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DOE OSTI2025

New H erwig7 underlying event tune: From RHIC to LHC energies

We present parameter sets corresponding to new underlying event tunes for the H erwig7.3 Monte Carlo event generator. The existing H erwig tunes are in good agreement with LHC data, however, they are not typically designed for center-of-mass energies below $\sqrt{𝑠}$ = 300 GeV. The tunes presented in this study can describe midrapidity data collected at the nominal RHIC energy of $\sqrt{𝑠}$ = 200 GeV as well as higher center-of-mass energies utilized by experiments at the LHC and Tevatron. The base “New Haven” tune is developed by fitting minimum-bias simulations of proton-proton ($𝑝⁢𝑝$) collisions to midrapidity identified hadron and jet data from the STAR experiment. The “Nashville” tune includes a separate set of parameters developed by tuning to Tevatron proton-antiproton ($𝑝\bar{⁢𝑝}$) data at $\sqrt{𝑠}$ = 300, 900 and 1960 GeV from CDF, and LHC $𝑝⁢𝑝$ measurements from CMS at $\sqrt{𝑠}$ =7 TeV, in addition to the STAR measurements. Both new tunes demonstrate significant improvements over the recommended default tune currently included in the latest version of H erwig for minimum bias production. As such, we advocate using these tunes for future simulation studies at midrapidity by experimental collaborations at RHIC (STAR and sPHENIX) and the LHC (ALICE, ATLAS, and CMS).

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2026

Evidence for $CP$ violation and measurement of $CP$-violating parameters in B$^0_\mathrm{s}$ $\to$ J/$\psi\,\phi$(1020) decays in pp collisions at $\sqrt{s} =$ 13 TeV

A pioneering machine-learning-based flavor-tagging algorithm combining same-side and opposite-side tagging is used to obtain the equivalent of 27$\,$000 tagged B$^0_\mathrm{s}$$\to$ J/$\psi\, \phi$(1020) decays from pp collisions at $\sqrt{s} =$ 13 TeV, collected by the CMS experiment and corresponding to an integrated luminosity of 96.5 fb$^{-1}$. A time- and flavor-dependent angular analysis of the $\mu^+\mu^-$K$^+$K$^-$ final state is used to measure parameters of the $\mathrm{B}^0_\mathrm{s}$-$\overline{\mathrm{B}}^0_\mathrm{s}$ system. The weak phase is measured to be $\phi_\mathrm{s}$ = $-$73 $\pm$ 23 (stat) $\pm$ 7 (syst) mrad, which, combined with a $\sqrt{s}$ = 8 TeV CMS result, gives $\phi_\mathrm{s}$ = $-$74 $\pm$ 23 mrad. This value differs from zero by 3.2 standard deviations, providing evidence for $CP$ violation in B$^0_\mathrm{s}$$\to$ J/$\psi\,\phi$(1020) decays. All measured physics parameters are found to agree with standard model predictions where available.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2026

Evidence of Z Z γ Production and Observation of 4 ℓ γ in Proton-Proton Collisions at s = 13 TeV

Evidence of the production of two Z bosons and a photon in proton-proton collisions is reported for the first time in CMS. The analysis uses data collected by the CMS experiment between 2016 and 2018 at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb - 1 . Evidence for the process p p → Z Z γ → 4 ℓ γ ( ℓ = e , μ ), with an observed (expected) significance of 3.7 (3.1) standard deviations in a fiducial region defined by p T γ > 20 GeV , | η γ | < 2.4 , Δ R ( ℓ , γ ) > 0.5 , m Z between 60 and 120 GeV, and the invariant mass of either of the two Z bosons combined with the photon ( m Z γ ) larger than 100 GeV, is reported. The measured (predicted) fiducial cross section is 60 - 22 + 27 ab ( 47.56 ± 0.04 ab ). Additionally, the inclusive production of p p → 4 ℓ γ is studied by removing the m Z γ requirement to include final state radiation where one Z boson decays to 2 ℓ γ , yielding an observed (expected) significance of 5.0 (4.2) standard deviations and a measured (predicted) fiducial cross section of 156 - 35 + 39 ab ( 99.97 ± 0.09 ab ).

