Spin physics at COMPASS present and future Gerhard
- Slides: 112
Spin physics at COMPASS: present and future Gerhard K. Mallot CERN/PH On behalf of the COMPASS Collaboration Varenna, July 2011 Enrico Fermi School (Course CLXXX), Varenna, 28 June - 11 July, 2011 G. K. Mallot/CERN
Plan • COMPASS II – Goals – Experiment – Results • • G. K. Mallot/CERN – Drell-Yan – DVCS/GPDs – Outlook Helicity distributions Gluon polarization Transverse spin TMDs Varenna, July 2011
Global effort: Pol. DIS/pp 1970 1980 1990 2000 SLAC E 80 E 130 E 142/3 E 154/5 CERN EMC SMC COMPASS I DESY HERMES JLab CLAS/HALL-A RHIC Phenix/Star • A worldwide effort since decades G. K. Mallot/CERN Varenna, July 2011
Laboratories SLAC CERN 49 Ge. V e– 160/280 Ge. V µ+ DESY RHIC JLab 27 Ge. V e± 6 Ge. V e – 250+250 Ge. V pp G. K. Mallot/CERN Varenna, July 2011
COMPASS@CERN LHC COMPASS SPS
COMPASS I: Goals • Founded 1996, approved 1998, first data 2002 • Goals of the semi-inclusive measurements – Helicity distributions – Gluon polarization – Transversity PDF – Meson and baryon spectroscopy , π polarizability (not discussed here) G. K. Mallot/CERN Varenna, July 2011
Experiment: Spectrometer 60 m long Hodoscopes E/HCAL 2 E/HCAL 1 SM 2 RICH 1 Muon Wall 2, MWPC SM 1 Polarised Target 160/200 Ge. V μ beam G. K. Mallot/CERN MWPC, Gems, Scifi, W 45 Scifi, Silicon Muon Wall 1 Straws, Gems Micromegas, DC, Scifi Varenna, July 2011
CERN muon beam 100− 200 Ge. V/c Eπ=180 Ge. V G. K. Mallot/CERN Varenna, July 2011
Polarized target system solenoid 2. 5 T dipole magnet 0. 6 T acceptance ± 180 mrad 3 He – 4 He dilution refrigerator (T~50 m. K) 6 Li. D/NH 3 (d/p) 50/90% pol. 40/16% dil. factor μ Recontructed interaction vertices G. K. Mallot/CERN Varenna, July 2011
Polarized target The coldest place @ CERN: 60 m. K, 1/30 of LHC magnets temperature G. K. Mallot/CERN Varenna, July 2011
Polarized target installation G. K. Mallot/CERN Varenna, July 2011
Polarized target performance Polarization of 6 Li. D in 2006 +53. 5% -52. 0% +56. 1% days G. K. Mallot/CERN Varenna, July 2011
Tracking example: GEMs Gaseous Electron Multiplier Gem foil G. K. Mallot/CERN Varenna, July 2011
GEMs -4100 V 0 V G. K. Mallot/CERN Varenna, July 2011 • 20 triple Gems detectors • in 10 stations • 40 coordinates • size 30 30 cm 2 • 12 ns time resolution • 50 μm space resolution • efficiency ≈97 % • Ar/CO 2 70/30 %
Particle identification: RICH • 80 m 3 (3 m C 4 F 10 radiator) • 116 UV mirrors • 5. 3 m 2 UV detectors – MWPC Cs. I photosensitive cathodes – 8 8 mm 2 pads • 84 k analog r/o channels • 2006: inner quarter with ma. PMTs G. K. Mallot/CERN Varenna, July 2011
RICH • π/K separation up to 60 Ge. V/c • Large angular acceptance G. K. Mallot/CERN Varenna, July 2011
RICH G. K. Mallot/CERN Varenna, July 2011
Results: Data taking: • 2002– 2004: • 2005: • 2006: • 2007: • 2008 -2009: • 2010: • 2011: G. K. Mallot/CERN polarized deuteron target (6 Li. D), longitudinal & transverse polarization CERN shutdown polarized deuteron target (6 Li. D), long. polarized proton target (NH 3), longitudinal & transverse polarization spectroscopy polarized proton target (NH 3) , transv. polarized proton target (NH 3) , long. Varenna, July 2011
Results: helicity structure G. K. Mallot/CERN Varenna, July 2011
