1 / 22

Yajun Mao ( Peking University ) for HERMES Collaboration

Yajun Mao ( Peking University ) for HERMES Collaboration. Outline. Particle Identification Search For pK S Resonance Systematic Studies Summary and Conclusions. The HERMES Spectrometer. hadron/positron separation combining signals from: TRD, calorimeter, preshower, RICH.

jesus
Download Presentation

Yajun Mao ( Peking University ) for HERMES Collaboration

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. Yajun Mao (Peking University) for HERMES Collaboration Yajun Mao, ICHEP'04, 16-22 Aug, 2004

  2. Outline Particle Identification Search For pKS Resonance Systematic Studies Summary and Conclusions Yajun Mao, ICHEP'04, 16-22 Aug, 2004

  3. The HERMES Spectrometer Yajun Mao, ICHEP'04, 16-22 Aug, 2004

  4. hadron/positron separation combining signals from: TRD, calorimeter, preshower, RICH hadron separation Dual radiator RICH forp, K, p Particle Identification Yajun Mao, ICHEP'04, 16-22 Aug, 2004

  5. Hadron identification: RICH p: 1 - 15 GeV p: 4 – 9 GeV • Lambda is well identified  protons are cleanly identified • Define appropriate event topology • Reject events fromL(1116) pp-within ±2sof ML • invariant mass calibration ± 2MeV direct reconstruction: detection of each decay particle, invariant mass reconstruction Event Reconstruction Yajun Mao, ICHEP'04, 16-22 Aug, 2004

  6. Reconstruction after all cuts Yajun Mao, ICHEP'04, 16-22 Aug, 2004

  7. add p to invariant mass Results Peak at: M= 1528 ±2.6 MeV • = 8 ± 2 MeV significance: 3.7 Yajun Mao, ICHEP'04, 16-22 Aug, 2004

  8. Peak at: 1527 ± 2.3 MeV • = 9.2 ± 2 MeV Significance: 4.3 The Signal and Its Background Combin. BG Event Mixing Known S*’s Yajun Mao, ICHEP'04, 16-22 Aug, 2004

  9. A Non-Zero Width For Q+ • Observed width FWHM: 19 – 24 MeV • Detector resolution (from MC) FWHM: 10 – 14.6 MeV • re-fit spectra with Breit-Wigner convolved with a Gaussian (fixed by MC) HERMES width: Γ = 17 ± 9 ± 3 MeV Yajun Mao, ICHEP'04, 16-22 Aug, 2004

  10. Q+Isospin • Well establishedL(1520)pK-with acceptance:1.5% • No peak structure for Q++pK+zero counts at 91% CL Q+not isotensorprobablyisoscalar Yajun Mao, ICHEP'04, 16-22 Aug, 2004

  11. hep-ex/0301020, PRL hep-ex/0304040, ? hep-ex/0307018, PRL hep-ex/0307083, PLB hep-ex/0309042, ? hep-ex/0311046, PRL Proc. Mong. Acad Sci. hep-ex/0312044, PLB hep-ex/0403011 hep-ex/0401024 hep-ex/0403044 hep-ex/0403051 hep-ex/0404003 http://na49info.cern.ch Summary of Positive Results Yajun Mao, ICHEP'04, 16-22 Aug, 2004

  12. Summary of Negative Results Yajun Mao, ICHEP'04, 16-22 Aug, 2004

  13. How Real Is The Peak? • check for • kinematical reflections • detector acceptance and cuts (PYTHIA6 MC / Toy MC) • Q+vsS*+ • is Q+a pentaquark or a previously unobservedS*+ • add a forth hadron • is the peak still there • can we guess the production process for the Q+ • can we supress background Yajun Mao, ICHEP'04, 16-22 Aug, 2004

  14. Kinematical Reflection • particle miss-identification • ghost tracks • PID “leaks” • remove L(1116) contribution Spectrum of events associated with L(1116) expect peak in M(p-p) if p+ is p and KS is L(1116) Yajun Mao, ICHEP'04, 16-22 Aug, 2004

  15. S*+ No peak in Lp+spectrum near 1530 MeV Q+vs S*+ • Is peak a newS*+or a pentaquark state • If peak is S*+⇒ also see a peak in M(Lp+) • if member of baryon octect: b.r.(Lp+)/(pKs)  3/2 • if member of decuplet: ~3/2 (M. Polyakov) Yajun Mao, ICHEP'04, 16-22 Aug, 2004

  16. The Mass Spectrum • relatively large BG, although good PID for proton and KS • what if we require one additional hadron? • could additional hadron help remove KS from other process? Yajun Mao, ICHEP'04, 16-22 Aug, 2004

  17. Requiring 4th HadronAsp Black requires 4th hadron (all species) only p Red specifies 4th hadron asp K & p Green specifies 4th hadron as notp Yajun Mao, ICHEP'04, 16-22 Aug, 2004

  18. high statistics K* Why Does Additional p Help? • remove • remove add new cut: |M(KSp)-892|<75 MeV Yajun Mao, ICHEP'04, 16-22 Aug, 2004

  19. standard cuts applied + K* veto +L veto • signal/noise: from 1:3 to 2:1  background is greatly reduced Mass Spectrum After Removing K* Yajun Mao, ICHEP'04, 16-22 Aug, 2004

  20. Production Process At HERMES can 4th hadron come from exclusive processes? associated K- or KS from exclusive processes goes backward • even decay pions from KS are inaccessible • PID threshold requires p(Q+) > 7 GeV tagged pions events can’t come from these exclusive processes  production process has to be at least partially inclusive • inclusive processes increase with higher energy • exclusive processes decrease with higher energy Yajun Mao, ICHEP'04, 16-22 Aug, 2004

  21. Direct reconstruction ofQ+invariant mass Mass: Intrinsic Width: Significance:~ 4s Q+is probably an isosinglet Requiring additional p improves signal/background, it eliminates KS contamination from various processes Production process is at least partially inclusive Anticipate doubling statistics by end of this summer Will soon report on X--search and Q+ from TOF (low p) HERMES Conclusions and Outlook Yajun Mao, ICHEP'04, 16-22 Aug, 2004

  22. Detector Mass Calibration HERMES Mass[MeV]496.8±0.2 1115.70±0.01 1522.7±1.9 1321.5 ±0.3 PDG Mass[MeV]497.67 1115.68 1519.5±1.0 1321.31±0.13 s width (data)[MeV] 6.2±0.2 2.6±0.1 4.4±3.7 3.1 ±0.3 s width (MC)[MeV]5.4 2.1 3.5 2.5 Decay Pcm[MeV/c]206 101 244 139(Lp-) HERMES can precisely measure the above known particles The MC well reproduce the data The systematic error estimated is about 1.9MeV Yajun Mao, ICHEP'04, 16-22 Aug, 2004

More Related