COMPASS experiment at CERN open charm results and

COMPASS experiment at CERN: open charm results and future hadron program O. Kouznetsov (CEA/Saclay) on behalf of the COMPASS Collaboration BEACH 08 26 june 2008 BEACH 08, Columbia, 22. 06 -28. 06 2008

COmmon 160 Ge. V polarized beam / 190 Ge. V beam Muon and two stage spectrometer SAS & LAS (~50 m) Proton HCALs, ECALs, RICH for particle ID, walls Apparatus for Lake LEMAN Structure and Spectroscopy LHC SPS CERN (France) N CERN (Suisse) In 2002 -2004 & 2006 -2007 COMPASS has recorded BEACH 08 26 june 2008 about 5× 1010 events ~ 2000 TB

NA 58 experiment at CERN 11 counties/20 Institutes/~230 physicists Czech Republic, Finland, France, Germany, India, Israel, Italy, Japan, Poland, Portugal and Russia Bielefeld, Bochum, Bonn, Burdwan/Calcutta, CERN, Dubna, Erlangen, Freiburg, Lisbon, Mainz, Moscow, Munich, Prage, Protvino, Saclay, Tel Aviv, Torino, Trieste, Warsaw and Yamagata Experiment is a merge of two programmes/collaborations: HMC (muon beam) & CHEOPS (hadron beam) 5/24/2021 BEACH 08 26 june 2008 3

Physics program of COMPASS Detector is advantageously located at M 2 SPS beam line with a variety of high intensity & h beams • Runs with muon beam (2002 -2004, 2006 -2007) - Gluon polarization G/G - g 1 spin structure function – Flavor decomposition of spin distributions – Transverse spin effects – Spin transfer in Lhyperon production – Vector meson production 5/24/2021 • Runs with hadron beams (2008 -2009) – Diffractive production – Search for new exotic states, glueballs or hybrids – Light meson spectroscopy – Production of doubly charmed baryons – Pion and kaon polarizabilities BEACH 08 26 june 2008 4

COMPASS in run NIM A 577(2007) 455 Trigger Hodoscopes ECALs & HCALs MWPCs m 0 SM 2 5 RICH Drift Chambers 6 Li. D target SM 1 m Filters/ Walls Straws 0 16 V Ge m veto 5/24/2021 Si Sci. Fi GEMs Micromegas BEACH 08 26 june 2008 5

COMPASS tracking detectors BEACH 08 26 june 2008

Micro. Megas (Micro Mesh Gas Detector) 3 stations, 12 coordinates size 40 x 40 cm 2 pitch 360 – 420 μm time res. < 10 ns space res. 70 -90 μm efficiency > 97% Ne/C 2 H 6/CF 4 80/10/10 % 5/24/2021 BEACH 08 26 june 2008 7

Ring Imaging Cherenkov Detector Identification of π, K and protons Cherenkov thresholds: π ≈ 3 Ge. V/c K ≈ 9 Ge. V/c p ≈ 17 Ge. V/c 3 m 2σ π/K separation at 43 Ge. V/c 6 m Mirror wall 5 m Cs. I MWPC Radiator: C 4 F 10 5/24/2021 BEACH 08 26 june 2008 8

COMPASS experimental hall 5/24/2021 BEACH 08 26 june 2008 9

What makes up the spin of nucleon? Naive quark model: valence quarks QCD: …additional contributions from gluons … … and angular momentum 1 = 1 Σ G 2 2 ΔG = ? 5/24/2021 BEACH 08 26 june 2008 10

Nucleon spin puzzle since 1988 ½= ½ΔΣ + ΔG + <Lz> quarks gluons orb. mom. “past” “present” “future” experiments Measurement of ΔG is important for two reasons: - as an element of nucleon spin puzzle possible role of axial anomaly in the a 0 interpretation (a 0 ≠ ΔΣ) a 0 (= ΔΣ) is measured to be ~0. 30 -0. 35 instead of expected 0. 6 5/24/2021 BEACH 08 26 june 2008 a 0 = 11

Photon Gluon Fusion (PGF) Open Charm → clean channel → but experimentally difficult ≈ 100 nb… limited statistics High-p. T Hadron Pairs N cross-section asymmetry A|| 5/24/2021 → easy to get a statistics → but physical background 2 cases Q 2 <1 Ge. V 2 (90% stat) & Q 2 > 1 Ge. V 2 (10% stat) BEACH 08 26 june 2008 12

Open charm D* tag D 0 → K π ND=8675 on ly D 0→ K π π 0 no D* tag D 0 → K π ND=37398 5/24/2021 BEACH 08 26 june 2008 - golden channel, weak MC dependence - small statistics, no vertex detector → no primary/secondary vertex separation 13

