The cross section of atomic electron Compton scattering gamma + e -> gamma' + e' was measured in the 4.400-5.475 GeV photon beam energy region by the PrimEx collaboration at Jefferson Lab with an accuracy of 2.6% and less. The results are consistent with theoretical predictions that include next-to-leading order radiative corrections. The measurements provide the first high precision test of this elementary QED process at beam energies greater than 0.1 GeV. (C) 2019 The Author(s). Published by Elsevier B.V.

Using the DIANA data on the charge-exchange reaction K^+n --> pK^0 on a bound neutron, in which the s-channel formation of the pentaquark baryon \Theta^+(1538) has been observed, we analyze the dependence of the background-subtracted \Theta^+ --> pK^0 signal on the K^0 emission angle in the pK^0 rest frame. The data are consistent with the angular dependence of an asymmetric form dW/d\cos\Theta_cms ~ (\cos\Theta_cms + A)^2 with a positive offset A. This form of the \cos\Theta_cms distribution suggests an interference between the nonresonant $s$-wave and the \Theta-mediated higher-wave contributions to the total amplitude of the charge-exchange reaction, and rules out the spin-parity assignment of 1/2$^-$ for the \Theta^+ baryon. The selection in \cos\Theta_cms based on the observed angular dependence of the \Theta^+ --> pK^0 signal allows to boost the statistical significance of the signal up to 7.1 standard deviations.

The Jefferson Laboratory PrimEx Collaboration has developed and implemented a method to control the tagged photon flux in photoprocluction experiments at the 1% level over the photon energy range from 4.9 to 5.5 GeV. This method has been successfully implemented in a high precision measurement of the neutral pion lifetime. Here, we outline the experimental equipment and the analysis techniques used to accomplish this. These include the use of a total absorption counter for absolute flux calibration, a pair spectrometer for online relative flux monitoring, and a new method for post-bremsstrahlung electron counting. (C) 2014 Elsevier B.V. All rights reserved.

High precision measurements of the differential cross sections for π0 photoproduction at forward angles for two nuclei, 12C and 208Pb, have been performed for incident photon energies of 4.9-5.5 GeV to extract the π0→γγ decay width. The experiment was done at Jefferson Lab using the Hall B photon tagger and a high-resolution multichannel calorimeter. The π0→γγ decay width was extracted by fitting the measured cross sections using recently updated theoretical models for the process. The resulting value for the decay width is Γ(π0→γγ)=7.82±0.14(stat)±0.17(syst)  eV. With the 2.8% total uncertainty, this result is a factor of 2.5 more precise than the current Particle Data Group average of this fundamental quantity, and it is consistent with current theoretical predictions.

A technique is presented for precision measurements of the area densities, ρT, of approximately 5% radiation length carbon and 208Pb targets used in an experiment at Jefferson Laboratory to measure the neutral pion radiative width. The precision obtained in the area density for the carbon target is ±0.050%, and that obtained for the lead target through an X-ray attenuation technique is ±0.43%.

We examine the sensitivity to ν_μ–> ν_e of a conceptual neutrino experiment that involves a neutrino superbeam, a Megaton-scale water Cherekov detector, and a "magic" baseline 7300 km. With realistic beam intensity and exposure time, the mixing parameter sin^2 2θ_13 and the sign of "atmospheric" mass-squared difference may be unambiguously probed down to sin^2 22θ_13 values below 10^-3.

The production ofD s relative toD + s as a function of xF with 600 GeV/c Σ − beam is measured in the interval 0.15 < xF < 0.7 by the SELEX (E781) experiment at Fermilab. The integrated charge asymmetries with 600 GeV/c Σ beam (0.53±0.06) and π beam (0.06 ± 0.11) are also compared. The results show the Σ beam fragments play a role in the production of D s , as suggested by the leading quark model.

