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CFNS Ad-hoc Workshop: Target fragmentation and diffraction physics with novel processes: Ultraperipheral, electron-ion, and hadron collisions

On-line meeting

On-line meeting

Abhay Deshpande (Stony Brook University) , Christian Weiss (Jefferson Lab) , Mark Strikman (Penn State University) , Marta Ruspa (Univ Piemonte Orientale & INFN, Torino) , Michael Murray (The University of Kansas (US))

Target fragmentation in deep-inelastic processes is emerging as a new field of study in hadronic and nuclear physics. Nucleon fragmentation in ep/γp/pp scattering provides new possibilities for measuring the spin/flavor decomposition of partonic structure and gives insight into multiparton correlations and hadronization dynamics (diquark fragmentation, quantum number transport). An important special case is diffractive scattering (rapidity gap events), where the nucleon remains intact or dissociates in a low-mass hadronic state. Nuclear fragmentation in eA/γA/pA scattering provides critical information on the nuclear configuration during the high-energy process (spectator tagging, centrality) and can be used to study nuclear final-state interactions and hadronization dynamics.

Target fragmentation measurements are performed in fixed-target (JLab, COMPASS, HERMES, earlier experiments) and collider experiments (HERA, RHIC, LHC, EIC) over a wide range of energy and momentum transfers, and with various hard processes probing the hadron (DIS, jets, heavy flavor production). In collider experiments the target fragments or diffractive protons/nuclei are detected with forward detectors integrated into the interaction region. The forward detection capabilities of the EIC offer excellent prospects for target fragmentation physics and have been explored and documented in the recent Yellow Report.

The workshop will review the physics opportunities in target fragmentation measurements in collider and fixed-target experiments. The goal is to formulate a coherent program combining the results of different experiments (energy range, type of probe) and define the context and objectives for target fragmentation measurements at EIC. The workshop will focus in particular on the following new directions:

  • Target fragmentation and diffraction with ultraperipheral pA/AA collisions (UPC). UPC at LHC reach the highest CM energies in electromagnetic scattering and induce hard processes identified by final states (dijets, heavy flavors). Target fragmentation can be measured with the present LHC forward and far-forward detectors. UPC and EIC are complementary (collision energy, photo vs. electroproduction) and could be combined to a comprehensive program of target fragmentation and diffraction
  • Nucleon fragmentation with variable energies and probes. Understanding of the dynamics of nucleon fragmentation in hard processes remains very limited. Existing data on leading proton/neutron production in DIS leave open many basic questions (e.g. baryon number transport). Progress could be made by: (i) Performing proton fragmentation studies with LHC data on leading proton/neutron production in pp collisions with hard processes, including correlations of the forward observables with the central event. The LHC pp data complement the HERA ep DIS data; their combination would broaden the basis for fragmentation studies. (ii) Exploring the energy dependence of nucleon fragmentation by combining DIS data from collider and fixed-target experiments, esp. the forthcoming JLab12 data. These studies could be performed in the next years and will sharpen the questions to be addressed in target fragmentation and diffraction measurements at the EIC.
  • Nuclear breakup in high-energy processes. Measurements of nuclear breakup in DIS processes at EIC have many interesting physics applications such as spectator tagging with light ions (D, 3He),  centrality selection in eA/γA collisions with heavy ions, and the identification of coherent nuclear scattering through veto detection. These applications rely on models of the nuclear breakup describing the energy/momentum/particle injection by the DIS process and the subsequent evolution of the nuclear system. An important question is how these models could be tested and improved using data from other high-energy processes (UPC, pA) before the start of EIC operations.

The workshop brings together theoretical and experimental researchers in quantum chromodynamics and hadron structure, high-energy ep/γp/pp scattering, ultraperipheral pA/AA collisions, nuclear breakup, and detector development, for an in-depth discussion of these topics.

The workshop is conducted in on-line format. The sessions are scheduled for 09:00-16:00 ET to allow for simultaneous participation from European and US timezones. Extensive time is reserved for topical discussions.

The previous 2020 CFNS Workshop "Target fragmentation physics with EIC" reviewed target fragmentation physics from a general perspective and documented the interest in future EIC measurements. The new workshop here continues this effort and focuses on the specific new developments described above.

  • Abhay Deshpande
  • Alessia Bruni
  • Bjoern Schenke
  • Christian Weiss
  • Daniel Tapia Takaki
  • Mark Strikman
  • Marta Ruspa
  • Michael Murray
  • Spencer Klein
  • Ted Rogers
  • Vadim Guzey
  • Yang-Ting Chien
  • Zhoudunming Tu