Open charm Gluon polarization G/G is extracted from the measured double spin asymmetry Aexp of the D 0 cross-section using the analysing power (a. LL), target polarisation (p. T) , beam polarisation (p ) , dilution factor (f) and signal purity S/(S+B) was parameterized ( ) as a function of kinematical variables and the RICH response; it’s given event-by-event Event weight: w=p f a. LL Preliminary (2002 -2006) result: ΔG/G = -0. 49 ± 0. 27 (stat) ± 0. 11 (syst) 5/24/2021 BEACH 08 26 june 2008 14

high p. T hadron pairs 10% of statistics QCDCompton gq - considerably higher statistics … but physical background, resolved photons processes (last 4) are important only for low Q 2 LO DIS qq qg gg New analysis for Q 2>1 Ge. V 2 was done using 2002 -2004 data. 5/24/2021 BEACH 08 26 june 2008 15

G/G measurements new high p. T point new charm point QCD fits | G| ≈ 0. 2− 0. 3 as direct measurements point to a small value of G …. . axial anomaly contribution is small a 0 ≈ 5/24/2021 BEACH 08 26 june 2008 16

In 2008 COMPASS will collect data from two production mechanisms with the same apparatus using p, and K projectiles Central production Diffractive scattering Large rapidity gap between scattered beam and X Beam particle looses ~10% of its energy Particles at large angles Possible source of glueballs 5/24/2021 Forward kinematics Large cross-section (~mb) Need to separate particles at very small angles Study of JPC-exotic mesons BEACH 08 26 june 2008 17

Beam: 190 Ge. V positive/negative hadrons Negative: 96% , 3. 5% K, 0. 5% p Positive: 75% K, 25% Beam intensity: 5· 106 had/s Luminosity: 0. 15 pb− 1 /day Target: liquid H 2, 40 cm long COMPASS in 2008 BEACH 08 26 june 2008

Detection of target recoil protons Simulated recoil protons from diffractive −p scattering Full acceptance for −t > 0. 06 (Ge. V/c)2 Efficiency ~100% for P>290 Me. V/c 5/24/2021 BEACH 08 26 june 2008 19

3 Events from Diffractive Dissociation at COMPASS 2004 pilot run: Exclusivity target stays intact Momentum transfer Diffraction on nucleons 5/24/2021 BEACH 08 26 june 2008 20

Invariant Mass of 3 System Well-known a 1(1260), a 2(1320), 2(1670) states come out correctly BNL-E 852 COMPASS: p =190 Ge. V/c BNL-E 852: p =18 Ge. V/c 4 M events in 3 days (full t-range) 250 k events 1(1600) but 450 k events in BNL-E 852 t-range its existence still questionable 5/24/2021 BEACH 08 26 june 2008 21

Mass of + - combinations from 3 events 5/24/2021 BEACH 08 26 june 2008 22

Partial Wave Analysis 5/24/2021 BEACH 08 26 june 2008 23

COMPASS results compared to PDG values n i m i l e r p 5/24/2021 y r a BEACH 08 26 june 2008 24

Exotics: 1(1600) in COMPASS preliminary Breit-Wigner parameters for 1(1600) 5/24/2021 BEACH 08 26 june 2008 25

Light exotics COMPASS 1(1600) 1 -+ 1660 ± 10 5/24/2021 BEACH 08 26 june 2008 269 ± 21 26

Glueballs mass spectrum Lattice calculation Lightest glueballs: • • Experimental candidates: • f 0(1500) (Crystal Barrel, WA 102) JPC=0++ mixing with isoscalar mesons! Higher masses: • exotic: JPC = 2+-, 0+ • M ~ 4. 3 Ge. V/c 2 [Y. Chen et al. , Phys. Rev. D 73, 014516 (2006)] 5/24/2021 BEACH 08 26 june 2008 27

Expected event rates (run 2008) • 190 Ge. V/c hadron beam L=0. 15 pb-1/day • Diffractive scattering: • ( 1)×BR( 1 + - -)=0. 6 b 4. 5· 103 ev. /day • e(DAQ)×e(reco)=5% • Goal for 2008: 1. 6· 105 1(1600) events in ~35 day • Central production: • (f 0)×BR(f 0 hh 4 g)=1. 5 b· 5%· 15%=11 nb • e(DAQ)×e(reco)=2% 30 ev. /day • Goal for 2008: 2· 103 f 0 ηη events in ~60 days 2. 5· 103 ev. /day • Goal for 2008: 1· 105 f 0 2 + 2 − events in ~60 days 5/24/2021 BEACH 08 26 june 2008 28

