COMPASS CERN Status prospect Alain Magnon CEASaclay On

COMPASS @ CERN Status, prospect Alain Magnon CEA/Saclay On behalf of COMPASS Collaboration A. Magnon HIX 2004 July 26, 2004

Content • COMPASS, physics programme • Spectrometer highlights • Preliminary physics results (2002) • Prospects beyond 2005 A. Magnon HIX 2004 July 26, 2004

COMPASS Collaboration Bielefeld, Bochum, Bonn (ISKP, PI), Burdwan and Calcutta, CERN, Dubna, Erlangen, Freiburg, Heidelberg, Helsinki, Lisbon, Mainz, Moscow (INR, LPI, MSU), Munich (LMU, TU), Nagoya, Prague, Protvino, Saclay, Tel Aviv, Torino (Univ. , INFN), Trieste (Univ. , INFN), Warsaw (SINS, TU) More than 250 physicists from 28 Institutes A. Magnon HIX 2004 July 26, 2004

Physics programme Hadron structure and spectroscopy Muon beam programme • Quarks and gluon polarisation in polarised (longitudinal) nucleons • Transverse spin distribution • Diffractive VM-production • DVCS -> GPDs (not approved yet) A. Magnon Hadron beam programme • Polarisibility of pions and kaons (Primakoff reaction) • Exotics q-states, glue balls • Semi-leptonic decays of charmed hadrons • Double charmed hadrons HIX 2004 July 26, 2004 4

Quark & gluon spin Nucleon spin: ½ = ½ ΔΣ + ΔG +<Lz > In polarised DIS, one measures flavor singlet axial matrix element a 0= ΔΣ – (as/2 p)nf ΔG All experiments (SLAC, EMC, SLAC, HERMES) confirm: a 0~ 0. 1, 0. 2 Imperative to measure A. Magnon ΔG HIX 2004 July 26, 2004

LHC COMPASS SPS A. Magnon HIX 2004 July 26, 2004

Spectrometer 2002 -> 2004 trigger-hodoscopes DW 45 SM 2 dipole RICH_1 straws Muon-filter 2, MW 2 HCAL 1 Gem_11 ECAL 2, HCAL 2 SM 1 dipole MWPC Gems Scifi Polarised Target SPS 160 Ge. V 2. 108 m/spill Muon-filter 1, MW 1 Veto straws, MWPC, Gems, Sci. Fi Silicon BMS A. Magnon Sci. Fi Gems, Sci. Fi, DCs, straws Micromegas, DC, Sci. Fi HIX 2004 July 26, 2004 7

Polarized target system +dipole magnet (0. 5 T) 3 He – 4 He dilution refrigerator (T~50 m. K) μ Reconstructed interaction vertices A. Magnon HIX 2004 July 26, 2004 8

6 Li. D polarisation in 2003 + 50% -> - 50% -> A. Magnon HIX 2004 July 26, 2004 9

Micromegas 6 stations, 12 coordinates size 40 x 40 cm 2 pitch 360 – 420 μm time res. < 10 ns space res. 70 μm efficiency > 97% Ne/C 2 H 6/CF 4 80/10/10 % A. Magnon HIX 2004 July 26, 2004 10

GEMs • 20 triple Gems detectors in 10 stations • 40 coordinates • size 30 x 30 cm 2 • 12 ns time resolution • 50 μm space resolution • efficiency ~ 97 % • Ar/CO 2 70/30 % -4100 V 0 V A. Magnon HIX 2004 July 26, 2004

Large Drift Chambers • 3 drift chambers • 24 coordinates • size 120 x 120 cm 2 • 7 mm drift cell • 170 μm space resolution • efficiency > 95 % • Ar/C 2 H 6/CF 4 45/45/10 % A. Magnon HIX 2004 July 26, 2004 12

Straws 10 mm straws 6 mm straws Hole 2 160 x 230 mm 10 mm straws • 15 double layers of 6 and 10 mm straws • size 325 x 242 cm 2 • resolution 270 μm • efficiency 85 – 98 % • Ar/CF 4/CO 2 74/20/6 % A. Magnon HIX 2004 July 26, 2004 13

PID with RICH Single event 116 VUV mirrors, surface area: 21 m 2 3 m 6 m vessel mirror wall radiator: C 4 F 10 Photon detection single photon: detection of VUV photons ring: (165 -200 nm) photons/ring 3 s p /K sep. 5. 3 m 2 MWPCs 16 Cs. I Photocathodes A. Magnon HIX 2004 July 26, 2004 84, 000 analog readout channels s =1. 2 mrad s =0. 4 mrad n ~14 up to 40 Ge. V/c 5 m photon detectors: Cs. I MWPC

COMPASS acceptance Excellent for non-perturbative & perturbative physics - small x. Bj & very small Q 2 > 100 (Ge. V/c)2 A. Magnon HIX 2004 July 26, 2004

Accumulated data Files -> 2002 & 2003: 500 TByte Data 2003 <- 225 Tb 1010 Events longitudinal polarization 3. 109 Events transverse polarization 0. 1% with Q²>1 (Ge. V/c)² (after all cuts) A. Magnon HIX 2004 July 26, 2004 16

