General MWG Meeting Summary 4/7/20

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Participants: Arun Tadepalli, David Richards, Dmitry Romanov, Rolf Ent, Huey-Wen Lin, Julia Furletova, Tim Hobbs, Vladimir Berdnikov, Tanja Horn, Jorge Segovia, Tobias Frederico, Richard Trotta, (Craig Roberts)


Overview of the Workshop on Perceiving the Emergence through Hadron Mass through AMBER@CERN

  • Omits recent lQCD progress on ratio u_kaon/u_pion
  • Omits progress on prediction of proton distribution functions, including dbar/ubar
  • QCD prediction for large-x behavior of pion PDF
  • many assumptions in calculations, inconsistencies in analysis (ref. JAM, questions on threshold resummation)
  • At any scale for which experiment can be interpreted in terms of parton distributions, then x~1--> qpi(x,ksi)prop(1-x)^(beta=2+gamma), gamma>0
  • Any DY or DIS (or similar) experiment or analysis thereof which returns a value of beta < 2 conflicts with QCD
  • Amongst all existing analyses of data for pion valence-quark PDFs, only Aicher (2010) employs a fully consistent NLO analysis, including threshold resummation.
  • Only Aicher (2010) result for qpi agrees with QCD.
  • All other analyses conflict with QCD.
  • Sea-quark distribution in pion is completely unknown - Access available, possibly, via comparison between pi+ and pi- beams on isoscalar target.
  • Both pion and nucleon contributions enter in the associated ratio:
  • numerator contains all combinations except valence-quark × valence-quark terms
  • denominator contains only valence-quark × valence-quark terms.
  • Worth rewriting this so that the sea-quark distributions in the pion (kaon) are displayed more explicitly.
  • Glue distribution. Assuming NRQCD ideas are correct for charm quarks, then JAM glue PDF cannot be correct. Comparison parameter-free continuum predictions by Ding et al. and JAM (see this figure) suggest
  • Valence-quark very different. Ding et al. consistent with pQCD prediction and entire profile confirmed by modern lQCD. JAM ignore soft-gluon resummation.
  • Glue almost identical. However, this common glue distribution is very different from earlier phenomenological analyses
  • Sea = very different. Mismatch in valence distribution had to go somewhere.
  • Meson PDAs and PDFs are related via light-front wave functions. Hence, expression of emergent hadronic mass (EHM) in one is also evident in the other. PDAs control hard exclusive processes. PDFs typically measured via inclusive processes. Appealing complementarity. Can one use diffractive scattering with two leading hadrons in the final state to access pion PDA?
  • Can one use diffractive scattering with two leading hadrons in the final state to access pion PDA? Great test of calculation frameworks that provide for a parameter free unification of both quantities, i.e. have a sound QCD-connected prediction for the meson LFWF.
  • E791 FNAL controversies
  • claim asymptotic profile at Q2=10 GeV2. Existing JLab data show this is unlikely.
  • Further, claim that broadened profile is needed at Q2 = 4 GeV2. Evolution between these two scales cannot change nonperturbative profile into perturbative profile.
  • Other topics covered include: Spectroscopy and hadron elastic and transition form factors


Discussion of the Workshop on Pion and Kaon Structure Function at the EIC at CFNS (June 2-5)

  • Topics of interest
  • Resummation
  • Meson PDA and PDF - light front wave function, so far only through the FF connection, what if have quasi-real meson target; LQCD: pion-pion operator and pion-vacuum operator
  • Large x PDF - what are the real questions, scale dependence, what is expected, complications
  • constraining the power of the (1-x) behavior is challenging, and even for the large body of proton structure pdf data it is difficult due to complications of analysis/interpretation in the large-x region,

including the evolution uncertainties (Q^2? W^2?)

  • compare high-x behavior from TDIS and COMPASS - can look process independence
  • Overall format (remote meeting)
  • Meet 4 hours per day: ET 8am - 1:00pm
  • Short talks (25+5min)
  • 4 days with 8 talks/day, plus 1 hour discussion each day
  • Mix of experiment, phenomenology, and 10-15 experiment talks
  • Action items:
  • Draft an agenda and circulate for comments
  • Check in with CFNS local organizer on plans
  • Find out about remote meeting options, e.g. Zoom

Preparation for the EIC (remote) Pavia Workshop (May 22-24)

  • Expect the Diffraction and Tagging Working group to reach out for contributions
  • Main report from the Meson SF group likely on experimental equipment - how one can access meson structure and implication on experimental equipment. Next Working Meeting on this topic: Monday 13 April
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