A measurement of the WZ$γ$ triboson production cross section is presented. The analysis is based on a data sample of proton-proton collisions at a center-of-mass energy of $\sqrt{s}$ = 13 TeV recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 138 fb$^{-1}$. The analysis focuses on the final state with three charged leptons, $\ell^\pmν\ell^+\ell^-$, where $\ell$ = e or $μ$, accompanied by an additional photon. The observed (expected) significance of the WZ$γ$ signal is 5.4 (3.8) standard deviations. The cross section is measured in a fiducial region, where events with an $\ell$ originating from a tau lepton decay are excluded, to be 5.48 $\pm$ 1.11 fb, which is compatible with the prediction of 3.69 $\pm$ 0.24 fb at next-to-leading order in quantum chromodynamics. Exclusion limits are set on anomalous quartic gauge couplings and on the production cross sections of massive axion-like particles.
The distributions of the variables used in the simultaneous fit for the nonprompt $l$ CR. The black points with error bars represent the data and their statistical uncertainties, whereas the shaded band represents the predicted uncertainties. The bottom panel in each figure shows the ratio of the number of events observed in data to that of the total SM prediction. The last bin of each plot has been extended to include the overflow contribution.
The distributions of the variables used in the simultaneous fit for the nonprompt $\gamma$ CR. The black points with error bars represent the data and their statistical uncertainties, whereas the shaded band represents the predicted uncertainties. The bottom panel in each figure shows the ratio of the number of events observed in data to that of the total SM prediction. The last bin of each plot has been extended to include the overflow contribution.
The distributions of the variables used in the simultaneous fit for the ZZ CR. The black points with error bars represent the data and their statistical uncertainties, whereas the shaded band represents the predicted uncertainties. The bottom panel in each figure shows the ratio of the number of events observed in data to that of the total SM prediction. The last bin of each plot has been extended to include the overflow contribution.
A search for $t$-channel exchange of leptoquarks (LQs) is performed in dimuon and dielectron spectra using proton-proton collision data collected at $\sqrt{s}$ = 13 TeV with the CMS detector at the CERN LHC. The data correspond to an integrated luminosity of 138 fb$^{-1}$. Eight scenarios are considered, in which up or down quarks couple to muons or electrons via a scalar or vector LQ exchange, for dilepton invariant masses above 500 GeV. The LQ masses are probed up to 5 TeV, beyond a regime probed by previous pair-production and single-production searches. The differential distributions of dilepton events are fit to templates that model the nonresonant LQ exchange and various standard model background processes. Limits are set on LQ-fermion coupling strengths for scalar and vector LQ masses in the 1$-$5 TeV range at 95% confidence level, establishing stringent limits on first- and second-generation LQs.
Observed and Expected UL exclusions on the $BR(H\to SUEP)$ of hadronic signals with $m_{A'} = 0.7\;GeV$ and $BR(A' \rightarrow ee) = BR(A' \rightarrow \mu\mu) = 0.15$ and $BR(A' \rightarrow \pi\pi) = 0.7$.
The observed data in the dielectron channel and the fitted signal-plus-background templates, shown for the $S_{e u}$ scenario with a candidate LQ mass of 2.5 TeV. Distributions of events are binned in the reconstructed dilepton mass, rapidity, and cosine theta.
Observed and Expected UL exclusions on the $BR(H\to S)$ of leptonic signals with $m_{A'} = 0.5\;GeV$ and $BR(A' \rightarrow ee) = BR(A' \rightarrow \mu\mu) = 0.2$ and $BR(A' \rightarrow \pi\pi) = 0.6$.
We report multi-differential measurements of strange hadron production ranging from mid- to target-rapidity in Au+Au collisions at a center-of-momentum energy per nucleon pair of $\sqrt{s_{\rm NN}}=3$ GeV with the STAR experiment at RHIC. $K^0_S$ meson and $\Lambda$ hyperon yields are measured via their weak decay channels. Collision centrality and rapidity dependences of the transverse momentum spectra and particle ratios are presented. Particle mass and centrality dependence of the average transverse momenta of $\Lambda$ and $K^0_S$ are compared with other strange particles, providing evidence of the development of hadronic rescattering in such collisions. The 4$\pi$ yields of each of these strange hadrons show a consistent centrality dependence. Discussions on radial flow, the strange hadron production mechanism, and properties of the medium created in such collisions are presented together with results from hadronic transport and thermal model calculations.
dN/dy of lambda for different centrality bins.
dN/dy of Ks0 for different centrality bins.
Rapidity dependence of Lambda/p for different centrality bins.
