arXiv subjects

Ankita Budhraja

Publications and source records attributed to Ankita Budhraja.

14 recordsLinked to original sources

arXiv2026

Higher-point Energy Correlators: Factorization in the Back-to-Back Limit & Non-perturbative Effects

N-point energy correlators are powerful observables for studying strong interactions, with applications ranging from extractions of the strong coupling $α_s$ to probes of jet modification in heavy-ion collisions and determination of the top-quark mass. Their practical use has, however, been limited by the complicated phase space for large N. Using a recently introduced parametrization that simplifies this structure, we study projected N-point correlators in two regimes: factorization in the back-to-back limit and leading non-perturbative effects in the collinear limit. While results in the back-to-back regime were previously limited to the energy-energy correlator, our approach allows us to derive the factorization theorem for arbitrary N. We compute the new ingredient, a one-loop jet function, needed for the next-to-next-to-leading-logarithmic resummation, which enables future $α_s$ extractions with complementary systematics. We further determine the analytic structure of leading non-perturbative power corrections for arbitrary N, including their dependence on the center-of-mass energy Q, the value of N, and the angular scale $x$. We present the first results for non-integer N<1, finding that the classical scaling in $x$ acquires an N-dependent modification, and that a new non-perturbative matrix element $\tildeΩ^{[N]}$ appears. In a certain approximation, $\tildeΩ^{[N]}$ can be related to the standard parameter $Ω_1$ relevant for N>1. Our analytic predictions are tested against the hadronization model in Pythia, finding good agreement. The results presented in this paper demonstrate the significant advancements enabled through our new parametrization of energy correlators.

hep-ph↗

arXiv2026

Using $γ$+jets to quantify medium-induced jet broadening in heavy-ion collisions

The structure of jets produced in high-energy nucleus-nucleus collisions carries information on parton energy loss and interaction in the quark-gluon plasma. This parton energy loss results in migration of jets in terms of transverse momentum, leading to a selection bias in inclusive jet measurements. Using the JEWEL event generator, we investigate a strategy to reduce selection bias and access medium-induced jet broadening, in an experimentally viable way. As a baseline, we first consider large-R $γ$+jet events, with little selection bias, which show a clear signal of medium-induced broadening in the jet girth. However, large-R is experimentally inaccessible due to the large underlying event fluctuations in heavy-ion collisions, so we re-cluster a collection of small-radius ($r_{\rm sub}$ = 0.2) jets as a proxy for the large-radius (R = 1.2) jet, which we refer to as a trimmed jet. We quantify to what extent trimmed jets recover signals of jet broadening and investigate its dependence on the subjet cone size and the minimum transverse momentum. We study the internal structure of the subjets to expose the dependence of jet quenching on different subjet configurations, finding a strong narrowing of PbPb jets for the 1-subjet configurations, and a visible signature of medium-induced broadening for sub-leading subjets. The jet radial profile reveals that contributions from medium-induced broadening are distinct from radiation in pp collisions. These contributions are not easily recovered using our trimming procedure, but are substantially enhanced in single-subjet configurations when considering the profile \emph{beyond} the subjet radius. This provides guidance for future experimental studies of jet-medium interactions using $γ$+jet in heavy-ion collisions.

hep-ph↗

arXiv2026

Exploiting $ν$-dependence of projected energy correlators in HICs

We extend the recently derived factorization formula for energy-energy correlators to study the analytic structure of general $ν$-point projected energy correlators in heavy ion collisions. The $ν$-point projected energy correlators (or, $ν$-correlators) are an analytically continued family of the integer $N$-point projected energy correlators, which probe correlations between $N$ final-state particles. By tracking the largest separation ($χ$) between the $N$ particles, in vacuum, their structure is closely related to the DGLAP splitting functions and exhibits a classical scaling behavior $\sim 1/χ$ which is modified by resummation through the anomalous dimensions. We show that, in a thermal medium, the $ν$-correlators display non-trivial angular scaling already at the leading order in perturbation theory. We find that for non-integer values, particularly $ν<1$, medium-induced jet function is enhanced compared to $ν>1$. This is particularly manifested in the ratios of $ν$-correlators with respect to the two-point energy correlator which encode an intrinsic angular information for $ν<1$ when compared to large $ν$ values. Moreover, for small-$ν$ values, the $ν$-correlators appear to saturate at $ν=0.01$. We further confirm our leading-order numerical computations against simulated events from JEWEL for the parton level production cross-section. Finally, we qualitatively discuss the effect of BFKL resummation for various values of $ν$.

