Search

A search is performed for long-lived massive neutral particles decaying to quark-antiquark pairs. The experimental signature is a distinctive topology of a pair of jets, originating at a secondary vertex. Events were collected with the CMS detector at the CERN LHC in proton-proton collisions at a center-of-mass energy of 8 TeV. The data analyzed correspond to an integrated luminosity of $18.5{\mathrm{fb}}^{-1}$. No significant excess is observed above standard model expectations. Upper limits at 95% confidence level are set on the production cross section of a heavy neutral scalar particle, $H$, in the mass range of 200 to 1000 GeV, decaying promptly into a pair of long-lived neutral $X$ particles in the mass range of 50 to 350 GeV, each in turn decaying into a quark-antiquark pair. For $X$ with mean proper decay lengths of 0.4 to 200 cm, the upper limits are typically $0.5–200\mathrm{fb}$. The results are also interpreted in the context of an R-parity-violating supersymmetric model with long-lived neutralinos decaying into a quark-antiquark pair and a muon. For pair production of squarks that promptly decay to neutralinos with mean proper decay lengths of $2–40\mathrm{cm}$, the upper limits on the cross section are typically $0.5–3\mathrm{fb}$. The above limits are the most stringent on these channels to date.

Using $e^{+}{e}^{-}$ collision data, corresponding to an integrated luminosity of $892{\mathrm{pb}}^{-1}$ collected at center-of-mass energies from 4.84 to 4.95 GeV with the BESIII detector, we search for the process $e^{+}{e}^{-}\to K^{+}{K}^{-}\psi (3770)$ by reconstructing two charged kaons and one $D$ meson from $\psi (3770)$. No significant signal of $e^{+}{e}^{-}\to K^{+}{K}^{-}\psi (3770)$ is found and the upper limits of the Born cross sections are reported at 90% confidence level.

We present measurements of elliptic and triangular azimuthal anisotropy of charged particles detected at forward rapidity $1<\left|\eta \right|<3$ in Au + Au collisions at $\sqrt{s_{{}_{NN}}}=200$ GeV, as a function of centrality. The multiparticle cumulant technique is used to obtain the elliptic flow coefficients $v_2\left\{2\right\},v_2\left\{4\right\},v_2\left\{6\right\}$, and $v_2\left\{8\right\}$, and triangular flow coefficients $v_3\left\{2\right\}$ and $v_3\left\{4\right\}$. Using the small-variance limit, we estimate the mean and variance of the event-by-event $v_2$ distribution from $v_2\left\{2\right\}$ and $v_2\left\{4\right\}$. In a complementary analysis, we also use a folding procedure to study the distributions of $v_2$ and $v_3$ directly, extracting both the mean and variance. Implications for initial geometrical fluctuations and their translation into the final-state momentum distributions are discussed.

Based on $(2712.4\pm 14.3)\times {10}^6\psi (3686)$ events, we investigate four hadronic decay modes of the $P$-wave charmonium spin-singlet state $h_c{(}^1{P}_1)\to h^{+}{h}^{-}{\pi }^0/\eta$ ($h=\pi$ or $K$) via the process $\psi (3686)\to {\pi }^0{h}_c$ at BESIII. The $h_c\to {\pi }^{+}{\pi }^{-}{\pi }^0$ decay is observed with a significance of $9.6\sigma$ after taking into account systematic uncertainties. Evidences for $h_c\to K^{+}{K}^{-}{\pi }^0$ and $h_c\to K^{+}{K}^{-}\eta$ are found with significances of $3.5\sigma$ and $3.3\sigma$, respectively, after considering the systematic uncertainties. The branching fractions of these decays are measured to be $\mathcal{B}(h_c\to {\pi }^{+}{\pi }^{-}{\pi }^0)=(1.36\pm 0.16\pm 0.14)\times {10}^{-3}$, $\mathcal{B}(h_c\to K^{+}{K}^{-}{\pi }^0)=(3.26\pm 0.84\pm 0.36)\times {10}^{-4}$, and $\mathcal{B}(h_c\to K^{+}{K}^{-}\eta )=(3.13\pm 1.08\pm 0.38)\times {10}^{-4}$, where the first uncertainties are statistical and the second are systematic. No significant signal of $h_c\to {\pi }^{+}{\pi }^{-}\eta$ is found, and the upper limit of its decay branching fraction is determined to be $\mathcal{B}(h_c\to {\pi }^{+}{\pi }^{-}\eta )<4.0\times {10}^{-4}$ at the 90% confidence level.