X-sect. asymmetries • Inclusive scattering • Semi-inclusive scattering G. K. Mallot/CERN Varenna, July 2011
Proton A 1 asymmetries incl. & semi-incl. asymmetries for identified π’s and K’s incl. π+ π – PLB 693 (2010) 227 G. K. Mallot/CERN Varenna, July 2011 K+ K−
Deuteron A 1 asymmetries Inclusive & semi-inclusive asymmetries for identified π’s and K’s incl. π+ π – PLB 680 (2009) 217– 224 G. K. Mallot/CERN Varenna, July 2011 K+ K−
g 1(x, Q 2) F 2(x, Q 2) p G. K. Mallot/CERN Varenna, July 2011
Structure function g 1(x, Q 2) p • very precise data • only COMPASS for x < 0. 01 (Q 2 > 1) • deuteron data: • ΔΣ= 0. 33± 0. 05 • Δs+Δs =− 0. 08± 0. 01± 0. 02 d • (ΔΣ = a 0, evol. to Q 2=∞) G. K. Mallot/CERN Varenna, July 2011
Bjorken sum rule from neutron β decay G. K. Mallot/CERN Varenna, July 2011 PLB 690 (2010) 466
Flavour distributions: Ds = Ds ? LO analysis of 5 p+5 d asymmetries, DSS FF PLB 693 (2010) 227 6 flavours: u, d, s, u, d, s No significant difference! Go on assuming Ds = Ds G. K. Mallot/CERN Varenna, July 2011
Flavour distributions LO analysis of 5 p+5 d asymmetries, DSS FF Line: NLO DSSV not including these data PLB 693 (2010) 227 PRD 80 (2009) 034030 5 -flavour fit, assuming Δs = Δs G. K. Mallot/CERN Varenna, July 2011
Flavour asymmetry? PLB 693 (2010) 227 • Rather small effect, Δu > Δd G. K. Mallot/CERN Varenna, July 2011
Truncated first moments Δs small, compatible with zero G. K. Mallot/CERN Varenna, July 2011
Inclusive data favour Δs < 0 J. Phys. : Conf. Ser. 295 012054 • Inclusive data only Δs ≈ − 0. 08± 0. 01 • Semi-inclusive point to Δs ≈ 0 • Shape of Δs(x) at small x unknown • Δs determination crucially depends on the fragm. functions used: DSS, DNS, HKNS, EMC, … G. K. Mallot/CERN Varenna, July 2011
Strange quark FFs DSS: PRD 75 (2007) DSS FF EMC: NPB 321 (1989) EMC FF PLB 693 (2010) 227 Measurements of K and π multiplicities are mandatory! G. K. Mallot/CERN Varenna, July 2011
Multiplicities for K’s and π’s LO: Unpolarised data For the z bins: 0. 20 − 0. 30 − 0. 45 − 0. 65 − 0. 85 Lines: MRST 04 PDF + DSS FF (LO) G. K. Mallot/CERN Varenna, July 2011 π+ π – K+ K−
K multiplicities, closer look • π multiplicities ± in agreement with LO calc. • Big deviations for K’s consequences for FF! • Data to be included in global analyses • Only 4 weeks of data, more to come Same bins as prev. page G. K. Mallot/CERN Varenna, July 2011
Gluon polarization EMC result 1987/88: quark spins contribute little to nucleon spin! ΔΣ compatible with zero Quark spin hidden by large gluon polarization via axial anomaly? G. K. Mallot/CERN Varenna, July 2011
Lepton-Photon Conf. 1989 G. Ross 1989 possible scenario: ∆G ≈ 6 (Q 2=10 Ge. V 2) ∆g/g(x) = 1 for xg > 0. 1 Let’s measure! G. K. Mallot/CERN Varenna, July 2011
Photon–gluon fusion (PGF) Gluon polarization is measurable in PGF • measure • calculate and using Monte Carlo G. K. Mallot/CERN Varenna, July 2011
Hadron production • Analysis of hadron-pair asymmetries: – open charm: single D meson cleanest process wrt physics background AROMA D 0 → K π π 0 – high-p. T hadron pairs with Q 2 > 1 Ge. V 2 – high-p. T hadron pairs with Q 2 < 1 Ge. V 2 – Single hadron production Q 2 < 0. 1 Ge. V 2 G. K. Mallot/CERN Varenna, July 2011 LEPTO PYTHIA NLO, Vogelsang et al.
