A search is performed for W' bosons decaying to a top and a bottom quark in the all-hadronic final state, in proton-proton collisions at a center-of-mass energy of 13 TeV. The analyzed data were collected by the CMS experiment between 2016 and 2018 and correspond to an integrated luminosity of 137 fb$^{-1}$. Deep neural network algorithms are used to identify the jet initiated by the bottom quark and the jet containing the decay products of the top quark when the W boson from the top quark decays hadronically. No excess above the estimated standard model background is observed. Upper limits on the production cross sections of W' bosons decaying to a top and a bottom quark are set. Both left- and right-handed W' bosons with masses below 3.4 TeV are excluded at 95% confidence level, and the most stringent limits to date on W' bosons decaying to a top and a bottom quark in the all-hadronic final state are obtained.
The reconstructed m$_{tb}$ distributions in data and expected background in signal region for the data taking period of 2016. Yield in each bin is divided by the corresponding bin width.
The reconstructed m$_{tb}$ distributions in data and expected background in validation region for the data taking period of 2016. Yield in each bin is divided by the corresponding bin width.
The reconstructed m$_{tb}$ distributions in data and expected background in signal region for the data taking period of 2017. Yield in each bin is divided by the corresponding bin width.
Jet production in lead-lead (PbPb) and proton-proton (pp) collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV is studied with the CMS detector at the LHC, using PbPb and pp data samples corresponding to integrated luminosities of 404 $\mu$b$^{-1}$ and 27.4 pb$^{-1}$, respectively. Jets with different areas are reconstructed using the anti-$k_\mathrm{T}$ algorithm by varying the distance parameter $R$. The measurements are performed using jets with transverse momenta ($p_\mathrm{T}$) greater than 200 GeV and in a pseudorapidity range of $|\eta|$$\lt$ 2. To reveal the medium modification of the jet spectra in PbPb collisions, the properly normalized ratio of spectra from PbPb and pp data is used to extract jet nuclear modification factors as functions of the PbPb collision centrality, $p_\mathrm{T}$ and, for the first time, as a function of $R$ up to 1.0. For the most central collisions, a strong suppression is observed for high-$p_\mathrm{T}$ jets reconstructed with all distance parameters, implying that a significant amount of jet energy is scattered to large angles. The dependence of jet suppression on $R$ is expected to be sensitive to both the jet energy loss mechanism and the medium response, and so the data are compared to several modern event generators and analytic calculations. The models considered do not fully reproduce the data.
Spectra of jets with |eta jet| < 2.0 for R = 0.2, for pp collisions and different centrality classes of PbPb collisions.
Spectra of jets with |eta jet| < 2.0 for R = 0.3, for pp collisions and different centrality classes of PbPb collisions.
Spectra of jets with |eta jet| < 2.0 for R = 0.4, for pp collisions and different centrality classes of PbPb collisions.
A search for heavy resonances decaying into a $W$ or $Z$ boson and a Higgs boson produced in proton$-$proton collisions at the Large Hadron Collider at $\sqrt{s} = 13$ TeV is presented. The analysis utilizes the dominant $W \to q \bar{q}^\prime$ or $Z \to q \bar{q}$ and $H \to b \bar{b}$ decays with substructure techniques applied to large-radius jets. A sample corresponding to an integrated luminosity of 139 fb$^{-1}$ collected with the ATLAS detector is analyzed and no significant excess of data is observed over the background prediction. The results are interpreted in the context of the Heavy Vector Triplet model with spin-1 $W^\prime$ and $Z^\prime$ bosons. Upper limits on the cross section are set for resonances with mass between 1.5 and 5.0 TeV, ranging from 6.8 to 0.53 fb for $W^\prime \to WH$ and from 8.7 to 0.53 fb for $Z^\prime \to ZH$ at the 95 % confidence level.
Observed and expected 95% CL upper limits on the cross section in the WH channel.
Observed and expected 95% CL upper limits on the cross section in the WH channel.
Observed and expected 95% CL upper limits on the cross section in the ZH channel.
