Lattice QCD study of the Boer-Mulders effect in a pion

Journal Article · Tue Mar 01 00:00:00 EST 2016 · Physical Review D

DOI:https://doi.org/10.1103/physrevd.93.054501· OSTI ID:1505597

Engelhardt, M. ^[1]; Hägler, P. ^[2]; Musch, B. ^[2]; Negele, J. ^[3]; Schäfer, A. ^[2]

---

1. New Mexico State Univ., Las Cruces, NM (United States)
2. Univ. of Regensburg, Regensburg (Germany)
3. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)

The three-dimensional momenta of quarks inside a hadron are encoded in transverse momentumdependent parton distribution functions (TMDs). Our work presents an exploratory lattice QCD study of a TMD observable in the pion describing the Boer-Mulders effect, which is related to polarized quark transverse momentum in an unpolarized hadron. The primary goal is to gain insight into the behavior of TMDs as a function of a Collins-Soper evolution parameter, $$\hat{ζ}$$, which quantifies the rapidity difference between the hadron momentum and a vector describing the trajectory of the struck quark, e.g., in a semiinclusive deep-inelastic scattering (SIDIS) process. The lattice calculation, performed at the pion mass m_π = 518 MeV, utilizes a definition of TMDs via hadronic matrix elements of a quark bilocal operator with a staple-shaped gauge connection; in this context, the evolution parameter is related to the staple direction. By parametrizing the aforementioned matrix elements in terms of invariant amplitudes, the problem can be cast in a Lorentz frame suited for the lattice calculation. Aided by the lower mass of the pion, compared to the nucleon studied previously, the present investigation of pion TMD observables constitutes an important step towards the quantitative study of the physically important regime of large relative rapidity where the dependence on $$\hat{ζ}$$ appears to approach a limit. Even though matching to perturbative evolution equations in $$\hat{ζ}$$ is not yet available, extrapolations based on Ansätze containing inverse powers of $$\hat{ζ}$$ yield stable results with an uncertainty as low as 20%, and both upper and lower bounds for the asymptotics are obtained. In passing, the similarity between the Boer-Mulders effects extracted in the pion and the nucleon is indicated.

• Research Organization: Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); New Mexico State Univ., Las Cruces, NM (United States); University of California, Berkeley, CA (United States); Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP); USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities Division; USDOE Office of Science (SC), National Energy Research Scientific Computing Center (NERSC)
• Grant/Contract Number: FG02-94ER40818; AC02-05CH11231; FG02-96ER40965; AC05-06OR23177
• OSTI ID: 1505597
• Alternate ID(s): OSTI ID: 1239861
• Journal Information: Physical Review D, Vol. 93, Issue 5; ISSN 2470-0010
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS