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Free, publiclyaccessible full text available August 1, 2024

Free, publiclyaccessible full text available September 1, 2024

A bstract A search for the electroweak production of a vectorlike quark T′, decaying to a top quark and a Higgs boson is presented. The search is based on a sample of protonproton collision events recorded at the LHC at $$ \sqrt{s} $$ s = 13 TeV, corresponding to an integrated luminosity of 138 fb − 1 . This is the first T′ search that exploits the Higgs boson decay to a pair of photons. For narrow isospin singlet T′ states with masses up to 1.1 TeV, the excellent diphoton invariant mass resolution of 1–2% results in an increased sensitivity compared to previous searches based on the same production mechanism. The electroweak production of a T′ quark with mass up to 960 GeV is excluded at 95% confidence level, assuming a coupling strength κ T = 0 . 25 and a relative decay width Γ /M T′ < 5%.more » « lessFree, publiclyaccessible full text available September 1, 2024

Abstract The Precision Proton Spectrometer (PPS) of the CMS and TOTEM experiments collected 107.7 fb 1 in protonproton (pp) collisions at the LHC at 13 TeV (Run 2). This paper describes the key features of the PPS alignment and optics calibrations, the proton reconstruction procedure, as well as the detector efficiency and the performance of the PPS simulation. The reconstruction and simulation are validated using a sample of (semi)exclusive dilepton events. The performance of PPS has proven the feasibility of continuously operating a nearbeam proton spectrometer at a high luminosity hadron collider.more » « lessFree, publiclyaccessible full text available September 1, 2024

A bstract A search for physics beyond the standard model (SM) in the final state with a hadronically decaying tau lepton and a neutrino is presented. This analysis is based on data recorded by the CMS experiment from protonproton collisions at a centerofmass energy of 13 TeV at the LHC, corresponding to a total integrated luminosity of 138 fb − 1 . The transverse mass spectrum is analyzed for the presence of new physics. No significant deviation from the SM prediction is observed. Limits are set on the production cross section of a W′ boson decaying into a tau lepton and a neutrino. Lower limits are set on the mass of the sequential SMlike heavy charged vector boson and the mass of a quantum black hole. Upper limits are placed on the couplings of a new boson to the SM fermions. Constraints are put on a nonuniversal gauge interaction model and an effective field theory model. For the first time, upper limits on the cross section of t channel leptoquark (LQ) exchange are presented. These limits are translated into exclusion limits on the LQ mass and on its coupling in the t channel. The sensitivity of this analysis extends into the parameter space of LQ models that attempt to explain the anomalies observed in B meson decays. The limits presented for the various interpretations are the most stringent to date. Additionally, a modelindependent limit is provided.more » « lessFree, publiclyaccessible full text available September 1, 2024

Abstract Threebody nuclear forces play an important role in the structure of nuclei and hypernuclei and are also incorporated in models to describe the dynamics of dense baryonic matter, such as in neutron stars. So far, only indirect measurements anchored to the binding energies of nuclei can be used to constrain the threenucleon force, and if hyperons are considered, the scarce data on hypernuclei impose only weak constraints on the threebody forces. In this work, we present the first direct measurement of the p–p–p and p–p– $$\Lambda $$ Λ systems in terms of threeparticle correlation functions carried out for pp collisions at $$\sqrt{s} = 13$$ s = 13 TeV. Threeparticle cumulants are extracted from the correlation functions by applying the Kubo formalism, where the threeparticle interaction contribution to these correlations can be isolated after subtracting the known twobody interaction terms. A negative cumulant is found for the p–p–p system, hinting to the presence of a residual threebody effect while for p–p– $$\Lambda $$ Λ the cumulant is consistent with zero. This measurement demonstrates the accessibility of threebaryon correlations at the LHC.more » « lessFree, publiclyaccessible full text available July 1, 2024