In a Quark-Gluon Plasma (QGP), the fundamental building blocks of matter, quarks and gluons, are under extreme conditions of temperature and density. A QGP could exist in the early stages of the Universe, and in various objects and events in the cosmos. The thermodynamic and hydrodynamic properties of the QGP are described by Quantum Chromodynamics (QCD) and can be studied in heavy-ion collisions. Despite being a key thermodynamic parameter, the QGP temperature is still poorly known. Thermal lepton pairs ($e^+e^-$ and $\mu^+\mu^-$) are ideal penetrating probes of the true temperature of the emitting source, since their invariant-mass spectra suffer neither from strong final-state interactions nor from blue-shift effects due to rapid expansion. Here we measure the QGP temperature using thermal $e^+e^-$ production at the Relativistic Heavy Ion Collider (RHIC). The average temperature from the low-mass region (in-medium $\rho^0$ vector-meson dominant) is $(1.99 \pm 0.24) \times 10^{12}$ K, consistent with the chemical freeze-out temperature from statistical models and the phase transition temperature from LQCD. The average temperature from the intermediate mass region (above the $\rho^0$ mass, QGP dominant) is significantly higher at $(3.40 \pm 0.55)\times 10^{12}$ K. This work provides essential experimental thermodynamic measurements to map out the QCD phase diagram and understand the properties of matter under extreme conditions.
The inclusive dielectron invariant mass spectra of 27 GeV in 0-80% centrality.
The inclusive dielectron invariant mass spectra of 54.4 GeV in 0-80% centrality.
The charged multiplicity normalzied excess yield of 27 GeV in 0-80% centrality.
Atomic nuclei are self-organized, many-body quantum systems bound by strong nuclear forces within femtometer-scale space. These complex systems manifest a variety of shapes, traditionally explored using non-invasive spectroscopic techniques at low energies. However, at these energies, their instantaneous shapes are obscured by long-timescale quantum fluctuations, making direct observation challenging. Here we introduce the ``collective flow assisted nuclear shape imaging'' method, which images the nuclear global shape by colliding them at ultrarelativistic speeds and analyzing the collective response of outgoing debris. This technique captures a collision-specific snapshot of the spatial matter distribution within the nuclei, which, through the hydrodynamic expansion, imprints patterns on the particle momentum distribution observed in detectors. We benchmark this method in collisions of ground state Uranium-238 nuclei, known for their elongated, axial-symmetric shape. Our findings show a large deformation with a slight deviation from axial symmetry in the nuclear ground state, aligning broadly with previous low-energy experiments. This approach offers a new method for imaging nuclear shapes, enhances our understanding of the initial conditions in high-energy collisions and addresses the important issue of nuclear structure evolution across energy scales.
Data from Figure 2, panel a, Au+Au, 0-0.5% Centrality, 0.2<p_{T}<3 GeV/c, systematics include non-flow difference in the two systems, but correlated non-flow systematics with the value of $\delta \left\langle v_{2}^{2}\right\rangle$ =+-3.2e-5 included
Data from Figure 2, panel a, U+U, 0-0.5% Centrality, 0.2<p_{T}<3 GeV/c, systematics include non-flow difference in the two systems, but correlated non-flow systematics with the value of $\delta \left\langle v_{2}^{2}\right\rangle$ =+-3.2e-5 included
Data from Figure 2, panel b, Au+Au, 0-0.5% Centrality, 0.2<p_{T}<3 GeV/c
The GlueX experiment at Jefferson Lab studies photoproduction of mesons using linearly polarized $8.5\,\text{GeV}$ photons impinging on a hydrogen target which is contained within a detector with near-complete coverage for charged and neutral particles. We present measurements of spin-density matrix elements for the photoproduction of the vector meson $\rho$(770). The statistical precision achieved exceeds that of previous experiments for polarized photoproduction in this energy range by orders of magnitude. We confirm a high degree of $s$-channel helicity conservation at small squared four-momentum transfer $t$ and are able to extract the $t$-dependence of natural and unnatural-parity exchange contributions to the production process in detail. We confirm the dominance of natural-parity exchange over the full $t$ range. We also find that helicity amplitudes in which the helicity of the incident photon and the photoproduced $\rho(770)$ differ by two units are negligible for $-t<0.5\,\text{GeV}^{2}/c^{2}$.
Spin-density matrix elements for the photoproduction of $\rho(770)$ in the helicity system. The first uncertainty is statistical, the second systematic. The systematic uncertainties for the polarized SDMEs $\rho^1_{ij}$ and $\rho^2_{ij}$ contain an overall relative normalization uncertainty of 2.1% which is fully correlated for all values of $-t$.
Spin-density matrix elements for the photoproduction of $\rho(770)$ in the helicity system. The first uncertainty is statistical, the second systematic. The systematic uncertainties for the polarized SDMEs $\rho^1_{ij}$ and $\rho^2_{ij}$ contain an overall relative normalization uncertainty of 2.1% which is fully correlated for all values of $-t$.
