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The SHMS 11 GeV/c Spectrometer in Hall C at Jefferson Lab

S. Ali, A. Ahmidouch, G. R. Ambrose, A. Asaturyan, C. Ayerbe Gayoso, J. Benesch, V. Berdnikov, H. Bhatt, D. Bhetuwal, D. Biswas, P. Brindza, M. Bukhari, M. Burton, R. Carlini, M. Carmignotto, M. E. Christy, C. Cotton, J. Crafts, D. Day, S. Danagoulian, A. Dittmann, D. H. Dongwi, B. Duran, D. Dutta, R. Ent, H. Fenker, M. Fowler, D. Gaskell, A. Hamdi, N. Heinrich, W. Henry, N. Hlavin, T. Horn, G. M. Huber, Y. Ilieva, J. Jarrell, S. Jia, M. K. Jones, M. Junaid, M. L. Kabir, N. Kalantarians, A. Karki, S. J. D. Kay, C. E. Keppel, V. Kumar, S. Lassiter, W. B. Li, D. Mack, S. Malace, J. McMahon, A. Mkrtchyan, H. Mkrtchyan, P. Monaghan, C. Morean, P. Nadel-Turonski, G. Niculescu, M. I. Niculescu, A. Nadeeshani, J. Pan, E Pooser, J. Okine, A. Ramos, J. Reinhold, B. Sawatzky, I. Steel, H. Szumila-Vance, V. Tadevosyan, J. Taylor, R. L. Trotta, A. Usman, C. Yero, M. Yurov, S. Zhamkochyan, S. A. Wood, J. Zhang

TL;DR

The SHMS in Hall C extends Jefferson Lab’s spectrometer capability to $11~\text{GeV}/c$ with a five-magnet optics system and a comprehensive detector suite, enabling precise momentum, angle, and particle-identity measurements for high-energy electron scattering. The paper details the integrated design, including magnet optics modeled with SNAKE/COSY/SIMC, shielding optimization, and a full detector stack (drift chambers, hodoscopes, Cherenkov counters, and calorimeters) calibrated for high-rate operation. It presents trigger/DAQ architecture, software (hcana), online monitoring, and commissioning results, demonstrating robust acceptance, rates, and subsystem performance across a broad kinematic range. The SHMS performance confirms reliable operation and suggests strong potential for future upgrades to even higher energies, broadening Hall C’s physics program and enabling precision studies of nucleon structure and QCD phenomena. The work thus delivers a validated, high-precision, large-acceptance spectrometer system capable of contributing to a wide range of high-energy nuclear physics experiments.

Abstract

The Super High Momentum Spectrometer (SHMS) has been built for Hall C at the Thomas Jefferson National Accelerator Facility (Jefferson Lab). With a momentum capability reaching 11 GeV/c, the SHMS provides measurements of charged particles produced in electron-scattering experiments using the maximum available beam energy from the upgraded Jefferson Lab accelerator. The SHMS is an ion-optics magnetic spectrometer comprised of a series of new superconducting magnets which transport charged particles through an array of triggering, tracking, and particle-identification detectors that measure momentum, energy, angle and position in order to allow kinematic reconstruction of the events back to their origin at the scattering target. The detector system is protected from background radiation by a sophisticated shielding enclosure. The entire spectrometer is mounted on a rotating support structure which permits measurements to be taken with a large acceptance over laboratory scattering angles from 5.5 to 40 degrees, thus allowing a wide range of low cross-section experiments to be conducted. These experiments complement and extend the previous Hall C research program to higher energies.

The SHMS 11 GeV/c Spectrometer in Hall C at Jefferson Lab

TL;DR

The SHMS in Hall C extends Jefferson Lab’s spectrometer capability to with a five-magnet optics system and a comprehensive detector suite, enabling precise momentum, angle, and particle-identity measurements for high-energy electron scattering. The paper details the integrated design, including magnet optics modeled with SNAKE/COSY/SIMC, shielding optimization, and a full detector stack (drift chambers, hodoscopes, Cherenkov counters, and calorimeters) calibrated for high-rate operation. It presents trigger/DAQ architecture, software (hcana), online monitoring, and commissioning results, demonstrating robust acceptance, rates, and subsystem performance across a broad kinematic range. The SHMS performance confirms reliable operation and suggests strong potential for future upgrades to even higher energies, broadening Hall C’s physics program and enabling precision studies of nucleon structure and QCD phenomena. The work thus delivers a validated, high-precision, large-acceptance spectrometer system capable of contributing to a wide range of high-energy nuclear physics experiments.

Abstract

The Super High Momentum Spectrometer (SHMS) has been built for Hall C at the Thomas Jefferson National Accelerator Facility (Jefferson Lab). With a momentum capability reaching 11 GeV/c, the SHMS provides measurements of charged particles produced in electron-scattering experiments using the maximum available beam energy from the upgraded Jefferson Lab accelerator. The SHMS is an ion-optics magnetic spectrometer comprised of a series of new superconducting magnets which transport charged particles through an array of triggering, tracking, and particle-identification detectors that measure momentum, energy, angle and position in order to allow kinematic reconstruction of the events back to their origin at the scattering target. The detector system is protected from background radiation by a sophisticated shielding enclosure. The entire spectrometer is mounted on a rotating support structure which permits measurements to be taken with a large acceptance over laboratory scattering angles from 5.5 to 40 degrees, thus allowing a wide range of low cross-section experiments to be conducted. These experiments complement and extend the previous Hall C research program to higher energies.

Paper Structure

This paper contains 63 sections, 17 equations, 70 figures, 6 tables.

Table of Contents

  1. Introduction
  2. Jefferson Lab Overview
  3. Hall C Experimental Program at 6 GeV
  4. Hall C 12 GeV Program
  5. Contents of the Following Sections
  6. Specifications for the upgraded Hall-C Spectrometer complex
  7. Design and Development of the SHMS Optics and Infrastructure
  8. Magnetic Optics
  9. The Magnets and Vacuum Channel
  10. Charged Particle Transport Models
  11. Shield House Layout, Shielding Design
  12. Design, Construction and Calibration of the SHMS Detectors
  13. Scintillator Trigger Hodoscope
  14. Design and Construction
  15. Quartz-bar Trigger Hodoscope
  16. ...and 48 more sections

Figures (70)

  • Figure 1: Schematic of hall and accelerator improvements as part of the Jefferson Lab 12 GeV Upgrade.
  • Figure 2: Inclusive $F_2$ structure functions measured in the resonance region compared to a DIS fit. When plotted vs. the Nachtmann variable $\xi$, the DIS fit agrees, on average, with the resonance region data, demonstrating quark-hadron duality PhysRevLett.85.1186.
  • Figure 3: Measurement of $R=\frac{\sigma_L}{\sigma_T}$ at low $Q^2$. The extraction of $R$ requires precise L-T separations with excellent control of point-to-point systematic uncertainties. Figure from PhysRevLett.98.142301.
  • Figure 4: Measurements of the charged pion form factor in Hall C (6 GeV era). Extraction of the pion form factor requires a precise L-T separation, as well as detection of the charged pion at small forward angles. Figure from Horn:2006tm.
  • Figure 5: Cross sections for semi-inclusive $\pi^+$ and $\pi^-$ production from hydrogen and deuterium. The cross sections are compared to a parameterization that uses fragmentation functions fit to high energy $e^+e^-$ collisions. Figure from Navasardyan:2006gv.
  • ...and 65 more figures