Performance of the prototype module of the GlueX electromagnetic barrel calorimeter

A photon beam test of the 4 m long prototype lead/scintillating-fibre module for the GlueX electromagnetic barrel calorimeter was carried out in Hall B at the Thomas Jefferson National Accelerator Facility with the objective of measuring the energy and timing resolutions of the module as well as the number of photoelectrons generated. Data were collected over an energy range of 150-650 MeV at multiple positions and angles along the module. Details of the analysis at the centre of and perpendicular to the module are shown herein; the results are σE / E = 5.4 % / sqrt(E (GeV)) ⊕ 2.3 %, σΔ T / 2 = 70 / sqrt(E) ps, and 660 photoelectrons for 1 GeV at each end of the module. © 2008 Elsevier B.V. All rights reserved

The GlueX beamline and detector

The GlueX experiment at Jefferson Lab has been designed to study photoproduction reactions with a 9-GeV linearly polarized photon beam. The energy and arrival time of beam photons are tagged using a scintillator hodoscope and a scintillating fiber array. The photon flux is determined using a pair spectrometer, while the linear polarization of the photon beam is determined using a polarimeter based on triplet photoproduction. Charged-particle tracks from interactions in the central target are analyzed in a solenoidal field using a central straw-tube drift chamber and six packages of planar chambers with cathode strips and drift wires. Electromagnetic showers are reconstructed in a cylindrical scintillating fiber calorimeter inside the magnet and a lead-glass array downstream. Charged particle identification is achieved by measuring energy loss in the wire chambers and using the flight time of particles between the target and detectors outside the magnet. The signals from all detectors are recorded with flash ADCs and/or pipeline TDCs into memories allowing trigger decisions with a latency of 3.3 . The detector operates routinely at trigger rates of 40 kHz and data rates of 600 megabytes per second. We describe the photon beam, the GlueX detector components, electronics, data-acquisition and monitoring systems, and the performance of the experiment during the first three years of operation

Observation of the B+^{+}→ Jψη′K+^{+} decay

International audienceThe B$^{+}$ → Jψη′K$^{+}$ decay is observed for the first time using proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of 9 fb$^{−1}$. The branching fraction of this decay is measured relative to the known branching fraction of the B$^{+}$ → ψ(2S)K$^{+}$ decay and found to be$\frac{\mathcal{B}\left({B}^{+}\to {J\psi \eta}^{\prime }{K}^{+}\right)}{\mathcal{B}\left({B}^{+}\to \psi (2S){K}^{+}\right)}=\left(4.91\pm 0.47\pm 0.29\pm 0.07\right)\times {10}^{-2},$where the first uncertainty is statistical, the second is systematic and the third is related to external branching fractions. A first look at the J/ψη′ mass distribution is performed and no signal of intermediate resonances is observed.[graphic not available: see fulltext