Prospects Prospects for for Studying Studying Heavy Heavy
Prospects Prospects for for Studying Studying Heavy Heavy Quarkonia Quarkonia with with ATLAS ATLAS at at the the LHC LHC Armin NAIRZ CERN on behalf of the ATLAS B-Physics Group Heavy Quarkonium Workshop, FNAL, September 2022, 2003 Outline Heavy Heavy Quarkonia Quarkonia Production Production at at the the LHC LHC
Recent Recent Developments Developments in in the the ATLAS ATLAS B-Physics B-Physics Trigger Trigger ATLAS ATLAS Studies Studies on on J/ J/ Recent RecentDevelopments Developments ATLAS ATLAS Studies Studies on on B Bc c Recent
RecentDevelopments Developments Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, 2003 2 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 (7.81012 ev @ 1 fb- ) bottom: 0.5 mb (0.51012 ev @ 1 fb1 ) top: 0.8 nb (0.8106 ev @ 1 fb1 ) 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 p T Prediction Armin NAIRZ of LHC rates by Heavy Quarkonium Workshop, FNAL, September 20-22, 2003 tuning models with Tevatron 3 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 Armin NAIRZ e.g. colour-singlet vs. colour-octet, factorisation
Heavy Quarkonium Workshop, FNAL, September 20-22, 2003 4 Heavy Quarkonia Production at the LHC III allow for better discrimination between different models of heavy quarkonia polarisation e.g. NRQCD vs. colourevaporation model LH C Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, 2003 5 B-Physics Trigger The ATLAS Trigger will consist of three levels Level-1 (40 MHz O(20 kHz))
Level-2 (O(20 kHz) O(1-5 kHz)) muons, Regions-of-Interest (RoIs) in the Calorimeters B-physics (classical scenario): muon with pT > 6 GeV, || < 2.4 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 21033 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 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 Armin NAIRZ
are promising (but further studies necessary) Heavy Quarkonium Workshop, FNAL, September 20-22, 2003 7 B-Physics Trigger III Di-muon trigger effective selection of channels with J/(+-), rare decays like B +-(X), etc.), 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
L = 11033 cm-2s-1 at EF mass and decay-length cuts, after vertex reconstruction trigger rates (21033 cm-2s-1): Armin NAIRZ~200 Hz after HeavyLVL2, Quarkonium Workshop, ~10 Hz after EF FNAL, September 20-22, 2003 8 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 hadronic trigger (e.g. ET>5 GeV) ~2 RoIs from fast simul. ~10 RoIs from full simul. (w/o BCID) electron-muon trigger (e.g. ET>2 GeV) bunch-crossing identification not yet implemented in full simulation ~1 RoI from fast simul. trigger rates (11033 cm-2s-1): ~200 Hz after LVL2, ~20 Hz after EF Fast simul. 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 fullfledged, 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 crosssection (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 Recent ATLAS Studies on J/ II /had separation
rec. eff. di-muon 63 selection 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 11 Recent ATLAS Studies on J/ III First preliminary results Primary Vertex Resolution PV < 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 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 fb1 , 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 older study (M. Sanchis et al., hep-ph/9506306, hep-ph/9510450) parametrised detector response (ID) estimate Armin NAIRZ Heavy QuarkoniumB Workshop, FNAL, September 20-22, 2003 of ~10000 c J/ events mass resolution = 40 MeV 13 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 gaugeinvariant sub-groups to simplify calculations, never done for gg QQ before) Armin NAIRZ PQCD to O(s4), 36 diagrams contributing Heavy Quarkonium Workshop, FNAL, September 20-22, 2003 14 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 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 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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