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Here are the publications for which I was a principle author!
Measurement of Proton-Number Fluctuations in Fixed-Target Au+Au Collisions at √sNN = 3.0, 3.2, 3.5, 3.9, and 4.5 GeV at the Relativistic Heavy-Ion Collider
STAR Collaboration (Principal Author) Targeted for PRL 2025
The STAR Collaboration at the Relativistic Heavy-Ion Collider has measured several hundred million relativistic gold nucleus collisions at center-of-mass energies from 3.0 to 4.5 GeV/nucleon. This paper reports on the measurement of proton-number fluctuations in the search for the critical point of the nuclear phase diagram. No signatures of criticality are observed in the proton-number kurtosis at these energies.
Effects of Pileup and Detector Decorrelations on High-order Cumulants in Heavy-ion Collisions
(How Not to Measure a False QCD Critical Point)
Zachary Sweger, Daniel Cebra, Xin Dong
arXiv:2410.12319, Physical Review C 111, 034902 (2025)
This paper attempts to open up the black box of high-order cumulants in heavy-ion collisions, and explains what kinds of experimental effects can cause large deviations in 4th, 5th, and 6th-order cumulants. We explain how easy it is to observe a false signature of a QCD critical point, and how to avoid doing so.
I was the lead author for this paper, designing models of the measurement of proton-number cumulants, and simulating these in UrQMD to demonstrate the potential pitfalls of various methods.
Modeling Backward-Angle (u-channel) Virtual Compton Scattering at an Electron-Ion Collider
Z. Sweger, S.R. Klein, Y. Ji, M. Kim, S. Yoo, Z. Zeng, D. Cebra, X. Dong
Physical Review C 108, 055205 (2023)
We explored the prospects for detecting photons from a u-channel production mechanism at the future Electron-Ion Collider.
I was the lead author for this paper, designing parameterized models of this physics process, simulating events as they would appear at the future collider, and evaluating how these events compare with projections for an EIC detector.
This paper was highlighted as an Editor's Suggestion for this issue of Physical Review C, and also got a shout-out from Berkeley Lab's Nuclear Science Division!
Backward-Angle (u-channel) Physics at an Electron-Ion Collider
D. Cebra, Z. Sweger, X. Dong, Y. Ji, S.R. Klein
In this paper, we discussed several interesting production channels of vector mesons at the Electron-Ion Collider, including u-channel ρ and ω production.
I was one of the lead authors, developing and evaluating simulations of u-channel meson production as it would occur at the EIC. I used these simulations to determine how to optimize detection of mesons produced via this mechanism.
Search for the Chiral Magnetic Effect with Isobar Collisions at √sNN = 200 GeV by the STAR Collaboration at the BNL Relativistic Heavy Ion Collider
The STAR Collaboration
The STAR Collaboration collected data from high-energy collisions of Ru-96 with Ru-96 and Zr-96 with Zr-96. By comparing collisions of two different mass-96 nuclei in a blind analysis, we attempted to observe a signature of the chiral magnetic effect. No such signature was observed.
I was one of the principle authors on this publication because I was responsible for pre-processing, correcting, and defining cuts for the data (unblinded) before others could analyze it. As part of this process I simulated Ru+Ru and Zr+Zr collisions with several nuclear shape hypotheses. See Section III for my contribution!
Designing and Benchmarking of a Proton-Recoil Neutron Detector
Zachary Sweger
Using neutrons produced by DD fusion, Lawrence Livermore National Lab was developing neutron imaging capabilities and needed non-invasive neutron detectors.
During my time with Berkeley's Department of Nuclear Engineering, I worked on the development, testing, and simulation of a proton-recoil neutron detector for Livermore. I tested this detector in a neutron beam at Berkeley Lab's 88-Inch Cyclotron. I then developed Geant simulations (pictured at left) of the experiment to determine that the detector signals were being overwhelmed by beam interactions with the aluminum detector casing. With this finding, I worked up a design for an improved detector.
Performance evaluation of an energy tuning assembly for neutron spectral shaping
J.E. Bevins, Z. Sweger, N. Munshi, B.L. Goldblum, J.A. Brown, D.L. Bleuel, L.A. Bernstein, R.N. Slaybaugh
Nuclear Instruments and Methods A, Vol. 923, Pages 79-87, ISSN 0168-9002 (2019)
James Bevins (then a PhD student in UC Berkeley's Department of Nuclear Engineering) designed an assembly of materials to tune the spectrum of neutrons from Livermore's National Ignition Facility. This assembly was tested in a neutron beam at Berkeley Lab's 88-Inch Cyclotron.
I helped to determine the activation of several test foils that were used to gauge the efficacy of the assembly. This involved analyzing the gamma spectrum of the foils post-irradiation, and determining and correcting for the efficiency of our high-purity Germanium detector.
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