1 / 25

B and onia prodution in ATLAS

B and onia prodution in ATLAS. Else Lytken (CERN) On behalf of the ATLAS collaboration HERA-LHC workshop May 2008. B and onia production in ATLAS. _. Take advantage of copious bb production at 14 TeV: (bb) ~500 b. ¯. Measure cross sections at new energy

yeriel
Download Presentation

B and onia prodution in ATLAS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. B and onia prodution in ATLAS Else Lytken (CERN) On behalf of the ATLAS collaboration HERA-LHC workshop May 2008

  2. B and onia production in ATLAS _ Take advantage of copious bb production at 14 TeV: (bb) ~500 b ¯ • Measure cross sections at new energy • , d/dpT, d/d(), d/d • B physics a window for new discoveries • Observe rare decays, measure CP violation parameters • Detailed understanding of the bb spectrum as background to other processes. • Commissioning/early physics: calibration, alignment, trigger efficiencies etc. ¯ Overlap E. Lytken (ATLAS Collaboration) HERA-LHC workshop May 2008

  3. Early physics with b’s and onia • Focus of this talk is on the measurements during commissioning phase/early physics: Linst = 1031 – 1032 cm-2s-1 Production of B’s and the quarkonia narrow resonances gives us a handle for first performance measurements complementary to and extending other SM “standard candles” such as W’s and Z’s. • For instance crucial for Higgs and SUSY searches to understand our performance with lower pT leptons • Lower luminosities means lower pT trigger thresholds possible, both for electrons and muons • Given the high rates our trigger menus have the flexibility to account for different luminosity scenarios E. Lytken (ATLAS Collaboration) HERA-LHC workshop May 2008

  4. ~1-2 kHz ~200 Hz Initial triggers: relevant examples For initial low luminosities can trigger on both low pT electrons and muons. Expected L1 rates and prescale factors:  2.5 s L=1031 L=1032  40 ms  4 s L2: confirm L1 signal + additional search in regions of interest EF: offline algorithms for final selection E. Lytken (ATLAS Collaboration) HERA-LHC workshop May 2008

  5. Inclusive b production cross section: +b-jet btrig=13.5% brec= 85% fb found from fitting transverse relative pT to templates: ATLAS With 15 pb-1 such a fit gives us: fbackgr= 77 ±4 % (c; ,K ) fb = 23 ± 2 % (b ; bc ) Transverse relative pT (GeV) E. Lytken (ATLAS Collaboration) HERA-LHC workshop May 2008

  6. Inclusive cross section: dimuons _ To distinguish bb  J/ X (indirect J/) from ppJ/ (prompt J/’s, ~ 2 ) Useful variable: the (pseudo-) proper time: Lxy = transverse decay length E. Lytken (ATLAS Collaboration) HERA-LHC workshop May 2008

  7. B measurements using excl. channels • Due to high cross sections and dedicated triggers we can reconstruct exclusive channels in early data • Reconstruction of the mass and lifetime of the B± meson from B± J/ K± decay very useful for calibration and alignment performance. • Requirements: • - dimuon trigger • displaced vertex (100 μm) • add. track with pT1.5 GeV • track and μμ fit to same vertex • m(μμ,track) within 120 MeV of B+ mass. ATLAS Results with 10 pb-1: (mB+) = 42.2 ± 1.3 MeV (total) = 29.8 ± 0.84 % E. Lytken (ATLAS Collaboration) HERA-LHC workshop May 2008

  8. B cross section with excl. channels Measurement of dB/pT using B+J/ K+ after 10 pb-1: (GeV) Acceptance + stat. (%) Total uncertainty (%) Available statisitics with 100 pb-1: E. Lytken (ATLAS Collaboration) HERA-LHC workshop May 2008

  9. NRQCD Quarkonia J/ • Among first measurements + theoretical interest: What is the production mechanism? • The Color Octet Mechanism agrees well with measured  shape from Tevatron Polarization measurements: CDF sees no sign of pol. for J/, and DØ (1S) measurements not consistent with predictions. More data with high-pT needed!  Tevatron data Color octet Color singlet (1s) kT factorization model E. Lytken (ATLAS Collaboration) HERA-LHC workshop May 2008

  10. Min bias ppJ/(ee) pp(ee)(1S) ppDrell-Yan(ee) Quarkonia in ATLAS: J/  e+e- Initial data: take advantage of electron trigger paths as well Current studies using 2EM3 Single-e triggers under investigation Later data (“low luminosity”, L=1033cm-2s-1) has to rely on single-μ b trigger also for J/(ee)X, (ee)X @ L1 trigger 1031 cm-2s-1 L1 (trig) ~ 27% L2, EF under optimization E. Lytken (ATLAS Collaboration) HERA-LHC workshop May 2008

