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Highlights from the COMPASS experiment QNP09, Beijing, September 2009 G. K. Mallot CERN/PH for the Collaboration
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Plan COMPASS Helicity structure (quarks) Gluon polarisation Transverse spin-structure of the nucleon A glimpse a hadron spectroscopy Outlook G. MallotQNP09, Beijing, September 2009
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COMPASS: QCD structure of hadrons data taking since 2002 nucleon spin-structure helicity distributions of qluons and quarks transverse spin structure hadron spectroscopy light mesons glue-balls exotic mesons polarisability of pion and kaon COMPASS RICH
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COMPASS key figures (muon beam) Large solid polarised target proton target (NH 3, 3 cells, e.g. +−+, ~85%, f 0.18 ) deuteron target ( 6 LiD, 2 cells, e.g. +−, ~50%, f 0.4) Polarised muon beam ~80% polarisation 5 10 7 muons/s, duty factor 20 − 33 % Nominal luminosity 5 10 32 cm -2 s -1 Particle ID RICH ( π /K: 9 − 50 GeV/c), ECals, HCals, Muon walls DAQ 250k channels up to 30 kHz, several PByte/year (hadron runs) G. MallotQNP09, Beijing, September 2009
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G. MallotQNP09, Beijing, September 2009 Three twist-2 PDFs Parton Distribution Functions q(x) f 1 q (x) q(x) g 1 q (x) T q(x) h 1 q (x) chiral odd, poorly known unpolarised PDF quark with momentum xP in a nucleon well known – unpolarised DIS helicity PDF quark with spin parallel to the nucleon spin in a longitudinally polarised nucleon known – polarised DIS transversity PDF quark with spin parallel to the nucleon spin in a transversely polarised nucleon
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TMD parton distributions 8 intrinsic transverse momentum dependent PDFs at LO Asymmetries with different angular dependences on hadron and spin azimuthal angles, Φ h and Φ s G. MallotQNP09, Beijing, September 2009 Sivers Boer– Mulders Transversity
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Results from transverse polarisation G. MallotQNP09, Beijing, September 2009 longitudinal
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Longitudinal asymmetries Semi-inclusive asymmetries with Inclusive asymmetry G. MallotQNP09, Beijing, September 2009
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Incl. & semi-incl. asymmetries proton, first measurement of A K, preliminary G. MallotQNP09, Beijing, September 2009 K+K+ K−K− π+π+ π –π – incl. new
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Incl. & semi-incl. asymmetries deuteron G. MallotQNP09, Beijing, September 2009 K+K+ K−K− π+π+ π –π – incl.
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Incl. deuteron asymmetry most precise measurement for x 1 GeV 2 G. MallotQNP09, Beijing, September 2009
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Structure function g 1 (x,Q 2 ) very precise data only data below x 1) deuteron data: a 0 = 0.33±0.03±0.05 Δs+ Δs =−0.08±0.01±0.02 (evol. to Q 2 =∞) G. MallotQNP09, Beijing, September 2009 p d new
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g 1 proton and g 1 NS G. MallotQNP09, Beijing, September 2009 new
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proton & deuteron g 1 (x,Q 2 ) unique kinematic domain important for global QCD analyses G. MallotQNP09, Beijing, September 2009 CLAS HERMES dp new
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The role of quark flavours LO analysis, preliminary G. MallotQNP09, Beijing, September 2009 new
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Flavour asymmetry? considerable asymmetry in the unpolarised case model predicts naturally asymmetry for pol. case only small effect (if at all) G. MallotQNP09, Beijing, September 2009 new
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G. MallotQNP09, Beijing, September 2009 Angular momentum of the nucleon small ~0.15 poorly known unknown 17 quarks gluons orbital
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measure calculate, and background by Monte Carlo Principle: Gluon polarisation enters via photon-gluon fusion (PGF) G. MallotQNP09, Beijing, September 2009 Hadron production in DIS via PGF 18 q q
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Analysed channels analysed data sets: – high-p T hadron pairs (no ID, pions/kaons) Q 2 > 1 GeV 2 L EPTO Q 2 < 1 GeV 2 / unmeasured P YTHIA – high-p T single hadron small Q 2 / unmeasured P YTHIA – single charmed meson quasi-real photons A ROMA, R APGAP All analyses in LO till n ow (plus parton showers) G. MallotQNP09, Beijing, September 2009 19
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cleanest process little physics background (LO, QCDC) observe asymmetry in D meson production statistics limited only one D meson via D →π K (BR ~ 4%) combinatorial background large drastically reduced when looking to D* decay in coincidence with slow pion Δg/g from open charm G. MallotQNP09, Beijing, September 2009 20
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Update on open charm 2002–2006 deuteron data new channels in D* sample sub-threshold kaons 3-body decay with non-observed π 0 old new G. MallotQNP09, Beijing, September 2009 update
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G. MallotQNP09, Beijing, September 2009 ΔG = 2.5 ΔG = 0.2 ΔG = 0.6 GRSV
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Δg/g from hadron pairs (LO) Panic, 10 November 2008 G.K. Mallot 23 high-Q 2 charm low-Q 2 (2004) (2000) single h LO data points at different scales 1 – 13 GeV 2 NLO fits to g 1 at 3 GeV 2 Δg/g is small around x 0.1 PLB 633 (2006) 25-32 confirmed by RHIC
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Results from longitudinal polarisation G. MallotQNP09, Beijing, September 2009 transverse
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Couple to chiral odd Collins FF Transversity PDF G. MallotQNP09, Beijing, September 2009 Azimuthal cross-section asymmetry:
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Collins Asymmetries G. MallotQNP09, Beijing, September 2009 h+h+ h−h− new new: full 2007 proton data set (statistics tripled) h+h+ h−h− proton deuteron
