Physics with Hadron Beams at COMPASS

Physics with Hadron Beams at COMPASS Bernhard Ketzer Technische Universität München MAMI and Beyond 2009 International Workshop on Hadron Structure and Spectroscopy 2009 30 March 2009

The Goal Understand hadrons from the dynamics of ofquarks and gluons non-perturbative regime of QCD Models: QM, bag, flux tube,... Effective theories: χpt,... Lattice-QCD

Experimental Tools Deep Inelastic Lepton Scattering and and related related hard hard e.m. e.m. processes processes Spectroscopy Processes at at low low Q2 Q 2 Nucleon Structure Helicity Transversity GPDs QCD Bound States Mass spectrum Gluonic excitations Multi-quark systems Hadron Structure at Low Energies Polarizabilities Chiral anomaly 2 λ = 1 Q

COMPASS at CERN COmmon Muon and and Proton Apparatus for for Structure and and Spectroscopy LHC LHC SPS SPS p up up to to 400 400 GeV GeV secondary hadrons (π, (π, K, K,...):...): 2 10 2 10 7 7 /s /s tertiary μ (polarized): 4 10 4 10 7 7 /s /s

The COMPASS Experiment Two-stage spectrometer large angular acceptance broad kinematical range ~250000 channels > 600 600TB/year MuonWall SM2 E/HCAL Beam Target E/HCAL SM1 RICH [hep-ex/0703049, NIM NIMA A 577, 577, 455 455 (2007)] (2007)] MuonWall 50 m Dipole magnets 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 600TB/year MuonWall SM2 E/HCAL E/HCAL SM1 50 m Beam Target RICH [hep-ex/0703049, NIM NIMA A 577, 577, 455 455 (2007)] (2007)] MuonWall Data taking periods: 2002-2004: 160 160 GeV/c μ + + 2004: 2 weeks 190 190 GeV/c π - - 2006-2007: 160 160 GeV/c μ + + 2008: 190 190 GeV/c π - -

Meson Spectroscopy = + + + +... ( qq) 0 ( qq)( qq) ( qq) 8 g Hybrids gg Glueballs Quark model: bound state of qq Quantum numbers: I G (J PC ) P=(-1) l+1, C=(-1) l+s, G=(-1) I+l+s QCD: other color-neutral configurations with same quantum numbers mixing Decoupling only only possible for for narrow states vanishing leading qq qqterm exotic J PC PC + + + :: 0,0,1,2,...

Glueballs Quenched L-QCD prediction Lightest glueballs: M ~ 1.7GeV/ c M ~ 2.4GeV/ c PC ( J PC ( J = 0 = 2 2 + + 2 + + ) ) Experimental candidate: f 0 (1500) (Crystal Barrel, WA102) J PC =0 ++ mixing with isoscalar mesons! [WA102, [WA102, Phys. Phys. Lett. Lett. B479, B479, 59 59 (2000) (2000) Events / 0.08 GeV COMPASS [Y. Chen et al., Phys. Rev. D 73, 014516 (2006)] M(ηη) (GeV)

Hybrids Light meson sector exotics J PC =1 + : π 1 (1400) (VES, E852, Crystal Barrel) π 1 (1600) (E852, VES) still controversial... R BR B Events / 0.04 GeV/c 2 M(3π) (GeV/c 2 ) [S.U. [S.U. Chung Chung et et al., al., PRD PRD 65, 65, 072001 072001 (2002)] (2002)] [A.R. [A.R. Dzierba Dzierba et et al., al., PRD PRD 73, 73, 072001 072001 (2006)] (2006)] COMPASS

Hadron Reactions at COMPASS Two Two production mechanisms studied in in parallel using proton, pion and andkaon projectiles Central production Diffractive dissociation Rapidity gap between p slow, h fast, X Beam particle looses ~10% of its energy Particles at large angles from X decays Possible source of glueballs (DPE) Forward kinematics Need to separate particles at very small angles Study of J PC -exotic mesons

Diffractive Reactions at COMPASS Example: π + Pb πππ + + 4πvertex in Pb target Exclusivity target stays intact Pb p a p c Momentum transfer t Q 2 = ( p ) a pc 2 Diffraction on on Pb Pb nuclei Diffraction on on nucleons

Invariant Mass of 3π System COMPASS: p π =190 π GeV/c 4M 4Mevents in in 3 days (full (full t t range) 450k events in in0.1<t <1.0 GeV GeV 2 2 /c /c 2 2 BNL852: p π =18 π =18 GeV/c 250k events π 1 (1600) 1

Invariant Mass of 3π System Acceptance

PWA Technique high s: t-channel Reggeon exchange Reflectivity basis in G-J frame ε = η of Regge trajectory Isobar model 1. Mass-independent PWA of angular distributions in 40 MeV mass bins indep 1 N r ε ε ε σ ( τ)= T ψ ( τ) ψ ( τ ) dτ ε = 1 r= 1 i ir i 42 partial waves i=j PC M ε [...]L [...]=isobar (ππ) S, f 0 (980), ρ(770), f 2 (1270), ρ 3 (1690) i 2 2

