ABSTRACT
The "standard" Hall A apparatus at Jefferson Lab (TOF and aerogel threshold Cherenkov detectors) does not provide complete identification for proton, kaon and pion. To this aim, a proximity focusing C(6)F(14)/CsI RICH (Ring Image CHerenkov) detector has been designed, built, tested and operated to separate kaons from pions with a pion contamination of a few percent up to 2.4GeV/c. Two quite different experimental investigations have benefitted of the RICH identification: on one side, the high-resolution hypernuclear spectroscopy series of experiments on carbon, beryllium and oxygen, devoted to the study of the lambda-nucleon potential. On the other side, the measurements of the single spin asymmetries of pion and kaon on a transversely polarized (3)He target are of utmost interest in understanding QCD dynamics in the nucleon. We present the technical features of such a RICH detector and comment on the presently achieved performance in hadron identification.
Subject(s)
Electrons , Elementary Particles , Mesons , Protons , Beryllium/chemistry , Carbon/chemistry , Elementary Particle Interactions , Equipment Design , Monte Carlo Method , Nuclear Physics , Oxygen/chemistry , Spectrum AnalysisABSTRACT
The ratio of the electromagnetic proton elastic form factors, G(p)(E)/G(p)(M), has been measured at Jefferson Lab up to Q(2) approximately 9(GeV/c)(2), by using the CEBAF 6GeV electron beam, and revealing an unexpected and challenging physical behaviour. The 2014 scheduled 12GeV upgrade will allow the measurement of G(p)(E)/G(p)(M) up to Q(2) approximately 15(GeV/c)(2), by taking advantage of the new large-acceptance forward spectrometer Super BigBite (SBS) in Hall A. Measurements of neutron form factors in the region around 10(GeV/c)(2), where quark confinement plays an important role, are expected to show the behaviour already observed in the proton case.
Subject(s)
Elementary Particles , Protons , Radiation Monitoring/instrumentation , Spectrum Analysis/instrumentation , Electrons , Elementary Particle Interactions , Equipment Design , NeutronsABSTRACT
The possibility of anisotropies in the speed of light relative to the limiting speed of electrons is considered. The absence of sidereal variations in the energy of Compton-edge photons at the European Synchrotron Radiation Facility's GRAAL facility constrains such anisotropies representing the first nonthreshold collision-kinematics study of Lorentz violation. When interpreted within the minimal standard-model extension, this result yields the two-sided limit of 1.6×10(-14) at 95% confidence level on a combination of the parity-violating photon and electron coefficients (κ(o+))(YZ), (κ(o+))(ZX), c(TX), and c(TY). This new constraint provides an improvement over previous bounds by 1 order of magnitude.
ABSTRACT
The analysis of the gammap-->etapi(0)p reaction has been performed using data from the GRAAL experiment. The total and differential cross sections and the beam asymmetry have been obtained from threshold up to 1.5 GeV of beam energy. The two resonances S11(1535) and Delta(1700) are expected to be excited in the intermediate states of this reaction. The results are used to test predictions based on the assumption that both resonances are dynamically generated from the meson-baryon interaction provided by chiral Lagrangians. The term involving the Delta(1700) excitation, followed by the decay into etaDelta(1232), is found to be dominant.
ABSTRACT
The emission time chronology of neutrons, protons, and deuterons from the E/A=61 MeV 36Ar+27Al reaction is deduced from two-particle correlation functions.
ABSTRACT
The double pi(0) photoproduction off the proton has been measured in the beam energy range of 0.65-1.5 GeV. The total and differential cross sections and the Sigma beam asymmetry were extracted. The total cross section measured for the first time in the third resonance region of the nucleon shows a prominent peak. The interpretation of these results by two independent theoretical models infers mostly the selective excitation of P11- and D13-nucleon resonances.
ABSTRACT
Experimental information has been derived from the neutron-proton correlation function in order to deduce the time sequence of neutrons and protons emitted at 45 degrees in the E/A = 45 MeV 58Ni + 27Al reaction.