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Quarkonium production at ATLAS

Quarkonium production at ATLAS. Erez Etzion Tel-Aviv University on behalf of the ATLAS Collaboration. QWG-6, Nara, Dec. 2008. Motivation. Large number of J/ ψ -> μ + μ - and  -> μ + μ - decays is expected at the LHC; Alignment and calibration of trigger & tracking.

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Quarkonium production at ATLAS

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  1. Quarkonium production at ATLAS Erez Etzion Tel-Aviv University on behalf of the ATLAS Collaboration QWG-6, Nara, Dec. 2008

  2. Motivation • Large number of J/ψ->μ+ μ- and  ->μ+ μ- decays is expected at the LHC; • Alignment and calibration of trigger & tracking. • Test bed for QCD calculations. • Prompt quarkonia a main source of background to other B processes. • Production was described via the Color Singlet Model. • Inconsistency with the Tevatron Xsection =>Color Octet Model suggested. • COM failed to predict quarkonia polarization dependence on its PT. • Alternative suggestions κT factorization. • ATLAS Physics plan is starting in summer 2009. • Key player in the early data taking. • At low luminosity can lower PT threshold to collect large sample. • ATLAS reach for PT >TEVATRON => enhance its analysis power. E. Etzion QWG-6 December 2008

  3. Tevatron ATLAS 1x106 J/y CDF 1.1 fb-1 60 pb-1 4.2x105  D0 1.3 fb-1 85 pb-1 Expected data at early LHC • ATLAS expects to achieve the current Tevatron onia yield at a couple of months with LHC at low luminosity ~1000 J/y’s per hour • 60 pb-1 should allow for competitive measurement of quarkonium polarization, with enough statistics in the crucial high pT region. • High pT data is important. Tevatron suffers from statistics in this region. • With 10 pb-1 ATLAS will be able to measure ratios of onia cross-sections, which can help to constrain NRQCD octet matrix elements. E. Etzion QWG-6 December 2008

  4. Quarkonium production cross-section Tevatron (@1.8 TeV) MC Onia production pT and the differential cross-section contributions from color singlet, color octet and singlet/octet of  . The dominant contribution at high pT range is the 3S1 color octet fragmentation (dashed dotted line). J/Ψ production cross section  production cross section LHC MC (@14 TeV) E. Etzion QWG-6 December 2008

  5. Previousmeasurements  polarization (You have already seen these figures many time this meeting ..) D0 July 19,2007 http://www-d0.fnal.gov/Run2Physics/WWW/results/prelim/B/B50/ CDF April 4, 2007 http://arxiv.org/abs/0704.0638v1/ CDF D0 kT factorization J/ψ polarization - CDF RUN II E. Etzion QWG-6 December 2008

  6. ATLAS Detector Muon DetectorsTile CalorimeterLiquid Argon Calorimeters T h e A T L A S E x p e r i m e n t 22 m 46 m Toroid MagnetsSolenoid MagnetSCT TrackerPixel DetectorTRT Tracker E. Etzion QWG-6 December 2008

  7. The Trigger system • LVL1 • hardware-based, identifies Regions of Interest (RoI) for further processing • LVL2 • Confirms LVL1 trigger • precision muon chamber and inner detector measurements in LVL1 RoI • EF • refines LVL2 selection using offline-like algorithms • full event, alignment and calibration data available hardware software E. Etzion QWG-6 December 2008

  8. η  Toroid pT of muons from different processes Muon chambers layout and curved muon tracks Level-1: muon trigger TGC (endcap) RPC (barrel) E. Etzion QWG-6

  9. B-physics trigger strategy: level-2 • B-Physics is accounted for 5 ÷ 10% of total trigger resources: it must be fast, efficient and selective • Semi-leptonic decays: di-muon final state Two Level-2 di-muon trigger algorithms: • Topological trigger Starts with a di- trigger at level-1 + confirmation at level-2 • Standalone  reconstruction • Combined  reconstruction • TrigDiMuon Starts with a single  trigger at level-1/level-2 and search for two • in a wider Region of Interest ( for low luminosity period) E. Etzion QWG-6 December 2008

  10. Tracking in Muon Spectrometer • The momentum of the muons is determined from the curvatures of their tracks in a toroidal magnetic field. • Muon tracks are identified and measured after their passage through ~2m of material. ATLAS Endcap • Track measurement with =60m intrinsic resolution in three precision measurement stations (MDT). ATLAS Barrel E. Etzion QWG-6 December 2008

