The production of heavy-quark (HQ) jets is a new area that addresses the mass effect of jet quenching in heavy-ion physics. This paper presents a theoretical study of HQ jet yield suppression in Pb+Pb collisions at the Large Hadron Collider (LHC) and focuses on the energy loss of HQ jets produced by different mechanisms. The $\textit{p+p}$ baseline is provided by the generator simulation of high-energy reactions of particles (SHERPA), and the jet-medium interactions are described by the SHELL transport model, which considers the elastic and inelastic partonic energy loss in the quark-gluon plasma (QGP). In $\textit{p+p}$ collisions, our numerical results indicate that the HQ jets from gluon splitting ( $ g \rightarrow Q $ -jet) are the dominant contribution at high $ p_T $ , displaying more dispersive structures than the HQ-initiated ( $ Q \rightarrow Q $ -jet). In nucleus-nucleus collisions, our calculations were consistent with the inclusive and b-jet $ R_{AA} $ recently measured by the ATLAS collaboration, revealing a remarkable manifestation of the mass effect of jet energy loss. As a result of the dispersive substructure, the $ g \rightarrow Q $ -jet loses more energy than the $ Q \rightarrow Q $ -jet in the QGP. Due to the significant contribution of $ g \rightarrow c $ -jet, the $ R_{AA} $ of $\textit{c}$-jet is comparable or even smaller than that of inclusive jet. To experimentally distinguish the $ g \rightarrow Q $ -jet and $ Q \rightarrow Q $ -jet, we propose event selection strategies based on their topological features and test their performances. By isolating the $ c \rightarrow c $ -jet, $ b \rightarrow b $ -jet, and the jets initiated by heavy quarks, we predicted that the order of their $ R_{AA} $ are in line with the mass hierarchy of energy loss. Future measurements on the $ R_{AA} $ of $ Q \rightarrow Q $ -jet and $ g \rightarrow Q $ -jet will provide a unique opportunity for testing the flavor/mass dependence of energy loss at the jet level.

China

Sa Wang

Shuang Li

Yao Li

Ben-Wei Zhang

Enke Wang

Probing the mass effect of heavy quark jets in high-energy nuclear collisions * Supported by the MajorProject of Basic and Applied Basic Research of Guangdong Province, China (2020B0301030008, 2023A1515011460), and the National Natural Science Foundation of China (11935007, 12035007, 12247127, 12375137). Sa Wang is supported by the Open Foundation of Key Laboratory of Quark and Lepton Physics (MOE) (QLPL2023P01) and the Talent Scientific Star-up Foundation of the China Three Gorges University, China (CTGU) (2024RCKJ013)

The charged Higgs boson ( $$H^\pm $$ ) with a mass below the top quark mass remains a viable possibility within the Type-I two-Higgs-doublet model under current constraints. While previous LHC searches have primarily focused on the $$H^\pm \rightarrow \tau ^\pm \nu $$ decay mode, the decay channel into an off-shell top quark and a bottom quark, $$H^\pm \rightarrow t^*b$$ , is leading or subleading for $$H^\pm $$ masses between 130 and 170 GeV. This study investigates the discovery potential of future colliders for this off-shell decay mode through pair-produced charged Higgs bosons decaying via $$H^+H^-\rightarrow t^*b\tau \nu \rightarrow bbjj\tau \nu $$ . We perform signal-to-background analyses at the HL-LHC and a prospective 100 TeV proton–proton collider, employing cut-flow strategies and the Boosted Decision Tree method. However, due to the softness of the $\textit{b}$ jets, signal significances fall below detection thresholds at these facilities. Extending our study to a multi-TeV muon collider (MuC), we demonstrate that a 3 TeV MuC achieves high signal significance, surpassing the $$5\sigma $$ threshold with an integrated luminosity of 1 ab $$^{-1}$$ and a 10% background uncertainty. Specifically, for $$M_{H^\pm } = 130$$ , 150, and 170 GeV, the significances are 13.7, 13.5, and 6.06, respectively. In contrast, a 10 TeV MuC requires 10 ab $$^{-1}$$ to achieve similar results. Our findings highlight the critical role of the MuC in probing the new signal channel $$H^\pm \rightarrow t^*b$$ , offering a promising avenue for future charged Higgs boson searches involving off-shell top quarks.

