HIGHLIGHTS FROM THE COMPASS EXPERIMENT @ CERN F. Bradamante University of Trieste and INFN Trieste on behalf of the Collaboration Sixth International Conference on Perspectives in Hadronic Physics Trieste, May 16, 2008

COmmon Muon and Proton Apparatus for Structure and Spectroscopy NA58 Czech Republic, Finland, France, Germany, India, Israel, Italy, Japan, Poland, Portugal, Russia Bielefeld, Bochum, Bonn, Burdwan, Calcutta, CERN, Dubna, Erlangen, Freiburg, Heidelberg, Helsinki, Lisbon, Mainz, Miyazaky, Moscow, Munich, Nagoya, Prague, Protvino, Saclay, Tel Aviv, Torino, Trieste, Warsaw 28 Institutes, ~230 physicists F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

a new spectrometer with outstanding performances COMPASS experiment: thought of in April ’94 Nov. ‘94 Trento workshop Trieste workshop @ICTP LoI encouraged March ’95 June ‘95 SPSLC in Cogne Proposal recommended approved by RB March ’96 Sept. ’96 Feb. ‘97 as NA58 Technical run 2000 Commissioning 2001 since 2002 taking data with a new spectrometer with outstanding performances merging of two programmes: HMC (muon beam) CHEOPS (hadron beam) F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

Physics program of COMPASS Experiments with muon beam ΔG/G g1 Transverse spin effects Flavor decomposition of spin distribution functions Vector meson production Spin transfer in Λ-hyperon production Experiments with hadron beams Pion and Kaon polarizabilities Diffractive production of exotic states Search for glueballs Light meson spectroscopy Production of double charmed baryons F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

LHC SPS luminosity: ~5 . 1032 cm-2 s-1 beam intensity: 2.108 m+/spill (4.8s/16.2s) beam momentum: 160 GeV/c longitudinally polarised muon beam longitudinally or transversely polarised target calorimetry particle identification LHC SPS N F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

The Spectrometer for the Muon Programme Trigger-hodoscopes μ Filter ECal & HCal 50 m SM1 SM2 RICH MWPC Straws 6LiD Target Gems TWO STAGE SPECTROMETER: 160 GeV μ Drift chambers Polarized beam and target Micromegas SAT, LAT, PID Silicon SciFi 0.003 < x < 0.5 10-3 < Q2 < 10 GeV2 F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

WHERE ARE WE ? physics results DG/G 1. pion polarizability in 2002, 2003, 2004, 2006 and 2007 COMPASS has taken data in the muon program configuration 160 GeV, polarized m beam 2002-2006 6LiD polarized target (~polarized deuterons) 2007 NH3 polarized target (~polarized protons) 2000 TB ~ 5·1010 events pilot run in 2004 for hadron program 2008: hadron beam at 190 GeV for diffractive and central production physics results DG/G 1. pion polarizability DS 2. PWA in diffractive Transversity scattering Cahn asymmetry Pentaquark Exclusive ρ0 Λ physics F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

THE COMPASS MUON PROGRAM TWO CLASSES OF PHENOMENA: LONGITUDINAL SPIN CASE TRANSVERSE SPIN CASE F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

 SPIN CRISIS LONGITUDINAL SPIN CASE: the beginning EMC 1988 G1p = 0.123  0.013  0.019 DS = 0.12  0.17  SPIN CRISIS F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

LONGITUDINAL SPIN CASE from polarised lepton – polarised nucleon DIS with and first moments: from measurement of EMC in 1988 and using complementary information from neutron and hyperon β–decay one obtained at variance with naïve expectation since necessity for measuring SMC, SLAC, HERMES and in SIDIS SMC, HERMES, COMPASS in SIDIS HERMES, COMPASS F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

LONGITUDINAL SPIN CASE physics results ΔG/G F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

MEASUREMENTS OF THE GLUON POLARIZATION FOUR LINES OF ATTACK: Double spin asymmetry of the OPEN CHARM cross-section in high energy µD scattering Double spin asymmetry of the HIGH-pt HADRON PAIRS in high energy µD DIS (Q2 > 1 GeV2) Double spin asymmetry of the high-pt hadron pairs in high energy µD scattering (Q2 < 1 GeV2) Measurement of g1 of the deuteron and QCD fit of all the world data F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

DG/G at COMPASS Photon Gluon Fusion N q = c cross section difference in charmed meson production → theory well understood → experiment challenging q = u,d,s cross section difference in 2+1 jet production in COMPASS: events with 2 hadrons with high-pt → experiment easy → theory more difficult F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

ΔG/G from Open Charm F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

D mass spectra D0 → K π D0 → K π π0 nD* = 8675 nD0 = 37398 APS, 13 April 2008 G.K. Mallot 15 F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

ΔG/G = -0.49 ± 0.27 (stat) ± 0.11 (syst) DG/G from open charm 2002 – 2006 data D0 + D* ΔG/G = -0.49 ± 0.27 (stat) ± 0.11 (syst) @ <xg> ~ 0.11, <m2> ~ 13 (GeV/c)2 preliminary 16 F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

