Prospects for Studying

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 LHC will be huge
• total cross-sections
• charm 7.8 mb (7.8?1012 ev _at_ 1 fb-1)
• bottom 0.5 mb (0.5?1012 ev _at_ 1 fb-1)
• top 0.8 nb (0.8?106 ev _at_ 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
• tuning models with Tevatron 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 LHC will produce heavy quarkonia with high 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 (RoIs) in the
  Calorimeters
• B-physics (classical scenario) muon with pT gt
  6 GeV, ? lt 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 of channels with J/?(??-),
  rare decays like B ? ??-(X), etc.
• minimum possible thresholds pT gt 5 GeV
  (Muon Barrel) pT gt 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. ETgt5 GeV)
• 2 RoIs from fast simul.
• 10 RoIs from full simul. (w/o BCID)
• electron-muon trigger (e.g. ETgt2 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
• ?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

Armin NAIRZ Heavy Quarkonium
Workshop, FNAL, September 20-22, 2003
11
12
Recent ATLAS Studies on J/? III
First preliminary results
Primary Vertex Resolution ?PV lt 15 ?m
Secondary Vertex Resolution ?xy 70 ?m (core) 150 ?m (tails)
Mass Resolution ?J/? 40 MeV
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 gt 6 GeV, ?
  lt 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 older study (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 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(?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