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COMPASS : a Facility to study QCD

COMPASS : a Facility to study QCD. 1. CO MMON M UON and P ROTON A PPARATUS for S TRUCTURE and S PECTROSCOPY. Studies until now 2011 : Nucleon Spin with high energy polarized  beams + polarized targets :

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COMPASS : a Facility to study QCD

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  1. COMPASS : a Facility to study QCD 1 COMMON MUONand PROTON APPARATUSfor STRUCTUREand SPECTROSCOPY • Studiesuntilnow 2011: • Nucleon Spin withhighenergypolarized beams+ polarizedtargets: • longitudinal spin: gluon and quark helicity distribution • transverse spin and transverse momentumdependent distribution • Spectroscopywithhadron beams+ LH2 (or solid) targets: • Search of hybrids and glueballs to betterunderstand quark and gluon • confinement N. d’Hose (CEA Saclay)

  2. COMPASS-II: a Facility to study QCD 1 COMMON MUONand PROTON APPARATUSfor STRUCTUREand SPECTROSCOPY New Program (SPSC-P-340) until ~2016 recommended by SPSC and approved by Research Board • Primakoffwithπ, K beam Test of Chiral Perturb. Theory • DVCS & DVMP withμbeams Transv. Spatial Distrib. withGPDs • SIDIS (with GPD prog.)  Strange PDF and Transv. Mom. Dep. PDFs • Drell-Yan withbeamsTransverse MomentumDependentPDFs

  3. SPS proton beam: 2.6 1013/spill of 9.6s each 48s, 400 GeV/c • Secondary hadron beams (, K, …): 6.108 /spill, 50-200 GeV/c • Tertiary muon beam (80% pol): 4.6108 /spill, 100-200 GeV/c • -> Luminosity ~ 1032 cm-2 s-1 GPD with+and a 2.5m long LH target • ~1.2 1032 cm-2 s-1 DYwith-and a 1.1m long NH3target 60m COMPASS LHC CNGS Gran Sasso 732 kms SPS high energy beams, broad kinematic range, large angular acceptance

  4. Meson Spectroscopy 3

  5. Hadron Reactions at COMPASS 4 • COMPASS: • production mechanismsstudied in parallelusingproton, pion and kaonbeams • H2, Ni and Pb targets • identification of charged and neutralparticles in a large and flat acceptance • 10 world statistics •  PWA analysis (international task force for COMPASS, JLab, PANDA…)

  6. Search of the controversialhybrids1-(1600) withJPC=1-+ in the reaction-p  1-(1600) p  -p  +--p + Pb (2009 data) 2.3M events + othertargets W, Ni

  7. Search of the controversialhybrids1-(1600) withJPC=1-+ in the reaction-p  1-(1600) p  -p  +--p JPCM(isobar,)L PRL104 (2010) 241803 Pb 2004 data a1(1260) 2(1670) a2(1320) 1(1600)

  8. Search of the controversialhybrids1-(1600) withJPC=1-+ in the reaction-p  1-(1600) p  -p  +--p JPCM(isobar,)L PRL104 (2010) 241803 Pb 2004 data a1(1260) 2(1670) Clear1-(1600) signal in +-- for Pb target Phase between1(1600) and a1(1260) a2(1320) 1(1600)

  9. Nuclear Medium effect 7 fromPb (2004) and H2 (2008) targets Pb H2 Pb Pb H2 Nucleareffect: Production of Spin Projection M=1 states enhanced for larger A Pb H2 Pb H2

  10. QCD atlowenergy: Primakoffexperimentswithπ, K or inverse Compton Scattering on π, K 8 π (or Κ) s = (p+p)2 = (CMenergy)2 t = (cos cm -1) γ π (or Κ) γ Q2 0 γ (s - mπ2) 2s The chiral perturbation theory (ChPT) predicts the low-energybehavior of the cross section with s varyingfromthreshold (mπ2) to a few mπ2 Deviation due to  polarisabilities the point-like cross section ismeasuredwith the muon beam

