Discussion 09-23-24

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Meeting Location

The 22 GeV Open Discussions will be held here:

• Date/Time: Monday, September 23 at 12:30 PM Jefferson Lab Local Time
• Physical Location: CEBAF Center F224/5
• Virtual Location: Zoom Meeting Number 161 111 8017 (The password is the two-digit number that appears before "GeV" in the first sentence of this section.)

Agenda

• Measuring the X(Y)Z at JLab22 (Sean Dobbs)

Comments and Questions

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Minutes/Notes (D.S. Carman)

Local participants at JLab: 13; Remote participants: 33

• This presentation continued the discussion on studies of spectroscopy of the so-called X, Y, and Z mesons that was started by Alessandro Pilloni at the Sep. 9 22 GeV discussion with a focus on theory status. Today’s discussion centered instead on experimental considerations of such a program at JLab22.

• Presentation points:
  • Review of status:
    • Overview of the cc (charmonium) spectrum augmented with the experimental evidence for the X, Y, and Z states.
    • Photoproduction experiments can have an impact on these studies to confirm states purported to have a non-qq nature.
    • The most relevant modes for initial exploration at JLab22 would focus on X, Z decays to J/Ψ+π, J/Ψ+ππ (these would be the “discovery” modes).
    • Studies of γp → cc are optimal using detectors with large acceptance - Hall B and Hall D at JLab.
  • Simulations are underway by Sean to study X and Z production in Hall D with GlueX:
    • Simulations have been done in the GlueX-II configuration based on the 2020 GlueX configuration without the DIRC, TRD, new high resolution FCAL.
    • Note that GlueX-III is approved to run at two times the luminosity of GlueX-II.
    • Studies have focused on γp → J/Ψ+π⁺π^- running for 1 year, assuming a total cross section of 500 pb^-1 with a BR of 5%.
      • Expected yields: N(Ψ(2S))=900, N(X(3872))=2300, N(Y(4260))=120
    • Another study has been done for γp → J/Ψ+πp to study both charged and neutral Z_c states.
  • Simulations are underway by Derek Glazier to study X and Z production in Hall B with CLAS12:
    • The baseline version of CLAS12 has been assumed augmented with a zero degree photon tagger (mentioned by Volker Burkert in the last discussion) to enable studies of quasi-real photoproduction (at tagging angles below 1 deg).
    • The studies have assumed a luminosity of 10³⁵ cm^-2s^-1 and 50 days of running.
      • Expected yields: N(X(3872))=2-3k, N(Z_c(3900))=25k
  • Work has begun to estimate backgrounds from existing measurements, specifically from data taken at COMPASS on μ^± N but more work is needed to make these studies realistic.

• Questions from discussion:
  • What about measuring open charm decays given the increased backgrounds that are to be expected?
  • What about measuring polarization observables?
  • What about establishing strange quark partners of states, e.g. Z_c → πJ/Ψ, Z_cs → KJ/Ψ?
  • What about radiative decays of X(3872)?
    • Can this be estimated? Are such studies useful?
    • How do backgrounds affect this channel?
  • The main comment from the discussion is that realistic backgrounds must be included in the different simulations to enable more realistic modeling and impact statements to be made.
    • Can such studies be advanced for the upcoming December 22 GeV workshop?