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Particle Identification and Reconstruction in HERMES Spectrometer

This paper discusses the particle identification and reconstruction techniques used in the HERMES spectrometer, specifically focusing on the detection and reconstruction of Q+ particles. The results of the analysis, including signal widths and significance, are presented along with a comparison to world data. The conclusion highlights the need for continued data taking with high density unpolarized targets.

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Particle Identification and Reconstruction in HERMES Spectrometer

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  1. The Q+search at E.C. Aschenauer DESY on behalf of the HERMES Collaboration DIS 2004

  2. The HERMES Spectrometer Internal Gas Target: unpol: H2,D2,He,N,Ne,Kr, Xe Kinematic Range: 0.02 < x < 0.8 at Q2 > 1 GeV2 and W > 2 GeV Reconstruction:Dp/p < 2%, Dq < 0.6 mrad Particle ID:TRD, Preshower,Calorimeter a1997: Cherenkov, 1998a: RICH + Muon-ID DIS 2004

  3. Particle Identification hadron/positron separation combining signals from: TRD, calorimeter, preshower, RICH hadron separation Dual radiator RICH forp,K, p DIS 2004

  4. Particle Reconstruction • Define appropriate event topology • Invariant Mass calibration ± 2MeV direct reconstruction: detection of each decay particle, invariant mass reconstruction • Hadron identification: RICH • p: 1 - 15 GeV p: 4 – 9 GeV • Suppress contamination from • L(1116) a pp- DIS 2004

  5. Results after all cuts • Peak at: • 1528 ±2.6 MeV • = 8 ± 2 MeV Significance: 3.7 add p to invariant mass DIS 2004

  6. The signal width • Q+ Monte Carlo with complete • detector simulation generated: M=1450 MeV , s=2 MeV reconstructed: M=1450 MeV , s=7 MeV DIS 2004

  7. The signal and its background • Peak at: • 1527 ±2.3 MeV • = 9.2 ± 2 MeV Significance: 4.3 Mixedevent background excited S* hyperons (not included in Pythia6) PYTHIA DIS 2004

  8. Is there a Q++ • Clear Signal for • L(1520) a pK- • No Signal for • Q++a pK+ • Q+ isoscalar DIS 2004

  9. Comparison with World Data Kn Mean: DIS 2004

  10. Conclusion and Outlook • Direct reconstruction ofQ+ invariant mass • Mass: • FWHM-Resolution: • Significance:~ 4 s • Q+ is probably an isosinglet • Continue data taking with high density unpolarised • targets DIS 2004

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