Hayrapetyan, Aram [Yerevan Phys. Inst.]↗
DOE OSTI2019

Centrality and pseudorapidity dependence of the transverse energy density in p Pb collisions at s N N = 5.02 TeV

The almost hermetic coverage of the CMS detector is used to measure the distribution of transverse energy, E T , over 13.2 units of pseudorapidity, η, for p Pb collisions at a center-of-mass energy per nucleon pair of s NN = 5.02 TeV. The huge angular acceptance exploits the fact that the CASTOR calorimeter at -6.6 < η < -5.2 is effectively present on both sides of the colliding system because of a switch in the proton-going and lead-going beam directions. This wide acceptance enables the study of correlations between well-separated angular regions and makes the measurement a particularly powerful test of event generators. For minimum bias p Pb collisions the maximum value of dE T / d η is 22GeV, which implies an E T per participant nucleon pair comparable to that of peripheral PbPb collisions at s NN =2.76TeV. The increase of dE T / d η with centrality is much stronger for the lead-going side than for the proton-going side. The η dependence of dE T / d η is sensitive to the η range in which the centrality variable is defined. Several modern generators are compared to these results but none is able to capture all aspects of the η and centrality dependence of the data and the correlations observed between different η regions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Correlations of azimuthal anisotropy Fourier harmonics with subevent cumulants in p Pb collisions at s N N = 8.16 TeV

Event-by-event long-range correlations of azimuthal anisotropy Fourier coefficients ($v_n$) in 8.16 TeV p Pb data, collected by the CMS experiment at the CERN Large Hadron Collider, are extracted using a subevent four-particle cumulant technique applied to very low multiplicity events. Each combination of four charged particles is selected from either two, three, or four distinct subevent regions of a pseudorapidity range from -2.4 to 2.4 of the CMS tracker, and with transverse momentum between 0.3 and 3.0 GeV. Using the subevent cumulant technique, correlations between $v_n$ of different orders are measured as functions of particle multiplicity and compared to the standard cumulant method without subevents over a wide event multiplicity range. At high multiplicities, the $v_2$ and $v_3$ coefficients exhibit an anticorrelation; this behavior is observed consistently using various methods. The $v_2$ and $v_4$ correlation strength is found to depend on the number of subevents used in the calculation. As the event multiplicity decreases, the results from different subevent methods diverge because of different contributions of noncollective or few-particle correlations. Correlations extracted with the four-subevent method exhibit a tendency to diminish monotonically toward the lowest multiplicity region (about 20 charged tracks) investigated. These findings extend previous studies to a significantly lower event multiplicity range and establish the evidence for the onset of long-range collective multiparticle correlations in small system collisions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Recombination of 𝐵 𝑐 mesons in ultrarelativistic heavy-ion collisions

High-energy heavy-ion collisions have been suggested as a favorable environment for the production of 𝐵 𝑐 mesons, due to a much larger abundance of charm and bottom quarks compared to elementary reactions. Motivated by recent CMS data for 𝐵$^{+}_{𝑐}$ production in Pb-Pb(5.02 TeV) collisions at the Large Hadron Collider (LHC), we deploy a previously developed transport approach for charmonia and bottomonia to evaluate the kinetics of 𝐵 𝑐 mesons throughout the fireball formed in these reactions. The main inputs to our approach are two transport parameters: the 𝐵 𝑐 's reaction rate and equilibrium limit. Both quantities are determined by previous calculations via a combination of charm and bottom sectors. In-medium binding energies of 𝐵 𝑐 mesons are calculated from a thermodynamic 𝑇 matrix with a lattice-QCD constrained potential, and figure in their inelastic reaction rates. Temperature-dependent equilibrium limits include charm- and bottom-quark fugacities based on their initial production. We compute the centrality dependence of inclusive 𝐵 𝑐 production and transverse-momentum (𝑝 𝑇 ) spectra using two different recombination models: instantaneous coalescence and resonance recombination. The main uncertainty in the resulting nuclear modification factors, 𝑅 AA , is currently associated with the 𝐵 𝑐 cross section in elementary 𝑝⁢𝑝 collisions, caused by the uncertainty in the branching ratio for the 𝐵$^{−}_{𝑐}$ → 𝐽/𝜓⁢𝜇 − ⁢$\overline{𝜈}$ decay. Our results indicate a large enhancement of the 𝑅 AA at low 𝑝 𝑇 , with significant regeneration contributions up to 𝑝 𝑇 ≃ 20GeV. Comparisons to CMS data are carried out but firm conclusions will require a more accurate value of the branching ratio, or alternative channels to measure the 𝐵 𝑐 production in 𝑝⁢ collisions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Two-particle Bose-Einstein correlations and their Lévy parameters in PbPb collisions at s N N = 5.02 TeV

