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DOE OSTI2023

The Forward Physics Facility at the High-Luminosity LHC

High energy collisions at the High-Luminosity Large Hadron Collider (LHC) produce a large number of particles along the beam collision axis, outside of the acceptance of existing LHC experiments. The proposed Forward Physics Facility (FPF), to be located several hundred meters from the ATLAS interaction point and shielded by concrete and rock, will host a suite of experiments to probe standard model (SM) processes and search for physics beyond the standard model (BSM). In this report, we review the status of the civil engineering plans and the experiments to explore the diverse physics signals that can be uniquely probed in the forward region. FPF experiments will be sensitive to a broad range of BSM physics through searches for new particle scattering or decay signatures and deviations from SM expectations in high statistics analyses with TeV neutrinos in this low-background environment. High statistics neutrino detection will also provide valuable data for fundamental topics in perturbative and non-perturbative QCD and in weak interactions. Experiments at the FPF will enable synergies between forward particle production at the LHC and astroparticle physics to be exploited. We report here on these physics topics, on infrastructure, detector, and simulation studies, and on future directions to realize the FPF’s physics potential.

47 OTHER INSTRUMENTATION↗
DOE OSTI2024

Medium-assisted enhancement of χ c 1 ( 3872 ) production from small to large colliding systems

Studies of exotic hadrons such as the χ c 1 ( 3872 ) state provide crucial insights into the fundamental force governing the strong interaction dynamics, with an emerging frontier to investigate their production in high energy collisions where a partonic medium is present. The latest experimental measurements from the Large Hadron Collider show an intriguing evolution pattern of the χ c 1 ( 3872 ) -to- ψ ( 2 S ) yield ratio from proton-proton collisions with increasing multiplicities toward proton-lead and lead-lead collisions. Here we propose a mechanism of medium-assisted enhancement for the χ c 1 ( 3872 ) production, which competes with the more conventional absorption-induced suppression and results in a nonmonotonic trend from small to large colliding systems. Realistic simulations from this model offer a quantitative description of all available data. Predictions are made for the centrality dependence of this observable in PbPb collisions as well as for its system-size dependence from OO and ArAr to XeXe and PbPb collisions. In both cases, a nonmonotonic behavior emerges as the imprint of the competition between enhancement and suppression and can be readily tested by future data. Published by the American Physical Society 2024

Physics↗
DOE OSTI2022

QLBT: a linear Boltzmann transport model for heavy quarks in a quark-gluon plasma of quasi-particles

Abstract We develop a new heavy quark transport model, QLBT, to simulate the dynamical propagation of heavy quarks inside the quark-gluon plasma (QGP) created in relativistic heavy-ion collisions. Our QLBT model is based on the linear Boltzmann transport (LBT) model with the ideal QGP replaced by a collection of quasi-particles to account for the non-perturbative interactions among quarks and gluons of the hot QGP. The thermal masses of quasi-particles are fitted to the equation of state from lattice QCD simulations using the Bayesian statistical analysis method. Combining QLBT with our advanced hybrid fragmentation-coalescence hadronization approach, we calculate the nuclear modification factor $$R_\mathrm {AA}$$ R AA and the elliptic flow $$v_2$$ v 2 of D mesons at the Relativistic Heavy-Ion Collider and the Large Hadron Collider. By comparing our QLBT calculation to the experimental data on the D meson $$R_\mathrm {AA}$$ R AA and $$v_2$$ v 2 , we extract the heavy quark transport parameter $$\hat{q}$$ q ^ and diffusion coefficient $$D_\mathrm {s}$$ D s in the temperature range of $$1-4~T_\mathrm {c}$$ 1 - 4 T c , and compare them with the lattice QCD results and other phenomenological studies.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Energy and scale dependence of $\hat{q}$ and the “JET puzzle”

