Spin physics at COMPASS p. 1/43

Transcription

1 Spin physics at Jan Friedrich Physik Department, TU München on behalf of the collaboration Spin physics at p. 1/43

2 In R. Hofstadter s footsteps... 5 years ago: At SLAC, few-hundred-mev electron scattering on the proton reveals internal structure effect, < r p >.8 fm Spin physics at p. /43

3 Deep Inelastic Scattering k k q P, M W Scaling: Nucleon has pointlike substructure Scaling violation obeys perturbative QCD evolution Spin physics at p. 3/43

4 Nucleon Spin quarks gluons < s z >= 1 = 1 Σ + G + orbital momenta L q+g Naive quark parton model (rel. corr.): Σ.75 QCD Ellis-Jaffe: Σ.6 Experimental access: Polarised lepton-nucleon DIS, spin aymmetries Spin physics at p. 4/43

5 Spin physics at p. 5/43 Outline at CERN Physics program: new results Quark and gluon polarisations: g d 1, G/G Transversity ρ production Λ polarisation Spectrometer upgrades and future running

6 CERN aerial view SPS Beam: Protons up to 4 GeV, 4.s/16.8s spills secondary hadron beams (π, K,...) tertiary muons: 8 /spill with 16 GeV/c, 8% polarisation LHC SPS Spin physics at p. 6/43

7 Collaboration Czech Republic, France, Germany, India, Israel, Italy, Japan, Poland, Portugal, Russia, CERN 4 physicists from 8 institutes Bielefeld, Bochum, Bonn, Burdwan/Calcutta, CERN, Dubna, Erlangen, Freiburg, Lisboa, Mainz, Moscow, Munich, Nagoya, Parg, Protvino, Saclay, Tel Aviv, Torino, Trieste, Warsaw Data acquisition, 3, 4 with muon beam on polarised LiD target Oct. 4: pilot hadron run (π ) Spin physics at p. 7/43

8 The COmmon Muon and Proton Apparatus for Structure and Spectroscopy stage spectrometer Spin physics at p. 8/43

9 The COmmon Muon and Proton Apparatus for Structure and Spectroscopy stage spectrometer small area tracking Silicon microstrips GEM foil Micromegas Spin physics at p. 9/43

10 The COmmon Muon and Proton Apparatus for Structure and Spectroscopy stage spectrometer small/large area tracking Straw detectors Spin physics at p. /43

11 The COmmon Muon and Proton Apparatus for Structure and Spectroscopy stage spectrometer. channels small/large area tracking particle identification 5 MB/s DAQ rate EM/Hadronic Calorimetry Muon filters RICH Spin physics at p. 11/43

12 The polarised target 3 4 He He Dilution fridge (5 mk) superconducting.5 T Solenoid.5 T Dipole Material: 6 LiD 5% polarisation Dilutation factor.4 two 6 cm long cells oppositely polarised Vertex distribution along Z, N trk > reversal: longitudinal every 8h transverse every week Vertex Position z / mm Spin physics at p. 1/43

13 Spin physics at p. 13/43 Physics Program structure muon beam gluon polarisation G/G longitudinal/transverse quark spin distributions Λ polarisation diffractive vector meson production hadron beam hadron structure via Primakoff effect spectroscopy muoproduction of hadrons dominated by quasi-real photoproduction charmed baryons gluonic systems exotic hadrons diffractive reactions

14 Polarised DIS γ * partons A 1 = σ 1/ σ 3/ σ + 1 / ~ q (x) Nucleon σ 1/ + σ 3/ g 1 F 1 γ * σ ~ q (x) partons 3 / Nucleon g 1 (x) QP M = 1 q e q q(x) = NLO QCD = 1 N f q e q [ q ( 1 + α ) s(q ) π δc q + α s(q ) π G δc ] G N f indirect access renormalization/factorization scheme dependent Spin physics at p. 14/43

15 New result for A d 1 (summary Alex Korzenev s talk) d A x SMC E143 E155 HERMES PRELIMINARY d A data x -.1 Spin physics at p. 15/43

