COMPASS experiment Status and reacent results

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COMPASS experiment Status and reacent results

• Ewa Rondio,
• Institute for Nuclear Studies,
  Warsaw, Poland
• Brookhaven, 3 May 2005

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The COMPASS Collaboration(230 Physicists from 12
Countries)
Bielefeld, Bochum, Bonn (ISKP PI), Erlangen,
Freiburg, Heidelberg, Mainz, München (LMU TU)
Dubna (LPP and LNP), Moscow (INR, LPI, State
University), Protvino
CERN
Warsaw (SINS), Warsaw (TU), Warsaw (UW)
Helsinki
Prag
Saclay
Nagoya
Lisboa
Torino(University,INFN) Trieste(University,INFN)
Burdwan, Calcutta
Tel Aviv
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COMPASS THE new fixed target facility at CERN
!COmmon Muon and Proton Apparatus for Structure
and Spectroscopy. - HISTORY

• 1996 COMPASS proposal
• 1997 conditional approval
• 1998 MoU
• 1999 2001 construction installation
• 2001 technical run
• 2002, 2003, 2004 data taking
• 2005 break at Cern (LHC)
• Restart in 2006
• at least until 2010

26. June 1998
Now ?2004
8. April 1999
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Physics Goals
Contribute to the understanding of the
non-perturbative physics of the nucleon

• nucleon spectroscopy
• Primakoff-Reactions
• polarizability of ? and K
• glue balls and hybrids
• charmed mesons and baryons
• semi-leptonic decays
• double-charmed baryons

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LHC

COMPASS
SPS

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The COMPASS Experiment
Beam 2 . 108 µ/ spill (4.8s / 16.2s)
Beam momentum 160 GeV/c Luminosity 5 .
1032 cm-2 s-1 Beam polarization -76
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COMPASS spectrometer
Muon filter 2
MWPCs
Beam 160 GeV µ 2.8 . 108 µ/spill
(4.8s/16.2s)
ECal2 Hcal2
SM2
50m
Muon filter 1
ECal1 Hcal1

RICH
GEM MWPCs SciFi
SM1
GEM MWPCs
Silicon SciFi

• Polarization
• Beam -76
• Target max. 57

Scintillating fibers
GEM Straws
Micromegas Drift chambers
Polarized target
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New detector technologies
MicroMegas
Trigger-System
Straws

Scintillating fiber trackers
calorimeter readout
GEM
Readout electronics
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Ring Imaging CHerenkov Counter (RICH)
116 VUV mirrors, surface area 21 m2
single photon s ?gt1.2 mrad ring s
?gt0.4 mrad photons/ring n 14 ?/K sep. up to 40
GeV/c
Photon detection 5.3 m2 MWPCs 16 CsI
Photocathodes 84,000 analog readout channels
detection of VUV photons (165-200 nm)
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hadron identification
?
K
p
By RICH
p(GeV/c)
and hadron calorimeters
q(mrad)
?
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COMPASS two programs

• ? with muon beam
• Muons
• data taking from 2002 -gt 2004
• will continue in 2006
• ? with hadron beam
• Hadrons
• pilot run in 2004

Main goal
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The Primakoff reaction
?, p1
?, p1
? Z ? ? Z ?
s1 ( p1 - k )2
?
?, k
first data taken in 2004 expected 30k events
?, k
Z, p2
Z, p2
t ( p2 p2 )2
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Muon program data 2002-2004 ongoing analysis

• A1d and influence on QCD fit
• Do and Do for ?G/G from open charm
• DG/G from high pT sample
• perturbative region (Q2gt1GeV2)
• and photoproduction region (Q2lt1GeV2)
• Transversity studies (Collins and Sivers
  asymmetries) for single and two hadrons
• L and L hyperon production
• Vector mesons
• Search for pentaquarks
• In this talk results with longitudinal target
  polarization

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Kinematic range covered

• Excellent for non-perturbative perturbative
  physics
• small xBj
• very small Q2 ? Q2 gt 100 (GeV/c)2

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polarized 6LiD target
4 possible spin combinations
reversed every 8 hours
or
reversed once a week
Polarization 50
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Asymmetry A1


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measurement of A1dalso test of the
detector and of systematic effects
controle
PLB 612, 154 (2005)
False asymmetries (combining configurations
with the same spin orientation)
Asymmetry for configuration With opposite spins -
Spin effects expected

• Weighting with fDPt was used to optimize
  statistical accuracy
• Asymmetry can be calculated for combinations
  without expected
• effect (false asymmetry) or where spin effect
  is expected (A1)

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DOUBLE SPIN ASYMMETRY A1d
COMPASS 20022003 data 34 Million DIS
events Q2 gt 1 (GeV/c)2 0.1 lt y lt
0.9 more to come ftom 2004
Data displayed at experimental ltQ2gt of every xBj
bin
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QCD fit with all DIS spin data, effect of Compass
A1D
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NLO evolution, calculations on grid (x,Q2)
scheme, ?2 minimization using Minuit