hep-ph↗

arXiv2025

Medium modifications to jet angularities using SCET with Glauber gluons

We perform a comprehensive analysis of medium modifications on ungroomed jet angularities, $τ_a$, within the framework of Soft-Collinear Effective Theory with Glauber gluons (SCET$_{\rm G}$). Angularities are a one-parameter family of jet substructure observables with angularity exponent $a < 2$ for infrared safety. Variation of the angularity exponent allows one to modify the relative weighting of the collinear-to-soft radiations in the jet, thereby giving access to different moments of the jet transverse momentum spectrum. In this article, we focus on $a<1$ and provide detailed results for $a=-1, 0$, and $0.5$. Within SCET$_{\rm G}$, the interactions between jet and medium constituents are mediated by off-shell Glauber gluons generated from the color sources in the medium. While medium modifications are incorporated into the jet function via the use of medium-induced splitting functions, the soft function remains unmodified for $a<1$. For all values of $a$, we find that compared to jets in vacuum, the medium-modified distributions are shifted towards smaller values of jet angularity and have a steeper fall. This redistribution of the ungroomed angularity spectrum is more apparent for a jet with a larger cone size and for higher values of $a$. We also present results for the medium sensitivity towards $p_T$ of the jet and for a jet initiated in a less central event ($10-30\%$ centrality). Finally, we provide the ratios of nucleus-nucleus and proton-proton differential angularity distributions for different angularity exponents, and for two values of the jet radius parameter.

hep-ph↗

arXiv2025

New Angles on Energy Correlators

Energy correlators have recently come to the forefront of jet substructure studies at colliders due to their remarkable properties: they naturally separate physics at different scales, are robust to contamination from soft radiation, and offer a direct connection with quantum field theory. The current parametrization used for energy correlators, however, is based on redundant pairwise angles with complex phase space restrictions. In this Letter, we introduce a new parametrization of energy correlators that features a simpler phase space structure and preserves information about the orientation of jet constituents. Further, our parametrization drastically reduces the computational cost to compute energy correlators on experimental data; whereas the time to compute a traditional projected $N$-point energy correlator scales as $M^N/N!$ on a jet with $M$ particles, our new parametrization achieves a scaling of $M^2 \log M$, remarkably independently of N. Even for N=3, this improved scaling is particularly important for studies of heavy ion collisions, and higher values of $N$ will enable new qualitative understanding of gauge theories. Theoretical calculations for our new energy correlators differ from those of traditional parametrizations only at next-to-next-to-leading logarithmic accuracy and beyond, and we expect that our simpler phase space structure will simplify those calculations. We also discuss how to extend our parametrization to resolved $N$-point energy correlators that encode angular distances between greater numbers of particles, yielding intuitive visualizations of jet substructure that are qualitatively different for different jet samples. We propose two possible generalizations for probing multi-prong jets and testing jet scaling behavior.

hep-ph↗

arXiv2025

FastEEC: Fast Evaluation of N-point Energy Correlators

Energy correlators characterize the asymptotic energy flow in scattering events produced at colliders, from which the microscopic physics of the scattering can be deduced. This view of collisions is akin to analyses of the Cosmic Microwave Background, and a range of promising phenomenological applications of energy correlators have been identified, including the study of hadronization, the deadcone effect, measuring $α_s$ and the top quark mass. While $N$-point energy correlators are interesting to study for larger values of $N$, their evaluation is computationally intensive, scaling like $M^N/N!$, where $M$ is the number of particles. In this Letter, we develop a fast, approximate method for their evaluation exploiting that correlations at a given angular scale are insensitive to effects at other (widely-separated) scales. This implies that the energy correlator can be computed on (sub)jets, effectively reducing M. Furthermore, we utilize a dynamical (sub)jet radius that allows us to obtain reliable results without restricting the angular scales being probed. For concreteness we focus on the projected energy correlator, which projects onto the largest separation between the $N$ directions. E.g.~for $N=7$ we find a speed up of up to four orders of magnitude, depending on the desired accuracy. We also consider the possibility of raising the energy to a power higher than one in the energy correlator, which has been proposed to reduce soft sensitivity, and further cuts back the required computation time. These higher-power correlators are not collinear safe, but as a byproduct our approach suggests a natural method to regularize them, such that they can be described using perturbation theory. This letter is accompanied by a public code that implements our method.