  11. PionPolarisabilities and Chiral predictions 9 The pion: fundamentalrole for QCD atlow-energy Goldstone boson (spontaneousbreaking of chiral symmetry) lightest quark-gluon bound state system  understandingitsinternal structure is a fundamental challenge The polarisabilitiesgive the deformation of the pion shape by an EM field > 0 S=0 diamagneticcontr. <0 • accuracy • 0.025 • 0.66 • Goal of • COMPASS • in 120 days 2-loopChPTprediction:  +  = (0.2 0.1) 10-4 fm3  -  = (5.7 1.0) 10-4 fm3 • Previousexperiments:  -  varies from 4 to 14 .10-4 fm3

  12. QCD athighenergy: DeepInelasticScattering 10 3 twist-2 PDFs Unpolarized PDF DeepInelasticScattering p  ’X or f1q(x) ’  Quark withmomentum x in a nucleon Q²xB γ* x Helicity PDF z p or g1q(x) Quark with spin parallel to the nucleon spin in a longitudinallypolarizednucleon x P Transversity PDF x boost y or h1q(x) Parton Distribution q ( x ) Px Quark with spin parallel to the nucleon spin In a transverselypolarizednucleon Chiral odd, accessible in SIDIS and DY

  13. Helicity quark distributions 11 Frompolarized semi-inclusive DIS analysis, Usingcharged pions and kaons which tag quark flavour on both proton and deuteronpolarizedtargets  Full quark flavourdecomposition (at LO) Longitudinal spin asymmetry quark Fragmentation Function (FF) Weneedunpolarized PDF (MRST04) and parameterization of FF from DSS (DeFlorian, Sassot, Stratmann, PRD75 (2007) 114010)

  14. LO Helicity quark distributions 12 • COMPASS • PLB693 (2010) 227 • full flavourseparation • at LO down to x=0.004 • o HERMES • PRD71 (2005) • DSSV predictionsat • NLO (DeFlorian, Sassot, Stratmann, Vogelsang PRD80 (2009) 034030) Good agreement with global fits to g1 inclusive data The flavorasymmetry of the seahelicity distributions is compatible with 0 (whilethereis a considerablewideasymmetry in the unpolarized case) s ~ 0 but the DSSV fit suggestsnegative values atsmaller x

  15. Transverse spin or momentum PDF 13 m p m p h+/- • SIDIS with transversely polarized target • Measure simultaneously two azimuthalasymmetries (h, S) Collins: Outgoing hadron direction & quark transverse spin Sivers:Nucleon spin & quark transverse momentum Sivers Collins at LO: Usual quark fragmentation function Collins fragmentation function, depends on spin =f1T(x) or h1q(x) Transversity PDF One Transverse Momentum PDF beyond the collinear approximation, quark transverse momentum (kT) effects

  16. Transversity from Collins asymmetry 14 Fit to AdCOLL(x) from COMPASS and ApCOLL(x) from HERMES and Collins fragmentation function from BELLE (e+e- scatt.) in good agreement with new proton data COMPASS proton 2007

  17. Sivers TMD from Sivers asymmetry 15 ComparisonwithpredictionsfromAnselminoet al., based on fit of Hermes-p and Compass–d data =f1T(x) Present proton data not in fit Positive hadrons COMPASS proton 2007 -COMPASS signal < HERMES signal -Possible W dependence -proton 2010 data to beanalysed Extraction of Siversfct (HERMES p and COMPASS d) Negative hadrons x

  18. 16 After SIDIS, Drell-Yan to studyTMDs Drell –Yan π- p +-X with intense pion beam (up to 109 /spill) with the transverselypolarised NH3target with the COMPASS spectrometerequippedwith an absorber - Cross sections: In SIDIS: convolution of a TMD with a fragmentation function In DY: convolution of 2 TMDs ‘’’’ complementary information and universality test ‘

  19. 17 Why DY isveryfavourableat COMPASS? dominated by the annihilation of a valenceanti-quarkfrom the pion and a valence quark from the polarised proton This willbe the onlysuchexperimentalmeasurement for at least 5-10 years • Access to TMDs for incoming pion  targetnucleon • (TMDs as Transversity, Sivers, Boer-Mulders, pretzelosity) large acceptance of COMPASS in the valence quark region for p and π where SSA are expected to be larger 1rst moment of Sivers function for u quark

