Final State Proton Research Articles

Search for toverline{t}H/Ato toverline{t}toverline{t} production in the multilepton final state in proton–proton collisions at sqrt{s} = 13 TeV with the ATLAS detector

A search for a new heavy scalar or pseudo-scalar Higgs boson (H/A) produced in association with a pair of top quarks, with the Higgs boson decaying into a pair of top quarks (H/A → toverline{t} ) is reported. The search targets a final state with exactly two leptons with same-sign electric charges or at least three leptons. The analysed dataset corresponds to an integrated luminosity of 139 fb−1 of proton–proton collisions collected at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC. Two multivariate classifiers are used to separate the signal from the background. No significant excess of events over the Standard Model expectation is observed. The results are interpreted in the context of a type-II two-Higgs-doublet model. The observed (expected) upper limits at 95% confidence level on the toverline{t}H/A production cross-section times the branching ratio of H/A → toverline{t} range between 14 (10) fb and 6 (5) fb for a heavy Higgs boson with mass between 400 GeV and 1000 GeV, respectively. Assuming that only one particle, either the scalar H or the pseudo-scalar A, contributes to the toverline{t}toverline{t} final state, values of tan β below 1.2 or 0.5 are excluded for a mass of 400 GeV or 1000 GeV, respectively. These exclusion ranges increase to tan β below 1.6 or 0.6 when both particles are considered.

Search for resonant WZ production in the fully leptonic final state in proton–proton collisions at mathbf {sqrt{s} = 13} TeV with the ATLAS detector

A search for a WZ resonance, in the fully leptonic final state (electrons or muons), is performed using 139 fb^{-1} of data collected at a centre-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider. The results are interpreted in terms of a singly charged Higgs boson of the Georgi–Machacek model, produced by WZ fusion, and of a Heavy Vector Triplet, with the resonance produced by WZ fusion or the Drell–Yan process. No significant excess over the Standard Model prediction is observed and limits are set on the production cross-section times branching ratio as a function of the resonance mass for these processes.

Correcting the BA coalescence factor at energies relevant for the GSI-HADES experiment and the RHIC Beam Energy Scan

We investigate the coalescence factors ${B}_{2}$ and ${B}_{3}$ at low collision energies ($\sqrt{{s}_{\mathrm{NN}}}<6$ GeV) with special focus on the HADES and RHIC-Beam Energy Scan (BES) experiments. It is shown that, in order to properly interpret the coalescence factors ${B}_{A}$, two important corrections are necessary: (I) ${B}_{2}$ has to be calculated using the proton $\ifmmode\times\else\texttimes\fi{}$ neutron yields in the denominator, instead of the square of the proton yield, and (II) the primordial proton (neutron) densities have to be used for the normalization and not the final-state (free) protons (neutrons). Both effects lead to a drastic reduction of ${B}_{2}$ and ${B}_{3}$ at low energies. This reduction decreases the discrepancy between the volumes extracted from Hanbury Brown--Twiss measurements and the volumes extracted from the coalescence factor ($V\ensuremath{\propto}1/{B}_{2}$). While at HADES and low RHIC-BES energies these corrections are substantial, they become irrelevant above $\sqrt{{s}_{\mathrm{NN}}}>6$ GeV. The proposed correction method is model independent and is only based on the measurement of protons, clusters, and charged pions.

Search for an anomalous excess of charged-current νe interactions without pions in the final state with the MicroBooNE experiment

