Bulletin of the American Physical Society
APS April Meeting 2017
Volume 62, Number 1
Saturday–Tuesday, January 28–31, 2017; Washington, DC
Session K13: Minisymposium: Physics Beyond Collinear FactorizationFocus
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Sponsoring Units: DNP GHP Chair: Renee Fatemi, University of Kentucky Room: Roosevelt 5 |
Sunday, January 29, 2017 1:30PM - 2:06PM |
K13.00001: Beyond Collinear Factorization Invited Speaker: Duff Neill Collinear factorization is the basis of many collider observables, and is one of the most highly tested bedrocks of QCD. And yet, it reveals a very limited picture of the nucleon, and the internal dynamics of the partons bound within. I will attempt to elucidate what observables do not fall into a naive collinear factorization framework, what sorts of pictures that have been proposed to replace it in these observables, and what one can learn about the nucleon. Time permitting, I will cover new developments in Soft Collinear Effective Field Theory that allow one to discuss and calculate both collinear factorization and spectator interactions on a first principles basis, hopefully paving the way to investigate the whole coherent structure of the nucleon, not just a single lucky parton involved in the hard interaction. [Preview Abstract] |
Sunday, January 29, 2017 2:06PM - 2:18PM |
K13.00002: Transverse momentum at work in high-energy scattering experiments Andrea Signori I will review some aspects of the definition and the phenomenology of Transverse-Momentum-Dependent distributions (TMDs) which are potentially interesting for the physics program at several current and future experimental facilities. First of all, I will review the definition of quark, gluon and Wilson loop TMDs based on gauge invariant hadronic matrix elements. Looking at the phenomenology of quarks, I will address the flavor dependence of the intrinsic transverse momentum in unpolarized TMDs, focusing on its extraction from Semi-Inclusive Deep-Inelastic Scattering. I will also present an estimate of its impact on the transverse momentum spectrum of W and Z bosons produced in unpolarized hadronic collisions and on the determination of the W boson mass. Moreover, the combined effect of the flavor dependence and the evolution of TMDs with the energy scale will be discussed for electron-positron annihilation. Concerning gluons, I will present from an effective theory point of view the TMD factorization theorem for the transverse momentum spectrum of pseudoscalar quarkonium produced in hadronic collisions. Relying on this, I will discuss the possibility of extracting precise information on (un)polarized gluon TMDs at a future Fixed Target Experiment at the LHC (AFTER@LHC). [Preview Abstract] |
Sunday, January 29, 2017 2:18PM - 2:30PM |
K13.00003: Transverse momentum distribution of hadrons within a jet Alexei Prokudin, Zhongbo Kang We consider the transverse momentum distribution of hadrons within a fully reconstructed jet. Within the framework of Soft Collinear Effective Theory (SCET), we demonstrate how such a distribution for inclusive jet production in proton-proton collisions can be expressed in a transverse momentum dependent (TMD) factorization formalism. We show the phenomenological application of such a formalism, for both unpolarized and polarized collisions (e.g., Collins azimuthal asymmetry), which has been measured at both RHIC and/or LHC. [Preview Abstract] |
Sunday, January 29, 2017 2:30PM - 2:42PM |
K13.00004: Helicity Evolution at Small x Matthew Sievert, Yuri Kovchegov, Daniel Pitonyak We construct small-$x$ evolution equations which can be used to calculate quark and anti-quark helicity TMDs and PDFs, along with the $g_1$ structure function. These evolution equations resum powers of $\as \, \ln^2 (1/x)$ in the polarization-dependent evolution along with the powers of $\as \, \ln (1/x)$ in the unpolarized evolution which includes saturation effects. The equations are written in an operator form in terms of polarization-dependent Wilson line-like operators. While the equations do not close in general, they become closed and self-contained systems of non-linear equations in the large-$N_c$ and large-$N_c \, \& \, N_f$ limits. After solving the large-$N_c$ equations numerically we obtain the following small-$x$ asymptotics for the flavor-singlet $g_1$ structure function along with quarks hPDFs and helicity TMDs (in absence of saturation effects): $g_1^S (x, Q^2) \sim \Delta q^S (x, Q^2) \sim g_{1L}^S (x, k_T^2) \sim \left( \frac{1}{x} \right)^{\alpha_{h}} \approx \left( \frac{1}{x} \right)^{2.31 \: {\sqrt{\frac{\alpha_s N_c}{2 \pi}}}}.$ \notag We also give an estimate of how much of the proton's spin may be at small $x$ and what impact this has on the so-called ``spin crisis.'' [Preview Abstract] |
Sunday, January 29, 2017 2:42PM - 2:54PM |
K13.00005: Searching for factorization-breaking effects via two-particle correlation measurements in hadronic collisions Christine Aidala Over the last decade and a half, studies initially focused on spin-momentum correlations in the proton have brought to the fore several deep, fundamental issues within QCD that come to light when nonperturbative transverse momenta are treated in hard scattering processes.~ Two-particle correlation measurements in proton-proton collisions provide sensitivity to nonperturbative transverse momentum effects and offer a means of searching for predicted factorization breaking in such processes. This factorization breaking leads to quantum correlations of partons across QCD bound states. Recent experimental measurements and their implications will be discussed. [Preview Abstract] |
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