Transcript Document

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
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Heavy Quarkonia Production at the LHC
Recent Developments in the ATLAS
B-Physics Trigger
ATLAS Studies on J/
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ATLAS Studies on Bc
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Armin NAIRZ
Recent Developments
Recent Developments
Heavy Quarkonium Workshop, FNAL, September 20-22, 2003
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Heavy Quarkonia Production at the LHC
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The production rates for
heavy quark flavours at the
LHC will be huge
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total cross-sections
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c,b cross-sections
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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106 ev @ 1 fb-1)
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
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tuning models with Tevatron data
extrapolating to LHC energies
Armin NAIRZ
Heavy Quarkonium Workshop, FNAL, September 20-22, 2003
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Heavy Quarkonia Production at the LHC II
LHC
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The LHC will produce heavy quarkonia with high pT in
large numbers
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assess importance of individual production mechanisms
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e.g. colour-singlet vs. colour-octet, factorisation
Armin NAIRZ
Heavy Quarkonium Workshop, FNAL, September 20-22, 2003
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Heavy Quarkonia Production at the LHC III
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allow for better discrimination
between different models of
heavy quarkonia polarisation
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e.g. NRQCD vs. colour-evaporation
model
LHC
Armin NAIRZ
Heavy Quarkonium Workshop, FNAL, September 20-22, 2003
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B-Physics Trigger
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The ATLAS Trigger will consist of three levels
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Level-1 (40 MHz  O(20 kHz))
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Level-2 (O(20 kHz)  O(1-5 kHz))
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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))
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muons, Regions-of-Interest (RoI’s) in the Calorimeters
B-physics (‘classical’ scenario): muon with pT > 6 GeV, || < 2.4
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)
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changes in detector geometry, possibly reduced detector at
start-up
tight funding constraints
Armin NAIRZ
Heavy Quarkonium Workshop, FNAL, September 20-22, 2003
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B-Physics Trigger II
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Alternatives to reduce resource requirements
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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
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B-physics trigger types (always single muon at LVL1)
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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
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
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B-Physics Trigger III
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Di-muon trigger
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effective selection of channels
with 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
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L = 11033 cm-2s-1
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
Armin NAIRZ
Heavy Quarkonium Workshop, FNAL, September 20-22, 2003
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B-Physics Trigger IV
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hadronic and electron-muon
final states triggers
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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
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hadronic trigger (e.g. ET>5 GeV)
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~2 RoI’s from fast simul.
~10 RoI’s from full simul. (w/o BCID)
electron-muon trigger (e.g. ET>2 GeV)
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bunch-crossing identification not yet
implemented in full simulation
~1 RoI from fast simul.
trigger rates (11033 cm-2s-1):
~200 Hz after LVL2, ~20 Hz after EF
Fast simul.
Recent ATLAS Studies on J/
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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
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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)
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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)
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background studies not yet included
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generation of events used colour-octet model in PYTHIA
(implemented by M. Sanchis)
Armin NAIRZ
Heavy Quarkonium Workshop, FNAL, September 20-22, 2003
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Recent ATLAS Studies on J/ II
/had separation
 rec. eff.
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di-muon 63 selection
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Armin NAIRZ
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
Heavy Quarkonium Workshop, FNAL, September 20-22, 2003
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Recent ATLAS Studies on J/ III
First preliminary
results
Primary Vertex
Resolution PV
Secondary Vertex
Resolution xy
Mass Resolution
J/
< 15 m
~70 m (core)
~150 m (tails)
~40 MeV
Studies on
J/ polarisation
in progress
Armin NAIRZ
Heavy Quarkonium Workshop, FNAL, September 20-22, 2003
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Bc Studies in ATLAS
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The expected large production rates at the LHC will
allow for precision measurements of Bc properties
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recent estimates for ATLAS (assuming f(b  Bc)~10-3, 20 fb-1,
LVL1 muon with pT > 6 GeV, || < 2.4)
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~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
hep-ph/9510450)
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(M. Sanchis et al., hep-ph/9506306,
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
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Bc Studies in ATLAS II
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Recent developments
several notes in preparation)
(C. Driouichi et al., hep-ph/0309120,
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.
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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
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Fragmentation Approximation Model
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Full Matrix Element approach (Lund-Beijing collaboration)
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based on “extended helicity” (grouping of Feynman diagrams into gauge-invariant
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PQCD to O(s4), 36 diagrams contributing
sub-groups to simplify calculations, never done for gg  QQ before)
Armin NAIRZ
Heavy Quarkonium Workshop, FNAL, September 20-22, 2003
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Bc Studies in ATLAS III
Results from FME generator
(BCVEGPY 1.0)
pseudo-rapidity
Bc*
Bc
rapidity
Bc Studies in ATLAS IV
First preliminary results
from full detector
simulation (Geant3) and
reconstruction
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‘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
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First preliminary results
from full detector
simulation (Geant3) and
reconstruction
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‘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
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