This article presents a measurement of νe interactions without pions in the final state using the MicroBooNE experiment and an investigation into the excess of low-energy electromagnetic events observed by the MiniBooNE Collaboration. The measurement is performed in exclusive channels with (1eNp0π) and without (1e0p0π) visible final-state protons using 6.86×1020 protons on target of data collected from the Booster Neutrino Beam at Fermilab. Events are reconstructed with the Pandora pattern recognition toolkit and selected using additional topological information from the MicroBooNE liquid argon time projection chamber. Using a goodness-of-fit test, the data are found to be consistent with the predicted number of events with nominal flux and interaction models with a p value of 0.098 in the two channels combined. A model based on the low-energy excess observed in MiniBooNE is introduced to quantify the strength of a possible νe excess. The analysis suggests that, if an excess is present, it is not consistent with a scaling of the νe contribution to the flux as predicted by the signal model used in the analysis. Combined, the 1eNp0π and 1e0p0π channels do not give a conclusive indication about the tested model, but separately, they both disfavor the low-energy excess model at >90% C.L. The observation in the most sensitive 1eNp0π channel is below the prediction and consistent with no excess. In the less sensitive 1e0p0π channel, the observation at low energy is above the prediction, while overall there is agreement over the full energy spectrum.8 MoreReceived 28 October 2021Accepted 18 February 2022DOI:https://doi.org/10.1103/PhysRevD.105.112004Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Physical SystemsNeutrinosParticles & Fields

Search for low-mass dilepton resonances in Higgs boson decays to four-lepton final states in proton–proton collisions at sqrt{s}=13,text {TeV}

A search for low-mass dilepton resonances in Higgs boson decays is conducted in the four-lepton final state. The decay is assumed to proceed via a pair of beyond the standard model particles, or one such particle and a {mathrm{Z}} boson. The search uses proton–proton collision data collected with the CMS detector at the CERN LHC, corresponding to an integrated luminosity of 137,text {fb}^{-1}, at a center-of-mass energy sqrt{s} = 13,text {TeV} . No significant deviation from the standard model expectation is observed. Upper limits at 95% confidence level are set on model-independent Higgs boson decay branching fractions. Additionally, limits on dark photon and axion-like particle production, based on two specific models, are reported.

The diffractive contribution to deep inelastic lepton-proton scattering: Implications for QCD momentum sum rules and parton distributions

The cross section for deep inelastic lepton-proton scattering (DIS) ℓp→ℓ′X includes a diffractive deep inelastic (DDIS) contribution ℓp→ℓ′p′X, in which the proton remains intact with a large longitudinal momentum fraction xF greater than 0.9 and small transverse momentum. The DDIS events, which can be identified with Pomeron exchange in the t-channel, account for approximately 10% of all of the DIS events. Thus, when one measures DIS, one automatically includes the leading-twist Bjorken-scaling DDIS events as a contribution to the DIS cross section, whether or not the final-state proton p′ is detected. In such events, the missing momentum fraction xp′∼0.9 carried by the final-state proton p′ in the DDIS events could be misidentified with the light-front momentum fraction carried by sea quarks or gluons in the protons' Fock structure. As we shall show in this article, the underlying QCD Pomeron-exchange amplitude which produces the DDIS events does not obey the operator product expansion nor satisfy momentum sum rules. Thus we conclude that the quark and gluon distributions measured in DIS experiments will be misidentified, unless the measurements explicitly exclude the DDIS events and that a correct determination of the parton distribution functions (PDFs) derived from the DIS data requires the explicit subtraction of the DDIS contribution from the full DIS cross section.

Theoretical description of semi-inclusive T2K, MINERνA and MicroBooNE neutrino-nucleus data in the relativistic plane wave impulse approximation

We present the results of semi-inclusive neutrino-nucleus cross sections within the plane wave impulse approximation (PWIA) for three nuclear models: relativistic Fermi gas, independent-particle shell model, and natural orbital shell model in comparison with the available $\mathrm{CC}0\ensuremath{\pi}$ measurements from the T2K, $\mathrm{MINER}\ensuremath{\nu}\mathrm{A}$, and MicroBooNE collaborations where a muon and at least one proton are detected in the final state. Results are presented as a function of the momenta and angles of the final particles, as well as in terms of the imbalances between proton and muon kinematics. The present semi-inclusive formalism is based on fully relativistic microscopic calculations and numerical integrations to produce both lepton and hadron kinematics without relying on further approximations. The analysis reveals that contributions beyond PWIA are crucial to explain the experimental measurements and that the study of correlations between final-state proton and muon kinematics can provide valuable information on relevant nuclear effects such as the Fermi motion and final-state interactions.

