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HEP ASTRO SEMINAR: Exploring the Nucleon’s Sea at SeaQuest

Monday, April 13, 2015
12:00 AM
335 West Hall

Quantum Chromodynamics (QCD) is completely consistent with measurements of properties of hadrons, the bound states of the strong interaction, and high energy interactions where predictions are possible; and because of this, QCD is widely believed to be the correct microscopic theory of nature’s strongest and shortest ranged force.  However, many features of these bound states– primarily due to the strong self-coupling of the gluon field, are at present incalculable from first principles.  Hadrons can be thought of as a complex “sea” of many coupled gluons and daughter quark-antiquark-pairs constrained by the valence structure of the hadron and QCD’s color-confinement property.  This leads to a variety of observables, ranging from the 98% of the nucleon’s mass (i.e. of the visible universe) which is dynamically generated in this field to several fascinating and unexpected features nucleon structure.  The sea has been shown to be a crucial component of the nucleon and while experimentally challenging to probe, may provide deep insights into the relevant degrees of freedom governing nonpurturbative aspects of nucleon structure.The E906/SeaQuest experiment detects pairs of muons produced in collisions between 120 GeV protons from the Fermilab Main Injector and fixed liquid hydrogen and deuterium, and heavier solid targets.  Due to the different momentum distributions of valence and sea partons in the nucleon, SeaQuest’s fixed target geometry selects events produced in processes involving valence quarks in the beam and sea quarks in the target, specifically via the Drell-Yan interaction and J/Psi production .  This allows for comparisons of sea quark distributions by comparing cross sections on different targets.  SeaQuest is studying topics including the asymmetry of the light antiquark sea, nuclear modification of sea distributions, energy loss in cold nuclear matter, transverse momentum dependent distribution functions, and will additionally explore the possibility of the existence of dark photons - one class of dark matter candidate.  Doing so, it will address several mysteries presented by its predecessor Fermilab E866/NuSea. SeaQuest, in which the University of Michigan plays a major role, began collecting production data just over one year ago and has overcome significant and unexpected experimental challenges.  Physics goals, experimental details, and first results - only just released - will be presented.

Christine Aidala (University of Michigan post doc)