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COMPASS experimentCOMPASS experimentStatus and Status and reacentreacent resultsresults
Ewa Ewa RondioRondio,,InstituteInstitute for for NuclearNuclear StudiesStudies, , WarsawWarsaw, , PolandPoland
BrookhavenBrookhaven, , 3 3 MayMay 20020055
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The COMPASS CollaborationThe COMPASS Collaboration(230 Physicists from 12 Countries)(230 Physicists from 12 Countries)
Bielefeld, Bochum, Bielefeld, Bochum, Bonn (ISKP & PI), Bonn (ISKP & PI), Erlangen, Freiburg, Erlangen, Freiburg, Heidelberg, Mainz, Heidelberg, Mainz, München (LMU & TU)München (LMU & TU)
HelsinkiHelsinki
SaclaySaclay
Tel AvivTel Aviv
Burdwan, Burdwan, CalcuttaCalcutta
Torino(University,INFN)Torino(University,INFN)Trieste(University,INFNTrieste(University,INFN))
Warsaw (SINS), Warsaw (SINS), Warsaw (TU)Warsaw (TU),,WarsawWarsaw (UW)(UW)
CERNCERN
NagoyaNagoya
PragPrag
Dubna (LPP and Dubna (LPP and LNP), Moscow (INR, LNP), Moscow (INR, LPI, State LPI, State University), ProtvinoUniversity), Protvino
LisboaLisboa
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1996 COMPASS proposal1996 COMPASS proposal1997 conditional approval1997 conditional approval1998 MoU 1998 MoU 1999 1999 –– 2001 construction 2001 construction
& installation& installation2001 technical run2001 technical run2002, 2003, 2004 data taking2002, 2003, 2004 data taking2005 2005 breakbreak atat Cern (LHC)Cern (LHC)Restart in 2006Restart in 2006at least until at least until 20102010
COMPASS: COMPASS: THETHE new fixed target facility at CERN !new fixed target facility at CERN !COCOmmonmmon MMuonuon andand PProtonroton AApparatus forpparatus for SStructuretructureandand SSpectroscopypectroscopy. . -- HISTORYHISTORY
8. April 1999
26. June 1998
Now Now àà20042004
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nucleon spin structurenucleon spin structure
Gluon Polarization Gluon Polarization ∆∆G/GG/G
transverse spin structure transverse spin structure function hfunction h11(x)(x)
Flavor dependent polarizedFlavor dependent polarizedquark helicity densities quark helicity densities ∆∆q(x)q(x)
spin dependent fragmentation spin dependent fragmentation
functions functions ∆∆DDΛΛ
ExclusExclusiveive VMVM--ProductionProductionq
Physics GoalsPhysics Goals
nucleon spectroscopynucleon spectroscopy
PrimakoffPrimakoff--ReactionsReactions-- polarizability of polarizability of ππ and Kand K
glue balls and hybridsglue balls and hybrids
charmed mesons and baryonscharmed mesons and baryons-- semisemi--leptonic decaysleptonic decays-- doubledouble--charmed baryonscharmed baryons
Contribute to the understanding of the Contribute to the understanding of the nonnon--perturbative physics of the nucleonperturbative physics of the nucleon
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COMPASSSPS
LHC
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The COMPASS ExperimentThe COMPASS Experiment
Beam: 2 . 108 µ+/ spill (4.8s / 16.2s) Beam momentum: 160 GeV/cLuminosity: ~5 . 1032 cm-2 s-1 Beam polarization: -76%
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Polarization:•Beam: -76%•Target: max. 57%
Beam: 160 GeV µ+
2.8 . 108 µ/spill (4.8s/16.2s)
Polarizedtarget
SM1RICH
ECal1 & Hcal1
Muon filter1
SM2
MWPCs
Micromegas &Drift chambers
ECal2 & Hcal2
Muon filter 2
GEM & MWPCsSciFi
GEM & MWPCs
GEM & Straws
SiliconSciFi Scintillating
fibers
~50m
COMPASS COMPASS spectrometerspectrometer
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Scintillating fiber trackers
GEM
MicroMegas
Readout electronics
Trigger-System
calorimeterreadout
Straws
New New detectordetector technologiestechnologies
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Single eventSingle event116 VUV mirrors, surface area: 21116 VUV mirrors, surface area: 21 mm22
Photon detection Photon detection
5.3 m5.3 m22 MWPCsMWPCs
16 16 CsICsI PhotocathodesPhotocathodes
84,000 analog readout channels84,000 analog readout channels
5 m5 m
6 m6 m3 m3 m
photon photon detectors:detectors:CsICsI MWPCMWPC
mirrormirrorwallwall
vesselvessel
radiator:radiator:CC44FF1010
single photon: s θ>1.2 mradring: s θ>0.4 mradphotons/ring n ~14
π/K sep. up to 40 GeV/c
detection of detection of VUVVUV photonsphotons(165(165--200 nm)200 nm)
RRing ing IImagingmaging CHCHerenkoverenkov CCounterounter ((RICHRICH))
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p(GeV
/c
p(GeV
/c))
θθ(mrad(mrad ))
…and hadron calorimeters
ΚΚ
pphadrons
e,µ
pp
ππΚΚ
By RICH
hadron hadron identificationidentification
ππ
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COMPASS – two programsCOMPASS COMPASS –– twotwo programsprograms
àà withwith muonmuon beambeamnn MuonsMuons: :
data data takingtaking fromfrom 2002 2002 --> 2004> 2004will will continuecontinue inin 20062006
àà withwith hadron hadron beambeamnn HadronsHadrons: :
pilot run pilot run inin 20042004
MainMain goalgoal GG
∆
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The The PrimakoffPrimakoff reactionreaction
ππ + Z + Z →→ ππ’’ + Z + + Z + γγ
2
20
23
)(cos
),(cos
tFd
dt
ttZddtd
dA
f
ϑϑωσ
πωα
ϑωσ πγ−
=
π, p1π’, p1’
s1 = ( p1’ - k’ )2
γ, k’
γ*, k
Z, p2 Z, p2’
t = ( p2’ – p2 )2
−+
++⋅+⋅= 3
22
2
2
)cos1(1
cos2)cos1(2
cos),(
ϑω
ϑβϑαα
ωπα
ϑϑωσ
π
ππππγ
π
πγ
m
mF
mdd
f
Thf
Electric & Magnetic polarizability
θfirstfirst data data takentaken inin 20042004expectedexpected ~~30k 30k eventsevents
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MuonMuon program : data 2002program : data 2002--20042004ongoingongoing analysisanalysis
nn AA11d d andand influence on QCD influence on QCD fitfit
nn DDoo andand DDoo* for * for ?? G/G from open charmG/G from open charmnn DDG/G G/G fromfrom „„high high ppTT” ” samplesample: :
perturbativeperturbative region (Qregion (Q22>1GeV>1GeV22) ) andand photoproduction region (Qphotoproduction region (Q22<1GeV<1GeV22))
nn TransversityTransversity studiesstudies ((CollinsCollins andand SiversSivers asymmetriesasymmetries) ) for single for single andand twotwo hadronshadrons
nn LL and and LL hyperonhyperon productionproductionnn Vector mesonVector mesonssnn SearchSearch for for pentaquarkspentaquarks
In In thisthis talk talk –– resultsresults withwith longitudinallongitudinal targettargetpolarizationpolarization
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Excellent for non-perturbative & perturbative physics Ø small xBjØ very small Q2 à Q2 > 100 (GeV/c)2
KinematicKinematic rangerange coveredcovered
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4 possible spin combinations:
1
2
reversed every 8 hours
two 60 cm long Target-Containerswith opposite polarization
superconductiveSolenoid (2.5 T)
3He – 4He Dilutionrefrigerator (T~50mK)
Dipole (0.5 T)
Polarization: ~50%
reversed once a week
3
4
or:
polarizedpolarized 66LiD LiD targettarget
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AsymmetryAsymmetry AA11
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measurementmeasurement ofof AA11dd
alsoalso test test ofof thethe detectordetector andand ofofsystematicsystematic effectseffects controlecontrole
1
12
du u
u ub
d
d dt
N NN
N NA
PP D N N Nf − −
= − + +
′ ′′ ′
n Weighting with fDPt was used to optimize statistical accuracy
n Asymmetry can be calculated for combinations without expectedeffect (false asymmetry) or where spin effect is expected (A1)
FalseFalse asymmetriesasymmetries((combiningcombining configurationsconfigurationswithwith thethe same spin same spin orientationorientation))
AsymmetryAsymmetry for for configurationconfigurationWithWith oppositeopposite spinsspins-- Spin Spin effectseffects expectedexpected
PLB 612, 154 (2005)PLB 612, 154 (2005)
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Data displayed at experimental <Q2> of every xBj bin
DOUBLE SPIN ASYMMETRY ADOUBLE SPIN ASYMMETRY A11dd
COMPASS:COMPASS:2002+2003 data
34 Million DIS eventsQ2 > 1 (GeV/c)2
0.1 < y < 0.9
moremore to to comecome ftomftom 20042004
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QCD QCD fitfit withwith allall DIS spin data, DIS spin data, effecteffect ofof CompassCompass AA11
DD
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MS
nn 10 10 parametersparameters fittedfittednn NDF : 173NDF : 173--1010nn ?? 2 2 probabilityprobability 14%14%
NLO NLO evolutionevolution, , calculationscalculations on on gridgrid (x,Q(x,Q22))
schemescheme, , ??2 2 mminimizationinimization usingusing MinuitMinuit
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CompassCompass gg11dd andand it’sit’s influence on influence on thethe QCD QCD fitfit
0.0240.02
2
0.04
24
9
20.077
0.23
202
7
0.
Q GeV=
+
+−
−
∆Σ =
∆Σ = withwith CompassCompass newnewdeuteriumdeuterium gg11 datadata
withoutwithout
MS schemescheme
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SemiSemi--inclusiveinclusive asymmetriesasymmetries–– alsoalso avalaiableavalaiable
ImprovementImprovement atat lowlow x, x, consistentconsistent withwith SMCSMC
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∆∆G/G at COMPASSG/G at COMPASS
Photon Gluon Fusion
N
q = c q = c cross section cross section differencedifferencein in charmed mesoncharmed mesonproductionproduction? theory well understood? theory well understood? experiment challenging? experiment challenging
qq= u,d,s = u,d,s cross section cross section difference in 2+1 jet difference in 2+1 jet productionproductionin COMPASS: in COMPASS: events withevents with2 hadrons with high 2 hadrons with high ppTT
? experiment? experimentalyaly easeasierier? theory difficult? theory difficult
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∆∆G/G: OPEN CHARMG/G: OPEN CHARM
GG
aA LLsxGssd
sxGssd
XccN
XccNccN
G
G ∆≈
∫∫=
∆=
∆∆
→
→
)ˆ,( )ˆ( ˆ
)ˆ,( )ˆ( ˆ
PGF
PGF
σ
σ
γ
γ
γ σσ
2ccMs =ˆ
∆σPGF at NLO: Bojak, Stratmann NPB 540 (1999) 345; Contogouris et al.
