Precision Meson Spectroscopy at COMPASS Bernhard Ketzer Technische

Precision Meson Spectroscopy at COMPASS Bernhard Ketzer Technische Universität München XLVII International Winter Meeting on Nuclear Physics Bormio, Italy 26 January 2009

The Goal Structure and dynamics of hadrons non-perturbative regime of QCD Theory: • Models: QM, bag, flux tube, . . . • Effective theories: c. PT, . . . • Lattice-QCD Q 2 Hard processes: Nucleon structure • Helicity • Transversity • GPDs Spectroscopy: Hadron mass spectrum Scattering at very low Q 2: Polarizabilities of p, K Gluonic excitations Multi-quark systems Chiral anomaly: F 3 p

COMPASS at CERN COmmon Muon and Proton Apparatus for Structure and Spectroscopy LHC SPS • p up to 400 Ge. V • secondary hadrons (p, K, . . . ): 2· 107/s • tertiary m (polarized): 4· 107/s

The COMPASS Experiment Two-stage spectrometer • large angular acceptance • broad kinematical range • ~250000 channels • > 600 TB/year Muon. Wall SM 2 E/HCAL m 50 Dipole magnets SM 1 Muon. Wall Target RICH Beam [hep-ex/0703049, NIM A 577, 455 (2007)] Tracking detectors RICH El. -mag. calorimeter Hadronic calorimeter Muon identification

The COMPASS Experiment Two-stage spectrometer • large angular acceptance • broad kinematical range • ~250000 channels • > 600 TB/year Muon. Wall SM 2 E/HCAL 50 SM 1 m Muon. Wall Target RICH Beam [hep-ex/0703049, NIM A 577, 455 (2007)] Data taking periods: • 2002 -2004: 160 Ge. V/c m+ • 2004: 2 weeks 190 Ge. V/c p • 2006 -2007: 160 Ge. V/c m+ • 2008: 190 Ge. V/c p-

QCD Exotic States Quark model: bound state of qq Quantum numbers: IG (JPC) P=(-1)l+1, C=(-1)l+s, G=(-1)I+l+s = QCD: other color-neutral configurations with same quantum numbers mixing + +. . . Hybrids Decoupling only possible for • narrow states Glueballs • vanishing leading qq term exotic JPC:

Glueballs Quenched L-QCD prediction Lightest glueballs: • • Experimental candidates: • f 0(1500) (Crystal Barrel, WA 102) JPC=0++ mixing with isoscalar mesons! COMPASS Higher masses: • exotic: JPC = 2+-, 0+ • M ~ 4. 3 Ge. V/c 2 [Y. Chen et al. , Phys. Rev. D 73, 014516 (2006)] PANDA (talk by D. Bettoni)

Hybrids Light meson sector exotics JPC=1 -+: • p 1(1400) (VES, E 852, Crystal Barrel) • p 1(1600) (E 852, VES) still controversial. . . COMPASS

Hybrids Light meson sector (< 2. 2 Ge. V/c 2): • p 1(1400) (VES, E 852, Crystal Barrel) • p 1(1600) (E 852, VES) still controversial. . . COMPASS Charmonium region: less populated • ground state predicted at 4. 3 – 4. 4 Ge. V/c 2 exotic: JPC=1 -+ narrow: 5 − 50 Me. V/c 2 ? PANDA

p 1(1600) – Positive Results in 3 p BNL E 852: p-+p p+p-p-+p’ • pp=18 Ge. V/c • limited statistics: 250 k ev. • rank 2 • mass dependent fit [S. U. Chung et al. , Phys. Rev. D 65, 072001 (2002)] VES: p-+A p+p-p-+A’ • pp=37 Ge. V/c • full coherence [Y. Khokhlov, Nucl. Phys. A 663, 596 c (2000)]

p 1(1600) – Negative Results in 3 p BNL E 852: p-+p p+p-p-+p’ • pp=18 Ge. V/c • full statistics: 2. 6 M ev. • rank 1 • extended wave set (2 -+ waves) • no mass dependent fit [A. R. Dzierba et al. , Phys. Rev. D 73, 072001 (2006)] VES: p-+A p+p-p-+A’ • pp=37 Ge. V/c • unlimited rank [D. V. Amelin, Phys. Atom. Nucl. 68, 359 (2005)]

Hadron Reactions at COMPASS Two production mechanisms studied in parallel using proton, pion and kaon projectiles Central production • Rapidity gap between pslow, hfast, X • Beam particle looses ~10% of its energy • Particles at large angles from X decays • Possible source of glueballs (DPE) Diffractive scattering • Forward kinematics • Large cross section (~mb) • Need to separate particles at very small angles • Study of JPC-exotic mesons

$Diffractive Reactions at COMPASS Example: • 4 p vertex in Pb target • Exclusivity$

Diffractive Reactions at COMPASS Example: • 4 p vertex in Pb target • Exclusivity target stays intact • Momentum transfer Diffractive Trigger

$Diffractive Reactions at COMPASS Example: • 4 p vertex in Pb target • Exclusivity$