Two-particle Bose–Einstein momentum correlation functions are studied for charged-hadron pairs in lead-lead collisions at a center-of-mass energy per nucleon pair of s NN = 5.02 TeV . The data sample, containing 4.27 × 10 9 minimum bias events corresponding to an integrated luminosity of 0.607 nb − 1 , was collected by the CMS experiment in 2018. The experimental results are discussed in terms of a Lévy-type source distribution. The parameters of this distribution are extracted as functions of particle pair average transverse mass and collision centrality. These parameters include the Lévy index or shape parameter α , the Lévy scale parameter R , and the correlation strength parameter λ . The source shape, characterized by α , is found to be neither Cauchy nor Gaussian, implying the need for a full Lévy analysis. Similarly to what was previously found for systems characterized by Gaussian source radii, a hydrodynamical scaling is observed for the Lévy R parameter. The λ parameter is studied in terms of the core-halo model. ©2024 CERN, for the CMS Collaboration 2024 CERN

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Search for long-lived particles using displaced jets in proton-proton collisions at $\sqrt{s}$ = 13 TeV

An inclusive search is presented for long-lived particles using displaced jets. The search uses a data sample collected with the CMS detector at the CERN LHC in 2017 and 2018, from proton-proton collisions at a center-of-mass energy of 13 TeV. The results of this search are combined with those of a previous search using a data sample collected with the CMS detector in 2016, yielding a total integrated luminosity of 132 fb - 1 . The analysis searches for the distinctive topology of displaced tracks and displaced vertices associated with a dijet system. For a simplified model, where pair-produced long-lived neutral particles decay into quark-antiquark pairs, pair production cross sections larger than 0.07 fb are excluded at 95% confidence level (C.L.) for long-lived particle masses larger than 500 GeV and mean proper decay lengths between 2 and 250 mm. For a model where the standard model-like Higgs boson decays to two long-lived scalar particles that each decays to a quark-antiquark pair, branching fractions larger than 1% are excluded at 95% C.L. for mean proper decay lengths between 1 mm and 340 mm. A group of supersymmetric models with pair-produced long-lived gluinos or top squarks decaying into various final-state topologies containing displaced jets is also tested. Gluino masses up to 2500 GeV and top squark masses up to 1600 GeV are excluded at 95% C.L. for mean proper decay lengths between 3 and 300 mm. The highest lower bounds on mass reach 2600 GeV for long-lived gluinos and 1800 GeV for long-lived top squarks. These are the most stringent limits to date on these models.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Hints of a new leptophilic Higgs sector?

We show that a new leptophilic Higgs sector can resolve some intriguing anomalies in current experimental data across multiple energy ranges. Motivated by the recent CMS excess in the resonant e μ channel at 146 GeV, we consider a leptophilic two-Higgs-doublet model, and propose a novel resonant production mechanism for the neutral components of the second Higgs doublet at the LHC using the lepton content of the proton. Interestingly, the same Yukawa coupling Y e μ ∼ 0.65 – 0.81 that explains the CMS excess also addresses the muon ( g − 2 ) anomaly. Moreover, the new Higgs doublet also resolves the recent CDF W -boson mass anomaly. The relevant model parameter space will be completely probed by future LHC data. Published by the American Physical Society 2024

Astronomy & Astrophysics↗
DOE OSTI2024

Combined search for electroweak production of winos, binos, higgsinos, and sleptons in proton-proton collisions at s = 13 TeV

A combination of the results of several searches for the electroweak production of the supersymmetric partners of standard model bosons, and of charged leptons, is presented. All searches use proton-proton collision data at s = 13 TeV recorded with the CMS detector at the LHC in 2016–2018. The analyzed data correspond to an integrated luminosity of up to 137 fb − 1 . The results are interpreted in terms of simplified models of supersymmetry. Two new interpretations are added with this combination: a model spectrum with the bino as the lightest supersymmetric particle together with mass-degenerate Higgsinos decaying to the bino and a standard model boson, and the compressed-spectrum region of a previously studied model of slepton pair production. Improved analysis techniques are employed to optimize sensitivity for the compressed spectra in the wino and slepton pair production models. The results are consistent with expectations from the standard model. The combination provides a more comprehensive coverage of the model parameter space than the individual searches, extending the exclusion by up to 125 GeV, and also targets some of the intermediate gaps in the mass coverage. © 2024 CERN, for the CMS Collaboration 2024 CERN

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Observation of the J / ψ → μ + μ − μ + μ − decay in proton-proton collisions at s = 13 TeV

