Precision Meson Spectroscopy at COMPASS Bernhard Ketzer Technische
Precision Meson Spectroscopy at COMPASS Bernhard Ketzer Technische Universität München International Joint Workshop CERN – JLAB – GSI FAIR Physics and Methods in Meson Spectroscopy 23 October 2008
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 • up to 580 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 • up to 580 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-
The COMPASS Experiment Two-stage spectrometer • large angular acceptance • broad kinematical range • ~250000 channels • up to 580 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-
Meson Spectroscopy 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 F. H. Heinsius)
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 target stays intact • Momentum transfer Diffractive Trigger
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 talk by Q. Weitzel 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 talk by Q. Weitzel 1. Mass-independent PWA of angular distributions in 40 Me. V mass bins 2. Mass-dependent c 2 fit to results of step 1 • 7 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 negligible
p 1(1600) • BW parameters for p 1(1600) • Leakage negligible
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
COMPASS in 2008 RPD Ring A RPD Ring B b b
COMPASS in 2008
COMPASS in 2008 Pixel. GEM detectors: • low mass • high rates: ~105 mm-2 s-1 • resolution: ~120 mm
COMPASS in 2008 DE=8 Me. V
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. Very 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× BNL E 852 statistics in ~35 days Central production: 10× WA 102 statistics in ~60 days Analysis chain (PWA) ready and tested on MC / real data 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
Kinematics: • 190 Ge. V/c p- on p target • Acceptance of RPD: -1. 0<x. F 2<-0. 8 • Acceptance of FH: 0. 66<x. F 1<0. 95 • With x 1=0. 2, x 2=0. 1 m. X=2. 7 Ge. V/c 2 Dy. Xp~4, Dy. Xp~3 m. X (Ge. V/c 2) Central Production at COMPASS Separation central production – diffraction?
Central Production MC: X 2 p+2 pf 1(1285) f 0(1370) f 0(1500) h 2(1645) h 2(1870) f 2(1950) f 0(2020) • Resonances & isobar states from previous CP experiments • Total intensities and individual resonances well reproduced
Central Production MC: X hh 4 g PWA 1: • Full interference of partial amplitudes • Mass-independent fit in 40 Me. V/c 2 mass bins • Mass-dependent fit with BW + Bgr PWA 2: • Arbitrary (partial) coherence of amplitudes • Accounts for averaging effects due to missing waves in model f 0(1370) f 2(2150) f 0(1500) f 2(1270) f 0(1710)
Systematic Studies
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
a 2(1320) • Two Breit Wigner functions required to describe phase motion • BW 1 for a 2(1320) • BW 2 for a 2(1700): M=1. 732 Ge. V/c 2, G=0. 194 Ge. V/c 2 (fixed PDG values)
a 4(2040) • Constant width BW used for a 4(2040) (branching ratios not known) • BW parameters
p(1800) • Constant width BW for p(1800) and low-mass background • BW parameters
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 will submit a common proposal Strong wish to involve new groups . . .
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