F.-H. Heinsius (Universität Freiburg) on behalf of the COMPASS collaboration Gluon polarization measurements at DIS 2004, Štrbské Pleso, 14.4.2004

F.-H. Heinsius (Universität Freiburg)

on behalf of the COMPASS collaboration

Gluon polarization measurements at

DIS 2004, Štrbské Pleso, 14.4.2004

Fritz-Herbert Heinsius DIS 2004

The COMPASS Collaboration

Broad Physics Program• G/G• semi inclusive DIS

– flavor dependent quark helicity density distributions q

– transverse quark spin distribution function h1(x)

– polarised fragmentation– vector mesons

• hadron spectroscopy with hadron beams

230 physicists from 12 countries 28 institutes


Spin of the Nucleon = ½ ħ

sdusdu

G

QCD analysisof g1(x,Q2)

Photon gluon fusion

open charm

high-pT

½

DIS: ≈0.3 (CERN, SLAC, DESY)

LG

Measure generalizedparton distributions

Lq


G from QCD Analysis of g1

polarised gluon distribution from QCD fits:

Blümlein & Böttcher: fit to polarised data of EMC, E142, E143, E155, SMC, Hermes Nucl. Phys. B636 (02) 225

Hermes (2000)


Spin of the Nucleon = ½ ħ

sdusdu

G

QCD analysisof g1(x,Q2)

Photon gluon fusion

open charm

high-pT

½

DIS: ≈0.3 (CERN, SLAC, DESY)

LG

Measure generalizedparton distributions

Lq


N

G/G at COMPASSPhoton gluon fusion

COMPASSSPS

LHC

Beam: 2 . 108 µ+/ spill (4.8s / 16.2s) Luminosity: ~5 . 1032 cm-2 s-1 Beam polarization: -76%Beam momentum: 160 GeV/c


G/G at COMPASS

N

Polarised 6LiD Target

Ptarget: 50%

Dilution: 40%

Two 60 cm long target cellswith opposite polarisation

Superconducting

Solenoid (2.5 T)

3He – 4He dilution refrigerator (T~50mK)

Dipol (0.5 T)

Reconstructed interaction vertices


G/G at COMPASS

q = c cross section difference in charmed meson production

→ theory well understood

→ experiment challenging

q = u,d,s cross section difference in 2+1 jet production.

In COMPASS: Events with 2 hadrons with high pT

→ experiment easy

→ theory difficult

Photon gluon fusion

N


COMPASS Spectrometer 2003/04


New Technologies for Tracking and Particle ID

Scintillating fiber trackers

GEM

MicroMegas

Readout electronics

Large areadrift detectors

TDC

RICHCsI & MWPC readout

Radiator: C4F10


and hadron calorimeters

hadronshadrons

Particle Identification

(mra

d)

(mra

d)

p(GeV/c)p(GeV/c)

pp

With RICH

Essential for reconstructionof D-Mesons


G/G: Open Charm

G

GaA LL

sxGssd

sxGssd

XccN

XccNccN

G

G

)ˆ,( )ˆ( ˆ

)ˆ,( )ˆ( ˆ

PGF

PGF

2ccMs ˆ

PGF at NLO: Bojak, Stratmann NPB 540 (1999) 345; Contogouris et al.

c

c

0*

0%) 4 (BR

KDD

KD

ccNT

cccc

ccccraw ADfPP

NN

NNA

76.0P

5.0TP

4.0f

)(yD

N

D

Photon-Gluon Fusion


Cuts:

zD > 0.2

|cos *| < 0.85 (Background)

10 < pK < 35 GeV/c

(RICH PID)MK

s-M

K

-m

[MeV

/c2]

MK -mD0 [MeV/c2]

D* tagging: D*→D0

KD0

KD KD

Cut on D0

MKs-MK -m [MeV/c2]

Fritz-Herbert Heinsius DIS 2004MK -mD0 [MeV/c2]

D* tagging : D*→D0 D0→K

KD0

KD

MK

s-M

K

-m

[MeV

/c2]