Results for Δg • All results compatible with zero! • Confirmed by RHIC results in pp NLO G. K. Mallot/CERN Varenna, July 2011
Single hadron production • • Calculations exist in NLO for small Q 2 large p. T Vogelsang et al. Theory applicable at COMPASS? YES! Preferred scale μ=p. T/2 Next steps: asymmetries, inclusion into global analyses of Δg Much more data on tape G. K. Mallot/CERN Varenna, July 2011
Results: transverse spin structure G. K. Mallot/CERN Varenna, July 2011
TMD parton distributions • 8 intrinsic-transverse-momentum dependent PDFs at LO • Azimuthal asymmetries with different angular modulations in the hadron and spin azimuthal angles, Φh and Φs aka Sivers Transversity Boer– Mulders G. K. Mallot/CERN Varenna, July 2011
Transversity PDF h 1 • Couple h 1 PDF to chiral-odd Collins FF Azimuthal cross-section asymmetry: G. K. Mallot/CERN Varenna, July 2011
Collins Asymmetries • large asymmetry for proton ~10% • zero deuteron result important opposite sign of u and d proton h+ h− deuteron h+ h− G. K. Mallot/CERN Varenna, July 2011
Collins proton: identified hadrons π x z PT positive negative K G. K. Mallot/CERN Varenna, July 2011
Collins: Comparison to Hermes • Good agreement G. K. Mallot/CERN Varenna, July 2011
Global Fit • Fit to COMPASS d, HERMES, BELLE (Collins FF, e+e-) • in good agreement with new proton data G. K. Mallot/CERN Varenna, July 2011
Transversity PDF h 1 via 2 -hadron • Alternative: couple h 1 to chiral-odd 2 -hadron interference FF cross-section asymmetry: G. K. Mallot/CERN Varenna, July 2011
two-hadron asymmetry • large asymmetries • interference FF and transversity sizable G. K. Mallot/CERN Varenna, July 2011
Comparison to a recent Fit • Recent fit (dominated by HERMES, COMPASS p not yet in) G. K. Mallot/CERN Varenna, July 2011
Sivers function • Sivers Asymmetry: • proposed (1990, Sivers) • thought to vanish (1993, Collins) • resurrected (2002, Brodsky, Hwang, Schmitt) • different sign in DY and SIDIS G. K. Mallot/CERN Varenna, July 2011
Proton Sivers Asymmetry • compatible with zero for the deuteron • non-zero asymmetry for pos. hadrons h+ h− G. K. Mallot/CERN Varenna, July 2011
• Hermes data show somewhat larger asymmetry for positive π’s G. K. Mallot/CERN Varenna, July 2011
Sivers as function of W • Tendency for asymmetries to increase towards small W, however some correlation with other kinematic variables π G. K. Mallot/CERN K Varenna, July 2011
Spin-averaged asymmetries • Unpolarized target 6 Li. D (deuteron) • Kinematic factor devided out • sin φ modulation is small cos “Cahn” cos 2 “ Boer. Mulders” G. K. Mallot/CERN Varenna, July 2011
COMPASS is more! • • Rich physics programme with hadron beams (2008, 2009, 2012) Proton, pion and kaon beams Pion/kaon polarizability Meson and baryon spectroscopy, PWA G. K. Mallot/CERN Varenna, July 2011
