The production of Z bosons associated with jets is measured in pp collisions at $\sqrt{s}$ = 13 TeV with data recorded with the CMS experiment at the LHC corresponding to an integrated luminosity of 36.3 fb$^{-1}$. The multiplicity of jets with transverse momentum $p_\mathrm{T}$$\gt$ 30 GeV is measured for different regions of the Z boson's $p_\mathrm{T}$(Z), from lower than 10 GeV to higher than 100 GeV. The azimuthal correlation $\Delta \phi$ between the Z boson and the leading jet, as well as the correlations between the two leading jets are measured in three regions of $p_\mathrm{T}$(Z). The measurements are compared with several predictions at leading and next-to-leading orders, interfaced with parton showers. Predictions based on transverse-momentum dependent parton distributions and corresponding parton showers give a good description of the measurement in the regions where multiple parton interactions and higher jet multiplicities are not important. The effects of multiple parton interactions are shown to be important to correctly describe the measured spectra in the low $p_\mathrm{T}$(Z) regions.
The measured cross section as a function of exclusive jet multiplicity, $N_{\text{jets}}$, when $p_T<10$ GeV
The measured cross section as a function of exclusive jet multiplicity, $N_{\text{jets}}$, when $10<p_T<30$ GeV
The measured cross section as a function of exclusive jet multiplicity, $N_{\text{jets}}$, when $30<p_T<50$ GeV
A search for the pair-production of vector-like quarks optimized for decays into a $Z$ boson and a third-generation Standard Model quark is presented, using the full Run 2 dataset corresponding to 139 fb$^{-1}$ of $pp$ collisions at $\sqrt{s}=13$ TeV, collected in 2015-2018 with the ATLAS detector at the Large Hadron Collider. The targeted final state is characterized by the presence of a $Z$ boson with high transverse momentum, reconstructed from a pair of same-flavour leptons with opposite-sign charges, as well as by the presence of $b$-tagged jets and high-transverse-momentum large-radius jets reconstructed from calibrated smaller-radius jets. Events with exactly two or at least three leptons are used, which are further categorized by the presence of boosted $W$, $Z$, and Higgs bosons and top quarks. The categorization is performed using a neural-network-based boosted object tagger to enhance the sensitivity to signal relative to the background. No significant excess above the background expectation is observed and exclusion limits at 95% confidence level are set on the masses of the vector-like partners $T$ and $B$ of the top and bottom quarks, respectively. In the singlet model, the limits allow $m_T > 1.27$ TeV and $m_B > 1.20$ TeV. In the doublet model, allowed masses are $m_T > 1.46$ TeV and $m_B >1.32$ TeV. In the case of 100% branching ratio for $T\rightarrow Zt$ and 100% branching ratio for $B\rightarrow Zb$, the limits allow $m_T > 1.60$ TeV and $m_B > 1.42$ TeV, respectively.
Expected and observed lower limits on B masses at 95% CL in the BR plane from the combination of the two analysis channels for all BR configurations when assuming a total BR of 100% for H, W and Z.
Expected and observed lower limits on T masses at 95% CL in the BR plane from the combination of the two analysis channels for all BR configurations when assuming a total BR of 100% for H, W and Z.
Expected and observed combined limits at 95% CL on the production cross-section of vector-like T for 100% $T\rightarrow Zt$.
Charge-dependent two- and three-particle correlations measured in Xe-Xe collisions at $\sqrt{s_{\mathrm{NN}}} = 5.44$ TeV are presented. Results are obtained for charged particles in the pseudorapidity range $|\eta|<0.8$ and transverse momentum interval $0.2 \le p_{\rm T}<5.0$ GeV/$c$ for different collision centralities. The three-particle correlator ${\gamma_{\alpha\beta}} \equiv {\langle \cos(\varphi_\alpha + \varphi_\beta - 2{\Psi_{\rm 2}}) \rangle}$, calculated for different combinations of charge sign $\alpha$ and $\beta$, is expected to be sensitive to the presence of the Chiral Magnetic Effect (CME). Its magnitude is similar to the one observed in Pb-Pb collisions in contrast to a smaller CME signal in Xe-Xe collisions than in Pb-Pb collisions predicted by Monte Carlo (MC) calculations including a magnetic field induced by the spectator protons. These observations point to a large non-CME contribution to the correlator. Furthermore, the charge dependence of ${\gamma_{\alpha\beta}}$ can be described by a blast wave model calculation that incorporates background effects and by the Anomalous Viscous Fluid Dynamics model with values of the CME signal consistent with zero. The Xe-Xe and Pb-Pb results are combined with the expected CME signal dependence on the system size from the MC calculations including a magnetic field to obtain the fraction of CME contribution in ${\gamma_{\alpha\beta}}$, $f_{\rm CME}$. The CME fraction is compatible with zero for the 30% most central events in both systems and then becomes positive. This yields an upper limit of 2% (3%) and 25% (32%) at 95% (99.7%) confidence level for the CME signal contribution to ${\gamma_{\alpha\beta}}$ in the 0-70% Xe-Xe and Pb-Pb collisions, respectively.