ccNT
cccc
ccccraw A D fPP
NN
NNA γµ=
+
−= ←
⇐←⇒
←⇐
←⇒ 76.0−≈µP
5.0≈TP
4.0≈f
)(yD
c
c
N
D
Photon-Gluon Fusion
( ) ++−++
+−
→→
→
πππ
π
0*
0%) 4 (BR
KDD
KD
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ComparisonComparison withwith 2002 data2002 data
1.21.2±±0.20.20.900.90±±0.090.090.780.78±±0.080.08S/BS/B
1.11.1265393326539332.77 2.77 ··1010--77
414181641418162.44 2.44 ··1010--77
BckgrdBckgrdBckgrdBckgrd//FluxFlux
1.51.5±±0.20.213271327±±161161
13.85 13.85 ··1010--1111
15871587±±1791799.34 9.34 ··1010--1111
DD00
DD00//FluxFlux
1.71.7±±0.20.2270270±±2525
2.82 2.82 ··1010--1111
281281±±26261.65 1.65 ··1010--1111
D*D*D*/D*/FluxFlux
1.81.89.589.58··10101212µµ/13.7 /13.7 daysdays1.701.70··10101313µµ/38.6 /38.6 daysdays
FluxFlux//#days#days
GainGainP1I+J/2003P1I+J/200320022002
And about the RICH (…)
ε: 52 ± 9 67 ± 10 1.3 ± 0.3p: 60 ± 11 56 ± 11 0.9 ± 0.3
Known factors: - Beam rec.: 1.05(JMLG) - Trigger: 1.20
- DAQ: 1.03- Pack. Fact: 1.011.31
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D* taggingD* tagging: D*? D: D*? D00 ππ( )ππKD →∗
MK
ππs-M
Kπ
-mπ
[MeV
/c2 ]
MKπ -mD0 [MeV/c2]πKD0 →
πKD0 →
n Cuts:
n zD > 0.2|cos θ*| < 0.85
(Background)
n 10 < pK < 35 GeV(RICH PID)
Cut on D*
MKπ -mD0 [MeV/c2]
317 D0
80% 2002 data
MKππs-MKπ -mπ [MeV/c2]
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AsymmetryAsymmetry for for eventsevents withwithcharmcharm productionproduction (D(D00 andand DD**))
D* D* isis cleanercleaner, but , but lowlowstatisticsstatistics
FromFrom herehere to to ?? G/GG/Gàà partonic partonic asymmetrirsasymmetrirs
aaLLLLPGFPGF areare neededneeded
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Partonic Partonic asymmetriesasymmetries areare calculatedcalculated fromfromparametrizationparametrization obtainedobtained for MC for MC simulatedsimulatedeventseventsàà goodgood descriptiondescription ofof data data withwith MC MC isis requiredrequiredàà whatwhat MC MC parametersparameters areare bestbest
n Result on ?G/Gcan be expected soon
from 2002-2004:σ(∆G/G) = 0.24 from open charm
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HadronHadron pairspairs withwith z „z „largelarge” ” ppTT
Idea Idea proposedproposed bybynn R.D.CarlitzR.D.Carlitz, , J.C.CollinsJ.C.Collins and and A.H.MuellerA.H.Mueller,,
Phys.Lett.BPhys.Lett.B 214, 229 (1988214, 229 (1988).).nn A.Bravar,D.vonA.Bravar,D.von HarrachHarrach and and A.KotzinianA.Kotzinian,,
Phys.Lett.BPhys.Lett.B 421, 349 (1998)421, 349 (1998) ..
UsedUsed inin thethe analysisanalysis ::
nn HERMES, HERMES, A.AirapetianA.Airapetian et al.,et al.,Phys.Rev.Lett.84, 2584 (2000Phys.Rev.Lett.84, 2584 (2000).).