The J / ψ → μ + μ − μ + μ − decay has been observed with a statistical significance in excess of five standard deviations. The analysis is based on an event sample of proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the CMS experiment in 2018 and corresponding to an integrated luminosity of 33.6 fb − 1 . Normalizing to the J / ψ → μ + μ − decay mode leads to a branching fraction of [ 10.1 − 2.7 + 3.3 ( stat ) ± 0.4 ( syst ) ] × 10 − 7 , a value that is consistent with the standard model prediction. © 2024 CERN, for the CMS Collaboration 2024 CERN

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Observation of the Ξ b − → ψ ( 2 S ) Ξ − decay and studies of the Ξ b ( 5945 ) 0 baryon in proton-proton collisions at s = 13 TeV

The first observation of the decay Ξ b − → ψ ( 2 S ) Ξ − and measurement of the branching ratio of Ξ b − → ψ ( 2 S ) Ξ − to Ξ b − → J / ψ Ξ − are presented. The J / ψ and ψ ( 2 S ) mesons are reconstructed using their dimuon decay modes. The results are based on proton-proton colliding beam data from the LHC collected by the CMS experiment at s = 13 TeV in 2016–2018, corresponding to an integrated luminosity of 140 fb − 1 . The branching fraction ratio is measured to be B ( Ξ b − → ψ ( 2 S ) Ξ − ) / B ( Ξ b − → J / ψ Ξ − ) = 0.8 4 − 0.19 + 0.21 ( stat ) ± 0.10 ( syst ) ± 0.02 ( B ) , where the last uncertainty comes from the uncertainties in the branching fractions of the charmonium states. New measurements of the Ξ b ( 5945 ) 0 baryon mass and natural width are also presented, using the Ξ b − π + final state, where the Ξ b − baryon is reconstructed through the decays J / ψ Ξ − , ψ ( 2 S ) Ξ − , J / ψ Λ K − , and J / ψ Σ 0 K − . Finally, the fraction of Ξ b − baryons produced from Ξ b ( 5945 ) 0 decays is determined. © 2024 CERN, for the CMS Collaboration 2024 CERN

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Observation of double J / ψ meson production in p Pb collisions at s NN = 8.16 TeV

The first observation of the concurrent production of two J / ψ mesons in proton-nucleus collisions is presented. The analysis is based on a proton-lead ( p Pb ) data sample recorded at a nucleon-nucleon center-of-mass energy of 8.16 TeV by the CMS experiment at the CERN LHC and corresponding to an integrated luminosity of 174.6 nb − 1 . The two J / ψ mesons are reconstructed in their μ + μ − decay channels with transverse momenta p T > 6.5 GeV and rapidity | y | < 2.4 . Events where one of the J / ψ mesons is reconstructed in the dielectron channel are also considered in the search. The p Pb → J / ψ J / ψ + X process is observed with a significance of 5.3 standard deviations. The measured inclusive fiducial cross section, using the four-muon channel alone, is σ ( p Pb → J / ψ J / ψ + X ) = 22.0 ± 8.9 ( stat ) ± 1.5 ( syst ) nb . A fit of the data to the expected rapidity separation for pairs of J / ψ mesons produced in single (SPS) and double (DPS) parton scatterings yields σ SPS p Pb → J / ψ J / ψ + X = 16.5 ± 10.8 ( stat ) ± 0.1 ( syst ) nb and σ DPS p Pb → J / ψ J / ψ + X = 5.4 ± 6.2 ( stat ) ± 0.4 ( syst ) nb , respectively. This latter result can be transformed into a lower bound on the effective DPS cross section, closely related to the squared average interparton transverse separation in the collision, of σ eff > 1.0 mb at 95% confidence level. © 2024 CERN, for the CMS Collaboration 2024 CERN

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Measurement of the Higgs boson mass and width using the four-lepton final state in proton-proton collisions at $\sqrt{s}$ =13 TeV

