November 21 (in-person)

David d'Enterria (CERN) 

Host: Spencer Klein

Title: Photon-photon physics at the LHC 

Abstract: The CERN LHC is not only the current energy-frontier collider for parton-parton collisions, but has proven a powerful photon collider providing photon-photon (γγ) collisions at center-of-mass energies and luminosities never reached before. By exploiting the large fluxes of quasireal photons emitted by the accelerated protons and heavy-ions, a very rich and unique range of SM and BSM measurements is open to study. Such γγ processes can be examined in particularly clean conditions in the so-called ultraperipheral collisions (UPCs) where the colliding hadrons interact without hadronic overlap, and survive their purely electromagnetic interaction. I will review the latest experimental and theoretical photon-photon physics results at the LHC including measurement of the anomalous tau lepton magnetic moment via γγ->tau+tau- production, observation of light-by-light scattering, and searches for axion- and graviton-like particles, among others. 

November 26 (in-person)

Miguel Arratia (UC Riverside) 

Host: John Arrington

Title: Spin Alignment of Quarks In the Nucleus 

Abstract: I will describe upcoming measurements with the CLAS12 detector at JLab, which aim to provide the first measurements of nuclear effects on the spin structure of bound protons — a completely unexplored area. These measurements will use a longitudinally polarized lithium-7 target and an 11 GeV polarized electron beam. I will discuss the physics motivations and the expected performance of the experiment for both inclusive and semi-inclusive scattering. Additionally, I will outline how these measurements could inform future upgrades for the EIC. I will also describe planned measurements of Lambda particles using the ePIC Zero-degree calorimeter. Lambda studies will be a unique tool, including for merging spin-related studies with studies of cold nuclear matter at the EIC.

December 03 (in person)

Ben Gilbert (Livermore)

Host: Spencer Klein

Title: Measurement of photonuclear dijet production in ultra-peripheral Pb+Pb collisions at the LHC with the ATLAS Detector

Abstract:  In ultra-relativistic heavy ion collisions, the charged ions produce an intense flux of equivalent photons. Photon-induced processes are the dominant interaction mechanism when the colliding nuclei have an impact parameter larger than the nuclear diameter. In these ultra-peripheral collisions (UPCs), the photon provides a clean, energetic probe of the partonic structure of the nucleus, analogous to deep inelastic scattering. This talk presents a measurement of jet production in UPCs performed with the ATLAS detector using high-statistics 2018 Pb+Pb data. Events are selected using requirements on jet production, rapidity gaps, and forward neutron emission to identify inclusive photo-nuclear hard-scattering processes. These measurements also include detailed studies of rapidity gap distributions and nuclear break-up effects, allowing for precise comparisons between data and theory for inclusive photo-nuclear processes. The measured cross-sections are compared to theoretical models in phase-space regions where significant nuclear PDF modifications are expected but not well constrained by world data, demonstrating the potential of these data to provide a strong new constraint on nPDF effects.

January 21 2025 (online)

Mi Ke (CCNU)

Host: Nu Xu

Title: Recent results on Baryon correlations at RHIC-STAR

Abstract: In high-energy nuclear collisions, the measurements of two-particle femtoscopy is a powerful and unique method for extracting information about the femtoscopic spatio-temporal properties of the source and characterising the final state interactions (FSI). However, measurements of baryon correlations are scarce. Understanding the strong interactions between baryons, especially nucleon-nucleon (N-N), hyperon-nucleon (Y-N) and hyperon-hyperon (Y-Y) interactions, are crucial for comprehending the equation-of-state (EoS) of the nuclear matter and inner structure of neutron star. Furthermore, baryon correlations involving light nuclei, which are loosely bound objects, are critical for understanding many-body interactions and the production mechanisms of light nuclei.

    In this talk, we will present recent results on baryon correlations measured with RHIC-STAR experiment, including p-p,  p-d, d-d, p-\Lambda, p-Xi^-, and d-\Lambda. Extracted source size parameters, driven by collision dynamics, and FSI parameterization, determined by the nature of the particle pairs under study, will be discussed within the framework of lattice calculations (interaction potentials) and hadronic transport model calculations.