The existence of a new spin-zero particle with a mass below the electroweak scale is predicted by several theoretical models. Searches for resonant production of photon pairs at the LHC are able to probe these models. We present a search for a narrow resonance produced through gluon fusion that decays into a pair of photons with an invariant mass between 10 and 70 GeV, using a proton-proton collision data set from the CMS experiment. This data set, corresponding to an integrated luminosity of 54.4 fb$^{-1}$, was recorded in 2018 at a center-of-mass energy of 13 TeV using a newly introduced diphoton trigger that enabled exploration of the low-mass diphoton spectrum. No significant excess above the expected background is observed. Upper limits are set on the product of the gluon fusion production cross section and the branching fraction of the diphoton decay of a narrow resonance. An interpretation of these limits within an effective field theory framework for axion-like particles is also provided.
Observed and expected 95% CL upper limits on the production cross section times branching ratio as a function of the resonance mass.
Recasting of the observed and expected 95% CL upper limits into the ALP parameter space as constraints on the decay constant f_a
The ATLAS experiment has performed a measurement of coherent exclusive $J/ψ\toμ^+μ^-$ production in ultraperipheral Pb+Pb collisions at $\sqrt{s_{\textrm{NN}}}=5.36$ TeV. The data was recorded at the Large Hadron Collider (LHC) during 2023, and corresponds to an integrated luminosity of 78 $μ$b$^{-1}$. Exclusive $J/ψ$ candidates were selected with a dedicated track-sensitive trigger based on the ATLAS transition radiation tracker. The analysis involves reconstruction of the dimuon invariant mass based on muon tracks from the inner detector, as the muon transverse momentum range of interest precludes the use of the standard muon reconstruction and identification algorithms. Differential cross sections are measured as a function of $J/ψ$ rapidity and are compared with theoretical predictions. After extrapolation to $\sqrt{s_{\textrm{NN}}}=5.02$ TeV, they are also compared with previous measurements performed by other experiments using data from LHC Run 2. While the results agree reasonably well with theoretical predictions, they are in tension with previous Run-2 results for the central rapidity region.
Differential cross section dσ/dy for coherent exclusive J/ψ production in ultraperipheral Pb+Pb collisions at sqrt(s_NN)=5.36 TeV as a function of J/ψ rapidity.
Differential cross section dσ/dy for coherent exclusive J/ψ production in ultraperipheral Pb+Pb collisions extrapolated to sqrt(s_NN)=5.02 TeV as a function of J/ψ rapidity.
The top-quark mass is measured using top-quark decays producing an isolated lepton and $J/ψ$ meson reconstructed in its $μ^+μ^-$ decay mode. The data sample was recorded with the ATLAS detector in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=13$ TeV during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 140 fb$^{-1}$. The measurement is based on the invariant mass $m(\ell μ^+μ^-)$ of the system made of the isolated lepton $\ell$ from the $W$ boson decay and the non-isolated $μ^+μ^-$ pair from a $J/ψ$ decay of a $b$-hadron, exploiting its sensitivity to the top-quark mass. An unbinned maximum-likelihood fit to the $m(\ell μ^+μ^-)$ distribution is performed to extract the top-quark mass. The top-quark mass is measured to be $m_{top} = 172.17 \pm 0.80 (stat) \pm 0.81 (syst) \pm 1.07 (recoil)$ GeV, with a total uncertainty of 1.56 GeV. The third uncertainty arises from changing the dipole parton shower gluon-recoil scheme used in top-quark decays.
Top mass measurement result.
Number of selected events in data after the final selection. Also shown are the expected numbers of $t\bar{t}$ and single-top-quark events, assuming a top-quark mass of $m_{top} = 172.5$ GeV, broken down into contributions with and without the $b\rightarrow J/\psi\rightarrow\mu^+\mu^-$ decay, and other background events, corresponding to the integrated luminosity of the data. The last two rows show the expected background fraction and the ratio of observed to expected events. The total uncertainty includes both statistical and systematic components, combined in quadrature.
Impact of sources of uncertainty in $m_{top}$. Each row of the table corresponds to a group of individual systematic variations. Uncertainties related to tt and single-top-quark processes are shown separately and are considered uncorrelated. For each systematic uncertainty listed, the first value corresponds to the uncertainty in $m_{top}$, and the second to the statistical precision of this uncertainty. The total systematic uncertainty and the corresponding statistical precision are calculated as discussed in Section 6. The total uncertainty is the sum in quadrature of the statistical and systematic uncertainties.