M. Mattson, G. Alkhazov, A. G. Atamantchouk, M. Y. Balatz, N. F. Bondar, P. S. Cooper, L. J. Dauwe, G. V. Davidenko, U. Dersch, A. G. Dolgolenko, G. B. Dzyubenko, R. Edelstein, L. Emediato, A. M. F. Endler, J. Engelfried, I. Eschrich, C. O. Escobar, A. V. Evdokimov, I. S. Filimonov, F. G. Garcia, M. Gaspero, I. Giller, V. L. Golovtsov, P. Gouffon, E. Gülmez, He Kangling, M. Iori, S. Y. Jun, M. Kaya, J. Kilmer, V. T. Kim, L. M. Kochenda, I. Konorov, A. P. Kozhevnikov, A. G. Krivshich, H. Krüger, M. A. Kubantsev, V. P. Kubarovsky, A. I. Kulyavtsev, N. P. Kuropatkin, V. F. Kurshetsov, A. Kushnirenko, S. Kwan, J. Lach, A. Lamberto, L. G. Landsberg, I. Larin, E. M. Leikin, Li Yunshan, M. Luksys, T. Lungov, V. P. Maleev, D. Mao, Mao Chensheng, Mao Zhenlin, P. Mathew, V. Matveev, E. McCliment, M. A. Moinester, V. V. Molchanov, A. Morelos, K. D. Nelson, A. V. Nemitkin, P. V. Neoustroev, C. Newsom, A. P. Nilov, S. B. Nurushev, A. Ocherashvili, E. Oliveira, Y. Onel, E. Ozel, S. Ozkorucuklu, A. Penzo, S. V. Petrenko, P. Pogodin, M. Procario, V. A. Prutskoi, E. Ramberg, G. F. Rappazzo, B. V. Razmyslovich, V. I. Rud, J. Russ, P. Schiavon, J. Simon, A. I. Sitnikov, D. Skow, V. J. Smith, M. Srivastava, V. Steiner, V. Stepanov, L. Stutte, M. Svoiski, N. K. Terentyev, G. P. Thomas, L. N. Uvarov, A. N. Vasiliev, D. V. Vavilov, V. S. Verebryusov, V. A. Victorov, V. E. Vishnyakov, A. A. Vorobyov, K. Vorwalter, J. You, Zhao Wenheng, Zheng Shuchen, and R. Zukanovich-Funchal

Coherent π+π−π− production in the interactions of a beam of 600GeV π mesons with C, Cu and Pb nuclei has been studied with the SELEX facility (Experiment E781 at Fermilab). The a2(1320) meson signal has been detected in the Coulomb (low q2) region. The Primakoff formalism used to extract radiative decay width of this meson yields Γ = 284± 25± 25 keV, which is the most precise measurement to

Total cross sections for and on beryllium, carbon, polyethylene and copper as well as total cross sections for protons on beryllium and carbon have been measured in a broad momentum range around 600GeV/c. These measurements were performed with a transmission technique adapted to the SELEX hyperon-beam experiment at Fermilab. We report on results obtained for hadron-nucleus cross sections and on results for tot( N) and tot( N), which were deduced from nuclear cross sections.

Novel detector schemes are proposed for the short-baseline neutrino experiments of next generation, aimed at exploring the large-Δm2 domain of νμ→ντ oscillations in the appearance mode. These schemes emphasize good spectrometry for charged particles and for electromagnetic showers and efficient reconstruction of π0→γγ decays. The basic elements are a sequence of relatively thin emulsion targets, immersed in magnetic field and interspersed with electronic trackers, and a fine-grained electromagnetic calorimeter built of lead glass. These elements act as an integral whole in reconstructing the electromagnetic showers. This conceptual scheme shows good performance in identifying the τ (quasi-) two-body decays by their characteristic kinematics and in selecting the electronic decays of the τ.

In parallel to charm hadroproduction the experiment Selex (E781) at Fermilab is pursuing a rich hyperon physics program. Selex employs a 600 GeV/c beam consisting of 50 % Σ− and π− each. The three-stage magnetic spectrometer covering 0.1 ≤ xF ≤ 1.0 features a high-precision silicon vertex system, broad-coverage particle identification using TRD and RICH, and a three-stage lead glass photon calorimeter. First results for the Σ− charge radius, total Σ−nucleon cross sections, and a new upper limit for the radiative width of the Σ(1385)− are presented.

Quasiexclusive reactions of neutral-meson production are studied in experiments at the SPHINX facility in the proton beam of the MEP accelerator (E(p) = 70 GeV). The cross sections and the parameters of the differential cross sections for pi(0), omega, and eta production in pN interactions in the deep-fragmentation region (x(F) > 0.79-0.86) are presented. The results of this experiment show that these reactions may be of paramount importance in searches for and study of exotic mesons.

The double strangeness production has been observed in two final states of annihilation of antiprotons at momentum less than 0.9 GeV/c on Xe nuclei: K+K+X (8 events) and K+K0ΛX (6 events). The probabilities of the reaction pXe → K+K+X vary from 2 · 10−5 (at rest) up to 7 · 10−5 (in flight). The reaction pXe → K+K0ΛX is observed only in flight with probability 3 · 10−4. The properties of the observed reactions are similar to those resulting from the cascade process with production of Ξ hyperon: pN → K∗−K∗, K∗ → Kπ, −K∗N → ΞK, ΞN → ΛΛ. The new upper limit on the production probability of the stable H(S = −2) dibaryon in the reaction Xe → K+K+H(H → Σ− p)X was obtained to be < 2 · 10− (90%C.L.).