The inclusive jet cross section is measured in $pp$ collisions with a center-of-mass energy of 7 TeV at the Large Hadron Collider using the CMS experiment. The data sample corresponds to an integrated luminosity of $34{\mathrm{pb}}^{-1}$. The measurement is made for jet transverse momenta in the range 18–1100 GeV and for absolute values of rapidity less than 3. The measured cross section extends to the highest values of jet $p_T$ ever observed and, within the experimental and theoretical uncertainties, is generally in agreement with next-to-leading-order perturbative QCD predictions.

In 2015, the PHENIX Collaboration has measured single-spin asymmetries for charged pions in transversely polarized $p+p$ collisions at the center-of-mass energy of $\sqrt{s}=200\mathrm{GeV}$. The pions were detected at central rapidities of $|\eta |<0.35$. The single-spin asymmetries are consistent with zero for each charge individually, as well as consistent with the previously published neutral-pion asymmetries in the same rapidity range. However, they show a slight indication of charge-dependent differences which may suggest a flavor dependence in the underlying mechanisms that create these asymmetries.

We report an investigation of the invariant mass spectrum of the two jets with highest transverse momentum in $pp\to W+2$-jet and $W+3$-jet events to look for resonant enhancement. The data sample corresponds to an integrated luminosity of $5.0{\mathrm{fb}}^{-1}$ collected with the CMS detector at $\sqrt{s}=7\mathrm{TeV}$. We find no evidence for the anomalous structure reported by the CDF Collaboration, and establish an upper limit of 5.0 pb at 95% confidence level on the production cross section for a generic Gaussian signal with mass near 150 GeV. Additionally, we exclude two theoretical models that predict a CDF-like dijet resonance near 150 GeV.

This Letter describes the search for an enhanced production rate of events with a charged lepton and a neutrino in high-energy $pp$ collisions at the LHC. The analysis uses data collected with the CMS detector, with an integrated luminosity of $5.0{\mathrm{fb}}^{-1}$ at $\sqrt{s}=7\mathrm{TeV}$, and a further $3.7{\mathrm{fb}}^{-1}$ at $\sqrt{s}=8\mathrm{TeV}$. No evidence is found for an excess. The results are interpreted in terms of limits on a heavy charged gauge boson ($W^{\prime }$) in the sequential standard model, a split universal extra dimension model, and contact interactions in the helicity-nonconserving model. For the last, values of the binding energy below 10.5 (8.8) TeV in the electron (muon) channel are excluded at a 95% confidence level. Interpreting the $\ell \nu$ final state in terms of a heavy $W^{\prime }$ with standard model couplings, masses below 2.90 TeV are excluded.

An inclusive search for supersymmetry using razor variables is performed in events with four or more jets and no more than one lepton. The results are based on a sample of proton-proton collisions corresponding to an integrated luminosity of $2.3{\mathrm{fb}}^{-1}$ collected with the CMS experiment at a center-of-mass energy of $\sqrt{s}=13\mathrm{TeV}$. No significant excess over the background prediction is observed in data, and 95% confidence level exclusion limits are placed on the masses of new heavy particles in a variety of simplified models. Assuming that pair-produced gluinos decay only via three-body processes involving third-generation quarks plus a neutralino, and that the neutralino is the lightest supersymmetric particle with a mass of 200 GeV, gluino masses below 1.6 TeV are excluded for any branching fractions for the individual gluino decay modes. For some specific decay mode scenarios, gluino masses up to 1.65 TeV are excluded. For decays to first- and second-generation quarks and a neutralino with a mass of 200 GeV, gluinos with masses up to 1.4 TeV are excluded. Pair production of top squarks decaying to a top quark and a neutralino with a mass of 100 GeV is excluded for top squark masses up to 750 GeV.