Conclusions Data taking with beam: 2002 -2004, 2006 -2007 Direct measurements results indicate small ΔG around x ≈ 0. 1; QCD analysis of g 1 shows the first moment of | G| ≈ 0. 2 -0. 3; G>0 and G<0 solutions describe data equally well G <Lz> 1/2 = 1/2 × 0. 3 + 0. 35 + 0. 0 1/2 = 1/2 × 0. 3 + 0. 0 + 0. 35 1/2 = 1/2 × 0. 3 - 0. 35 + 0. 7 but direct measurements cannot yet discriminate between them Pilot run with beam: 2004 (3 days) Diffractive reactions being studied: 3 Major partial waves are correctly reconstructed Statistics 2×higher than BNL-E 852 in 1 year Looking forward to many new results from 2008 hadron run 5/24/2021 BEACH 08 26 june 2008 29

Backup slides 5/24/2021 BEACH 08 26 june 2008 30

Data taking… Up to 2008 COMPASS has collected data for program with a polarised muon beam • • • beam momentum/polarisation: 160 Ge. V/c /~80% beam intensity: 2 x 108 μ+/spill (4. 8 s/16. 2 s) luminosity: ~5 x 1032 cm-2 s-1 up to 2006 6 Li. D target (~ 50% polarized deuterons) in 2007 NH 3 target (~ 90% polarized protons) recorded about 5× 1010 events ~ 2000 TB 2004: a short pilot run for hadron program 2008: hadron run with 190 Ge. V - beam for diffractive and central production is going on 5/24/2021 BEACH 08 26 june 2008 31

Nucleon spin decomposition Proton spin sum rule: ½ = ½∆ + ΔG + Lz Total quark spin (cf singlet axial charge a 0) ∆ = Δu + Δd + Δs Net quark spin contributions ∆q Net strange quark spin ∆s Net gluon spin ∆G Orbital angular momentum Lz 5/24/2021 BEACH 08 26 june 2008 32

Asymmetry measurement upstream downstream two oppositely polarized 60 cm long target cells: upstream (u), downstream (d) cells polarization reversal every 8 hours counting rate asymmetry in two target cells gives the cross-section asymmetry A|| target polarisation PT ≈ dilution factor f ≈ beam polarisation PB ≈ depolarisation factor D ≈ 5/24/2021 BEACH 08 26 june 2008 0. 50 0. 40 0. 80 0. 60 33

Measurements of the gluon polarization two approaches: direct and indirect & three methods & four measurements 1. Double spin asymmetry of the OPEN CHARM cross-section in high energy μD scattering (first direct method) 2. Double spin asymmetry of the high-pt HADRON PAIRS in high energy μD DIS: Q 2 > 1 Ge. V 2 (second direct method) 3. Double spin asymmetry of the high-pt HADRON PAIRS in high energy μD scattering: Q 2 < 1 Ge. V 2 (second direct method) 4. Measurement of g 1 of the deuteron and QCD fit of all the world data (indirect method) BEACH 08 26 june 2008

high p. T hadron pairs PGF contribution enhancement p. T > 0. 7 Ge. V/c 10% of statistics p. T 12 + p. T 22 > 2. 5 (Ge. V/c)2 x. F, z > 0. 1 m(h 1, h 2) > 1. 5 Ge. V/c 2 Q 2 < 1 Ge. V 2 ← analysis → Q 2 > 1 Ge. V 2 90% ← statistics from total → 10% 50% ← resolved photons contribution → ---QCD-C, LO ← another background → QCD-C, LO PYTHIA ← MC generator used → LEPTO 5/24/2021 BEACH 08 26 june 2008 35

Gluon polarization: direct measurements • open charm: ΔG/G = -0. 49 ± 0. 27 (stat) ± 0. 11 (syst) <x> ~ 0. 11, <μ 2> ~ 13 Ge. V 2 2002 -2006 • high-p. T pairs, Q 2>1 Ge. V 2 : ΔG/G = 0. 08 ± 0. 10 (stat) ± 0. 05(syst) <x> = 0. 082 , μ 2 ~ 3 Ge. V 2 2002– 2004 • high-p. T pairs, Q 2<1 Ge. V 2 : ΔG/G = 0. 016 ± 0. 058 (stat) ± 0. 055 (syst) <x> = 0. 085, μ 2 = 3 Ge. V 2 2002– 2004 5/24/2021 BEACH 08 26 june 2008 36

Signal purity: parametrisation D 0 → K π no D* tag 5/24/2021 BEACH 08 26 june 2008 D 0 → K π D* tag 37

Weighted mass spectra 5/24/2021 BEACH 08 26 june 2008 38

Mesons beyond the NQM 5/24/2021 BEACH 08 26 june 2008 39

Glueballs mass spectrum 5/24/2021 BEACH 08 26 june 2008 40

PWA results Major partial waves are correctly reconstructed, acceptance distorsions almost absent COMPASS 2004 hadron run (preliminary) BNL 1994 run (PRD 65, 072001 (2002)) 5/24/2021 BEACH 08 26 june 2008 41