The production of single top quarks and top antiquarks via the $t$-channel exchange of a virtual $W$ boson is measured in proton-proton collisions at a centre-of-mass energy of 13 TeV at the Large Hadron Collider. The full Run 2 data sample recorded with the ATLAS detector in the years 2015-2018 is used, corresponding to an integrated luminosity of 140 fb$^{-1}$. The absolute and normalised production cross-sections are measured differentially as a function of the transverse momentum and absolute rapidity of the top quark and top antiquark. In addition, the ratio of top quark to top antiquark production cross-sections is measured. The measured distributions are compared with next-to-leading-order quantum chromodynamics predictions obtained with different combinations of matrix-element generators, parton-shower programs and proton parton distribution functions, as well as to next-to-next-to-leading-order calculations. Overall, good agreement is observed between the measurements and the theoretical predictions. For most measured distributions, the sensitivity to differences between the predictions is limited by the systematic uncertainties in the measurement. The measured differential distributions are also interpreted in an effective field theory approach to constrain the Wilson-Coefficient $C_{Qq}^{3,1}$ associated with a four-quark operator. The interpretation accounts for the effect of the selection efficiency, which is altered significantly by non-zero contributions from $C_{Qq}^{3,1}$.
------- Overview of the HEPData record ------- Event selection on detector level: one charged lepton with $p_\text{T}(\ell) > 28$ GeV two jets with $p_\text{T}(j) > 30$ GeV and $|\eta(j)|<4\text{.}5$ one b-tag (DL1r, 60% WP) $E_\text{T}^{miss} > 30$ GeV $m_\text{T}(W) > 50$ GeV $p_\text{T}(\ell) > 40$ GeV $\cdot\frac{|\Delta\Phi(j_1,\ell)|}{\pi}$ $m(\ell b) < 160$ GeV ------- The criteria above define the $\ell^{\pm}$ selection ------- $D_{nn}\geq0\text{.}93$ ------- The criteria above define the signal regions $\ell^{\pm}$ SRs ------- Data/MC comparisons: <ul> <li> $\ell^+$ selection (<a href="167734?version=1&table=Figure%202a">Figure 2a</a> ) <li> $\ell^-$ selection (<a href="167734?version=1&table=Figure%202b">Figure 2b</a> ) Variables in the $\ell^{\pm}$ SRs: <li> $p_T(\ell^+\nu b)$ (<a href="167734?version=1&table=Figure%203a">Figure 3a</a> ) <li> $p_T(\ell^-\nu b)$ (<a href="167734?version=1&table=Figure%203b">Figure 3b</a> ) <li> $|y(\ell^+\nu b)|$ (<a href="167734?version=1&table=Figure%203c">Figure 3c</a> ) <li> $|y(\ell^-\nu b)|$ (<a href="167734?version=1&table=Figure%203d">Figure 3d</a> ) Yields in the $\ell^{\pm}$ SRs: <a href="167734?version=1&table=Table%203">Table 3</a> Uncertainy breakdown into categories: Absolute cross sections: <li> $p_T(t)$ (<a href="167734?version=1&table=Figure%204a">Figure 4a</a> ) <li> $p_T(t)$ (<a href="167734?version=1&table=Table%206">Table 6</a> ) <li> $p_T(\bar{t})$ (<a href="167734?version=1&table=Figure%204b">Figure 4b</a> ) <li> $p_T(\bar{t})$ (<a href="167734?version=1&table=Table%207">Table 7</a> ) <li> $|y(t)|$ (<a href="167734?version=1&table=Figure%204c">Figure 4c</a> ) <li> $|y(t)|$ (<a href="167734?version=1&table=Table%208">Table 8</a> ) <li> $|y(\bar{t})|$ (<a href="167734?version=1&table=Figure%204d">Figure 