16 New data for g d 1 (x) N g PRELIMINARY N g 1 N g 1 calculated with QCD fit 1 calculated with QCD fit N g 1 QCD fit 1 calculated with LSS,GRSV,BB QCD fit QCD fit of LSS, GRSV, BB -1 x 1 data only: Γ N 1 (Q = 3GeV ) =.5 ±.8 stat ±. evol ±.51 sys Σ =.33 ±.3 stat ±.6 sys Spin physics at p. 16/43

17 G/G Spin physics at p. 17/43

18 Direct measurement of G/G q = u, d, (s): high p T hadron pair µ γ* _ q scale Q or p T high statistics (theor.) difficult background g q q = c: open charm p Photon Gluon Fusion scale 4m c theor. cleaner channel hard to access experimentally Spin physics at p. 18/43

19 Experimental asymmetry and G/G A µn LL = 1 P T fp b D N target polarisation P T.5 dilution factor f =.4 beam polarisation P B.8 depolarisation factor D.6 N N + N A µn LL = ap GF LL G G S S + B + ABackground LL a P GF LL from leading order M.E. (γ-g-kinematics from AROMA MC) Spin physics at p. 19/43

20 Open charm via D and D decays D D π soft D K π (MeV) M kππs -M kπ -M π M Kπ -M D (MeV) 4 Preliminary M Kππs -M Kπ -M π (MeV) Spin physics at p. /43

21 D signals N / MeV/c D S eff = candidates in -4 N(D ) ± 64 Mass.9 ± 1.1 MeV/c Sigma 6.6 ± 1. MeV/c preliminary D* candidates in -4 m(d )-m(d )[MeV/c ] lit N / MeV/c S eff =1966 +/- 51 N(D ) 3869 ± 4 Mass 4.9 ±.8 MeV/c Sigma 8.6 ±.9 MeV/c 1 preliminary m(d )-m(d )[MeV/c ] lit Spin physics at p. 1/43

22 G/G from open charm Data -4 G/G G/G preliminary D* D D* + D D*+D G/G =.57 ±.41 stat at < x g >=.15 and < µ >= 13 GeV Spin physics at p. /43

23 G/G from high-p T pairs enrich PGF events with high-p T cuts p T >.7 GeV/c p T 1 + p T >.5 GeV/c x F >.1, z > µ+d µ + h(high p ) + X T preliminary m(h1, h) > 1.5 GeV/c Σ p T [GeV ] Spin physics at p. 3/43

24 G/G from high-p T pairs enrich PGF events with high-p T cuts p T >.7 GeV/c p T 1 + p T >.5 GeV/c x F >.1, z >.1 m(h1, h) > 1.5 GeV/c µ+d µ + h(high p ) + X T preliminary distinguish Q regions Q [GeV ] Spin physics at p. 4/43

25 contributing high-p T processes Spin physics at p. 5/43

26 contributing high-p T processes Spin physics at p. 6/43

27 high p T, low Q < 1 (GeV/c) Spin physics at p. 7/43

28 Spin physics at p. 8/43 Results for G/G from high-p T Q > 1(GeV/c) preliminary from -3 data: G/G =.6 ±.31 stat ±.6 syst < x g >.13 Q < 1(GeV/c) new result including 4 data: G/G =.16 ±.58 stat ±.55 syst < x g >.85-3:.4 ±.89 stat ±.57 syst, published in PLB 633 (6) 5 Scale in both cases µ = 3 GeV

29 Results on G/G R G(x)dx =.5 G/G HERMES, all Q SMC Q >1 (GeV/c), Q >1 (GeV/c) (-3,prelim), Q <1 (GeV/c) (-4,prelim), open charm (-4,prelim) R G(x)dx =.6. - R G(x)dx = GRSV-max -.6 GRSV-std GRSV-min -1 x G Also consistent with the RHIC A LL (π ) measurement Spin physics at p. 9/43

