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Chan Kim defends his PhD Thesis!

Prof. Strakovsky introduces Chan to the assembled committee over Zoom.

On Nov. 23rd, Chan Kim successfully defended his PhD thesis, titled “Measurement of the Helicity Asymmetry E for the γp → π0p reaction in the Resonance Region.” Chan analyzed data from the “FROST” experiment at Jefferson Lab, which used a polarized proton target in the form of frozen butanol beads. A polarized photon beam was scattered from the target, and Chan was interested in collisions that produced a single pi0 meson. In his analysis, Chan determined the slight difference in scattering rates when the photons and protons had their spins aligned versus anti-aligned. This can help reveal excited baryon resonances and in turn help us better understand the different ways quarks can bind together.

Dr. Kim explains the Frozen Spin Target (FROST) used in the experiment.
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Two new experiments on short-range correlations are underway at Jefferson Lab!

Data is coming in on two of our group’s new experiments at Jefferson Lab investigating how protons and neutrons form short-range correlations within nuclei. In experimental hall B, we are colliding electrons accelerated to an energy of 6 Giga-electron Volts (GeV) on, hydrogen, deuterium, helium, carbon, argon, calcium, and tin nuclei, with the goal of knocking out protons and neutrons and detecting the emerging particles in the CLAS12 spectrometer. At the same time in experimental hall D, we are colliding photons with energies in the range of 8 to 8.5 GeV on deuterium, helium, and carbon, hoping to cause reactions that produce short-lived mesons that we can identify with the GlueX spectrometer. We are still in the early stages of calibrating the instruments, and teams are working around the clock to make sure the data is looking good, but we are already starting to see the reactions we expect!

Hall B
In our first day’s data, scattering on hydrogen, we can clearly see elastic scattering, resonance production, and deep inelastic scattering
The Hall B analysis team, including Erin, Sara, and Tyler goes over the previous day’s data in the daily analysis meeting.
Hall D
The Hall D team, including Phoebe, coordinates on detector calibrations.

The first trickle of data already show signatures of rho meson and Delta baryon photo-production.
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Group has strong showing at APS Division of Nuclear Physics Fall Meeting

Tyler Kutz presenting his invited talk showing preliminary results from the BAND Experiment.

Our group was well-represented at this year’s APS Division of Nuclear Physics Fall Meeting. Our headliner was Tyler, who was gave an invited talk titled “First results from neutron-tagged DIS measurements at JLab with CLAS12 and BAND.” Other talks by group members were:

  • Erin Seroka: “Comparing Simulated and Measured 3He Neutron-to-Proton Knockout Ratios”
  • Sara Ratliff: “Upcoming High-Statistics Exclusive Measurements of SRCs at CLAS-12”
  • Phoebe Sharp: “Using Generalized Contact Formalism and Real Photon Beams to Explore Short Range Nuclear Structure”
  • Bill Briscoe: “A Nuclear Education Hub (NEH) for Training the Next Generation Nuclear Workforce”
  • Igor Strakovsky: “Threshold Upsilon-meson Photoproduction at EIC and EicC”
  • Axel Schmidt: “The LAD Experiment: measuring medium-modification using spectator-tagged deep inelastic scattering”

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PANIC! It’s the Particles and Nuclei International Conference.

Our group was well represented at the 2021 edition of the Particles and Nuclei International Conference, which was held remotely after being originally planned to be held in Lisbon, Portugal. We had three contributions:

The talks have been archived on YouTube, and you can watch below.

https://youtu.be/NlbBhUZrSok?t=3415
https://youtu.be/uNJmqzS8zwY?t=5341
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Giovanni Angelini defends his PhD Thesis!

(Almost) Dr. Angelini deftly responds to a question from the thesis committee.

Today, our group celebrates our newest doctor! Giovanni Angelini successfully defended his PhD thesis, titled “Probing Quark Dynamics in Semi-Inclusive Charged Pion Electroproduction with CLAS12.” This was an immensely impressive piece of work that charted both beam single-spin asymmetries as well as pion multiplicities over four-dimensional phase space. These results are some of the first to come from the CLAS collaboration after the 12 GeV upgrade, and are well on their way to publication. In fact, the π+ beam spin asymmetry results are already on the arXiv (arXiv:2101.03544 [hep-ex]) and are undergoing peer review.

The multiplicity analysis was performed preserving the full dimensionality of the data, i.e., binned by x, Q2, z, and PT.

We are also thrilled that Dr. Angelini has accepted a lecturer position in the physics department at American University! We wish both for his continued to success and that we’ll see him around town this fall.

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New paper on the EMC Effect published in “Physical Review Research”

One of the key results is the calculated double ratio of the structure function for bound nucleons relative to free nucleons at x=0.6 (where the EMC Effect is large) relative to x=0.3 (where the EMC Effect is minimal). This will be measured by BAND and LAD!

The EMC Effect is typically observed as a change in quark structure in a heavy nucleus relative to deuterium, one proton weakly bound to one neutron. But that doesn’t mean that the quarks in deuterium also don’t experience some change in their momentum distribution relative to an unbound proton and neutron. In a new paper titled, “Short-range correlations and the nuclear EMC effect in deuterium and helium-3,” Prof. Schmidt and collaborators calculate the size of this change when assuming that this modification depends on nucleon virtuality—roughly how fast the a nucleon is moving. Depending on the assumptions one makes about the structure of the free neutron, or about the dependence of the modification on the Bjorken-x variable, the results can be wildly different. One highly relevant application of the calculation is to make predictions for the BAND and LAD experiments, pictured above.

The paper appears in the April-June issue of journal Physical Review Research, vol. 3.

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