4d</a> ) <li> $|y(\bar{t})|$ (<a href="167734?version=1&table=Table%209">Table 9</a> ) <li> $p_T(t \text{ or }\bar{t})$ (<a href="167734?version=1&table=Figure%204e">Figure 4e</a> ) <li> $p_T(t \text{ or }\bar{t})$ (<a href="167734?version=1&table=Table%2010">Table 10</a> ) <li> $|y(t \text{ or }\bar{t})|$ (<a href="167734?version=1&table=Figure%204f">Figure 4f</a> ) <li> $|y(t \text{ or }\bar{t})|$ (<a href="167734?version=1&table=Table%2011">Table 11</a> ) Normalised cross sections: <li> $p_T(t)$ (<a href="167734?version=1&table=Figure%205a">Figure 5a</a> ) <li> $p_T(t)$ (<a href="167734?version=1&table=Table%2012">Table 12</a> ) <li> $p_T(\bar{t})$ (<a href="167734?version=1&table=Figure%205b">Figure 5b</a> ) <li> $p_T(\bar{t})$ (<a href="167734?version=1&table=Table%2013">Table 13</a> ) <li> $|y(t)|$ (<a href="167734?version=1&table=Figure%205c">Figure 5c</a> ) <li> $|y(t)|$ (<a href="167734?version=1&table=Table%2014">Table 14</a> ) <li> $|y(\bar{t})|$ (<a href="167734?version=1&table=Figure%205d">Figure 5d</a> ) <li> $|y(\bar{t})|$ (<a href="167734?version=1&table=Table%2015">Table 15</a> ) Parton-level cross-sections with full breakdown of uncertainties and theoretical predictions: Absolute cross sections: <li> $p_T(t)$ (<a href="167734?version=1&table=Figure%206a">Figure 6a</a> ) <li> $p_T(\bar{t})$ (<a href="167734?version=1&table=Figure%206b">Figure 6b</a> ) <li> $|y(t)|$ (<a href="167734?version=1&table=Figure%206c">Figure 6c</a> ) <li> $|y(\bar{t})|$ (<a href="167734?version=1&table=Figure%206d">Figure 6d</a> ) <li> $p_T(t \text{ or }\bar{t})$ (<a href="167734?version=1&table=Figure%206e">Figure 6e</a> ) <li> $|y(t \text{ or }\bar{t})|$ (<a href="167734?version=1&table=Figure%206f">Figure 6f</a> ) Normalised cross sections: <li> $p_T(t)$ (<a href="167734?version=1&table=Figure%207a">Figure 7a</a> ) <li> $p_T(\bar{t})$ (<a href="167734?version=1&table=Figure%207b">Figure 7b</a> ) <li> $|y(t)|$ (<a href="167734?version=1&table=Figure%207c">Figure 7c</a> ) <li> $|y(\bar{t})|$ (<a href="167734?version=1&table=Figure%207d">Figure 7d</a> ) $\chi^2$ probabilities for the theoretical predictions: <li> $p_T$ distributions (<a href="167734?version=1&table=Table%204">Table 4</a> ) <li> $|y|$ distributions (<a href="167734?version=1&table=Table%205">Table 5</a> ) Selection efficiencies of the MC EFT signal samples: <li> $p_T(t)$ (<a href="167734?version=1&table=Figure%2014a">Figure 14a</a> ) <li> $p_T(\bar{t})$ (<a href="167734?version=1&table=Figure%2014b">Figure 14b</a> ) Best fits for cross-section dependence on $C_{Qq}^{3,1}$: <a href="167734?version=1&table=Table%2022">Table 22</a> Migration matrices: <li> $p_T(t)$ (<a href="167734?version=1&table=Figure%2016a">Figure 3a</a> ) <li> $p_T(\bar{t})$ (<a href="167734?version=1&table=Figure%2016b">Figure 3b</a> ) <li> $|y(t)|$ (<a href="167734?version=1&table=Figure%2016c">Figure 3c</a> ) <li> $|y(\bar{t})|$ (<a href="167734?version=1&table=Figure%2016d">Figure 3d</a> ) Additional material (in order of entries): Unscaled event yields in both SRs: <li> (<a href="167734?version=1&table=Event%20yields%20%24%5Cell%5E%2B%24%20SR%20no%20SFs"> $\ell^+$ SR </a> ) <li> (<a href="167734?version=1&table=Event%20yields%20%24%5Cell%5E-%24%20SR%20no%20SFs"> $\ell^-$ SR </a> ) Statistical