COMPASS experiment Status and reacent results

Transcription

1 COMPASS experiment Status and reacent results Ewa Rondio, Institute for Nuclear Studies, Warsaw, Poland Brookhaven, 3 May 2005

2 The COMPASS Collaboration (230 Physicists from 12 Countries) Dubna (LPP and LNP), Moscow (INR, LPI, State University), Protvino CERN Bielefeld, Bochum, Bonn (ISKP & PI), Erlangen, Freiburg, Heidelberg, Mainz, München (LMU & TU) Warsaw (SINS), Warsaw (TU), Warsaw (UW) Prag Helsinki Nagoya Saclay Torino(University,INFN) Trieste(University,INFN) Lisboa Burdwan, Calcutta Tel Aviv

3 COMPASS: THE new fixed target facility at CERN! COmmon Muon and Proton Apparatus for Structure and Spectroscopy. - HISTORY 1996 COMPASS proposal 1997 conditional approval 1998 MoU construction & installation 2001 technical run 2002, 2003, 2004 data taking 2005 break at Cern (LHC) Restart in 2006 at least until June 1998 Now 8. April

4 Physics Goals Contribute to the understanding of the non-perturbative physics of the nucleon nucleon spin structure nucleon spectroscopy Gluon Polarization G/G transverse spin structure function h 1 (x) Flavor dependent polarized quark helicity densities q(x) spin dependent fragmentation functions D Λ Exclusive VM-Production q Primakoff-Reactions - polarizability of π and K glue balls and hybrids charmed mesons and baryons - semi-leptonic decays - double-charmed baryons

5 LHC COMPASS SPS

6 The COMPASS Experiment Beam: µ + / spill (4.8s / 16.2s) Beam momentum: 160 GeV/c Luminosity: ~ cm -2 s -1 Beam polarization: -76%

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

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9 New detector technologies Trigger-System MicroMegas Straws Readout electronics calorimeter readout Scintillating fiber trackers GEM

10 Ring Imaging CHerenkov Single event 116 VUV mirrors, surface area: 21 m 2 erenkov Counter (RICH) 3 m vessel 6 m photon detectors: CsI MWPC mirror wall 5 m radiator: C 4 F 10 Photon detection 5.3 m 2 MWPCs 16 CsI Photocathodes 84,000 analog readout channels single detection photon: of θ>1.2 mrad ring: VUV photons θ>0.4 mrad ( nm) photons/ring n ~14 π/k sep. up to 40 GeV/c

11 hadron identification By RICH p Κ π and hadron calorimeters θ(mrad (mrad) p(gev/c) Κ hadrons π p e,µ

12 COMPASS two programs with muon beam Muons: data taking from > > 2004 will continue in 2006 Main goal with hadron beam Hadrons: pilot run in 2004 G G

13 The Primakoff reaction π, p 1 π, p 1 π + Z π + Z + γ s 1 = ( p 1 -k ) 2 first data taken in 2004 expected ~30k events γ*, k Z, p 2 Z, p 2 θ γ, k 3 2 d σ α f Z = dtdωd cosϑ πω dσ πγ ( ω, ϑ ) d cos ϑ t t 2 t 0 dσ πγ ( ω, ϑ) d cosϑ F A ( t) 2 t= ( p 2 p 2 ) 2 Electric & Magnetic polarizability πα f Th mπ ω α π (1 + cos ϑ ) + 2β π cos ϑ = F + 2 πγ 3 mπ α f ω 1 + (1 cos ϑ ) mπ

14 Muon program : data ongoing analysis A d 1 and influence on QCD fit D o and D o * for G/G from open charm G/G from high p T sample: perturbative region (Q 2 >1GeV 2 ) and photoproduction region (Q 2 <1GeV 2 ) Transversity studies (Collins and Sivers asymmetries) for single and two hadrons and hyperon production Vector mesons Search for pentaquarks In this talk results with longitudinal target polarization

15 Kinematic range covered Excellent for non-perturbative & perturbative physics small x Bj very small Q 2 Q 2 > 100 (GeV/c) 2

16 polarized 6 LiD target 4 possible spin combinations: 3 He 4 He Dilution refrigerator (T~50mK) superconductive Solenoid (2.5 T) Dipole (0.5 T) 1 2 reversed every 8 hours or: two 60 cm long Target-Containers with opposite polarization 3 4 reversed once a week Polarization: ~ 50%

17 Asymmetry A 1

18 Asymmetry can be calculated for combinations without expected effect (false asymmetry) or where spin effect is expected (A 1 ) A measurement of A d 1 also test of the detector and of systematic effects controle 1 1 Nu Nd N u N d = 2 PP t b fd Nu + Nd N u + N d PLB 612, 154 (2005) False asymmetries (combining configurations with the same spin orientation) Asymmetry for configuration With opposite spins - Spin effects expected Weighting with fdp t was used to optimize statistical accuracy

19 DOUBLE SPIN ASYMMETRY A d 1 COMPASS: data 34 Million DIS events Q 2 > 1 (GeV/c) < y < 0.9 more to come ftom 2004 Data displayed at experimental <Q 2 > of every x Bj bin

20 QCD fit with all DIS spin data, effect of Compass A D 1

21 NLO evolution, calculations on grid (x,q 2 ) MS scheme, χ 2 minimization using Minuit 10 parameters fitted NDF : Χ 2 probability 14%

22 Compass g d 1 and it s influence on the QCD fit Q 2 = 4GeV 2 MS scheme Σ = Σ = with Compass new deuterium g 1 data without

