Pion Polarizabilities and Hybrid Meson Structure at CERN COMPASS

CERN COMPASS can investigate pion-photon interactions, to achieve a unique Primakoff Coulomb physics program, centered on pion polarizability and hybrid meson structure studies. COMPASS uses 100-280 GeV beams (muon, pion) and a virtual photon target, and magnetic spectrometers and calorimeters to measure the complete kinematics of pion-photon reactions. The COMPASS experiment is scheduled to begin data runs in 2001. Pion polarizabilities and hybrid mesons can be studied via the Primakoff reactions pion + gamma ---> pion + gamma and pion + gamma ---> Hybrid. The electric (alpha) and magnetic (beta) pion and Kaon polarizabilities characterize their deformation in an electromagnetic field, as occurs during gamma-pion Compton scattering. They depend on the rigidity of their internal structures as composite particles, and are therefore important quantities to test the validity of theoretical models. The polarizability measurement will provide an important new test of QCD chiral dynamics. The studies of quark-antiquark-gluon hybrid mesons would improve our understanding of these exotic mesons. COMPASS may improve previous Primakoff polarizability and Hybrid studies by two to three orders of magnitude. Appendixes A (Pion and Kaon Polarizabilities at COMPASS) and B (Hybrid Meson Structure at COMPASS) of this contribution include evaluations submitted to the APS DNP Town Meeting White Paper Committee. These summarize (1) the fundamental scientific issues addressed, (2) major achievements since the last DNP long range plan, (3) the short and long term U.S. outlook, (4) comparison of U.S. and global effort, (5) other issues.Comment: 13 pages, 3 figures, Invited Talk at the APS DNP Town Meeting on Electromagnetic & Hadronic Physics, Dec. 2000, Jefferson Lab., including evaluations submitted to APS DNP Town Meeting White Paper Committe

Pion and Kaon Polarizabilities at CERN COMPASS

The electric alpha and magnetic beta pion Compton polarizabilities characterize the pion's deformation in the electromagnetic field of the gamma during gamma-pi Compton scattering. The pion polarizabilities are key observables, and provide stringent tests of our understanding of chiral symmetry, its spontaneous breakdown, the role of explicit symmetry breaking in QCD. The chi_PT effective Lagrangian, using data from radiative pion beta decay, predicts the pion electric and magnetic polarizabilities alpha = -beta = 2.7 +- 0.4, in standard polarizability units. The polarizabilities deduced by Antipov et al. in their low statistics Primakoff experiment (~ 7000 events) were about three times larger than this prediction. For pion polarizability, gamma-pi scattering will be measured in CERN COMPASS via radiative pion Primakoff scattering (pion Bremsstrahlung) in the nuclear Coulomb field: pi + Z --> pi' + gamma + Z; equivalent to gamma + pi --> gamma + pi Compton scattering for laboratory gamma's of order 1 GeV incident on a target pion at rest. The pion polarizabilities are determined by their effect on the shape of the measured gamma-pi Compton scattering angular distribution. One can expect from COMPASS a total measurement uncertainty for alpha of order 0.4 for the pion polarizability. COMPASS can also carry out a first measurement of Kaon ploarizabilities. New high precision pion and Kaon polarizability measurements via radiative pion and Kaon scattering data from COMPASS will provide important new tests of the QCD chiral dynamics polarizability prediction.Comment: Contribution to Advanced Study Institute, "Symmetries and Spin" - Praha-SPIN-2002, Workshop Chairman, M. Finger, http://mfinger.home.cern.ch/mfinger/praha2002/ Prague, Czech Republic, July 2002, 15 pages, 9 figure

Pion Polarizabilities at CERN COMPASS

The electric alpha and magnetic beta pion Compton polarizabilities characterize the pion's deformation in the electromagnetic field of the gamma during gamma-pi Compton scattering. The chi_PT effective Lagrangian, using data from radiative pion beta decay, predicts the pion electric and magnetic polarizabilities alpha = -beta = 2.7 +- 0.4. The polarizabilities deduced by Antipov et al. in their low statistics Primakoff experiment (~ 7000 events) were about three times larger than this prediction. For pion polarizability, gamma-pi scattering will be measured in CERN COMPASS via radiative pion Primakoff scattering (pion Bremsstrahlung) in the nuclear Coulomb field: pi + Z --> pi' + gamma + Z; equivalent to gamma + pi --> gamma + pi Compton scattering for laboratory gamma's of order 1 GeV incident on a target pi at rest. The pion polarizabilities are determined by their effect on the shape of the measured gamma-pi Compton scattering angular distribution. One can expect from COMPASS a total measurement uncertainty for alpha, of order 0.4. New high precision pion polarizability measurements via radiative pion scattering data from COMPASS will provide important new tests of the QCD chiral dynamics polarizability prediction.Comment: Contribution to International Workshop on Hadron Structure and Hadron Spectroscopy, http://www.ts.infn.it/conferences/iwts2002/, Trieste, Italy, Feb. 2002; for the COMPASS collaboratio

Primakoff Physics for CERN COMPASS Hadron Beam: Hadron Polarizabilities, Hybrid Mesons, Chiral Anomaly, Meson Radiative Transitions

We describe a hadron physics program attainable with a partially instrumented CERN COMPASS spectrometer, involving tracking detectors and moderate-size ECAL2/HCAL2 calorimeters. COMPASS can realize a state-of-the-art hadron beam physics program based on hadron polarizability, hybrid mesons, chiral anomaly, and meson radiative transition studies. We review here the physics motivation for this hadron beam program. We describe the beam, detector, trigger requirements, and hardware/software requirements for this program. The triggers for all this physics can be implemented for simultaneous data taking. The program is based on using a hadron beam (positive/negative pion, kaon, proton) in COMPASS.Comment: Contribution to the Proceedings of the Charles U./JINR and International U. (Dubna) CERN COMPASS Summer School, Charles University, Prague, Czech Republic, August 1997, Eds. M. Chavleishvili and M. Finger Tel Aviv U. Preprint TAUP TAUP-2473-98. 26 pages, 11 figures, late

Hybrid Meson Structure at COMPASS

We describe a pion physics program attainable with the CERN COMPASS spectrometer, involving tracking detectors and an electromagnetic calorimeter. COMPASS can realize state-of-the-art pion beam hybrid meson and meson radiative transition studies. We review here the physics motivation for this program. We describe the beam, detector, trigger requirements, and hardware/software requirements for this program. The triggers for all this hybrid meson physics can be implemented for simultaneous data taking. We will investigate hybrid meson production via pion-photon Primakoff and pion-Pomeron diffractive interactions. We will determine new properties of quark-antiquark-gluon hybrid mesons, using unique production methods, to improve our understanding of these exotic mesons. The CERN COMPASS experiment uses 100-280 GeV beams (muon, pion), and magnetic spectrometers and calorimeters, to measure the complete kinematics of pion-photon and pion-Pomeron reactions. The COMPASS experiment is currently under construction, and scheduled to begin data runs in 2001. We carry out simulation studies to optimize the beam, detector, trigger, and hardware/software for achieving high statistics data with low systematic uncertainties in the hybrid meson component of this program. We will improve previous Primakoff Hybrid studies by three orders of magnitude. We implement special detectors and triggers for hybrid meson production reactions. We propose to prepare for these COMPASS pion beam hybrid studies by setting up with muon beam tests.Comment: 12 pages, 2 figures, Contributions to the International Workshop on Hadron Physics with High Energy Muon and Hadron Beams at Fixed Target Experiments, Workshop Chairmen S. Paul and F. Bradamante, Technical University Munich, Oct. 199