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The COMPASS Experiment at CERN

The COMPASS Experiment at CERN. Horst Fischer University Freiburg. The COMPASS Experiment First look on the data Vertex reconstruction Hadron identification Outlook. COMPASS Physics Objectives. COMPASS should rather be seen as a facility and not as a single experiment.

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The COMPASS Experiment at CERN

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  1. The COMPASS Experiment at CERN HorstFischer University Freiburg • The COMPASS Experiment • First look on the data • Vertex reconstruction • Hadron identification • Outlook

  2. COMPASS Physics Objectives COMPASS should rather be seen as a facility and not as a single experiment Nucleon Spin Structure • Gluon polarization G(x)/G • Flavour-dependent helicity functions q(x) • Transverse-spin distribution functions Tq(x) • Spin-dependent fragmentation (D q) Nucleon Spectroscopy • Primakoff reactions • Polarizability of  and K • Glueballs and hybrids • Charmed mesons and baryons • Semileptonic decays • Double-charmed baryons

  3. Measurement of the Gluon Polarization • Direct measurement of DG/G: • Photon-Gluon-Fusion: • Production of open charm • Events with two jets Event Signature: • Beam and scattered Muon • Production of D0 or D* • or Measure cross-section asymmetry

  4. The COMPASS Experiment Beam:160 GeV µ+ 2.8. 108 µ/spill (4.8s/16.2s) Muon filter 2 MWPCs ECal2 & Hcal2 ~50m SM2 Muon filter 1 ECal1 & Hcal1 RICH GEM & MWPCs SciFi SM1 GEM & MWPCs Silicon SciFi Scintillating fibers • Polarization: • Beam: -76% • Target: max. 57% GEM & Straws Micromegas &Drift chambers Polarized target

  5. The Experiment in the hall(upstream)

  6. The Experiment in the hall (downstream)

  7. The COMPASS Polarized Target • Dynamic Nuclear Polarization • Dilution factor: ~50% • Maximum Polarization: • – 49% + 57% • Spin relaxation time: • Longitudinal spin (2.5 T): too long to be measured • Transverse spin (0.5 T): >1000 hours 3He – 4He dilution refrigerator (T~50mK)

  8. RICH-1 Photon detectors: MWPCs with CsI photocathodes, 5.3 m2 + 84,000 ch analog read-out an event from on-line display VUV mirror wall, 21 m2, 116 mirrors

  9. And that is what comes out: The typical event

  10. Kinematic Range accessible with the Present Setup • Statistics: • Targetlongitudinal: • 57 days, 173k spills • Target transverse: • 19 days, 52k spills • ~22k triggers/spill • Total: 5 Gev (3.8Gev, 1.2Gev) • Expectations: • 29000 D0 and 3800 D* • inside cuts@ 100% reconstruction efficiency • ALL plots are preliminary!

  11. Vertex Reconstruction Data (2002) Monte Carlo

  12. Hadron Identification By the RICH… …and by hadronic sampling calorimeters K B, : hadrons p K e, :

  13. Hadron reconstruction without and with RICH 2 hadrons Decay: NK+ K- one or two Kaons identified in RICH both Kaons identified in RICH Kaon identification

  14. K *(892) K*  K0  p(K*) > 15GeV/c m(K*) – PDG [MeV] m(K*) – PDG [MeV] COMPASS: N(K*+) > N(K*-)

  15. 7 7 Reconstruction of and • expected from 2002 run: • : 58k • Q2>1: 46k • ~ 1 / 2 7 7 7 K0 7 7

  16. Outlook • Successful reconstruction of K0, 7, N and K* demonstrates the functioning of spectrometer and software  Now we are attacking the D0 and D* • Need to increase the statistics on DST level and improve the calibration-data grid • COMPASS is part of the long range planning of CERN (2010)

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