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

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

Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, The production rates for heavy quark flavours at the LHC will be huge  total cross-sections charm: 7.8 mb (7.8  fb -1 ) bottom: 0.5 mb (0.5  fb -1 ) top: 0.8 nb (0.8  fb -1 )  c,b cross-sections equal for high p T in LO PQCD, differences expected from NLO (p T spectrum for c softer) mass effects visible for low p T Prediction of LHC rates by  tuning models with Tevatron data  extrapolating to LHC energies Heavy Quarkonia Production at the LHC

Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, The LHC will produce heavy quarkonia with high p T in large numbers  assess importance of individual production mechanisms e.g. colour-singlet vs. colour-octet, factorisation Heavy Quarkonia Production at the LHC II LHC

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

Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, 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 p T > 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  cm -2 s -1 )  changes in detector geometry, possibly reduced detector at start-up  tight funding constraints B-Physics Trigger

Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, 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) B-Physics Trigger II

Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, Di-muon trigger  effective selection of channels with J/  (  +  - ), rare decays like B   +  - (X), etc.  minimum possible thresholds: p T > 5 GeV (Muon Barrel) p T > 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  cm -2 s -1 ): ~200 Hz after LVL2, ~10 Hz after EF B-Physics Trigger III L = 1  cm -2 s -1

hadronic and electron-muon final states triggers  require low-E T (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. E T >5 GeV) ~2 RoI’s from fast simul. ~10 RoI’s from full simul. (w/o BCID)  electron-muon trigger (e.g. E T >2 GeV)  ~1 RoI from fast simul.  trigger rates ( 1  cm -2 s -1 ): ~200 Hz after LVL2, ~20 Hz after EF B-Physics Trigger IV Fast simul.

Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, 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 p T vs. vertexing cuts)  background studies not yet included  generation of events used colour-octet model in PYTHIA (implemented by M. Sanchis) Recent ATLAS Studies on J/ 

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

Recent ATLAS Studies on J/  III Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, Primary Vertex Resolution  PV < 15  m Secondary Vertex Resolution  xy ~70  m (core) ~150  m (tails) Mass Resolution  J/  ~40 MeV First preliminary results Studies on J/  polarisation in progress

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

Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, Recent developments (C. Driouichi et al., hep-ph/ , several notes in preparation) Since the production of B c is suppressed by the hard production of an additional cc pair, also MC generation of B c events using standard tools is CPU intensive.  example: 100,000 PYTHIA pp events  ~1 B c event (which does not necessarily survive the ATLAS LVL1 Trigger selection)  Implementation of two MC generators in PYTHIA 6.2  Fragmentation Approximation Model  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(  s 4 ), 36 diagrams contributing B c Studies in ATLAS II

Results from FME generator (BCVEGPY 1.0) B c Studies in ATLAS III pseudo-rapidity rapidity BcBc Bc*Bc*

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

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