covariance matrices for all measurements: Absolute cross sections: <li> (<a href="167734?version=1&table=Statistical%20covariance%20%24p_%5Ctext%7BT%7D(t)%24%20absolute"> $p_T(t)$ </a> ) <li> (<a href="167734?version=1&table=Statistical%20covariance%20%24p_%5Ctext%7BT%7D(%5Cbar%7Bt%7D)%24%20absolute"> $p_T(\bar{t})$</a> ) <li> (<a href="167734?version=1&table=Statistical%20covariance%20%24%7Cy(t)%7C%24%20absolute"> $|y(t)|$</a> ) <li> (<a href="167734?version=1&table=Statistical%20covariance%20%24%7Cy(%5Cbar%7Bt%7D)%7C%24%20absolute"> $|y(\bar{t})|$</a> ) <li> (<a href="167734?version=1&table=Statistical%20covariance%20%24p_%5Ctext%7BT%7D(t%20%5C%2C%20%5Ctext%7Bor%7D%5C%2C%20%20%5Cbar%7Bt%7D)%24"> $p_T(t \text{ or }\bar{t})$</a> ) <li> (<a href="167734?version=1&table=Statistical%20covariance%20%24%7Cy(t%20%5C%2C%20%5Ctext%7Bor%7D%5C%2C%20%20%5Cbar%7Bt%7D)%7C%24"> $|y(t \text{ or }\bar{t})|$</a> ) Normalised cross sections: <li> (<a href="167734?version=1&table=Statistical%20covariance%20%24p_%5Ctext%7BT%7D(t)%24%20normalised"> $p_T(t)$ </a> ) <li> (<a href="167734?version=1&table=Statistical%20covariance%20%24p_%5Ctext%7BT%7D(%5Cbar%7Bt%7D)%24%20normalised" > $p_T(\bar{t})$ </a> ) <li> (<a href="167734?version=1&table=Statistical%20covariance%20%24%7Cy(t)%7C%24%20normalised"> $|y(t)|$ </a> ) <li> (<a href="167734?version=1&table=Statistical%20covariance%20%24%7Cy(%5Cbar%7Bt%7D)%7C%24%20normalised"> $|y(\bar{t})|$ </a> ) Statistical cross-correlation between variables: Absolute cross sections: <li> (<a href="167734?version=1&table=Cross%20correlation%20%24tq%24%20absolute"> $tq$ </a> ) <li> (<a href="167734?version=1&table=Cross%20correlation%20%24%5Cbar%7Bt%7Dq%24%20absolute"> $\bar{t}q$</a> ) Normalised cross sections: <li> (<a href="167734?version=1&table=Cross%20correlation%20%24tq%24%20normalised"> $tq$ </a> ) <li> (<a href="167734?version=1&table=Cross%20correlation%20%24%5Cbar%7Bt%7Dq%24%20normalised"> $\bar{t}q$ </a> ) Full covariance matrices for all measurements: Absolute cross sections: <li> (<a href="167734?version=1&table=Covariance%20%24p_%5Ctext%7BT%7D(t)%24%20absolute"> $p_T(t)$ </a> ) <li> (<a href="167734?version=1&table=Covariance%20%24p_%5Ctext%7BT%7D(%5Cbar%7Bt%7D)%24%20absolute"> $p_T(\bar{t})$</a> ) <li> (<a href="167734?version=1&table=Covariance%20%24%7Cy(t)%7C%24%20absolute"> $|y(t)|$</a> ) <li> (<a href="167734?version=1&table=Covariance%20%24%7Cy(%5Cbar%7Bt%7D)%7C%24%20absolute"> $|y(\bar{t})|$</a> ) <li> (<a href="167734?version=1&table=Covariance%20%24p_%5Ctext%7BT%7D(t%20%5C%2C%20%5Ctext%7Bor%7D%5C%2C%20%20%5Cbar%7Bt%7D)%24"> $p_T(t \text{ or }\bar{t})$</a> ) <li> (<a href="167734?version=1&table=Covariance%20%24%7Cy(t%20%5C%2C%20%5Ctext%7Bor%7D%5C%2C%20%20%5Cbar%7Bt%7D)%7C%24"> $|y(t \text{ or }\bar{t})|$</a> ) Normalised cross sections: <li> (<a href="167734?version=1&table=Covariance%20%24p_%5Ctext%7BT%7D(t)%24%20normalised"> $p_T(t)$ </a> ) <li> (<a href="167734?version=1&table=Covariance%20%24p_%5Ctext%7BT%7D(%5Cbar%7Bt%7D)%24%20normalised"> $p_T(\bar{t})$ </a> ) <li> (<a href="167734?version=1&table=Covariance%20%24%7Cy(t)%7C%24%20normalised"> $|y(t)|$ </a> ) <li> (<a href="167734?version=1&table=Covariance%20%24%7Cy(%5Cbar%7Bt%7D)%7C%24%20normalised"> $|y(\bar{t})|$ </a> ) Statistical uncertainty on systematic