Nucleon spin and structure studies with COMPASS DAPNIA

Nucleon spin and structure studies with COMPASS DAPNIA Stephane Platchkov CERN and CEA-Saclay On behalf of the COMPASS Collaboration 23/11/2020 S. Platchkov, PANIC 05 1

The COMPASS collaboration n Composed of n n 230 physicists 28 institutions 11 countries LHC COMPASS Data taking n n 23/11/2020 2002, 2003, 2004 2005: SPS stopped SPS S. Platchkov, PANIC 05 2

The nucleon spin puzzle Quark contribution to the nucleon spin 1990 - 2005 : EMC, SMC, Hermes, SLAC : DS 0. 20 – 0. 25 instead of ~0. 60 (QPM) The nucleon spin is more complicated than anticipated ? Study Gluon contribution to the spin And also many other spin observables… 23/11/2020 S. Platchkov, PANIC 05 3

Physics program of COMPASS n Experiments with muon beam n n n n Gluon spin contribution Quark spin contribution Flavor decomposition of spin distribution functions Transverse spin distribution functions Transversity – two hadron correlations Vector meson production Spin transfer in L-hyperon production Pentaquarks 23/11/2020 n Experiments with hadron beams n n n Pion and Kaon polarizabilities Diffractive production of exotic states Search for glueballs Light meson spectroscopy Production of double charmed baryons Other Compass talks at Panic 05 J. Nassalski – Delta-G A. Bressan – Transversity-1 h R. Joosten – Transversity-2 h J. Friedrich – Pentaquarks, hadrons A. Sandacz – r production, DVCS S. Platchkov, PANIC 05 4

COMPASS “first” period (2002 – 2004) n Large amount of data collected with muon beam n n n First data with hadron beam n n Longitudinally polarized target n About 78% of the total Transversely polarized target n About 22% of the total “Pilot” hadron run in 2004 This talk: n 23/11/2020 Quick overview of available COMPASS data n Mainly 2002+2003 n Data from 2004 being analyzed S. Platchkov, PANIC 05 5

The COMPASS Spectrometer Trigger-hodoscopes μ Filter ECal & HCal Sci. Fi m 0 5 SM 2 RICH MWPC SM 1 6 Li. D Target Silicon 0 16 G 23/11/2020 e. V μ Gems Straws Drift chambers Micromegas S. Platchkov, PANIC 05 Two stage spectrometer Polarized beam and target ~75% ≥ 50% SAT, LAT, PID 0. 003<x<0. 5, 10 -3<Q 2<10 Ge. V 2 6

Quark spin content: inclusive DIS asymmetry Data taken in 2002 and 2003 Good agreement with previous experiments Improved statistics at low x (Factor of ~2) 23/11/2020 S. Platchkov, PANIC 05 7

Quark spin content: g 1 d(x) structure function n Use Data taken in 2002 and 2003 Phys. Lett. B 612(2005)154. Also: new precise proton data from HERMES New COMPASS QCD fit to the world data on g 1(x) (Q 2=3 Ge. V 2, NLO): DS(MS) = 0. 22 + 0. 03 without COMPASS data DS(MS) = 0. 25 + 0. 02 with COMPASS data 23/11/2020 S. Platchkov, PANIC 05 8

Semi-inclusive DIS n Objectives: n n h Measure semi-inclusive spin asymmetries + + n for p , K K Ks Determine individual flavor spin distributions (isoscalar target): Preliminary data 2002 and 2003 Kinematics range down to x = 0. 003, Q 2>1 In progress… High accuracy data 23/11/2020 S. Platchkov, PANIC 05 9

Transversity – Collins and Sivers asymmetries Full description of the nucleon Nucleon PDFs: Unpolarized Helicity Transversity Collins: probes transverse spin quark distribution Dtq(x) Sivers: probes intrinsic transverse momentum Data taken in 2002 only Collins PRL 94 (2005) 202002 Sivers See A. Bressan’talk Session III. 7 Asymmetries are compatible with 0 Possible explanation: cancellation of Du. T and Dd. T in isoscalar targets? 23/11/2020 S. Platchkov, PANIC 05 10