South Korea

Jinheung Kim

Soojin Lee

Prasenjit Sanyal

Jeonghyeon Song

Austria

Daohan Wang

Discovery prospects for the light charged Higgs boson decay to an off-shell top quark and a bottom quark at future high-energy colliders

In this study, we explore the phenomenological signatures associated with a light fermiophobic Higgs boson, <math><msub><mi>h</mi><mi>f</mi></msub></math>, within the type-I two-Higgs-doublet model at the HL-LHC. Our meticulous parameter scan illuminates an intriguing mass range for <math><msub><mi>m</mi><msub><mi>h</mi><mi>f</mi></msub></msub></math>, spanning <math><mo>[</mo><mn>1</mn><mo>,</mo><mn>10</mn><mo>]</mo><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>. This mass range owes its viability to substantial parameter points, largely due to the inherent challenges of detecting the soft decay products of <math><msub><mi>h</mi><mi>f</mi></msub></math> at contemporary high-energy colliders. Given that this light <math><msub><mi>h</mi><mi>f</mi></msub></math> ensures <math><mi>Br</mi><mo>(</mo><msub><mi>h</mi><mi>f</mi></msub><mo>→</mo><mi>γ</mi><mi>γ</mi><mo>)</mo><mo>≃</mo><mn>1</mn></math>, <math><mi>Br</mi><mo>(</mo><msup><mi>H</mi><mo>±</mo></msup><mo>→</mo><msub><mi>h</mi><mi>f</mi></msub><msup><mi>W</mi><mo>±</mo></msup><mo>)</mo><mo>≃</mo><mn>1</mn></math>, and <math><msub><mi>M</mi><msup><mi>H</mi><mo>±</mo></msup></msub><mo>≲</mo><mn>330</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>, we propose a golden discovery channel: <math><mi>p</mi><mi>p</mi><mo>→</mo><msub><mi>h</mi><mi>f</mi></msub><msup><mi>H</mi><mo>±</mo></msup><mo>→</mo><mi>γ</mi><mi>γ</mi><mi>γ</mi><mi>γ</mi><msup><mo>ℓ</mo><mo>±</mo></msup><mi>ν</mi></math>, where <math><msup><mo>ℓ</mo><mo>±</mo></msup></math> includes <math><msup><mi>e</mi><mo>±</mo></msup></math> and <math><msup><mi>μ</mi><mo>±</mo></msup></math>. However, a significant obstacle arises as the two photons from the <math><msub><mi>h</mi><mi>f</mi></msub></math> decay mostly merge into a single jet due to their proximity within <math><mi>Δ</mi><mi>R</mi><mo>&lt;</mo><mn>0.4</mn></math>. This results in a final state characterized by two jets, rather than four isolated photons, thus intensifying the QCD backgrounds. To tackle this, we devise a strategy within delphes to identify jets with two leading subparticles as photons, termed diphoton jets. Our thorough detector-level simulations across 18 benchmark points predominantly show signal significances exceeding the <math><mn>5</mn><mi>σ</mi></math> threshold at an integrated luminosity of <math><mn>3</mn><mtext> </mtext><mtext> </mtext><msup><mi>ab</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></math>. Furthermore, our approach facilitates accurate mass reconstructions for both <math><msub><mi>m</mi><msub><mi>h</mi><mi>f</mi></msub></msub></math> and <math><msub><mi>M</mi><msup><mi>H</mi><mo>±</mo></msup></msub></math>. Notably, in the intricate scenarios with heavy charged Higgs bosons, our application of machine learning techniques provides a significant boost in significance.

Jin-Hwan Cho

Probing light fermiophobic Higgs boson via diphoton jets at the HL-LHC

Jet tagging is a crucial classification task in high energy physics. Recently the performance of jet tagging has been significantly improved by the application of deep learning techniques. In this study, we introduce a new architecture for jet tagging: the particle dual attention transformer (P-DAT). This novel transformer architecture stands out by concurrently capturing both global and local information, while maintaining computational efficiency. Regarding the self attention mechanism, we have extended the established attention mechanism between particles to encompass the attention mechanism between particle features. The particle attention module computes particle level interactions across all the particles, while the channel attention module computes attention scores between particle features, which naturally captures jet level interactions by taking all particles into account. These two kinds of attention mechanisms can complement each other. Further, we incorporate both the pairwise particle interactions and the pairwise jet feature interactions in the attention mechanism. We demonstrate the effectiveness of the P-DAT architecture in classic top tagging and quark–gluon discrimination tasks, achieving competitive performance compared to other benchmark strategies.

Minxuan He

Quark/gluon discrimination and top tagging with dual attention transformer

Jet substructure observable basis is a systematic and powerful tool for analyzing the internal energy distribution of constituent particles within a jet. In this work, we propose a novel method to insert neural networks into jet substructure basis as a simple yet efficient interpretable IRC-safe deep learning framework to discover discriminative jet observables. The Energy Flow Polynomial (EFP) could be computed with a certain summation order, resulting in a reorganized form which exhibits hierarchical IRC-safety. Thus inserting non-linear functions after the separate summation could significantly extend the scope of IRC-safe jet substructure observables, where neural networks can come into play as an important role. Based on the structure of the simplest class of EFPs which corresponds to path graphs, we propose the Hierarchical Energy Flow Networks and the Local Hierarchical Energy Flow Networks. These two architectures exhibit remarkable discrimination performance on the top tagging dataset and quark-gluon dataset compared to other benchmark algorithms even only utilizing the kinematic information of constituent particles.

