A Partial-Wave Analysis of Centrally Produced Two-Pseudoscalar Final States in pp Reactions at COMPASS

COMPASS is a fixed-target experiment at CERN SPS which focused on light-quark hadron spectroscopy during the data taking in 2008 and 2009. A world-leading data set was collected with a 190GeV/c hadron beam impinging on a liquid hydrogen target in order to study the central production of glueball candidates. In this report, we motivate double-Pomeron exchange as a relevant production process for mesons without valence quark content. We select a centrally produced sample from the COMPASS data set recorded with a proton beam and introduce a decomposition into partial waves. Particular attention is paid to inherent mathematical ambiguities in the amplitude analysis of two-pseudoscalar final states. Furthermore, we show a simple parametrisation for the centrally produced K+K- system which can describe the mass dependence of the fit results with sensible Breit-Wigner parameters.Comment: Proceedings for 51st International Winter Meeting on Nuclear Physics, 21-25 January 2013, Bormio (Italy

The COMPASS Hadron Spectroscopy Programme

COMPASS is a fixed-target experiment at the CERN SPS for the investigation of the structure and the dynamics of hadrons. The experimental setup features a large acceptance and high momentum resolution spectrometer including particle identification and calorimetry and is therefore ideal to access a broad range of different final states. Following the promising observation of a spin-exotic resonance during an earlier pilot run, COMPASS focused on light-quark hadron spectroscopy during the years 2008 and 2009. A data set, world leading in terms of statistics and resolution, has been collected with a 190GeV/c hadron beam impinging on either liquid hydrogen or nuclear targets. Spin-exotic meson and glueball candidates formed in both diffractive dissociation and central production are presently studied. Since the beam composition includes protons, the excited baryon spectrum is also accessible. Furthermore, Primakoff reactions have the potential to determine radiative widths of the resonances and to probe chiral perturbation theory. An overview of the ongoing analyses will be presented. In particular, the employed partial wave analysis techniques will be illustrated and recent results will be shown for a selection of final states.Comment: 3rd International Conference on Nuclear and Particle Physics with CEBAF at Jefferson Lab, October 3-8, 2010, Dubrovnik, Croati

Partial-Wave Analysis of the Centrally Produced {\pi}+{\pi}- System in pp Reactions at COMPASS

COMPASS is a fixed-target experiment at CERN SPS which investigates the structure and spectroscopy of hadrons. During nine weeks in 2008 and 2009, a 190 GeV/c proton beam impinging on a liquid hydrogen target was used in order to study the production of exotic mesons and glueball candidates at central rapidities. As no bias on the production mechanism was introduced by the trigger system, the contribution from diffractive dissociation of the beam proton poses a challenge. We select a centrally produced sample by kinematic cuts and introduce a model to describe the data in terms of partial waves. Preliminary fits are presented, which are consistent with results from previous experiments. Particular attention is paid to the ambiguities in the amplitude analysis of the two-pseudoscalar final state.Comment: Sixth International Conference on Quarks and Nuclear Physics, April 16-20, 2012, Ecole Polytechnique, Palaiseau, Paris PoS (QNP2012) 09

Meson spectroscopy with COMPASS

The COMPASS fixed-target experiment at CERN SPS is dedicated to the study of hadron structure and dynamics. In the physics programme using hadron beams, the focus is on the detection of new states, in particular the search for $J^{PC}$ exotic states and glueballs. After a short pilot run in 2004 (190 GeV/c negative pion beam, lead target), we started our hadron spectroscopy programme in 2008 by collecting an unprecedented statistics with a negative hadron beam (190 GeV/c) on a liquid hydrogen target. A similar amount of data with positive hadron beam (190 GeV/c) has been taken in 2009, as well as some additional data with negative beam on nuclear targets. The spectrometer features a large angular acceptance and high momentum resolution and also good coverage by electromagnetic calorimetry, crucial for the detection of final states involving $\pi^0$ or $\eta$. A first important result is the observation of a significant $J^{PC}$ spin exotic signal consistent with the disputed $\pi_1(1600)$ in the pilot run data. This result was recently published. We present an overview of the status of various ongoing analyses on the 2008/09 data.Comment: 6 pages, 6 figures, to appear in the proceedings of the International Nuclear Physics Conference 2010, Vancouver, Canada, 04-09 Jul 201

Beam Asymmetry Σ for the Photoproduction of η and ή Mesons at Eγ = 8.8GeV

We report on the measurement of the beam asymmetry Σ for the reactions →γp→pη and →γp→pη′ from the GlueX experiment using an 8.2–8.8-GeV linearly polarized tagged photon beam incident on a liquid hydrogen target in Hall D at Jefferson Laboratory. These measurements are made as a function of momentum transfer −t with significantly higher statistical precision than our earlier η measurements and are the first measurements of η′ in this energy range. We compare the results to theoretical predictions based on t-channel quasiparticle exchange. We also compare the ratio of Ση to Ση′ to these models as this ratio is predicted to be sensitive to the amount of s¯s exchange in the production. We find that photoproduction of both η and η′ is dominated by natural parity exchange with little dependence on −t