Here, we present an attempt to probe the underlying structure of the quark-gluon plasma (QGP) at high resolution, based on the extracted jet transport coefficient $\hat{q}$. We argue that the exchanged momentum $\textit{k}$ between the hard parton and the medium varies over a range of scales, and for $\textit{k}$ ≥ 1 GeV, $\hat{q}$ can be expressed in terms of a parton distribution function (PDF). Because the mass of a QGP constituent is unknown, we define a scaling variable $x_N$ to represent the ratio of the parton momentum to the momentum of a self-contained section of the plasma which has a mass of 1 GeV. This scaling variable is used to parametrize the QGP-PDF. Calculations based on this reconstructed $\hat{q}$ are compared to data sensitive to the hardcore of jets, i.e., the single hadron suppression in terms of the nuclear modification factor $R_{ A A}$ and the azimuthal anisotropy parameter $v_2$ as a function of transverse momentum $p_T$, centrality, and energy of the collision. It is demonstrated that the scale evolution of the QGP-PDF is responsible for the reduction in the normalization of $\hat{q}$ between fits to the Relativistic Heavy-Ion Collider and the Large Hadron Collider data; a puzzle, first discovered by the JET Collaboration.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Performance Before and After Irradiation of Pixelated 3D Silicon Sensors for the HL-LHC CMS Tracker

The Large Hadron Collider (LHC) particle accelerator at European Center for Nuclear Research (CERN) will be shut down starting in 2026 to achieve the High Luminosity Large Hadron Collider (HL-LHC) upgrade. The upgrade will allow for higher fluences, in order to increase the probability of detecting increasingly rare particles, and to obtain higher precision measurements of known particles. To accommodate the new accelerator conditions, many aspects of the Compact Muon Solenoid (CMS) detector will be upgraded; of particular interest for this thesis are the silicon pixel detectors located in the inner tracker. These will be replaced and upgraded to accommodate the higher fluences of the HL-LHC upgrade, as well as to replace existing sensors which have sustained radiation damage. In order for the new sensors to operate under high luminosity conditions, they must be increasingly radiation hard, and in order to detect rare particles, they must be increasingly more precise. The performance of one Centro Nacional de Microelectronica (CNM) 3D silicon sensor before and after undergoing irradiation at fluences similar to those which will be observed at the HL-LHC was investigated to determine radiation hardness and precision. Data was collected at Fermi National Laboratory (Fermilab), in the Fermi National Laboratory Test Beam Facility (FTBF) silicon tracker telescope, which can be used to determine the number of particles, and tracks made by high energy protons passing through. The sensor was also irradiated at Fermilab in the Irradiation Test Area (ITA). Prior to data collection a tuning procedure is carried out to determine ideal bias voltage operating conditions, mask noisy and dead pixels, adjust to the ideal threshold, and map sensor gain. Data is then collected at the FTBF, where the sensor is installed in the center of the FTBF silicon telescope. Variables, including angle and bias voltage, are varied throughout data collection. Data is then processed using an alignment software to determine the exact telescope geometry, along with the tracks which were observed passing through the sensor and telescope. Sensor performance was found to be comparable before and after irradiation, with irradiated results showing slightly lower efficiencies and cluster sizes. Position resolution is comparable both before and after irradiation, and similar distributions of cluster shape are observed. After irradiation, the sensor shows increasing collected charge with bias, an indication of increased width of the depletion region. Peak charge pre-irradiation is higher than post-irradiation peak charge, indicating the irradiated results are not taken under fully-depleted conditions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Jet quenching and medium response in high-energy heavy-ion collisions: a review

Jet quenching has been used successfully as a hard probe to study properties of the quark-gluon plasma (QGP) in high-energy heavy-ion collisions at both the relativistic heavy-ion collider and the large hadron collider. Furthermore, we will review recent progresses in theoretical and phenomenological studies of jet quenching with jet transport models. Special emphasis is given to effects of jet-induced medium response on a wide variety of experimental observables and their implications on extracting transport properties of the QGP in heavy-ion collisions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Entanglement enabled intensity interferometry in ultrarelativistic ultraperipheral nuclear collisions