30 Transversity Spin physics at p. 3/43

31 Transversity q = - T q = - Accessible at via Azimuthal single hadron Collins asymmetry Azimuthal distribution of -hadron plane Transverse Λ polarisation as analyser measured 5% with transversely polarised Deuteron target. Spin physics at p. 31/43

32 Single hadron asymmetries µ µ' γ h p T h s' Φ S ΦC y s φ s' φ h z φ s x Collins Correlation of outgoing hadron direction and transverse quark spin Sivers Correlation of nucleon spin and transverse quark momentum A Col = q e q T q D h q q e q q D h q A Siv = q e q f 1T q Dh q q e q q D h q published results from : PRL 94 (5) Spin physics at p. 3/43

33 - -1 Collins asymmetry theoretical calc. Efremov et al. PRD73 (6) 945 A Coll..1 all hadrons leading hadrons Goeke et. al positive hadrons -4 data -.1 A Coll.1 preliminary x Bj negative hadrons z [GeV/c] p t Spin physics at p. 33/43

34 - -1 Sivers asymmetry theoretical calc. Anselmino et al. hep-ph/51149 A Siv..1 all hadrons leading hadrons Anselmino et. al positive hadrons -4 data -.1 A Siv.1 preliminary x Bj negative hadrons z [GeV/c] p t Spin physics at p. 34/43

35 -hadron asymmetries Independent access to T q 3 x l l S φ S φ R two hadron plane dn/dm inv 15 P 1 R T P h P 5 scattering plane y x [GeV/c ] M inv z Spin physics at p. 35/43

36 Transversity from hadrons A RS..1 all +/- pairs -4 data -.1 preliminary x Bj.5 1 M inv [GeV/c ].5 1 z A ΦRS T q(x)h h q (z, M h ) transversity signal compatible with zero T q(x) or H q h (z, M h ) small Spin physics at p. 36/43

37 Transversity in Λ polarisation Self-analysing weak decay with asymmetry α = 64.% PT Λ = f P q N D T (y) e q T q T D Λ/q (z) q e q q D Λ/q (z) [%] Λ P T Preliminary -4 All +3 transversity data All Q.1 < y < x Bj [%] Λ P T All +3 transversity data Q > 1 (GeV/c).1 < y <.9 Preliminary -1 1 x Bj Spin physics at p. 37/43

38 Exclusive vector meson production Spin physics at p. 38/43

39 Exclusive ρ production ρ A Diffractive production of ρ, φ, J/Ψ measures spin density matrix elements (double spin asymmetry) preliminary + 3 data HERMES quasi-photoprod. data (d) HERMES electroprod. data (d) -1 1 Q [GeV ] ρ A data HERMES quasi-photoprod. data (d) HERMES electroprod. data (d) preliminary wide Q region covered high Q measurement of GPD s (future!) -1 x Bj Spin physics at p. 39/43

40 Spontanous Λ polarisation Large polarisations known from (unpolarised) hadron production p + Be Λ X (Fermilab at 3 GeV/c: 8%) [%] P y 6 4 Λ [%] P y 6 4 Λ preliminary x F preliminary [GeV/c] p T Events 7 6 Events x F [GeV/c] P Λ T = +.7 ±.9 stat ± 1.1 sys % p T Spin physics at p. 4/43

41 upgrades 6 Spin physics at p. 41/43

42 Summary New results Improved measurement of g d 1 Phys. Lett. B61 (5)154 Precise g1 d data as input for QCD fits High-p T : Most precise G/G measurement up to now (is it small? - or a node at x g.1) PLB 633 (6) 5 direct measurement via open charm Transversity: Very precise (small) deuteron asymmetries PRL 94 (5) More precise results on the way! Spin physics at p. 4/43

43 Spin physics at p. 43/43 Outlook Improved setup in 6 FoM expected to be increased by.3 Transverse spin: First measurements with proton (NH 3 ) target Hadron beam in 7 (central production with 3 GeV protons on lh target) 8- complete the approved programme beyond: potential for GPD, transversity, spectroscopy