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Comparison to HERMES large asymmetry ~10% good agreement in common x range zero deuteron result important opposite sign of u and d quark transversity PDF G. MallotQNP09, Beijing, September 2009 h+h+ h-h- COMPASS HERMES proton sign change and D nn y applied for HERMES data
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Global Fit Fit to COMPASS d, HERMES, BELLE (FF, e + e - ) in good agreement with new proton data G. MallotQNP09, Beijing, September 2009
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Alternative: couple to chiral odd 2-hadron interference FF Transversity PDF G. MallotQNP09, Beijing, September 2009 cross-section asymmetry:
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two-hadron asymmetry large asymmetries interference FF and transversity sizable G. MallotQNP09, Beijing, September 2009
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Comparison to a recent Fit Recent fit (COMPASS p not yet in) G. MallotQNP09, Beijing, September 2009
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Sivers Asymmetry: proposed (1990, Sivers) though to vanish (1993, Collins) resurrected (2002, Brodsky, Hwang, Schmitt) different sign in DY and SIDIS Sivers function G. MallotQNP09, Beijing, September 2009
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Proton Sivers Asymmetry compatible with zero for the deuteron large effect seen by HERMES, not confirmed by COMPASS clarification needed G. MallotQNP09, Beijing, September 2009 h−h− h+h+
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Longitudinal spin transfer to & G. MallotQNP09, Beijing, September 2009 Λ Λ non-zero D LL related to polarisation of strange (anti) quarks (?)
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Physics with hadron beams 2004:Pilot run with 190 GeV/c π − beam and heavy targets ( Pb), few days only 2008:full year with LH 2 target (40 cm) with recoil detector, mainly π − beam (4% K), some data with p/ π + beam(75/25%) 2009:LH2 target, Pb, Ni positive and negative beams more: Ismail UMAN: Thu, 24.09. Parallel 5C Room:B326 G. MallotQNP09, Beijing, September 2009
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Hadron Spectroscopy @ COMPASS Central productionDiffractive dissociation Rapidity gap between p slow, h fast, X Beam particle looses little of its energy Particles at large angles from X decays Possible source of glueballs (DPE) Forward kinematics Particles at small angles Study of J PC -exotic mesons
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Example: 3 π final state (2004 data) COMPASS: p π =190 GeV/c 4M events in 3 days (full t range) 450k events in 0.1<t’<1.0 GeV 2 /c 2 COMPASS: p π =190 GeV/c 4M events in 3 days (full t range) 450k events in 0.1<t’<1.0 GeV 2 /c 2 BNL852: p π =18 GeV/c 250k events π 1 (1600) BNL852: p π =18 GeV/c 250k events π 1 (1600) this and following slides: from B. Ketzer
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Invariant Mass of 3 System Acceptance
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a 1 (1260) and 2 (1670) from PWA 42 waves considered in PWA 6 dominant waves in mass fit B. Ketzer, Int. J. Mod. Phys. A 24, 245 (2009)
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1 (1600)and 2 (1670) J PC =1 −+ exotic wave in slow phase motion wrt 2 (1670)
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1 (1600) and a 1 (1260) strong phase motion wrt a 1 (1260)
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Leakage Study 1150000 events generated from 15 dominant waves including J PC =2 −+ M=0,1 excluding J PC =1 −+ exotic wave full reconstruction + PWA less than 5% leakage into 1 −+ wave
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Outlook huge amount of spectroscopy data collected in 2008/2009 approved 2 year measurements with muon beam and pol. proton target transversity, Sivers, Boer-Mulders longitudinal: g 1, g 1 NS, flavour separation, Δs plans for measurements of the pion and (maybe) kaon electrical and magnetic polarisabilities and further spectroscopy studies after analysis 08/09 data proposal for GPD and Drell-Yan measurements in preparation G. MallotQNP09, Beijing, September 2009
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G. MallotQNP09, Beijing, September 2009
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G. MallotQNP09, Beijing, September 2009
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G. MallotQNP09, Beijing, September 2009
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G. MallotQNP09, Beijing, September 2009
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Transverse spin structure Collins asymmetry: match HERMES precision at large x improve precision at small x higher Q 2 G. MallotQNP09, Beijing, September 2009 h+h+ h−h−
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Longitudinal Spin Structure proton g 1 (x) small x behaviour very interesting only COMPASS can provide further data until the advent of a pol. ep collider G. MallotQNP09, Beijing, September 2009
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Non-singlet structure function non-singlet structure function: Bjorken sum rule G. MallotQNP09, Beijing, September 2009
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Flavour separated PDFs projection for flavour separation from semi-inclusive asymmetries G. MallotQNP09, Beijing, September 2009
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PWA Technique t-channel Reggeon exchange Reflectivity basis in G-J frame At high s: = of Regge trajectory Isobar model 1. Mass-independent PWA of angular distributions in 40 MeV mass bins 42 partial waves i=J PC M [...]L [...]=isobar ( ) S, f 0 (980), (770), f 2 (1270), 3 (1690)
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Waves used in PWA
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Summary of Waves Publication being prepared, to be submitted
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Summary of Waves
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