$\langle \cos(\varphi_{\alpha} - \varphi_{\beta}) \rangle$ (opposite charge pairs) as a function of centrality in Xe-Xe collisions at $\sqrt{s_{\rm NN}} = 5.44$ TeV.
$\langle \cos(\varphi_{\alpha} - \varphi_{\beta}) \rangle$ (same charge pairs) as a function of centrality in Xe-Xe collisions at $\sqrt{s_{\rm NN}} = 5.44$ TeV.
$\langle \cos(\varphi_{\alpha} + \varphi_{\beta} - 2\Psi_{2}) \rangle$ (opposite charge pairs) as a function of centrality in Xe-Xe collisions at $\sqrt{s_{\rm NN}} = 5.44$ TeV.
Multijet events at large transverse momentum ($p_\mathrm{T}$) are measured at $\sqrt{s}$ = 13 TeV using data recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 36.3 fb$^{-1}$. The multiplicity of jets with $p_\mathrm{T}$$>$ 50 GeV that are produced in association with a high-$p_\mathrm{T}$ dijet system is measured in various ranges of the $p_\mathrm{T}$ of the jet with the highest transverse momentum and as a function of the azimuthal angle difference $\Delta\phi_{1,2}$ between the two highest $p_\mathrm{T}$ jets in the dijet system. The differential production cross sections are measured as a function of the transverse momenta of the four highest $p_\mathrm{T}$ jets. The measurements are compared with leading and next-to-leading order matrix element calculations supplemented with simulations of parton shower, hadronization, and multiparton interactions. In addition, the measurements are compared with next-to-leading order matrix element calculations combined with transverse-momentum dependent parton densities and transverse-momentum dependent parton shower.
Jet multiplicity measured for a leading-pT jet ($p_{T1}$) with 200 < $p_{T1}$ < 400 GeV and for an azimuthal separation between the two leading jets of $0 < \Delta\Phi_{1,2} < 150^{\circ}$. The full breakdown of the uncertainties is displayed, with PU corresponding to Pileup, PREF to Trigger Prefering, PTHAT to the hard-scale (renormalization and factorization scales), MISS and FAKE to the inefficienties and background, LUMI to integrated luminosity. With JES, JER and stat. unc. following the notation in the paper.
Jet multiplicity measured for a leading-pT jet ($p_{T1}$) with 200 < $p_{T1}$ < 400 GeV and for an azimuthal separation between the two leading jets of $150 < \Delta\Phi_{1,2} < 170^{\circ}$. The full breakdown of the uncertainties is displayed, with PU corresponding to Pileup, PREF to Trigger Prefering, PTHAT to the hard-scale (renormalization and factorization scales), MISS and FAKE to the inefficienties and background, LUMI to integrated luminosity. With JES, JER and stat. unc. following the notation in the paper.
Jet multiplicity measured for a leading-pT jet ($p_{T1}$) with 200 < $p_{T1}$ < 400 GeV and for an azimuthal separation between the two leading jets of $170 < \Delta\Phi_{1,2} < 180^{\circ}$. The full breakdown of the uncertainties is displayed, with PU corresponding to Pileup, PREF to Trigger Prefering, PTHAT to the hard-scale (renormalization and factorization scales), MISS and FAKE to the inefficienties and background, LUMI to integrated luminosity. With JES, JER and stat. unc. following the notation in the paper.
The elliptic ($v_2$) and triangular ($v_3$) azimuthal anisotropy coefficients in central $^{3}$He+Au, $d$+Au, and $p$+Au collisions at $\mbox{$\sqrt{s_{\mathrm{NN}}}$}$ = 200 GeV are measured as a function of transverse momentum ($p_{\mathrm{T}}$) at mid-rapidity ($|\eta|<$0.9), via the azimuthal angular correlation between two particles both at $|\eta|<$0.9. While the $v_2(p_{\mathrm{T}})$ values depend on the colliding systems, the $v_3(p_{\mathrm{T}})$ values are system-independent within the uncertainties, suggesting an influence on eccentricity from sub-nucleonic fluctuations in these small-sized systems. These results also provide stringent constraints for the hydrodynamic modeling of these systems.