• 10 parameters fitted
• NDF 173-10
• ?2 probability 14

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Compass g1d and its influence on the QCD fit
scheme
with Compass new deuterium g1 data without
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Semi-inclusive asymmetries also avalaiable
Improvement at low x, consistent with SMC
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DG/G at COMPASS
Photon Gluon Fusion

• q c cross section differencein charmed
  meson production
• ? theory well understood
• ? experiment challenging
• q u,d,s cross section difference in 21 jet
  productionin COMPASS events with 2 hadrons
  with high pT
• ? experimentaly easier
• ? theory difficult

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DG/G OPEN CHARM
DsPGF at NLO Bojak, Stratmann NPB 540 (1999)
345 Contogouris et al.
Photon-Gluon Fusion
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Comparison with 2002 data
2002 P1IJ/2003 Gain
Flux/days 1.701013m/38.6 days 9.581012m/13.7 days 1.8
D D/Flux 28126 1.65 10-11 27025 2.82 10-11 1.70.2
D0 D0/Flux 1587179 9.34 10-11 1327161 13.85 10-11 1.50.2
S/B 0.780.08 0.900.09 1.20.2
Bckgrd Bckgrd/Flux 4141816 2.44 10-7 2653933 2.77 10-7 1.1
Known factors - Beam rec. 1.05 (JMLG) -
Trigger 1.20 - DAQ 1.03 - Pack.
Fact 1.01
1.31
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D tagging D?D0 p

• Cuts
• zD gt 0.2
• cos ? lt 0.85
• (Background)
• 10 lt pK lt 35 GeV
• (RICH PID)

MKpps-MKp -mp MeV/c2
MKp -mD0 MeV/c2
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Asymmetry for events with charm production (D0
and D)

• D is cleaner, but low
• statistics
• From here to ?G/G
• partonic asymmetrirs
• aLLPGF are needed

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Partonic asymmetries are calculated from
parametrization obtained for MC simulated
events? good description of data with MC is
required? what MC parameters are best

• Result on ?G/G
• can be expected soon
• from 2002-2004

s(DG/G) 0.24 from open charm
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Hadron pairs with z large pT

• Idea proposed by
• R.D.Carlitz, J.C.Collins and A.H.Mueller,
  Phys.Lett.B 214, 229 (1988).
• A.Bravar,D.von Harrach and A.Kotzinian,
• Phys.Lett.B 421, 349 (1998) .
• Used in the analysis
• HERMES, A.Airapetian et al.,
• Phys.Rev.Lett.84, 2584 (2000).
• SMC, B.Adeva et al.,
• Phys.Rev.D 70, 0102002 (2004)

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• where AlN?lhhX measured asymmetry,
• ?q/q approximated using A1 asymmetry
  ?N,
• ?aLL? partonic asymmetry,
• R fraction of contributing
  processes

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DG/G pairs of high pT hadrons
Photon Gluon Fusion

• Current fragmentation
• xF gt 0.1
• z gt 0.1
• 2 high pT hadrons
• pT gt 0.7 GeV/c
• pT12 pT22 gt 2.5 GeV2
• m(h1h2) gt 1.5 GeV

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DG/G pairs of high pT hadrons

• with Q2 gt1 GeV2, 0.4 lt y lt 0.9

Asymmetry in production of hadron pairs with high
pT result for 20022003 data

from this using RPGF obtained from MC
with
Uses only 10 of data

• Analysis done with LEPTO generator
• Initial and final state parton showers used
• Fragmentation function parameters modified
• kT statndard value (0.44)

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For Q2lt1GeV2 much more datadifficulties with
additional processes contributing (Pythia)
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Low Q2 scattering Pythia simulation
Contributing processes - sample after high pT
selections
signal
background
Contribution from the structure of the photon
Contribution from the structure of the nucleon
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Systematic errors

• Quark polarization in the photon

for VMD minimum and maximum scenarios
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MC uncertainties

• Missing NLO scale dependence,
• parton shower on/off
• tuning of parameters and data/MC
• parton fragmentation
• partons kT in nucleon and photon

biggest uncertainty from kT in photon
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Data/MC
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From 2002 and 2003 data Obtained by averaging
results for min. and max scenario in VDM
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Single hadons, low Q2
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Expected precission on the asymmetryteoretical
calculations byB. Jaeger, A. Schaefer and M.
Stratmann in NLO
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SUMMARY AND OUTLOOK

• CERN is again contributing to the NUCLEON SPIN
  PUZZLE

• Compass running in 2002-2004 brought interesting
  PHYSICS RESULTS, some already published
• MANY MORE IN PREPARATION
• data taking restarts in 2006

• Approved program untill 2010 with muon beams on
  polarized targets and hadron beams

After ? study of GPDS with DVCS and exclusive
mezon production on hydrogen target (recoil
detector)