23 Semi-inclusive inclusive asymmetries also avalaiable Improvement at low x, consistent with SMC

24 G/G at COMPASS N Photon Gluon Fusion q = c cross section difference in charmed meson production theory well understood experiment challenging q= = u,d,s cross section difference in 2+1 jet production in COMPASS: events with 2 hadrons with high p T experimentaly easier theory difficult

25 G/G: OPEN CHARM A cc γn = σ σ γn ccx γn ccx = dsˆ σ dsˆ σ PGF PGF ( sˆ) G( x ( sˆ) G( x G G, sˆ), sˆ) a LL G G ˆ 2 s = M cc σ PGF at NLO: Bojak, Stratmann NPB 540 (1999) 345; Contogouris et al. Photon-Gluon Fusion c D 0 K π + (BR 4 %) c D D * + D 0 π + ( + ) + K π π N A raw N N cc cc = N cc + N cc = P µ P T f D A cc γn P µ P T 0.5 f 0.4 D(y )

26 Comparison with 2002 data Flux/#days µ/38.6 days D* D*/Flux D 0 D 0 /Flux 2002 P1I+J/ ± ± Gain µ/13.7 days ± ± ± ±0.2 S/B 0.78± ± ±0.2 Bckgrd Bckgrd/Flux Known factors: - Beam rec.: 1.05 (JMLG) - Trigger: DAQ: Pack. Fact: And about the RICH ( ) ε: 52 ± 9 67 ± ± 0.3 p: 60 ± ± ± 0.3

27 D* tagging: : D* D 0 π D ( Kπ )π D 0 Kπ M Kππ s -M Kπ -m π [MeV/c2 ] Cut on D* Cuts: 80% 2002 data z D > 0.2 cos θ* < D (Background) 0 10 < p K < 35 GeV (RICH PID) D 0 Kπ M Kπ -m D 0 [MeV/c 2 ] M Kπ -m D 0 [MeV/c 2 ] M Kππ s -M Kπ -m π [MeV/c2 ]

28 Asymmetry for events with charm production (D 0 and D * ) D* is cleaner,, but low statistics From here to G/G partonic asymmetrirs PGF are needed a PGF LL

29 Partonic asymmetries are calculated from parametrization obtained for MC simulated events good description of data with MC is required what MC parameters are best Result on G/G can be expected soon from : σ( G/G) = 0.24 from open charm

30 Hadron pairs with z large large p T Idea proposed by R.D.Carlitz, J.C.Collins and A.H.Mueller, Phys.Lett.B 214, 229 (1988). A.Bravar,D.von Harrach and A.Kotzinian, Phys.Lett.B 421, 349 (1998). Used in the analysis : HERMES, A.Airapetian et al., Phys.Rev.Lett.84, 2584 (2000). SMC, B.Adeva et al., Phys.Rev.D 70, (2004)

31 A ln lhhx = G G q q a a LL LL LP PGF R R LP PGF + + a LL QCDC R QCDC where: A ln lhhx measured asymmetry, q/q approximated using A 1 asymmetry γn, <a LL > partonic asymmetry, R fraction of contributing processes

32 G/G: pairs of high p T hadrons Photon Gluon Fusion h 1 h 2 N Current fragmentation x F > 0.1 z > high p T hadrons p T > 0.7 GeV/c p T12 + p T22 > 2.5 GeV 2 m(h 1 h 2 ) > 1.5 GeV

33 G/G: pairs of high p T hadrons with Q2 >1 GeV 2, 0.4 < y < 0.9 hh A Asymmetry in production of hadron pairs with high p T : result for data ( stat) 0.013( syst) D = ± ± from this using R PGF obtained from MC G = 0.06 ± 0.31 ± 0.06 with η = 0.13 G Analysis done with LEPTO generator Initial and final state parton showers used Fragmentation function parameters modified k statndard value (0.44) Uses only ~10% of data

34 For Q 2 <1GeV 2 much more data difficulties with additional processes contributing (Pythia) A ( stat) 0.003( syst) D = ± ±

35 Low Q 2 scattering Pythia simulation Contributing processes - sample after high p T selections A LL = LO R PGF a PGF LL qqcd q qq q + RqQCD all + Rq q all q q ( neglected ) R ( neglected ) + R + G G lowp T signal background Contribution from the the structure of of the the nucleon photon

36 Systematic errors : Quark polarization in the photon γ γ γ qq VMD q = q + q for VMD minimum and maximum scenarios q q q γ γ γ VMD VMD VMD

37 MC uncertainties Missing NLO: NLO: scale dependence, parton shower on/off off tuning of parameters and data/mc parton fragmentation partons k T in nucleon and photon biggest uncertainty from k T in photon

38 Data/MC

39 From 2002 and 2003 data G = ± 0.089( stat) ± 0.057( syst) G Obtained by averaging results for min. and max scenario in VDM

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41 Single hadons, low Q 2

42 Expected precission on the asymmetry teoretical calculations by B. Jaeger,, A. Schaefer and M. Stratmann in NLO

43 SUMMARY AND OUTLOOK CERN is again contributing to the NUCLEON SPIN PUZZLE Compass running in brought interesting PHYSICS RESULTS, some already published MANY MORE IN PREPARATIONP data taking restarts in 2006 Approved program untill ~2010 with muon beams on polarized targets and hadron beams After study study of GPDS with DVCS and exclusive mezon production on hydrogen target (+recoil detector)