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Beam Polarization and Polarimetry at EIC



on Zoom
Dave Gaskell, E. C. Aschenauer (BNL)

Hadron structure cannot be understood without unraveling spin structure. This fact has been acknowledged in the recent assessment of the EIC Science by National Academy of Sciences by identifying the understanding the origin of the internal angular momentum or spin of nucleons, as one of the three central scientific issues that would be addressed by an EIC. While past or existing DIS experiments were and are very successful in determining the polarized quark structure of the nucleon and of some light nuclei, none matches the unique capabilities of an EIC by being able to change at the same machine between longitudinal, transverse, and (for deuteron only) tensor polarization states and with being able to collide polarized electron beams with polarized protons, deuteron, and Helium-3 beams over a broad kinematic range.

The proposed Electron-Ion Collider (EIC) will present the opportunity to achieve unprecedented statistical precision in many reaction channels studying the spin structure of nucleons.  Given this high precision, it is imperative that the forthcoming results achieve systematic uncertainties at a comparable level. In particular, knowledge of the electron and hadron beam polarization is likely to be a limiting systematic uncertainty for many single-spin and double-spin asymmetry measurements.  Polarimetry approaching the 1% level is desired, yet presents many fundamental and practical challenges.

Attaining high polarization level of electron, proton and light ion beams in the EIC rests both on experience from previous polarized beam accelerators and on novel approaches. EIC accelerator design has to fully address challenges of various spin depolarizing mechanisms and provide efficient polarization direction control at experimental areas.

The generation of polarized beams and the evolution of the beam polarization as the beam propagates through the machine are of course closely coupled with polarimetry.  Accurate polarimetry provides valuable feedback for setup and tuning of the accelerator, while knowledge of the machine properties that impact beam polarization is important for accurate and precise polarization measurements.

The aim of this proposed workshop is to bring together experts in electron and hadron beam polarimetry as well as experts in polarized beams in accelerators.

Due to the ongoing COVID-19 pandemic, we will hold the workshop online (through Zoom). To facilitate a wider collaboration we have decided to split the workshop over 3 separate days with a reduce schedule (June 26th, June 29th and July 1st). Please register in order to get connection information.


  • Abhay Deshpande
  • Alexander Bazilevsky
  • Amy Sy
  • Ana Sofia Nunes
  • Anatoli Zelenski
  • Andrea Bressan
  • Andreas Lehrach
  • Andrei Poblaguev
  • Anna Martin
  • Arshak Asaturyan
  • Asia Parker
  • Athira K V
  • Boris Militsyn
  • Carlos Hernandez-Garcia
  • Chandan Ghosh
  • Christian Weiss
  • Christoph Montag
  • Ciprian Gal
  • Daniel Moser
  • Dannie Steski
  • Dave Gaskell
  • Dave Gassner
  • David Morrison
  • David Sagan
  • David Sagan
  • Desmond Barber
  • Donald Jones
  • Douglas Higinbotham
  • Elena Long
  • Eliana Gianfelice
  • Eric Voutier
  • Fanglei Lin
  • Fatiha Benmokhtar
  • francois meot
  • Frank Rathmann
  • Georg Hoffstaetter
  • Grigor Atoian
  • H.-Ulrich (Uli) Wienands
  • Haixin Huang
  • Hamlet Mkrtchyan
  • Indranil Mazumdar
  • Iris Halilovic
  • J. Scott Berg
  • Jared Burleson
  • Jay Desai
  • Jim Ellison
  • Joe Grames
  • Juan Carlos Cornejo
  • Jyoti Biswas
  • Kurt Aulenbacher
  • Marcy Stutzman
  • Matt Poelker
  • Matthew Musgrave
  • Max Bruker
  • Michael Finger
  • Miroslav Finger
  • Muhammad Junaid
  • Nicholaos Tsoupas
  • Nigel Buttimore
  • Nikolai Nikolaev
  • Oleg Eyser
  • Oleksii Beznosov
  • Omar Hassan
  • Peter Thieberger
  • Prajwal Mohanmurthy
  • Rolf Ent
  • Rosario Turrisi
  • Shan hong Chen
  • Sheren Alsalmi
  • Stefan Schmitt
  • Thomas Roser
  • Timothy Gay
  • Vadim Ptitsyn
  • Valery Kubarovsky
  • Valery Tyukin
  • Vasiliy Morozov
  • Vincent Schoefer
  • Vitalii Okorokov
  • Walter Wittmer
  • Weibin Zhang
  • wenhao xia
  • William Schmidke
  • Wolfram Fischer
  • Wouter Deconinck
  • Yuhong Zhang
  • Yuji Goto
  • Yury Filatov
  • Yuxiang Zhao
  • Zhe Duan
  • Zhiwen Zhao
  • Zhongling Ji
    • 1
      Speaker: Abhay Deshpande (Stony Brook University)
    • 2
      Physics drivers for polarized beam
      Speaker: Andrea Bressan
    • 3
      EIC accelerator design
      Speakers: Christoph Montag (BNL), Christoph Montag (BNL)
    • 4
      Physics with polarized positrons
      Speaker: Dr Eric Voutier
    • 5
      Possibilities of polarized positrons
      Speaker: Joe Grames (Jefferson Lab)
    • 10:15 AM
      Streching break
    • 6
      What is planned at ILC
      Speaker: Jenny List (DESY)
    • 7
      Polarization Upgrade and Polarimetry at the SuperKEKB Facility

