Antiquark Flavor Asymmetry Research Articles

Drell-Yan Experiment: Studying Anti-Quarks in the Proton

The internal structure of the proton is one of the most vital topic in the present hadron physics. At a high-energy scale the proton reveals its complicated parton structure which is beyond the scope of the Quark Parton Model (QPM), i.e. quarks (q), anti-quarks (q̄) and gluons (g). Gluons and anti-quarks are dynamically created via q → q + g and g → q + q̄, respectively. The dynamics of the proton structure is being investigated in both experiment and theory.The Drell-Yan process in proton+proton collisions is the reaction in which a quark in one proton and an anti-quark in the other proton annihilate into a virtual photon and then create a muon pair: q + q̄ → γ* → μ+ + μ−. This process is suited to study the anti-quarks in the proton, and many experiments measuring the Drell-Yan process have been carried out in the past 20 years. The E906/SeaQuest experiment at Fermi National Accelerator Lab (FNAL) in USA is a Drell-Yan experiment being prepared now to explore a new kinematic region with very high statistics. The main purpose of this experiment is to precisely measure the asymmetry of ū and d̄ distributions in the proton at the xBj range from 0.25 to 0.45.In this paper, the anti-quark flavor asymmetry in the proton and the past Drell-Yan experiments are summarized, and the status of the E906 experiment is reported.

Polarized antiquark flavor asymmetry in Drell–Yan pair production

We investigate the role of the flavor asymmetry of the nucleon's polarized antiquark distributions in Drell-Yan lepton pair production in polarized nucleon-nucleon collisions at HERA (fixed-target) and RHIC energies. It is shown that the large polarized antiquark flavor asymmetry predicted by model calculations in the large-N_c limit (chiral quark-soliton model) has a dramatic effect on the double spin asymmetries in high mass lepton pair production, as well as on the single spin asymmetries in lepton pair production through $W^\pm$-bosons at $M^2 = M_W^2$.

Transversity distributions and Drell-Yan spin asymmetries

We discuss transversity distributions and Drell-Yan transverse double spin asymmetries. First, the antiquark flavor asymmetry Δ T u Δ T d is discussed by using two different descriptions, a meson-cloud model and a Pauli exclusion model. We find that both calculations produce a significant Δ T d excess over Δ T u . Next, we study its effects on the transverse spin asymmetry A TT and on the Drell-Yan proton-deuteron asymmetry Δ Tσ pd 2Δ Tσ pp . We find that the ratio Δ Tσ pd 2Δ Tσ pp is very useful for investigating the flavor asymmetry effect.

Flavor asymmetry of antiquark distributions in the nucleon

Violation of the Gottfried sum rule was suggested by the New Muon Collaboration in measuring proton and deuteron F 2 structure functions. The finding triggered many theoretical studies on physics mechanisms for explaining the antiquark flavor asymmetry u ̄ − d ̄ in the nucleon. Various experimental results and proposed theoretical ideas are summarized. Possibility of finding the flavor asymmetry in Drell–Yan experiments is discussed together with other processes, which are sensitive to the u ̄ / d ̄ asymmetry.

Measurement of the Light Antiquark Flavor Asymmetry in the Nucleon Sea

A precise measurement of the ratio of Drell-Yan yields from an 800GeV/c proton beam incident on hydrogen and deuterium targets is reported. Over 140 000 Drell-Yan muon pairs with dimuon mass Mμ+μ−≥4.5GeV/c2 were recorded. From these data, the ratio of antidown ( d¯) to antiup ( u¯) quark distributions in the proton sea is determined over a wide range in Bjorken x. A strong x dependence is observed in the ratio d¯/u¯, showing substantial enhancement of d¯ with respect to u¯ for x<0.2. This result is in fair agreement with recent parton distribution parametrizations of the sea. For x>0.2, the observed d¯/u¯ ratio is much nearer unity than given by the parametrizations.Received 9 December 1997DOI:https://doi.org/10.1103/PhysRevLett.80.3715©1998 American Physical Society