Physics results 2002 data • Vector meson production ρ, φ and J/ψ. Exclusive r 0 production • Λ & Λ hyperons, production and polarization • Collins asymmetry (Transverse spin) • (Longitudinal spin) : Flavour decomposition of polarized PDF A 1 d Open-charm (DG/G) Spin asymmetry from high p. T hadrons pairs (DG/G) A. Magnon HIX 2004 July 26, 2004

Exclusive r 0 production m cuts : n > 30 Ge. V, Em’ > 20 Ge. V Log 10 Q 2 > -2 0. 5<Mpp <1 Ge. V -2. 5<Emiss<2. 5 Ge. V 0. 15<pt 2<0. 5 Ge. V 2 W A. Magnon HIX 2004 July 26, 2004 18

Exclusive r 0 production High precision measurement of spin density matrix element • s-channel helicity conservation • t-channel natural Parity Exchange A. Magnon HIX 2004 July 26, 2004 19

Exclusive r 0 production If SCHC -> A. Magnon HIX 2004 July 26, 2004 20

Exclusive r 0 production r 041 -1= 0 if SCHC holds small violation of SCHC ? r 31 -1 requires polarized lepton A. Magnon HIX 2004 July 26, 2004 21

Transverse spin Collins asymmetry ΦC = Φ h + Φ S – π A h+ = A 0 ± A 1 sin(ΦC) AColl = A 1 / (DNN. f. P) AColl h 1 q(x, Q 2) hx. BJ A. Magnon HIX 2004 July 26, 2004 zhad 22

A 1 d from inclusive scattering 2002 data only “Longitudinal spin virtual photon asymmetry” 6. 5 106 DIS evts Q 2 > 1 Ge. V/c 2 0. 1 < y < 0. 9 COMPASS/SMC beam time ~ 1/7 A. Magnon HIX 2004 July 26, 2004 23

ΔG/G determination from open charm Photon-Gluon-Fusion: 1. 2 D 0 per PGF cc event D 0 c c D*+ D 0 ps+ ~ 30%(*) K - p +p s + (*)cuts A. Magnon K-p+ BR = 4% HIX 2004 July 26, 2004 on ps 30% -> ~20 % 24

MKpps- MKp - mp ΔG/G determination from open charm MKp-m. D 0 A. Magnon HIX 2004 July 26, 2004 25

ΔG/G from high p. T hadrons pairs h - h h Photon Gluon Fusion (PGF) h Leading process h h Gluon radiation (Compton) PT 12 + PT 22 > 2. 5 Ge. V/c 2, PT 1(2) > 0. 7 Ge. V/c, no Q 2 cut preliminary (2002 data) Ag*d = - 0. 065 ± 0. 036 (stat) ± 0. 010 (syst) <xg> ~ 0. 1 A. Magnon HIX 2004 July 26, 2004 26

s(ΔG/G) from high p. T hadrons pairs Monte Carlo study is required to subtract contribution of background before anything can be said on ΔG/G. In progress Assuming (Phytia-LO) : R_PGF ~ From preliminary analysis of 2002 data ¼ Thesis Colin Bernet s(ΔG/G) ~ 0. 17 “ΔG/G” = 0. ** A. Magnon HIX 2004 July 26, 2004 27

Projection for s(DG/G) If 2004 as expected, projection for 2002 -2004 data: s(DG/G) = 0. 05 high p. T all Q 2 s(DG/G) = 0. 16 high p. T Q 2>1 s(DG/G) = 0. 24 charm A. Magnon HIX 2004 July 26, 2004 ssyst from resolved g + LO/NLO ? ? HELP from theorists !!

Running in 2002, 2003 and 2004 2002 scheduled e. SPS preparation 2003 2004 106 d 90 d 110 d 21 d . 89 . 63 . 80 ~30 d 7 d 7 d ~7 d e. Spectro (. 90 TGT) . 77 . 85 data taking 44 d 39 d 62 d 30/9 49/13 (L/T) 33/11 160 Ge. V muons A. Magnon 2004 HIX 2004 July 26, 2004 . 85 ~8 d hadrons 29

COMPASS > 2005 SPS off in 2005 SPS restart in 2006 • COMPASS is in the “ 5 years midterm plan” of CERN • Principal SPS users (apart LHC) are neutrinos/CNGS and COMPASS A. Magnon HIX 2004 July 26, 2004

COMPASS > 2010 (Villars/SPSC) - Upgrades of the PS/SPS complex - Possible upgrades of M 2 and luminosity increase R. Garoby M. Leberig - Unpolarized parton distributions J. Pretz - Deeply Virtual Compton Scattering M. Diehl & N. D’Hose - Exclusive production of vector mesons H. Fischer - Measurements of F 2 and FL E. M. Kabuss - Hadronisation & related topics in SIDIS A. Kotzinian - Shadowing effects in nuclear parton distributions - Detector concepts - Toroidal spectrometer - Polarisation observables - hadron programme R. A. Magnon HIX 2004 July 26, 2004 G. Smirnov F. H. Heinsius (I. Savin) F. Bradamante Bertini (S. Paul)

Conclusions • Muon programme well on the tracks, will continue beyond 2005 • Preliminary longitudinal (and transverse) spin asymmetries • Green light (CERN) for pilot hadron run in 2004 • Thinking beyond 2010 (VILLARS) has started ! A. Magnon HIX 2004 July 26, 2004