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

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

1996 COMPASS proposal 1997 conditional approval 1998 MoU 1999 – 2001 construction & installation 2001 technical run 2002, 2003, 2004 data taking 2005 break at Cern (LHC) Restart in 2006 at least until 2010 at least until 2010 COMPASS: THE new fixed target facility at CERN ! COmmon Muon and Proton Apparatus for Structure and Spectroscopy. - HISTORY 8. April June 1998 Now  2004

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

COMPASS SPS LHC

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

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

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

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

p(GeV/c)  (mrad) …and hadron calorimeters  p hadrons e,μe,μ p   By RICH hadron identification hadron identification 

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

The Primakoff reaction  + Z   ’ + Z +  , p 1  ’, p 1 ’ s 1 = ( p 1 ’ - k’ ) 2 , k’  *, k Z, p 2 Z, p 2 ’ t = ( p 2 ’ – p 2 ) 2 Electric & Magnetic polarizability  first data taken in 2004 expected ~30k events

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

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

4 possible spin combinations: 1 2 reversed every 8 hours Polarization: ~ 50% reversed once a week 3 4 or: polarized 6 LiD target

Asymmetry A 1

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

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

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

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

Compass g 1 d and it’s influence on the QCD fit with Compass new deuterium g 1 data without scheme

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

 G/G at COMPASS Photon Gluon Fusion N 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 → experimentaly easier → theory difficult

 G/G: OPEN CHARM  PGF at NLO: Bojak, Stratmann NPB 540 (1999) 345; Contogouris et al. N D Photon-Gluon Fusion

Comparison with 2002 data 2002P1I+J/2003Gain Flux/#days 1.70·10 13  /38.6 days 9.58·10 12  /13.7 days 1.8 D*D*/Flux 281± · ± · ±0.2 D 0 D 0 /Flux 1587± · ± · ±0.2 S/B 0.78± ± ±0.2 BckgrdBckgrd/Flux · · And about the RICH (…)  : 52 ± 9 67 ± ± 0.3 p: 60 ± ± ± 0.3 Known factors: - Beam rec.: 1.05 (JMLG) - Trigger: DAQ: Pack. Fact:

D* tagging: D* → D 0  M K  s -M K  -m  [MeV/c 2 ] M K  -m D 0 [MeV/c 2 ] Cuts: z D > 0.2 |cos  *| < 0.85 (Background) 10 < p K < 35 GeV (RICH PID) Cut on D* M K  -m D 0 [MeV/c 2 ] 317 D 0 80% 2002 data M K  s -M K  -m  [MeV/c 2 ]

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

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 ΔG/G can be expected soon from :  (  G/G) = 0.24 from open charm

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

where: A lN  lhhX measured asymmetry, Δq/q approximated using A 1 asymmetry  N,  a LL  partonic asymmetry, R fraction of contributing processes

 G/G: pairs of high p T hadrons Current fragmentation Current fragmentation –x F > 0.1 –z > high p T hadrons 2 high p T hadrons –p T > 0.7 GeV/c –p T1 2 + p T2 2 > 2.5 GeV 2 –m(h 1 h 2 ) > 1.5 GeV Photon Gluon Fusion h1h1 h2h2 N

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

For Q 2 <1GeV 2 much more data difficulties with additional processes contributing (Pythia)

Low Q 2 scattering – Pythia simulation Contributing processes - sample after „high p T ” selections Contribution from the structure of the nucleon Contribution from the structure of the photon signal background

Systematic errors : Quark polarization in the photon Quark polarization in the photon for VMD – minimum and maximum scenarios

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

Data/MC

From 2002 and 2003 data Obtained by averaging results for min. and max scenario in VDM

Single hadons, low Q 2

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

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