In this paper, we report the measurement relative to the production of forward neutrons in proton-proton collisions at $\mathrm{\sqrt{s} = 13~TeV}$ obtained using the LHCf Arm2 detector at the Large Hadron Collider. The results for the inclusive differential production cross section are presented as a function of energy in three different pseudorapidity regions: $\eta > 10.76$, $8.99 < \eta < 9.22$ and $8.81 < \eta < 8.99$. The analysis was performed using a data set acquired in June 2015 that corresponds to an integrated luminosity of $\mathrm{0.194~nb^{-1}}$. The measurements were compared with the predictions of several hadronic interaction models used to simulate air showers generated by Ultra High Energy Cosmic Rays. None of these generators showed good agreement with the data for all pseudorapidity intervals. For $\eta > 10.76$, no model is able to reproduce the observed peak structure at around $\mathrm{5~TeV}$ and all models underestimate the total production cross section: among them, QGSJET II-04 shows the smallest deficit with respect to data for the whole energy range. For $8.99 < \eta < 9.22$ and $8.81 < \eta < 8.99$, the models having the best overall agreement with data are SIBYLL 2.3 and EPOS-LHC, respectively: in particular, in both regions SIBYLL 2.3 is able to reproduce the observed peak structure at around $\mathrm{1.5-2.5~TeV}$.
Inclusive neutron (and antineutron) production cross section in $\eta > 10.76$
Inclusive neutron (and antineutron) production cross section in $8.99 < \eta < 9.22$
Inclusive neutron (and antineutron) production cross section in $8.81 < \eta < 8.99$
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 $m_\mathrm{H} =$ 125.09 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 $\pm$ 0.22. The combination of this result with searches by the CMS experiment for H $\to\mathrm{b\overline{b}}$ in other production processes yields an observed (expected) significance of 5.6 (5.5) standard deviations and a signal strength of 1.04 $\pm$ 0.20.
Expected and observed significances, in number of standard deviations, and observed signal strengths for the VH production process with H-->b bbar. Results are shown separately for 2017 data, combined Run 2 (2016 and 2017 data), and for the combination of the Run 1 and Run 2 data. For the 2017 analysis, results are shown separately for the individual mu value for each channel from a combined simultaneous fit to all channels. All results are obtained for mH=125.09 GeV. Data are from Table 2 and 2016 added from Figure 1b.
Best-fit value of the H-->b bbar signal strength with its 1 sigma systematic (red) and total (blue) uncertainties for the five individual production modes considered, as well as the overall combined result. The vertical dashed line indicates the standard model expectation. All results are extracted from a single fit combining all input analyses, with mH = 125.09 GeV. Data from Figure 3.
A measurement of jet substructure observables is presented using \ttbar events in the lepton+jets channel from proton-proton collisions at $\sqrt{s}=$ 13 TeV recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. Multiple jet substructure observables are measured for jets identified as bottom, light-quark, and gluon jets, as well as for inclusive jets (no flavor information). The results are unfolded to the particle level and compared to next-to-leading-order predictions from POWHEG interfaced with the parton shower generators PYTHIA 8 and HERWIG 7, as well as from SHERPA 2 and DIRE2. A value of the strong coupling at the Z boson mass, $\alpha_S(m_\mathrm{Z}) = $ 0.115$^{+0.015}_{-0.013}$, is extracted from the substructure data at leading-order plus leading-log accuracy.
Distribution of $\lambda_{0}^{0}$ (N) reconstructed from charged particles with pt > 1 GeV, unfolded to the particle level.
Distribution of $\lambda_{0}^{2}$ ($p_{T}^{d,*})$ reconstructed from charged particles with pt > 1 GeV, unfolded to the particle level.
Distribution of $\lambda_{0.5}^{1}$ (LHA) reconstructed from charged particles with pt > 1 GeV, unfolded to the particle level.