      SuperKEKB is an unpolarized electron-positron collider designed for a luminosity of 8 × 1035 cm−2s−1 with a 4 GeV positron beam (Low Energy Ring - LER) and 7 GeV electron beam (High Energy Ring - HER). To enable precision measurements of the weak neutral couplings in the Belle II experiment, an upgrade is under consideration to polarize the HER to 70% by injecting polarized electrons (due to the short beam lifetime, Sokolov-Ternov self-polarization is impractical). In most areas of the HER the spin will be oriented transversely, but around the interaction region spin rotators will align the spin longitudinally. In addition to Mott polarimetry in the injector, we will measure the stored beam polarization to a precision of 0.5% with a combination of Compton polarimetry and measurements of the forward-backward asymmetries in e+e → τ+τ events at the interaction point. This will allow measurements of sin2 θWeff with a combined uncertainty comparable to the Z0 world average measured uncertainty of ±0.00016 from LEP and SLD, but made at a significantly lower energy scale of 10.58 GeV.

      Speaker: Wouter Deconinck
    • 8
      Transparent Spin Mode for Polarized Beams in the EIC

      The transparent spin (TS) technique has been proposed as an efficient high-flexible method to control the beam polarization, from acceleration to long-term maintenance and real-time spin manipulation during an experimental run of a collider. Attractiveness of the TS method is that it allows for manipulation of the polarization using small insertions of weak magnetic fields (stationary or quasi-static) not affecting the orbital dynamics. The TS mode allows one to do frequent coherent spin flips of the beam to reduce experiment’s systematic errors, and carry out ultrahigh precision experiments. The TS mode may allow one to significantly expand the capabilities of polarized beam experiments at the RHIC-based EIC at BNL in the US. It makes it possible to manipulate the polarizations of proton and 3He beams during experiments in the collider’s entire energy range. The TS mode is also considered for spin control of polarized deuterons near the energies corresponding to integer spin resonances. The talk presents schemes for proton and deuteron polarization control using the TS mode in RHIC.

      Speaker: Yuri Filatov (MIPT)
    • 12:05 PM
    • 9
      Physics with polarized Deuterons
      Speaker: Ellie Long (University of New Hempshire)
    • 10
      Feasibility of Polarized Deuteron Beam
      Speaker: Haixin Huang (Brookhaven National Lab)
    • 11
      Polarised beams in particle colliders
      Speakers: Mei Bai, Mei Bai (BNL)
    • 12
    • 13
      Experience from RHIC leading the way to EIC
      Speaker: William Schmidke (BNL)
    • 14
      Experience from COSY
      Speaker: Frank Rathmann (Forschungszentrum Jülich)
    • 15
      Elastic e-D scattering for deuteron polarimetry
      Speaker: Barak Schmookler (Stony Brook University)
    • 16
      He-3 polarimetry / polarised targets
      Speaker: Gordon Cates (University of Virginia)
    • 10:00 AM
      Streching break
    • 17
      Absolute polarization measurement of the 200 MeV proton beam at Linac.