hep-ph↗

arXiv2025

$ν$-point energy correletors with FastEEC: small-$x$ physics from LHC jets

In recent years, energy correlators have emerged as a powerful tool for studying jet substructure, with promising applications such as probing the hadronization transition, analyzing the quark-gluon plasma, and improving the precision of top quark mass measurements. The projected $N$-point correlator measures correlations between $N$ final-state particles by tracking the largest separation between them, showing a scaling behavior related to DGLAP splitting functions. These correlators can be analytically continued in $N$, commonly referred to as $ν$-correlators, allowing access to non-integer moments of the splitting functions. Of particular interest is the $ν\to 0$ limit, where the small momentum fraction behavior of the splitting functions requires resummation. Originally, the computational complexity of evaluating $ν$-correlators for $M$ particles scaled as $2^{2M}$, making it impractical for real-world analyses. However, by using recursion, we reduce this to $M 2^M$, and through the FastEEC method of dynamically resolving subjets, $M$ is replaced by the number of subjets. This breakthrough enables, for the first time, the computation of $ν$-correlators for LHC data. In practice, limiting the number of subjets to 16 is sufficient to achieve percent-level precision, which we validate using known integer-$ν$ results and convergence tests for non-integer $ν$. We have implemented this in an update to FastEEC and conducted an initial study of power-law scaling in the perturbative regime as a function of $ν$, using CMS Open Data on jets. The results agree with DGLAP evolution, except at small $ν$, where the anomalous dimension saturates to a value that matches the BFKL anomalous dimension.

hep-ph↗

arXiv2024

Jet observables in heavy ion collisions : a white paper

This paper presents an overview of a survey of jet substructure observables used to study modifications of jets induced by interaction with a Quark Gluon Plasma. We further outline ideas that were presented and discussed at the \textit{New jet quenching tools to explore equilibrium and non-equilibrium dynamics in heavy-ion collisions} workshop, which was held in February 2024 at the ECT$^{*}$ in Trento, Italy. The goal of this white paper is to provide a brief report on the study of jet quenching observables earlier conducted and to present new ideas that could be relevant for future explorations.

hep-ph↗

arXiv2024

Leptophilic ALPs with TWIST data for polarized muon decays

We study the production of axion-like particles (ALPs) in association with electrons and neutrinos in the muon decay process. For this purpose, we compute the decay width of the muon to a four-body channel using a $d=7$ effective operator that couples the ALP to the Standard model fermions, namely leptons and neutrinos. Assuming a dominant coupling of the ALP to the dark sector, we only consider ALP decays to invisible final states. To obtain constraints on our model using the existing measurements, we leverage data from the TRIUMF Weak Interaction Symmetry Test (TWIST) experiment and obtain bounds on the ALP-lepton coupling for masses in the range of $0 < m_ϕ < m_μ/4$, as allowed by kinematics. Using the precision of current TWIST measurements, we obtain an order of magnitude estimation necessary for future searches to further constrain the parameter space for such a setup. Furthermore, we find that keeping realistic considerations, the new physics contribution can possibly be enhanced even with a minimalistic modification to the fiducial area used in the experiment potentially allowing for stringer constraints. At the end, in an attempt to relax the assumption that ALP decays to invisible only, we also investigate its stability and find potential longevity within collider environments for the mass range considered in this study.

hep-ph↗

arXiv2023

Effect of magnetic field on jet transport coefficient $\hat{q}$

We report the estimation of jet transport coefficient, $\hat{q}$ for quark- and gluon-initiated jets using a simple quasi-particle model in absence and presence of magnetic field. This model introduces a temperature and magnetic field-dependent degeneracy factor of partons, which is tuned by fitting the entropy density of lattice quantum chromodynamics data. At a finite magnetic field, $\hat{q}$ for quark jets splits into parallel and perpendicular components whose magnetic field dependence comes from two sources: the field-dependent degeneracy factor and the phase space part guided from the shear viscosity to entropy density ratio. Due to the electrically neutral nature of gluons, the estimation of $\hat{q}$ for gluon jets is affected only by the field-dependent degeneracy factor. In presence of a finite magnetic field, we find a significant enhancement in $\hat{q}$ for both quark- and gluon-initiated jets at low temperature, which gradually decreases towards high temperature. We compare the obtained results with the earlier calculations based on the anti-de Sitter/conformal field theory correspondence, and a qualitatively similar trend is observed. The change in $\hat{q}$ in presence of magnetic field is, however, quantitatively different for quark- and gluon-initiated jets. This is an interesting observation which can be explored experimentally to verify the effect of magnetic field on $\hat{q}$.

