A search for heavy spin-1 and spin-2 resonances decaying into a top-antitop-quark pair has been performed with 140 fb$^{-1}$ of proton-proton collision data collected by the ATLAS experiment at the Large Hadron Collider at a centre-of-mass energy of $\sqrt{s}=13$ TeV. Final states with either exactly one electron or muon, or exactly two leptons ($ee$, $μμ$ or $eμ$), large missing transverse momentum, and two jets, at least one of which must be identified as likely containing a b-hadron decay, are considered. The search targets resonances with both narrow and broad widths relative to the detector resolution, and with masses in the range of 0.4-5.0 TeV. No significant deviation from the Standard Model prediction is observed. Exclusion limits are set on the production cross-section times branching ratio for hypothetical $Z'$ bosons, Kaluza-Klein gravitons, and Kaluza-Klein gluons that decay into top-quark pairs.
Selection efficiency times acceptance (Eff x Acc) for the ljets final state as a function of the tt̄ invariant mass at the parton level before the emission of FSR, for the (a) Z', (b) G<sub>KK</sub>, and (c) g<sub>KK</sub> signals. The selections in the resolved topology only (short-dashed magenta), the merged topology only (dashed blue) and the inclusive topology (solid black) are shown. The error bars correspond to the statistical uncertainty. All tt̄ decay modes are considered.
Selection efficiency times acceptance (Eff x Acc) for the ljets final state as a function of the tt̄ invariant mass at the parton level before the emission of FSR, for the (a) Z', (b) G<sub>KK</sub>, and (c) g<sub>KK</sub> signals. The selections in the resolved topology only (short-dashed magenta), the merged topology only (dashed blue) and the inclusive topology (solid black) are shown. The error bars correspond to the statistical uncertainty. All tt̄ decay modes are considered.
Selection efficiency times acceptance (Eff x Acc) for the ljets final state as a function of the tt̄ invariant mass at the parton level before the emission of FSR, for the (a) Z', (b) G<sub>KK</sub>, and (c) g<sub>KK</sub> signals. The selections in the resolved topology only (short-dashed magenta), the merged topology only (dashed blue) and the inclusive topology (solid black) are shown. The error bars correspond to the statistical uncertainty. All tt̄ decay modes are considered.
Measurements of the variation of anisotropic flow-plane angles ($Ψ_n$) with rapidity, commonly known as the flow-plane decorrelation, provide important insights into the initial conditions of the matter produced in heavy-ion collisions. In this paper, using data collected by the STAR experiment, we report the first measurement of the four-plane correlator observable $T_{n}\{ba;dc\}=\langle\langle\sin [n(Ψ^{b}_{n}-Ψ^{a}_{n})]\sin[n(Ψ^{d}_{n}-Ψ^{c}_{n})]\rangle\rangle$, where superscripts $a$, $b$, $c$, and $d$ denote sequential pseudorapidity ($η$) regions with $a$ corresponding to the most backward region, $b$ and $c$ close to mid-rapidity with $η_b<0$ and $η_c>0$, and $d$ being the most forward. The measurement is performed for the elliptic and triangular flow (i.e. $n=2$ and $3$) in Au+Au and isobar (Ru+Ru, Zr+Zr) collisions at $\sqrt{s_{_{\mathrm{NN}}}}$ = 200 GeV. The goal of calculating the correlation of the flow-plane angle variations from backward to mid-central, and from mid-central to forward regions, is to probe the systematic variation of flow angle over a wide $η$ range. In mid-central collisions ($10-30\%$ centrality), we find $T_{2}\{ba;dc\}= -0.004\pm 0.001 (\rm stat)\pm0.002(\rm syst)$ independent of the collision system. Such a small value of $T_{2}$ favors a ''random-walk'' variation of the flow-plane angles, where the rapidity correlation length is smaller than the entire region under study. These measurements provide new information on the decorrelation patterns in the system and offer a quantitative estimate of possible systematic variations in anisotropic flow angles such as ''twist'' between forward and backward regions. This opens new opportunities for understanding the three-dimensional structure and the time evolution of the quark-gluon plasma created in heavy-ion collisions.
The second harmonic sub-event plane resolutions from the TPC, EPD, and BBC.
The third harmonic sub-event plane resolutions from the TPC and EPD.
Resolution $Res(T_{2})$ plots for the Q-level calculations using Ru+Ru and Zr+Zr collisions for the second-order anisotropic flow.