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

Waves used in PWA

Major Waves a 1 (1260) 1 π 2 (1670) 2 a 2 (1320) 2

π 1 (1600) BW parameters for π 1 (1600) M ( ) + 0.000 0.064 = 1.660 ± 0.010 GeV/ c 2 ( ) +0.042 0.064 Γ = 0.269 ± 0.021 GeV / c 2 Leakage negligible

Summary of Waves Publication being prepared, to be submitted to PRL

COMPASS in 2008

COMPASS in 2008 RPD Ring A RPD Ring B β β

COMPASS in 2008

COMPASS in 2008 PixelGEM detectors: low mass high rates: ~10 5 mm -2 s -1 resolution: ~120 μm

COMPASS in 2008 E g >2.0 GeV and E pi0 > 10 GeV 11000 N evt 10000 9000 8000 7000 hmp2 Entries 429320 Mean 0.1325 RMS 0.0469 χ 2 / ndf 36.39 / 30 N( π 0 ) 1.912e+04 ± 410 Mass 0.1355 ± 0.0001 σ 0.008079 ± 0.000167 p3 1.329e+04 ± 89 p4-6.462e+04 ± 612 p5 1.286e+05 ± 2445 p6-1.054e+05 ± 6585 6000 5000 4000 ΔE=8 MeV 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.22 2 (GeV/c ) M gg

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 GeV/c hadron beam Target: 40cm liquid hydrogen Diffractive dissociation: 96% π -, 3.5% K -, 0.5% p π - p π 1 (1600)p, π 1 (1600) 3π: 120000 events exp. Very Preliminary

190 GeV/c hadron beam Target: 40cm liquid hydrogen Statistics in 2008 Diffractive dissociation: 96% π -, 3.5% K -, 0.5% p π - p π 1 (1600)p, π 1 (1600) 3π: 120000 events exp. Central production: 75% p, 25% π + π + p π + f 0 (1500)p, Early f 0 (1500) ηη 4γ: 1400 events exp. North Area stop stop due due to to LHC LHC problems f 0 (1500) 4π : 100000 events exp. only a few days of testing... to be done in 2009

χpt χpt (2-loop): α π Pion Polarizabilities Describe response to to external e.m. e.m. fields stiffness of of system electric polarizability d = α E magnetic polarizability μ = β H = (2.9 ± 0.5) 10 4 fm 3 Experiments: pion pion Compton scattering π γ π γ π γγ β π = ( 2.8 ± 0.5) 10 4 fm 3 PLUTO DM1 DM2 Mark II Lebedev Mami A2 Serpukhov

Cross Section Ratio 3 2 N ω σ mπ ω R( ω)= = 1 + βπ, απ + βπ = 0 N ( ω) dσ 2 α 1 ω Prim exp( ) d γπ 3 Thomson MC γπ ( ) muon beam R(ω) for different values of α π (β π ) Cross check with μ beam

Q 2 Distributions from Pilot Run ( ωθ) 3 2 2 2 d σ α Ζ Q Q 2 dσ min 2 γπ, = F 2 4 Z ( Q ) d d dcos dcos Q ω θ πω Q θ

Z 2 Dependence of Cross Section ( ωθ) 3 2 2 2 d σ α Ζ Q Q 2 dσ min 2 γπ, = F 2 4 Z ( Q ) d d dcos dcos Q ω θ πω Q θ

2009 Primakoff Measurement Major improvements: Detector performance: ECAL, μid Optimized target: 58 Ni Radiative corrections Beyond Weizsäcker-Williams approach Interference with diffractive amplitudes Suppression of π π 0 background MC description of setup Prospects (4 weeks): σ stat ~0.33 10-4 fm 3 σ sys ~0.16 10-4 fm 3 independent extaction of α π, β π with σ stat ~0.5 10-4 fm 3 α π (s) first measurement of α K

Primakoff Reactions with Neutral Mesons Primakoff π 0 production Chiral Perturbation Theory Prediction: F 3π (0)=9.7±0.1 GeV -3 Experiment (Serpukhov): F 3π (0)=12.9±0.9±0.5 GeV -3 F 3π π F (0) (0) =, f ± = ( 130.7 ± 0.4) MeV π πα f 2 ± π

Conclusions COMPASS started physics program with hadron beams in 2008 High angular resolution for charged particles Final states with neutral and charged particles Observation of resonances in different production / decay channels Light meson spectroscopy with lh2 target Experiment upgrade Diffractive reactions: 10 BNL E852 statistics Central production: 10 WA102 statistics Analysis chain (PWA) ready and tested on MC / real data Primakoff reactions: polarizabilities of π and K, chiral anomaly New physics results from 2004 π pilot run PWA for π + π - π - (high t ): strong signal in exotic 1 -+ wave at 1.6 GeV/c 2 PWA for low t ongoing PWA for π + π + π π π started: higher masses, b 1 π, f 1 π decay channels