  11. Tracking in the Inner Detector Pixel Detectors -The silicon sensors closest to the collision point. (Resolution: σφ=12 μm, σz=66 μm) Strip Detectors – additional layers of silicon narrow strips aimed to provide additional position measurements. (5cm<radii<50cm) Resolution :σφ=16μm,σz=580μm Transition Radiation Tracker (TRT)- collections of gas-wire drift detectors consist of 4mm-straw tubes with thin wires in the center. (50<radii<100 cm). Resolution :σ=170μm per straw . PT resolution The silicon pixel and strip detectors provide about 10 azimuthal position measurements, each with precision of 10 - 20 microns. The TRT provides about 36 azimuthal position measurements, each with precision of 150 microns. ATLAS Impact par. resolution J/ψ secondary vtx resolution E. Etzion QWG-6 December 2008

  12. Low mass sources J/ψ ATLAS Upsilon E. Etzion QWG-6 December 2008

  13. Vertex separation • ‘Pseudo-proper time’ cut of <0.2 ps gives prompt J/y efficiency of 95% with 5% contamination • Cut of >0.15 ps gives bbJ/yX efficiency of 80% with 20% prompt J/y contamination Prompt ATLAS Indirect E. Etzion QWG-6 December 2008

  14. Low mass sources (after selection) ATLAS J/ψ Upsilon E. Etzion QWG-6 December 2008

  15. J/y ¡ Reconstruction of prompt quarkonia From all m+m- pairs in J/y mass range, ~96% of generated events reconstructed Mass resolution 54 MeV. • Can reconstruct muons from Inner Detector tracks, muon spectrometer standalone, or combined muon information From all m+m- pairs in ¡ mass range, ~92% of generated events reconstructed. Mass resolution 168 MeV. With cut on Pt(mu)>10GeV + Background Corresponding to 10 pb-1

  16. Reconstructed onia transverse momentum • Studies of high pT onia production are important as the high momenta accessible by the LHC and beyond the reach of the Tevatron • Acceptance of onia is ratio of MC generated to reconstructed in each pT bin • Onia acceptance rises to a plateau at >12 GeV • Acceptance of ¡ much better at low pT’s due to mass J/y(m6m4) acceptance ¡(m6m4) acceptance Errors on simulated statistics correspond to approximately 10 days of low luminosity data-taking E. Etzion QWG-6 December 2008

  17. Onia acceptance with pseudorapidity • J/y muons produced close in DR, hence J/y distribution reflects single muon acceptance • Situation for ¡somewhat different: • ¡ have dip at central h due to decay kinematics (muon h’s themselves do not have dip) • DR broader for ¡,so smearing is greater • Reconstructed ¡’s follow MC closely – still have best acceptance in endcap region, but losses in barrel have smaller fluctuations J/y(m6m4) acceptance ¡(m6m4) acceptance

  18. Oniadecay muon angular separation ∆R DR defined as =(Dh2+Df2)1/2 • Muons from J/y have typical DR<0.5 • Effective cut-off at DR>0.6 due to J/y kinematics • In contrast, muons from ¡ are free to be produced with large separation DR differences have implications for c reconstruction and studies of hadronic activity from onia ∆R (m6m4) E. Etzion QWG-6 December 2008

  19. cdecays cc→J/Ψ+γevents • For J/y, ~30% of total cross-section from cc feed-down • For ¡, ~50% of total cross-section from cb feed-down • Interested in c decays to J/y or ¡ and a photon: low c reconstruction efficiency due to the difficulty in retrieving this photon • Preliminary studies suggest we can recover few % of those c events from reconstructed J/y’s or ¡ cc2(3556) cc1(3510) • mmg-mm invariant mass difference determines whether cc0, cc1 or cc2 was reconstructed • Currently see little defined structure, resolution can be dramatically improved by using conversions cc0(3415) g angular distribution g PT M(µµγ)-M(µµ) 19 M(MeV)

  20. Polarization definition J/Ψ rest frame • Polarizations studies were using the angular distribution of the daughter particles, m+, produced in the particle decay. • The angle, θ*, is measured with respect to the direction of the movement in the ATLAS lab frame. • The polarization parameter α, defined as • Transverse polarization a=+1refers to helicity±1. • Longitudinal (helicity0) polarization a=-1. • Un-polarized production consists of equal fractions of helicity states +1, 0 and -1, and corresponds to α= 0. J/Ψ lab direction E. Etzion QWG-6 December 2008

  21. Angulardistribution of J/Ψ decay J/Ψ rest frame J/Ψ lab direction Long Trans • One way to measure the polarization is to fit it to the weighted sum of two MC samples produced with transversally and longitudinally polarization.