A search for dark matter is conducted in final states containing a photon and missing transverse momentum in proton$-$proton collisions at $\sqrt{s}$ = 13 TeV. The data, collected during 2015$-$2018 by the ATLAS experiment at the CERN LHC, correspond to an integrated luminosity of 139 fb$^{-1}$. No deviations from the predictions of the Standard Model are observed and 95% confidence-level upper limits between 2.45 fb and 0.5 fb are set on the visible cross section for contributions from physics beyond the Standard Model, in different ranges of the missing transverse momentum. The results are interpreted as 95% confidence-level limits in models where weakly interacting dark-matter candidates are pair-produced via an s-channel axial-vector or vector mediator. Dark-matter candidates with masses up to 415 (580) GeV are excluded for axial-vector (vector) mediators, while the maximum excluded mass of the mediator is 1460 (1470) GeV. In addition, the results are expressed in terms of 95% confidence-level limits on the parameters of a model with an axion-like particle produced in association with a photon, and are used to constrain the coupling $g_{aZ\gamma}$ of an axion-like particle to the electroweak gauge bosons.
Distribution of $E^{miss}_T$ in data and for the expected SM background in the SRs after performing the 'simplified shape fit'. The error bars are statistical, and the dashed band includes statistical and systematic uncertainties determined by the fit. The expectations for the simplified model for two different values of $m_{\chi}$ and $m_{med}$, and with $g_{q}=0.25$ and $g_{\chi}=1.0$ and for the ALP model are also shown. The lower panel shows the ratio of data to expected background event yields.
Distribution of $E^{miss}_T$ in data and for the expected SM background in the SRs after performing the 'simplified shape fit'. Overflows are included in the fourth bin of each distribution. The error bars are statistical, and the dashed band includes statistical and systematic uncertainties determined by the fit. The expectations for the simplified model for two different values of $m_{\chi}$ and $m_{med}$, and with $g_{q}=0.25$ and $g_{\chi}=1.0$ and for the ALP model are also shown. The lower panel shows the ratio of data to expected background event yields.
Distribution of $E^{miss}_T$ in data and for the expected SM background in the Single-Muon CR after performing the 'simplified shape fit'. The $E^{miss}_T$ calculation in this CR does not include the muon contribution. The error bars are statistical, and the dashed band includes statistical and systematic uncertainties determined by the fit. The lower panel shows the ratio of data to expected background event yields.
A search for the pair production of heavy leptons as predicted by the type-III seesaw mechanism is presented. The search uses proton-proton collision data at a centre-of-mass energy of 13 TeV, corresponding to 139 fb$^{-1}$ of integrated luminosity recorded by the ATLAS detector during Run 2 of the Large Hadron Collider. The analysis focuses on the final state with two light leptons (electrons or muons) of different flavour and charge combinations, with at least two jets and large missing transverse momentum. No significant excess over the Standard Model expectation is observed. The results are translated into exclusion limits on heavy-lepton masses, and the observed lower limit on the mass of the type-III seesaw heavy leptons is 790 GeV at 95% confidence level.
Cross-sections of the type-III seesaw process for mass points used in the analysis. Branching ratios into at least two leptons are presented with the corresponding effective cross-section.
Expected and observed 95 % CLs exclusion limits for the type-III seesaw process with the corresponding one- and two-standard-deviation bands, showing the 95 % CL upper limit on the cross-section.
Selection efficiencies in percentage relative to the events with at least two leptons for signal mass points used in the analysis. The efficiency is defined as the ratio of expected signal events in a signal region compared with the number of expected events produced, for integrated luminosity 139 fb$^{-1}$.
We present the first large-acceptance measurement of event-wise mean transverse momentum mean p_t fluctuations for Au-Au collisions at nucleon-nucleon center-of-momentum collision energy sqrt{s_{NN}} = 130 GeV. The observed non-statistical mean p_t fluctuations substantially exceed in magnitude fluctuations expected from the finite number of particles produced in a typical collision. The r.m.s. fractional width excess of the event-wise mean p_t distribution is 13.7 +/- 0.1(stat) +/- 1.3(syst)% relative to a statistical reference, for the 15% most-central collisions and for charged hadrons within pseudorapidity range |eta|<1, 2pi azimuth and 0.15 < p_t < 2 GeV/c. The width excess varies smoothly but non-monotonically with collision centrality, and does not display rapid changes with centrality which might indicate the presence of critical fluctuations. The reported mean p_t fluctuation excess is qualitatively larger than those observed at lower energies and differs markedly from theoretical expectations. Contributions to mean p_t mean fluctuations from semi-hard parton scattering in the initial state and dissipation in the bulk colored medium are discussed.