ΔG/G from High-pt hadron pairs F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

ΔG/G from High-pt hadrons, Q2 > 1 (GeV/c)2 PGF and background PGF QCD- Compton LO DIS Anreicherung von PGF mit high pt Schnitten F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

ΔG/G from High-pt hadrons, Q2 > 1 (GeV/c)2 2002 – 2004 data: High pT, Q2 > 1 GeV/c2 ΔG/G = 0.08 ± 0.10 (stat) ± 0.05(syst) @ <xg> = 0.082 (range: 0.055 – 0.123), m2 ~ 3 (GeV/c)2 Anreicherung von PGF mit high pt Schnitten preliminary F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

ΔG/G from High-pt hadrons PGF low Q2 all Q2 LO DIS resolved photon QCD- Compton Anreicherung von PGF mit high pt Schnitten F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

ΔG/G from High-pt hadrons, Q2 < 1 (GeV/c)2 2002 – 2004 data: High pT, Q2 < 1 GeV/c2 ΔG/G = 0.016 ± 0.058 (stat) ± 0.055 (syst) @ <xg> = 0.085, m2 = 3 GeV2 Anreicherung von PGF mit high pt Schnitten preliminary F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

Gluon Polarization COMPASS preliminary results high-pT pairs, Q2>1GeV2 : 2002–2004 ΔG/G = 0.08 ± 0.10 (stat) ± 0.05(syst) @ <xg> = 0.082 (range: 0.055 – 0.123), m2 ~ 3 (GeV/c)2 high-pt pairs, Q2< 1GeV2 : 2002–2004 ΔG/G = 0.016 ± 0.058 (stat) ± 0.055 (syst) @ <xg> = 0.085, m2 = 3 GeV2 open charm: 2002–2006 ΔG/G = -0.49 ± 0.27 (stat) ± 0.11 (syst) @ <xg> ~ 0.11, <m2> ~ 13 (GeV/c)2 F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

Summary of results new high-pT point new charm point G.K. Mallot F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

g1d F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

g1 of the deuteron (2002-2003) Phys Lett B 612 (2005) 154 most precise measurement for 0.004 < x < 0.03 new NLO QCD fit, precision of a0 improves factor 2 (Q2 = 4 GeV2) F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

CONCLUSION from ΔG MEASUREMENTS: ΔG SMALL more precise measurements will come soon COMPASS 2006 RHIC RUN6 …. interest in orbital angular momentum GPD’s because helicity of quark must flip Ji’s SUM RULE F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

more on LONGITUDINAL SPIN CASE MEASUREMENT OF VALENCE QUARK POLARISATION F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

valence quark polarisation hadron asymmetries F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

valence quark polarisation comparison with other experiments F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

The Transverse Spin Case F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

Transverse Spin case Large effects observed in hadronic interactions F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

Transverse Spin case Large effects observed in hadronic interactions at leading order a third PDF is necessary for a complete description of the structure of the nucleon Theoretical developments: q(x) Dq(x) DTq(x) DTq(x) being chiral-odd, it can be measured only in conjunction with another chiral-odd partner: Collins function DY SIDIS measurable in e+e- hadrons relevance of transverse momentum dependent (TMD) PDF and FF Sivers function Many Workshops in recent years on Transverse Momentum, spin, and position distributions of partons in hadrons F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

Collins and Sivers angles Transversity – single hadron - 1 Collins and Sivers angles C = h - S’  S = h - S S ’ azimuthal angle of spin vector of fragmenting quark (S’’ = p - S) h azimuthal angle of hadron momentum F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

Transversity – single hadron - 2 first measurements of transverse spin asymmetries in DIS of high energy muons on a transversely polarized deuteron target published single hadron asymmetries from 2002-2004 runs Collins: related to transverse quark distributions Sivers: related to intrinsic kT Phys Rev Lett 94 (2005) 202002 Nucl Phys B765 (2007) 31 F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

Collins asymmetry for pions and kaons preliminary 2002-2004 data proton (virtual photon asymm) (lepton beam 2002-05  DIS07) final CERN-PH-EP/2008-002 hep-ex/0802.2160 (PRL) 2003-2004 data deuteron (virtual photon asymm) COMPASS sign convention F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

Independent Measurement of the Collins FF measurable in e+e– annihilation first attempts to measured it from the correlation between the azimuthal angles of p‘s from e+e– annihilation using LEP data last years: great news from BELLE the Collins FF is being measured in e+e– annihilation, and it is different from zero! measurement of the correlation between the azimuthal angles of p‘s in the near jet and in the far jet from e+e– annihilation 547 fb-1 charm corrected data sample, UL and UC double ratios spin2004 ref? F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

