End-Cap) • actual thresholds determined by LVL1 rate • at LVL2 and EF: confirmation of muons using the ID and Muon Precision Chambers • at EF mass and decay-length cuts, after vertex reconstruction • trigger rates (21033 cm-2s-1): ~200 Hz after LVL2, ~10 Hz after EF L = 11033 cm-2s-1 Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, 2003 8

  9. B-Physics Trigger IV • hadronic and electron-muon final states triggers • require low-ET(Jet or EM)RoI from LVL1, together with a single muon; reconstruct tracks at LVL2 in RoI only • results from detailed fast simulation, and partly from full simulation • bunch-crossing identification not yet implemented in full simulation • hadronic trigger (e.g. ET>5 GeV) • ~2 RoI’s from fast simul. • ~10RoI’s from full simul. (w/o BCID) • electron-muon trigger (e.g. ET>2 GeV) • ~1 RoI from fast simul. • trigger rates (11033 cm-2s-1): ~200 Hz after LVL2, ~20 Hz after EF Fast simul.

  10. Recent ATLAS Studies on J/ • The current main emphasis in lies on ‘technical issues’(validating/optimising trigger and offline s/w architecture, performance, etc.), not on doing full-fledged, detailed physics analyses • shown results are taken from a study on the performance of a staged detector in an initial period of 1 fb-1 • study on measuring the direct J/production cross-section (N. Panikashvili, M. Smizanska) • will be one of the first B-physics measurements in ATLAS • large J/rate after LVL1, direct J/contribution not known • important to find the best strategy to select b-events (e.g. interplay/optimisation of pT vs. vertexing cuts) • background studies not yet included • generation of events used colour-octet model in PYTHIA (implemented by M. Sanchis) Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, 2003 10

  11. Recent ATLAS Studies on J/ II /had separation  rec. eff. • di-muon 63 selection • 3possiblewhen Tile Calorimeter information is additionally taken into account (for /hadron separation) • production cross-section 5 nb • trigger efficiencies not yet taken into account Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, 2003 11

  12. Recent ATLAS Studies on J/ III First preliminary results Studies on J/polarisation in progress Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, 2003 12

  13. Bc Studies in ATLAS • The expected large production rates at the LHC will allow for precision measurements of Bc properties • recent estimates for ATLAS(assuming f(b  Bc)~10-3, 20 fb-1, LVL1 muon with pT > 6 GeV, || < 2.4) • ~5600 Bc J/events • ~100 Bc Bsevents • Channels studied so far: Bc  J/  (mass measurement), Bc J/  (clean signature, ingredient for |Vcb| determ.) • Example of an olderstudy (M. Sanchis et al., hep-ph/9506306, hep-ph/9510450) • parametrised detector response (ID) • estimate of ~10000 Bc  J/  events • mass resolution Bc= 40 MeV • accuracy of mass measurement ~0.5 MeV Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, 2003 13

  14. Bc Studies in ATLAS II • Recent developments (C. Driouichi et al., hep-ph/0309120, several notes in preparation) Since the production of Bc is suppressed by the hard production of an additional cc pair, also MC generation of Bc events using standard tools is CPU intensive. • example: 100,000 PYTHIA pp events ~1 Bc event(which does not necessarily survive the ATLAS LVL1 Trigger selection) • Implementation of two MC generators in PYTHIA 6.2 • Fragmentation ApproximationModel • Full Matrix Element approach (Lund-Beijing collaboration) • based on “extended helicity” (grouping of Feynman diagrams into gauge-invariant sub-groups to simplify calculations, never done for gg  QQ before) • PQCD to O(s4), 36 diagrams contributing Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, 2003 14

  15. Bc Studies in ATLAS III Results from FME generator (BCVEGPY 1.0) pseudo-rapidity Bc* Bc rapidity

  16. Bc Studies in ATLAS IV First preliminary results from full detector simulation (Geant3) and reconstruction • ‘initial layout’ (staged detector) • channel Bc J/ • mass resolution Bc= 74 MeV Fast simul. mass resolution J/ = 41 MeV Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, 2003 16

  17. First preliminary results from full detector simulation (Geant3) and reconstruction • ‘initial layout’ (staged detector) • channel Bc J/ • mass resolution Bc= 74 MeV Fast simul. mass resolution J/ = 41 MeV Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, 2003 17

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