Spin Physics from COMPASS G. Mallot/CERN On Behalf of the Compass Collaboration Spin 2003, Seattle 4-7 August, 2003

Seattle 2003G. Mallot2 Contents Spectrometer and data taking 2002 A first look at the 2002 data –Lambda –Exclusive ρ and φ, J/ψ –Transversity –Flavour separation Status of Δg at COMPASS –High-p T hadron pairs –D * signal Prospects

Seattle 2003G. Mallot3 COMPASS 12 Countries 28 Institutes >200 physicists muon & hadron beam programmes

Seattle 2003G. Mallot4 What did COMPASS do the last years? Preface April 1999 since April 2002

Seattle 2003G. Mallot5 The COMPASS Spectrometer SM1 SM2 RICH1 Polarised Target E/HCAL1 Muon Wall 1 Muon Wall 2, MWPC SPS 160 GeV  beam Micromegas, SDC, Scifi Straws, Gems MWPC, Gems, Scifi, W45 (not shown) E/HCAL2 Hodoscopes Scifi, Silicon

Seattle 2003G. Mallot6 Spectrometer 2002

Seattle 2003G. Mallot7 Polarised target μ 6 LiD ± 50 % polarisation 50 % dilution factor 2.5 T 50 mK

Seattle 2003G. Mallot8 Target system +dipole magnet (0.5T) 3 He – 4 He dilution refrigerator (T~50mK) μ Reconstructed interaction vertices

Seattle 2003G. Mallot9 RICH-1 80 m 3 (3 m C 4 F 10 radiator) 116 VUV mirrors 5.3 m 2 VUV detectors –MWPC CsI photo- sensitive cathodes –8x8 mm 2 pads 84k analog r/o channels

Seattle 2003G. Mallot10 RICH-1 performance = 25 photons = 25 photons  = 0.23 mrad Data  = 0.39 mrad = 15 photons = 15 photons single event, low intensity 80 % C 4 F 10, 2050V Cherenkov angle for rings with β  1 MC:

Seattle 2003G. Mallot Run ‘initial spectrometer layout’ essentially complete 160 GeV/c muons, 2·10 8 μ + /4 s every16.8 s, P beam  80 % 6 LiD target, P target  50 % Polarisation reversal by magnet field rotation every 8 h 200 k readout channels, kB/event data taking: –24 days setup (about 2/3 of equipment new) –57 days longitudinal target polarisation –19 days transverse 5 billion events recorded, 260 TByte total

Seattle 2003G. Mallot12 Central Data Recording Design value: 35MB/s 3TB/day 260 TByte in ~100 days 5 billion events May 27 Sep 18 GB

Seattle 2003G. Mallot13 Reconstruction stability K 0 yield as function of run number zero suppressed target polarisation

Seattle 2003G. Mallot14 First Analysis Results Λ and Λ hyperon production Vector meson production ρ, φ and J/ψ ΔG/G from high-p T hadron pairs Flavour decomposition of pol. PDF Transversity and Collins asymmetry

Seattle 2003G. Mallot15 Lambda production Armenteros-Podolanski p T [GeV/c]

Seattle 2003G. Mallot16 Lambda data vs MC K0K0 Λ Λ pxFxF Q2Q2 Monte Carlo Data

Seattle 2003G. Mallot17 Lambda polarization? K0K0 Λ Λ mass 1/6 of 2002 Statistics good potential for polarisation measurement

Seattle 2003G. Mallot18 Exclusive ρ and φ production |t’| < 0.5 GeV < W < 16 GeV Q 2 > GeV 2 E. Burtin, GPD session-1

Seattle 2003G. Mallot19 Invariant masses 16 % of total 2002 statistics no MC corrections yet

Seattle 2003G. Mallot20 Interference of ρ 0 and ππ Q 2, -t’ Söding parametrization No accept. corr. E. Burtin, GPD session-1 -t

Seattle 2003G. Mallot21 Angular distributions p T > 0.15 GeV Q 2 > 0.05 GeV 2 E. Burtin, GPD session-1

Seattle 2003G. Mallot22 J/ψ production J/ψ μ + μ - First look mainly elastic

Seattle 2003G. Mallot23 Collins asymmetry Z-distribution of leading hadron the Collins asymmetry A UT for positive leading hadron Estimated error from 2002 data, extrapolated from analysed sample

Seattle 2003G. Mallot24 Flavour separation Δq Looks very promising in particular for Δs ! Can the first moment of Δs be positive? Low-x data essential!

Seattle 2003G. Mallot25 Δg: high-p T hadron pairs Q 2 (GeV/c) p T (GeV/c) μ, μ ’ + 2 hadrons in plots only 5% of 2002 data x m(ππ) (GeV/c) 2 ρ0ρ0 K0K0

Seattle 2003G. Mallot26 High-p T hadron pairs  for ΔG/G analysis we’ll use (p T,i > 1.1 GeV/c)  extrapolated to full 2002 statistics Q 2 >1 GeV 2 : events all Q 2 : events from 2002 data: δ(ΔG/G)  0.31; Q 2 >1 GeV 2  0.1; all Q 2 Can data with Q 2 <1 GeV 2 be interpreted (resolved photon)? note: 2002 data correspond about to Hermes , Hermes used all data

Seattle 2003G. Mallot27 Open charm Photon-gluon fusion: 1.2 D 0 per PGF cc event c c g BR 4 % D 0 from D * about 20 % or:

Seattle 2003G. Mallot28 Open charm, cuts most of 2002 data, prel. RICH and tracking z D > 0.2 (background reduction) | cos(θ * ) | < 0.85 (background reduction) 10 < p K < 35 GeV/c (Rich πK sep.) define: M(D * ) – [M(D 0 )+M(π)]

Seattle 2003G. Mallot29 tagging Choose: 3.1 < ΔM Kππ < 9.1 MeV

Seattle 2003G. Mallot30 tagging 3.1 < ΔM Kππ < 9.1 MeV 317 D 0

Seattle 2003G. Mallot31 Outlook 2003 muon run, poor beam up to now 2004 long SPS run of 150 days (?) –muon plus 4 week hadron pilot run (?) –new target magnet with larger acceptance (?) 2005 CERN accelerator shutdown 2006 – 2010 –request in preparation –CERN council: COMPASS should continue in 2006 more hardware to come: ECAL (π 0 ), RICH, DAQ,…

Seattle 2003G. Mallot32 Summary COMPASS is up and running Lots of high statistics data to come First glance at open charm PGF with polarised target and beam Good perspectives for ΔG from high-p T hadron pairs (π,K) Promising perspectives for running after 2005 and with LHC.