Beam Charge Asymmetry Monitors for Low Intensity Continuous Electron Beam

Experimental Hall B at Jefferson Lab typically operates with CW electron beam currents in the range of 1 - 10 nA. This low beam current coupled with a 30 Hz flip rate of the beam helicity required the development of new devices to measure and monitor the beam charge asymmetry. We have developed four independent devices with sufficient bandwidth for readout at 30 Hz rate: a synchrotron light monitor (SLM), two backward optical transition radiation monitors (OTR) and a Faraday Cup. Photomultipliers operating in current mode provided the readout of the light from the SLM and the OTRs, while high bandwidth electronics provided the readout from the Faraday cup. Using {approximately}6 helicity pairs, we measured the beam charge asymmetry to a statistically accuracy which is better than 0.05%. We present the results from the successful operation of these devices during the fall 2000 physics program. The reliability and the bandwidth of the devices allowed us to control the gain on the source laser by means of a feedback loop

Determination of two-photon exchange via

The proton elastic form factor ratio shows a discrepancy between measurements using the Rosenbluth technique in unpolarized beam and target experiments and measurements using polarization degrees of freedom. The proposed explanation of this discrepancy is uncorrected hard two-photon exchange (TPE), a type of radiative correction that is conventionally neglected. The effect size and agreement with theoretical predictions has been tested recently by three experiments. While the results support the existence of a small two-photon exchange effect, they cannot establish that theoretical treatments are valid. At larger momentum transfers, theory remains untested. This proposal aims to measure two-photon exchange over an extended and so far largely untested $$Q^2$$ and $$\varepsilon$$ range with high precision using the CLAS12 experiment. Such data are crucial to clearly confirm or rule out TPE as the driver for the discrepancy as well as test several theoretical approaches, believed valid in different parts of the tested $$Q^2$$ range

Characteristics of Yerevan High Transparency Scintillators

Optical transmission, light output and time characteristics are given for long scintillator strips fabricated at the Yerevan Physics Institute using the extrusion method. It is shown that at 45% relative (to anthracene) light output, good transmission (2.5/2.9 m attenuation length with photomultiplier direct readout and 3/3.5 m attenuation length fiber readout) and time characteristics (average decay time 2.8 nsec) were obtained

The CLAS Forward Electromagnetic Calorimeter

The CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab utilizes six iron-free superconducting coils to provide an approximately toroidal magnetic field. The six sectors are instrumented individually to form six independent spectrometers. The forward region (8deg < (theta) < 45deg) of each sector is equipped with a lead-scintillator electromagnetic sampling calorimeter (EC), 16 radiation lengths thick, using a novel triangular geometry with stereo readout. With its good energy and position resolution, the EC is used to provide the primary electron trigger for CLAS. It is also used to reject pions, reconstruct pi-0 and eta decays and detect neutrons, This paper treats the design, construction and performance of the calorimeter