A measurement of the Higgs boson mass and width via its decay to two 𝑍 bosons is presented. Proton-proton collision data collected by the CMS experiment, corresponding to an integrated luminosity of 138 fb −1 at a center-of-mass energy of 13 TeV, is used. The invariant mass distribution of four leptons in the on-shell Higgs boson decay is used to measure its mass and constrain its width. This yields the most precise single measurement of the Higgs boson mass to date, 125.04 ± 0.12 GeV, and an upper limit on the width Γ 𝐻 < 330 MeV at 95% confidence level. A combination of the on- and off-shell Higgs boson production decaying to four leptons is used to determine the Higgs boson width, assuming that no new virtual particles affect the production, a premise that is tested by adding new heavy particles in the gluon fusion loop model. This result is combined with a previous CMS analysis of the off-shell Higgs boson production with decay to two leptons and two neutrinos, giving a measured Higgs boson width of 3.0$^{+2.0}_{−1.5}$ MeV, in agreement with the standard model prediction of 4.1 MeV. The strength of the off-shell Higgs boson production is also reported. The scenario of no off-shell Higgs boson production is excluded at a confidence level corresponding to 3.8 standard deviations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Improved bounds on the heavy neutrino productions at the LHC

The Majorana neutrino in the type-I seesaw and the pseudo-Dirac neutrinos in the inverse seesaw can have sizable mixings with the light neutrinos in the standard model, through which the heavy neutrinos can be produced at the LHC. We study a variety of initial states such as quark- quark, quark-gluon and gluon-gluon as well as photon mediated processes in producing the heavy neutrinos. For the Majorana heavy luminosities, respectively, we obtain direct upper bounds on the light-heavy neutrino mixing angles. For the pseudo-Dirac heavy neutrino production neutrino production, we consider a same-sign dilepton plus dijet as the signal events. Using the recent ATLAS and CMS data at √s = 8 TeV with 20.3 and 19.7 fb -1 we consider the final sate with a trilepton plus missing energy as the signal events. By using the recent anomalous multilepton search by CMS at √s = 8 TeV with 19.5 fb -1 luminosity, we obtain upper bounds on the mixing angles. Taking the varieties of initial states into account, the previously obtained upper bounds on the mixing angles have been improved. Finally, we scale our results at the 8 TeV LHC to obtain a prospective search reach at the 14 TeV LHC with high luminosities.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Measurement of charged pion, kaon, and proton production in proton-proton collisions at $\sqrt{s}=13$ TeV

Transverse momentum spectra of charged pions, kaons, and protons are measured in proton-proton collisions at s=13 TeV with the CMS detector at the LHC. The particles, identified via their energy loss in the silicon tracker, are measured in the transverse momentum range of pT≈0.1–1.7 GeV/c and rapidities |y|<1. The pT spectra and integrated yields are compared to previous results at smaller s and to predictions of Monte Carlo event generators. The average pT increases with particle mass and charged particle multiplicity of the event. Comparisons with previous CMS results at s=0.9, 2.76, and 7 TeV show that the average pT and the ratios of hadron yields feature very similar dependences on the particle multiplicity in the event, independently of the center-of-mass energy of the pp collision.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Search for Dark Matter and Supersymmetry with a Compressed Mass Spectrum in the Vector Boson Fusion Topology in Proton-Proton Collisions at $\sqrt{s} =$ 8 TeV

A first search for pair production of dark matter candidates through vector boson fusion in proton-proton collisions at s=8 TeV is performed with the CMS detector. The vector boson fusion topology enhances missing transverse momentum, providing a way to probe supersymmetry, even in the case of a compressed mass spectrum. The data sample corresponds to an integrated luminosity of 18.5 fb−1, recorded by the CMS experiment. The observed dijet mass spectrum is consistent with the standard model expectation. In an effective field theory, dark matter masses are explored as a function of contact interaction strength. The most stringent limit on bottom squark production with mass below 315 GeV is also reported, assuming a 5 GeV mass difference with respect to the lightest neutralino.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Observation of Higgs Boson Decay to Bottom Quarks

Here, the observation of the standard model (SM) Higgs boson decay to a pair of bottom quarks is presented. The main contribution to this result is from processes in which Higgs bosons are produced in association with a W or Z boson (VH), and are searched for in final states including 0, 1, or 2 charged leptons and two identified bottom quark jets. The results from the measurement of these processes in a data sample recorded by the CMS experiment in 2017, comprising 41.3 fb -1 of proton-proton collisions at $\sqrt{s}$ = 13 TeV, are described. When combined with previous VH measurements using data collected at $\sqrt{s}$ = 7, 8, and 13 TeV, an excess of events is observed at m H =125 GeV with a significance of 4.8 standard deviations, where the expectation for the SM Higgs boson is 4.9. The corresponding measured signal strength is 1.01 ± 0.22. The combination of this result with searches by the CMS experiment for H→$b\bar{b}$ in other production processes yields an observed (expected) significance of 5.6 (5.5) standard deviations and a signal strength of 1.04±0.20.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