Collins asymmetries: SUMMARY The facts: HERMES has measured on a proton target non-zero Collins asymmetries for π+ and π- COMPASS has measured on a deuteron target Collins asymmetries compatible with zero BELLE has produced the first results on Collins FF Conclusion: Collins mechanism is a real phenomenon universality of Collins FF transversity can be measured in SIDIS Present picture Collins: DTu ~ - DTd DT0D(fav.) ~ - DT0D(unfav) To extract TMD DF and FF GLOBAL ANALISYS are necessary F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

HERMES, COMPASS, BELLE F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

Sivers asymmetry for pions and kaons preliminary 2002-2005 data proton (DIS07) CERN-PH-EP/2008-002 hep-ex/0802.2160 (PRL) 2003-2004 data deuteron F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

S.J. Brodsky and S. Gardner, PLB643 (2006) 22 Sivers asymmetry the measured asymmetry on deuteron compatible with zero has been interpreted as Evidence for the Absence of Gluon Orbital Angular Momentum in the Nucleon S.J. Brodsky and S. Gardner, PLB643 (2006) 22 refs! F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

BIG DISCOVERY POTENTIAL SUMMARY AND OUTLOOK a technically challenging new experiment is IN OPERATION SINCE 2002 “LHC” technologies detectors read-out data handling a privileged situation at CERN MANY PHYSICS RESULTS have been produced MANY MORE IN THE PIPE-LINE COMPASS is foreseen to run up to the end of the present mid-term plan of CERN (2010) BIG DISCOVERY POTENTIAL with some upgrade COMPASS might be an interesting option even in the second decade of this century F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

SPARE SLIDES F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

Transversity: two hadrons - 1 F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

Transversity: two hadrons - 2 all +/- combinations precise measurement of few % systematics seems well under control also compatible with zero interesting to see proton in 2006 F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

Exclusive ρ0 production F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

Exclusive ρ0 production (2002 data) - 1 F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

Exclusive ρ0 production - 2 ANGULAR DISTRIBUTIONS 0.01 < Q² < 0.05 < Q² < 0.3 < Q² < 0.6 < Q² < 2.0 < Q² 0.01 < Q² < 0.05 < Q² < 0.3 < Q² < 0.6 < Q² < 2.0 < Q² < 10 GeV2 preliminary, statistical errors only, limited by MC corrected for acceptance, smearing and efficiency (MC:DIPSI gen) background not subtracted F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

Exclusive ρ0 production - 3 0.01 < Q² < 0.05 < Q² < 0.3 < Q² < 0.6 < Q² < 2.0 < Q² < 10 GeV2 measurement of r 04 00 2002 distribution : Spin density matrix element: Tλρ λγ are helicity amplitudes meson photon F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

measurement of r and Im r Exclusive ρ0 production - 4 measurement of r and Im r 0.01 < Q² < 0.05 < Q² < 0.3 < Q² < 0.6 < Q² < 2.0 < Q² < 10 GeV2 0 4 1-1 3 1-1 distribution : beam polarisation Spin density matrix element: if SCHC holds weak violation F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

Pentaquark search F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

Φ(1860) Pentaquark search - 1 motivated by NA49 report of pentaquark candidate COMPASS has large sample of the double-strange Ξ– baryon (18000 Ξ–, 11000 Ξ+) from 2002-2003 data search for Ξ– π– resonance Φ(1860)– – → Ξ– π– → Λπ– π– → p π–π–π– F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

Φ(1860) Pentaquark search - 2 Ξ(1530)0 Eur Phys J C41 (2005) 469 compare to yields opposite-sign pairs: Ξ(1530)0 → Ξ– π+ , 1700 and 920 evts like-sign pairs: evts <79 and <89 at 99% CL (expected ~400) F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

Transversity: Λ polarization 2002-2003 data F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

Longitudinal polarization of Λ and antiΛ in DIS F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

Λ POLARIZATION (2002 data) - 1 - + ’+  V1 V2 q Event selection N() N() E665 750 650 NOMAD 8087 649 HERMES 1996-2000 10568 1687 COMPASS 2002 7919 5062 COMPASS 2003 34789 20651 The events considered were selected according to those criteria: the primary vertex has to be reconstructed, for this reason I ask for the detection of the incoming and out coming muon, then in the same event must be present a V0 secondary vertex, a marker for the lambda decay. The background to such typology are the combinatorial background, the pair production, the k0 decay, and the lambda bar decay. To reject such background several cuts were applied: the request that the primary vertex must be in the target, the distance between the primary and the secondary vertex must be greater that 400 mm, in order to reject the pair production a transversal momentum for the positive charged particle greater than 20 MeV/c was asked, also a cut on the angle theta here represented was used in order to reject the fake vertex constructed with the scattered muon. To reject this combinatorial back ground a chi square selection was applied, the vertex with best chi2 were taken, another angular cut was applied to be sure that the secondary vertex coming from the primary vertex and it is not generated by secondary interaction. All those cuts where optimized using the MC simulation. F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

Λ POLARIZATION 2002 data F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

Λ POLARIZATION 2002 data F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics