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DOE OSTI2018

Inclusive search for a highly boosted Higgs boson decaying to a bottom quark-antiquark pair

An inclusive search for the standard model Higgs boson (H) produced with large transverse momentum (pT) and decaying to a bottom quark-antiquark pair (bb¯) is performed using a data set of pp collisions at s=13 TeV collected with the CMS experiment at the LHC. The data sample corresponds to an integrated luminosity of 35.9 fb-1. A highly Lorentz-boosted Higgs boson decaying to bb¯ is reconstructed as a single, large radius jet, and it is identified using jet substructure and dedicated b tagging techniques. The method is validated with Z→bb¯ decays. The Z→bb¯ process is observed for the first time in the single-jet topology with a local significance of 5.1 standard deviations (5.8 expected). For a Higgs boson mass of 125 GeV, an excess of events above the expected background is observed (expected) with a local significance of 1.5 (0.7) standard deviations. The measured cross section times branching fraction for production via gluon fusion of H→bb¯ with reconstructed pT>450 GeV and in the pseudorapidity range -2.5<η<2.5 is 74±48(stat)-10+17(syst) fb, which is consistent within uncertainties with the standard model prediction.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2018

Search for Dark Matter Annihilation in Galaxy Groups

We use 413 weeks of publicly available Fermi Pass 8 gamma-ray data combined with recently developed galaxy group catalogs to search for evidence of dark matter annihilation in extragalactic halos. In our study, we use luminosity-based mass estimates and mass-to-concentration relations to infer the J factors and associated uncertainties for hundreds of galaxy groups within a redshift range z ≲ 0.03. Here we employ a conservative substructure boost factor model, which only enhances the sensitivity by an $\mathscr{O}$(1) factor. No significant evidence for dark matter annihilation is found, and we exclude thermal relic cross sections for dark matter masses below ~ 30 GeV to 95% confidence in the $b\bar{b}$ annihilation channel. These bounds are comparable to those from Milky Way dwarf spheroidal satellite galaxies. The results of our analysis increase the tension but do not rule out the dark matter interpretation of the Galactic Center excess. We provide a catalog of the galaxy groups used in this study and their inferred properties, which can be broadly applied to searches for extragalactic dark matter.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2018

Measurement of the Splitting Function in $pp$ and Pb-Pb Collisions at $\sqrt{s_{_{\mathrm{NN}}}} =$ 5.02 TeV

Data from heavy ion collisions suggest that the evolution of a parton shower is modified by interactions with the color charges in the dense partonic medium created in these collisions, but it is not known where in the shower evolution the modifications occur. The momentum ratio of the two leading partons, resolved as subjets, provides information about the parton shower evolution. This substructure observable, known as the splitting function, reflects the process of a parton splitting into two other partons and has been measured for jets with transverse momentum between 140 and 500 GeV, in pp and PbPb collisions at a center-of-mass energy of 5.02 TeV per nucleon pair. In central PbPb collisions, the splitting function indicates a more unbalanced momentum ratio, compared to peripheral PbPb and pp collisions.. The measurements are compared to various predictions from event generators and analytical calculations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2018

Stellar Wakes from Dark Matter Subhalos

Here we propose a novel method utilizing stellar kinematic data to detect low-mass substructure in the Milky Way’s dark matter halo. By probing characteristic wakes that a passing dark matter subhalo leaves in the phase-space distribution of ambient halo stars, we estimate sensitivities down to subhalo masses of ∼10 7 M ⊙ or below. The detection of such subhalos would have implications for dark matter and cosmological models that predict modifications to the halo-mass function at low halo masses. We develop an analytic formalism for describing the perturbed stellar phase-space distributions, and we demonstrate through idealized simulations the ability to detect subhalos using the phase-space model and a likelihood framework. Our method complements existing methods for low-mass subhalo searches, such as searches for gaps in stellar streams, in that we can localize the positions and velocities of the subhalos today.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2018

Search for Pair-Produced Resonances Each Decaying into at Least Four Quarks in Proton-Proton Collisions at s = 13 TeV

This letter presents the results of a search for pair-produced particles of masses above 100 GeV that each decay into at least four quarks. Using data collected by the CMS experiment at the LHC in 2015-2016, corresponding to an integrated luminosity of 38.2 fb$^{-1}$, reconstructed particles are clustered into two large jets of similar mass, each consistent with four-parton substructure. No statistically significant excess of data over the background prediction is observed in the distribution of average jet mass. Pair-produced squarks with dominant hadronic $R$-parity-violating decays into four quarks and with masses between 0.10 and 0.72 TeV are excluded at 95% confidence level. Similarly, pair-produced gluinos that decay into five quarks are also excluded with masses between 0.10 and 1.41 TeV at 95% confidence level. Furthermore, these are the first constraints that have been placed on pair-produced particles with masses below 400 GeV that decay into four or five quarks, bridging a significant gap in the coverage of $R$-parity-violating supersymmetry parameter space.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2019

Search for Low-Mass Quark-Antiquark Resonances Produced in Association with a Photon at $\sqrt{s} = 13 \mathrm{ TeV}$

A search for narrow low-mass resonances decaying to quark-antiquark pairs is presented. The search is based on proton-proton collisions events collected at 13 TeV by the CMS detector at the CERN LHC. The data sample corresponds to an integrated luminosity of $\mathrm{35.9 fb^{-1}}$, recorded in 2016. The search considers the case where the resonance has high transverse momentum due to initial-state radiation of a photon. To study this process, the decay products of the resonance are reconstructed as a single large-radius jet with two-pronged substructure. The signal is identified as a localized excess in the jet invariant mass spectrum. No evidence for such a resonance is observed in the mass range 10 to 125 GeV. Upper limits at the 95% confidence level are set on the coupling strength of vector resonances decaying to quark pairs. The results obtained with this novel technique provide the first direct constraints on quark-antiquark resonance masses below 50 GeV obtained at a hadron collider.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2019

Search for physics beyond the standard model in events with overlapping photons and jets

Results are reported from a search for new particles that decay into a photon and two gluons, in events with jets. Novel jet substructure techniques are developed that allow photons to be identified in an environment densely populated with hadrons. The analyzed proton-proton collision data were collected by the CMS experiment at the LHC, in 2016 at $ \sqrt{s}$ = 13 TeV, and correspond to an integrated luminosity of 35.9 fb -1 . The spectra of total transverse hadronic energy of candidate events are examined for deviations from the standard model predictions. No statistically significant excess is observed over the expected background. The first cross section limits on new physics processes resulting in such events are set. The results are interpreted as upper limits on the rate of gluino pair production, utilizing a simplified stealth supersymmetry model. The excluded gluino masses extend up to 1.7 TeV, for a neutralino mass of 200 GeV and exceed previous mass constraints set by analyses targeting events with isolated photons.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2020

OmniFold: A Method to Simultaneously Unfold All Observables

Collider data must be corrected for detector effects (“unfolded”) to be compared with many theoretical calculations and measurements from other experiments. Unfolding is traditionally done for individual, binned observables without including all information relevant for characterizing the detector response. We introduce OmniFold, an unfolding method that iteratively reweights a simulated dataset, using machine learning to capitalize on all available information. Our approach is unbinned, works for arbitrarily high-dimensional data, and naturally incorporates information from the full phase space. We illustrate this technique on a realistic jet substructure example from the Large Hadron Collider and compare it to standard binned unfolding methods. This new paradigm enables the simultaneous measurement of all observables, including those not yet invented at the time of the analysis.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

First Observation of Λπ + and Λπ - Signals near the $\bar{K}$N⁡(I=1) Mass Threshold in Λ$^+_c$ → Λ⁢π + ⁢π + π - Decay