The primary goal of the AEgIS experiment is to precisely measure the free fall of antihydrogen within Earth's gravitational field. To this end, a cold ~50K antihydrogen beam has to pass through two grids forming a moiré deflectometer before annihilating onto a position-sensitive detector, which shall determine the vertical position of the annihilation vertex relative to the grids with micrometric accuracy. Here we introduce a vertexing detector based on a modified mobile camera sensor and experimentally demonstrate that it can measure the position of antiproton annihilations with an accuracy of $0.62^{+0.40}_{-0.22}\mu m$, which represents a 35-fold improvement over the previous state-of-the-art for real-time antiproton vertexing. Importantly, these antiproton detection methods are directly applicable to antihydrogen. Moreover, the sensitivity to light of the sensor enables the in-situ calibration of the moiré deflectometer, significantly reducing systematic errors. This sensor emerges as a breakthrough technology for achieving the \aegis scientific goals and has been selected as the basis for the development of a large-area detector for conducting antihydrogen gravity measurements.
The distribution in thickness of the tracks in recorded antiprotons events as well as for 4-MeV protons. We attribute the higher-thickness peak of the antiproton distribution to tracks left in the sensor by protons and the lower peak to tracks left by pions. The distribution in thickness of tracks left by 4-MeV protons within the detector matches the topmost part of the distribution in thickness of proton tracks. We attribute the difference between the distributions mainly to the difference in energy spectrum of the protons.
The reconstructed position of antiproton annihilations recorded with the grid installed onto the sensor.
A histogram of the distance of the annihilations events from the nearest edge.
This letter presents the first measurement of the angle between different jet axes (denoted as ${\Delta}R$) in Pb$-$Pb collisions. The measurement is carried out in the 0$-$10% most-central events at $\sqrt{s_{\rm NN}} = 5.02$ TeV. Jets are assembled by clustering charged particles at midrapidity using the anti-$k_{\rm T}$ algorithm with resolution parameters $R=0.2$ and $0.4$ and transverse momenta in the intervals $40 < p_{\rm T}^{\rm ch jet} < 140$ GeV/$c$ and $80 < p_{\rm T}^{\rm ch jet} < 140$ GeV/$c$, respectively. Measurements at these low transverse momenta enhance the sensitivity to quark$-$gluon plasma (QGP) effects. A comparison to models implementing various mechanisms of jet energy loss in the QGP shows that the observed narrowing of the Pb$-$Pb distribution relative to pp can be explained if quark-initiated jets are more likely to emerge from the medium than gluon-initiated jets. These new measurements discard intra-jet $p_{\rm T}$ broadening as described in a model calculation with the BDMPS formalism as the main mechanism of energy loss in the QGP. The data are sensitive to the angular scale at which the QGP can resolve two independent splittings, favoring mechanisms that incorporate incoherent energy loss.
$\Delta R_{\rm axis}$ distribution for WTA$\textendash$Standard for jets of $R=0.2$, in the interval $40<p_{\rm T}^{\rm ch \ jet}<60 \ {\rm GeV}/c$. The corresponding pp baseline can be found in: https://www.hepdata.net/record/ins2182727?version=1.
Pb$\textendash$Pb/pp ratio distribution for WTA$\textendash$Standard for jets of $R=0.2$, in the interval $40<p_{\rm T}^{\rm ch \ jet}<60 \ {\rm GeV}/c$. The corresponding pp baseline can be found in: https://www.hepdata.net/record/ins2182727?version=1.
$\Delta R_{\rm axis}$ distribution for WTA$\textendash$Standard for jets of $R=0.2$, in the interval $60<p_{\rm T}^{\rm ch \ jet}<80 \ {\rm GeV}/c$. The corresponding pp baseline can be found in: https://www.hepdata.net/record/ins2182727?version=1.
The Higgs boson (H) decay width is determined from the ratio of off- and on-shell production of H $\to$ WW $\to$ e$νμν$ using proton-proton collision data corresponding to an integrated luminosity of 138 fb$^{-1}$ collected at $\sqrt{s}$ = 13 TeV by the CMS experiment at the LHC. The off-shell signal strength is measured as $μ_\text{off-shell}$ = 1.2$^{+0.8}_{-0.7}$. The Higgs boson total decay width is $Γ_\text{H}$ = 3.9$^{+2.7}_{-2.2}$ MeV, in agreement with the standard model prediction. The uncertainty in this result represents a factor of three improvement over the previous CMS result in this decay channel.
Post-fit VBF off-shell DNN output distribution in the VBF off-shell SR. Different contributions to background are indicated by the colour-filled histograms. The grey-hatched error band shows total uncertainties. The ratio of observations to total expectations is given in the lower panel, together with the total uncertainties after fitting, indicated by the grey-hatched band.
