QCD和輕強(qiáng)子暑期班

1、2022-3-16Weilin Yu QCD和輕強(qiáng)子暑期班1 2022-3-16Weilin Yu QCD和輕強(qiáng)子暑期班2OutlineParticle IdentificationSearch For pKS ResonanceSystematic StudiesSummary and Conclusions2022-3-16Weilin Yu QCD和輕強(qiáng)子暑期班3The HERMES Experiment2022-3-16Weilin Yu QCD和輕強(qiáng)子暑期班4The HERMES SpectrometerBeam: 27.6 GeV e+/e- from HERA accelerat

2、orTrack reconstruction: Dp/p 2%, Dq 0.6 mradParticle ID: TRD, Preshower, Calorimeter (hadron/lepton sep.) dual radiator RICH (p p, K, p separation)2022-3-16Weilin Yu QCD和輕強(qiáng)子暑期班5Particle Identificationhadron/positron separationcombining signals from: hadron separationDual radiator RICH for p p, K, p2

3、022-3-16Weilin Yu QCD和輕強(qiáng)子暑期班6Decay Mode:Q+ Ks p or K+nComposed of 4 quarks and one antiquarks . Has strangeness S=+1 .Allowed by the Standard Quark Model. What is a Pentaquark Q+2022-3-16Weilin Yu QCD和輕強(qiáng)子暑期班7 Q+0Se +D+XpK+X Define appropriate event topology Hadron identification: RICH p p: 1 - 15 Ge

4、V p: 4 9 GeV Lambda is well identified protons are cleanly identified Reject events from L L(1116) pp p- - within 2s of ML L invariant mass calibration 1.9MeVdirect reconstruction: detection of each decay particle, invariant mass reconstructionEvent Reconstruction2022-3-16Weilin Yu QCD和輕強(qiáng)子暑期班8Identi

5、fication0SKafter all cuts2022-3-16Weilin Yu QCD和輕強(qiáng)子暑期班9ResultsUnbinned fit is used: result independent of bin size and starting pointPeak at:M= 1528 2.6 MeVs= 8 2 MeVSignificance: 3.72022-3-16Weilin Yu QCD和輕強(qiáng)子暑期班10The Signal and its BackgroundPeak at:1527 2.3 MeVs= 9.2 2 MeVSignificance: 4.3PYTHIA6m

6、ixed event backgroundKnown S*s (excluded in Pythia6)2022-3-16Weilin Yu QCD和輕強(qiáng)子暑期班11 Observed width FWHM: 19 24 MeV Detector resolution (from MC) FWHM: 10 14.6 MeV re-fit spectra with Breit-Wigner convoluted with a Gaussian (fixed by MC) HERMES intrinsic width: = 17 9 3 MeVA Non-Zero Width for Q+?202

7、2-3-16Weilin Yu QCD和輕強(qiáng)子暑期班12 Well established L(1520) pK- - with acceptance:1.5% No peak structure for Q Q+ pK+ + zero counts at 91% CL Q Q+ not isotensor probably isoscalarQ+ Isospin2022-3-16Weilin Yu QCD和輕強(qiáng)子暑期班13hep-ex/0301020, PRLhep-ex/0304040, ?http:/na49info.cern.chhep-ex/0404003hep-ex/0403051

8、hep-ex/0403044hep-ex/0401024hep-ex/0403011hep-ex/0312044, PLBProc. Mong. Acad Sci.hep-ex/0307018, PRLhep-ex/0311046, PRLhep-ex/0307083, PLBhep-ex/0309042, ?Summary of Positive Results2022-3-16Weilin Yu QCD和輕強(qiáng)子暑期班14Summary of Null Results0 null results published, only 3 on arXiv so far (7-18-04) need

9、 null results to be published2022-3-16Weilin Yu QCD和輕強(qiáng)子暑期班15 check for kinematical reflections detector acceptance and cuts (PYTHIA6 MC / Toy MC) Q Q+ + vs S S* *+ + is Q Q+ + a pentaquark or a previously unobserved S*+ add a forth hadron is the peak still there can we guess the production process f

10、or the Q+ can we supress backgroundHow real is the Peak?2022-3-16Weilin Yu QCD和輕強(qiáng)子暑期班16 particle miss-identification ghost tracks PID “l(fā)eaks”expect peak in M(p p- -p)if p p+ + is p and KS is L(1116)Spectrum of events associated with L(1116) remove L(1116) contributionKinematical Reflection2022-3-16W

11、eilin Yu QCD和輕強(qiáng)子暑期班17 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?The Mass Spectrum2022-3-16Weilin Yu QCD和輕強(qiáng)子暑期班18Green specifies 4th hadron as not pRed specifies 4th hadron as pBlack req

12、uires 4th hadron (all species)Mass Spectrum after requiring4th hadron as p ponly pK & p2022-3-16Weilin Yu QCD和輕強(qiáng)子暑期班19 remove remove add new cut: |M(KSp)-892|75 MeV 00LSppK K p*0()Sp KpKpWhy does additional p p help?high statistics K*pp p+-2022-3-16Weilin Yu QCD和輕強(qiáng)子暑期班20 standard cuts applied +

13、K* veto + L veto background is greatly reduced signal/noise: from 1:3 to 2:1Mass Spectrum After Removing K*2022-3-16Weilin Yu QCD和輕強(qiáng)子暑期班21 Direct reconstruction of Q Q+ invariant mass Mass: Intrinsic Width: Significance: 4 s s Q Q+ is probably an isosinglet Requiring additional p improves signal/bac

14、kground, it eliminates KS contamination from various processes Anticipate doubling statistics this year Will soon report on X- search and Q Q+ + from TOF (low p)0seDXK p+X+ + Q Q + +15282.6()2.1()statsystM MeV1793 MeV+ +Q Q Conclusions and Outlook2022-3-16Weilin Yu QCD和輕強(qiáng)子暑期班22HERMES MassMeV 496.80.2 1115.700.01 1522.71.9 1321.5 0.3 PDG MassMeV 497.67 1115.68 1519.51.0 1321.310.13s s width (data)MeV 6.20.2 2.60.1 4.43.7 3.1 0.3s s width (MC)MeV 5.4 2.1 3.5 2.5 Decay P