uncertainties evaluated with the bootstrap method: Absolute cross sections: <li> (<a href="167734?version=1&table=Bootstrap%20systematics%20%24p_%5Ctext%7BT%7D(t)%24%20absolute"> $p_T(t)$ </a> ) <li> (<a href="167734?version=1&table=Bootstrap%20systematics%20%24p_%5Ctext%7BT%7D(%5Cbar%7Bt%7D)%24%20absolute"> $p_T(\bar{t})$</a> ) <li> (<a href="167734?version=1&table=Bootstrap%20systematics%20%24%7Cy(t)%7C%24%20absolute"> $|y(t)|$</a> ) <li> (<a href="167734?version=1&table=Bootstrap%20systematics%20%24%7Cy(%5Cbar%7Bt%7D)%7C%24%20absolute"> $|y(\bar{t})|$</a> ) Normalised cross sections: <li> (<a href="167734?version=1&table=Bootstrap%20systematics%20%24p_%5Ctext%7BT%7D(t)%24%20normalised"> $p_T(t)$ </a> ) <li> (<a href="167734?version=1&table=Bootstrap%20systematics%20%24p_%5Ctext%7BT%7D(%5Cbar%7Bt%7D)%24%20normalised"> $p_T(\bar{t})$ </a> ) <li> (<a href="167734?version=1&table=Bootstrap%20systematics%20%24%7Cy(t)%7C%24%20normalised"> $|y(t)|$ </a> ) <li> (<a href="167734?version=1&table=Bootstrap%20systematics%20%24%7Cy(%5Cbar%7Bt%7D)%7C%24%20normalised"> $|y(\bar{t})|$ </a> )
Post-fit agreement between data and the expected distributions in events containing a positively charged lepton. The experimental, background-related and MC statistical uncertainties are incorporated in the uncertainty bands. The region $D_{nn} > 0.93$ is excluded from the fit.
Post-fit agreement between data and the expected distributions in events containing a negatively charged lepton. The experimental, background-related and MC statistical uncertainties are incorporated in the uncertainty bands. The region $D_{nn} > 0.93$ is excluded from the fit.
The inclusive top quark pair ($t\bar{t}$) cross-section $σ_{t\bar{t}}$ has been measured in $\sqrt{s}=13$ TeV proton-proton collisions, using 140 fb$^{-1}$ of data collected by the ATLAS experiment at the Large Hadron Collider. Using events with an opposite-charge $eμ$ pair and $b$-tagged jets, the cross-section is measured to be: $\begin{equation}\nonumber σ_{t\bar{t}} = 829.3 \pm 1.3\,\mathrm{(stat)}\ \pm 8.0\,\mathrm{(syst)}\ \pm 7.3\,\mathrm{(lumi)}\ \pm 1.9\,\mathrm{(beam)}\,\mathrm{pb}, \end{equation}$ where the uncertainties reflect the limited size of the data sample, experimental and theoretical systematic effects, the integrated luminosity, and the proton beam energy, giving a total uncertainty of 1.3%. The result is used to determine the top quark pole mass via the dependence of the predicted cross-section on $m_t^\mathrm{pole}$, giving $m_t^\mathrm{pole}=172.8^{+1.5}_{-1.7}$ GeV. The same event sample is used to measure absolute and normalised differential cross-sections for the $t\bar{t}\rightarrow eμν\barνb\bar{b}$ process as a function of single-lepton and dilepton kinematic variables. Complementary measurements of $eμb\bar{b}$ production, treating both $t\bar{t}$ and $Wt$ events as signal, are also provided. Both sets of differential cross-sections are compared to the predictions of various Monte Carlo event generators, demonstrating that the state-of-the-art generators Powheg MiNNLO and Powheg $bb4l$ describe the data better than Powheg hvq. The sensitivity of some of the measured differential distributions to quasi-bound-state formation near the $t\bar{t}$ threshold is investigated in an addendum.
