Prospects for Studying

Heavy Quarkoniawith ATLAS at the LHC

Prospects for Studying

Heavy Quarkoniawith ATLAS at the LHCArmin NAIRZ

CERNon behalf of the

ATLAS B-Physics Group

Heavy Quarkonium Workshop, FNAL, September 20-22, 2003

Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, 2003 2

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

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

Outline

Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, 2003 3

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-

1)bottom: 0.5 mb (0.51012 ev @ 1 fb-

1)top: 0.8 nb (0.8106 ev @ 1 fb-

1)

c,b cross-sectionsequal 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

Heavy Quarkonia Production at the LHC

Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, 2003 4

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

Heavy Quarkonia Production at the LHC II

LHC

Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, 2003 5

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, 2003 6

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 21033 cm-2s-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, 2003 7

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 luminositiesadd 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, 2003 8

Di-muon trigger 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

at EF mass and decay-length cuts, after vertex reconstruction

trigger rates (21033 cm-2s-1): ~200 Hz after LVL2, ~10 Hz after EF

B-Physics Trigger III

L = 11033 cm-2s-1

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. ~10 RoI’s from full simul. (w/o BCID)

electron-muon trigger (e.g. ET>2 GeV) ~1 RoI from fast simul.

trigger rates (11033 cm-2s-1): ~200 Hz after LVL2, ~20 Hz after EF

B-Physics Trigger IV

Fast simul.

Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, 2003 10

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)

Recent ATLAS Studies on J/

di-muon 63 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, 2003 11

Recent ATLAS Studies on J/ III

Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, 2003 12

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, 2003 13

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 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

Bc Studies in ATLAS

Armin NAIRZ Heavy Quarkonium Workshop, FNAL, September 20-22, 2003 14

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(s

4), 36 diagrams contributing

Bc Studies in ATLAS II

Results from FME generator (BCVEGPY 1.0)

Bc Studies in ATLAS III

pseudo-rapidity

rapidityBc

Bc*

First preliminary results from full detector simulation (Geant3) and reconstruction

‘initial layout’ (staged detector)

channel Bc J/ mass resolution Bc

= 74

MeV

Bc Studies in ATLAS IV

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