We report the total and differential cross sections for $J/\psi$ photoproduction with the large acceptance GlueX spectrometer for photon beam energies from the threshold at 8.2~GeV up to 11.44~GeV and over the full kinematic range of momentum transfer squared, $t$. Such coverage facilitates the extrapolation of the differential cross sections to the forward ($t = 0$) point beyond the physical region. The forward cross section is used by many theoretical models and plays an important role in understanding $J/\psi$ photoproduction and its relation to the $J/\psi-$proton interaction. These measurements of $J/\psi$ photoproduction near threshold are also crucial inputs to theoretical models that are used to study important aspects of the gluon structure of the proton, such as the gluon Generalized Parton Distribution (GPD) of the proton, the mass radius of the proton, and the trace anomaly contribution to the proton mass. We observe possible structures in the total cross section energy dependence and find evidence for contributions beyond gluon exchange in the differential cross section close to threshold, both of which are consistent with contributions from open-charm intermediate states.
$\gamma p \rightarrow J/\psi p$ total cross sections in bins of beam energy. The first uncertainties are statistical, and the second are systematic. There is an additional fully correlated systematic uncertainty of 19.5% on the total cross section, not included here.
$\gamma p \rightarrow J/\psi p$ differential cross sections 8.2–9.28 GeV beam energy range, average $t$ and beam energy in bins of $t$. The first cross section uncertainties are statistical, and the second are systematic. The overall average beam energy is 8.93 GeV. There is an additional fully correlated systematic uncertainty of 19.5% on the total cross section, not included here.
$\gamma p \rightarrow J/\psi p$ differential cross sections 9.28–10.36 GeV beam energy range, average $t$ and beam energy in bins of $t$. The first cross section uncertainties are statistical, and the second are systematic. The overall average beam energy is 9.86 GeV. There is an additional fully correlated systematic uncertainty of 19.5% on the total cross section, not included here.
A combination of measurements of the inclusive top-quark pair production cross-section performed by ATLAS and CMS in proton-proton collisions at centre-of-mass energies of 7 and 8 TeV at the LHC is presented. The cross-sections are obtained using top-quark pair decays with an opposite-charge electron-muon pair in the final state and with data corresponding to an integrated luminosity of about 5 fb$^{-1}$ at $\sqrt{s}=7$ TeV and about 20 fb$^{-1}$ at $\sqrt{s}=8$ TeV for each experiment. The combined cross-sections are determined to be $178.5 \pm 4.7$ pb at $\sqrt{s}=7$ TeV and $243.3^{+6.0}_{-5.9}$ pb at $\sqrt{s}=8$ TeV with a correlation of 0.41, using a reference top-quark mass value of 172.5 GeV. The ratio of the combined cross-sections is determined to be $R_{8/7}= 1.363\pm 0.032$. The combined measured cross-sections and their ratio agree well with theory calculations using several parton distribution function (PDF) sets. The values of the top-quark pole mass (with the strong coupling fixed at 0.118) and the strong coupling (with the top-quark pole mass fixed at 172.5 GeV) are extracted from the combined results by fitting a next-to-next-to-leading-order plus next-to-next-to-leading-log QCD prediction to the measurements. Using a version of the NNPDF3.1 PDF set containing no top-quark measurements, the results obtained are $m_t^\text{pole} = 173.4^{+1.8}_{-2.0}$ GeV and $\alpha_\text{s}(m_Z)= 0.1170^{+ 0.0021}_{-0.0018}$.
Full covariance matrix including all systematic uncertainties expressed as nuisance parameters. With the exception of the cross section parameters, all parameters were normalised to 1 before the fit. Therefore, the diagonal elements represent the constraint in quadrature.
Full covariance matrix including all systematic uncertainties expressed as nuisance parameters. With the exception of the cross section parameters, all parameters were normalised to 1 before the fit. Therefore, the diagonal elements represent the constraint in quadrature.
Notwithstanding decades of progress since Yukawa first developed a description of the force between nucleons in terms of meson exchange, a full understanding of the strong interaction remains a major challenge in modern science. One remaining difficulty arises from the non-perturbative nature of the strong force, which leads to the phenomenon of quark confinement at distances on the order of the size of the proton. Here we show that in relativistic heavy-ion collisions, where quarks and gluons are set free over an extended volume, two species of produced vector (spin-1) mesons, namely $\phi$ and $K^{*0}$, emerge with a surprising pattern of global spin alignment. In particular, the global spin alignment for $\phi$ is unexpectedly large, while that for $K^{*0}$ is consistent with zero. The observed spin-alignment pattern and magnitude for the $\phi$ cannot be explained by conventional mechanisms, while a model with a connection to strong force fields, i.e. an effective proxy description within the Standard Model and Quantum Chromodynamics, accommodates the current data. This connection, if fully established, will open a potential new avenue for studying the behaviour of strong force fields.
