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ATHENA Exclusive & Tagging WG
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https://bnl.zoomgov.com/j/1606845139?pwd=MFJRV0hubS9FWTJyNGxvRERMRUxtdz09
Here are a few notes from the July 16th ATHENA exclusive and tagging meeting. The agenda and slides are available on Indico:
https://indico.bnl.gov/event/12378/
1) Meeting time. Our current time is somewhat problematic, because our meetings start 1 hour after the ATHENA WG convenors meeting, and the convenors meetings consistently run over their scheduled 1-hour length, often by ~ 30 minutes. The exclusive and tagging convenors are discussing possible solutions, but there are limited options that are both West-Coast friendly and Europe friendly, and not already heavily occupied.
2) Athira Vijayakumar gave us a presentation on elastic J/psi production, where she compared different approaches to J/psi reconstruction. She also looked at the tagging efficiency for separating production where the proton dissociates (vs. it remaining intact) and for separating incoherent and coherent production in eA. In both cases, tagging efficiency is lower than desired, and we need to pay attention to the forward production. She also noted that Sartre and BeAGLE have different approaches to nuclear breakup.
3) Zhangbu Xu gave a presentation on "Why we must have Low-pT TOF for exclusive VM production?" showing how exclusive rho+direct pipi production is a background for exclusive phi production, and proposed the inclusion of LGAD silicon timing detectors to use TOF to reject the dipion backgrounds.
4) Justin Stevens (with Derek Glazier) discussed the choice of a spectroscopy golden channel, and proposed ep -> ep J/psi pi^+pi^-, through the X(3872) and the Y(4260). They also showed the backgrounds from non-exclusive processes, estimated using PYTHIA. These channels occur via Pomeron exchange, so are spread over a wide range of rapidity, whereas a Reggeon-exchange mediated process would be mostly near to threshold energies, so concentrated at forward rapidity. An alternative is to choose a channel that includes a pi^0, to test ATHENA calorimetry with soft(er) photons, which seem to have attracted little attention in ATHENA.
We tentatively agreed that ep -> ep J/psi pi^+pi^- should be our golden channel, subject to further discussion on this mailing list (not everyone was on the call. If you would prefer a Reggeon-exchange mediated process, a final state involving pi^0, or other some other change, please speak up. Otherwise, we will stick with ep -> ep J/psi pi^+pi^-.
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