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Transcript of PHYSICS RESULTS FROM COMPASS F. Bradamante University of Trieste and INFN Trieste on behalf of the...
PHYSICS RESULTS FROM COMPASS
F. BradamanteUniversity of Trieste and INFN Trieste
on behalf of the Collaboration
Workshop on Hadron Structure at J-PARC
November 30, 2005
F. Bradamante, Workshop on Hadron Structure, J-PARC
COmmon Muon and Proton Apparatus for Structure and Spectroscopy NA58
Czech Republic, Finland, France, Germany, India, Israel, Italy, Japan, Poland, Portugal, Russia
Bielefeld, Bochum, Bonn, Burdwan, Calcutta, CERN,
Dubna, Erlangen, Freiburg, Heidelberg, Helsinki, Lisbon,
Mainz, Miyazaky, Moscow, Munich, Nagoya, Prague, Protvino,
Saclay, Tel Aviv, Torino, Trieste, Warsaw
28 Institutes, ~230 physicists
F. Bradamante, Workshop on Hadron Structure, J-PARC
Physics program of COMPASS
• Experiments with muon beam
• ΔG/G
• g1
• Transverse spin effects
• Flavor decomposition of spin distribution functions
• Vector meson production
• Spin transfer inΛ-hyperon production
• Experiments with hadron beams
• Pion and Kaon polarizabilities
• Diffractive production of exotic states
• Search for glueballs
• Light meson spectroscopy
• Production of double charmed baryons
F. Bradamante, Workshop on Hadron Structure, J-PARC
N
SPS
LHC
luminosity: ~5 . 1032 cm-2 s-1
beam intensity: 2.108 µ+/spill (4.8s/16.2s)
beam momentum: 160 GeV/c
longitudinally polarised muon beamlongitudinally or transversely polarised
targetcalorimetry particle identification
F. Bradamante, Workshop on Hadron Structure, J-PARC
The Spectrometer
SM1SM1
SM2SM2
66LiD TargetLiD Target
160 GeV
160 GeV μμ
RICH
ECal & HCalμ Filter
Trigger-hodoscopes
SiliconMicromegas
SciFi
Gems
Drift chambers
Straws
MWPC
TWO STAGE SPECTROMETER:Polarized beam and target
SAT, LAT, PID
0.003 < x < 0.510-3 < Q2 < 10 GeV2
50 m
F. Bradamante, Workshop on Hadron Structure, J-PARC
WHERE ARE WE ?
• in 2002, 2003, and 2004 COMPASS has taken data in the muon program configuration
• physics results
1. G/G
2. 3. Transversity
4. Pentaquark
5. Exclusive ρ0
6. Λ physics
• pilot run in 2004 for hadron program
3·1010 events ~ 1000 TB
•
160 GeV, polarized beam6LiD polarized target (~polarized deuterons)
• 2005: no beam
F. Bradamante, Workshop on Hadron Structure, J-PARC
physics resultsphysics results
ΔΔG/GG/G
F. Bradamante, Workshop on Hadron Structure, J-PARC
G/G at COMPASS
Photon Gluon Fusion
N
q = c cross section differencein charmed meson production
→ theory well understood
→ experiment challenging
q = u,d,s cross section difference in 2+1 jet productionin COMPASS: events with 2 hadrons with high-pt
→ experiment easy
→ theory more difficult
F. Bradamante, Workshop on Hadron Structure, J-PARC
ΔΔG/GG/Gfrom Open Charmfrom Open Charm
F. Bradamante, Workshop on Hadron Structure, J-PARC
MK - MD0(PDG) [MeV/c2]
MK
- (
MK
+ M
) [M
eV
/c2]
ΔG/G from Open Charm - 1
MK
- (
MK
+ M
) (
Me
V)
D* (2002)
MK - (MK + M) [MeV/c2]
KDDD soft00*
F. Bradamante, Workshop on Hadron Structure, J-PARC
MK - MD0(PDG) [MeV/c2]
MK
- (
MK
+ M
) [M
eV
/c2]
MK
- (
MK
+ M
) (
Me
V)
D* (2002)
MK - (MK + M) [MeV/c2]
D0 (2002)
MK - MD0(PDG) [MeV/c2]
ΔG/G from Open Charm - 2
KDDD soft00*
F. Bradamante, Workshop on Hadron Structure, J-PARC
D0 (2003)1100 events
D0 (untagged, 2003) 4200 events
COMPASS preliminary
COMPASS preliminary
D0 (2002)400 events
COMPASS preliminary
D0 (untagged, 2002)1400 events
COMPASS preliminary
ΔG/G from Open Charm - 3
F. Bradamante, Workshop on Hadron Structure, J-PARC
First measurement of ΔG/G with Open Charm tagging
with 2004 data: 0.73 0.43
