Event: 2024 Fall Meeting of the APS Division of Nuclear Physics

Venue: Hilton Park Plaza, Boston, USA

Time: Tuesday, October 8 at 2:24-2:36pm ET

We begin by using Hybrid Model calculations to reproduce experimental results published by ATLAS in 2023 on R_AA for R = 1.0 jets in Pb+Pb collisions. These jets are identified via first reconstructing anti-kt R = 0.2 subjets and then reclustering them. Following ATLAS, we investigate how R_AA for these large-radius jets depends on the angle between the two subjets involved in the final clustering step of the R = 1.0 jet. We also study the dependence of R_AA for these jets on the resolution length of QGP, defined such that the medium can only resolve partons in the jet shower that are separated by more than this length scale. Our investigation suggests that measurements like those pioneered by ATLAS can constrain the resolution length of QGP.

We make further use of this setup by analyzing the response of the medium to the passage of large-radius R = 2.0 jets containing two R = 0.2 subjets, produced in gamma-jet events, and identified as above. We introduce novel jet-shape observables that allow us to visualize the angular shape of the soft hadrons originating from the wakes that wide jets with two skinny subjets excite in the droplet of QGP, as a function of the angular separation between the subjets. We find that even when the two hard subjets are 0.8 to 1.0 radians apart, a single broad wake is produced. When the two subjets are even farther apart the presence of two sub-wakes is revealed. In our Monte Carlo study, the new observables that we introduce allow us to visualize how jet structure shapes jet wakes unambiguously. We close by showing that similar clarity may be achieved experimentally by measuring the jet shape observables we have introduced using only those hadrons with low transverse momenta.

*This work was supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics grant DE-SC0011090. The work of ASK was supported by a Euretta J. Kellett Fellowship, awarded by Columbia University.

Presentation Info: https://meetings.aps.org/Meeting/DNP24/Session/F04.3

Event: Jet Modification and Hard-Soft Correlations [Soft Jet 2024]

Venue: University of Tokyo, Tokyo, Japan

Time: Saturday, September 28 at 2:30-2:50pm JT

We begin by using Hybrid Model calculations to reproduce experimental results published by ATLAS in 2023 on R_AA for R = 1.0 jets in Pb+Pb collisions. These jets are identified via first reconstructing anti-kt R = 0.2 subjets and then reclustering them. Following ATLAS, we investigate how R_AA for these large-radius jets depends on the angle between the two subjets involved in the final clustering step of the R = 1.0 jet. We also study the dependence of R_AA for these jets on the resolution length of QGP, which suggests that measurements like those pioneered by ATLAS can constrain this property of QGP.

We also use this setup to analyze the response of the medium to the passage of large-radius R = 1.0 jets containing two R = 0.2 subjets, produced in gamma-jet events, and identified as above. We introduce novel jet-shape observables that allow us to visualize the angular shape of the soft hadrons originating from wakes that wide jets with two skinny subjets excite in the droplet of QGP, as a function of the angular separation between the subjets. We find that even when two hard subjets are 0.8 to 1.0 radians apart, a single broad wake is produced. When the two subjets are even farther apart, the presence of two sub-wakes is revealed. We show that the way in which the structure of hard jets shapes their soft wakes can be visualized with similar clarity in experiments by measuring the observables we have introduced using only soft hadrons with low transverse momenta.

Finally, we study the effects of Rutherford-like scattering (aka elastic or Moliere scattering) on two-point energy correlators within the context of the Hybrid Model. We compare Hyrbid Model calculations to recent CMS measurements of the two-point energy correlator in Pb+Pb collisions. We demonstrate that our Hybrid Model calculations agree with the CMS measurements only when elastically scattered particles in the medium produce their own wakes.