Post-fit ggF off-shell DNN output distribution in the 2-jets ggF off-shell SR. Different contributions to background are indicated by the colour-filled histograms. The grey-hatched error band shows total uncertainties. The ratio of observations to total expectations is given in the lower panel, together with the total uncertainties after fitting, indicated by the grey-hatched band.
Post-fit ggF off-shell DNN output distribution in the 1-jet ggF off-shell SR. Different contributions to background are indicated by the colour-filled histograms. The grey-hatched error band shows total uncertainties. The ratio of observations to total expectations is given in the lower panel, together with the total uncertainties after fitting, indicated by the grey-hatched band.
A search is conducted for standard model Higgs bosons with large transverse momentum ($p_\mathrm{T}$) decaying to bottom quark pairs and produced in association with a hadronically decaying W or Z boson at the LHC. The result is based on a dataset of proton-proton collisions at a center-of-mass energy of 13 TeV collected with the CMS detector in 2016$-$2018, corresponding to an integrated luminosity of 138 fb$^{-1}$. Boosted Higgs, W, and Z boson decays are reconstructed using large-radius jets with $p_\mathrm{T}$$\gt$ 450 GeV and identified with heavy-flavor classifiers based on a graph convolutional neural network. The observed signal strength relative to the standard model expectation is $μ$ = 0.7$2^{+0.75}_{-0.71}$ including statistical and systematic uncertainties.
Post-fit distributions for Signal and Background processes.
Fitted signal strengths
Production fraction ratios of B$^+$, B$^0$, and B$^0_\mathrm{s}$ mesons are measured in proton-proton collisions at $\sqrt{s}$ = 13 TeV using a special data set recorded in 2018 with high-rate triggers designed to collect an unbiased sample of $10^{10}$ b hadrons with the CMS experiment at the LHC. These data allow the use of the open-charm decays of B mesons (B$_\mathrm{(s)}$$\to$$π$D$_\mathrm{(s)}$) where the D meson decays into fully hadronic final states. Production fraction ratios as functions of B meson transverse momentum ($p_\mathrm{T}$) and rapidity ($y$) are measured using the open-charm decays in the kinematic range of 8 $\lt$$p_\mathrm{T}$$\lt$ 60 GeV and $\lvert y \rvert$$\lt$ 2.25. In addition, the same data are used to measure the relative production fraction ratios with the charmonium decay channels (B$_\mathrm{(s)}$$\to$ X$\,$J/$ψ$ with X indicating a K$^+$, K$^*$(892)$^0$, or $ϕ$(1020) meson) with the J/$ψ$ meson decaying into a pair of muons. By utilizing known branching fractions, precision theoretical calculations, and the open-charm results, the production fraction ratios in the charmonium samples are determined with an absolute normalization for the first time. These results also improve several world-average values of the ratios of branching fractions of B meson decays to charmonium and open-charm states. Finally, we test isospin invariance in B meson production in proton-proton collisions and observe that it holds within the experimental precision.
The invariant mass distribution of $B^+$ candidates, corrected using the $D^0$ meson mass, is shown for $13 < p_{T} < 18$ GeV along with the corresponding fit.
The invariant mass distribution of $B^0$ candidates, corrected using the $D^-$ meson mass, is shown for $18 < p_{T} < 23$ GeV along with the corresponding fit.
The invariant mass distribution of $B_s^{0}$ candidates, corrected using the $D^-_{s}$ meson mass, is shown for $23 < p_{T} < 28$ GeV along with the corresponding fit.
Meson-baryon systems with strangeness content provide a unique laboratory for investigating the strong interaction and testing theoretical models of hadron structure and dynamics. In this work, the measured correlation functions for oppositely charged $Ξ-{\rm K}$ and $Ξ-π$ pairs obtained in high-multiplicity pp collisions at $\sqrt{s} = 13$ TeV at the LHC are presented. For the first time, high-precision data on the $Ξ-{\rm K}$ interaction are delivered at small relative momenta. The scattering lengths, extracted via the Lednický-Lyuboshits expression of the pair wavefunction, indicate a repulsive and a shallow attractive strong interaction for the $Ξ-{\rm K}$ and $Ξ-π$ systems, respectively. The $Ξ(1620)$ and $Ξ(1690)$ states are observed in the $Ξ-π$ correlation function and their properties, mass and width, are determined. These measurements are in agreement with other available results. Such high-precision data can help refine the understanding of these resonant states, provide stronger constraints for chirally motivated potentials, and address the key challenge of describing the coupled-channel dynamics that may give rise to molecular configurations.