hep-ph↗

arXiv2023

A twisted tale of the transverse-mass tail

We propose a tantalizing possibility that misinterpretation of the reconstructed missing momentum may have yielded the observed discrepancies among measurements of the $W$-mass in different collider experiments. We introduce a proof-of-principle scenario characterized by a new physics particle, which can be produced associated with the $W$-boson in hadron collisions and contributes to the net missing momentum observed in a detector. We show that these exotic events pass the selection criteria imposed by various collaborations at reasonably high rates. Consequently, in the presence of even a handful of these events, a fit based on the ansatz that the missing momentum is primarily due to neutrinos (as it happens in the Standard Model), yields a $W$-boson mass that differs from its true value. Moreover, the best fit mass depends on the nature of the collider and the center-of-mass energy of collisions. We construct a barebones model that demonstrates this possibility quantitatively while satisfying current constraints. Interestingly, we find that the nature of the new physics particle and its interactions appear as a variation of the physics of Axion-like particles after a field redefinition.

hep-ph↗

arXiv2020

Heavy Particle Jet Identification with Zest

We introduce a new jet observable {\em zest} defined on exclusively constructed jets and study its potential to discriminate jets originated from Standard Model heavy particles like $W,~Z$ bosons and top quark from gluon initiated jets. Zest exhibits properties such as boost invariance, stability against global color exchange among partons, and inclusion or exclusion of a few soft particles in the jet. We also observe that for gluon jets, zest distribution is mostly insensitive to the jet mass. These properties make zest a suitable candidate for vetoing gluon jets at the colliders. Zest when used in conjunction with other substructure observables that are uncorrelated to it can further improve gluon jet veto. We generalize zest and show that in one limit it is synonymous to particle multiplicity and in the other limit, it projects only the leading particle. Optimization on the parameter of generalized zest further improves the discrimination ability of the observable. We find that for the top quark-initiated jets, the discrimination provided by generalized zest is in close comparison with a class of machine learning-based top taggers. We propose that studying other non-linear infrared and collinear unsafe observables may help in unveiling the hidden physics of machine learning-based observables.

hep-ph↗

arXiv2020

One-loop Angularity Distributions with Recoil using Soft-Collinear Effective Theory

Angularities are event shapes whose sensitivity to the splitting angle of a collinear emission is controlled by a continuous parameter $b$, with $ -1 < b < \infty$. When measured with respect to the thrust axis, this class of QCD observables includes thrust ($b=1$) and jet broadening ($b=0$), the former being insensitive to the recoil of soft against collinear radiation, while the latter being maximally sensitive to it. Presently available analytic results for angularity distributions with $b \neq 0$ can be applied only close to the thrust limit since recoil effects have so far been neglected. As a first step to establish a comprehensive theoretical framework based on Soft-Collinear Effective Theory valid for all recoil-sensitive angularities, we compute for the first time angularity distributions at one-loop order in $α_s$ for all values of $b$ taking into account recoil effects. In the differential cross section, these amount to novel sub-leading singular contributions and/or power corrections, where the former are characterized by fractional powers of the angularity and contribute appreciably close to the peak region, also for $b \gtrsim 0.5$. Our calculations are checked against various limits known in the literature and agree with the numerical output of the Event2 generator.

hep-ph↗

arXiv2017

Jet Identification with Zest

We present a new observable zest and demonstrate its potential to differentiate between jets originated by gluons, top quark and vector bosons. Zest has salient properties such as boost invariance, stability against global color flow of partons and inclusion or exclusion of a few soft particles to the jet. For a gluon jet, zest distribution is also insensitive to the jet mass. We show that when zest is used in conjunction with other observables, it can yield high gluon rejection while retaining high signal sample.

hep-ph↗