v2 and v3 in 0-10% He+Au collisions at 200 GeV
v2 and v3 in 0-10% d+Au collisions at 200 GeV
v2 and v3 in UC p+Au collisions at 200 GeV
The production of the $\psi(2S)$ charmonium state was measured with ALICE in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV, in the dimuon decay channel. A significant signal was observed for the first time at LHC energies down to zero transverse momentum, at forward rapidity ($2.5<y<4$). The measurement of the ratio of the inclusive production cross sections of the $\psi(2S)$ and J/$\psi$ resonances is reported as a function of the centrality of the collisions and of transverse momentum, in the region $p_{\rm T}<12$ GeV/$c$. The results are compared with the corresponding measurements in pp collisions, by forming the double ratio $[\sigma^{\psi(2S)}/\sigma^{J/\psi}]_{\rm{Pb-Pb}}/[\sigma^{\psi(2S)}/\sigma^{J/\psi}]_{\rm{pp}}$. It is found that in Pb-Pb collisions the $\psi(2S)$ is suppressed by a factor of $\sim 2$ with respect to the J/$\psi$. The $\psi(2S)$ nuclear modification factor $R_{\rm AA}$ was also obtained as a function of both centrality and $p_{\rm T}$. The results show that the $\psi(2S)$ resonance yield is strongly suppressed in Pb-Pb collisions, by a factor up to $\sim 3$ with respect to pp. Comparisons of cross section ratios with previous SPS findings by the NA50 experiment and of $R_{\rm AA}$ with higher-$p_{\rm T}$ results at LHC energy are also reported. These results and the corresponding comparisons with calculations of transport and statistical models address questions on the presence and properties of charmonium states in the quark-gluon plasma formed in nuclear collisions at the LHC.
Ratio of the $\psi$(2S) over J/$\psi$ cross sections, not corrected for the branching ratio, shown as a function of centrality
Double ratio of the $\psi$(2S) over J/$\psi$ cross sections in Pb--Pb and pp collisions shown as a function of centrality
Nuclear modification factor of the $\psi$(2S) shown as a function of centrality
The study of the azimuthal anisotropy of inclusive muons produced in p-Pb collisions at $\sqrt{s_{\rm NN}} = 8.16$ TeV, using the ALICE detector at the LHC is reported. The measurement of the second-order Fourier coefficient of the particle azimuthal distribution, $v_2$, is performed as a function of transverse momentum $p_{\rm T}$ in the 0-20% high-multiplicity interval at both forward ($2.03 < y_{\rm CMS} < 3.53$) and backward ($-4.46 < y_{\rm CMS} < -2.96$) rapidities over a wide $p_{\rm T}$ range, $0.5 < p_{\rm T} < 10$ GeV/$c$, in which a dominant contribution of muons from heavy-flavour hadron decays is expected at $p_{\rm T} > 2$ GeV/$c$. The $v_2$ coefficient of inclusive muons is extracted using two different techniques, namely two-particle cumulants, used for the first time for heavy-flavour measurements, and forward-central two-particle correlations. Both techniques give compatible results. A positive $v_2$ is measured at both forward and backward rapidities with a significance larger than $4.7\sigma$ and $7.6\sigma$, respectively, in the interval $2 < p_{\rm T} < 6$ GeV/$c$. Comparisons with previous measurements in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV, and with AMPT and CGC-based theoretical calculations are discussed. The findings impose new constraints on the theoretical interpretations of the origin of the collective behaviour in small collision systems.
Inclusive muon $v_{2}^{\mu}$ as a function of $p_{\mathrm{T}}$ is measured by two-particle correlation method at forward rapidities in high-multiplicity (0$-$20%) p$-$Pb collisions at $\sqrt{s_\mathrm{NN}}$= 8.16 TeV. The event activity is estimated with the V0M estimator.
Inclusive muon $v_{2}^{\mu}$ as a function of $p_{\mathrm{T}}$ is measured by two-particle cumulant method at forward rapidities in high-multiplicity (0$-$20%) p$-$Pb collisions at $\sqrt{s_\mathrm{NN}}$= 8.16 TeV. The event activity is estimated with the V0M estimator.
Inclusive muon $v_{2}^{\mu}$ as a function of $p_{\mathrm{T}}$ is measured by two-particle correlation method at backward rapidities in high-multiplicity (0$-$20%) p$-$Pb collisions at $\sqrt{s_\mathrm{NN}}$= 8.16 TeV. The event activity is estimated with the V0M estimator.
The first study of the shapes of jets arising from bottom (b) quarks in heavy ion collisions is presented. Jet shapes are studied using charged hadron constituents as a function of their radial distance from the jet axis. Lead-lead (PbPb) collision data at a nucleon-nucleon center-of-mass energy of $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV were recorded by the CMS detector at the LHC, with an integrated luminosity of 1.69 nb$^{-1}$. Compared to proton-proton collisions, a redistribution of the energy in b jets to larger distances from the jet axis is observed in PbPb collisions. This medium-induced redistribution is found to be substantially larger for b jets than for inclusive jets.