The $\Xi$K correlation function.
The genuine $\Xi$K correlation function.
The $\Xi\pi$ correlation function.
In this letter, the first measurement of the femtoscopic correlation of protons and $Σ^+$ hyperons is presented and used to study the p$-Σ^+$ interaction. The measurement is performed with the ALICE detector in high-multiplicity triggered pp collisions at $\sqrt{s} = 13$ TeV. The $Σ^+$ hyperons are reconstructed using a missing-mass approach in the decay channel to $\textrm{p} + π^0$ with $π^0\rightarrowγγ$, while both $Σ^+$ and protons are identified using a machine learning approach. These techniques result in a high reconstruction efficiency and purity, which allows the measurement of the p$-Σ^+$ correlation function for the first time. Thanks to the high significance achieved in the p$-Σ^+$ correlation signal, it is possible to discriminate between the predictions of different models of the N$-Σ$ interaction and to accomplish a first determination of the p$-Σ^+$ scattering parameters.
Raw correlation function $C(k^{*})$ of $\textrm{p}-\Sigma^+$ and $\bar{\textrm{p}}-\bar{\Sigma}^-$ in high-multiplicity triggered pp collisions at $\sqrt{{s}}=13$ TeV. The data points are shifted to the center of gravity of the mixed-event distribution.
Corrected (genuine) correlation function $C(k^{*})$ of $\textrm{p}-\Sigma^+$ and $\bar{\textrm{p}}-\bar{\Sigma}^-$ in high-multiplicity triggered pp collisions at $\sqrt{{s}}=13$ TeV. The data points are corrected by the genuine $\lambda$ parameter, assuming that the non-genuine correlation function is unity (flat). No momentum unfolding is applied to the data points. The data points are shifted to the center of gravity of the mixed-event distribution.
The vacuum is now understood to possess a rich and complex structure, characterized by fluctuating energy fields and a condensate of virtual quark-antiquark pairs. The spontaneous breaking of the approximate chiral symmetry, signaled by the nonvanishing quark condensate $\langle q\bar{q}\rangle$, is dynamically generated through topologically nontrivial gauge configurations such as instantons. The precise mechanism linking the chiral symmetry breaking to the mass generation associated with quark confinement remains a profound open question in Quantum Chromodynamics (QCD) - the fundamental theory of strong interaction. High energy proton-proton collisions could liberate virtual quark-antiquark pairs from the vacuum that subsequently undergo confinement to form hadrons, whose properties could serve as probes into QCD confinement and the quark condensate. Here, we report evidence of spin correlations in $Λ\barΛ$ hyperon pairs inherited from spin-correlated strange quark-antiquark virtual pairs. Measurements by the STAR experiment at the Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National Laboratory reveal a relative polarization signal of $(18 \pm 4)\%$ that links the virtual spin-correlated quark pairs from the QCD vacuum to their final-state hadron counterparts. Crucially, this correlation vanishes when the hyperon pairs are widely separated in angle, consistent with the decoherence of the quantum system. Our findings provide a new experimental paradigm for exploring the dynamics and interplay of quark confinement and entanglement.
$\mathrm{d}N/\mathrm{d}\cos\theta^\star$ distributions of decay (anti-)protons for short-range pairs ($|\Delta y| < 0.5$ and $|\Delta \phi| < \pi/3$) $\Lambda\bar{\Lambda}$, $\Lambda\Lambda$, and $\bar{\Lambda}\bar{\Lambda}$ hyperon pairs measured at mid-rapidity ($|y| < 1$).
$\mathrm{d}N/\mathrm{d}\cos\theta^\star$ distributions of decay (anti-)protons for long-range pairs ($0.5 < |\Delta y| < 2.0$ or $\pi/3 <|\Delta \phi| < \pi$) $\Lambda\bar{\Lambda}$, $\Lambda\Lambda$, and $\bar{\Lambda}\bar{\Lambda}$ hyperon pairs measured at mid-rapidity ($|y| < 1$).
Spin correlation $P_\mathrm{\Lambda_1\Lambda_2}$ of short-range $\Lambda\bar{\Lambda}$ (1), $\Lambda\Lambda$ (2), and $\bar{\Lambda}\bar{\Lambda}$ (3) hyperon pars and $K^0_\mathrm{S}K^0_\mathrm{S}$ (4) meson pairs.
Forum