Search

A search for quark compositeness in the form of quark contact interactions, based on hadronic jet pairs (dijets) produced in proton-proton collisions at $\sqrt{s}=7\mathrm{TeV}$, is described. The data sample of the study corresponds to an integrated luminosity of $2.9{\mathrm{pb}}^{-1}$ collected with the CMS detector at the LHC. The dijet centrality ratio, which quantifies the angular distribution of the dijets, is measured as a function of the invariant mass of the dijet system and is found to agree with the predictions of the standard model. A statistical analysis of the data provides a lower limit on the energy scale of quark contact interactions. The sensitivity of the analysis is such that the expected limit is 2.9 TeV; because the observed value of the centrality ratio at high invariant mass is below the expectation, the observed limit is 4.0 TeV at the 95% confidence level.

We present the first upper-limit measurement of the branching fractions of the isospin-violating transitions ${\chi }_{c0,2}\to {\pi }^0{\eta }_c$. The measurements are performed using $106\times 10^6$ $\psi (3686)$ events accumulated with the BESIII detector at the BEPCII $e^{+}{e}^{-}$ collider at a center-of-mass energy corresponding to the $\psi (3686)$ mass. We obtained upper limits on the branching fractions at a 90% confidence level of $B({\chi }_{c0}\to {\pi }^0{\eta }_c)<1.6\times 10^{-3}$ and $B({\chi }_{c2}\to {\pi }^0{\eta }_c)<3.2\times 10^{-3}$.

Using $2.93{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ collision data taken at a center-of-mass energy of 3.773 GeV by the BESIII detector at the BEPCII, we measure the branching fractions of the singly Cabibbo-suppressed decays $D\to \omega \pi \pi$ to be $\mathcal{B}(D^0\to \omega {\pi }^{+}{\pi }^{-})=(1.33\pm 0.16\pm 0.12)\times {10}^{-3}$ and $\mathcal{B}(D^{+}\to \omega {\pi }^{+}{\pi }^0)=(3.87\pm 0.83\pm 0.25)\times {10}^{-3}$, where the first uncertainties are statistical and the second ones systematic. The statistical significances are $12.9\sigma$ and $7.7\sigma$, respectively. The precision of $\mathcal{B}(D^0\to \omega {\pi }^{+}{\pi }^{-})$ is improved by a factor of 2.1 over prior measurements, and $\mathcal{B}(D^{+}\to \omega {\pi }^{+}{\pi }^0)$ is measured for the first time. No significant signal for $D^0\to \omega {\pi }^0{\pi }^0$ is observed, and the upper limit on the branching fraction is $\mathcal{B}(D^0\to \omega {\pi }^0{\pi }^0)<1.10\times {10}^{-3}$ at the 90% confidence level. The branching fractions of $D\to \eta \pi \pi$ are also measured and consistent with existing results.

Non-$D\overline{D}$ decay $\psi (3770)\to \rho \pi$ is searched for using a data sample of $(17.3\pm 0.5)\mathrm{p}{\mathrm{b}}^{-1}$ taken at the center-of-mass energy of 3.773 GeV by the BESII detector at the BEPC. No $\rho \pi$ signal is observed, and the upper limit of the cross section is measured to be $\sigma (e^{+}{e}^{-}\to \rho \pi )<6.0\mathrm{pb}$ at 90% C. L. Considering the interference between the continuum amplitude and the $\psi (3770)$ resonance amplitude, the branching fraction of $\psi (3770)$ decays to $\rho \pi$ is determined to be $\mathcal{B}(\psi (3770)\to \rho \pi )\in (6.0\times {10}^{-6},2.4\times {10}^{-3})$ at 90% C. L. This is in agreement with the prediction of the $S$- and $D$-wave mixing scheme of the charmonium states for solving the “$\rho \pi$ puzzle” between $J/\psi$ and $\psi (2S)$ decays.