Measurements of production cross sections of the Higgs boson in the four-lepton final state in proton\u2013proton collisions at sqrt{s} = 13,text {TeV}

Production cross sections of the Higgs boson are measured in the {mathrm{H}} rightarrow {mathrm{Z}} {mathrm{Z}} rightarrow 4ell (ell ={mathrm{e}},{{{upmu }}_{mathrm{}}^{mathrm{}}} ) decay channel. A data sample of proton–proton collisions at a center-of-mass energy of 13,text {TeV}, collected by the CMS detector at the LHC and corresponding to an integrated luminosity of 137,text {fb}^{-1} is used. The signal strength modifier mu , defined as the ratio of the Higgs boson production rate in the 4ell channel to the standard model (SM) expectation, is measured to be mu =0.94 pm 0.07 ,text {(stat)} ^{+0.09}_{-0.08} ,text {(syst)} at a fixed value of m_{{mathrm{H}}} = 125.38,text {GeV} . The signal strength modifiers for the individual Higgs boson production modes are also reported. The inclusive fiducial cross section for the {mathrm{H}} rightarrow 4ell process is measured to be 2.84^{+0.23}_{-0.22} ,text {(stat)} ^{+0.26}_{-0.21} ,text {(syst)} ,text {fb} , which is compatible with the SM prediction of 2.84 pm 0.15 ,text {fb} for the same fiducial region. Differential cross sections as a function of the transverse momentum and rapidity of the Higgs boson, the number of associated jets, and the transverse momentum of the leading associated jet are measured. A new set of cross section measurements in mutually exclusive categories targeted to identify production mechanisms and kinematical features of the events is presented. The results are in agreement with the SM predictions.

The Gluon Exchange Model for diffractive and inelastic collisions

We propose a new model for a homogeneous description of hadron-hadron and hadron-nucleus collisions, the Gluon Exchange Model, fundamentally based on color octet (gluon) exchange. In proton-proton collisions we provide an exact description of the final state proton and neutron spectrum including the proton diffractive peak. In proton-nucleus reactions we find that the projectile proton diquark cannot survive in more than about half of multiple proton-nucleon processes and consequently must be very frequently disintegrated, leading to long transfers of baryon number over rapidity space.

First Measurement of Differential Charged Current Quasielasticlike ν_{μ}-Argon Scattering Cross Sections with the MicroBooNE Detector.

We report on the first measurement of flux-integrated single differential cross sections for charged-current (CC) muon neutrino (ν_{μ}) scattering on argon with a muon and a proton in the final state, ^{40}Ar (ν_{μ},μp)X. The measurement was carried out using the Booster Neutrino Beam at Fermi National Accelerator Laboratory and the MicroBooNE liquid argon time projection chamber detector with an exposure of 4.59×10^{19} protons on target. Events are selected to enhance the contribution of CC quasielastic (CCQE) interactions. The data are reported in terms of a total cross section as well as single differential cross sections in final state muon and proton kinematics. We measure the integrated per-nucleus CCQE-like cross section (i.e., for interactions leading to a muon, one proton, and no pions above detection threshold) of (4.93±0.76_{stat}±1.29_{sys})×10^{-38} cm^{2}, in good agreement with theoretical calculations. The single differential cross sections are also in overall good agreement with theoretical predictions, except at very forward muon scattering angles that correspond to low-momentum-transfer events.

Evidence for tbar{t}tbar{t} production in the multilepton final state in proton\u2013proton collisions at sqrt{s}=13\xa0text {TeV} with the ATLAS detector

A search is presented for four-top-quark production using an integrated luminosity of 139 fb^{-1} of proton–proton collision data at a centre-of-mass energy of 13~text {TeV} collected by the ATLAS detector at the LHC. Events are selected if they contain a same-sign lepton pair or at least three leptons (electrons or muons). Jet multiplicity, jet flavour and event kinematics are used to separate signal from the background through a multivariate discriminant, and dedicated control regions are used to constrain the dominant backgrounds. The four-top-quark production cross section is measured to be 24^{+7}_{-6} fb. This corresponds to an observed (expected) significance with respect to the background-only hypothesis of 4.3 (2.4) standard deviations and provides evidence for this process.

