Experimental review of DG Alain Magnon DAPNIASPh N

Experimental review of DG Alain Magnon DAPNIA/SPh. N (CEA Saclay) & COMPASS (CERN) A. Magnon Alain Magnon 1

Content • The nucleon spin problem; why measure DG ? • Present knowledge of DG • Ongoing experiments : RHIC spin, HERMES, COMPASS • Summary A. Magnon Alain Magnon 2

Quark & gluon spin Nucleon spin: ½ = ½ ΔΣ + ΔG +<Lz > quark gluon contribution Orbital angular contribution momentum Naive quark parton model + relativistic corrections DS ~ 0. 60 QCD ; Ellis-Jaffe assuming Ds = 0 , DS ~ 0. 60 A. Magnon Alain Magnon 3

Spin structure function g 1 • Various p. QCD global analysis of world data on g 1 ( p, d, n ) with different assumptions and parametrisations • Need knowledge of F & D meson octet decay constant & assumption of SU(3)F EMC . 09 +/-. 14 “DS” =~0. 12 0. 2+/- 0. 3 • Quark contribution to spin DS small, very different from expectations ~0. 6 x. BJ A. Magnon Alain Magnon 4

Interpretation In polarised DIS, one measures flavor singlet axial matrix element a 0 = ΔΣ – (as/2 p)nf ΔG(*) All experiments (SLAC, EMC, SLAC, HERMES) confirm: a 0 ~ 0. 2 ÷ 0. 3 Imperative to measure ΔG (*)Scheme dependent, Q 2 dep. omitted A. Magnon Alain Magnon 2. 5 ? 5

Dq (DG) from inclusive data Duv(x) and Ddv(x) well constrained DG(x) not : shape and sum unknown 1 ∫DG(x)dx 0 - SMC global QCD analysis at Q 02 = 1 Ge. V 2 : 1. +/- 1. 2 - Blümlein-Böttcher at Q 02 = 2 Ge. V 2: 1. +/- 0. 6 A. Magnon Alain Magnon 6

Dq & DG from inclusive data g 1 F 2 p p Need more precise data on g 1(x, Q 2) and better coverage in x and Q 2 Need direct measurements A. Magnon Alain Magnon 7

Direct Measurements • RHIC (polarized) collider p -> p • HERMES, COMPASS e, m -> N A. Magnon Alain Magnon 8

RHIC polarized protons collider ST A R A. Magnon Alain Magnon 9

ΔG/G – RHIC p p A. Magnon Alain Magnon 10

pp -> π0/prompt g + X π0 prompt γ Excellent agreement with NLO & NLL calculation with collider data ! A. Magnon Alain Magnon 11

ΔG - Phenix: ALL for π0 2003/4 A. Magnon Outlook 2005/7 Alain Magnon 12

ΔG - Phenix: ALL for π0 Y. Fukao, spin 2004 A. Magnon Alain Magnon 13

ΔG – Star: ALL for jets (2005) STAR 1. 0 Inclusive Jets : LO W. Vogelsang 0. 8 qg 0. 6 2005 0. 4 gg qq 0. 2 0. 0 0 5 10 15 20 25 30 p. T (Ge. V) A. Magnon Alain Magnon 14

ΔG at RHIC – summary & outlook • Various channels, large coverage in xg - Jet/leading hadron production : First results of ALL pp p 0 +X from PHENIX Very good perspective for p+- at PHENIX and jets at STAR - Direct photon production: hard scale 100 Ge. V 2, xg reconstructed in STAR - Heavy flavours, . . . • RHIC Spin program on track, major effort to reach performance A. Magnon Run s 1/2(Ge. V) 3 200 0. 27 0. 35 4 + 5 200 >0. 40 10 >5 200 0. 70 320 500 0. 70 800 Alain Magnon Pbeam L(pb-1) 15

ΔG/G from Photon-Gluon Fusion • Strategies to suppress background: 1) Open charm production: q = c unique, no background charm fragmentation, 1. 2 D 0 per event D 0 -> K- π+ (BR 4%), D*+(~20%) -> D 0 π+ 2) High-PT hadron pair production: q=u, d, s sk. T(intr) = 450 Me. V/c sp. T(frag) = 350 Me. V/c Photon-Gluon Fusion A. Magnon • p. QCD scale set by: 1) ŝ > 4 mc 2 or 2) ŝ > (pt 1+pt 2)2 Alain Magnon 16

ΔG/G from high-PT hadron pair production e, m h 1 N h 2 Photon Gluon Fusion Leading Order Process QCD-Compton measured a. LL : calculable partonic asymmetries R : Monte-Carlo (Lepto/Phytia depending on Q 2) A. Magnon Alain Magnon 17

HERMES DESY RHIC Spin &Roadmap • 27. 5 Ge. V e • Pure atomic H or D targets • Spectrometer with complete hadron identification A. Magnon Alain Magnon 18

HERMES ALL from high PT hadrons Proton target • Statistics decreases with p. T • Need good description of background (also polarized) A. Magnon Alain Magnon 19

ΔG/G from HERMES 27. 5 Ge. V e on p <xg> = 0. 17 <Q 2> = 0. 06 (Ge. V/c)2 <p 2 T> = 2. 1 (Ge. V/c)2 Promising channel, but … theoretical uncertainty A. Airapetian et al. A. Magnon might be large Alain Magnon 20

COMPASS EXPERIMENT Beam: 2. 108 µ+/ spill (4. 8 s / 16. 2 s) Luminosity: ~ 4. 1032 cm-2 s-1 Beam polarisation: 76% Beam momentum: 160 Ge. V/c COMPASS A. Magnon LHC SPS Alain Magnon 21