An important tool in studying the subfemtoscale spacetime structure of matter in ultrarelativistic heavy-ion collisions is Hanbury Brown–Twiss (HBT) intensity interferometry of identical particles in the final state of the collisions. We propose that a variant of the entanglement enabled intensity interferometry (𝐸 2 ⁢𝐼 2 ) framework introduced by Cotler and Wilczek can provide a powerful alternative to HBT interferometry in extracting fundamental nonperturbative features of quantum chromodynamics at high energies. We apply this framework to demonstrate that the spatial distributions of color singlet (pomeron) configurations in nuclei are sensitive to measurements of exclusive resonant decays of 𝜌 mesons into 𝜋 ± pairs in ultrarelativistic ultraperipheral nuclear collisions (UPCs) at the Relativistic Heavy Ion Collider and the Large Hadron Collider. A preliminary analysis suggests that the model-independent extraction of pomeron distributions will require careful treatment of the interplay of 𝐸 2 ⁢𝐼 2 in the vector meson exclusive decay with the incoherent cross section for exclusive vector meson production. The 𝐸 2 ⁢𝐼 2 framework developed here is quite general. It can also be employed as a tool to extract information on the spin structure of pomeron couplings as well as enhance the discovery potential for rare odderon configurations from exclusive vector meson decays into few-particle final states both in UPCs and at the Electron-Ion Collider.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Progress and challenges in small systems

We present a comprehensive review of the theoretical and experimental progress in the investigation of novel high-temperature quantum chromodynamics phenomena in small systems at both the Relativistic Heavy Ion Collider and the Large Hadron Collider. We highlight the challenges and opportunities associated with studying small systems, by which we generally mean collision systems that involve at least one light ion or even a photon projectile. Here, we discuss perspectives on possible future research directions to better understand the underlying physics at work in the collisions of small systems.

collective behavior↗
DOE OSTI2024

Progress and challenges in small systems

Here, we present a comprehensive review of the theoretical and experimental progress in the investigation of novel high-temperature quantum chromodynamics phenomena in small systems at both the Relativistic Heavy Ion Collider and the Large Hadron Collider. We highlight the challenges and opportunities associated with studying small systems, by which we generally mean collision systems that involve at least one light ion or even a photon projectile. We discuss perspectives on possible future research directions to better understand the underlying physics at work in the collisions of small systems.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Nuclear modification of leading hadrons and jets within a virtuality ordered parton shower

In this work, the event generator based on the higher-twist energy loss formalism—Modular All Twist Transverse-scattering Elastic-drag and Radiation (M ATTER )—is further developed and coupled to a hydrodynamic model for studying jet modification in relativistic nuclear collisions. The probability of parton splitting is calculated using the Sudakov form factor that is constructed by a combination of vacuum and medium-induced splitting functions; and the full parton showers are simulated, including both energy-momentum and space-time evolutions of all jet partons. With the assumption that partons below a virtual scale of 1 GeV is absorbed by the medium, this framework is able to provide a reasonable description of the nuclear modification of both leading hadrons and jets at high transverse momentum at the BNL Relativistic Heavy Ion Collider and the CERN Large Hadron Collider.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Evaluation of HPK n + - p planar pixel sensors for the CMS Phase-2 upgrade

To cope with the challenging environment of the planned high luminosity upgrade of the Large Hadron Collider (HL-LHC), scheduled to start operation in 2029, CMS will replace its entire tracking system. The requirements for the tracker are largely determined by the long operation time of 10 years with an instantaneous peak luminosity of up to 7.5 × 10 34 cm –2 s –1 in the ultimate performance scenario. Depending on the radial distance from the interaction point, the silicon sensors will receive a particle fluence corresponding to a non-ionizing energy loss of up to $\Phi_{\text {eq}}$ = 3.5 × 10 16 cm –2 . Here this paper focuses on planar pixel sensor design and qualification up to a fluence of $\Phi_{\text {eq}}$ = 1.4 × 10 16 cm –2 . For the development of appropriate planar pixel sensors an R&D program was initiated, which includes $n^+ -p$ sensors on 150 mm (6”) wafers with an active thickness of 150 μm with pixel sizes of 100 × 25 μm 2 and 50 × 50 μm 2 manufactured by Hamamatsu. Single chip modules with ROC4Sens and RD53A readout chips were made. Irradiation with protons and neutrons, as well was an extensive test beam campaign at DESY were carried out. This paper presents the investigation of various assemblies mainly with ROC4Sens readout chips. It demonstrates that multiple designs fulfill the requirements in terms of breakdown voltage, leakage current and efficiency. The single point resolution for 50 × 50 μm 2 pixels is measured as 4.0 μm for non-irradiated samples, and 6.3 μm after irradiation to $\Phi_{\text {eq}}$ = 7.2 × 10 15 cm –2 .