What’s next? • Focus on transverse structure of the nucleon • Transverse size and orbital angular momentum (GPDs) • Restricted universality of T-odd TMDs (Sivers, Boer-Mulders), sign change from SIDIS to DY, additional TMDs (pretzelocity, worm-gear) • COMPASS-II Proposal wwwcompass. cern. ch/compass/proposal/compass. II_proposal/compass-II_proposal. pdf • Other new facilitites/experiments • JLAB, RHIC, JLAB 11 Ge. V, JPARC, • ENC, e. RHIC/ELIC, NICA/SPD G. K. Mallot/CERN Varenna, July 2011
COMPASS-II • Generalized Parton Distributions (GPD) • Drell-Yan • Pion (and kaon) Polarizabilities Approved December 2010 G. K. Mallot/CERN Varenna, July 2011
GPD’s • • ~ Novel concept, universal, H, H, E, E~ H (E) nucleon helicity (non)conservation Nucleon form factors and PDFs as limiting cases Correlating transverse spatial and longitudinal momentum degrees of freedom (‘tomography’) Total orbital momentum: X. -D. Ji, PRL 78 (1997) 610 x is not x-Bjorken G. K. Mallot/CERN Varenna, July 2011
Orbital angular momentum JHEP 06 (2008) 066 A model-dependent case-study G. K. Mallot/CERN Varenna, July 2011
DVCS • DVCS is the cleanest process to determine GPDs • need a world-wide effort • Global analysis over large kinematic range mandatory • COMPASS-II: from HERA to JLAB 12 Ge. V kinematics G. K. Mallot/CERN Varenna, July 2011
DVCS • DVCS can be separated from BH and the GPD H can constrained the cross section using different charge Deep VCS & spin (eμ& Pμ) combinations of the μ beam • Note: μ± have opposite polarization at COMPASS Charge & Spin difference and sum: Bethe-Heitler Related to: H (x= , , t) P dx H (x, , t) /(x- ) G. K. Mallot/CERN Varenna, July 2011
`Tomography’ • Subtract BH from , intergrate over φ unpol. DVCS x-sect • ξ=0 t = −ΔT 2 , no long. transfer μ μ’ * θ p • Transverse size as function of longitudinal momentum fraction Independent of a GPD parametrisation! G. K. Mallot/CERN Varenna, July 2011
COMPASS-II projection • COMPASS-II projection, 2 years of data taking • Pilot run 2012 • x. B region unique to COMPASS G. K. Mallot/CERN Varenna, July 2011
BH vs DVCS simulation • Rapid variation of relative contributions with x. B • Normalisation of BH contributon at small x. B G. K. Mallot/CERN Varenna, July 2011
BH vs DVCS data • Test runs in 2008/2009 – 40 cm long H 2 target • Clear DVCS signal, BH can be subtracted G. K. Mallot/CERN Varenna, July 2011
COMPASS II proj. data set • Charge & spin asymmetry • Sensitive to GPD H models • Cancelation of several experimental uncertainties • Easier to measure than absolute cross-sections μ’ * • Asymmetries, sums and differences in μ 2 6 x. B 4 Q bins as function of φ • Simulation for 2 years data taking, 160 Ge. V/c and a 2. 5 m long liquid H 2 target • Not shown: Deeply virtual vector meson production G. K. Mallot/CERN Varenna, July 2011 p θ
Proj. charge & spin difference ’=0. 8 ’=0. 05 G. K. Mallot/CERN Varenna, July 2011
Proj. charge & spin asymmetry G. K. Mallot/CERN Varenna, July 2011
Semi-inclusive DIS • COMPASS I had 6 Li. D and NH 3 (i. e. deuterons for unpol. ) • COMPASS II pure hydrogen target in parallel with DVCS – Acosφ, Acos 2φ, Asinφ for proton – Hadron multiplicities for FF, strange quark PDF Proj. for 1 week G. K. Mallot/CERN Varenna, July 2011