Absolute differential cross-section in the fiducial region as a function of lepton pT. The first column gives the tt->em cross-section including contributions from leptonic tau decays, and the second gives the tt->em cross-section without including the leptonic tau contributions. Columns three and four give the corresponding results for the embb cross-sections. Systematic uncertainties are given for ttbar modelling (ttmod), lepton calibration (lept), jet and b-tagging calibration (jet), backgrounds (bkg) and integrated luminosity and beam energy (leb). The last bin includes overflow beyond the upper bin boundary. The corresponding correlation matrices are given in Tables 27 to 30 and the covariance matrices in Tables 131 to 134
Absolute differential cross-section in the fiducial region as a function of lepton |eta|. The first column gives the tt->em cross-section including contributions from leptonic tau decays, and the second gives the tt->em cross-section without including the leptonic tau contributions. Columns three and four give the corresponding results for the embb cross-sections. Systematic uncertainties are given for ttbar modelling (ttmod), lepton calibration (lept), jet and b-tagging calibration (jet), backgrounds (bkg) and integrated luminosity and beam energy (leb). The corresponding correlation matrices are given in Tables 31 to 34 and the covariance matrices in Tables 135 to 138
Absolute differential cross-section in the fiducial region as a function of dilepton pT. The first column gives the tt->em cross-section including contributions from leptonic tau decays, and the second gives the tt->em cross-section without including the leptonic tau contributions. Columns three and four give the corresponding results for the embb cross-sections. Systematic uncertainties are given for ttbar modelling (ttmod), lepton calibration (lept), jet and b-tagging calibration (jet), backgrounds (bkg) and integrated luminosity and beam energy (leb). The last bin includes overflow beyond the upper bin boundary. The corresponding correlation matrices are given in Tables 35 to 38 and the covariance matrices in Tables 139 to 142
A study of angular correlations inside jets induced by gluon polarization is performed using proton-proton collisions at a center-of-mass energy of $\sqrt{s}$ = 13.6 TeV. The data correspond to an integrated luminosity of 34.7 fb$^{-1}$, collected in 2022 with the CMS detector at the LHC. The details of the parton shower are investigated using jets reconstructed with the anti-$k_\mathrm{T}$ algorithm and subsequently declustered with the Cambridge$-$Aachen algorithm. A novel analysis technique is developed to identify characteristic features of the jet substructure and to select intermediate gluon splittings into quark-antiquark pairs. An observable sensitive to gluon polarization in the parton shower is measured and compared with PYTHIA 8 and HERWIG 7 model predictions, with and without angular correlations induced by the gluon spin. The results are consistent with models that incorporate gluon polarization and strongly disfavor those that neglect them.
DNN output qqbar score for a jet identified in the qqbar class in the data and in the different MC simulations.
Delta phi distribution in data and MC simulations for the inclusive sample
Delta phi distribution in data and MC simulations in the qqbar category with score qq > 0.6 cut
High-energy partons lose energy while propagating through the hot, strongly interacting medium produced in ultrarelativistic nucleus-nucleus collisions, leading to a suppression of particle production at high transverse momentum ($p_\mathrm{T}$). The dependence of this energy loss on the size of the colliding nuclear system has yet to be firmly established experimentally. This Letter presents a systematic study of charged-particle suppression across four different nucleus-nucleus collision systems using nuclear modification factors ($R_\mathrm{AA}$) measured by the CMS Collaboration at the CERN LHC. Previous CMS measurements of $R_\mathrm{AA}$ in oxygen-oxygen, xenon-xenon, and lead-lead collisions are recast with identical $p_\mathrm{T}$ intervals and are complemented by the first measurement of the charged-particle $R_\mathrm{AA}$ in neon-neon collisions at $\sqrt{s_\mathrm{NN}}$ = 5.36 TeV. The neon-neon data correspond to an integrated luminosity of 0.76 nb$^{-1}$. The $R_\mathrm{AA}$ in all collision systems examined show similar qualitative trends, but have a magnitude which is ordered with the nucleon number A. The $R_\mathrm{AA}$ feature a downward slope at low $p_\mathrm{T}$, a local minimum at around 5$-$7 GeV, and an upward slope with increasing $p_\mathrm{T}$. The $R_\mathrm{AA}$ are also compared in terms of A$^{1/3}$, which is proportional to the nuclear radius. Models including only initial-state nuclear effects fail to reproduce the observed trends, whereas energy loss models reproduce the trends in the region $p_\mathrm{T}$$\gt$ 9.6 GeV.