Slides: https://indico.cern.ch/event/1403965/contributions/6057581/

Event: 12th International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions [Hard Probes 2024]

Venue: Dejima Messe, Nagasaki, Japan

Time: Wednesday September 25, at 9:40-10:00am JT

We begin by using Hybrid Model calculations to reproduce experimental results published by ATLAS in 2023 on R_AA for R = 1.0 jets in Pb+Pb collisions. These jets are identified via first reconstructing anti-kt R = 0.2 subjets and then reclustering them. Following ATLAS, we investigate how R_AA for these large-radius jets depends on the angle between the two subjets involved in the final clustering step of the R = 1.0 jet. We also study the dependence of R_AA for these jets on the resolution length of QGP, which suggests that measurements like those pioneered by ATLAS can constrain this property of QGP.

We make further use of this setup by analyzing the response of the medium to the passage of large-radius R = 2.0 jets containing two R = 0.2 subjets, produced in gamma-jet events, and identified as above. We introduce novel jet-shape observables that allow us to visualize the angular shape of the soft hadrons originating from the wakes that wide jets with two skinny subjets excite in the droplet of QGP, as a function of the angular separation between the subjets. We find that even when the two hard subjets are 0.8 to 1.0 radians apart, a single broad wake is produced. When the two subjets are even farther apart the presence of two sub-wakes is revealed. We show that the way in which jet structure shapes jet wakes can be visualized with similar clarity in experiments by measuring the observables we have introduced using only those hadrons with low transverse momenta.

Slides: https://indico.cern.ch/event/1339555/contributions/6040802/

Event: CTP Graduate Student Seminar

Venue: Cosman Room, Center for Theoretical Physics, MIT

Time: Friday, September 13 at 12:30-1:30pm ET

Microseconds after the Big Bang, our universe was filled with a hot, strongly coupled, liquid phase of QCD-matter called Quark Gluon Plasma (QGP). Physicists are able to recreate droplets of this primordial liquid in high energy collisions of large nuclei. Such “heavy ion collisions” also produce highly energetic sprays of particles called “jets” that traverse and interact with the expanding droplet of QGP. Since these interactions with the plasma modify the jets produced in heavy ion collisions, such jets allow us to probe the properties of these tiny droplets of Big Bang matter. One such modification includes a loss in the total energy of a jet as it traverses the QGP produced in a collision. This lost energy is deposited into the plasma, sourcing wakes. The wakes left by jets that plow through droplets of QGP are yet to be unambiguously observed in experiments.

In this talk, I describe my recent efforts to image and characterize the structure of such jets and the wakes they produce. My work employs a Monte Carlo model of heavy ion collisions that incorporates holographic calculations of energy loss experienced by light quarks and gluons as they traverse the strongly coupled plasma. I show that the wakes produced by jets in this model can be imaged using two observables of interest: correlation functions of the energies of final-state hadrons produced in heavy ion collisions (energy correlators) and the angular distributions of the energies of those final-state hadrons with low-momenta (jet shapes). Finally, I introduce a novel modification to the latter observable that enables us to characterize how the structure of jets shapes the structure of their wakes. The theoretical calculations I perform may be realized in experiments, thereby illuminating an avenue to image and characterize the structure of jet-induced wakes in nature.

Slides: https://columbia.edu/~ask2262/Talks/2024/kudinoor-mit-ctp-seminar-2024-09-13.pdf

Event: Energy Correlators at the Collider Frontier [Workshop]

Venue: Mainz Institute for Theoretical Physics, Johannes Gutenberg-Universität Mainz

Time: Wednesday, July 10 at 12:00-12:30 PM CET

This talk, which is the fourth in a coordinated sequence of four talks, will be an analysis of coordinate choices and the effects of jet wakes on three-point energy correlators. Using energy-energy-energy correlators to “image” the wakes that jets excite in the hydrodynamic fluid produced in a heavy ion collision is the goal of the work that is described in this four-talk series, and the Hybrid strong/weak coupling model of heavy ion collisions is a tool that will be employed in obtaining the new results presented in each talk. This is the abstract for the whole sequence of four talks.