  22. Polarization derivation D-is the measured sample T-is the transversally polarized content β - is the transversally polarized fraction L-is the longitudinally polarized content B-is the background sample N 1,2 - are the Normalization parameters 9-12 13-15 a of the sample was set to 0.5 12-13 Statistics of 6 fb-1 15-17 17-21 >21 E. Etzion QWG-6 December 2008

  23. cosθ*acceptance and di-muon trigger • Using di-muon trigger, both muons from J/Ψ must have relatively large pT. • => Severally affects the polarization angle distribution. • In the J/ Ψ pT range, a fraction of ~60% (m6m4 trig.) of the sample is lost. • cosθ*~0 - events where both muons have roughly equal pT. • While for cosθ*=±1 one muon’s pT should be very high compared to the second one. Originally flat (geometrical acceptation) E. Etzion QWG-6 December 2008

  24. Single muon m10 trigger to the rescue • Using a single m10 trigger: • Second muon can be reconstructed offline from track (>0.5 GeV pT) • |cos q*| ~ 1 corresponds to a configuration where one muon is fast, the other slow • Provides similar pT range of onia to m6m4 configuration • Go from a distribution in m6m4 (blue curve) to that in m10 (black curve) m6m4 m10m1 J/y ¡ • Invariant mass distributions in m10 suffer from larger, but manageable, backgrounds. E. Etzion QWG-6 December 2008

  25. ‘MEASURED’ DISTRIBUTIONS ACCEPTANCE (from Monte Carlo predictions) Combined polarization measurement 9-12 GeV 12-13 GeV 13-15 GeV ATLAS ATLAS 17-21 GeV pT>21 GeV 15-17 GeV m6m4 sample in red m10+track sample in blue E. Etzion QWG-6 December 2008

  26. E = ±0.03 E = ±0.01 E = ±0.01 Err = ±0.03 Err = ±0.03 Err = ±0.17 E = ±0.29 E = ±0.05 E = ±0.04 E = ±0.14 E = ±0.18 E = ±0.13 Err = ±0.04 Err = ±0.06 Err = ±0.04 E = ±0.05 E = ±0.06 E = ±0.09 Combined polarization measurement -II • Measured distributions from m6m4 and m10 are corrected for their individual acceptances and efficiencies • Both samples normalised to each other using overlapping high pT events • Use pre-defined acceptance mask to combine the two (now non-overlapping) datasets and make a fit to the corrected distributions (total errors shown below) • Fit polarization in bins of pT ATLAS ATLAS LONGITUDINAL AND TRANSVERSE SAMPLE UNPOLARISED SAMPLE E. Etzion QWG-6 December 2008

  27. Splash event from first LHC run E. Etzion QWG-6 December 2008

  28. LHC Problems in the inter-connects • 1/10,000 interconnects between magnets Caused the problem E. Etzion QWG-6 December 2008

  29. Millions of Cosmic ray events • Reconstruction in good shape for different magnet and detector configurations • • Conditions are continuously updated E. Etzion QWG-6 December 2008

  30. Summary - J/Ψ and ¡ in early ATLAS data • ATLAS is designed to probe the O( 1 TeV) scale but will have some useful measurements in the heavy quarks physics sector. • ATLAS is running and took (cosmic data) study trigger and tracking. • LHC Physics program is expected at summer 2009 (starting @ 10 TeV) • The Quarkonia ->m+m-- key player in the analysis of LHC early data. • Useful for event quality monitoring ,calibration and alignment. • Directly produced J/Ψ are main background to J/Ψ produced in B hadrons (key channel in the B Physics program). • Interesting to study the polarization PT dependence. • With its high PT reach, can improve the existing measurements. • The errors on J/y polarisation with 10 pb-1of data are expected to be of similar magnitude to that of Tevatron1 fb-1of data, (in the important high pT area). • Similar results can be achieved for ¡ but need 100 pb-1of data to reach same precision, due to increase backgrounds. • Its going to be interesting! E. Etzion QWG-6 December 2008

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