DVCS – main new equipment ECAL 2 ECAL 1 50 m New electromagnetic calorimeter, ECAL 0 Liquid hydrogen target, 2. 5 m long Proton Time-Of-Flight detector, 4. 0 m long G. K. Mallot/CERN Varenna, July 2011
Experimental setup: Camera • 2 barrels 4 m long scintillators • ~ 300 ps timing resolution • 2. 5 m long LH 2 target Gandalf Readout Project: 1 GHz digitalisation of the PMT signal to cope for high rate G. K. Mallot/CERN Varenna, July 2011
Geometry target region beam G. K. Mallot/CERN LH 2 target Varenna, July 2011
ECAL 0 • new ECAL 0 large angle calorimeter • Multipixel Avalanche Photodiode readout ECAL 0 2. 20 m 248 modules (12 12 cm 2) of 9 cells read by 9 MAPDs G. K. Mallot/CERN Varenna, July 2011
Drell−Yan Process • No fragmentation function involved • Convolution of two PDFs • Best: pol. antiproton−proton (longterm) • Simpler: negative pion on pol. proton (short-term) • Pion valence anti-u annihilates with proton u G. K. Mallot/CERN Varenna, July 2011 ‘
Restricted universality in SIDIS and DY T-odd TMD `gauge link changes sign for T-odd TMD’, restricted universality of T-odd TMDs SIDIS: FSI DY: ISI J. C. Collins, PLB 536 (2002) 43 Sivers G. K. Mallot/CERN Boer-Mulders Varenna, July 2011
Future DY experiments 2014 RHIC An. DY collider pp pol. 5002 > 2013 G. K. Mallot/CERN Varenna, July 2011
Drell−Yan muon pair mass regions 4 < M + - < 9 Ge. V Safe region 2 < M + - < 2. 5 Ge. V possible region Combinatorial background < 1: 1 G. K. Mallot/CERN J/ψ region Varenna, July 2011
COMPASS-II Polarised Drell-Yan • COMPASS-II: 190 Ge. V/c − beam on transversely pol. proton target • − valence u-antiquark picks nucleon’s u quark in valence region (u-quark dominance) • Access to transversity , the T-odd Sivers and Boer-Mulders TMDs G. K. Mallot/CERN Varenna, July 2011
Major rearrangement of target region Quench and Exhaust Lines Cable trays Transfer Line Control Racks Absorber Pol. target He-pipes Micro Wave guides G. K. Mallot/CERN Varenna, July 2011
COMPASS polarized DY xp x x. F=x −xp G. K. Mallot/CERN x. F Varenna, July 2011
More projections x. F=x -xp G. K. Mallot/CERN x. F=x -xp Varenna, July 2011 x. F=x -xp
COMPASS-II schedule 2012 Primakoff scattering: DVCS pilot run: 2013 Accelerator shutdown 2014 Drell-Yan : 2015− 2016 DVCS and DVMP: Unpolarized SIDIS: Polarizabilities of and K t-slope, transverse size Universality of TMDs Study GPDs, “nucleon tomography” FF, strangeness PDF, TMDs Caveat: CERN Accelerator schedule not fixed beyond Nov 2012 G. K. Mallot/CERN Varenna, July 2011
Summary • Wealth of data from COMPASS, more to come, e. g – COMPASS: 2010 p transverse, 2011 p longitudinal – Single hadron production asymmetries (ΔG) – Hadron spectroscopy • Focus shifting to 3 D structure of the nucleon • COMPASS II will make major contributions • Exciting times ahead (also off-LHC) G. K. Mallot/CERN Varenna, July 2011
(Nucleon) Spin is fun G. K. Mallot/CERN Varenna, July 2011
G. K. Mallot/CERN Varenna, July 2011