KD0

MK -mD0 [MeV/c2]

317 D0

80% 2002 data

Cut on D*


G/G: Prospects from Open Charm

• First reconstruction of charmed mesons with polarised target and beam

• Very challenging

because – vertex reconstruction inside

massive target– event rate small compared

to background

• Improvements– gains in 2003 and 2004

spectrometer performance– double beam time in 2004– better beam reconstruction– several improvements in

reconstruction algorithms and analysis methods

→Projected error on G/G from 2002-2004 data: 0.24


G/G: Pairs of High pT Hadrons

• Current fragmentation– xF > 0.1

– z > 0.1

• 2 high pT hadrons

– pT > 0.7 GeV/c

– pT12+ pT2

2 > 2.5 (GeV/c)2

– m(h1h2) > 1.5 GeV/c2

Photon Gluon Fusion

h1

h2

N


COMPASS Result

Improvements:

• 2003 and expected 2004 data will give a factor of 4 more data

• better reconstruction algorithm

12

12

21

21

2

1

NN

NN

NN

NN

PDfPA

BT

d

two target cells, opposite polarisation,polarisation flipped every 8 hours

up to now systematic error contains only studies on false asymmetries due to target or spectrometer effects

2002 data.. 010.0036.0065.0 syststatdA

Asymmetry in production of hadron pairs with high pT:


How to get ΔG/G

Photon Gluon Fusion QCD-ComptonLeading Order

DISLOq

q

D

a

G

G

D

a

D

AA

tot

ComComLL

tot

PGFPGFLL

hhNLLd

ˆˆ

fractions of cross section determined by Monte Carlo

50 and 1 .ˆˆ ComLL

PGFLL aa


Additional Background

Resolved Photon

VMD - Pomeron

Relevant forQ2<1 (GeV/c)2


Next Steps in high-pT Analysis

Monte Carlo studies are in progress:• PYTHIA

– simulates all processes– PYTHIA used in HERMES analysis (Q2 unmeasured)

• LEPTO– simulates PGF, QCD-Compton and LO DIS– LEPTO used in SMC analysis (Q2>1 (GeV/c)2 selected)

• Projected error on G/G for 2002-2004 data (assuming fraction of PGF events is ¼ ):

0.05 [0.16 for Q2>1 (GeV/c)2]


Expected error on ΔG/G

More COMPASS physics• Inclusive and semi-

inclusive asymmetries M. Leberig

• Transverse asymmetry AUT for charged pions H. Fischer

COMPASS SummaryFirst glance at open charm PGF with polarised target and beam

Good perspectives for ΔG from high-pT hadron pairs

proposal


End of Talk


G/G at COMPASSOpen charm

First reconstruction of charmed mesons with polarised target and beam:

High pT hadron pairs

Measured asymmetry from

2002 data:

KDby tagged KD0

MK -mD0 [MeV/c2]

317 D0

80% 2002 data

.. 010.0036.0065.0 syststatdA


High pT cuts


COMPASS Acceptance


detection of detection of VUVVUV photons photons(165-200 nm)(165-200 nm)

Ring Imaging CHerenkov Counter (RICH)

116 VUV mirrors, surface area: 21 m116 VUV mirrors, surface area: 21 m22

Photon detection Photon detection

5.3 m5.3 m22 MWPCs MWPCs

16 CsI Photocathodes16 CsI Photocathodes

84,000 analog readout channels84,000 analog readout channels

5 m

5 m

6 m6 m3 m3 m

photon photon detectors:detectors:CsI MWPCCsI MWPC

mirrormirrorwallwall

vesselvessel

radiator:radiator:

CC44FF1010

Single eventSingle event

single photon:1.2 mradring: 0.4 mradphotons/ring n ~143/K sep. up to 40 GeV/c

Documents

F.-H. Heinsius (Universität Freiburg) on behalf of the COMPASS collaboration Gluon polarization measurements at DIS 2004, Štrbské Pleso, 14.4.2004