Event frequency distribution on $\sqrt{n}(\langle p_t\rangle - \hat{p}_t)/\sigma\hat{p}_t$ for 80% of primary charged hadrons in $|\eta|$ < 1 for 183k central events
Difference in upper panel between data and gamma reference
Centrality dependences of the measured charge independent (CI) and charge dependent (CD) difference factors $\Delta\sigma_{p_t:n}$ plus the corresponding values extrapolated to 100% tracking efficiency. Statistical errors $\pm$ 0.5 MeV/c; systematic errors are $\pm$ 9%. Difference factors extrapolated to 100% tracking efficiency and no secondary particle contamination. Uncertainties are $\pm$ 12%.
We report the first measurements of transverse single-spin asymmetries for inclusive jet and jet + $\pi^{\pm}$ production at midrapidity from transversely polarized proton-proton collisions at $\sqrt{s} = 500$ GeV. The data were collected in 2011 with the STAR detector sampled from 23 pb$^{-1}$ integrated luminosity with an average beam polarization of 53%. Asymmetries are reported for jets with transverse momenta $6 < p_{T, jet} < 55$ GeV/c and pseudorapidity $|\eta| < 1$. Presented are measurements of the inclusive-jet azimuthal transverse single-spin asymmetry, sensitive to twist-3 initial-state quark-gluon correlators; the Collins asymmetry, sensitive to quark transversity coupled to the polarized Collins fragmentation function; and the first measurement of the "Collins-like" asymmetry, sensitive to linearly polarized gluons. Within the present statistical precision, inclusive-jet and Collins-like asymmetries are small, with the latter allowing the first experimental constraints on gluon linear polarization in a polarized proton. At higher values of jet transverse momenta, we observe the first non-zero Collins asymmetries in polarized-proton collisions, with a statistical significance of greater than $5\sigma$. The results span a range of x similar to results from SIDIS but at much higher $Q^{2}$. The Collins results enable tests of universality and factorization-breaking in the transverse momentum-dependent formulation of perturbative quantum chromodynamics.
Inclusive jet asymmetries $A_{UT}^{\sin(\theta_S)}$ as a function of particle-jet $p_T$.
Inclusive jet asymmetries $A_{UT}^{\sin(\theta_S)}$ as a function of particle-jet $p_T$.
Collins-like asymmetries as a function of particle-jet $p_T$.
The STAR Collaboration reports measurements of the longitudinal double-spin asymmetry, $A_{LL}$, for neutral pions produced at forward directions in polarized proton-proton collisions, at a center-of-mass energy of $510$ GeV. Results are given for transverse momenta in the range $2
Longitudinal Double-Spin Asymmetry, $A_{LL}$ vs $\pi^0$ transverse momentum in polarized pp collisions at $\sqrt{s}$ = 510 GeV. $\pm 6.7\%$ polarization scale uncertainty not shown.
Longitudinal Double-Spin Asymmetry, $A_{LL}$ vs $\pi^0$ transverse momentum in polarized pp collisions at $\sqrt{s}$ = 510 GeV. $\pm 6.7\%$ polarization scale uncertainty not shown.