A comprehensive study of analyzing powers in the proton\u2013deuteron break-up channel at 135 MeV

A measurement of the analyzing powers for the ^2hbox {H}(vec {p},pp)n break-up reaction was carried out at KVI exploiting a polarized-proton beam at an energy of 135,hbox {MeV}. The scattering angles and energies of the final-state protons were measured using the Big Instrument for Nuclear-polarization Analysis (BINA) with a nearly 4pi geometrical acceptance. In this work, we analyzed a large number of kinematical geometries including forward–forward configurations in which both the final-state particles scatter to small polar angles and backward–forward configurations in which one of the final-state particles scatters to large polar angles. The results are compared with Faddeev calculations based on modern nucleon–nucleon (NN) and three-nucleon (3N) potentials. Discrepancies between polarization data and theoretical predictions are observed for configurations corresponding to small relative azimuthal angles between the two final-state protons. These configurations show a large sensitivity to 3N force effects.

Quasi-free limit in the deuteron-deuteron three-body break-up process

Detailed measurements of vector and tensor analyzing powers of the ^{2}{\rm H}(\vec d,dp){n} break-up process are presented. The data were obtained using a polarized deuteron-beam with an energy of 65 MeV/nucleon impinging on a liquid-deuterium target. The experiment was conducted at the AGOR facility at KVI using the BINA 4\piπ-detection system. The focus of this contribution is to analyze data of the dddd scattering process in the regime at which the neutron acts as a spectator, which we refer to as the quasi-free (QF) limit. To achieve this, events for which the final-state deuteron and proton are coplanar have been analyzed and the data have been sorted for various reconstructed momenta of the missing neutron. In the limit of vanishing neutron momentum and at small deuteron-proton momentum transfer, the data match very well with measured and predicted spin observables of the elastic deuteron-proton scattering process. The agreement deteriorates rapidly with increasing neutron momentum and deuteron-proton momentum transfer. The results of coplanar configurations in four-body phase space are compared with the results of recent available theoretical calculations based on the Single-Scattering Approximation.

Measurement of differential cross sections for single diffractive dissociation in sqrt{s} = 8 TeV pp collisions using the ATLAS ALFA spectrometer

A dedicated sample of Large Hadron Collider proton-proton collision data at centre-of-mass energy sqrt{s} = 8 TeV is used to study inclusive single diffractive dissociation, pp → X p. The intact final-state proton is reconstructed in the ATLAS ALFA forward spectrometer, while charged particles from the dissociated system X are measured in the central detector components. The fiducial range of the measurement is −4.0 < log10ξ < −1.6 and 0.016 < |t| < 0.43 GeV2, where ξ is the proton fractional energy loss and t is the squared four-momentum transfer. The total cross section integrated across the fiducial range is 1.59 ± 0.13 mb. Cross sections are also measured differentially as functions of ξ, t, and ∆η, a variable that characterises the rapidity gap separating the proton and the system X . The data are consistent with an exponential t dependence, dσ/dt ∝ eBt with slope parameter B = 7.65 ± 0.34 GeV−2. Interpreted in the framework of triple Regge phenomenology, the ξ dependence leads to a pomeron intercept of α(0) = 1.07 ± 0.09.

Pion-proton correlation in neutrino interactions on nuclei

In neutrino-nucleus interactions, a proton produced with a correlated pion might exhibit a left-right asymmetry relative to the lepton scattering plane even when the pion is absorbed. Absent in other proton production mechanisms, such an asymmetry measured in charged-current pionless production could reveal the details of the absorbed-pion events that are otherwise inaccessible. In this study, we demonstrate the idea of using final-state proton left-right asymmetries to quantify the absorbed-pion event fraction and underlying kinematics. This technique might provide critical information that helps constrain all underlying channels in neutrino-nucleus interactions in the GeV regime.