Wei Shen

Jin Yang

Hierarchical high-point Energy Flow Network for jet tagging

We conduct a comprehensive analysis of the potential for discovering lepton flavor violation (LFV) phenomena associated with the <math><mi>Z</mi></math> and Higgs bosons at the LHeC and FCC-he. Our thorough investigation highlights the exceptional suitability of electron-proton colliders for probing these rare new physics signals, due to their distinct advantages, such as negligible pileups, minimal QCD backgrounds, electron-beam polarization <math><msub><mi>P</mi><mi>e</mi></msub></math>, and the ability to distinguish charged-current from neutral-current processes. In our analysis of LFV of the <math><mi>Z</mi></math> boson, we employ an innovative indirect probe, utilizing the <math><mi>t</mi></math>-channel mediation of the <math><mi>Z</mi></math> boson in the process <math><mi>p</mi><msup><mi>e</mi><mo>−</mo></msup><mo>→</mo><mi>j</mi><msup><mi>τ</mi><mo>−</mo></msup></math>. For LFV in the Higgs sector, we examine direct observations of the on-shell decays of <math><mi>H</mi><mo>→</mo><msup><mi>e</mi><mo>+</mo></msup><msup><mi>τ</mi><mo>−</mo></msup></math> and <math><mi>H</mi><mo>→</mo><msup><mi>μ</mi><mo>±</mo></msup><msup><mi>τ</mi><mo>∓</mo></msup></math> through the charged-current production of <math><mi>H</mi></math>. Focusing on <math><mi>H</mi><mo>→</mo><msup><mi>e</mi><mo>+</mo></msup><msup><mi>τ</mi><mo>−</mo></msup></math> is highly efficient due to the absence of positron-related backgrounds in the charged-current modes at electron-proton colliders. Through a dedicated signal-to-background analysis using the boosted decision tree algorithm, we show that the LHeC with a total integrated luminosity of <math><mn>1</mn><mtext> </mtext><msup><mrow><mi>ab</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></math> can establish significantly lower <math><mn>2</mn><mi>σ</mi></math> bounds than the HL-LHC with <math><mn>3</mn><mtext> </mtext><msup><mrow><mi>ab</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></math>. Specifically, we find <math><mi>Br</mi><mo>(</mo><mi>Z</mi><mo>→</mo><mi>e</mi><mi>τ</mi><mo>)</mo><mo>&lt;</mo><mn>2.2</mn><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>7</mn></mrow></msup></math>, <math><mi>Br</mi><mo>(</mo><mi>H</mi><mo>→</mo><mi>e</mi><mi>τ</mi><mo>)</mo><mo>&lt;</mo><mn>1.7</mn><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>4</mn></mrow></msup></math>, and <math><mi>Br</mi><mo>(</mo><mi>H</mi><mo>→</mo><mi>μ</mi><mi>τ</mi><mo>)</mo><mo>&lt;</mo><mn>1.0</mn><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>4</mn></mrow></msup></math> when we apply the optimal cut on the boosted decision tree output. Furthermore, our study reveals the exceptional precision of the FCC-he in measuring the LFV signatures of the <math><mi>Z</mi></math> and Higgs bosons, indicating a promising potential for future discoveries in this fascinating field.

Adil Jueid

Exploring lepton flavor violation phenomena of the <math><mi>Z</mi></math> and Higgs bosons at electron-proton colliders

Most of the experimental searches of the non-Standard Model Higgs boson(s) at the LHC rely on the QCD induced production modes. However, in some beyond Standard Model frameworks, the additional Higgs bosons can have fermiophobic behaviour. The type I two Higgs doublet model considered here is a perfect example where all the additional Higgs bosons exhibit fermiophobic nature over a large region of parameter space. Thus the electroweak productions of these new Higgs bosons are more dominant over the QCD induced processes. In scenarios with light pseuodoscalar (A) which is bound to decay dominantly to   <math> <mi>b</mi> <mover> <mi>b</mi> <mo>¯</mo> </mover> </math>  $$ b\overline{b} $$ , even being fermiophobic, the 4b + W state via pp → H  ±  A → (AW)A → 4b + W and followed by the leptonic decay of W boson can surpass the QCD initiated 4b final state. However, the signal gets overshadowed by large   <math> <mi>t</mi> <mover> <mi>t</mi> <mo>¯</mo> </mover> </math>  $$ t\overline{t} $$ +jets background and hence constructing a suitable discriminator based on the signal hypothesis and signal topology is necessary. We devised a χ 2 variable as the most suitable signal-background discrimintor to reduce the background by a sizable amount and showed the discovery reach (&gt; 3σ) of the electroweak initiated    final state at the LHC.

