294 research outputs found

    Halla A JLaba nakon postizanja 12 GeV

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    An overview is presented of the planned physics program for JLab\u27s Hall A following the 12 GeV upgrade with emphasis on the equipment needed to achieve the desired experimental goals. Results of simulations of sample experiments with anticipated uncertainties are presented.Predstavlja se plan fizičkih istraživanja u Halli A JLaba nakon podizanja energije na 12 GeV, s naglaskom na potrebnu opremu za postizanje željenih eksperimentalnih ciljeva. Izlažu se ishodi simulacija nekih mjerenja s očekivanim pogreškama

    Halla A JLaba nakon postizanja 12 GeV

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    An overview is presented of the planned physics program for JLab\u27s Hall A following the 12 GeV upgrade with emphasis on the equipment needed to achieve the desired experimental goals. Results of simulations of sample experiments with anticipated uncertainties are presented.Predstavlja se plan fizičkih istraživanja u Halli A JLaba nakon podizanja energije na 12 GeV, s naglaskom na potrebnu opremu za postizanje željenih eksperimentalnih ciljeva. Izlažu se ishodi simulacija nekih mjerenja s očekivanim pogreškama

    A Search for Sigma^0_5, N^0_5 and Theta^++ Pentaquark States

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    A high-resolution (sigma_instr. = 1.5 MeV) search for narrow states (Gamma < 10 MeV) with masses of M_x approx 1500-1850 MeV in ep -> e'K^+ X, e'K^- X and e' pi^+ X electroproduction at small angles and low Q^2 was performed. These states would be candidate partner states of the reported Theta^+(1540) pentaquark. No statistically significant signal was observed in any of the channels at 90% C.L. Upper limits on forward production were determined to be between 0.7% and 4.2% of the Lambda(1520) production cross section, depending on the channel and the assumed mass and width of the state.Comment: 5 pages, 5 figures, to appear in Phys. Rev. C, update with responses to referee suggestion

    Performance of the Two Aerogel Cherenkov Detectors of the JLab Hall A Hadron Spectrometer

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    We report on the design and commissioning of two silica aerogel Cherenkov detectors with different refractive indices. In particular, extraordinary performance in terms of the number of detected photoelectrons was achieved through an appropriate choice of PMT type and reflector, along with some design considerations. After four years of operation, the number of detected photoelectrons was found to be noticeably reduced in both detectors as a result of contamination, yellowing, of the aerogel material. Along with the details of the set-up, we illustrate the characteristics of the detectors during different time periods and the probable causes of the contamination. In particular we show that the replacement of the contaminated aerogel and parts of the reflecting material has almost restored the initial performance of the detectors.Comment: 18 pages, 9 Figures, 4 Tables, 44 Reference

    Search for a new gauge boson in the AA' Experiment (APEX)

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    We present a search at Jefferson Laboratory for new forces mediated by sub-GeV vector bosons with weak coupling α\alpha' to electrons. Such a particle AA' can be produced in electron-nucleus fixed-target scattering and then decay to an e+ee^+e^- pair, producing a narrow resonance in the QED trident spectrum. Using APEX test run data, we searched in the mass range 175--250 MeV, found no evidence for an Ae+eA'\to e^+e^- reaction, and set an upper limit of α/α106\alpha'/\alpha \simeq 10^{-6}. Our findings demonstrate that fixed-target searches can explore a new, wide, and important range of masses and couplings for sub-GeV forces.Comment: 5 pages, 5 figures, references adde

    Polarization transfer in the d(epol,e' ppol)n reaction up to Q^2=1.61 (GeV/c)^2

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    The recoil proton polarization was measured in the d(epol,e' ppol)n reaction in Hall A of the Thomas Jefferson National Accelerator Facility (JLab). The electron kinematics were centered on the quasielastic peak (x_{Bj}~1) and included three values of the squared four-momentum transfer, Q^2=0.43, 1.00 and 1.61 (GeV/c)^2. For Q^2=0.43 and 1.61 (GeV/c)^2, the missing momentum, p_m, was centered at zero while for Q^2=1.00 (GeV/c)^2 two values of p_m were chosen: 0 and 174 MeV/c. At low p_m, the Q^2 dependence of the longitudinal polarization, P_z', is not well described by a state-of-the-art calculation. Further, at higher p_m, a 3.5 sigma discrepancy was observed in the transverse polarization, P_x'. Understanding the origin of these discrepancies is important in order to confidently extract the neutron electric form factor from the analogous d(epol,e' npol)p experiment.Comment: 6 pages, 4 figures; updated text, figures and table

    The Quasielastic 3He(e,e'p)d Reaction at Q^2 = 1.5 GeV^2 for Recoil Momenta up to 1 GeV/c

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    We have studied the quasielastic 3He(e,e'p)d reaction in perpendicular coplanar kinematics, with the energy and momentum transferred by the electron fixed at 840 MeV and 1502 MeV/c, respectively. The 3He(e,e'p)d cross section was measured for missing momenta up to 1000 MeV/c, while the A_TL asymmetry was extracted for missing momenta up to 660 MeV/c. For missing momenta up to 150 MeV/c, the measured cross section is described well by calculations that use a variational ground-state wave function of the 3He nucleus derived from a potential that includes three-body forces. For missing momenta from 150 to 750 MeV/c, strong final-state interaction effects are observed. Near 1000 MeV/c, the experimental cross section is more than an order of magnitude larger than predicted by available theories. The A_TL asymmetry displays characteristic features of broken factorization, and is described reasonably well by available models.Comment: 5 pages, 3 figures, submitted to Physical Review Letters, v3: changed conten

    Cross Section Measurement of Charged Pion Photoproduction from Hydrogen and Deuterium

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    We have measured the differential cross section for the gamma n --> pi- p and gamma p --> pi+ n reactions at center of mass angle of 90 degree in the photon energy range from 1.1 to 5.5 GeV at Jefferson Lab (JLab). The data at photon energies greater than 3.3 GeV exhibit a global scaling behavior for both pi- and pi+ photoproduction, consistent with the constituent counting rule and the existing pi+ photoproduction data. Possible oscillations around the scaling value are suggested by these new data The data show enhancement in the scaled cross section at a center-of-mass energy near 2.2 GeV. The cross section ratio of exclusive pi- to pi+ photoproduction at high energy is consistent with the prediction based on one-hard-gluon-exchange diagrams
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