Hadron resonance gas model and high multiplicities in p–p, p–Pb and Pb–Pb collisions at the LHC

Recent work on the particle composition (hadrochemistry) of the final state in proton–proton (p–p), proton–lead (p–Pb) and lead–lead (Pb–Pb) collisions as a function of the charged particle multiplicity ([Formula: see text]) is reviewed. It is argued that for high multiplicities (at least about 20 charged hadrons in the mid-rapidity interval), consistent results are obtained in the thermal model.

Search for resonant WZ production in the fully leptonic final state in proton–proton collisions at [formula omitted] with the ATLAS detector

A search for a heavy resonance decaying into WZ in the fully leptonic channel (electrons and muons) is performed. It is based on proton–proton collision data collected by the ATLAS experiment at the Large Hadron Collider at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 36.1 fb−1. No significant excess is observed over the Standard Model predictions and limits are set on the production cross section times branching ratio of a heavy vector particle produced either in quark–antiquark fusion or through vector-boson fusion. Constraints are also obtained on the mass and couplings of a singly charged Higgs boson, in the Georgi–Machacek model, produced through vector-boson fusion.

Characterization of nuclear effects in muon-neutrino scattering on hydrocarbon with a measurement of final-state kinematics and correlations in charged-current pionless interactions at T2K

This paper reports measurements of final-state proton multiplicity, muon and proton kinematics, and their correlations in charged-current pionless neutrino interactions, measured by the T2K ND280 near detector in its plastic scintillator (C$_8$H$_8$) target. The data were taken between years 2010 and 2013, corresponding to approximately 6$\times10^{20}$ protons on target. Thanks to their exploration of the proton kinematics and of kinematic imbalances between the proton and muon kinematics, the results offer a novel probe of the nuclear-medium effects most pertinent to the (sub-)GeV neutrino-nucleus interactions that are used in accelerator-based long-baseline neutrino oscillation measurements. These results are compared to many neutrino-nucleus interaction models which all fail to describe at least part of the observed phase space. In case of events without a proton above a detection threshold in the final state, a fully consistent implementation of the local Fermi gas model with multinucleon interactions gives the best description of the data. In the case of at least one proton in the final state the spectral function model agrees well with the data, most notably when measuring the kinematic imbalance between the muon and the proton in the plane transverse to the incoming neutrino. A clear indication of existence of multinucleon interactions is observed. The effect of final-state interactions is also discussed.

Polarization Observables T and F in $$\pi ^0$$ Photoproduction Off the Proton with CLAS g9 Experiment

Pion photoproduction in the $$\gamma p \rightarrow \pi ^0 p$$ reaction has been measured in the FROST experiment at the Thomas Jefferson National Accelerator Facility. In this experiment, circularly polarized photons with energies up to 3.082 GeV impinged on a transversely polarized frozen-spin target. Final-state protons were detected in the CEBAF Large Acceptance Spectrometer. Preliminary results of the polarization observables T and F have been extracted. The data generally agree with predictions of present partial-wave analyses, but also show marked differences. The data will constrain further partial wave analyses and improve the extraction of proton resonance properties.

Search for excited quarks of light and heavy flavor in γ + jet final states in proton–proton collisions at [formula omitted

A search is presented for excited quarks of light and heavy flavor that decay to γ+jet final states. The analysis is based on data corresponding to an integrated luminosity of 35.9fb−1 collected by the CMS experiment in proton–proton collisions at s=13TeV at the LHC. A signal would appear as a resonant contribution to the invariant mass spectrum of the γ+jet system, above the background expected from standard model processes. No resonant excess is found, and upper limits are set on the product of the excited quark cross section and its branching fraction as a function of its mass. These are the most stringent limits to date in the γ+jet final state, and exclude excited light quarks with masses below 5.5 TeV and excited b quarks with masses below 1.8 TeV, assuming standard model like coupling strengths.