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Bi-monthly meeting of MIT-BNL He3-ABS Collaboration
Prajwal Mohan Murthy
Zhengqiao Zhang
Richard Milner
Frank Rathmann
Vera Shmakova
Prajwal introduced Zhengqiao’s updated simulations on beam/target breakup processes for polarized He-3 polarimetry at the EIC. The work extends studies originally started in Fall 2024 and combines:
DPMJet interaction modeling
Geant4 tracking through the IR4 lattice and detector geometry
p + He-3
d + He-3
He-3 + He-3
In the He-3 + He-3 configuration:
dominant inelastic channel is simultaneous breakup of both beam and target.
In the d + He-3 configuration:
deuteron breakup often precedes target breakup.
if the target breaks up, beam breakup almost always accompanies it.
Target breakup behavior depends mainly on momentum transfer to the target and is relatively independent of projectile species at comparable kinematics.
Current optimized geometry (for He-3 + He-3):
97% tagging efficiency.
Important clarification:
this is fragment-identification efficiency, not polarimetry systematic uncertainty.
efficiency quantifies the ability to identify the origin of emitted nucleons from breakup channels.
Prajwal to update tables with latest deuteron results from Zhengqiao.
Possible future optimization for d + He-3 by repositioning taggers.
Accelerator group requested estimates of beam loss caused by interactions with the polarized jet target.
Based on discussions with accelerator experts (including Vadim):
particles deflected beyond approximately 1 mrad are effectively lost from machine acceptance.
Estimate derived from:
~150 μrad angular spread
using 3–5σ beam envelope criteria.
Prajwal presented calculations for:
Rutherford scattering
Coherent nucleon scattering
Electron scattering in the target
Charge-transfer reactions
Inelastic fragmentation channels from DPMJet studies
Coherent nucleon scattering is unexpectedly significant:
comparable to Rutherford contributions near 1 mrad.
Electron scattering contributes primarily at very low angles.
Charge-transfer reactions:
mostly negligible,
but may contribute at the ~1% level in some channels.
Fragmentation channels remain nonzero even at low scattering angles.
Team now has a substantially more comprehensive inventory of beam-loss channels than previously available.
A dedicated beam-loss section has been added to the manuscript.
Frank emphasized that the forward tagger system should not be viewed solely as a polarimetry tool.
Treat the setup as a fixed-target experiment inside the collider.
Explore:
spin-physics measurements
recoil studies
upgraded detector capabilities
additional observables beyond CNI polarimetry
Richard Milner suggested possible future deployment concepts involving:
polarized internal gas targets in the electron ring
DIS physics opportunities using electrons
The collaboration should begin considering broader physics opportunities now, even if outside current project scope.
These possibilities should be mentioned in the manuscript conclusion/future outlook.
Prajwal to circulate manuscript draft once current sections are complete.
Richard to potentially contribute future-physics outlook material.
Additional conclusion text to discuss expanded fixed-target physics program possibilities.
Prajwal presented preliminary target-polarization systematic estimates:
optimistic estimate around 0.2%.
Both Richard and Frank strongly advised caution:
Sub-percent claims are likely unrealistic for a first-generation device.
Referees would likely challenge such precision claims heavily.
More realistic early-stage precision:
several percent (~3–5%).
Discussion focused heavily on:
RF fields from the circulating beam
magnetic-field perturbations
bunch-structure-induced depolarization
Hydrogen targets exhibit strong hyperfine-coupled beam depolarization effects.
He-3 is fundamentally different:
closed electron shell
no direct hyperfine-mediated electron-to-nucleus coupling
Hermes observed beam-induced depolarization effects in polarized hydrogen targets.
Strong holding fields and optimized field geometries mitigated these effects.
Prajwal noted:
Wall-relaxation effects for He-3 are extremely small.
Dominant concern is beam-induced magnetic perturbations.
Current estimates indicate:
depolarization times potentially as short as a few seconds under beam conditions.
Proposed holding field:
0.3–0.4 T.
Strong holding fields help suppress depolarization effects.
Beam-induced depolarization scales approximately as:
proportional to 1/B²
Revise manuscript claims from sub-percent precision to more realistic ~4% initial expectations.
Add explicit discussion that current depolarization studies are incomplete.
Reach out to Ed Kinney (University of Colorado / Hermes expert) for feedback and possible collaboration.
Prajwal to send relevant manuscript section to Ed Kinney for comments.
Manuscript nearing completion.
Remaining section: polarimetry statistical precision estimates.
Fragmentation and beam-loss studies are now substantially more complete.
Forward tagger efficiencies appear promising (~97%).
Broader fixed-target spin-physics opportunities should be explored.
Sub-percent polarimetry claims should be avoided at this stage.
Beam-induced depolarization remains a major open issue requiring further simulation and experimental study.
External expertise (e.g., Ed Kinney) should be brought into the discussion.
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