Abstract A newly developed observable for correlations between symmetry planes, which characterize the direction of the anisotropic emission of produced particles, is measured in Pb–Pb collisions at $$\sqrt{s_\text {NN}}$$ s NN = 2.76 TeV with ALICE. This socalled Gaussian Estimator allows for the first time the study of these quantities without the influence of correlations between different flow amplitudes. The centrality dependence of various correlations between two, three and four symmetry planes is presented. The ordering of magnitude between these symmetry plane correlations is discussed and the results of the Gaussian Estimator are compared with measurements of previously used estimators. The results utilizing the new estimator lead to significantly smaller correlations than reported by studies using the Scalar Product method. Furthermore, the obtained symmetry plane correlations are compared to stateoftheart hydrodynamic model calculations for the evolution of heavyion collisions. While the model predictions provide a qualitative description of the data, quantitative agreement is not always observed, particularly for correlators with significant nonlinear response of the medium to initial state anisotropies of the collision system. As these results provide unique and independent information, their usage in future Bayesian analysis can further constrain our knowledge on the properties of the QCD matter produced in ultrarelativistic heavyion collisions.more » « lessFree, publiclyaccessible full text available July 1, 2024

Free, publiclyaccessible full text available August 1, 2024

A bstract The production of π ± , K ± , and $$ \left(\overline{\textrm{p}}\right)\textrm{p} $$ p ¯ p is measured in pp collisions at $$ \sqrt{s} $$ s = 13 TeV in different topological regions of the events. Particle transverse momentum ( p T ) spectra are measured in the “toward”, “transverse”, and “away” angular regions defined with respect to the direction of the leading particle in the event. While the toward and away regions contain the fragmentation products of the nearside and awayside jets, respectively, the transverse region is dominated by particles from the Underlying Event (UE). The relative transverse activity classifier, R T = N T /〈 N T 〉, is used to group events according to their UE activity, where N T is the measured chargedparticle multiplicity per event in the transverse region and 〈 N T 〉 is the mean value over all the analysed events. The first measurements of identified particle p T spectra as a function of R T in the three topological regions are reported. It is found that the yield of high transverse momentum particles relative to the R T integrated measurement decreases with increasing R T in both the toward and the away regions, indicating that the softer UE dominates particle production as R T increases and validating that R T can be used to control the magnitude of the UE. Conversely, the spectral shapes in the transverse region harden significantly with increasing R T . This hardening follows a mass ordering, being more significant for heavier particles. Finally, it is observed that the p T differential particle ratios $$ \left(\textrm{p}+\overline{\textrm{p}}\right)/\left({\uppi}^{+}+{\uppi}^{}\right) $$ p + p ¯ / π + + π − and (K + + K − ) / ( π + + π − ) in the low UE limit ( R T → 0) approach expectations from Monte Carlo generators such as PYTHIA 8 with Monash 2013 tune and EPOS LHC, where the jetfragmentation models have been tuned to reproduce e + e − results.more » « lessFree, publiclyaccessible full text available June 1, 2024

Abstract This article presents new measurements of the fragmentation properties of jets in both proton–proton (pp) and heavyion collisions with the ALICE experiment at the Large Hadron Collider (LHC). We report distributions of the fraction z r of transverse momentum carried by subjets of radius r within jets of radius R . Chargedparticle jets are reconstructed at midrapidity using the anti k T algorithm with jet radius R = 0 . 4, and subjets are reconstructed by reclustering the jet constituents using the anti k T algorithm with radii r = 0 . 1 and r = 0 . 2. In proton–proton collisions, we measure both the inclusive and leading subjet distributions. We compare these measurements to perturbative calculations at nexttoleading logarithmic accuracy, which suggest a large impact of threshold resummation and hadronization effects on the z r distribution. In heavyion collisions, we measure the leading subjet distributions, which allow access to a region of harder jet frag mentation than has been probed by previous measurements of jet quenching via hadron fragmentation distributions. The z r distributions enable extraction of the partontosubjet fragmentation function and allow for tests of the universality of jet fragmentation functions in the quark–gluon plasma (QGP). We find no significant modification of z r distributions in Pb–Pb compared to pp collisions. However, the distributions are also consistent with a hardening trend for z r < 0 . 95, as predicted by several jet quenching models. As z r → 1 our results indicate that any such hardening effects cease, exposing qualitatively new possibilities to disentangle competing jet quenching mechanisms. By comparing our results to theoretical calculations based on an independent extraction of the partontojet fragmentation function, we find consistency with the universality of jet fragmentation and no indication of factorization breaking in the QGP.more » « lessFree, publiclyaccessible full text available June 1, 2024