Longitudinal spin transfer to & 2003/2004 data 69500 Λ 41600 Λ Λ Λ • Large (!) DLL for Λ related to antistrange quark distribution G. K. Mallot/CERN Varenna, July 2011
G. K. Mallot/CERN Varenna, July 2011
COMPASS-2: the near future • COMPASS-2 is a new experiment – Recommended by the CERN SPSC: Sept. 29, 2010. – Approved by the CERN Research Board: Dec. 1, 2010. • COMPASS-2 physics – 4 main topics 1. DVCS and DVMP : 2. Unpolarized SIDIS : TMDs 3. Drell-Yan : 4. Primakoff scattering : Study GPDs, “nucleon tomography” Fragmentation Functions, s-PDFs, Universality of TMDs Polarizabilities of and K • Data taking – 2012, SPS/LHC shutdown, 2014, 2015, 2016 G. K. Mallot/CERN Varenna, July 2011
Polarized Drell-Yan measurements • COMPASS – 190 Ge. V pion beam – Transversely polarized NH 3 target – Spectrometer ready for muon detection – SIDIS : – DY: • Dominated by u/u annihilation • Access to TMDs, complementary to SIDIS – Universality of TMDs – Test of factorization: opposite sign expected: G. K. Mallot/CERN Varenna, July 2011
DY cross section expansion • Expansion in LO quark parton model Arnold, Metz and Schlegel, Phys. – polarized target nucleon – Access 4 TMDs: Rev. D 79: 034005, 2009. • Sivers, Boer-Mulders, Pretzelosity, Transversity – Convolution with the pion f 1 or BM distributions Siv • Access 4 TMDs – asymmetry modulation: BM Pr Tr G. K. Mallot/CERN Varenna, July 2011
Polarized Drell-Yan – expected results Sivers Boer-Mulders 2 x 5 months of data taking 6. 108 pions/spill 1. 1 m NH 3 target Mass: 4<M <9 Ge. V DY beam test in 2008 Pretzelosity G. K. Mallot/CERN Transversity Varenna, July 2011
Drell-Yan preparation Upgrade of the spectrometer • New beam telescope (Sci-Fi) • Thick hadron absorber/beam dump • Vertex detector • Displacement of the target G. K. Mallot/CERN Varenna, July 2011
Sivers asymmetry: identified hadrons Positive hadrons: slightly positive signal Negative hadrons: the asymmetry is compatible with zero Varenna, July 2011 G. K. Mallot/CERN
Sivers: COMPASS data vs fit (Anselmino et al. ) Anselmino et al. , Eur. Phys. J. A 39 (2009)89 Update in S. Mellis, DIS 2011. Updated fit with the latest HERMES and COMPASS data (Mellis, 2011) Opposite transverse momentum for u and d quarks G. K. Mallot/CERN Additional results in Arnold et al. , ar. Xiv: 0805. 2137 (2008). Varenna, July 2011
Accessing DG: QCD fits to world data (DIS, SIDI From Leader, Spin-2008 S) From DSSV, PRL 101, 2008 LSS-06 : Phys. Rev. D 73, 2006 AAC’ 06 : Phys. Rev. D 74, 2006 DSSV-08: Phys. Rev. Lett. 101, 2008 DG(x) may be: positive, negative, or sign-changing! – Shape of DG(x)? – Needed are dedicated measurements of DG(x) » G. K. Mallot/CERN Varenna, July 2011
Accessing DG: Photon-Gluon Fusion (2 methods) n High-p. T hadron pairs (q=u, d, s) n Physical background Rely on MC estimates n 2 cases: n n Open Charm production (q=c) n n Q 2>1 (Ge. V/c)2 Q 2<1 (Ge. V/c)2 Photon-Gluon Fusion Detect D° K-p+ and D* D° + Clean channels (no u, d, s quarks) Low statistics COMPASS data: n n n hi-p. T, Q 2>1 : 3 points, data from 2002 -2007 Hi-p. T, Q 2<1 : 1 point, data from 2002 -2004 Open charm: 1 point, data from 2002 -2007 G. K. Mallot/CERN Varenna, July 2011 5 DG/G points
