MainPage:Nuclear:EICGlobalStudies

⇐ Back to the Main_Page

Key Physics Questions

• How do mass and radii of light quark systems (pion/kaon) emerge from QCD - role of dynamical chiral symmetry breaking

• Interplay of strong mass and Higgs mechanism

• Possible contribution of theory, experiment, global fits, phenomenology, lattice, as discussed during workshop:
  • Theory: decomposition of mass, contributions from quarks and gluons in energy-momentum tensor whose moments are related to Parton Distribution Functions (PDFs and GPDs), and structure functions and form factors, which can be measured; fundamental questions include: how cancellations work to end up with pion mass, how mass decomposition works in chiral limit; pion and kaon are fundamental: pion mass is unnaturally light, kaon has one heavy quark and can provide information on strong and Higgs mass production mechanism
  • Lattice: calculate expectation values (matrix elements as function of quark mass, moments of PDFs) towards mass decomposition, chiral limit?
  • Experiment/Global Fit: feasibility and projections for pion and kaon structure function and form factor measurements at EIC, models for rate projections, rates, requirement on detectors, e.g. calorimeter resolution, neutral vs. charged particle detection, etc., global fits and impact on PDFs and GPDs, feasibility of measurement with heavier quarks (charm) in addition to pi/K

• Further details in the attached write-up by Craig Roberts.
  

Parton Distributions in Pion and Kaon

The structure functions in terms of sea quarks and gluons are expected to be different for pions, kaons, and nucleons and to provide basic information about their origin of mass.

Experimental data are sparse. As a result, there has been persistent doubt about the behavior of the pion's valence quark structure function at large Bjorken-x and virtually nothing is known about the contribution of sea quarks and gluons. The Electron-Ion Collider with an acceptance optimized for forward physics has the potential for accessing pion and kaon structure functions over a large kinematic region through the Sullivan process. This would allow for measurements testing if the origin of mass is encoded in the differences of gluons in pions, kaons, and nucleons, and measurements that could serve as a test of assumptions used in the extraction of structure functions and the pion and kaon form factors.

In this work we are going to calculate structure functions for pion and kaon from the Sullivan process with flexible choices of x and Q2 bins, and evaluate the uncertainties and potential to constrain, e.g. the gluon PDFs.

some slides

Latest news

Workshop 2018

• A few notes from the pion/kaon workshop, as well as suggestions for next steps for our kaon (pion) modeling based on discussion with Nobuo below. Perhaps we can have a meeting in mid-June to discuss these further.
  • (Nick) Finalize reproducing pion global fit. Two possible issues that may be the reason for observed mismatch with F2_LN y-dependence in Fig. 6 of PRD 93, 054011, 2016:
  • k_perp integration has experimental cutoffs not stated explicitly in 2016 paper - cutoffs listed in paper by H1 collaboration
  • x is x_B, not x_π in these figures

• (Nick, Nobuo, Tanja, ...) Develop global fit for kaons - two steps:
  • Develop model to determine relative numbers of kaons produced - could use pion data and parameterize flux factor
  • Adapt pion global fit framework for kaons - Python or Mathematica

• (Richard, Nobuo,...) Test impact of current theory assumptions on pion global fit by releasing (see 2018 paper or Nobuo's talk for details):
  • momentum sum rules
  • symmetric sea
  • splitting function exponent at high x
  • parameters

• (Richard, Vladimir, Tanja,...) Use fixed statistical uncertainties (1%, 3%, 10%) and determine corresponding experimental conditions (luminosity, detector acceptance and resolution) for pion structure function measurements at EIC; ultimately need to use realistic binning and projected statistics from Fast Monte Carlo and detector simulation; repeat for kaon

• Note on Nobuo et al. 2018 paper: uses Nobuo's own fit to nucleon PDFs instead of HERAPDF1.5 that was used in PRD 93 (2016). Also, several theoretical assumptions are made that make errors in Fig. 2 appear very small - not all are justifiable experimentally. Needs to be investigated

Simulations and web fitter global fits

Simulations	⇒
PDF Fitter	⇒	Durham Reaction Database PDF Plotter	HERA Fitter

References

• J.F. Owens, Phys. Rev. D, Vol. 30, Issue 5 (1984), 943.

• M. Glueck, E. Reya, A. Vogt, Z. Phys. C 53 (1992), 651.

• M. Alberg, E. M. Henley, Phys. Lett. B611 (2005) 111.

• M. Alberg, J. Tibbals, Phys. Lett. B709 (2012) 370.

Workshops

• Pion and Kaon Structure Function at an Electron-Ion Collider, Workshop at ANL 2017

• Pion and Kaon Structure Function at an Electron-Ion Collider, Workshop at CUA 2018

The EIC Collaboration

• CUA/VSL
  • Name 1
  • Name 2

• UConn
  • Nobou Sato