1. On behalf of COMPASS Collaboration
CERN
Status, prospect
Alain Magnon CEA/Saclay
On behalf of COMPASS Collaboration
A.Magnon
HIX2004 July 26, 2004

2. Content COMPASS, physics programme Spectrometer highlights
Preliminary physics results (2002)
Prospects beyond 2005
A.Magnon
HIX2004 July 26, 2004

3. 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
HIX2004 July 26, 2004

4. Hadron structure and spectroscopy
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)
Hadron beam programme
Polarisibility of pions and kaons
(Primakoff reaction)
Exotics q-states, glue balls
Semi-leptonic decays of charmed hadrons
Double charmed hadrons
A.Magnon
HIX2004 July 26, 2004

5. Imperative to measure ΔG
Quark & gluon spin
Nucleon spin: ½ = ½ ΔΣ + ΔG +<Lz >
In polarised DIS, one measures
flavor singlet axial matrix element
a0= ΔΣ – (as/2p)nf ΔG
All experiments (SLAC,EMC,SMC,
SLAC, HERMES) confirm:
a0~ 0.1, 0.2
Imperative to measure ΔG
A.Magnon
HIX2004 July 26, 2004

6. LHC
COMPASS
SPS
A.Magnon
HIX2004 July 26, 2004

7. Spectrometer 2002 -> 2004 trigger-hodoscopes SPS 160 GeV
DW45
straws
SM2 dipole
Muon-filter2,MW2
RICH_1
HCAL1
Gem_11
SM1 dipole
ECAL2,HCAL2
Polarised Target
MWPC Gems Scifi
SPS 160 GeV
2.108m/spill
Muon-filter1,MW1
Veto
straws,MWPC,Gems,SciFi
Gems,SciFi,DCs,straws
Silicon
SciFi
Micromegas,DC,SciFi
BMS
A.Magnon
HIX2004 July 26, 2004

8. Polarized target system
3He – 4He dilution
refrigerator (T~50mK)
+dipole magnet (0.5T) μ
Reconstructed
interaction vertices
A.Magnon
HIX2004 July 26, 2004

9. 6LiD polarisation in 2003 + 50% -> - 50% -> A.Magnon
+ 50% ->
- 50% ->
A.Magnon
HIX2004 July 26, 2004

10. Micromegas 6 stations, 12 coordinates size 40x40 cm2
pitch 360 – 420 μm
time res. < 10 ns
space res. 70 μm
efficiency > 97%
Ne/C2H6/CF4 80/10/10 %
A.Magnon
HIX2004 July 26, 2004

11. GEMs 20 triple Gems detectors in 10 stations 40 coordinates
size 30x30 cm2
12 ns time resolution
50 μm space resolution
efficiency ~ 97 %
Ar/CO2 70/30 %
-4100 V 0V
A.Magnon
HIX2004 July 26, 2004

12. Large Drift Chambers 3 drift chambers 24 coordinates size 120x120 cm2
7 mm drift cell
170 μm space resolution
efficiency > 95 %
Ar/C2H6/CF4 45/45/10 %
A.Magnon
HIX2004 July 26, 2004

13. Straws 15 double layers of 6 and 10 mm straws size 325x242cm2
Hole
160 x 230 mm 2
15 double layers of 6 and 10 mm straws
size 325x242cm2
resolution 270 μm
efficiency 85 – 98 %
Ar/CF4/CO2 74/20/6 %
A.Magnon
HIX2004 July 26, 2004

14. PID with RICH Single event 3 m 116 VUV mirrors, surface area: 21 m2
photon
detectors:
CsI MWPC
mirror
wall
vessel
radiator:
C4F10
Photon detection
5.3 m2 MWPCs
16 CsI Photocathodes
84,000 analog readout channels
single photon: s =1.2 mrad
ring: s =0.4 mrad
photons/ring n ~14
3s p /K sep. up to 40 GeV/c
detection of
VUV photons
( nm)
A.Magnon
HIX2004 July 26, 2004

15. COMPASS acceptance
Excellent for non-perturbative & perturbative physics
- small xBj & very small Q2  Q2 > 100 (GeV/c)2
A.Magnon
HIX2004 July 26, 2004

16. Accumulated data Files -> 2003 <- 225 Tb 2002 & 2003:
500 TByte Data
1010 Events
longitudinal polarization
3.109 Events
transverse polarization
0.1% with Q²>1 (GeV/c)²
(after all cuts)
2003
<- 225 Tb
A.Magnon
HIX2004 July 26, 2004