A search for charged Higgs boson decaying to a charm and a bottom quark (H$^+\to$ c$\overline{\mathrm{b}}$) is performed using 19.7 fb$^{-1}$ of pp collision data at $\sqrt{s} =$ 8 TeV. The production mechanism investigated in this search is $\mathrm{t\overline{t}}$ pair production in which one top quark decays to a charged Higgs boson and a bottom quark and the other decays to a charged lepton, a neutrino, and a bottom quark. Charged Higgs boson decays to $\mathrm{c\overline{b}}$ are searched for, resulting in a final state containing at least four jets, a charged lepton (muon or electron), and missing transverse momentum. A kinematic fit is performed to identify the pair of jets least likely to be the bottom quarks originating from direct top quark decays and the invariant mass of this pair is used as the final observable in the search. No evidence for the presence of a charged Higgs boson is observed and upper limits at 95% confidence level of 0.8-0.5% are set on the branching fraction $\mathcal{B}$(t $\to$ H$^+$b), assuming $\mathcal{B}$(H$^+\to$ $\mathrm{c\overline{b}}) =$ 1.0 and $\mathcal{B}$(t $\to$ H$^+$b) $+$ $\mathcal{B}$(t $\to$ Wb) = 1.0, for the charged Higgs boson mass range 90-150 GeV.
The 95% CL upper limits on the branching fraction of top quark to a charged Higgs boson and bottom quark depending on the expected charged Higgs mass. For this limit calculation, B(t --> H+ b) + B(t --> W b) = 1.0 and B(H+ --> cb) = 1.0 are assumed.
Measurements of the $\pi^{\pm}$, $K^{\pm}$, and proton double differential yields emitted from the surface of the 90-cm-long carbon target (T2K replica) were performed for the incoming 31 GeV/c protons with the NA61/SHINE spectrometer at the CERN SPS using data collected during 2010 run. The double differential $\pi^{\pm}$ yields were measured with increased precision compared to the previously published NA61/SHINE results, while the $K^{\pm}$ and proton yields were obtained for the first time. A strategy for dealing with the dependence of the results on the incoming proton beam profile is proposed. The purpose of these measurements is to reduce significantly the (anti)neutrino flux uncertainty in the T2K long-baseline neutrino experiment by constraining the production of (anti)neutrino ancestors coming from the T2K target.
Double differential yiedls of positively charged pions emitted from the surface of the T2K replica target, in the polar angle range from 0 to 20 mrad and in the longitudinal range from 0 to 18cm, as a function of momentum. The normalization is per proton on target.
Double differential yiedls of positively charged pions emitted from the surface of the T2K replica target, in the polar angle range from 20 to 40 mrad and in the longitudinal range from 0 to 18cm, as a function of momentum. The normalization is per proton on target.
Double differential yiedls of positively charged pions emitted from the surface of the T2K replica target, in the polar angle range from 40 to 60 mrad and in the longitudinal range from 0 to 18cm, as a function of momentum. The normalization is per proton on target.
This Letter presents a search for heavy charged long-lived particles produced in proton-proton collisions at $\sqrt{s} = 13$ TeV at the LHC using a data sample corresponding to an integrated luminosity of 36.1 fb$^{-1}$ collected by the ATLAS experiment in 2015 and 2016. These particles are expected to travel with a velocity significantly below the speed of light, and therefore have a specific ionisation higher than any high-momentum Standard Model particle of unit charge. The pixel subsystem of the ATLAS detector is used in this search to measure the ionisation energy loss of all reconstructed charged particles which traverse the pixel detector. Results are interpreted assuming the pair production of $R$-hadrons as composite colourless states of a long-lived gluino and Standard Model partons. No significant deviation from Standard Model background expectations is observed, and lifetime-dependent upper limits on $R$-hadron production cross-sections and gluino masses are set, assuming the gluino always decays in two quarks and a stable neutralino. $R$-hadrons with lifetimes above 1.0 ns are excluded at the 95% confidence level, with lower limits on the gluino mass ranging between 1290 GeV and 2060 GeV. In the case of stable $R$-hadrons, the lower limit on the gluino mass at the 95% confidence level is 1890 GeV.
