Welcome

• Abhay Deshpande (Stony Brook University)

Physics drivers for polarized beam

• Andrea Bressan

EIC accelerator design

• Christoph Montag (BNL)
• Christoph Montag (BNL)

Physics with polarized positrons

• Eric Voutier

Possibilities of polarized positrons

• Joe Grames (Jefferson Lab)

What is planned at ILC

• Jenny List (DESY)

Polarization Upgrade and Polarimetry at the SuperKEKB Facility

• Wouter Deconinck

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 θ_W^eff 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.

Transparent Spin Mode for Polarized Beams in the EIC

• Yuri Filatov (MIPT)

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.

Physics with polarized Deuterons

• Ellie Long (University of New Hempshire)

Feasibility of Polarized Deuteron Beam

• Haixin Huang (Brookhaven National Lab)

Polarised beams in particle colliders

• Mei Bai
• Mei Bai (BNL)

Discussion

Experience from RHIC leading the way to EIC

• William Schmidke (BNL)

Experience from COSY

• Frank Rathmann (Forschungszentrum Jülich)

Elastic e-D scattering for deuteron polarimetry

• Barak Schmookler (Stony Brook University)

He-3 polarimetry / polarised targets

• Gordon Cates (University of Virginia)

Absolute polarization measurement of the 200 MeV proton beam at Linac.

• Andrei Poblaguev (BNL)

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.

Development of absolute polarimeter for the low energy $\bf^3\mathrm{He}^{++}$ ion beam

• Grigor Atoian (Brookhaven National Lab)

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)

Can absolute polarization of the $^3\mathrm{He}$ beams at EIC be precisely measured by HJET?

• Andrei Poblaguev (BNL)

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.

Light Ion Polarimetry at the EIC

• Ana Sofia Nunes (Brookhaven National Laboratory)

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.

Light ion polarimetry at high energy

• Nigel Buttimore (Trinity College Dublin)

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.

Polarimetry based on forward neutrons in pA scattering

• William Schmidke (BNL)

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.

Improvement of proton polarization for EIC

• Vincent Schoefer (CAD)

Polarized He3 in EIC

• francois meot (bnl)

Bmad and PTC spin simulations

• David Sagan (Cornell)

Discussion

HERA Polarimetry (FP cavity in collider)

• Stefan Schmitt (DESY)

Lepton polarimetry at JLab

• Kent Paschke (University of Virginia)

Compton Polarimeter laser options

• Ciprian Gal (Stony Brook University)

Precision Mott Polarimetry

• Tim Gay (University of Nebraska)

High-Precision 5 MeV Mott Polarimetry at CEBAF+ T.J.Gay* 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. 1JLab 2UDS-Milano 3ODU 4GWU and 5UNL +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).

Low-energy polarimetry

• Kurt Aulenbacher (Johannes Gutenberg Universitaet Mainz)

Spin rotator design and spin matching

• Vadim Ptitsyn (C-AD, BNL)

Compact spin rotator design

• Fanglei Lin (Thomas Jefferson National Accelerator Facility)

EIC electron polarization studies

• Eliana Gianfelice (FNAL)

Acceleration of electrons in RCS

• Vahid Ranjbar (BNL)

Fast spin tracking and spin matching with stochastic one turn maps

• Oleksii Beznosov (University of New Mexico)

IR related effects

• Vasiliy Morozov (Thomas Jefferson National Accelerator Facility)

Discussion