He3-ABS: Bi-monthly Meeting

Thursday 21 May 2026, 10:00 → 11:30 America/New_York

https://mit.zoom.us/j/92275675151 (Zoom)

Prajwal Mohan Murthy (MIT LNS)

Bi-monthly meeting of MIT-BNL He3-ABS Collaboration

Meeting Minutes — Thursday, May 21 @ 10:00 AM (Zoom)

Attendees

• Prajwal Mohan Murthy

• Zhengqiao Zhang

• Richard Milner

• Frank Rathmann

• Vera Shmakova

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1. DPMJet + Geant4 Fragmentation and Tagging Studies

Overview

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

Physics Cases Studied

• p + He-3

• d + He-3

• He-3 + He-3

Main Findings

• 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.

Tagging Performance

• 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.

Action Items

• Prajwal to update tables with latest deuteron results from Zhengqiao.

• Possible future optimization for d + He-3 by repositioning taggers.

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2. Beam Loss Mechanisms in the Polarimeter

Motivation

Accelerator group requested estimates of beam loss caused by interactions with the polarized jet target.

Beam-Loss Criterion

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.

Beam-Loss Processes Evaluated

Prajwal presented calculations for:

1. Rutherford scattering

2. Coherent nucleon scattering

3. Electron scattering in the target

4. Charge-transfer reactions

5. Inelastic fragmentation channels from DPMJet studies

Key Observations

• 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.

Conclusion

• 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.

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3. Broader Physics Opportunities with the Target Station

Discussion Initiated by Frank Rathmann

Frank emphasized that the forward tagger system should not be viewed solely as a polarimetry tool.

Suggestions

• 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

Additional Ideas

Richard Milner suggested possible future deployment concepts involving:

• polarized internal gas targets in the electron ring

• DIS physics opportunities using electrons

Consensus

• 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.

Action Items

• 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.

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4. Polarimetry Precision and Depolarization Discussion

Initial Estimate

Prajwal presented preliminary target-polarization systematic estimates:

• optimistic estimate around 0.2%.

Immediate Feedback

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%).

Beam-Induced Depolarization

Discussion focused heavily on:

• RF fields from the circulating beam

• magnetic-field perturbations

• bunch-structure-induced depolarization

Important Clarification

• 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 Experience

• Hermes observed beam-induced depolarization effects in polarized hydrogen targets.

• Strong holding fields and optimized field geometries mitigated these effects.

Current Understanding

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.

Holding Field Discussion

• 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

Action Items

• 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.

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5. Manuscript Timeline

Status

• Manuscript nearing completion.

• Remaining section: polarimetry statistical precision estimates.

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Overall Meeting Conclusions

1. Fragmentation and beam-loss studies are now substantially more complete.

2. Forward tagger efficiencies appear promising (~97%).

3. Broader fixed-target spin-physics opportunities should be explored.

4. Sub-percent polarimetry claims should be avoided at this stage.

5. Beam-induced depolarization remains a major open issue requiring further simulation and experimental study.

6. External expertise (e.g., Ed Kinney) should be brought into the discussion.

Source transcript:

Agenda

Convener: Prajwal Mohan Murthy (MIT LNS)

1 Prajwal

Speaker: Prajwal Mohan Murthy (MIT LNS)

2 Frank