Jet shapes, $\rho(\Delta r)$, for inclusive and b jets as function of $\Delta r$ from pp and PbPb collisions at $\sqrt{s_{NN}} = 5.02$ TeV.
Jet shapes, $\rho(\Delta r)$, for inclusive and b jets as function of $\Delta r$ from pp and PbPb collisions at $\sqrt{s_{NN}} = 5.02$ TeV.
Jet shapes, $\rho(\Delta r)$, for inclusive and b jets as function of $\Delta r$ from pp and PbPb collisions at $\sqrt{s_{NN}} = 5.02$ TeV.
The path-length dependent parton energy loss within the dense partonic medium created in lead-lead collisions at a nucleon-nucleon center-of-mass energy of $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV is studied by determining the azimuthal anisotropies for dijets with high transverse momentum. The data were collected by the CMS experiment in 2018 and correspond to an integrated luminosity of 1.69 nb$^{-1}$. For events containing back-to-back jets, correlations in relative azimuthal angle and pseudorapidity ($\eta$) between jets and hadrons, and between two hadrons, are constructed. The anisotropies are expressed as the Fourier expansion coefficients $v_n$, $n = $ 2-4 of these azimuthal distributions. The dijet $v_n$ values are extracted from long-range (1.5 $\lt$$\vert\Delta\eta\vert$$\lt$ 2.5) components of these correlations, which suppresses the background contributions from jet fragmentation processes. Positive dijet $v_2$ values are observed which increase from central to more peripheral events, while the $v_3$ and $v_4$ values are consistent with zero within experimental uncertainties.
The dijet $v_{n}$ data points factorized using different associated hadron pT bins for 0-10 % centrality bin. The data points are corrected for the jet reconstruction bias effects.
The dijet $v_{n}$ data points factorized using different associated hadron pT bins for 10-30 % centrality bin. The data points are corrected for the jet reconstruction bias effects.
The dijet $v_{n}$ data points factorized using different associated hadron pT bins for 30-50 % centrality bin. The data points are corrected for the jet reconstruction bias effects.
Anomalies in past neutrino measurements have led to the discovery that these particles have non-zero mass and oscillate between their three flavors when they propagate. In the 2010's, similar anomalies observed in the antineutrino spectra emitted by nuclear reactors have triggered the hypothesis of the existence of a supplementary neutrino state that would be sterile i.e. not interacting via the weak interaction. The STEREO experiment was designed to study this scientific case that would potentially extend the Standard Model of Particle Physics. Here we present a complete study based on our full set of data with significantly improved sensitivity. Installed at the ILL (Institut Laue Langevin) research reactor, STEREO has accurately measured the antineutrino energy spectrum associated to the fission of 235U. This measurement confirms the anomalies whereas, thanks to the segmentation of the STEREO detector and its very short mean distance to the core (10~m), the same data reject the hypothesis of a light sterile neutrino. Such a direct measurement of the antineutrino energy spectrum suggests instead that biases in the nuclear experimental data used for the predictions are at the origin of the anomalies. Our result supports the neutrino content of the Standard Model and establishes a new reference for the 235U antineutrino energy spectrum. We anticipate that this result will allow to progress towards finer tests of the fundamental properties of neutrinos but also to benchmark models and nuclear data of interest for reactor physics and for observations of astrophysical or geo-neutrinos.
12B prediction used for the control of the energy scale. The three most intense beta decay branches of 12B have been taken into account, covering 99.94% of the total decay rate. The corresponding spectra are given in bins of 50 keV, normalized to their respective branching ratio. The [no rad. corr] notation stands for the fact that we didn't include the radiative corrections in our nominal simulation, as all radiated photons should be absorbed in the STEREO target volume. However the full effect of these corrections is included in the uncertainty of the predicted spectrum. It can be deduced from the comparison with the full calculation of the beta branches given here as well.
STEREO IBD Spectrum for phase-II and phase-III. The spectra are given in nu/day and normalized to reactor power in cm2/fission/MeV with 22 250keV-wide measured-energy bins, ranging from 1.625MeV (lower edge of lowest bin) to 7.125 MeV (upper edge of highest bin). The normalized rates (cm2/fission/MeV) are split between U5 and non-U5 components (Aluminium and Off-Equilibrium corrections).
STEREO Global Covariance Matrix for phase-II and phase-III. The matrix is given as a 44x44 matrix, with 44 bins for phase-II (bins 1-22) and phase-III (bins 23-44) corresponding to the prompt spectra with 22 250-keV bins, ranging from 1.625 to 7.125 MeV; it is expressed in (cm2/fission/MeV)².
Forum