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2024

Measurements of Lund subjet multiplicities in 13 TeV proton-proton collisions with the ATLAS detector

This Letter presents a differential cross-section measurement of Lund subjet multiplicities, suitable for testing current and future parton shower Monte Carlo algorithms. This measurement is made in dijet events in 140 fb -1 of $\sqrt{s}$ =13 TeV proton–proton collision data collected with the ATLAS detector at CERN's Large Hadron Collider. The data are unfolded to account for acceptance and detector-related effects, and are then compared with several Monte Carlo models and to recent resummed analytical calculations. The experimental precision achieved in the measurement allows tests of higher-order effects in QCD predictions. Most predictions fail to accurately describe the measured data, particularly at large values of jet transverse momentum accessible at the Large Hadron Collider, indicating the measurement's utility as an input to future parton shower developments and other studies probing fundamental properties of QCD and the production of hadronic final states up to the TeV-scale.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Search for resonance in inclusive and b-tagged dijet mass spectra in proton-proton collision at $\sqrt{s}$ = 13 TeV and constraints on dark matter and other models

Two analyses searching for new heavy resonances and interpreting the result with dark matter are presented in this dissertation. The first analysis searches for resonances decaying into dijet final states using the proton-proton collision data at center mass of $\sqrt{s}=13$ TeV with the CMS detector at Large Hadron Collider in2016, corresponding to a total integrated luminosity of 36 fb -1 . No significant evidence for the production of new particles is observed. A simplified model of interactions between quarks and dark matter is used to interpret the result. The second analysis searches for resonances decaying into dijet final states using the proton-proton collision data at center mass of $\sqrt{s}=13$ TeV with the CMS detector at Large Hadron Collider in 2016, 2017, and 2018, corresponding to a total integrated luminosity of 137.5 fb -1 . A b-tagger named DeepJet is used to examine the events with jets containing B hadrons. No evidence of new heavy resonances is observed, as well. The 95% confidence level cross-section upper limit is set on excited b-quark b* and Coloron models. Limits are also set on a simplified model of interactions between b-quarks and dark matter.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

New PHENIX Results on Mid-Rapidity Bottom and Charm Production in Au+Au collisions at $\sqrt{s_{NN}}$= 200 GeV

Energy loss of quarks in the hot and dense medium has been studied for decades. Both the experimental and theoretical efforts have hinted that the energy loss is quark mass dependent. Although experiments at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) have found that the electrons from heavy quarks are less or similarly suppressed compared to the light hadrons, the mass ordering of the suppression between charm and bottom quarks is not yet clear due to large experimental uncertainties. We have fully exploited the events recorded at mid-rapidity in Au+Au collisions at center-of-mass energy of 200 GeV by the PHENIX experiment at RHIC to study the invariant yield of electrons from open heavy flavors. Latest results on the nuclear modification factors for charm and bottom separated heavy flavor electrons are reviewed in this proceeding. The implications of these results on the understanding of the quark mass and medium size dependence of the energy loss are also discussed.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2022

The ATLAS inner detector trigger performance in pp collisions at 13 TeV during LHC Run 2

