Session E07: Instrumentation: Low-Q Electron Scattering and Polarimetry

Target-Chamber-Post Vetos for the MUSE Experiment

The MUon-proton Scattering Experiment (MUSE) is currently operating at the PiM1 beam line of the Paul Scherrer Institute. MUSE seeks to provide insight into the proton radius puzzle by extracting the proton charge radius. MUSE will obtain precise cross sections and form factors from simultaneous measurements of elastic electron-proton and muon-proton scattering from a liquid-hydrogen target using lepton beams of both charge polarities, allowing direct measurement and then cancellation of two-photon effects. To determine the charge radius with sufficient precision, thorough understanding of the MUSE detector system and beam properties is required. The structural integrity of the large-scattering-window target chamber is maintained by two forward-angle support posts. Particles that scatter from these support posts are known to contaminate data; a new veto detector, the Target Chamber Post Veto (TCPV), was installed in 2022 to reduce these post-scattered backgrounds. In this presentation, I will discuss recent efforts towards characterizing the operation of the TCPV and evaluating its efficiency as a veto detector for MUSE.   

Luminosity Determination for MUSE

The physics goals of the MUon Scattering Experiment (MUSE) in measuring the proton radius require the use of a mixed particle beam that includes electrons, muons, and pions. MUSE uses the mixed particle beam at Paul Scherrer Institute in Switzerland, which presents unique challenges in calculating the beam luminosity. In order for the flux of each particle species to be accurately measured, several different factors must be taken into account including background rates, dead time, exclusion of particles due to dead time and multiple triggers within a single event. This presentation will discuss efforts to account for corrections in luminosity calculations for the cross section analysis.   

Performance of GEM Detectors for MUSE

The Muon Scattering Experiment (MUSE) at Paul Scherrer Institute (PSI) is designed to simultaneously measure the proton charge radius with elastic scattering of electrons and muons of either charge polarity. Due to the large emittance of the secondary beam, it is necessary to have a beamline detector for event-by-event beam particle tracking. A telescope of Gas Electron Multipliers (GEM), exposed to a high flux of beam particles is used to reconstruct the incoming tracks with high spatial resolution while presenting minimal material for the beam to pass through. In this presentation, I will discuss the effects of noise suppression techniques such as channel flagging, interpolation, and cross-talk suppression that are used to improve the GEM beam tracker performance. In addition, the multi-sample readout allows to reconstruct the time dependence of proper GEM signals and to further reject backgrounds.   

Comparison of GEM Performance with 1D and 2D Clusters (MUSE)

The difference between the proton radius measured by hydrogen spectroscopy and electron scattering, and the proton radius measured with muon spectroscopy, known as the proton radius puzzle, has been unresolved for over a decade. The MUSE experiment at Paul-Scherrer Institute (PSI) was designed to provide the first high precision muon scattering radius measurement to resolve the puzzle. The MUSE experiment simultaneously measures electron and muon scattering, and measures alternately with both beam polarities as a check of higher-order corrections that might affect the radius extraction. The experiment is composed of many hardware components which includes a Gas Electron Multiplier (GEM) telescope to determine particle trajectories. This presentation will give an overview of the formation of 1D and 2D clusters, charge sharing, and the tracking performance of the GEM detectors by comparing the 1D clusters and the 2D clusters.



  

Scattered Particle Tracking and Vertex Reconstruction in the MUSE Experiment

The “Proton Radius Puzzle” was sparked when the proton radius was measured with muons to be ~ 0.842 ± 0.001fm, a deviation of about 5σ from the CODATA average value when measured with electrons at the time. Possible explanations include violation of lepton universality, two photo exchange effects or underestimated systematic uncertainties in extracting the form factor from our scattering data. The MUon Scattering Experiment (MUSE) aims to perform new measurements of the proton radius using simultaneous e-p and μ-p scattering, with both positive and negative polarity leptons at the πM1 beamline located in the Paul Scherrer Institute. This unique setup allows us to perform several high-precision tests of the various explanations of the radius puzzle. The experiment will use a liquid hydrogen target with precision tracking via straw tube detectors (STT) for a precise position measurement coupled with a scintillator array (SPS) for precise timing. In this talk, we will show how efficiently and precise one can determine tracks from the STT/SPS combination using a χ² minimization. We will also show vertices reconstructed using the STT and GEM detectors which precisely determine the lepton scattering angle.   

Calorimeter in MUSE Experiment

The MUon proton Scattering Experiment (MUSE) at the PiM1 beam line of the Paul Scherrer Institute is simultaneously measuring the elastic scattering of electrons and muons from a liquid hydrogen target to extract the charge radius of the proton. Both beam polarities will be measured over the course of the experiment. By comparing the four scattering cross sections, the experiment will provide unique muon proton scattering data with a precision sufficient to address the proton radius puzzle, and will directly measure two-photon exchange effects for both muons and electrons. Measuring precise cross sections requires understanding both the incident beam energy and the radiative corrections. MUSE will use a lead-glass calorimeter located downstream in the beam to investigate and control radiative corrections by suppressing high energy initial state photons. In this presentation, we will discuss the calibration of the detector by measuring its response to particles with various energies. Latest data and comparison to simulation will be shown to demonstrate the performance of the detector.   