= 0.15 ± 0.08 @ 73.008.1
gxG
G
ΔG/G from Open Charm - 4
F. Bradamante, Workshop on Hadron Structure, J-PARC
ΔΔG/GG/Gfrom from High-High-pptt hadron pairs hadron pairs
F. Bradamante, Workshop on Hadron Structure, J-PARC
PGF LO DIS
QCD-Compton
PGF and background
tot
CQCDCQCDLL
tot
LOLOLL
tot
PGFPGFLLLL
D
aA
D
aA
G
G
D
a
D
A
11
ΔG/G from High-pt hadrons, Q2 > 1 (GeV/c)2 - 1
F. Bradamante, Workshop on Hadron Structure, J-PARC
ΔG/G from High-pt hadrons, Q2 > 1 (GeV/c)2 - 2
Data – Monte Carlo (LEPTO) comparison
Q2 leading hadron: p leading hadron: pt
F. Bradamante, Workshop on Hadron Structure, J-PARC
Results from Monte Carlo:
Ratio of PGF events
05.075.0
07.034.0
DaPGFLL
tot
PGF
13.0gx
gx
ΔG/G from High-pt hadrons, Q2 > 1 (GeV/c)2 - 3
syst.stat. 06.031.006.0 G
G
with 2004 data: 0.31 0.22
Gluon polarisation
F. Bradamante, Workshop on Hadron Structure, J-PARC
PGF
LO DIS
QCD-Compton
all Q2
ΔG/G from High-pt hadrons
F. Bradamante, Workshop on Hadron Structure, J-PARC
PGF
LO DIS
QCD-Compton
low Q2 all Q2
resolved photon
ΔG/G from High-pt hadrons
F. Bradamante, Workshop on Hadron Structure, J-PARC
0 0.1 0.2 0.3
PGF
QCD-C
LO DIS
qq‘→ qq‘
qg→ qg
gg→ gg
low pt
directresolv.
Results from PYTHIA
Background • as for
Q2 > 1 (GeV/c)2
• additional background from resolvedphoton events
• additional processes sensitive to gluonsin the nucleon
neglect LO DIS and low pt
ΔG/G from High-pt hadrons, Q2 < 1 (GeV/c)2 - 1
F. Bradamante, Workshop on Hadron Structure, J-PARC
Determination of ΔG/G
2002 + 2003: ALL/D = 0.002 ± 0.019stat. ± 0.003syst
095.0gxsyst.stat. 057.0089.0024.0 G
G
photonsyst. MCsyst. exp.stat. 018.0052.0014.0089.0024.0 G
G
with 2004 data: 0.089 0.06
hep-ex/0511028, CERN-PH-EP/2005-049, Phys. Lett. B
ΔG/G from High-pt hadrons, Q2 < 1 (GeV/c)2 - 2
F. Bradamante, Workshop on Hadron Structure, J-PARC
G/G from high-pt: results 2002-2003 data
results favour small ΔG or
ΔG crosses 0 around xg ≈ 0.1
2
1
3
GRSV2000 with1 G = 2.52 G = 0.63 G = 0.2
Glück et al.,Phys. Rev. D63(2001) 094005
preliminary
hep-ex/0511028 accepted PLB
F. Bradamante, Workshop on Hadron Structure, J-PARC
gg11dd
F. Bradamante, Workshop on Hadron Structure, J-PARC
g1 of the deuteron (2002-2003)
• most precise measurement for 0.004 < x < 0.03
• new NLO QCD fit, precision of a0 improves factor 2 (Q2 = 4 GeV2)
Phys Lett B 612 (2005) 154
F. Bradamante, Workshop on Hadron Structure, J-PARC
TransversityTransversity
single hadronsingle hadron
two hadronstwo hadrons
ΛΛ
F. Bradamante, Workshop on Hadron Structure, J-PARC
Collins and Sivers angles
C = h - S’
S = h - S
S ’ azimuthal angle of spin vector of fragmenting quark (S’’ = - S)
h azimuthal angle of hadron momentum
Transversity – single hadron - 1
F. Bradamante, Workshop on Hadron Structure, J-PARC
Transversity – single hadron - 2
first measurements of transverse spin asymmetries in DIS of high energy
muons on a transversely polarized deuteron target
published single hadron asymmetries from 2002 run
• Collins: related to transverse quark distributions
• Sivers: related to intrinsic kTPhys Rev Lett 94 (2005) 202002
F. Bradamante, Workshop on Hadron Structure, J-PARC
Transversity: two hadrons - 1
PR PPP 2
PPR T21
21
SRS'RRS
F. Bradamante, Workshop on Hadron Structure, J-PARC
Transversity: two hadrons - 2
• precise measurement of few %• systematics seems well under
control• also compatible with zero• interesting to see proton in 2006
all +/- combinations
F. Bradamante, Workshop on Hadron Structure, J-PARC
Transversity: two hadrons - 2
2002-2003 data
weighted average
with h1 always positive