Diffractive Reactions at COMPASS Example: • 4 p vertex in Pb target • Exclusivity target stays intact • Momentum transfer Diffraction on Pb nuclei Diffraction on nucleons

Invariant Mass of 3 p System COMPASS: pp=190 Ge. V/c • 4 M events in 3 days (full t range) • 450 k events in 0. 1<t’<1. 0 Ge. V 2/c 2 BNL 852: pp=18 Ge. V/c • 250 k events p 1(1600)

Acceptance Invariant Mass of 3 p System

PWA Technique • t-channel Reggeon exchange • Reflectivity basis in G-J frame • At high s: e = h of Regge trajectory • Isobar model 1. Mass-independent PWA of angular distributions in 40 Me. V mass bins • 42 partial waves i=JPCMe[. . . ]L [. . . ]=isobar ( pp)S, f 0(980), r(770), f 2(1270), r 3(1690)

PWA Technique • t-channel Reggeon exchange • Reflectivity basis in G-J frame • At high s: e = h of Regge trajectory • Isobar model 1. Mass-independent PWA of angular distributions in 40 Me. V mass bins 2. Mass-dependent c 2 fit to results of step 1 • 6 waves • Parameterized by BW • Coherent background for some waves

Waves used in PWA

a 1(1260) and p 2(1670) • BW for a 1(1260) + bgr • BW for p 2(1670)

p 1(1600) • BW parameters for p 1(1600)

Leakage Study • 1150000 events generated from 15 dominant waves • including JPC=2 -+ M=0, 1 • excluding JPC=1 -+ exotic wave • full reconstruction + PWA less than 5% leakage into 1 -+ wave

Summary of Waves Publication being prepared, to be submitted

Summary of Waves

Hadron Run 2008/2009 Goal: Explore hadron spectrum up to 2. 2 Ge. V/c 2 and beyond • Collect 10× existing statistics • Search for gluonic excitations (hybrids, glueballs) • Settle properties of f 0(1500) (0++ glueball candidate) • Clarify exotic nature of p 1(1400), p 1(1600) • Investigate other new / disputed states • Investigate central production at different beam momenta • K- diffractive dissociation • Beam: up to 250 Ge. V/c p, p, K

COMPASS in 2008

COMPASS in 2008 Target region: • Recoil Proton Detector (TOF) • 20 Silicon Microstrips Planes operated at 200 K to avoid radiation damage

COMPASS in 2008

COMPASS in 2008 RPD Ring A RPD Ring B b b

COMPASS in 2008

COMPASS in 2008 Pixel. GEM detectors: • very low mass: 0. 2% X 0 • high rates: ~105 mm-2 s-1 • resolution: ~120 mm

COMPASS in 2008 ECAL: • ~800 Shashlik modules • rad. hard: dose >1 k rad • 80 MHz sampling ADC DE=8 Me. V

$COMPASS in 2008 Trigger components: Diffractive Trigger=BT RPD !Veto • Beam trigger • RPD$

COMPASS in 2008 Trigger components: Diffractive Trigger=BT RPD !Veto • Beam trigger • RPD full/empty=14/1 • Cedars • Veto: Hodo || Sandwich || BK • Mainz Counter • Forward Hodoscope

Statistics in 2008 • 190 Ge. V/c hadron beam • Target: 40 cm liquid hydrogen • Diffractive dissociation: 96% p-, 3. 5% K-, 0. 5% p • p-p p 1(1600)p, p 1(1600) 3 p: 120000 events exp. • Central production: 75% p, 25% p+ • p+p p+f 0(1500)p, (1500) due hh 4 g: 1400 events exp. Early Northf 0 Area stop to LHC problems • f 0(1500) 4 p : only a few days of testing. . . 100000 events exp.

Statistics in 2008 • 190 Ge. V/c hadron beam • Target: 40 cm liquid hydrogen • Diffractive dissociation: 96% p-, 3. 5% K-, 0. 5% p • p-p p 1(1600)p, p 1(1600) 3 p: 120000 events exp. Preliminary 1 Run only

Conclusions COMPASS getting started with light meson spectroscopy High angular resolution for charged particles Final states with neutral and charged particles Observation of resonances in different production / decay channels Hadron beam running from 2008 on with l. H 2 target Experiment upgrade, diffractive running with p- beam 2008 Diffractive reactions: 10× world statistics in ~35 days Central production: 10× world statistics in ~60 days New physics results from 2004 p pilot run PWA for p+p-p- (high t’): strong signal in exotic 1 -+ wave at 1. 6 Ge. V/c 2 PWA for low t’ started PWA for p+p+p-p-p- started Data from muoproduction m. A m’XA’, X 4 p being analyzed

Spare Slides

COMPASS Future Plans 2008 2009 Hadron Spectroscopy 2010 2011 . . . p, p, K beam 2012 2013 Transversity m beam: Collins, Sivers DIS / SIDIS m beam: Dq at low x, high precision 2014 GPDs: DVCS, HEMP m beam Drell-Yann p beam DCB COMPASS submitted Lo. I, common proposal to follow Strong wish to involve new groups . . .