Sixth International Conference on Perspectives in Hadronic Physics May Highlights from the COMPASS experiment at CERN.

Transcription

1 Sixth International Conference on Perspectives in Hadronic Physics May 2008 Highlights from the COMPASS experiment at CERN. F. Bradamante University of trieste / INFN Trieste Italy

2 HIGHLIGHTS FROM THE COMPASS 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

3 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

4 COMPASS experiment: thought of in April 94 Trento workshop Nov. 94 Trieste LoI March 95 encouraged June 95 SPSLC in Cogne Proposal March 96 recommended Sept. 96 approved by RB 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)

5 Physics program of COMPASS Experiments with muon beam ΔG/G g 1 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

6 longitudinally polarised muon beam longitudinally or transversely polarised target calorimetry particle identification luminosity: ~ cm -2 s -1 beam intensity: μ + /spill (4.8s/16.2s) beam momentum: 160 GeV/c LHC SPS N

7 The Spectrometer for the Muon Programme Trigger-hodoscopes μ Filter ECal & HCal SM2 50 m 6 LiD Target 160 GeV μ SciFi SM1 RICH Micromegas Silicon Gems Drift chambers Straws MWPC TWO STAGE SPECTROMETER: Polarized beam and target SAT, LAT, PID < x < < Q 2 < 10 GeV 2

8 WHERE ARE WE? in 2002, 2003, 2004, 2006 and 2007 COMPASS has taken data in the muon program configuration 160 GeV, polarized μ beam LiD polarized target (~polarized deuterons) 2007 NH 3 polarized target (~polarized protons) pilot run in 2004 for hadron program physics results 1. ΔG/G 1. pion polarizability 2. ΔΣ 2. PWA in diffractive 3. Transversity scattering 4. Cahn asymmetry 5. Pentaquark 6. Exclusive ρ 0 7. Λ physics 2000 TB ~ events 2008: hadron beam at 190 GeV for diffractive and central production

9 THE COMPASS MUON PROGRAM TWO CLASSES OF PHENOMENA: LONGITUDINAL SPIN CASE TRANSVERSE SPIN CASE

10 LONGITUDINAL SPIN CASE: the beginning EMC 1988 Γ 1 p = ± ± ΔΣ = 0.12 ± 0.17 SPIN CRISIS

11 LONGITUDINAL SPIN CASE from polarised lepton polarised nucleon DIS dσ = dσ ± dδσ 4 2 dδσ e y y 2 = 9 2 cosα 1- γ g γ g2 dx dy 4π Q with p Γ 1 g 2 ( x) e [ Δq( x) + q( x) ] 1 q Δ q Γ g 1 first moments: = (x) dx 1 2 y y 2 y sinα cosϕ 1 γ γ g1 + g and Δq = q - q Δq = Δq(x) dx from measurement of EMC in 1988 and using complementary information from neutron and hyperon β decay one obtained Δ Σ = Δu + Δd + Δs = 0.12 ± 0.17 at variance with naïve expectation since 1 1 = ΔΣ + ΔG + L 2 2 necessity for measuring q, g n Γ 1 Δq and Δq in SIDIS ΔG in SIDIS SMC, SLAC, HERMES SMC, HERMES, COMPASS HERMES, COMPASS

12 LONGITUDINAL SPIN CASE physics results ΔG/G

13 MEASUREMENTS OF THE GLUON POLARIZATION FOUR LINES OF ATTACK: 1. Double spin asymmetry of the OPEN CHARM cross-section in high energy µd scattering 2. Double spin asymmetry of the HIGH-p t HADRON PAIRS in high energy µd DIS (Q 2 > 1 GeV 2 ) 3. Double spin asymmetry of the high-p t hadron pairs in high energy µd scattering (Q 2 < 1 GeV 2 ) 4. Measurement of g 1 of the deuteron and QCD fit of all the world data

14 ΔG/G at COMPASS Photon Gluon Fusion q = c cross section difference in charmed meson production theory well understood experiment challenging N q = u,d,s cross section difference in 2+1 jet production in COMPASS: events with 2 hadrons with high-p t experiment easy theory more difficult

15 ΔG/G from Open Charm

16 D mass spectra D 0 K + π D 0 * D + π s K + π+ π s D 0 K+ π nd 0 = nd* = 8675 D 0 K π π 0 D 0 K π APS, 13 April 2008 G.K. Mallot 15

17 ΔG/G from open charm data D 0 + D* ΔG/G = ± 0.27 (stat) ± 0.11 <x g > ~ 0.11, <μ 2 > ~ 13 (GeV/c) 2 preliminary 16