1 +/- combination per events: pt ordering
F. Bradamante, Workshop on Hadron Structure, J-PARC
Transversity: Λ polarization
2002-2003 data
F. Bradamante, Workshop on Hadron Structure, J-PARC
Pentaquark searchPentaquark search
F. Bradamante, Workshop on Hadron Structure, J-PARC
motivated by NA49 report of pentaquark candidate
• COMPASS has large sample of the double-strange Ξ–
baryon (18000 Ξ–, 11000 Ξ+) from 2002-2003 data
• search for Ξ– π– resonance
Φ(1860)– – → Ξ– π– → Λπ– π– → p π–π–π–
Φ(1860) Pentaquark search - 1
F. Bradamante, Workshop on Hadron Structure, J-PARC
Φ(1860) Pentaquark search - 2
compare to yields
• opposite-sign pairs: Ξ(1530)0 → Ξ– π+ , 1700 and 920 evts
• like-sign pairs: evts <79 and <89 at 99% CL
(expected ~400)
Ξ(1530)0
Ξ(1530)0
Eu
r P
hys
J C
41 (
2005
) 46
9
F. Bradamante, Workshop on Hadron Structure, J-PARC
Exclusive Exclusive ρρ00 productionproduction
F. Bradamante, Workshop on Hadron Structure, J-PARC
Exclusive ρ0 production (2002 data) - 1
F. Bradamante, Workshop on Hadron Structure, J-PARC
Exclusive ρ0 production - 2
ANGULAR DISTRIBUTIONS
0.01 < Q² < 0.05 < Q² < 0.3 < Q² < 0.6 < Q² < 2.0 < Q²0.01 < Q² < 0.05 < Q² < 0.3 < Q² < 0.6 < Q² < 2.0 < Q² < 10 GeV2
preliminary, statistical errors only, limited by MC
corrected for acceptance, smearing and efficiency (MC:DIPSI gen)background not subtracted
F. Bradamante, Workshop on Hadron Structure, J-PARC
LT
200
20104
00 )(σ
Tδ)(εT~r
measurement
of r 0400
Exclusive ρ0 production - 3
0.01 < Q² < 0.05 < Q² < 0.3 < Q² < 0.6 < Q² < 2.0 < Q² < 10 GeV2
TσLσSCHC
θ1)cos(3r)r(14
3) W(cos 204
000400
distribution :
Spin density matrix element:
Tλρ λγ are helicity amplitudes
meson photon
2002
F. Bradamante, Workshop on Hadron Structure, J-PARC
measurement of r
and Im r
0 4 1-1
Exclusive ρ0 production - 4
0.01 < Q² < 0.05 < Q² < 0.3 < Q² < 0.6 < Q² < 2.0 < Q² < 10 GeV2
distribution :
Spin density matrix element:
31-1
φ2cosr21 [2
1)φ( 04
11
W ]φ2sin1Pr2 2311 Im
beam polarisation
LT
2
10*111104
11 σδ)(εσ
Tδ)(ε)TRe(Tr
...3
11r Im 0
0
if SCHC holds
weak violation
F. Bradamante, Workshop on Hadron Structure, J-PARC
Longitudinal polarizationLongitudinal polarization
of of ΛΛ and anti and antiΛΛ in DIS in DIS
F. Bradamante, Workshop on Hadron Structure, J-PARC
Event selection p
-
+
’+
V1
V2
N() N()
E665 750 650
NOMAD 8087 649
HERMES1996-2000
10568 1687
COMPASS2002
7919 5062
COMPASS2003
34789 20651
Λ POLARIZATION (2002 data) - 1
F. Bradamante, Workshop on Hadron Structure, J-PARC
Λ POLARIZATION
)cos1(2cos
PN
d
dN tot
2002 data
F. Bradamante, Workshop on Hadron Structure, J-PARC
Λ POLARIZATION
2002 data
F. Bradamante, Workshop on Hadron Structure, J-PARC
NEAR FUTURE (2006-2010)Workshop on Future Physics @ COMPASSYellow Report CERN-2004-011, 22 Nov. 2004
• IMPORTANT UPGRADE of the SPECTROMETER ONGOINGRICHTRACKINGE.M. CALORIMETERSO. D. P.T. MAGNETVeto System
• 2006 MUON RUNNING100 days 6LiD Longitudinal Polarization 30 days NH3 Transverse Polarization
• 2007 HADRON RUNNINGCENTRAL PRODUCTIONwith 300 GeV hadron beam and LH2 target
• 2008- 2010 COMPLETE THE APPROVED MUON and HADRON PROGRAMME
F. Bradamante, Workshop on Hadron Structure, J-PARC
• a technically challenging new experiment is IN OPERATION SINCE 2002
SUMMARY AND OUTLOOK
“LHC” technologies detectorsread-outdata handling
• FIRST PHYSICS RESULTS have been produced MANY MORE IN THE PIPE-LINE
BIG DISCOVERY POTENTIAL
• a privileged situation at CERN
• with some upgrade COMPASS might be an interesting option even in the second decade of this century
• COMPASS is foreseen to run up to the end of the present mid-term plan of CERN (2010)