Charged-particle transverse momentum spectrum in NeNe collisions.
Charged-particle nuclear modification factor in NeNe collisions.
Charged-particle nuclear modification factor in OO collisions.
Energetic quarks and gluons traversing a hot and dense quark-gluon plasma deposit energy and momentum into the medium before hadronizing to collimated sprays of particles, known as jets. This energy-momentum deposition is expected to produce medium responses, collectively known as jet wakes, with ``diffusion wake'' denoting a depletion of particles in the direction opposite to the propagating jet. These phenomena are studied by comparing dijet-hadron correlations measured in lead-lead (PbPb) and proton-proton (pp) collisions to assess jet-induced modifications of bulk particle production. The analysis uses PbPb and pp data recorded at a nucleon-nucleon center-of-mass energy $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV with the CMS detector at the CERN LHC. By exploring how the dijet-hadron correlation distributions differ for various pseudorapidity separations of the two jets in the dijet, the presence of a jet diffusion wake is firmly established. The wake has a significance greater than 5 standard deviations for charged particles in the transverse momentum range 1 $\lt$$p_\mathrm{T}$$\lt$ 2 GeV. The measurements are compared with various model predictions with and without jet wake effects, providing new insights into quark-gluon plasma properties and the formation of jet-induced wakes.
The difference of the near-side charged-particle yields $\mathrm{R^{asym}}-\mathrm{R^{sym}}$ in the charged-particles transverse momentum range $1 < p^{\mathrm{ch}}_{\mathrm{T}} < 2$ GeV as a function of $\Delta\eta^{\mathrm{ch}, \mathrm{jet}_{1}}$ in pp and $0-30\%$, $30-50\%$, and $50-80\%$ PbPb collisions.
The difference of the near-side charged-particle yields $\mathrm{R^{asym}}-\mathrm{R^{sym}}$ in the charged-particles transverse momentum range $2 < p^{\mathrm{ch}}_{\mathrm{T}} < 4$ GeV as a function of $\Delta\eta^{\mathrm{ch}, \mathrm{jet}_{1}}$ in pp and $0-30\%$, $30-50\%$, and $50-80\%$ PbPb collisions.
Particle yield differences $\mathrm{R^{asym}}-\mathrm{R^{sym}}$ as a function of $\Delta\eta^{\mathrm{ch}, \mathrm{jet}_{1}}$ for central $(0-30\%)$ PbPb collisions. The results correspond to the charged-particle transverse momentum range $1 < p^{\mathrm{ch}}_{\mathrm{T}} < 2$ GeV for $\mathrm{R^{asym}}$ with $\Delta\eta^{\mathrm{jet}_{1}, \mathrm{jet}_{2}} \in (0.5, 1.0)$, $\Delta\eta^{\mathrm{jet}_{1}, \mathrm{jet}_{2}} \in (1.0, 1.5)$, and $\Delta\eta^{\mathrm{jet}_{1}, \mathrm{jet}_{2}} \in (1.5, 2.0)$. The result for $2 < p^{\mathrm{ch}}_{\mathrm{T}} < 4$ GeV corresponds to $\mathrm{R^{asym}}$ with $\Delta\eta^{\mathrm{jet}_{1}, \mathrm{jet}_{2}} \in (1.0, 1.5)$.
