Optimizing Reconstruction Efficie ncy with Small -R R 0.4 and Large -R R 1.0 Jets Sophie Kadan1 Evelyn Thomson2

2025-04-29 0 0 1.07MB 26 页 10玖币

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Optimizing → Reconstruction Efficiency with Small-R (R = 0.4) and Large-R (R

= 1.0) Jets

Sophie Kadan1, Evelyn Thomson2

University of Pennsylvania1,2, sokadan@sas.upenn.edu1

ABSTRACT

Many beyond the Standard Model searches by the ATLAS experiment at the CERN Large

Hadron Collider employ jets to simplify event reconstruction. Two types of jets have been

studied to optimize the selection and reconstruction of a final state with many jets

originating from four b-quarks. A large-R (R = 1.0) jet combines particle shower products

into one jet that spans 2 radians, while a small-R (R = 0.4) jet gives finer-grained

information. In this talk, we consider the pair production of charginos with R-parity

violating (RPV) decays to a charged lepton and a Higgs boson, which subsequently decays

to two b quarks. In studies of Monte Carlo simulation, we found that parameters such as

the distance between Higgs bosons and the distance between b-jets were relevant in

selecting the most accurate small-R jet reconstructions. These parameters were then used

to refine small-R jet selection, increasing reconstruction efficiency across a wide range of

possible chargino masses compared to a selection using large-R jets. To extend these

findings to a model with a RPV decay directly to two b quarks and a lepton without the

intermediate Higgs boson, machine learning techniques are now being explored.

TABLE OF CONTENTS

1 Introduction....……………………………………..…………………………..……… 1

1.1 The Standard Model (SM) ………………………………………………...….1

1.2 Beyond the Standard Model (BSM)……………………………...…...………1

1.3 Recent Searches for BSM Predictions at the LHC ………………………….2

1.4 Using Jets to Improve Future Search Sensitivity…………..…………………3

2 The ATLAS Detector…………………………………….…………………………….5

3 Simulated Samples …………………………………………………………………….6

4 Object Reconstruction …………………………………………………………...……6

4.1 Lepton Selection ………...……………………………………………………..6

4.2 Large-R Reconstruction ...…………………………………………………….6

4.3 Small-R Reconstruction ...……………………………………………………..7

4.4 Varied-R Reconstruction ...……………………………………………………7

5 Simulated Results .……………………………………………………………………..8

5.1 Higgs and Chargino Reconstruction ………………….....………………….……….10

5.2 Discrepancies in Jet Performance ……………........…………..………………12

6 Truth Sample Analysis……………………………………………………………….13

6.1 Truth Jet Performance ………………………………………………………13

6.2 Increasing Reconstruction Efficiency .………………………………………14

7 Conclusion .……………………………………………………………………………21

8 References ...…………………………………………………………………………..22

CONFLICTS OF INTEREST

On behalf of all authors, the corresponding author states that there is no conflict of interest.

1 Introduction

1.1 The Standard Model (SM)

The Standard Model (SM) of particle physics describes all known particles and their

interactions. This model predicts matter to be fundamentally composed of generations of

quarks and leptons, characterized by mass, electric charge, and spin. SM particles interact

via the exchange of gauge bosons, which act as force carriers [1, 2]. Specifically, the

strong, weak, and electromagnetic forces arise from these elementary gauge bosons—

encompassing much of physics as we know it [2].

The recent discovery of the Higgs boson has further unified the electromagnetic and

weak forces, introducing a source of elementary particle mass. Specifically, this mass is

derived via Higgs field interactions, whose strength determines fundamental properties

such as atom size and proton stability. Furthermore, interactions with the scalar Higgs field

are consistent with experimental observations: they predict that W and Z bosons carry

mass while photons and gluons remain massless. Uniting particles and their forces, the

Higgs boson discovery thus completes the Standard Model [3].

While its predicted particles have all been experimentally confirmed, the Standard

Model nonetheless has many shortcomings. For example, SM predictions do not provide a

quantum description of gravity, the fourth fundamental force [4, 5]. Likewise, the Standard

Model does not account for the low mass of the Higgs boson: termed the Hierarchy

Problem, SM predictions overestimate the Higgs mass due to its interactions with virtual

particles. Corrections must thus be made at scales where new physics is relevant [6].

1.2 Beyond the Standard Model (BSM)

To reconcile SM issues, many Beyond the Standard Model (BSM) theories have been

developed. One such theory is Supersymmetry (SUSY), which introduces a “superpartner”

for each currently known particle [4]. This theory maps particles of spin one half to those

of integer spin and vice versa, establishing a symmetry that connects fermions and bosons

[7]. Because superpartners of equal mass to their partners have not yet been discovered,

supersymmetry is presumed to be a broken symmetry. To reduce potentially incorrect

assumptions, the Minimal Supersymmetric Standard Model (MSSM) has been established

as a SUSY model that only considers the minimal number of new particles [8].

SUSY is attractive in its potential ability to solve the Hierarchy Problem via loop

corrections that its superpartners provide [5, 8]. Local SUSY also necessarily includes a

spin-2 gravition (and spin-3/2 gravitino), a fundamental particle that carries the

gravitational force. Finally, the prediction of superpartners creates viable candidates for

dark matter: when R-parity is conserved, the lightest supersymmetric particle (LSP) is

considered; when R-parity is violated, SM products of the LSP decay are studied instead.

By permitting the LSP to have electric and color charges, RPV coupling introduces new

BSM possibilities [9].

1.3 Recent Searches for BSM Predictions at the LHC

The ATLAS Collaboration searches for signatures of physics beyond the Standard

Model via the Large Hadron Collider (LHC), discussed in Chapter 2. ATLAS employs

theoretical methods to predict the contents and locations of targets in its searches. Previous

R-party-violating (RPV) searches have focused on the minimal B-L extension of the

MSSM, which allows for the further decay of the LSP [9]. In this model, interactions that

do not conserve differences in baryon and lepton number have small couplings, preventing

rapid proton decay [10].

Figure 1: Possible decays of the Wino chargino LSP. The decay in Figure 1b) has been the

focus of recent ATLAS searches.

Recent searches have focused on the decay of the Wino chargino LSP. Shown in

Figure 1, the general massive chargino state decays into three potential RPV

channels—each with final products that contain different levels of abundance and visibility

in the detector. For example, the decay in Figure 1a can only be observed in the detector as

missing energy, while the decay in Figure 1c yields quark and lepton traces that are

difficult to interpret [9]. Most easily detected is the decay in Figure 1b, which produces

many leptons from a single resonance. Recent pair production analyses have therefore

focused on this decay [10].

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Optimizing→ReconstructionEfficiencywithSmall-R(R=0.4)andLarge-R(R=1.0)JetsSophieKadan1,EvelynThomson2UniversityofPennsylvania1,2,sokadan@sas.upenn.edu1ABSTRACTManybeyondtheStandardModelsearchesbytheATLASexperimentattheCERNLargeHadronCollideremployjetstosimplifyeventreconstruction.Twotypesofjetshaveb...

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Optimizing Reconstruction Efficie ncy with Small -R R 0.4 and Large -R R 1.0 Jets Sophie Kadan1 Evelyn Thomson2

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