The cross section of bottom quark-antiquark ($b\overline{b}$) production in $p+p$ collisions at $\sqrt{s}=510\mathrm{GeV}$ is measured with the PHENIX detector at the Relativistic Heavy Ion Collider. The results are based on the yield of high mass, like-sign muon pairs measured within the PHENIX muon arm acceptance ($1.2<|y|<2.2$). The $b\overline{b}$ signal is extracted from like-sign dimuons by utilizing the unique properties of neutral $B$ meson oscillation. We report a differential cross section of $d{\sigma }_{b\overline{b}\to {\mu }^{\pm }{\mu }^{\pm }}/dy=0.16\pm 0.01(\mathrm{stat})\pm 0.02(\mathrm{syst})\pm 0.02(\text{global})\mathrm{nb}$ for like-sign muons in the rapidity and $p_T$ ranges $1.2<|y|<2.2$ and $p_T>1\mathrm{GeV}/c$, and dimuon mass of $5–10\mathrm{GeV}/c^2$. The extrapolated total cross section at this energy for $b\overline{b}$ production is $13.1\pm 0.6(\mathrm{stat})\pm 1.5(\mathrm{syst})\pm 2.7(\text{global})\mu \mathrm{b}$. The total cross section is compared to a perturbative quantum chromodynamics calculation and is consistent within uncertainties. The azimuthal opening angle between muon pairs from $b\overline{b}$ decays and their $p_T$ distributions are compared to distributions generated using ps pythia6, which includes next-to-leading order processes. The azimuthal correlations and pair $p_T$ distribution are not very well described by pythia calculations, but are still consistent within uncertainties. Flavor creation and flavor excitation subprocesses are favored over gluon splitting.

A search for neutral minimal supersymmetric standard model (MSSM) Higgs bosons in $pp$ collisions at the LHC at a center-of-mass energy of 7 TeV is presented. The results are based on a data sample corresponding to an integrated luminosity of $36{\mathrm{pb}}^{-1}$ recorded by the CMS experiment. The search uses decays of the Higgs bosons to tau pairs. No excess is observed in the tau-pair invariant-mass spectrum. The resulting upper limits on the Higgs boson production cross section times branching fraction to tau pairs, as a function of the pseudoscalar Higgs boson mass, yield stringent new bounds in the MSSM parameter space.

A search for physics beyond the standard model in events with at least three leptons is presented. The data sample, corresponding to an integrated luminosity of $19.5{\mathrm{fb}}^{-1}$ of proton-proton collisions with center-of-mass energy $\sqrt{s}=8\mathrm{TeV}$, was collected by the CMS experiment at the LHC during 2012. The data are divided into exclusive categories based on the number of leptons and their flavor, the presence or absence of an opposite-sign, same-flavor lepton pair (OSSF), the invariant mass of the OSSF pair, the presence or absence of a tagged bottom-quark jet, the number of identified hadronically decaying $\tau$ leptons, and the magnitude of the missing transverse energy and of the scalar sum of jet transverse momenta. The numbers of observed events are found to be consistent with the expected numbers from standard model processes, and limits are placed on new-physics scenarios that yield multilepton final states. In particular, scenarios that predict Higgs boson production in the context of supersymmetric decay chains are examined. We also place a 95% confidence level upper limit of 1.3% on the branching fraction for the decay of a top quark to a charm quark and a Higgs boson ($t\to cH$), which translates to a bound on the left- and right-handed top-charm flavor-violating Higgs Yukawa couplings, ${\lambda }_{tc}^H$ and ${\lambda }_{ct}^H$, respectively, of $\sqrt{|{\lambda }_{tc}^H{|}^2+|{\lambda }_{ct}^H{|}^2}<0.21$.

A search for pair-produced heavy vectorlike charge-$2/3$ quarks, $T$, in $pp$ collisions at a center-of-mass energy of 7 TeV, is performed with the CMS detector at the LHC. Events consistent with the flavor-changing-neutral-current decay of a $T$ quark to a top quark and a $Z$ boson are selected by requiring two leptons from the $Z$-boson decay, as well as an additional isolated charged lepton. In a data sample corresponding to an integrated luminosity of $1.14{\mathrm{fb}}^{-1}$, the number of observed events is found to be consistent with the standard model background prediction. Assuming a branching fraction of 100% for the decay $T\to tZ$, a $T$ quark with a mass less than $475\mathrm{GeV}/c^2$ is excluded at the 95% confidence level.

Results are presented from a search for the pair production of third-generation scalar and vector leptoquarks, as well as for top squarks in $R$-parity-violating supersymmetric models. In either scenario, the new, heavy particle decays into a $\tau$ lepton and a $b$ quark. The search is based on a data sample of $pp$ collisions at $\sqrt{s}=7\mathrm{TeV}$, which is collected by the CMS detector at the LHC and corresponds to an integrated luminosity of $4.8{\mathrm{fb}}^{-1}$. The number of observed events is found to be in agreement with the standard model prediction, and exclusion limits on mass parameters are obtained at the 95% confidence level. Vector leptoquarks with masses below 760 GeV are excluded and, if the branching fraction of the scalar leptoquark decay to a $\tau$ lepton and a $b$ quark is assumed to be unity, third-generation scalar leptoquarks with masses below 525 GeV are ruled out. Top squarks with masses below 453 GeV are excluded for a typical benchmark scenario, and limits on the coupling between the top squark, $\tau$ lepton, and $b$ quark, ${\lambda }_{333}^{\prime }$ are obtained. These results are the most stringent for these scenarios to date.

We present measurements of $e^{+}{e}^{-}$ production at midrapidity in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{{}_{NN}}}=200$ GeV. The invariant yield is studied within the PHENIX detector acceptance over a wide range of mass ($m_{ee}<5 \mathrm{GeV}/c^2$) and pair transverse momentum ($p_T<5 \mathrm{GeV}/c$) for minimum bias and for five centrality classes. The $e^{+}{e}^{-}$ yield is compared to the expectations from known sources. In the low-mass region ($m_{ee}=0.30–0.76 \mathrm{GeV}/c^2$) there is an enhancement that increases with centrality and is distributed over the entire pair $p_T$ range measured. It is significantly smaller than previously reported by the PHENIX experiment and amounts to $2.3\pm 0.4\left(\mathrm{stat}\right)\pm 0.4\left(\mathrm{syst}\right)\pm 0.2\left(\mathrm{model}\right)$ or to $1.7\pm 0.3\left(\mathrm{stat}\right)\pm 0.3\left(\mathrm{syst}\right)\pm 0.2\left(\mathrm{model}\right)$ for minimum bias collisions when the open heavy-flavor contribution is calculated with pythia or mc@nlo, respectively. The inclusive mass and $p_T$ distributions, as well as the centrality dependence, are well reproduced by model calculations where the enhancement mainly originates from the melting of the $\rho$ meson resonance as the system approaches chiral symmetry restoration. In the intermediate-mass region ($m_{ee}=1.2–2.8 \mathrm{GeV}/c^2$), the data hint at a significant contribution in addition to the yield from the semileptonic decays of heavy-flavor mesons.

A search for narrow resonances decaying into dijet final states is performed on data from proton-proton collisions at a center-of-mass energy of 8 TeV, corresponding to an integrated luminosity of $18.8{\mathrm{fb}}^{-1}$. The data were collected with the CMS detector using a novel technique called data scouting, in which the information associated with these selected events is much reduced, permitting collection of larger data samples. This technique enables CMS to record events containing jets at a rate of 1 kHz, by collecting the data from the high-level-trigger system. In this way, the sensitivity to low-mass resonances is increased significantly, allowing previously inaccessible couplings of new resonances to quarks and gluons to be probed. The resulting dijet mass distribution yields no evidence of narrow resonances. Upper limits are presented on the resonance cross sections as a function of mass, and compared with a variety of models predicting narrow resonances. The limits are translated into upper limits on the coupling of a leptophobic resonance $Z_B^{\prime }$ to quarks, improving on the results obtained by previous experiments for the mass range from 500 to 800 GeV.

We report the transverse single-spin asymmetries of $J/\psi$ production at forward and backward rapidity, $1.2<|y|<2.2$, as a function of $J/\psi$ transverse momentum ($p_T$) and Feynman-$x$ ($x_F$). The data analyzed were recorded by the PHENIX experiment at the Relativistic Heavy Ion Collider in 2015 from $p+p$, $p+\mathrm{Al}$, and $p+\mathrm{Au}$ collisions with transversely polarized proton beams at $\sqrt{s_{NN}}=200\mathrm{GeV}$. At this collision energy, single-spin asymmetries for heavy-flavor particle production of $p+p$ collisions provide access to the spin-dependent gluon distribution and higher-twist correlation functions inside the nucleon, such as the gluon Qiu-Sterman and trigluon correlation functions. $\mathrm{Proton}+\mathrm{nucleus}$ collisions offer an excellent opportunity to study nuclear effects on the correlation functions. The data indicate a positive asymmetry at the two-standard-deviation level in the $p+p$ data for $2\mathrm{GeV}/c<p_T<10\mathrm{GeV}/c$ at backward rapidity and negative asymmetries at the two-standard-deviation level in the $p+\mathrm{Au}$ data for $p_T<2\mathrm{GeV}/c$ at both forward and backward rapidity, while in $p+\mathrm{Al}$ collisions the asymmetries are consistent with zero within the range of experimental uncertainties.

We present measurements of the elliptic flow ($v_2$) as a function of transverse momentum ($p_T$), pseudorapidity ($\eta$), and centrality in $d+\mathrm{Au}$ collisions at $\sqrt{s_{\mathit{NN}}}=200$, 62.4, 39, and 19.6 GeV. The beam-energy scan of $d+\mathrm{Au}$ collisions provides a testing ground for the onset of flow signatures in small collision systems. We measure a nonzero $v_2$ signal at all four collision energies, which, at midrapidity and low $p_T$, is consistent with predictions from viscous hydrodynamic models. Comparisons with calculations from parton transport models (based on the ampt Monte Carlo generator) show good agreement with the data at midrapidity to forward ($d$-going) rapidities and low $p_T$. At backward (Au-going) rapidities and $p_T>1.5\mathrm{GeV}/c$, the data diverges from ampt calculations of $v_2$ relative to the initial geometry, indicating the possible dominance of nongeometry related correlations, referred to as nonflow. We also present measurements of the charged-particle multiplicity ($d{N}_{\mathrm{ch}}/d\eta$) as a function of $\eta$ in central $d+\mathrm{Au}$ collisions at the same energies. We find that in $d+\mathrm{Au}$ collisions at $\sqrt{s_{\mathit{NN}}}=200$ GeV the $v_2$ scales with $d{N}_{\mathrm{ch}}/d\eta$ over all $\eta$ in the PHENIX acceptance. At $\sqrt{s_{\mathit{NN}}}=62.4$, and 39 GeV, $v_2$ scales with $d{N}_{\mathrm{ch}}/d\eta$ at midrapidity and forward rapidity, but falls off at backward rapidity. This departure from the $d{N}_{\mathrm{ch}}/d\eta$ scaling may be a further indication of nonflow effects dominating at backward rapidity.

A first measurement of the polarization of $W$ bosons with large transverse momenta in $pp$ collisions is presented. The measurement is based on $36{\mathrm{pb}}^{-1}$ of data recorded at $\sqrt{s}=7\mathrm{TeV}$ by the CMS detector at the LHC. The left-handed, right-handed, and longitudinal polarization fractions ($f_L$, $f_R$, and $f_0$, respectively) of $W$ bosons with transverse momenta larger than 50 GeV are determined by using decays to both electrons and muons. The muon final state yields the most precise measurement: $(f_L-f_R{)}^{-}=0.240\pm 0.036(\mathrm{stat})\pm 0.031(\mathrm{syst})$ and $f_0^{-}=0.183\pm 0.087(\mathrm{stat})\pm 0.123(\mathrm{syst})$ for negatively charged $W$ bosons and $(f_L-f_R{)}^{+}=0.310\pm 0.036(\mathrm{stat})\pm 0.017(\mathrm{syst})$ and $f_0^{+}=0.171\pm 0.085(\mathrm{stat})\pm 0.099(\mathrm{syst})$ for positively charged $W$ bosons. This establishes, for the first time, that $W$ bosons produced in $pp$ collisions with large transverse momenta are predominantly left-handed, as expected in the standard model.