The design and performance of the inner detector trigger for the high level trigger of the ATLAS experiment at the Large Hadron Collider during the 2016–2018 data taking period is discussed. In 2016, 2017, and 2018 the ATLAS detector recorded 35.6 fb –1 , 46.9 fb –1 , and 60.6 fb –1 respectively of proton–proton collision data at a centre-of-mass energy of 13 TeV. In order to deal with the very high interaction multiplicities per bunch crossing expected with the 13 TeV collisions the inner detector trigger was redesigned during the long shutdown of the Large Hadron Collider from 2013 until 2015. An overview of these developments is provided and the performance of the tracking in the trigger for the muon, electron, tau and b-jet signatures is discussed. The high performance of the inner detector trigger with these extreme interaction multiplicities demonstrates how the inner detector tracking continues to lie at the heart of the trigger performance and is essential in enabling the ATLAS physics programme.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

An implementation of neural simulation-based inference for parameter estimation in ATLAS

Neural simulation-based inference (NSBI) is a powerful class of machine-learning-based methods for statistical inference that naturally handles high-dimensional parameter estimation without the need to bin data into low-dimensional summary histograms. Such methods are promising for a range of measurements, including at the Large Hadron Collider, where no single observable may be optimal to scan over the entire theoretical phase space under consideration, or where binning data into histograms could result in a loss of sensitivity. This work develops a NSBI framework for statistical inference, using neural networks to estimate probability density ratios, which enables the application to a full-scale analysis. It incorporates a large number of systematic uncertainties, quantifies the uncertainty due to the finite number of events in training samples, develops a method to construct confidence intervals, and demonstrates a series of intermediate diagnostic checks that can be performed to validate the robustness of the method. As an example, the power and feasibility of the method are assessed on simulated data for a simplified version of an off-shell Higgs boson couplings measurement in the four-lepton final states. This approach represents an extension to the standard statistical methodology used by the experiments at the Large Hadron Collider, and can benefit many physics analyses.

frequentist statistics↗
DOE OSTI2024

Custodial symmetry breaking and Higgs boson signatures at the LHC

We discuss the simplest model that predicts a tree-level modification of the ρ parameter from a shift in the W -mass without changing the prediction for the Z mass. This model predicts a new neutral Higgs and two charged Higgses, with very similar masses and suppressed couplings to the Standard Model fermions. We discuss the decay properties of these new scalar bosons, and the main signatures at the Large Hadron Collider. Comparing these signatures for the first time to the latest measurements, we show that while masses around 200 GeV are excluded for some scenarios, over a wide range of model parameter space the new bosons can have a mass close to the electroweak scale without violating existing limits from experimental searches or destroying the agreement with measurements. We investigate the scenario where the new neutral Higgs is fermiophobic and has a large branching ratio into W gauge bosons and/or photons, and show that this could lead to a signal in the diphoton mass spectrum at low Higgs masses. We discuss the different signatures that can motivate new measurements and searches at the Large Hadron Collider. Published by the American Physical Society 2024

Astronomy & Astrophysics↗
DOE OSTI2021

Deciphering the R Ψ m correlator in search for the chiral magnetic effect in relativistic heavy ion collisions

The chiral magnetic effect (CME) is extensively studied in heavy-ion collisions at the BNL Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). An azimuthal correlator called R Ψ m was proposed to measure the CME. By observing the same R Ψ 2 and R Ψ 3 (convex) distributions from A Multi-Phase Transport (ampt) model, by contrasting data and model as well as large and small systems and by event shape engineering (ESE), a recent preprint (arXiv:2006.04251v1) from STAR suggests that the R Ψ m observable is sensitive to the CME signal and relatively insensitive to backgrounds, and their Au + Au data are inconsistent with known background contributions. Our ampt results contradict those from a recent preprint by STAR. Our toy model simulations demonstrate that R Ψ 2 is sensitive to both the CME signal and physics backgrounds. Toy model simulations of isobar collisions show similar centrality dependence and magnitudes for the relative R Ψ 2 strengths as well as the relative Δ γ strengths. We conclude that R Ψ 2 and the inclusive Δ γ are essentially the same.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