PHYSICS RESULTS FROM COMPASS F. Bradamante University of Trieste and INFN Trieste on behalf of the Collaboration Workshop on Hadron Structure at J-PARC

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


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


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


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


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


physics resultsphysics results

ΔΔG/GG/G


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


ΔΔG/GG/Gfrom Open Charmfrom Open Charm


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*



MK

- (

MK

+ M

) [M

eV

/c2]

MK

- (

MK

+ M

) (

Me

V)

D* (2002)

MK - (MK + M) [MeV/c2]

D0 (2002)



KDDD soft00*


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



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



ΔΔG/GG/Gfrom from High-High-pptt hadron pairs hadron pairs


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



Data – Monte Carlo (LEPTO) comparison

Q2 leading hadron: p leading hadron: pt


Results from Monte Carlo:

Ratio of PGF events

05.075.0

07.034.0

DaPGFLL

tot

PGF

13.0gx

gx


syst.stat. 06.031.006.0 G

G

with 2004 data: 0.31 0.22

Gluon polarisation


PGF

LO DIS

QCD-Compton

all Q2

ΔG/G from High-pt hadrons


PGF

LO DIS

QCD-Compton

low Q2 all Q2

resolved photon

ΔG/G from High-pt hadrons


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


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


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


gg11dd


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


TransversityTransversity

single hadronsingle hadron

two hadronstwo hadrons

ΛΛ


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


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


Transversity: two hadrons - 1

PR PPP 2

PPR T21

21

SRS'RRS



• precise measurement of few %• systematics seems well under

control• also compatible with zero• interesting to see proton in 2006

all +/- combinations



2002-2003 data

weighted average

with h1 always positive

1 +/- combination per events: pt ordering


Transversity: Λ polarization

2002-2003 data


Pentaquark searchPentaquark search


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


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


Exclusive Exclusive ρρ00 productionproduction


Exclusive ρ0 production (2002 data) - 1


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


LT

200

20104

00 )(σ

Tδ)(εT~r

measurement

of r 0400


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


measurement of r

and Im r

0 4 1-1


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


Longitudinal polarizationLongitudinal polarization

of of ΛΛ and anti and antiΛΛ in DIS in DIS


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


Λ POLARIZATION

)cos1(2cos

PN

d

dN tot

2002 data


Λ POLARIZATION

2002 data


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


• 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)

Documents

PHYSICS RESULTS FROM COMPASS F. Bradamante University of Trieste and INFN Trieste on behalf of the Collaboration Workshop on Hadron Structure at J-PARC