17. Physics results 2002 data
Vector meson production ρ, φ and J/ψ. Exclusive r0 production
Λ & Λ hyperons, production and polarization
Collins asymmetry (Transverse spin)
(Longitudinal spin) :
Flavour decomposition of polarized PDF
A1d
Open-charm (DG/G)
Spin asymmetry from high pT hadrons
pairs (DG/G)
A.Magnon
HIX2004 July 26, 2004

18. Exclusive r0 production
m cuts : n > 30 GeV, Em’ > 20 GeV
Log10 Q2 > -2
0.5<Mpp <1 GeV
-2.5<Emiss<2.5 GeV
0.15<pt2<0.5 GeV2 W
A.Magnon
HIX2004 July 26, 2004

19. Exclusive r0 production
High precision measurement
of spin density matrix element
s-channel helicity conservation
t-channel natural Parity Exchange
A.Magnon
HIX2004 July 26, 2004

20. Exclusive r0 production
If SCHC ->
A.Magnon
HIX2004 July 26, 2004

21. Exclusive r0 production
r041-1= 0 if SCHC holds
small violation
of SCHC ?
r31-1 requires
polarized lepton
A.Magnon
HIX2004 July 26, 2004

22. Transverse spin Collins asymmetry
ΦC = Φh + ΦS – π
A = A0 ± A1 sin(ΦC)
AColl = A1 / (DNN.f.P)
AColl h1q(x,Q2) h+ h-
xBJ
zhad
A.Magnon
HIX2004 July 26, 2004

23. “Longitudinal spin virtual photon asymmetry”
A1d from inclusive scattering
“Longitudinal spin virtual photon asymmetry”
2002 data only
DIS evts
Q2 > 1 GeV/c2
0.1 < y < 0.9
COMPASS/SMC beam time ~ 1/7
A.Magnon
HIX2004 July 26, 2004

24. ΔG/G determination from open charm
Photon-Gluon-Fusion: 1.2 D0 per PGF cc event
D K-p BR = 4% c
D* D0ps+ ~ 30%(*)
K-p+ps+ c
(*)cuts on ps 30% -> ~20 %
A.Magnon
HIX2004 July 26, 2004

25. ΔG/G determination from open charm
mD*-mD0-mp = 5.9 MeV
(3/ stat)
317 D0
MKpps- MKp - mp
MKp-mD0
A.Magnon
HIX2004 July 26, 2004

26. ΔG/G from high pT hadrons pairs
Leading process
Gluon radiation (Compton)
Photon Gluon Fusion
(PGF) -
PT12 + PT22 > 2.5 GeV/c2, PT1(2) > 0.7 GeV/c, no Q2 cut
preliminary (2002 data)
Ag*d = ± (stat) ± (syst)
<xg> ~ 0.1
A.Magnon
HIX2004 July 26, 2004

27. s(ΔG/G) from high pT 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 ~ ¼
Thesis Colin Bernet
From preliminary analysis of 2002 data
s(ΔG/G) ~ 0.17
“ΔG/G” = 0.**
A.Magnon
HIX2004 July 26, 2004

28. Projection for s(DG/G)
If 2004 as expected, projection for data:
ssyst from
resolved g +
LO/NLO ??
HELP from
theorists !!
s(DG/G) = 0.05 high pT all Q2
s(DG/G) = 0.16 high pT Q2>1
s(DG/G) = 0.24 charm
A.Magnon
HIX2004 July 26, 2004

29. Running in 2002, 2003 and 2004
scheduled d d d
eSPS
preparation ~30 d d d
eSpectro (.90TGT)
data taking d d d
(L/T) / / /13
2004
21 d
.80
~7 d
.85
~8 d
160 GeV muons
hadrons
A.Magnon
HIX2004 July 26, 2004

30. COMPASS > 2005 SPS off in 2005 SPS restart in 2006
COMPASS is in the “5 years mid-
term plan” of CERN
Principal SPS users (apart LHC) are
neutrinos/CNGS and COMPASS
A.Magnon
HIX2004 July 26, 2004

31. COMPASS > 2010 (Villars/SPSC)
- Upgrades of the PS/SPS complex R. Garoby - Possible upgrades of M2 and luminosity increase 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 F2 and FL E.M. Kabuss - Hadronisation & related topics in SIDIS A. Kotzinian - Shadowing effects in nuclear parton distributions G. Smirnov - Detector concepts F.H. Heinsius - Toroidal spectrometer (I. Savin) - Polarisation observables F. Bradamante - hadron programme R. Bertini (S.Paul)
A.Magnon
HIX2004 July 26, 2004

32. 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
HIX2004 July 26, 2004