Using 58 million $J/\psi$ events taken with the BES II detector at the Beijing Electron Positron Collider, the decay $J/\psi \to \gamma f_2(1270)f_2(1270)\to \gamma {\pi }^{+}{\pi }^{-}{\pi }^{+}{\pi }^{-}$ is observed, and the branching fraction $Br(J/\psi \to \gamma f_2{f}_2)=(9.5\pm 0.7\pm 1.6)\times {10}^{-4}$ is measured for the first time, where the quoted errors are statistical and systematic, respectively. The branching fraction of $J/\psi \to \gamma {\eta }_c$, ${\eta }_c\to f_2{f}_2$ is also measured to be $Br(J/\psi \to \gamma {\eta }_c)·Br({\eta }_c\to f_2{f}_2)=(1.3\pm {0.3}_{-0.4}^{+0.3})\times {10}^{-4}$. The nonresonant branching fraction of $J/\psi \to \gamma f_2{f}_2$ is $Br(J/\psi \to \gamma f_2{f}_2)=(8.2\pm 0.8\pm 1.7)\times {10}^{-4}.$

Using 58 million $J/\psi$ events accumulated with the BES II detector, branching fractions for the ${\eta }_c\to VV$ decays, ${\eta }_c\to \rho \rho$, ${\eta }_c\to K^{*}{\overline{K}}^{*}$, ${\eta }_c\to \omega \omega$, and ${\eta }_c\to \varphi \varphi$, are measured. The branching fractions are $Br({\eta }_c\to \rho \rho )=(1.23\pm 0.37\pm 0.50)\times {10}^{-2}$, $Br({\eta }_c\to K^{*}{\overline{K}}^{*})=(10.3\pm 2.6\pm 4.3)\times {10}^{-3}$, $Br({\eta }_c\to \omega \omega )<6.3\times {10}^{-3}$ (90% C.L.), and $Br({\eta }_c\to \varphi \varphi )=(2.5\pm 0.5\pm 0.9)\times {10}^{-3}$. The process ${\eta }_c\to \omega \varphi$ is also searched for, and the 90% C.L. upper limit $Br({\eta }_c\to \omega \varphi )<1.7\times {10}^{-3}$ is obtained for this process.

Using data collected with the BESIII detector operating at the Beijing Electron Positron Collider, we search for the process $e^{+}{e}^{-}\to {\eta }_c\eta {\pi }^{+}{\pi }^{-}$. The search is performed using five large datasets recorded at center-of-mass energies of 4.23, 4.26, 4.36, 4.42, and 4.60 GeV. The ${\eta }_c$ meson is reconstructed in 16 exclusive decay modes. No signal is observed in the ${\eta }_c$ mass region at any center-of-mass energy. The upper limits on the reaction cross sections are determined to be 6.2, 10.8, 27.6, 22.6 and 23.7 pb at the 90% confidence level at the center-of-mass energies listed above.

A search for new physics is performed in events with two same-sign isolated leptons, hadronic jets, and missing transverse energy in the final state. The analysis is based on a data sample corresponding to an integrated luminosity of $4.98{\mathrm{fb}}^{-1}$ produced in $pp$ collisions at a center-of-mass energy of 7 TeV collected by the CMS experiment at the LHC. This constitutes a factor of 140 increase in integrated luminosity over previously published results. The observed yields agree with the standard model predictions and thus no evidence for new physics is found. The observations are used to set upper limits on possible new physics contributions and to constrain supersymmetric models. To facilitate the interpretation of the data in a broader range of new physics scenarios, information on the event selection, detector response, and efficiencies is provided.