nn SMC, SMC, B.AdevaB.Adeva et al.,et al.,Phys.Rev.DPhys.Rev.D 70, 0102002 (2004)70, 0102002 (2004)
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where: AlN→lhhX measured asymmetry, ? q/q approximated using A1 asymmetry γN,<aLL> partonic asymmetry, R fraction of contributing processes
⟩⟨+⟩⟨
∆
+⟩⟨=
∧∧
∧→
QCDCQCDCLL
LPLPLL
PGFPGFLL
lhhXlN
RaRaqq
RaG
? GA
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∆∆G/G: G/G: pairs pairs ofof highhigh ppTT hadronshadrons
nn Current fragmentationCurrent fragmentation–– xxFF >> 0.10.1–– zz >> 0.10.1
nn 2 high 2 high ppTT hadronshadrons–– ppTT > 0.7 > 0.7 GeV/GeV/cc–– ppT1T1
22+ + ppT2T222 >> 2.2.5 5 GeVGeV22
–– mm(h(h11hh22) > 1.5 ) > 1.5 GeVGeV
Photon Gluon Fusion
h1
h2
N
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Asymmetry in production of hadron pairs with high pT:result for 2002+2003 data
AnalysisAnalysis donedone withwith LEPTO generatorLEPTO generatornn InitialInitial andand finalfinal statestate partonparton showersshowers usedusednn FragmentationFragmentation functionfunction parametersparameters modifiedmodifiednn kkTT statndardstatndard valuevalue (0.44)(0.44)
∆∆G/G: G/G: pairs pairs ofof highhigh ppTT hadronshadronsnn withwith Q2 >1 GeVQ2 >1 GeV22, 0.4 < y < 0.9, 0.4 < y < 0.9
0.015 0.080( ) 0.013( )hhA
stat systD
= − ± ±
from this using RPGF obtained from MC
0.06 0.31 0.06G
G∆
= ± ± 0.13η =with
UsesUses onlyonly~~10% 10% ofof
datadata
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For QFor Q22<1GeV<1GeV22 much much moremore datadatadifficultiesdifficulties withwith additionaladditionalprocessesprocesses contributingcontributing ((PythiaPythia))
0.002 0.019( ) 0.003( )A
stat systD
= ± ±P
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LowLow QQ22 scatteringscattering –– PythiaPythia simulationsimulation
ContributingContributing processesprocesses -- samplesample afterafter „„highhigh ppTT”” selectionsselections
( ) ( )T
qQCD qqqQCD LL q
L
LO low
PG
q
FPGF LL
p
L
LL
R
q qR a R a
neglecte
GR
q q
d R negl
a
t
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ec ed
G
′′
∆ ∆+ +
∆
=
+ +
ContributionContribution fromfrom thethestructurestructure ofof thethe nucleonnucleonContributionContribution fromfrom thethestructurestructure ofof thethe photonphoton
signalsignalbackgroundbackground
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SystematicSystematic errorserrors ::
nn QuarkQuark polarizationpolarizationinin thethe photonphoton
VMDqqq q qγ γ γ∆ = ∆ + ∆
for VMD for VMD –– minimum minimum andand maximummaximum scenariosscenarios
VMD VMD VMDq q qγ γ γ− ≤ ∆ ≤
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MC MC uncertaintiesuncertaintiesnn MissingMissing NLO: NLO: scalescale dependencedependence, ,
partonparton showershower on/on/offoff
nn tuningtuning ofof parametersparameters andand data/MCdata/MCpartonparton fragmentationfragmentationpartonspartons kkTT inin nucleonnucleon andand photonphoton
biggestbiggestuncertaintyuncertaintyfromfrom kkTTinin photonphoton
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Data/MCData/MC
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0.024 0.089( ) 0.057( )G
stat systG
∆= ± ±
From 2002 and 2003 data
Obtained by averaging resultsfor min. and max scenario in VDM
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Single Single hadonshadons, , lowlow QQ22
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ExpectedExpected precissionprecission on on thethe asymmetryasymmetryteoreticalteoretical calculationscalculations bybyB. B. JaegerJaeger, A. , A. SchaeferSchaefer andand M. M. StratmannStratmann inin NLONLO
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nn CERN is again contributing to the CERN is again contributing to the NUCLEON SPIN NUCLEON SPIN PUZZLEPUZZLE
SUMMARY AND OUTLOOKSUMMARY AND OUTLOOK
nn CompassCompass runningrunning inin 20022002--2004 2004 broughtbrought interestinginterestingPHYSICS RESULTSPHYSICS RESULTS, , somesome alreadyalready publishedpublished
MANY MORE IN PMANY MORE IN PREPARATIONREPARATION
data data takingtaking restartsrestarts inin 20062006
AfterAfteràà studystudy ofof GPDS GPDS withwith DVCS DVCS andandexclusiveexclusive mezon mezon productionproduction on on hydrogenhydrogen
targettarget (+(+recoilrecoil detectordetector) )
nn ApprovedApproved program program untilluntill ~~2010 2010 withwith muonmuon beamsbeamson on polarizedpolarized targetstargets andand hadron hadron beamsbeams