      The $200\,\mathrm{MeV}$ polarimeter at Linac is based on the elastic proton-carbon scattering at $16.2^\circ$ angle, where the analyzing power reaches almost absolute maximum which was experimentally established with high accuracy of $99.35\pm0.15\,\%$ . The elastically and inelastically scattered protons are clearly separated by the difference in the propagation through adjustable thickness copper absorber and energy deposition of the stopped protons in the detectors. The elastic scattering polarimeter used for calibration of a high rate inclusive $12^\circ$ polarimer for the on-line polarization tuning and monitoring. In Run 2017 a new WFD based DAQ was developed for better elastic scattering isolation. Preliminary results showed, that experimental uncertainties in the absolute polarization measurements are expected to be $σ_P^\mathrm{syst}<0.6\,\%$ and $σ_P^\mathrm{stat}\sim0.4\,\%/\mathrm{hour}$. We plan further DAQ and detectors improvements in the next polarized proton Run.

      Speaker: Andrei Poblaguev (BNL)
    • 18
      Development of absolute polarimeter for the low energy $\bf^3\mathrm{He}^{++}$ ion beam

      For the Electron-Ion Collider, a polarized ${}^3\mathrm{He}^{++}$ ion source is being constructed at the Electron Beam Ionization Source (EBIS) of the Brookhaven National Laboratory. For precision determination of the ${}^3\mathrm{He}$ polarization, the ${}^3\mathrm{He}$ beam, after acceleration to 6 MeV at EBIS, will be elastically scattered off a gas ${}^4\mathrm{He}$ target. For such a scattering, the analyzing power $A_\mathrm{N}(E_\mathrm{beam},\theta_\mathrm{CM})$ can reach absolute, $100\%$, maximum at some points in the beam energy / center of mass scattering angle plane [1]. Several such points were found in Refs. [2, 3] including $(E_\mathrm{beam}=5.3\,\mathrm{MeV}, \theta_\mathrm{CM}=91^\circ)$.

      The vertically polarized $6\,\mathrm{MeV}$ ${}^3\mathrm{He}^{++}$ ion beam will enter, through a thin window (to minimize the energy loss of the beam), to the scattering chamber filled with ${}^4\mathrm{He}$ gas at a pressure of $\sim5\,\mathrm{Torr}$. Two left-right symmetric Si strip detectors (with vertically oriented strips) will be used to detect both scattered $^3\mathrm{He}$ and recoil $^4\mathrm{He}$ particles in every event. Good energy and time resolution of the detectors will allow us to recognize $^3\mathrm{He}$ and $^4\mathrm{He}$ signals and to eliminate background events. A spin rotator will provide the beam spin-flip to suppress the acceptance and intensity related systematic errors.

      For the polarimeter calibration, we plan to scan the $^3\mathrm{He}$ energy (by variation the entrance window thickness) and to measure the spin-correlated asymmetry dependence on scattering angle $\theta_\mathrm{CM}$. Analyzing power $A_\mathrm{N}=100\%$ can be attributed to the absolute maximum found in these measurements.

      [1] G. Plattner et al., “Absolute calibration of spin – 1/2 polarization”, Phys. Lett. B 36, 211 (1971)
      [2] D.M. Hardy et al., “Polarization in $^3\mathrm{He}$ + $^4\mathrm{He}$ elastic scattering”, Phys. Lett. B 31, 355 (1970)
      [3] W.R. Boykin, S.D. Baker, D.M. Hardy, “Scattering of $^3\mathrm{He}$ and $^4\mathrm{He}$ from polarized $^3\mathrm{He}$ between 4 and 10 MeV”, Nucl. Phys. A 195, 241 (1972)

      Speaker: Mr Grigor Atoian (Brookhaven National Lab)
    • 19
      Can absolute polarization of the $^3\mathrm{He}$ beams at EIC be precisely measured by HJET?

      A possibility to precisely measure absolute vertical polarization of the EIC ${}^3\mathrm{He}$ beams using the polarized hydrogen gas jet target (HJET) is discussed. By concurrent measurement of $a_h$ and $a_p$, the beam $h^\uparrow p$ and jet $p^\uparrow h$ spin asymmetries for the detected recoil protons, the He3 beam polarization can be approximated by $P_\mathrm{beam}=P_\mathrm{jet}\times a_h\kappa_p/a_p\kappa_h$, where $\kappa_p=1.793$ and $\kappa_h = -1.398$ are derived from the magnetic moments $\mu_p$ and $\mu_h$, and $P_\mathrm{jet}\approx0.957$ is the jet polarization determined by a conventional Breit-Rabi polarimeter. The result does not depend on the actual parameters of $hp$ scattering: total cross-section $\sigma_\mathrm{tot}$, forward real-to-imaginary ratio $\rho$, or Coulomb phase $\delta_C$.