The number of events in each CR, VR, and SR for the predicted background, for the expected contribution from the signal model normalised to $36.1$ fb$^{-1}$, and in the observed data. The predicted background includes the statistical and systematic uncertainties, respectively. The uncertainty in the signal yield includes all systematic uncertainties except that in the theoretical cross-section.
The number of events in each CR, VR, and SR for the predicted background, for the expected contribution from the signal model normalised to $36.1$ fb$^{-1}$, and in the observed data. The predicted background includes the statistical and systematic uncertainties, respectively. The uncertainty in the signal yield includes all systematic uncertainties except that in the theoretical cross-section.
Expected number of $R$-hadron signal events at different stages of the selection, normalised to $36.1$ fb$^{-1}$. Shown for three different signal points is the number of events expected and the number of events expected in which the selected track has been matched to a generated $R$-hadron. If the gluino decays, it decays to a 100 GeV $\tilde{\chi}^{0}$ and SM quarks.
Results are reported from a search for long-lived particles in proton-proton collisions at $\sqrt{s} =$ 13 TeV delivered by the CERN LHC and collected by the CMS experiment. The data sample, which was recorded during 2015 and 2016, corresponds to an integrated luminosity of 38.5 fb$^{-1}$. This search uses benchmark signal models in which long-lived particles are pair-produced and each decays into two or more quarks, leading to a signal with multiple jets and two displaced vertices composed of many tracks. No events with two well-separated high-track-multiplicity vertices are observed. Upper limits are placed on models of $R$-parity violating supersymmetry in which the long-lived particles are neutralinos or gluinos decaying solely into multijet final states or top squarks decaying solely into dijet final states. For neutralino, gluino, or top squark masses between 800 and 2600 GeV and mean proper decay lengths between 1 and 40 mm, the analysis excludes cross sections above 0.3 fb at 95% confidence level. Gluino and top squark masses are excluded below 2200 and 1400 GeV, respectively, for mean proper decay lengths between 0.6 and 80 mm. A method is provided for extending the results to other models with pair-produced long-lived particles.
Distribution of the distance between vertices in the $x$-$y$ plane, $d_{VV}$, for simulated multijet signals with $m$ = 800 GeV, production cross section 1 fb, and $c\tau$ = 0.3, 1.0, and 10 mm, with the background template overlaid. All vertex and event selection criteria have been applied. The last bin includes the overflow events.
Signal efficiency as a function of signal mass and lifetime for the multijet signal samples. All vertex and event selection criteria have been applied, as well as the requirement $d_{VV}$ > 0.4 mm.
Signal efficiency as a function of signal mass and lifetime for the dijet signal samples. All vertex and event selection criteria have been applied, as well as the requirement $d_{VV}$ > 0.4 mm.
A search for the pair production of resonances, each decaying to two quarks, is reported. The search is conducted separately for heavier resonances (masses above 400 GeV), where each of the four final-state quarks generates a hadronic jet resulting in a four-jet signature, and for lighter resonances (masses between 80 and 400 GeV), where the pair of quarks from each resonance is collimated and reconstructed as a single jet resulting in a two-jet signature. In addition, a b-tagged selection is applied to target resonances with a bottom quark in the final state. The analysis uses data collected with the CMS detector at the CERN LHC, corresponding to an integrated luminosity of 35.9 fb$^{-1}$, from proton-proton collisions at a center-of-mass energy of 13 TeV. The mass spectra are analyzed for the presence of new resonances, and are found to be consistent with standard model expectations. The results are interpreted in the framework of $R$-parity-violating supersymmetry assuming the pair production of scalar top quarks decaying via the hadronic coupling $\lambda_{312}"$ or $\lambda_{323}"$, and upper limits on the cross section as a function of the top squark mass are set. These results probe lower masses than previously explored at the LHC, and extend the top squark mass limits in the $\widetilde{\mathrm{t}}$$\to$qq$'$ scenario.