Spectrometer 2002 -> 2004 trigger-hodoscopes DW 45 SM 2 dipole RICH_1 straws Muon-filter 2, MW 2 HCAL 1 Gem_11 ECAL 2, HCAL 2 SM 1 dipole MWPC Gems Scifi Polarised Target SPS 160 Ge. V 2. 108 m/spill Muon-filter 1, MW 1 Veto straws, MWPC, Gems, Sci. Fi Silicon Sci. Fi A. Magnon Gems, Sci. Fi, DCs, straws Micromegas, DC, Sci. Fi Alain Magnon 22

Inclusive longitudinal spin asymetry A 1 d COMPASS has the potential to digest high luminosity and get high precision results A. Magnon Alain Magnon 23

Inclusive longitudinal spin asymetry A 1 d Low x region important for precision on DS A. Magnon Alain Magnon 24

Pairs of hadrons with high p. T h 1 h 2 N Photon Gluon Fusion current fragmentation: x. F > 0. 1 z > 0. 1 event cuts: 2 2 Q > 1 (Ge. V/c) , x. Bj < 0. 05 0. 1 < y < 0. 9 A. Magnon Alain Magnon • 2 high pt hadrons: pt > 0. 7 Ge. V/c pt 12+pt 22 > 2. 5 (Ge. V/c)2 m(h 1 h 2) > 1. 5 Ge. V/c 2 25

Result for high p. T asymmetry Asymmetry for high-pt hadron pairs at Q 2 > 1 (Ge. V/c)2: 2002/2003 data Aγ* d = - 0. 015 ± 0. 080 (stat. ) ± 0. 013 (syst. ) Systematic uncertainty contains contributions from: - target and beam polarisation measurement (5% resp. 3%) - upper limit on false asymmetries (0. 013) - determination of depolarisation and dilution factors, D and f (5% each) A. Magnon Alain Magnon 26

Preliminary determination of ΔG/G cut on x. Bj < 0. 05: Relative Fractions determined by Monte Carlo (LEPTO) Photon Gluon Fusion A. Magnon QCD-Compton Alain Magnon Leading Order 27

Data Monte Carlo comparison Use LEPTO Monte Carlo for Q 2>1 (Ge. V/c)2 including RADGEN Determination of the fraction of PGF events in LEPTO: σPGF/σtot = 0. 34 ± 0. 07 (syst. ) • Variation of the cut on pt 2 • Standard and modified* set of fragmentation parameters * A. Magnon Alain Magnon SMC, B. Adeva et al. , Phys. Rev. D 70: 012002, 2004 28

COMPASS result for ΔG/G = 0. 06 ± 0. 31 stat. ± 0. 06 syst. 2002/03 data Q 2 > 1 (Ge. V/c)2 at <xg> = 0. 13 ± 0. 08 10% of statistics A. Magnon GSA, B, C: T. Gehrmann and W. Sterling, Z. Phys. C 65 (1994) 461. Alain Magnon 29

Q 2 < 1 Ge. V/c 2, additional background for all Q 2 : 10 times more data Projection for 2002 -2004 data (all Q 2): Statistical error on ΔG/G of 0. 05 Relevant for Q 2< 1 (Ge. V/c)2, uncertainty due to unknown spin content of the resolved photon A. Magnon Alain Magnon 30

ΔG/G from open charm c c D 0 D* + K- π+ (BR 4%) D 0 π+ + c. c. Special trigger: quasi real photoproduction Ds. PGF at NLO: Bojak, Stratmann NPB 540 (1999) 345; A. P. Contogouris and G. Grispos, Phys. Rev. D 62 (2000). A. Magnon Alain Magnon ŝ = m 2 cc 31

ΔG/G from open charm Asymmetry determination with full 2002 -2004 statistics: Expected error on ΔG/G from 2002 -2004 data: 0. 24 A. Magnon Alain Magnon 32

Expected errors on ΔG/G COMPASS Summary First COMPASS result for high pt hadron pairs with Q 2 > 1 (Ge. V/c)2 • more data in 2004 • 10 times more data at Q 2<1 (Ge. V/c)2 Good perspectives for ΔG/G from open charm by D 0 mesons A. Magnon Alain Magnon COMPASS will resume data taking 2006 and continue until ≥ 2010 33

Future Fixed Target RHIC Spin. Programme Roadmapat CERN Villars meeting, 22 -28 Sept. CERN seminar Villars by John DAINTON “ FT hadron program remains very competitive …………. COMPASS complete in medium term - ΔG/G, transversity, polarisability, spectroscopy - SPSC p. o. t. concern prioritise COMPASS longer term - GPD measurements would be unique” Conclusions (personal) by Michelangelo MANGANO “ COMPASS A. Magnon m beam … flagship experiment ” Alain Magnon 34

RHICSummary Spin Roadmap • Two new facilities are operationnal RHIC & COMPASS • First COMPASS result for DG/G from high pt hadron pairs with Q 2 > 1 Ge. V/c 2 • Excellent prospects for RHIC and COMPASS • Very exciting times ahead of us ! A. Magnon Alain Magnon 35

Additional slides RHIC Spin Roadmap A. Magnon Alain Magnon 36

Expected errors on ΔG/G COMPASS preliminary, high PT, Q 2 >1 (Ge. V/c)2 STAR @ RHIC error & 1/(L P 4)1/2 proposal L=320 pb-1 P=70% A. Magnon Alain Magnon 37