G. K. Mallot/CERN Varenna, July 2011
G. K. Mallot/CERN Varenna, July 2011
DVCS – main new equipment ECAL 2 ECAL 1 50 m New electromagnetic calorimeter, ECAL 0 Liquid hydrogen target, 2. 5 m long Proton Time-Of-Flight detector, 4. 0 m long G. K. Mallot/CERN Varenna, July 2011
G. K. Mallot/CERN Varenna, July 2011
COMPASS spectrometer G. K. Mallot/CERN Varenna, July 2011
COMPASS spectrometer G. K. Mallot/CERN Varenna, July 2011
Flavour asymmetry? • considerable asymmetry in the unpolarised case • model predicts naturally asymmetry for pol. case • Rather small effect, u-bar > d-bar G. K. Mallot/CERN Varenna, July 2011
Inclusive data favour Δs < 0 Inclusive only, Δs ≈ − 0. 08± 0. 01 Inclusive + semi-incusive, Δs ≈ − 0. 08± 0. 01 J. Phys. : Conf. Ser. 295 012054 G. K. Mallot/CERN Varenna, July 2011
Δg/g from PGF open charm • cleanest process • little physics background (LO, QCDC) • observe asymmetry in D meson production • • statistics limited only one D meson via D → πK (BR ~ 4%) combinatorial background large drastically reduced when looking to D* decay in coincidence with slow pion G. K. Mallot/CERN Varenna, July 2011 g c c
Δg/g from open charm D 0 → K π π 0 G. K. Mallot/CERN Varenna, July 2011
p. T dependence of single hadrons • Good description of data by NLO p. QCD • Considerable scale dependence • Validates determination of Δg from high-p. T hadron distributions at COMPASS energies G. K. Mallot/CERN Varenna, July 2011
Accessing DG: summary of measurements LSS ’ 10 DSSV ‘ 08 Measurements are compatible with 0 – large values of DG seem excluded But: Sign of DG is yet ambiguous The shape of DG(x) is still unknown, data constrain a limited region The contribution of DG to the nucleon spin is not determined G. K. Mallot/CERN Varenna, July 2011
High p. T hadron cross sections Absolute cross-section measurement quasi real photo production of hadron μ+ d → μ + h±X 2004 data, 4 weeks Huge statistics: rapidity bins COMPASS Q 2<0. 1 √s =17 Ge. V In agreement with NLO p. QCD, within theory’s uncertainty over 6 orders of magnitude Settles theory framework for ΔG high p T Next step: produce spin asymmetries ALL(p. T) for same events
From inclusive reactions to exclusive reactions Deep Inelastic Scattering p ’X γ* p ’p’ Q²x B * x x+ z p Q² p x- GPDs t x P P’ x P y x boost PDF q( x ) Px x boost GPD H( x, , t ) ( Px, b ) Varenna, July 2011 in 1 dimension in 1+2 dimensions G. K. Mallot/CERN z b y from Nicole D’Hose ’ Deeply Virtual Compton Scattering
PDF, GPD, TMD PDF GPD TMD For theory see: Ji, PRL 2003, Belitsky, Ji, Yuan PRD 2004 Meissner, Metz, Schlegel, JHEP 0908: 056 2009 G. K. Mallot/CERN Varenna, July 2011
Diffractive dissociation into 3 final states 2008 data, p target Mass of outgoing 3 system charged mode: - p --> - + - p PWA: ~ 24 M events (acceptance corr. ) G. K. Mallot/CERN Varenna, July 2011 neutral mode: - p --> - 0 0 p PWA: ~ 1 M events