  20. Experimental check of the change of sign of TMDsconfrontingDrell-Yan and SIDIS results 18 The T-oddcharacter of the Boer-Mulders and Siversfunction impliesthatthesefunctions are processdependent In order not to beforced to vanish by time-reversal invariance the SSA requires an interaction phase generated by a rescattering of the struck parton in the field of the hadron remnant FSI ISI Needexperimentalverification Test of consistency of the approach Boer-Mulders Sivers COMPASS + HERMES have alreadymeasured non zeroSivers SSA in SIDIS

  21. 19 Resultsfrom test measurements in 2009 2009 with an absorber up to 1.5 108/spill (without radioprotection pb) 3domains of study Expected: 3600±600 J/ and 110±22 DY Measured: 3170±70 J/ and 84±10 DY 1- safedomain for Drell-Yan 4 < M+- < 9 GeV 2-reasonabledomain for Drell-Yan 2 < M+- < 2.5 GeV Large Combinatorial Background S/B ~ 1 Open charmdecays (from D0) smallerthan 15% of signal 4 < M+- < 9 GeV 2 < M+- < 2.5 GeV 3-domain for J/ mechanism M+-GeV 2.9 < M+- < 3.2 GeV 2.9 < M+- < 3.2 GeV if q-qbardominates over g-g fusion Drell-Yan canbeconsidered

  22. 20 Predictions for Drell-Yan at COMPASS Siversfunctionin the safedimuon mass region 4 < M+- < 9 GeV 2 years of data 190 GeVpion beam 6 .108π-/spill (of 9.6s) 1.1 m transv. pol. NH3target Lumi=1.2 1032 cm-2s-1 Blue line withgrey band: Anselmino et al., PRD79 (2009) Black solid and dashed: Efremov et al., PLB612 (2005) Black dot-dashed: Collins et al., PRD73 (2006) Squares: Bianconi et al., PRD73 (2006) Green short-dashed: Bacchetta et al., PRD78 (2008) The change of signcanalreadybeseen in 1 year

  23. from inclusive reactions to exclusive reactions 21 *  Q² x+ x- p GPDs t DeepInelasticScattering Deeply Virtual Compton Scattering p  ’X p ’p’ ’  Q²xB γ* x z p P’ z x P x P b y y x boost x boost Distrib. de Partons q ( x ) Generalized Partons Distrib. H(x,,t ) Px • ( Px,b) Observation of the Nucleon Structure in 1 dimension in 1+2 dimensions

  24. Exploring the 3-dimensional phase-space structure of the nucleon 22 From Wigner phase-space-distributions (Ji, PRL 2003, Belitsky, Ji, Yuan PRD 2004) Wecanbuild « mother-distributions » (Meissner, Metz, Schlegel, JHEP 0908:056 2009) and derive • GPD: Generalised Parton Distribution (position in the transverse plane) • TMD:TransverseMomentum Distribution (momentum in the transv. plane) k PDF GPD TMD New researchfields

  25. 23 Generalized Partons Distributions (H,E,…) • Allow for a unified description of formfactors and • parton distributions • Allow for transverse imaging (nucleontomography) and giveaccess to total angularmomentum(through E)  x  0.003 x  0.03 x  0.3 Impact parameterb Longitudinal momentum fraction x Tomographicparton images of the nucleon

  26. 24 Whatmakes COMPASS unique for GPDs? • CERN High energymuonbeam • 100 - 190 GeV • μ+andμ-available • 80% Polarisation • with opposite polarization • Will explore • the intermediatexBjregion • Uncoveredregionbetween • ZEUS+H1 and HERMES+Jlab • before new collidersmaybe • available • presentlyonly 2 actors: • Jlab and COMPASS • Transverse structure at • x~10-2 essential input for • phenemenology of high- • energy pp collision (LHC) B

  27. 25 Experimental requirements for DVCS μ p  μ’ p  μ’ Phase 1 ~ 2.5 m LiquidHydrogen Target ~ 4 m Recoil Proton Detector (RPD)  SM2 ECAL2 SM1 ECAL1 • ECALsupgraded • + ECAL0 before SM1 μ p’