Using the data sample of 980 fb -1 collected with the Belle detector operating at the KEKB asymmetric-energy e + ⁢e - collider, we present the results of an investigation of the Λ⁢π + and Λ⁢π - invariant mass distributions looking for substructure in the decay Λ$^+_c$ → Λ⁢π + π + π - . We find a significant signal in each mass distribution. When interpreted as resonances, we find for the Λπ + (Λ⁢π - ) combination a mass of 1434.3 ± 0.6⁢(stat) ± 0.9⁢(syst) MeV/c 2 [1438.5 ± 0.9⁢(stat) ± 2.5⁢(syst) MeV/c 2 ], an intrinsic width of 11.5 ± 2.8⁢(stat) ± 5.3⁢(syst) MeV/c 2 [33.0 ± 7.5⁢(stat) ± 23.6⁢(syst) MeV/c 2 ] with a significance of 7.5⁢σ (6.2⁢σ). As these two signals are very close to the $\bar{K}N$ threshold, we also investigate the possibility of a $\bar{K}N$ cusp, and find that we cannot discriminate between these two interpretations due to the limited size of the data sample.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2024

Study of High-Transverse-Momentum Higgs Boson Production in Association with a Vector Boson in the qqbb Final State with the ATLAS Detector

This Letter presents the first study of Higgs boson production in association with a vector boson (V=W or Z) in the fully hadronic qqbb final state using data recorded by the ATLAS detector at the LHC in proton-proton collisions at $\sqrt{s}$=13 TeV and corresponding to an integrated luminosity of 137 fb –1 . The vector bosons and Higgs bosons are each reconstructed as large-radius jets and tagged using jet substructure techniques. Dedicated tagging algorithms exploiting b-tagging properties are used to identify jets consistent with Higgs bosons decaying into $b\bar{b}$. Dominant backgrounds from multijet production are determined directly from the data, and a likelihood fit to the jet mass distribution of Higgs boson candidates is used to extract the number of signal events. The VH production cross section is measured inclusively and differentially in several ranges of Higgs boson transverse momentum: 250–450, 450–650, and greater than 650 GeV. The inclusive signal yield relative to the standard model expectation is observed to be μ=1.4$^{+1.0}_{–0.9}$ and the corresponding cross section is 3.1±1.3⁢(stat)$^{+1.8}_{–1.4}$(syst.) pb.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2024

Measurement of Energy Correlators inside Jets and Determination of the Strong Coupling α S ( m Z )

Energy correlators that describe energy-weighted distances between two or three particles in a hadronic jet are measured using an event sample of s = 13 TeV proton-proton collisions collected by the CMS experiment and corresponding to an integrated luminosity of 36.3 fb − 1 . The measured distributions are consistent with the trends in the simulation that reveal two key features of the strong interaction: confinement and asymptotic freedom. By comparing the ratio of the measured three- and two-particle energy correlator distributions with theoretical calculations that resum collinear emissions at approximate next-to-next-to-leading-logarithmic accuracy matched to a next-to-leading-order calculation, the strong coupling is determined at the Z boson mass: α S ( m Z ) = 0.122 9 − 0.0050 + 0.0040 , the most precise α S ( m Z ) value obtained using jet substructure observables. © 2024 CERN, for the CMS Collaboration 2024 CERN

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2025

Universality in the Near-Side Energy-Energy Correlator

We investigate the energy-energy correlator (EEC) of hadrons produced on the same side in e + e − annihilation or in leading jets in p p collisions. We observe a remarkable universality of the correlator. Using a nonperturbative transverse momentum dependent (TMD) fragmentation function to model the transition from the “free-hadron” region to the perturbative collinear region, we are able to describe the near-side shapes and peaks over a wide range of energy for both the e + e − annihilation and the p p jet substructure measurements in terms of just two parameters. We present further predictions for the ratio of the projected three-point energy correlator to the EEC. The excellent agreement between our calculations and the experimental data may provide new insights into the role of nonperturbative physics for EECs, and suggests the possibility of exploring nonperturbative TMDs using theoretical tools developed for the energy correlators. Published by the American Physical Society 2025