Collins asymmetries – near future COMPASS transverse spin “polarimeters”: Covered by: Collins asymmetry A. Bressan Two-hadron correlation R. Joosten L-polarization In progress… COMPASS Proton Expected 2006 data (30 d) COMPASS Deuteron Combined 2002 -2004 data Accurate data to come 23/11/2020 S. Platchkov, PANIC 05 11

Longitudinal polarization of L and L hyperons n Physics in the current fragmentation region n n Spin transfer from q to L Test of the strange quark asymmetry of the sea Data from 2003 only With 2004 data: much improved statistics 23/11/2020 S. Platchkov, PANIC 05 12

Determination of DG/G n Select Photon Gluon Fusion process n n Via Open Charm production - + n Detect D° K p and D*+ D°p+ n Clean channel (no c quarks) n High combinatorial background Via High-pt hadron pairs n Good S/B ratio n Physics background (QCDC, LODIS, Resolved photons contributions D*+→D 0π+ (2003) 1100 events COMPASS preliminary § Rely on MC estimates 23/11/2020 S. Platchkov, PANIC 05 13

Determination of DG/G – Two methods Open Charm High-pt pairs Data 2002+2003 Calculation: Glück et al. , Phys. Rev. D 63 (2001) 094005 DG=2. 5 DG=0. 6 DG=0. 16 Present accuracy: 0. 73 DG/G(xg=0. 1) = 0. 024 ± 0. 089(stat) ± 0. 057(syst) With 2004 data 0. 43 Most precise value of DG/G today With 2006 data 0. 24 (estimate) 23/11/2020 See talk by J. Nassalski, PDF-II S. Platchkov, PANIC 05 14

Search for Φ-- Pentaquarks NA 49: Peak at 1860 ± 8 Me. V n n Several “evidence papers” on pentaquarks published Motivated by NA 49 findings n n Ali et al. PRL 92 (2004) 042003 Search for the process: Check of COMPASS analysis: Look for COMPASS : 1700 events NA 49 : 150 events COMPASS does not confirm NA 49 23/11/2020 S. Platchkov, PANIC 05 See talk by J. Friedrich, Pentaquarks session 15

COMPASS upgrades for 2006 n New solenoid magnet n n Larger acceptance 70 mrad 180 mrad è n RICH upgrade n n n Expect +30% FOM Central region: ma. PMT system n More photons n Improved S/N Outer region: New faster electronics n Improved S/N è Expect +60% FOM Other upgrades: n n n Large Drift Chamber Full ECAL coverage Etc… 23/11/2020 S. Platchkov, PANIC 05 16

COMPASS Programme n The near future (2006 – 2010) n n Compass Factor of Merit Strategy n n n Improved COMPASS Factor of Merit n New OD magnet 1. 3 n Upgraded RICH 1. 5 n Full ECAL coverage 1. 2 n Other… 1. 1 n Total Fo. M improvement: ≥ 2. 3 Strategy: muon beam in 2006, hadron beam in 2007, … è Precise data to come! Long term future (beyond 2010) n n Plans to use DVCS to measure GPD n Benefit from the high muon energy (190 Ge. V) n Try to access orbital momentum L Additional detectors being developed 23/11/2020 S. Platchkov, PANIC 05 17

Summary - Results n New COMPASS results n n n Better spectrometer in 2006 n n Improved measurement of the g 1 deuteron structure function Most precise DG/G measurement up to now First COMPASS results on tranversity Accurate results on semi-inclusive DIS No evidence for pentaquarks è And a lot of data being analyzed Expected Factor Of Merit increase: ≥ 2. 3 More precise results are coming…. 23/11/2020 S. Platchkov, PANIC 05 18