Probing the electroweak    final state in type I 2HDM at the LHC

The light fermiophobic Higgs boson h f in the type-I two-Higgs-doublet model can evade the current search programs at the LHC since its production through the quark-antiquark annihilation and gluon fusion is not feasible. The particle can be more elusive if the model retains stability up to the Planck scale because the efficient discovery channels are missing from the existing search chart. Through the comprehensive scanning, we show that all the viable parameter points with the Planck cutoff scale require   <math> <msub> <mi>m</mi> <msub> <mi>h</mi> <mi>f</mi> </msub> </msub> <mo>∈</mo> </math>  $$ {m}_{h_f}\in $$  [80, 120] GeV and   <math> <msub> <mi>M</mi> <mrow> <mi>A</mi> <mo>/</mo> <msup> <mi>H</mi> <mo>±</mo> </msup> </mrow> </msub> <mo>∈</mo> </math>  $$ {M}_{A/{H}^{\pm }}\in $$  [90, 150] GeV. Since h f h f → γγW + W  −  and H  ±  → τ  ±  ν/h f W  ±  are dominant in this case, two final states are more efficient to probe h f than the conventional search mode of 4γ + W  ±  /Z. One is τ  ±  νγγ from pp → H  ± (→ τ  ±  ν)h f(→ γγ) and the other is    (ℓ  ±  = e  ±  , μ  ± ) from pp → H  ± (→ h f W  ± )h f → γγW + W  −  W  ± , pp → H  ± (→ h f W  ± )A(→ h f Z) → γγW + W  −  W  ±  Z, and pp → H +(→ h f W +)H  − (→ h f W  − ) → γγW + W  −  W + W  − . The inclusive    consists of a same-sign dilepton, two prompt photons, and missing transverse energy. We perform the signal-background analysis at the detector level. With the total integrated luminosity of 300 fb −1 and the 5% background uncertainty, two proposed channels at the 14 TeV LHC yield signal significances above five in the entire viable parameter space of the fermiophobic type-I with a high cutoff scale.

τ  ±  νγγ and    to probe the fermiophobic Higgs boson with high cutoff scales

A Higgsino in supersymmetric standard models can play the role of a dark matter particle. In conjunction with the naturalness criterion, the Higgsino mass parameter is expected to be around the electroweak scale. In this work, we explore the potential of probing the nearly degenerate light Higgsinos with machine learning at the LHC. By analyzing jet images and other jet substructure information, we use the convolutional neural network to enhance the signal significance. We find that our deep learning jet image method can improve the previous result based on the conventional cut flow by about a factor of 2 at the High-Luminosity LHC.

Huifang Lv

Lei Wu

Deep learning jet images as a probe of light Higgsino dark matter at the LHC

The scenario of multi-sector SUSY breaking predicts pseudo-goldstinos which are not absorbed by the gravitino and their mass can be as low as <math><mi>O</mi><mo>(</mo><mn>0.1</mn><mo>)</mo></math> GeV. Since the interactions of pseudo-goldstinos are not so weak as gravitino, a produced higgsino can decay to a pseudo-goldstino plus a Higgs boson insider the detector at the LHC, and thus the higgsino pair production can lead to the signal of Higgs pair plus missing energy. For the scenario of natural SUSY which requires rather light higgsinos, such events may sizably outnumber the Higgs pair events predicted by the SM and be accessible at the HL-LHC (14 TeV with a luminosity of 3 <math><msup><mrow><mi>ab</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></math>). In this work we examine the observability of such Higgs pair plus missing energy from the decay of light higgsinos produced at the HL-LHC. Considering three channels of the Higgs-pair decay (<math><mi>b</mi><mi>b</mi><mi>W</mi><msup><mrow><mi>W</mi></mrow><mrow><mo>⁎</mo></mrow></msup></math>, <math><mi>b</mi><mi>b</mi><mi>γ</mi><mi>γ</mi></math>, <math><mi>b</mi><mi>b</mi><mi>b</mi><mi>b</mi></math>), our detailed Monte Carlo simulations for the signal and backgrounds show that the best channel is <math><mi>b</mi><mi>b</mi><mi>b</mi><mi>b</mi><mo>+</mo><mspace width="0.25em"></mspace><mo>/</mo><msub><mrow><mi>E</mi></mrow><mrow><mi>T</mi></mrow></msub></math>, whose statistical significance can reach 2σ level for a light higgsino allowed by current experiments. This is over the SM Higgs pair result which is about 1.8σ.