Liu, Xiaohui (ORCID:0000000277011205)↗

DOE OSTI2025

Search for Quasiparticle Scattering in the Quark-Gluon Plasma with Jet Splittings in 𝑝⁢𝑝 and Pb-Pb Collisions at $\sqrt{s_{NN}}$ = 5.02 TeV

The ALICE Collaboration reports measurements of the large relative transverse momentum (𝑘 𝑇 ) component of jet substructure in 𝑝⁢𝑝 and Pb-Pb collisions at center-of-mass energy per nucleon pair $\sqrt{s_{NN}}$ = 5.02 TeV. Enhancement in the yield of such large-𝑘 T emissions in head-on Pb-Pb collisions is predicted to arise from partonic scattering with quasiparticles of the quark-gluon plasma. The analysis utilizes charged-particle jets reconstructed by the anti-𝑘 T algorithm with resolution parameter 𝑅 = 0.2 in the transverse-momentum interval 60 < 𝑝 T,ch,jet < 80 GeV/𝑐. The soft drop and dynamical grooming algorithms are used to identify high transverse momentum splittings in the jet shower. Comparison of measurements in Pb-Pb and 𝑝⁢𝑝 collisions shows medium-induced narrowing, corresponding to yield suppression of high-𝑘 𝑇 splittings, in contrast to the expectation of yield enhancement due to quasiparticle scattering. The measurements are compared to theoretical model calculations incorporating jet modification due to jet-medium interactions (“jet quenching”), both with and without quasiparticle scattering effects. These measurements provide new insight into the underlying mechanisms and theoretical modeling of jet quenching.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2018

Controlled vapor crystal growth of N a 4 I r 3 O 8 : A three-dimensional quantum spin liquid candidate

In this work, we report the successful bulk single-crystal growth of the hyperkagome lattice iridate Na 4 Ir 3 O 8 (Na438) by vapor transport using a sealed aluminum oxide tube as a container. Crystals were characterized by magnetization, x-ray diffraction, and energy-dispersive x-ray measurements, confirming their identity and properties. Single-crystal x-ray diffraction experiments revealed superlattice peaks indexed on a propagation vector q=(1/3,1/3,1/3) based on the cubic substructure with cell parameter a=8.986(1)Å. This superlattice is three-dimensional and fully coherent. Polarization analysis rules out spin and/or orbital order as the underlying origin of the modulation and points to long-range ordering of Na ions at the notionally disordered Na sites as a plausible origin for the observed superlattice.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Tuning the structural and antiferromagnetic phase transitions in UCr 2 Si 2 : Hydrostatic pressure and chemical substitution

Structural phase transitions in $\textit{f}$-electron materials have attracted sustained attention both for practical and basic science reasons, including the fact that they offer an environment to directly investigate relationships between structure and the $\textit{f}$-state. Here we present results for UCr 2 Si 2 , where structural (tetragonal → monoclinic) and antiferromagnetic phase transitions are seen at $T_S$ = 205 K and $T_N$ = 25 K, respectively. We also provide evidence for an additional second-order phase transition at $T_X$ = 280 K. We show that $T_X$, $T_S$, and $T_N$ respond in distinct ways to the application of hydrostatic pressure and Cr → Ru chemical substitution. In particular, hydrostatic compression increases the structural ordering temperature, eventually causes it to merge with $T_X$, and destroys the antiferromagnetism. In contrast, chemical substitution in the series UCr 2– x Ru x Si 2 suppresses both $T_S$ and $T_N$, causing them to approach zero temperature near $\textit{x}$ ≈ 0.16 and 0.08, respectively. The distinct $\textit{T–P}$ and ${T–x}$ phase diagrams are related to the evolution of the rigid Cr-Si and Si-Si substructures, where applied pressure semiuniformly compresses the unit cell, and Cr → Ru substitution results in uniaxial lattice compression along the tetragonal $\textit{c}$-axis and an expansion in the $\textit{ab}$-plane. These results in this work provide insights into an interesting class of strongly correlated quantum materials in which degrees of freedom associated with $\textit{f}$-electron magnetism, strong electronic correlations, and structural instabilities are readily controlled.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Structural and electronic properties of the first iridium containing mixed B-site spinel oxide: Cu [ Ir 1.5 Cu 0.5 ] O 4