      Corrections of a few percent to the value of $P_\mathrm{beam}$ due to the term $\sim m^2/s$ in the electromagnetic spin-flip amplitude and due to hadronic spin-flip amplitudes $r_5^{hp}$ and $r_5^{ph}$ are well determined. Since the ${}^3\mathrm{He}$ ground state is mostly fully space-symmetric $S$ state, the $hp$ spin-flip amplitudes can be readily related with sufficient accuracy, $r_p^{hp}=r_5^{pp}/3$ and $r_5^{ph}=r_5^{pp}$, to the amplitude measured in elastic $pp$ scattering. Considering the experimental uncertainty in the value of $r_5^{pp}$ as well as the uncertainties in the measurement of $a_h/a_p$, we can expect $\sigma_P^\mathrm{syst}\leq0.9\,\%$ accuracy for the absolute ${}^3\mathrm{He}$ beam polarization at EIC.

      Since only the recoil proton is detected in HJET measurements, the acquired data may be contaminated by inelastic (${}^3\mathrm{He}$ break-up) events. However, since only low energy protons in the small solid angle at 90 degree are counted, the inelastic component is strongly suppressed. Analyzing Run 16 data with a deuteron beam, we found that data contamination by the break-up events should not exceed a few percent. In addition, the inelastic corrections are significantly canceled in the $a_h/a_p$ ratio. Thus, the anticipated alteration of the measured $P_\mathrm{beam}$ due to ${}^3\mathrm{He}$ break-up can be neglected.

      Speaker: Andrei Poblaguev (BNL)
    • 12:00 PM
    • 20
      Light Ion Polarimetry at the EIC

      Polarization of high energy proton beams has successfully been measured at RHIC with elastic proton-proton and proton-Carbon scattering. The analyzing power is not known from first principles and has to be measured.

      The observed background to the elastic scattering events needs to be much better understood because of the much shorter bunch spacing at EIC. This background can cause a simple dilution of the elastic scattering events or it can bias the polarization.

      It will therefore be very informative to use the existing RHIC facilities in the next few years to assess as much information as possible for light ion polarimetry, namely event rates, both for elastic scattering and for backgrounds (including breakup), and analyzing powers.

      A programme of simulations was initiated to prepare the mentioned measurements and to understand the EIC conditions. A first step is to simulate the proton-proton interactions at RHIC, for which the event generator Pythia6 is being used. Dpmjet3 is the event generator of choice to, first, reproduce Pythia6 results and, afterwards, to simulate interactions with light ions, as it is prepared to describe the interactions at low momentum transfer relevant for the polarimeters. The energy loss of the particles in the silicon sensors is to be described by Geant4. Simulation results will be presented and discussed.

      Speaker: Ana Sofia Nunes (Brookhaven National Laboratory)
    • 21
      Light ion polarimetry at high energy

      Peripheral scattering of polarized proton, deuteron, and Helium-3 ions on light nuclei, and other nuclei, provides a method of evaluating the level of polarization of high energy beams. The asymmetry of recoils resulting from elastic collision can indicate the analyzing power required for polarimetry provided a number of quantities are known with sufficient accuracy.

      Among the items needed is the Coulomb phase, $\delta_C \propto ZZ'\alpha$, encoding second order electromagnetic corrections to the scattering of charge $Z$ ions on nuclei of charge $Z'$. This phase varies from about 7% to 12% as $ZZ'$ ranges from 4 (3He-3He) to 12 (3He-12C) in the interference region. The behavior of the analyzing power as a function of momentum transfer is discussed, avoiding the assumption that $\delta_C$ is small as is common for the case of polarized proton proton scattering.

      An expression for the momentum transfer at which the size of the analyzing power reaches a maximum is presented that involves electromagnetic form factors, the hadronic slope of the near forward differential cross section, and to first order, a contribution from the single helicity-flip hadronic amplitude normalized to the imaginary non-flip hadronic amplitude. The extreme value of the analyzing power is also noted, a value that depends upon the total cross section of the reaction and $\rho$, the real to imaginary ratio of the spin-averaged hadronic amplitude.

      Speaker: Nigel Buttimore (Trinity College Dublin)
    • 22
      Polarimetry based on forward neutrons in pA scattering

      The PHENIX collaboration has observed a large azimuthal asymmetry
      of forward neutrons produced in polarized pA collisions. The data
      are well described by a model incorporating photons from the high Z
      nucleus photoproducing low mass baryonic states from the polarized
      proton. The model is based on well known electromagnetic effects and
      well measured photoproduction processes.