  11. J/  e+e- N = # good pion tracks Ne = same + misid. as e’s R = N / Ne Two electron id methods explored: • Low pT version of standard ATLAS isolated electron cut based on shower shapes, associated to high quality tracks with E/p >0.7, conversion veto, and transition radiation hits • Less efficient for electrons from b’s  2nd method (pT 2 GeV/c) extrapolates in narrow window to calorimeter and uses likelihood ratio (similar variables) “b-electrons” After offline selection 100 pb-1: ~230k J/’s and ~43k ’s Expect to measure m(J/) to ~0.6% d/dm (nb/0.5GeV) L1 + offline selection E. Lytken (ATLAS Collaboration) HERA-LHC workshop May 2008 Mee (GeV)

  12. J/  μ+μ- L1 combined L2 combined • Current studies use a combination dimuon trigger, (trig) = 87% L1, 97% L2, with analysis cuts of 6 and 4 GeV • Rate  1 Hz expected at EF for all quarkonium  μμ (incl ’, (2,3S) ) 10 J/ J/ E. Lytken (ATLAS Collaboration) HERA-LHC workshop May 2008

  13. Dimuons: Results Require: muons from same vertex and proper time < 0.2 ps With pT1  6 GeV, pT2 4 GeV: 15k J/’s per 1 pb-1 2.5k ’s (1S) 1-2 days with L = 1031cm-2s-1 Bkg w/o vertex cuts With 10 pb-1: S/B = 60 for J/ and 10 for  d/dpT ~ 1 % for J/ , ~5 % for  10 pb-1: also measurement of c J/()  ~ 1 fb-1: b ()  E. Lytken (ATLAS Collaboration) HERA-LHC workshop May 2008

  14. P(-) P(J/) * P(+) Polarization Measure high-pT polarization to distinguish production models 10+t ATLAS 64 Dimuon triggers: little or no information for high cos* Single-: combined with  0.5 GeV track gives access to these values (~ pT range but larger pT(+,-) ) Single-u trigger => larger background Still: S/B = 1.2 (J/) and 0.05 (Upsilon) x103 Long. pol. ( = -1) Combine and fit to measured distribution in slices of pT Shown: 12  pT 13 GeV Trvs. pol. ( = +1) E. Lytken (ATLAS Collaboration) HERA-LHC workshop May 2008

  15. * = ATLAS ~10 pb-1 * = ATLAS ~10 pb-1 J/ 0.8 fb-1 * * * * * * * * NRQCD * * Polarization results Already with 10 pb-1: measure J/ pol. to same precision as TeV with 1.3 fb-1 - but with interesting high pT data! Same precision for  polarization studies can be reached after ~100 pb-1 Crude superimpose of ATLAS stat uncertainties with 10 pb-1 assuming =0 : E. Lytken (ATLAS Collaboration) HERA-LHC workshop May 2008

  16. Quarkonia as a monitoring tool Perfect alignment • Offline and online monitoring with J/’s and ’s important to have a low pT data point in addition to Z’s • Given the large statistics expected should be able to use this already in the beginning • Check mass shift as a function of • pT: momentum scale, energy loss • curvature diff: detector misalignments •  and : magnetic field, material effects 6 pb-1 1 week w. L=1031 Example of identifying a problem E. Lytken (ATLAS Collaboration) HERA-LHC workshop May 2008

  17. Summary and outlook • ATLAS well prepared for B and quarkonia cross section measurements in initial low luminosity period • Early data studies will also help us during commissioning • For cross section measurements already enough statistics with the early data! (10 pb-1 or less) • Key measurements based on muon triggers but in initial period will also have electron channels for comparison • Stay tuned for the next chapter in J/ and Upsilon high-pT polarization measurements! E. Lytken (ATLAS Collaboration) HERA-LHC workshop May 2008

  18. Backup

  19. Single-muon trigger: S/B Most relevant for J/ studies …    E. Lytken (ATLAS Collaboration) HERA-LHC workshop May 2008

  20. Polarization measurement E. Lytken (ATLAS Collaboration) HERA-LHC workshop May 2008

  21. More on polarization Resolution of reconstructed cos* is ~0.0015 J/  Combined measurement Unpolarized 17<pT <21 GeV E. Lytken (ATLAS Collaboration) HERA-LHC workshop May 2008

  22. Acceptance pT cuts (trigger and offline) means pT(J/)  10 GeV, whereas non-zero A for Upsilons also at ~0 RoI’s based on trigger towers of  x  ~ 0.1 x 0.1 R separation between leptons also affects sensitivity to material effects J/ Upsilon (6,4)-cuts E. Lytken (ATLAS Collaboration) HERA-LHC workshop May 2008

  23. Electron efficiencies “standard cuts” “b electrons” Efficiency of single electrons based on MC truth (EM3:e5;e5) E. Lytken (ATLAS Collaboration) HERA-LHC workshop May 2008

  24. Inclusive b production After fit E. Lytken (ATLAS Collaboration) HERA-LHC workshop May 2008

  25. The 3 production mechanisms LO: Flavour creation NLO: Gluon splitting NLO: Flavour excitation, sensitive to PDF’s E. Lytken (ATLAS Collaboration) HERA-LHC workshop May 2008

More Related