  28. 26 Contributions of DVCS and BH atE=160 GeV  μ’ * θ μ p  Deep VCS Bethe-Heitler d  |TDVCS|2 + |TBH|2 + InterferenceTerm Monte-Carlo Simulation for COMPASS set-upwith only ECAL1+2 • Missing • DVCS acceptance • without ECAL0 BH dominatesstudy of InterferenceDVCS dominates excellent  Re TDVCSstudyof dDVCS/dt referenceyieldor Im TDVCS Transverse Imaging

  29. 27  μ’ * θ μ p  Deeply Virtual Compton Scattering dσ(μpμp) = dσBH + dσDVCSunpol+ PμdσDVCSpol + eμaBHRe ADVCS +eμ PμaBHIm ADVCS Phase 1: DVCSexperimentto studythe transverse imaging with+, - beam+ unpolarized2.5m long LH2 (proton) target SCS,U  d( +) +d( -)  Using SCS,Uand integration over  dDVCS/dt~exp(-B|t|) and BH subtraction

  30. DVCS: Transverse imaging at COMPASS 28 dDVCS/dt ~ exp(-B|t|) 2 years of data 160 GeV muon beam 2.5m LH2target global = 10% withoutany model wecanextract B(xB) • B(xB) = ½ < r2 (xB) > r is the transverse size of the nucleon

  31. DVCS: Transverse imaging at COMPASS dDVCS/dt ~ exp(-B|t|) 14 • Transverse size • of the nucleon ? 1. 0.5 0.65 0.02 fm H1 PLB659(2008) COMPASS xB withoutany model wecanextract B(xB) • B(xB) = ½ < r2 (xB) > r is the transverse size of the nucleon

  32. DVCS: Transverse imaging at COMPASS dDVCS/dt ~ exp(-B|t|) ansatzatsmallxB inspired by ReggePhenomenology: B(xB) = b0 + 2 α’ln(x0/xB) α’slope of Reggetraject • B with an accuracy of 0.1 GeV-2 • α’with an accuracy 2.5 • ifα’ 0.26 with ECAL1+2 • ifα’ 0.125 with ECAL0+1+2 with the projecteduncertainties wecandetermine :

  33. 29 Deeply Virtual Compton Scattering dσ(μpμp) = dσBH + dσDVCSunpol+ PμdσDVCSpol +eμaBHRe ADVCS +eμ PμaBHIm ADVCS Phase 1: DVCSexperimentto constrainGPD H with+, - beam+ unpolarized2.5m long LH2 (proton) target  d( +) -d( -) and Re(F1 H) DCS,U andIm(F1 H) SCS,U  d( +) +d( -) • Im H (,t)=H(x= ,,t) • ReH (,t)= PdxH(x,,t) /(x-)   xB / (2-xB)

  34. 30  μ’ * θ μ p  Beam Charge and Spin Difference (usingDCS ,U) Comparison to different models ’=0.8 ’=0.05 2 years of data 160 GeV muon beam 2.5m LH2target global = 10% Systematicerror bands assuming a 3% charge-dependenteffect between+ and - (control with inclusive evts, BH…)

  35. 2008-9 tests: observation of BH and DVCS events 31 • During the hadron program with 1m long recoil proton detector (RPD) and 40cm long LH2 target • and the 2 existing ECAL1 and ECAL2 • 2008:observation of exclusive single photon production, • εglobal = 0.13 +/- 0.05 confirmedεglobal = 0.1 as assumed for simulations • 2009: observation of BH and DVCS events • 10 BH eventsexpected • ~30 « pure » DVCS events • with ~10 0 contamination

  36. 32 Summary for GPD @ COMPASS • GPDsinvestigatedwith Hard Exclusive Photon and Meson Production • the t-slope of the DVCS cross section ……………… LH2target + RPD……phase 1 •  transverse distribution of partons • the Beam Charge and Spin Sum and Difference and Asymm…………….phase 1 •  Re TDVCS and Im TDVCS for GPD H determination • the Transverse Target Spin Asymm………polarised NH3target + RPD……phase 2 •  GPD E and angularmomentum of partons (future addendum)