18 ΔG/G from High-p t hadron pairs

19 ΔG/G from High-p t hadrons, Q 2 > 1 (GeV/c) 2 PGF and background A D LL a D ΔG σ G σ a D σ σ PGF PGF LO LO LL LL + A + A tot 1 tot 1 a QCD C LL D σ QCD C σ tot PGF LO DIS QCD- Compton

20 ΔG/G from High-p t hadrons, Q 2 > 1 (GeV/c) data: High p T, Q 2 > 1 GeV/c 2 ΔG/G = 0.08 ± 0.10 (stat) ± <x g > = (range: ), μ 2 ~ 3 (GeV/c) 2 preliminary

21 ΔG/G from High-p t hadrons low Q 2 PGF all Q 2 resolved photon LO DIS QCD- Compton

22 ΔG/G from High-p t hadrons, Q 2 < 1 (GeV/c) data: High p T, Q 2 < 1 GeV/c 2 ΔG/G = ± (stat) ± <x g > = 0.085, μ 2 = 3 GeV 2 preliminary

23 Gluon Polarization COMPASS preliminary results high-p T pairs, Q 2 >1GeV 2 : ΔG/G = 0.08 ± 0.10 (stat) ± <x g > = (range: ), μ 2 ~ 3 (GeV/c) 2 high-p t pairs, Q 2 < 1GeV 2 : ΔG/G = ± (stat) ± <x g > = 0.085, μ 2 = 3 GeV 2 open charm: ΔG/G = ± 0.27 (stat) ± 0.11 <x g > ~ 0.11, <μ 2 > ~ 13 (GeV/c) 2

24 Summary of results new highp T point new charm point G.K. Mallot

25 g 1 d

26 g 1 of the deuteron ( ) Phys Lett B 612 (2005) 154 most precise measurement for < x < 0.03 new NLO QCD fit, precision of a 0 improves factor 2 (Q 2 = 4 GeV 2 )

27 CONCLUSION from ΔG MEASUREMENTS: ΔG SMALL 1 2 more precise measurements will come soon 1 = Δ Σ + 2 ΔG + L q, g interest in orbital angular momentum GPD s COMPASS 2006 RHIC RUN6. Ji s SUM RULE J q (t) 1 q q = dx x (H + E ) 2

28 more on LONGITUDINAL SPIN CASE MEASUREMENT OF VALENCE QUARK POLARISATION

29 valence quark polarisation hadron asymmetries

30 valence quark polarisation comparison with other experiments

31 The Transverse Spin Case

32 Transverse Spin case Large effects observed in hadronic interactions

33 Transverse Spin case Large effects observed in hadronic interactions Theoretical developments: at leading order a third PDF is necessary for a complete description of the structure of the nucleon q(x) Δq(x) Δ T q(x) Δ T q(x) being chiral-odd, it can be measured only in conjunction with another chiral-odd partner: Collins function DY Δ T q ΔTq relevance of e+e- hadrons transverse momentum dependent (TMD) PDF and FF SIDIS Δ T q FF measurable in Sivers function Many Workshops in recent years on Transverse Momentum, spin, and position distributions of partons in hadrons

34 Transversity single hadron - 1 Collins and Sivers angles Φ C = φ h - φ S Φ S = φ h - φ S φ S azimuthal angle of spin vector of fragmenting quark (φ S = π - φ S ) φ h azimuthal angle of hadron momentum

35 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 runs Collins: related to transverse quark distributions Sivers: related to intrinsic k Phys Rev Lett 94 (2005) T Nucl Phys B765 (2007) 31 A Coll A Siv x z h p T (GeV/c)

36 Collins asymmetry for pions and kaons preliminary data proton (virtual photon asymm) (lepton beam DIS07) final CERN-PH-EP/ hep-ex/ (PRL) data deuteron (virtual photon asymm) COMPASS sign convention

37 Independent Measurement of the Collins FF measurable in e + e annihilation first attempts to measured it from the correlation between the azimuthal angles of π 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 π 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

38 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: Δ T u~ -Δ T d Δ T0 D(fav.) ~ - Δ T0 D(unfav) To extract TMD DF and FF GLOBAL ANALISYS are necessary

39 HERMES, COMPASS, BELLE

40 Sivers asymmetry for pions and kaons preliminary data proton (DIS07) A Siv COMPASS HERMES π+ - π COMPASS HERMES CERN-PH-EP/ hep-ex/ (PRL) data deuteron A Siv COMPASS HERMES x Bj COMPASS HERMES x Bj -0.2 K + K x Bj x Bj

41

42 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

43 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