The production cross section of a top quark pair in association with a photon is measured in proton-proton collisions at a center-of-mass energy of 13 TeV. The data set, corresponding to an integrated luminosity of 137 fb$^{-1}$, was recorded by the CMS experiment during the 2016-2018 data taking of the LHC. The measurements are performed in a fiducial volume defined at the particle level. Events with an isolated, highly energetic lepton, at least three jets from the hadronization of quarks, among which at least one is b tagged, and one isolated photon are selected. The inclusive fiducial $\mathrm{t\overline{t}}\gamma$ cross section, for a photon with transverse momentum greater than 20 GeV and pseudorapidity $\lvert \eta\rvert$$\lt$ 1.4442, is measured to be 798 $\pm$ 7 (stat) $\pm$ 48 (syst) fb, in good agreement with the prediction from the standard model at next-to-leading order in quantum chromodynamics. The differential cross sections are also measured as a function of several kinematic observables and interpreted in the framework of the standard model effective field theory (EFT), leading to the most stringent direct limits to date on anomalous electromagnetic dipole moment interactions of the top quark and the photon.
The measured inclusive ttgamma cross section in the fiducial phase space compared to the prediction from simulation using Madgraph_aMC@NLO at a center-of-mass energy of 13 TeV.
The measured inclusive ttgamma cross section in the fiducial phase space compared to the prediction from simulation using Madgraph_aMC@NLO at a center-of-mass energy of 13 TeV.
The first direct, model-independent measurement is presented of the modulus of the Cabibbo-Kobayashi-Maskawa (CKM) matrix elements $|V_\mathrm{tb}|$, $|V_\mathrm{td}|$, and $|V_\mathrm{ts}|$, in final states enriched in single top quark $t$-channel events. The analysis uses proton-proton collision data from the LHC, collected during 2016 by the CMS experiment, at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. Processes directly sensitive to these matrix elements are considered at both the production and decay vertices of the top quark. In the standard model hypothesis of CKM unitarity, a lower limit of $|V_\mathrm{tb}|$ $>$ 0.970 is measured at the 95% confidence level. Several theories beyond the standard model are considered, and by releasing all constraints among the involved parameters, the values $|V_\mathrm{tb}| =$ 0.988 $\pm$ 0.024, and $|V_\mathrm{td}|^2 + |V_\mathrm{ts}|^2 =$ 0.06 $\pm$ 0.06, where the uncertainties include both statistical and systematic components, are measured.
Values of the third-row elements of the CKM matrix inferred from low-energy measurements with the respective values of the top quark decay branching fractions. The q in bs{V_{tq}} and \mathcal{B}(t o Wq) in the first column refers to b, s, and d quarks, according to the quark label shown in the header row.
The first search for the Z boson decay to $\tau\tau\mu\mu$ at the CERN LHC is presented, based on data collected by the CMS experiment at the LHC in proton-proton collisions at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 138 fb$^{-1}$. The data are compatible with the predicted background. For the first time, an upper limit at the 95% confidence level of 6.9 times the standard model expectation is placed on the ratio of the Z $\to$ $\tau\tau\mu\mu$ to Z $\to$ 4$\mu$ branching fractions. Limits are also placed on the six flavor-conserving four-lepton effective-field-theory operators involving two muons and two tau leptons, for the first time testing all such operators.
Distribution of $m_{4\mu}$ after the maximum likelihood fit of the background-only model (stacked histograms) to the data (black points). The nuisance parameters are set to their post-fit values and the signal (black dotted line) is overlaid, scaled to the upper limit on its cross section of 6.9 times the SM expectation. The gray shaded areas in both panels correspond to the total uncertainty in the background prediction. The black vertical bars indicate the statistical uncertainty in the data.
Observed limits at the 95% CL on $C_{\mathrm{LL}}^{2233}$ vs. $C_{\mathrm{LR}}^{2332}$ (red) showing the full range.
Observed limits at the 95% CL on $C_{\mathrm{LR}}^{2233}$ vs. $C_{\mathrm{LL}}^{2332}$ (orange) showing the full range.
A search is presented for single production of a vector-like T quark with charge 2/3 $e$, in the decay channel featuring a top quark and a Z boson, with the top quark decaying hadronically and the Z boson decaying to neutrinos. The search uses data collected by the CMS experiment in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 137 fb$^{-1}$ recorded at the CERN LHC in 2016-2018. The search is sensitive to a T quark mass between 0.6 and 1.8 TeV with decay widths ranging from negligibly small up to 30% of the T quark mass. Reconstruction strategies for the top quark are based on the degree of Lorentz boosting of its final state. At 95% confidence level, the upper limit on the product of the cross section and branching fraction for a T quark of small decay width varies between 15 and 602 fb, depending on its mass. For a T quark with decay widths between 10 and 30% of its mass, this upper limit ranges between 16 and 836 fb. For most of the studied range, the results provide the best limits to date. This is the first search for single T quark production based on the full Run 2 data set of the LHC.
Distribution of the transverse mass $M_T$ reconstructed from the top quark and the missing transverse energy in the merged validation region with 0 forward jets. Data are compared to backgrounds are after the data-driven extraction is performed.
Distribution of the transverse mass $M_T$ reconstructed from the top quark and the missing transverse energy in the merged validation region with at least 1 forward jet. Data are compared to backgrounds are after the data-driven extraction is performed.
Distribution of the transverse mass $M_T$ reconstructed from the top quark and the missing transverse energy in the merged validation region with 0 forward jets. Data are compared to backgrounds are after the data-driven extraction is performed.
Results are presented from a search for physics beyond the standard model in proton-proton collisions at $\sqrt{s} =$ 13 TeV in channels with two Higgs bosons, each decaying via the process H $\to$$\mathrm{b\bar{b}}$, and large missing transverse momentum. The search uses a data sample corresponding to an integrated luminosity of 137 fb$^{-1}$ collected by the CMS experiment at the CERN LHC. The search is motivated by models of supersymmetry that predict the production of neutralinos, the neutral partners of the electroweak gauge and Higgs bosons. The observed event yields in the signal regions are found to be consistent with the standard model background expectations. The results are interpreted using simplified models of supersymmetry. For the electroweak production of nearly mass-degenerate higgsinos, each of whose decay chains yields a neutralino ($\tilde{\chi}^0_1$) that in turn decays to a massless goldstino and a Higgs boson, $\tilde{\chi}^0_1$ masses in the range 175 to 1025 GeV are excluded at 95% confidence level. For the strong production of gluino pairs decaying via a slightly lighter $\tilde{\chi}^0_2$ to H and a light $\tilde{\chi}^0_1$, gluino masses below 2330 GeV are excluded.
Pre-fit background covariance matrix $\sigma_{xy}$ for the 22 analysis bins, ordered as in Fig. 10.
Pre-fit background covariance matrix $\sigma_{xy}$ for the 22 analysis bins, ordered as in Fig. 10.
Pre-fit background covariance matrix $\sigma_{xy}$ for the 22 analysis bins, ordered as in Fig. 10.
Results on $\phi$ meson production in inelastic p+p collisions at CERN SPS energies are presented. They are derived from data collected by the NA61/SHINE fixed target experiment, by means of invariant mass spectra fits in the $\phi \to K^+K^-$ decay channel. They include the first ever measured double differential spectra of $\phi$ mesons as a function of rapidity $y$ and transverse momentum $p_T$ for proton beam momenta of 80 GeV/c and 158 GeV/c, as well as single differential spectra of $y$ or $p_T$ for beam momentum of 40 GeV/c. The corresponding total $\phi$ yields per inelastic p+p event are obtained. These results are compared with existing data on $\phi$ meson production in p+p collisions. The comparison shows consistency but superior accuracy of the present measurements. The emission of $\phi$ mesons in p+p reactions is confronted with that occurring in Pb+Pb collisions, and the experimental results are compared with model predictions. It appears that none of the considered models can properly describe all the experimental observables.
Energy dependence of ratios of total yields of $\phi$ mesons to mean total yields of pions produced in in minimum bias p+p collisions at CERN SPS energies.
Energy dependence of double ratios of total yields of $\phi$ mesons to mean total yields of pions in central Pb+Pb collisions over minimum bias p+p collisions at CERN SPS energies.
Energy dependence of total yields of $\phi$ mesons produced in minimum bias p+p collisions at CERN SPS energies.
Measurements of charged pion and kaon production in central Pb+Pb collisions at 40, 80 and 158 AGeV are presented. These are compared with data at lower and higher energies as well as with results from p+p interactions. The mean pion multiplicity per wounded nucleon increases approximately linearly with s_NN^1/4 with a change of slope starting in the region 15-40 AGeV. The change from pion suppression with respect to p+p interactions, as observed at low collision energies, to pion enhancement at high energies occurs at about 40 AGeV. A non-monotonic energy dependence of the ratio of K^+ to pi^+ yields is observed, with a maximum close to 40 AGeV and an indication of a nearly constant value at higher energies.The measured dependences may be related to an increase of the entropy production and a decrease of the strangeness to entropy ratio in central Pb+Pb collisions in the low SPS energy range, which is consistent with the hypothesis that a transient state of deconfined matter is created above these energies. Other interpretations of the data are also discussed.
The energy dependence of the K+/PI+ ratio at y = 0 in PB PB and AU AU collisions. This table includes the present NA49 data as well as other data CT.= The commmon systematic error on the NA49 points is +-7%. including PHENIX and AGS data.
The energy dependence of the K-/PI- ratio at y = 0 in PB PB and AU AU collisions. This table includes the present NA49 data as well as other data includingPHENIX and AGS data, and preliminary E895 data.. The commmon systematic error on the NA49 points is +-7%.
The energy dependence of the ratio of the K+ to PI+ multiplicities in full phase space from PB PB and AU AU collisions. This table includes the present NA49 data as well as other data including AGS data.. The commmon systematic error on the NA49 points is +-7%.
For comparison of inclusive jet cross sections measured at hadron-hadron colliders to next-to-leading order (NLO) parton-level calculations, the energy deposited in the jet cone by spectator parton interactions must first be subtracted. The assumption made at the Tevatron is that the spectator parton interaction energy is similar to the ambient level measured in minimum bias events. In this paper, we test this assumption by measuring the ambient charged track momentum in events containing large transverse energy jets at $\sqrt{s}=1800$ GeV and $\sqrt{s}=630$ GeV and comparing this ambient momentum with that observed both in minimum bias events and with that predicted by two Monte Carlo models. Two cones in $\eta$--$\phi$ space are defined, at the same pseudo-rapidity, $\eta$, as the jet with the highest transverse energy ($E_T^{(1)}$), and at $\pm 90^o$ in the azimuthal direction, $\phi$. The total charged track momentum inside each of the two cones is measured. The minimum momentum in the two cones is almost independent of $E_T^{(1)}$ and is similar to the momentum observed in minimum bias events, whereas the maximum momentum increases roughly linearly with the jet $E_T^{(1)}$ over most of the measured range. This study will help improve the precision of comparisons of jet cross section data and NLO perturbative QCD predictions. %this is new The distribution of the sum of the track momenta in the two cones is also examined for five different $E_T^{(1)}$ bins. The HERWIG and PYTHIA Monte Carlos are reasonably successful in describing the data, but neither can describe completely all of the event properties.
Average PT inside the max and min cone for cm energy 1800 GeV.
A study of strange particle production in muon neutrino charged current interactions has been performed using the data from the NOMAD experiment. Yields of neutral strange particles K0s, Lambda, AntiLambda have been measured. Mean multiplicities are reported as a function of the event kinematic variables Enu, W2 and Q2 as well as of the variables describing particle behaviour within a hadronic jet: xF, z and pT2. Decays of resonances and heavy hyperons with identified K0s and Lambda in the final state have been analyzed. Clear signals corresponding to K*+-, Sigma*+-, Xi- and Sigma0 have been observed.
Measured yields as a function of E, the neutrino energy.
Ratios of measured yields for K0S/LAMBDA and LAMBDA/LAMBDABAR as a functionof E, the neutrino energy.
Using data samples collected with the BESIII detector at the BEPCII collider, we measure the Born cross section of $e^{+}e^{-}\rightarrow p\bar{p}$ at 12 center-of-mass energies from 2232.4 to 3671.0 MeV. The corresponding effective electromagnetic form factor of the proton is deduced under the assumption that the electric and magnetic form factors are equal $(|G_{E}|= |G_{M}|)$. In addition, the ratio of electric to magnetic form factors, $|G_{E}/G_{M}|$, and $|G_{M}|$ are extracted by fitting the polar angle distribution of the proton for the data samples with larger statistics, namely at $\sqrt{s}=$ 2232.4 and 2400.0 MeV and a combined sample at $\sqrt{s}$ = 3050.0, 3060.0 and 3080.0 MeV, respectively. The measured cross sections are in agreement with recent results from BaBar, improving the overall uncertainty by about 30\%. The $|G_{E}/G_{M}|$ ratios are close to unity and consistent with BaBar results in the same $q^{2}$ region, which indicates the data are consistent with the assumption that $|G_{E}|=|G_{M}|$ within uncertainties.
Summary of the Born cross section $\sigma_\text{Born}$, the effective FF $|G|$, and the related variables used to calculate the Born cross sections at the different c.m.energies $\sqrt{s}$, where $N_\text{obs}$ is the number of candidate events, $N_\text{bkg}$ is the estimated background yield, $\varepsilon^\prime=\varepsilon\times(1+\delta)$ is the product of detection efficiency $\varepsilon$ and the radiative correction factor $(1+\delta)$, and $L$ is the integrated luminosity. The first errors are statistical, and the second systematic.
Forum