520 research outputs found
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The CEBAF Large Acceptance Spectrometer (CLAS)
No full textThe CEBAF Large Acceptance Spectrometer (CLAS) is used to study photo- and electro-induced nuclear and hadronic reactions by providing efficient detection of neutral and charged particles over a good fraction of the full solid angle. A collaboration of about thirty institutions has designed, assembled, and commissioned CLAS in Hall B at the Thomas Jefferson National Accelerator Facility. The CLAS detector is based on a novel six-coil toroidal magnet which provides a largely azimuthal field distribution. Trajectory reconstruction using drift chambers results in a momentum resolution of 0.5% at forward angles. Cerenkov counters, time-of-flight scintillators, and electromagnetic calorimeters provide good particle identification. Fast triggering and high data acquisition rates allow operation at a luminosity of 10{sup 34} nucleon cm {sup -2}s{sup -1}. These capabilities are being used in a broad experimental program to study the structure and interactions of mesons, nucleons, and nuclei using polarized and unpolarized electron and photon beams and targets. This paper is a comprehensive and general description of the design, construction and performance of CLAS
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Physics with CLAS
No full textThe authors describe the physics program and the experimental equipment of the CEBAF Large Acceptance Spectrometer, CLAS. The spectrometer is located in Hall B, one of the three experimental areas at the Continuous Electron Beam Accelerator Facility (CEBAF) operated by the Thomas Jefferson National Accelerator Facility. They review the program to study baryon resonances to demonstrate the multi-particle detection capabilities of the CLAS detector
Bayesian Analysis of Pentaquark Signals from CLAS Data
No full textWe examine the results of two measurements by the CLAS collaboration, one of which claimed evidence for a Θ+ pentaquark, while the other found no such evidence. The unique feature of these two experiments was that they were performed with the same experimental setup. Using a Bayesian analysis, we find that the results of the two experiments are in fact compatible with each other, but that the first measurement did not contain sufficient information to determine unambiguously the existence of a Θ+. Further, we suggest a means by which the existence of a new candidate particle can be tested in a rigorous manner
Polarization observables in few nucleon systems with CLAS
No full textThe CEBAF Large Acceptance Spectrometer (CLAS), housed in Hall-B at the Thomas Jefferson National Accelerator Facility provides us with the experimental tools to study strongly-interacting matter and its dynamics in the transition from hadronic to partonic degrees of freedom in nuclear interactions. In this paper we discuss the progress made in understanding the relevant degrees of freedom using polarisation observables of deuteron photodisintegration in the few-GeV photon-energy region. We also address progress made in studying the interaction between Hyperons and Nucleons via polarisation observables, utilising high-statistics experiments that provided us with the large data samples needed to study final-state interactions, as well as perform detailed studies on initial-state effects. The polarisation observables presented here provide us with unique experimental tools to study the underlying dynamics of both initial and final-state interactions, as well as the information needed to disentangle signal from background contributions
DVCS with longitudinally polarized target using CLAS at 6 GeV
No full textDeeply Virtual Compton Scattering (DVCS) is one of the simplest processes that can be described in terms of Generalized Parton Distributions (GPDs). The target single‐spin asymmetry (target SSA) in the reaction ep⃗→epγ is directly proportional to the imaginary part of the DVCS amplitude, and gives access to a combination of GPDs namely H̃, H, and E. This asymmetry will be measured in a dedicated experiment at Jefferson Lab using the CEBAF 6‐GeV polarized electron beam, a polarized solid‐state 14NH3 target, and the CEBAF Large Acceptance Spectrometer (CLAS) together with the Inner Calorimeter (IC). The expected asymmetry from leading‐order calculations is in the range of 20% to 40%, depending on the kinematics and on the GPD model used. The DVCS amplitude will be mapped out in the Q2 region from 1 to 4 GeV2, xB from 0.15 to 0.55 and −t from 0.1 to 2 GeV2 providing new constraints on the GPDs
Suppression of neutral pion production in deep-inelastic scattering off nuclei with the CLAS detector
No full textWe present the first three-fold differential measurement for neutral pion multiplicity ratios produced in semi-inclusive deep-inelastic electron scattering on carbon, iron and lead nuclei normalized to deuterium from CLAS at Jefferson Lab. We found that the neutral pion multiplicity ratio is maximally suppressed for the leading hadrons (energy fraction z approaching unity), suppression varying from 25% in carbon up to 75% in lead. An enhancement of the multiplicity ratio at low z and high p2T is observed, suggesting an interconnection between these two variables. This behavior is qualitatively similar to the previous two-fold differential measurement of charged pions by the HERMES Collaboration and recently - by CLAS Collaboration. The largest enhancement was observed at high pT2 for heavier nuclei, namely iron and lead, while the smallest enhancement was observed for the lightest nucleus, carbon. This behavior suggests a competition between partonic multiple scattering, which causes enhancement, and hadronic inelastic scattering, which causes suppression
Electroproduction of phi(1020) mesons at 1.4 \u3c= Q(2) \u3c= 3.8 GeV2 measured with the CLAS spectrometer
No full textElectroproduction of exclusive ϕ vector mesons has been studied with the CLAS detector in the kinematic range 1.
Differential Cross Sections for Λ (1520) Using Photoproduction at CLAS
No full textThe reaction p → K+Λ (1520) using photoproduction data from the CLAS g12 experiment at Jefferson Lab is studied. The decay of Λ(1520) into two exclusive channels, Σπ+π- and Σ-π+, is studied from the detected K+, π+, and π- particles. A good agreement is established for the Λ(1520) differential cross sections with the previous CLAS measurements. The differential cross sections as a function of center-of-mass angle are extended to higher photon energies. Newly added are the differential cross sections as a function of invariant four-momentum transfer t, which is the natural variable to use for a theoretical model based on a Regge-exchange reaction mechanism. No new N* resonances decaying into the K+Λ (1520) final state are found
Experimental study of the P11(1440) and D13(1520) resonances from the CLAS data on ep→e′π+π−p
No full textThe transition helicity amplitudes from the proton ground state to the P11(1440) and D13(1520) excited states (γvpN∗ electrocouplings) were determined from the analysis of nine independent one-fold differential π+π−p electroproduction cross sections off a proton target, taken with CLAS at photon virtualities of 0.2
Suppression of neutral pion production in deep-inelastic scattering off nuclei with the CLAS detector
No full textWe present the first three-fold differential measurement for neutral pion
multiplicity ratios produced in semi-inclusive deep-inelastic electron
scattering on carbon, iron and lead nuclei normalized to deuterium from CLAS at
Jefferson Lab. We found that the neutral pion multiplicity ratio is maximally
suppressed for the leading hadrons (energy fraction z approaching unity),
suppression varying from 25% in carbon up to 75% in lead. An enhancement of the
multiplicity ratio at low z and high p2T is observed, suggesting an
interconnection between these two variables. This behavior is qualitatively
similar to the previous two-fold differential measurement of charged pions by
the HERMES Collaboration and recently - by CLAS Collaboration. The largest
enhancement was observed at high pT2 for heavier nuclei, namely iron and lead,
while the smallest enhancement was observed for the lightest nucleus, carbon.
This behavior suggests a competition between partonic multiple scattering,
which causes enhancement, and hadronic inelastic scattering, which causes
suppression
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