Global spin alignment of $\phi$ and $K^{*0}$ vector mesons in heavy-ion collisions. The measured matrix element $\rho_{00}$ as a function of beam energy for the $\phi$ and $K^{*0}$ vector mesons within the indicated windows of centrality, transverse momentum ($p_T$) and rapidity ($y$). The open symbols indicate ALICE results for Pb+Pb collisions at 2.76 TeV at $p_{T}$ values of 2.0 and 1.4 GeV/c for the $\phi$ and $K^{*0}$ mesons, respectively, corresponding to the $p_{T}$ bin nearest to the mean $p_{T}$ for the 1.0 – 5.0 GeV/$c$ range assumed for each meson in the present analysis. The red solid curve is a fit to data in the range of $\sqrt{s_{NN}} = 19.6$ to 200 GeV, based on a theoretical calculation with a $\phi$-meson field. Parameter sensitivity of $\rho_{00}$ to the $\phi$-meson field is shown in Ref.5. The red dashed line is an extension of the solid curve with the fitted parameter $G_s^{(y)}$. The black dashed line represents $\rho_{00}=1/3.$
Global spin alignment of $\phi$ and $K^{*0}$ vector mesons in heavy-ion collisions. The measured matrix element $\rho_{00}$ as a function of beam energy for the $\phi$ and $K^{*0}$ vector mesons within the indicated windows of centrality, transverse momentum ($p_T$) and rapidity ($y$). The open symbols indicate ALICE results for Pb+Pb collisions at 2.76 TeV at $p_{T}$ values of 2.0 and 1.4 GeV/c for the $\phi$ and $K^{*0}$ mesons, respectively, corresponding to the $p_{T}$ bin nearest to the mean $p_{T}$ for the 1.0 – 5.0 GeV/$c$ range assumed for each meson in the present analysis. The red solid curve is a fit to data in the range of $\sqrt{s_{NN}} = 19.6$ to 200 GeV, based on a theoretical calculation with a $\phi$-meson field. Parameter sensitivity of $\rho_{00}$ to the $\phi$-meson field is shown in Ref.5. The red dashed line is an extension of the solid curve with the fitted parameter $G_s^{(y)}$. The black dashed line represents $\rho_{00}=1/3.$
Example of combinatorial background subtracted invariant mass distributions and the extracted yields as a function of $\cos \theta^*$ for $\phi$ and $K^{*0}$ mesons. \textbf{a)} example of $\phi \rightarrow K^+ + K^-$ invariant mass distributions, with combinatorial background subtracted, integrated over $\cos \theta^*$; \textbf{b)} example of $K^{*0} (\overline{K^{*0}}) \rightarrow K^{-} \pi^{+} (K^{+} \pi^{-})$ invariant mass distributions, with combinatorial background subtracted, integrated over $\cos \theta^*$; \textbf{c)} extracted yields of $\phi$ as a function of $\cos \theta^*$; \textbf{d)} extracted yields of $K^{*0}$ as a function of $\cos \theta^*$.
Partons traversing the strongly interacting medium produced in heavy-ion collisions are expected to lose energy depending on their color charge and mass. We measure the nuclear modification factors for charm- and bottom-decay electrons, defined as the ratio of yields, scaled by the number of binary nucleon-nucleon collisions, in $\sqrt{s_{\rm NN}}$ = 200 GeV Au+Au collisions to $p$+$p$ collisions ($R_{\rm AA}$), or in central to peripheral Au+Au collisions ($R_{\rm CP}$). We find the bottom-decay electron $R_{\rm AA}$ and $R_{\rm CP}$ to be significantly higher than that of charm-decay electrons. Model calculations including mass-dependent parton energy loss in a strongly coupled medium are consistent with the measured data. These observations provide clear evidence of mass ordering of charm and bottom quark energy loss when traversing through the strongly coupled medium created in heavy-ion collisions.
Fit to the $\rm log_{10}(DCA/cm)$ of candidate electrons with $p_{\rm T}$ $\in$ [3.5,4.5] GeV/$c$ in 0-80% Au+Au collisions at $\sqrt{s_{\rm NN}}=200$ GeV, where the DCA is defined as the 3D distance-of-closest approach of the track to the primary vertex. The solid blue line shows the full template fit, and the various other lines show the individual components. The bottom panel shows the residual distribution of the template fit scaled by the statistical uncertainties.
Invariant yield of the electrons from decays of prompt $J/\psi$, $\Upsilon$, Drell-Yan and light vector mesons in 0-80% Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV.
Invariant yield of heavy flavor hadron decayed electrons in 0-80% Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV.
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