      We will discuss possible application of this process to polarimetry of
      high energy polarized proton beams. A simple target/detector system
      will be described, based on standard detector technology. Rate estimates
      will be presented, based on feasible targets and realized RHIC and
      planned EIC polarized proton beams. Possible tests at RHIC runs in
      the next few years will be outlined.

      Speaker: William Schmidke (BNL)
    • 23
      Improvement of proton polarization for EIC
      Speaker: Vincent Schoefer (CAD)
    • 24
      Polarized He3 in EIC
      Speaker: francois meot (bnl)
    • 25
      Bmad and PTC spin simulations
      Speaker: David Sagan (Cornell)
    • 26
    • 27
      HERA Polarimetry (FP cavity in collider)
      Speaker: Stefan Schmitt (DESY)
    • 28
      Lepton polarimetry at JLab
      Speaker: Kent Paschke (University of Virginia)
    • 29
      Compton Polarimeter laser options
      Speaker: Ciprian Gal (Stony Brook University)
    • 30
      Precision Mott Polarimetry

      High-Precision 5 MeV Mott Polarimetry at CEBAF+
      University of Nebraska - Lincoln
      We report on the design and performance of a Mott polarimeter optimized for a nominal 5-MeV electron beam from the CEBAF injector. The rf time structure of this beam allows the use of time-of-flight in the electron detection, making it possible to isolate those detected electrons that originate from the scattering foil, and resulting in measured scattering asymmetries which are exceptionally stable over a broad range of beam conditions, beam currents, and target foil thicknesses. In two separate series of measurements from two different photocathode electron sources, we measured the Mott scattering asymmetries produced by an approximately 86% transversely polarized electron beam incident on ten Au foils with nominal thicknesses between 50 and 1000 nm. The statistical uncertainty of the measured asymmetry from each foil is below 0.25%. Within this statistical precision, the measured asymmetry was unaffected by ±1-mm shifts in the beam position on the target, and by beam current changes and dead-time effects over a wide range of beam currents. The overall uncertainty of our beam polarization measurement, arising from the uncertainty in the value of the scattering asymmetry at zero foil thickness as determined from our fits to the measured asymmetries versus scattering foil thicknesses, the estimated systematic effects, and the (dominant) uncertainty from the calculation of the theoretical Sherman function, is 0.61%. GEANT4 calculations give results for the asymmetry versus foil thickness in good agreement with our measurements. Future measurements at different beam energies and with target foils of different atomic numbers will seek to bound uncertainties from small effects such as radiative corrections to the calculation of the polarimeter analyzing power. A simultaneous high-precision measurement of the beam polarization with a different polarimeter, AESOP (Accurate Electron Spin Optical Polarimeter), under development at the University of Nebraska, is expected to allow a high-precision comparison of our measured asymmetries with theoretical calculations of the Mott analyzing power. Finally, the improved precision of the current Mott polarimeter along with similar improvements to other Jefferson Lab GeV-energy polarimeters warrants another “Spin Dance” precision comparison of all of these polarimeters.
      This work was done in collaboration with J. M. Grames1, C. K. Sinclair1, M. Poelker1, X. Roca-Maza2, M. Stutzman1, R. Sulieman1, Md. A. Mamun1,3, M. McHugh4, D. Moser1, J. Hansknecht1, B. Moffit1, and Keith Foreman5.
      4GWU and

      +Work supported in part by NSF Grants No. PHY-1505794, 1632778, and 1806771 (TJG, KF), Department of Energy Grant DE-AC05-84ER40150, and the European Union’s Horizon 2020 Research and Innovation program 1508 under Grant No. 654002 (XR-M).

      Speaker: Tim Gay (University of Nebraska)
    • 9:45 AM
      Streching break
    • 31
      Low-energy polarimetry
      Speaker: Kurt Aulenbacher (Johannes Gutenberg Universitaet Mainz)
    • 32
      Spin rotator design and spin matching
      Speaker: Vadim Ptitsyn (C-AD, BNL)
    • 33
      Compact spin rotator design
      Speaker: Fanglei Lin (Thomas Jefferson National Accelerator Facility)
    • 34
      EIC electron polarization studies
      Speaker: Eliana Gianfelice (FNAL)
    • 12:15 PM
    • 35
      Acceleration of electrons in RCS
      Speaker: Vahid Ranjbar (BNL)
    • 36
      Fast spin tracking and spin matching with stochastic one turn maps
      Speaker: Oleksii Beznosov (University of New Mexico)
    • 38