Recently, the projected N-point energy correlators (ENCs) have seen a resurgence of interest for hadronic collisions at RHIC and the LHC to probe vacuum QCD.  Here, we will show that the full three-point energy-energy-energy correlation (EEEC) function can be useful for studying the shape of energy flow within jets. In vacuum, it has been shown that these correlators elucidate the collinear singularity of vacuum QCD. For the first time, we will show how EEEC can uniquely characterize the energy flow originating from the jet-induced medium response in heavy-ion collisions. In heavy-ion collisions, jets formed from hard-scattered partons experience an overall energy loss and have a modified internal structure compared to vacuum jets. This is due to interactions between the energetic partons in a jet shower and the strongly coupled quark-gluon plasma (QGP). As the jet traverses the QGP, it loses momentum to the medium, momentum which becomes a wake in the droplet of QGP and subsequently becomes soft particles carrying momentum in the jet direction. A quantitative description of this “medium response” is an area of active investigation. For this study, we utilize the Hybrid Model that implements a hydrodynamical medium response via the wake. We will show that measuring three-point correlation functions offer promising experimental avenues for imaging this wake of the jet as when the three angles are well-separated the three-point correlator is dominated by the medium response. Along the way, we will introduce new coordinates for specifying the three angles that are well-suited to the case when these angles are far from collinear, as in the regime where the EEEC is dominated by particles coming from jet wakes.

Slides: https://indico.mitp.uni-mainz.de/event/358/contributions/4990/

Event: Conference on Everything

Venue: Wolfson Hall, Churchill College, Cambridge University

Time: Saturday, April 27 at 5:30-5:45 PM BST

Microseconds after the Big Bang, our universe was filled with a hot, dense, nearly-frictionless liquid phase of matter called Quark Gluon Plasma (QGP). This soup of quark and gluons is the origin of matter — including the protons and neutrons — we see around us today. In the hopes of unraveling our cosmic origin story, physicists recreate tiny droplets of QGP in nuclear collisions at incredibly high energies. In this talk, I introduce the physics that governs QGP, explain how it is studied in heavy ion (nuclear) collision experiments, and describe the theoretical techniques that I use to probe the earliest, hottest, and most liquid liquid of our universe.

Event: Part III Student Seminars in Mathematics

Venue: MR 13, Center for Mathematical Sciences, Cambridge University

Time: Saturday, March 14 at 1:00-1:50 PM BST

During relativistic heavy ion collisions a deconfined, strongly coupled, hot-QCD phase of matter called quark gluon plasma (QGP) is formed. Over the last decade, formal advancements like the AdS/CFT duality have helped shed light on the otherwise intractable strongly coupled regime of QCD phenomenology. In this talk, I describe the basics of the AdS/CFT duality and its applications to my research on the substructure of jets and their wakes in heavy ion collisions. I also demonstrate how wake-substructure depends nontrivially on the substructure of the jets from which wakes originate. Finally, I explain how this nontrivial dependence between jet and wake-substructures reveals signatures for observing jet-wakes in experiments.

Slides: https://columbia.edu/~ask2262/Talks/2024/kudinoor-cambridge-cms-2024-03-14.pdf

Event: Part III Student Seminars in Mathematics

Venue: Potter Room (MR 19), Center for Mathematical Sciences, Cambridge University

Time: Thursday, November 30 at 1:00-1:40 PM BST

During relativistic heavy ion collisions a deconfined, strongly coupled, hot-QCD phase of matter called quark gluon plasma (QGP) is formed. Over the last decade, formal advancements like the AdS/CFT duality have helped shed light on the otherwise intractable strongly coupled regime of QCD phenomenology. In this introductory talk, I describe the basics of the AdS/CFT duality and its applications to heavy ion collisions in the context of my research on the hybrid strong/weak coupling model of QGP physics.

Event: 2-Minute Thesis Conference

Venue: Wolfson Hall, Churchill College, Cambridge University

Time: Tuesday, November 21 at 5:30-6:30 PM BST

Microseconds after the Big Bang, before atoms even formed, our universe was filled with a frictionless liquid of subatomic particles called quarks and gluons. Today we study this liquid, called a quark gluon plasma, in nuclear collisions at incredibly high energies.

This talk is accessible to the general public.