Geometrically frustrated systems populated with large spin-orbit coupled ions are an ideal setting for the exploration of novel exotic states of matter. In this study we present an example of iridium on a mixed B-site spinel oxide structure: Cu [ Ir 1.498 ( 2 ) Cu 0.502 ( 2 ) ] O 4 . Synchrotron XRD refinements reveal a face-centered-cubic structure with space group F d 3 ¯ m and mixed Cu-Ir site disorder within the B 2 O 4 rocksalt substructure. Electrical properties reveal a metallic state within the 50–600-K range with a Kondo effect at T < 50 K . X-ray absorption spectroscopy (XAS) measurements show a mixed Cu 1 + / 2 + and Ir 3 + / 4 + charge partitioned picture, which suggests a metallic/band description with reduced on-site Coulomb interactions. Spin-glass-like freezing is seen at T g = 49 K , and the hysteresis behavior for T > T g resembles that of a strongly frustrated magnet. DFT calculations show sizable hybridization between the Cu 3 d and Ir 5 d states with an effective mixed Ir 3 + / 4 + charge partitioned picture, supporting the electronic and XAS results.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Coexistence of commensurate and incommensurate antiferromagnetic ground states in Co 𝑥 ⁢NbSe 2 single crystal

In Co 𝑥 ⁢NbSe 2 , crystal symmetry and cobalt site occupation drive the formation of two distinct magnetic phases. At 𝑥=1/4, the centrosymmetric structure (𝑃⁢6 3 /𝑚⁢𝑚⁢𝑐) promotes Co-Co interactions leading to the formation of an 𝐴-type antiferromagnetic structure phase with a transition temperature of 𝑇$^𝐴_𝑁$=169K. At 𝑥=1/3, the noncentrosymmetric structure (𝑃⁢6 3 ⁢22) induces a lower-temperature magnetic phase with 𝑇$^S_𝑁$=28K. We report the coexistence of both substructures within a superlattice, with a nuclear propagation vector of (1/3, 1/3, 0) relative to the host lattice. Single crystals of Co 0.28 ⁢NbSe 2 exhibit both magnetic transitions, with 𝑇$^𝐴_𝑁$ corresponding to the 𝑥∼1/4 phase and 𝑇$^S_𝑁$ corresponding to the 𝑥∼1/3 phase. Magnetic susceptibility and specific heat measurements confirm these transitions, although only the high-temperature 𝑇$^𝐴_𝑁$ phase significantly affects resistivity. We successfully isolate each phase in powder samples, while single crystals with an intercalation ratio of 𝑥=0.28 display the coexistence of both phases in a single sample. Using single-crystal neutron diffraction, we solved the magnetic structure of the high-temperature centrosymmetric phase (𝑇$^𝐴_𝑁$), and neutron powder diffraction revealed the double-𝑞 magnetic structure of the low-temperature noncentrosymmetric phase (𝑇$^S_𝑁$).

RKKY interaction↗

DOE OSTI2025

Weakly supervised anomaly detection with event-level variables

We introduce a new topology for weakly supervised anomaly detection searches, diobject plus X. In this topology, one looks for a resonance decaying to two standard model particles produced in association with other anomalous event activity (X). This additional activity is used for classification. We demonstrate how anomaly detection techniques which have been developed for dijet searches focusing on jet substructure anomalies can be applied to event-level anomaly detection in this topology. To robustly capture event-level features of multiparticle kinematics, we employ new physically motivated variables derived from the geometric structure of a collision’s phase space manifold. As a proof of concept, we explore the application of this approach to several benchmark signals in the di-𝜏 and di-𝜇 plus X final states. We demonstrate that our anomaly detection approach can reach discovery-level significances for signals that would be missed in a conventional bump-hunt approach.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