Deconvolution of the measured asymmetry at the MOLLER Experiment

The MOLLER experiment aims to measure the parity-violating asymmetry A_PV in the polarized electron-electron scattering. At Moller experiment kinematics, A_PV is predicted to be ~33 ppb with an uncertainty of 0.8 ppb. Measuring the A_PV would directly determine the weak mixing angle at low Q² with the best precision that matches Z-pole measurements. High detector segmentation and integration running mode are required in order to make such a precise determination. The segmentation of the Moller main integrating detector will allow for the deconvolution of the asymmetries from various background processes. This talk will overview the deconvolution analysis to extract the asymmetry of the Moller scattered electrons from the background processes.   

Fabrication and Testing of Tracking Detectors for MOLLER Experiment at JLab

The upcoming MOLLER experiment at JLab aims to measure the parity-violating asymmetry of longitudinally polarized electrons scattering off unpolarized electrons in a high power liquid Hydrogen target. This crucial measurement aims to enhance sensitivity in the search for new physics beyond the standard model. Gas Electron Multiplier (GEM) detectors will be utilized in this experiment to facilitate spectrometer calibration and background measurements. The design and fabrication of a fully functional prototype GEM detector module were successfully completed at the University of Virginia. The prototype module underwent testing for low rate environments with cosmic-ray  particles and for high environments using X-rays with a CERN Scalable Readout System (SRS)  readout system based on the APV-25 chip. Additionally, the module is undergoing testing with the experiment's DAQ system at JLab. Furthermore, track-based efficiencies will be obtained for the prototype module by operating it together with Super BigBite GEM tracker layers at JLab using cosmic particles. The findings of these performance tests will be presented.   

Electron detectors for Compton Polarimetry for the MOLLER experiment

High Voltage Monolithic Active Pixel Sensors (HVMAPS) are a new type of electron detector. This hybrid pixel detector combines the semiconductor sensor elements that detect high energy particles with the readout electronics in one element. The demand for fast, high resolution and low noise detectors by experiments conducted at the LHC initiated the development of hybrid pixel detectors, first being developed at CERN in the 1980s [1]. Each pixel has its own integrated readout electronics. The manufacturing process provides high levels of customization like radiation thickness and radiation length, thereby allowing the control of material budget for detectors, where scattering could be an issue. HVMAPS have been used as detectors for the Mu3e experiment [2]. As thin as 50 microns, the latest version of the HVMAPS, (MuPix Version 11) are the ideal electron detector for applications in the MOLLER experiment at Jefferson Lab [3], The experiment proposes to measure the asymmetry of parity violating scattering, APV, in polarized electron-electron scattering, thereby measuring the Weinberg angle to a greater precision. The HVMAPS will be used for two aspects of the experiment: the Compton polarimeter, and the main detectors, for tracking the path and position of electrons respectively. This presentation will discuss the implementation of the HVMAPS for the Compton polarimeter.

[1] Philip Garrou, C Bower, and P Ramm. Introduction to 3d integration. In Handbook of 3D Integration Vol 1-Technology and Applications of 3D Integrated Circuits. Wiley-VCH, 2008.

[2] Niklaus Berger, Mu3e Collaboration, et al. The mu3e experiment. Nuclear Physics B-Proceedings Supplements, 248:35–40, 2014.

[3] Mammei, Juliette. "The MOLLER experiment." arXiv preprint arXiv:1208.1260 (2012).   

Measurement of the beam polarization via Moller Polarimetry for the SBS GEn Experiment.

In this conference, we will showcase the Møller polarimetry outcomes of the GEn experiment conducted at Hall A of Jefferson Lab. The GEn experiment aims to determine the electric form factor of the neutron at high four-momentum transfer values of up to 10.2 GeV² through the scattering of beam electrons off of a Helium-3 fixed-target. To ascertain the polarization of the electron beam at Hall A of JLab, the Hall A Møller Polarimeter is utilized. The accurate measurement of beam polarization plays a pivotal role in optimizing the experimental efficacy of the GEn experiment. Discussed here will be the preliminary beam polarization results and systematics analysis for polarimetry performed for the GEn experiment.   

Neutron beam-spot simulation and measurement for various energy bins

During the 2022 maintenance outage, the installation was completed for the new generation of spallation target-moderator-reflector-shield (TMRS), known as Mark-IV for Manuel Lujan Jr. Neutron Scattering Center (Lujan Center) at the Los Alamos Neutron Science Center (LANSCE). This paper discusses the importance of combining various techniques to ensure high-quality beam delivery to nuclear physics experiments. Advanced laser tracker survey technology was used to inform geometry in the Monte Carlo N-Particle Transport (MCNP) code for beam spot simulation. The beam spot was experimentally measured both by active high-speed gated imaging (utilizing a PI-Max4 imaging camera) and passively using image plates.

 

Experimental beam-spot images acquired by PI-Max4 with various scintillators were analyzed for each energy decade from 1 meV to 1 MeV by our Python scripts. The measured beam-spot distributions agree very well with our prediction by MCNP simulations and so it confirms the alignment importance for one of our flight paths to ensure uniform beam-spot distributions in the full energy range.