Signal efficiency as a function of stop mass for the inclusive and b-tagged selections. Efficiency is estimated from the number of events in the simulated sample passing the full signal selection in a two sigma window around the true mass compared with the total number of events generated. No generator-level requirements are applied in the generation.
Boosted search average pruned mass distribution for data (black points) and for the total background prediction for the inclusive selection.
Boosted search average pruned mass distribution for data and for the total background prediction for the b-tagged selection.
A combination of the searches for pair-produced vector-like partners of the top and bottom quarks in various decay channels ($T$$\rightarrow$$Zt/Wb/Ht$, $B$$\rightarrow$$Zb/Wt/Hb$) is performed using 36.1 fb$^{-1}$ of $pp$ collision data at $\sqrt{s}$ = 13 TeV with the ATLAS detector at the Large Hadron Collider. The observed data are found to be in good agreement with the Standard Model background prediction in all individual searches. Therefore, combined 95% confidence-level upper limits are set on the production cross-section for a range of vector-like quark scenarios, significantly improving upon the reach of the individual searches. Model-independent limits are set assuming the vector-like quarks decay to Standard Model particles. A singlet $T$ is excluded for masses below 1.31 TeV and a singlet $B$ is excluded for masses below 1.22 TeV. Assuming a weak isospin $(T,B)$ doublet and $|V_{Tb}| \ll |V_{tB}|$, $T$ and $B$ masses below 1.37 TeV are excluded.
Expected and observed 95% lower limits on the vector-like top quark mass as a function of the branching ratio, asumming that the vector-like quarks exclusively decay to SM particles (and third generation quarks).
Expected and observed 95% lower limits on the vector-like bottom quark mass as a function of the branching ratio, asumming that the vector-like quarks exclusively decay to SM particles (and third generation quarks).
Expected and observed 95% upper limits on the vector-like top quark pair-production signal strength (i.e. the ratio sigma_exclusion/sigma_VLQ) as a function of the branching ratio for a vector-like quark mass of 800 GeV, asumming that the vector-like quarks exclusively decay to SM particles (and third generation quarks). If interpreting these results in models with decays to non-Standard-Model particles, one must check that the additional decays will not end up in any control regions of the relevant analyses.
A search is presented for massive narrow resonances decaying either into two Higgs bosons, or into a Higgs boson and a W or Z boson. The decay channels considered are HH$\to \mathrm{b\overline{b}}\tau^{+}\tau^{-}$ and VH$ \to \mathrm{q\overline{q}}\tau^{+}\tau^{-}$, where H denotes the Higgs boson, and V denotes the W or Z boson. This analysis is based on a data sample of proton-proton collisions collected at a center-of-mass energy of 13 TeV by the CMS Collaboration, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. For the TeV-scale mass resonances considered, substructure techniques provide ways to differentiate among the hadronization products from vector boson decays to quarks, Higgs boson decays to bottom quarks, and quark- or gluon-induced jets. Reconstruction techniques are used that have been specifically optimized to select events in which the tau lepton pair is highly boosted. The observed data are consistent with standard model expectations and upper limits are set at 95% confidence level on the product of cross section and branching fraction for resonance masses between 0.9 and 4.0 TeV. Exclusion limits are set in the context of bulk radion and graviton models: spin-0 radion resonances are excluded below a mass of 2.7 TeV at 95% confidence level. In the spin-1 heavy vector triplet framework, mass-degenerate W' and Z' resonances with dominant couplings to the standard model gauge bosons are excluded below a mass of 2.8 TeV at 95% confidence level. There are the first limits for these decay channels at $\sqrt{s}=$ 13 TeV.
Observed 95% CL upper limits on the product of the production cross section and the branching fraction for a new spin-0 resonance decaying to HH, as a function of the resonance mass hypothesis.
Observed 95% CL upper limits on the product of the production cross section and the branching fraction for a new spin-2 resonance decaying to HH, as a function of the resonance mass hypothesis.
Observed 95% CL upper limits on the product of the production cross section and the branching fraction for a new spin-1 W prime resonance decaying to WH, as a function of the resonance mass hypothesis.
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