  37. 33 Conclusions • Only selected topics among the large harvest of (present • and incoming) results on Spin and Spectroscopy • The main topics of COMPASS-II are: • GPD with DVCS and DVMP • TMD with DY and SIDIS • precise unpolarised PDF measurements • Chiral perturbation theory - soft QCD • + updated programs on spectroscopy, DY, GPD… • Jlab 12 GeV, huge luminosity, very promising facility • and for the next 10 years, before ENC, EIC, eRHIC, LHeC, • COMPASS@CERN can be a major player in QCD physics • using its unique 200 GeVhadron and polarisedmuonbeams

  38. PionPolarisabilities measurement 5 Polarisabilityeffectwithincreasing s atbackwardor forward angle • The 3 components • ( - ), ( + ), • (2 - 2) • canbemeasured point-like case for ChPTprediction

  39. 15 The Drell-Yan process in π-p • Access to TMDs for incoming pion targetnucleon • TMD as Transversity, Sivers, Boer-Mulders, pretzelosity Hadron plane Collins-Soper frame (of virtual photon) , lepton plane wrt hadron plane targetrest frame Starget transverse spin vector /virtual photon Lepton plane

  40. 17 DY and COMPASS set-up π- 190 GeV • Key elementsfor a small cross section investigation at high luminosity • Absorber (lesson from 2007-8 tests) to reduce secondary particle flux • COMPASS Polarised Target • Tracking system and beam telescope • Muon trigger (LAS of particular importance - 60% of the DY acceptance) • RICH1, Calorimetry – also important to reduce the background

  41. 19 Resultsfrom test measurements in 2009 <Pt> = 1 GeV/c  COMPASS sensitive to TMDs xF=x-xp

  42. 21 Predictions for Drell-Yan at COMPASS -0.2 < xF < 0.85 xF=x-xp xF=x-xp xF=x-xp xF=x-xp Statisticalaccuracyfrom 0.01 to 0.02 in twoyears

  43. 21 Predictions for Drell-Yan at COMPASS xF=x-xp xF=x-xp xF=x-xp xF=x-xp Statisticalaccuracy 12% in twoyears

  44. 22 Summary for Drell-Yan @ COMPASS • First everpolarisedDrell-Yan experiment sensitive to TMDs • Pure valence u dominance because of the -beam • Key measurements: • TMDsuniversalitySIDIS DY • change of sign check from SIDIS to DY for Siversand Boer-Mulders • study of J/production mechanism • After a series of beam tests, the feasibilityisproven • In a phase 2 (future addendum), • measurementwithanti-protonbeamswillbeenvisaged

  45. QCD athighenergy: DeepInelasticScattering 11 Whileunpolarised light quark PDF wellconstrained, strange quark distributions are not sowellknown DeepInelasticScattering p  ’X ’  Q²xB γ* x z p x P x boost y COMPASS with SIDIS Parton Distribution q ( x ) Px

  46. Semi-Inclusive Deep Inelastic Scattering 8 Semi-Inclusive DIS measurementsduring GPD program with a pure proton target with RICH detector and Calorimeters Charge separation and identification K+, K-, K0, +, -, 0, … Major progress as compared to previousexperimentsto improveUnpolarised PDF Hadron multiplicitiesat LO PDF quark Fragmentation Function depend on x depend on z (fraction of energy of the outgoing hadron) Final goal: extensive measurements (x,z,…) to provide input to NLO global analysis for PDF and FF

  47. Projection of errors for s(x) 9 Short term goal: LO analysisfrom COMPASS data aloneintegrated over z Projection for 1 weekwith 2.5m LH2 target highstatistics

  48. Semi-Inclusive Deep Inelastic Scattering 11 Semi-Inclusive DIS measurementsduring GPD program with a pure proton target with RICH detector and Calorimeters Unpol. cross section: Cahneffect info on <kT> Boer-Mulders TMD  Collins FF + Cahneffect measurement of Acosh and Acos 2h + knowledge of Collins FF  Boer-Mulders TMD determination

  49. Projection of errors for Acoshand Acos 2h 12 14 • Projection proton (LH2) • 1 week • COMPASS 2004 deuteron • 4 weeks • Input for • global analysis + flavorseparationusing RICH particle identification

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