12/13/2019

Transverse momentum dependent soft function and PDF from LaMET on lattice

Yizhuang Liu, T.D. Lee Institute
12:00 PM Friday, Knudsen 5-137

In the talk I will present our recent work on lattice TMDPDF and soft factor. I will show that the TMD soft function (or soft factor) in the off-light-cone scheme is equivalent to an equal-time form factor, thus can be simulated on lattice from Euclidean HQET or from large momentum light-meson form factor. This extends the large momentum effective theory (LaMET) to the case with two light-cone directions. With the help of the off-light-cone soft factor and lattice calculable quasi-TMDPDF one can match to physically important light-cone TMDPDF using perturbation theory. I will also present certain interesting relations between soft-factors and rapidity-regularization-independent factorization scheme directly in terms of quasi-TMDPDF.

11/13/2019

Initial Conserved Charges in Nuclear Geometry

Mauricio Martinez Guerrero, North Carolina State University
2:00 PM Wednesday, Knudsen 4-134

In the modeling of the initial conditions for high energy nuclear collisions, it is usually assumed that the energy density is composed almost entirely of gluon fields. However, quarks, which constitute a minority of the overall energy density, carry conserved charges such as baryon number and electric charge which are sensitive to entirely different transport properties of the QGP. We present a new model for reconstructing the initial distribution of quarks and antiquarks in a heavy ion collision by sampling the (g-->qqbar) splitting function over the initial energy density. In this way, we provide a new numerical tool which can be used to supplement models for the initial energy density with the associated conserved charges. As a result, we find a strong flavor dependence of the initial geometries of different quarks, as characterized by their initial eccentricities. Importantly, we find that the strange quark geometry differs significantly from the geometry of the bulk energy density in an event, reflecting the geometry of the hot spots rather than the geometry of the bulk. This new tool for the initial conditions, when coupled to a charge-conserving viscous hydrodynamics code, will open the door to studying a wealth of new charge and flavor dependent correlations and transport parameters of the QGP.

10/23/2019

XENON1T and beyond: the search for the heavy and light dark matter Particles

Kaixuan Ni, UCSD
12:00 PM Wednesday, Knudsen 4-134

Large underground detectors made significant progresses in recent years to push the sensitivity for dark matter detection. In particular, the XENON1T experiment with the world’s first ton-scale liquid xenon time projection chamber, located at Gran Sasso Underground Laboratory in Italy, is leading the frontier of heavy dark matter searches. Recently, the experiment also reported new constraints for light (sub-GeV) dark matter interactions with ordinary matter. In this talk, I will review these recent results and also present new efforts, including XENONnT, LBECA, DARWIN experiments that will continue to search for heavy and light dark matter particles with unprecedented sensitivity in the next decade.

8/14/2019

The inner life of protons: QCD at work from the LHC to IceCube

Juan Rojo, VU University
12:00 PM Wednesday, Knudsen 4-134

The determination of the partonic structure of the proton, quantified by the Parton Distribution Functions (PDFs), is a central component of the physics program at the Large Hadron Collider (LHC). In this talk, I review our current understanding of the quark and gluon structure of the proton, which emphasis for the implications for LHC phenomenology and searches for new physics. I will then also discuss other recent perspectives of the nucleon structure for applications in other fields, in particular their impact in high-energy neutrino telescopes and for the characterization of the quark-gluon plasma in heavy ion collisions.

7/15/2019

Jets, TMDs and resummation

Wounter Waalewijn, University of Amsterdam & Nikhef
12:00 PM Monday, Knudsen 4-134

I will discuss (i) my recent calculation of the jet shape at NLL’, (ii) a new method I proposed to extract transverse momentum dependent distributions parton distributions, using jets in semi-inclusive deep-inelastic scattering (iii) the resummation of multiple logarithms, considering beam thrust and qT for the Drell-Yan process as a concrete example.

6/03/2019

Precision phenomenology at hadron colliders

Xiaohui Liu, Beijing Normal University
12:00 PM Monday, Knudsen 4-134

In the past few years, tremendous progress has been made in pushing the theoretical accuracy for understanding the processes at the hadron colliders out of the first principles. In this talk, I will give a short review on the collider physics precision frontier. Selected topics related to the Higgs, the electroweak gauge bosons and the jets will be presented to highlight the current status of the precision predictions for the collider phenomenology.

05/03/2019

Precision Jet Substructure with the ATLAS Detector at 13 TeV

Benjamin Nachman, Lawrence Berkeley National Laboratory
12:00 PM Friday, Knudsen 4-134

We are in the midst of a QCD renaissance, with significant advances in both experimental and theoretical studies of jet substructure. I will discuss recent developments from the ATLAS experiment, including the first measurement of a jet substructure quantity at a hadron collider to be compared with next-to-next-to-leading-logarithm calculations as well as a recent measurement of gluon splitting inside large-radius jets. These measurements are part of an exciting program to measure fundamental parameters of the Standard Model, search for new particles, study quantum properties of inherently interesting emergent phenomena, and tune Monte Carlo event generators. I will conclude by briefly discussing future directions at the interface of jet physics and machine learning and quantum information.

02/08/2019

Are there higher order corrections to Chiral Magnetic (vortical) Effects?

Defu Hou, Central China Normal University, China
12:00 PM Friday, Knudsen 4-134

Anomaly induced transport phenomena in systems with chiral fermions have attracted wide interests ranging from high energy physics to condensed matter physics. Because of the non-renormalization theorem of chiral anomalies, it is normally expected that the chiral magnetic (vortical) currents are free from higher order corrections. In this talk, I will present our study on the radiative corrections to chiral magnetic current at both zero and nonzero temperature. Our motivation is a radiative correction to the matrix element of the anomalous Ward identity in massless QED stemming from a three-loop diagram where the two photons coming from the one-loop anomalous triangle are re-scattered. Through the interplay between the Ward identity and the infrared subtlety of the fermion loop integral, we obtain the 3-loop corrections to the chiral magnetic current at zero temperature. The correction does not invalidate the Adler-Bardeen theorem but will contribute to the chiral magnetic current of massless fermions at zero temperature. At a nonzero temperature, the infrared subtlety disappeared in a static magnetic field and the three-loop diagram does not contribute to the chiral magnetic current any more. The generalization to all orders of the massless QED and the QCD corrections are discussed. We will also present possible higher-order corrections to the chiral vortical effect.

01/28/2019 - 01/30/2019

UCLA 2019 Santa Fe Jets and Heavy Flavor Workshop
Location: IDRE Portal, Math Sciences Building 5628

01/07/2019

Holographic real-time dynamics near a critical point

Maximilian Attems, Universidade de Santiago de Compostela, Spain
11:00 AM Monday, Knudsen 4-134

Ever since the discovery of the quark-gluon plasma (QGP) the location of the critical point in the QCD phase diagram - the end point of the first-order transition between hadron matter and QGP - has been a main research goal for heavy-ion collision experiments. We use the gauge/gravity duality to study as first a four-dimensional, strongly-coupled gauge theory with a first-order thermal phase transition. In the dual gauge theory we calculate the evolution and saturation of the spinodal instability. We uncover a new surprising example of the applicability of hydrodynamics to systems with large gradients. We discover with shockwave collisions that in theories with a first-order phase transition, a long-lived, quasi-static state may be formed. Moreover, we show the Mueller-Israel-Stewart-type formulation of hydrodynamics to fail to describe pressures near a critical point.