Baryon Spectroscopy at COMPASS

At the COMPASS experiment, diffractive dissociation of the beam proton is one of the dominant processes for the 190GeV/c positive hadron beam impinging on a liquid hydrogen target. The status of the analysis of the reactions pp -> p_f pi^+ pi^- p_s and pp -> p_f K^+ K^- p_s is presented, where dominant features of the light-baryon spectrum become clearly visible. Furthermore, partial-wave analysis techniques to disentangle these spectra are discussed

Central Production of Two-Pseudoscalar Final States at COMPASS

COMPASS is a fixed-target experiment at CERN SPS which focused on light-quark meson spectroscopy during the data-taking periods in 2008 and 2009. The central exclusive production of glueball candidates is studied with a 190GeV/c proton beam impinging on a liquid hydrogen target. We select centrally produced systems with two pseudo-scalar mesons in the final state. The decay of this system is decomposed in terms of partial waves, with particular attention paid to the inherent mathematical ambiguities of the amplitude analysis. We show that simple parametrisation are able to describe the mass dependence of the fit results with sensible Breit-Wigner parameters.Comment: Presented at EDS Blois 2013 (arXiv:1309.5705

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

Program hadronske spektroskopije sustavom COMPASS

(for the COMPASS Collaboration) COMPASS is a fixed-target experiment at the CERN SPS for the investigation of the structure and 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 190 GeV/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.COMPASS je mjerni sustav s mirnom metom za istraživanje građe i dinamike hadrona pri ubrzivaču SPS u CERNu. Taj sustav odlikuje spektrometar visokog impulsnog razlučivanja s velikim zahvaćanjem, mjerenjem energije i prepoznavanjem čestica, pa je posebno pogodan za opažanje u širokom području različitih konačnih stanja. Nakon ohrabrujućih opažanja rezonancije s egzotičnim spinom tijekom ranijih probnih mjerenja, u 2008. i 2009. su mjerenja s COMPASSom bila usmjerena na hadronsku spektroskopiju lakih kvarkova. S hadronskim snopom 190 GeV/c na meti vodika ili atomskih jezgara postignuti su najbolji svjetski ishodi u pogledu statistike i razlučivanja. U tijeku su proučavanja mezona s egzotičnim spinom i gluonske lopte koji su dobiveni difraktivnim razdvajanjem odnosno središnjim sudarima. Kako snop sadrži također protone, dobivaju se također barioni u uzbudnom stanju. Nadalje, Primakoffove reakcije pružaju određivanja radijativnih širina rezonancija i ispitivanja kiralne teorije smetnje. U radu se opisuju analize u tijeku. Posebice se predstavljaju primijenjene tehnike analize parcijalnim valovima i prikazuju ishodi za niz odabranih konačnih stanja

Program hadronske spektroskopije sustavom COMPASS

(for the COMPASS Collaboration) COMPASS is a fixed-target experiment at the CERN SPS for the investigation of the structure and 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 190 GeV/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.COMPASS je mjerni sustav s mirnom metom za istraživanje građe i dinamike hadrona pri ubrzivaču SPS u CERNu. Taj sustav odlikuje spektrometar visokog impulsnog razlučivanja s velikim zahvaćanjem, mjerenjem energije i prepoznavanjem čestica, pa je posebno pogodan za opažanje u širokom području različitih konačnih stanja. Nakon ohrabrujućih opažanja rezonancije s egzotičnim spinom tijekom ranijih probnih mjerenja, u 2008. i 2009. su mjerenja s COMPASSom bila usmjerena na hadronsku spektroskopiju lakih kvarkova. S hadronskim snopom 190 GeV/c na meti vodika ili atomskih jezgara postignuti su najbolji svjetski ishodi u pogledu statistike i razlučivanja. U tijeku su proučavanja mezona s egzotičnim spinom i gluonske lopte koji su dobiveni difraktivnim razdvajanjem odnosno središnjim sudarima. Kako snop sadrži također protone, dobivaju se također barioni u uzbudnom stanju. Nadalje, Primakoffove reakcije pružaju određivanja radijativnih širina rezonancija i ispitivanja kiralne teorije smetnje. U radu se opisuju analize u tijeku. Posebice se predstavljaju primijenjene tehnike analize parcijalnim valovima i prikazuju ishodi za niz odabranih konačnih stanja

First Results of the PixelGEM Central Tracking System for COMPASS

For its physics program with a high-intensity hadron beam of up to 2e7 particles/s, the COMPASS experiment at CERN requires tracking of charged particles scattered by very small angles with respect to the incident beam direction. While good resolution in time and space is mandatory, the challenge is imposed by the high beam intensity, requiring radiation-hard detectors which add very little material to the beam path in order to minimize secondary interactions. To this end, a set of triple-GEM detectors with a hybrid readout structure consisting of pixels in the beam region and 2-D strips in the periphery was designed and built. Successful prototype tests proved the performance of this new detector type, showing both extraordinary high rate capability and detection efficiency. The amplitude information allowed to achieve spatial resolutions about a factor of 10 smaller than the pitch and a time resolution close to the theoretical limit imposed by the layout. The PixelGEM central tracking system consisting of five detectors, slightly improved with respect to the prototype, was completely installed in the COMPASS spectrometer in spring 2008