In scattering experiments, high-virtuality partons, i.e., quarks and gluons, initiate a series of additional parton emissions to create collimated sprays of particles known as jets. This paper presents a measurement of the Lund jet plane (LJP) of high-energy jets produced in lead-lead (PbPb) collisions and compares the results to data for proton-proton (pp) collisions. The LJP is formed by iteratively declustering the constituents of a jet into consecutive emissions and recording the relative transverse momentum ($k_\mathrm{T}$) and angle of the resulting emission with respect to its emitter. The angular distributions of two different $k_\mathrm{T}$ slices of the LJP are investigated for jets with radius parameter of 0.4 and transverse momentum in the range 200$-$1000 GeV. The PbPb (pp) data were recorded by the CMS experiment in 2018 (2017) and correspond to an integrated luminosity of 1.7 nb$^{-1}$ (301 pb$^{-1}$) at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The measurement was designed to test whether the earliest jet emissions are produced before the formation of the quark-gluon plasma (QGP) in PbPb collisions. Within the experimental uncertainties, no significant difference is observed between the angular distribution of high-$k_\mathrm{T}$ emissions in \pp and PbPb collisions, which is consistent with these emissions occurring early in the jet evolution, before substantial interaction with the QGP.
The unfolded highest kT distribution in pp collisions for kT bin 10-20 GeV. Normalised to number of jets and by bin width.
The unfolded highest kT distribution in pp collisions for kT bin 20-40 GeV. Normalised to number of jets and by bin width.
The unfolded ratio of highest kT distribution in pp and PbPb collisions for kT bin 10-20 GeV. Normalised to number of jets and by bin width.
Searches for electroweak production of chargino pairs, $\tilde{\chi}^{+}_{1}\tilde{\chi}^{-}_{1}$, and of chargino and next-to-lightest neutralino, $\tilde{\chi}^{\pm}_{1}\tilde{\chi}^{0}_{2}$, are presented. The models explored assume that the charginos decay into a $W$ boson and the lightest neutralino, $\tilde{\chi}^{\pm}_1 \rightarrow W^{\pm} \tilde{\chi}^{0}_{1}$. The next-to-lightest neutralinos are degenerate in mass with the chargino and decay to $\tilde{\chi}^{0}_{1}$ and either a $Z$ or a Higgs boson, $\tilde{\chi}^{0}_{2} \rightarrow Z \tilde{\chi}^{0}_{1}$ or $h \tilde{\chi}^{0}_{1}$. The searches exploit the presence of a single isolated lepton and missing transverse momentum from the $W$ boson decay products and the lightest neutralinos, and the presence of jets from hadronically decaying $Z$ or $W$ bosons or from the Higgs boson decaying into a pair of $b$-quarks. The searches use 139 fb$^{-1}$ of $\sqrt{s}= 13$ TeV proton-proton collisions data collected by the ATLAS detector at the Large Hadron Collider between 2015 and 2018. No deviations from the Standard Model expectations are found, and 95% confidence level exclusion limits are set. Chargino masses ranging from 260 to 520 GeV are excluded for a massless $\tilde{\chi}^{0}_{1}$ in chargino pair production models. Degenerate chargino and next-to-lightest neutralino masses ranging from 260 to 420 GeV are excluded for a massless $\tilde{\chi}^{0}_{1}$ for $\tilde{\chi}^{0}_{2} \rightarrow Z \tilde{\chi}^{0}_{1}$. For decays through an on-shell Higgs boson and for mass-splitting between $\tilde{\chi}^{\pm}_{1} / \tilde{\chi}^{0}_{2}$ and $\tilde{\chi}^{0}_{1}$ as small as the Higgs boson mass, mass limits are improved by up to 40 GeV in the range of 200-260 GeV and 280-470 GeV compared to previous ATLAS constraints.
The post-fit $m_{eff}$ distributions in the exclusion signal regions SRLM for the C1C1-WW models. The uncertainty bands plotted include all statistical and systematic uncertainties. The dashed lines represent the benchmark signal samples. The overflow events, where present, are included in the last bin.
The post-fit $m_{eff}$ distributions in the exclusion signal regions SRLM for the C1N2-WZ models. The uncertainty bands plotted include all statistical and systematic uncertainties. The dashed lines represent the benchmark signal samples. The overflow events, where present, are included in the last bin.
The post-fit $m_{eff}$ distributions in the exclusion signal regions SRMM for the C1C1-WW models. The uncertainty bands plotted include all statistical and systematic uncertainties. The dashed lines represent the benchmark signal samples. The overflow events, where present, are included in the last bin.
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