The azimuthal anisotropic flow of identified and unidentified charged particles has been systematically studied in Cu+Au collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV for harmonics $n=$ 1-4 in the pseudorapidity range $|\eta|<1$. The directed flow in Cu+Au collisions is compared with the rapidity-odd and, for the first time, the rapidity-even components of charged particle directed flow in Au+Au collisions at $\sqrt{s_{_{NN}}}$ = 200~GeV. The slope of the directed flow pseudorapidity dependence in Cu+Au collisions is found to be similar to that in Au+Au collisions, with the intercept shifted toward positive $\eta$ values, i.e., the Cu-going direction. The mean transverse momentum projected onto the spectator plane, $\langle p_x\rangle$, in Cu+Au collision also exhibits approximately linear dependence on $\eta$ with the intercept at about $\eta\approx-0.4$, closer to the rapidity of the Cu+Au system center-of-mass. The observed dependencies find natural explanation in a picture of the directed flow originating partly due the "tilted source" and partly due to the rapidity dependent asymmetry in the initial density distribution. Charge-dependence of the $\langle p_x\rangle$ was also observed in Cu+Au collisions, indicating an effect of the initial electric field created by charge difference of the spectator protons in two colliding nuclei. The rapidity-even component of directed flow in Au+Au collisions is close to that in Pb+Pb collisions at $\sqrt{s_{_{NN}}}$ = 2.76 TeV, indicating a similar magnitude of dipole-like fluctuations in the initial-state density distribution. Higher harmonic flow in Cu+Au collisions exhibits similar trends to those observed in Au+Au and Pb+Pb collisions and is qualitatively reproduced by a viscous hydrodynamic model and a multi-phase transport model. For all harmonics with $n\ge2$ we observe an approximate scaling of $v_n$ with the number of constituent quarks.
Directed flow $v_1(\eta)$ and $<p_x>(\eta)$ of charged particles measured with respect to the target and projectile spectator planes in 10%-40% centrality for Cu+Au collisions.
Directed flow $v_1(\eta)$ and $<p_x>(\eta)$ of charged particles measured with respect to the target and projectile spectator planes in 10%-40% centrality for Au+Au collisions.
Conventional and fluctuation components of directed flow $v_1(\eta)$ and momentum shift $<p_x>/<p_T>(\eta)$ of charged particles in 10%-40% centrality for Cu+Au and Au+Au collisions.
The longitudinal spin transfer, $D_{LL}$, from high energy polarized protons to $\Lambda$ and $\bar{\Lambda}$ hyperons has been measured for the first time in proton-proton collisions at $\sqrt{s} = 200 \mathrm{GeV}$ with the STAR detector at RHIC. The measurements cover pseudorapidity, $\eta$, in the range $|\eta| < 1.2$ and transverse momenta, $p_\mathrm{T}$, up to $4 \mathrm{GeV}/c$. The longitudinal spin transfer is found to be $D_{LL}= -0.03\pm 0.13(\mathrm{stat}) \pm 0.04(\mathrm{syst})$ for inclusive $\Lambda$ and $D_{LL} = -0.12 \pm 0.08(\mathrm{stat}) \pm 0.03(\mathrm{syst})$ for inclusive $\bar{\Lambda}$ hyperons with $<\eta> = 0.5$ and $<p_\mathrm{T}> = 3.7 \mathrm{GeV}/c$. The dependence on $\eta$ and $p_\mathrm{T}$ is presented.
The spin transfer $D_{LL}$ to (a) $\Lambda$ and (b) $\bar{\Lambda}$ hyperons produced at positive pseudorapidity with respect to the polarized proton beam from $MB$, $JP$, and $HT$ data versus hyperon transverse momenta $p_{T}$. The sizes of the statistical and systematic uncertainties are indicated by the vertical bars and bands, respectively. For clarity, the HT data points have been shifted slightly in $p_{T}$. The dotted vertical lines indicate the $p_{T}$ intervals in the analysis of HT and JP data.
The spin transfer $D_{LL}$ to (a) $\Lambda$ and (b) $\bar{\Lambda}$ hyperons produced at positive pseudorapidity with respect to the polarized proton beam from $MB$, $JP$, and $HT$ data versus hyperon transverse momenta $p_{T}$. The sizes of the statistical and systematic uncertainties are indicated by the vertical bars and bands, respectively. For clarity, the HT data points have been shifted slightly in $p_{T}$. The dotted vertical lines indicate the $p_{T}$ intervals in the analysis of HT and JP data.
The spin transfer $D_{LL}$ to (a) $\Lambda$ and (b) $\bar{\Lambda}$ hyperons produced at positive pseudorapidity with respect to the polarized proton beam from $MB$, $JP$, and $HT$ data versus hyperon transverse momenta $p_{T}$. The sizes of the statistical and systematic uncertainties are indicated by the vertical bars and bands, respectively. For clarity, the HT data points have been shifted slightly in $p_{T}$. The dotted vertical lines indicate the $p_{T}$ intervals in the analysis of HT and JP data.
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