Using a sample of $4.48\times {10}^8\psi (3686)$ events collected with the BESIII detector at the BEPCII collider, we study the two-photon decays of the pseudoscalar mesons ${\pi }^0$, $\eta$, ${\eta }^{\prime }$, $\eta (1405)$, $\eta (1475)$, $\eta (1760)$, and $X(1835)$ in $J/\psi$ radiative decays using $\psi (3686)\to {\pi }^{+}{\pi }^{-}J/\psi$ events. The ${\pi }^0$, $\eta$, and ${\eta }^{\prime }$ mesons are clearly observed in the two-photon mass spectra, and the branching fractions are determined to be $B(J/\psi \to \gamma {\pi }^0\to 3\gamma )=(3.57\pm 0.12\pm 0.16)\times {10}^{-5}$, $B(J/\psi \to \gamma \eta \to 3\gamma )=(4.42\pm 0.04\pm 0.18)\times {10}^{-4}$, and $B(J/\psi \to \gamma {\eta }^{\prime }\to 3\gamma )=(1.26\pm 0.02\pm 0.05)\times {10}^{-4}$, where the first error is statistical and the second is systematic. No clear signal for $\eta (1405)$, $\eta (1475)$, $\eta (1760)$ or $X(1835)$ is observed in the two-photon mass spectra, and upper limits at the 90% confidence level on the product branching fractions are obtained.

Based on a sample of 1.31 billion $J/\psi$ events collected with the BESIII detector, we report the study of the doubly radiative decay ${\eta }^{\prime }\to \gamma \gamma {\pi }^0$ for the first time, where the ${\eta }^{\prime }$ meson is produced via the $J/\psi \to \gamma {\eta }^{\prime }$ decay. The branching fraction of ${\eta }^{\prime }\to \gamma \gamma {\pi }^0$ inclusive decay is measured to be $\mathcal{B}({\eta }^{\prime }\to \gamma \gamma {\pi }^0{)}_{\mathrm{Incl}}=(3.20\pm 0.07(\mathrm{stat})\pm 0.23(\mathrm{sys}))\times {10}^{-3}$, while the branching fractions of the dominant process ${\eta }^{\prime }\to \gamma \omega$ and the nonresonant component are determined to be $\mathcal{B}({\eta }^{\prime }\to \gamma \omega )\times \mathcal{B}(\omega \to \gamma {\pi }^0)=(23.7\pm 1.4(\mathrm{stat})\pm 1.8(\mathrm{sys}))\times {10}^{-4}$ and $\mathcal{B}({\eta }^{\prime }\to \gamma \gamma {\pi }^0{)}_{\mathrm{NR}}=(6.16\pm 0.64(\mathrm{stat})\pm 0.67(\mathrm{sys}))\times {10}^{-4}$, respectively. In addition, the $M_{\gamma \gamma }^2$-dependent partial widths of the inclusive decay are also presented.

Using $58\times {10}^6$ $J/\psi$ and $14\times {10}^6$ $\psi (2S)$ events collected by the BESII detector at the BEPC, branching fractions or upper limits for the decays $J/\psi$ and $\psi (2S)\to \Lambda \overline{\Lambda }{\pi }^0$ and $\Lambda \overline{\Lambda }\eta$ are measured. For the isospin violating decays, the upper limits are determined to be $\mathcal{B}(J/\psi \to \Lambda \overline{\Lambda }{\pi }^0)<6.4\times {10}^{-5}$ and $\mathcal{B}[\psi (2S)\to \Lambda \overline{\Lambda }{\pi }^0]<4.9\times {10}^{-5}$ at the 90% confidence level. The isospin conserving process $J/\psi \to \Lambda \overline{\Lambda }\eta$ is observed for the first time, and its branching fraction is measured to be $\mathcal{B}(J/\psi \to \Lambda \overline{\Lambda }\eta )=(2.62\pm 0.60\pm 0.44)\times {10}^{-4}$, where the first error is statistical and the second one is systematic. No $\Lambda \overline{\Lambda }\eta$ signal is observed in $\psi (2S)$ decays, and $\mathcal{B}[\psi (2S)\to \Lambda \overline{\Lambda }\eta ]<1.2\times {10}^{-4}$ is set at the 90% confidence level. Branching fractions of $J/\psi$ decays into ${\Sigma }^{+}{\pi }^{-}\overline{\Lambda }$ and ${\overline{\Sigma }}^{-}{\pi }^{+}\Lambda$ are also reported, and the sum of these branching fractions is determined to be $\mathcal{B}(J/\psi \to {\Sigma }^{+}{\pi }^{-}\overline{\Lambda }+\mathrm{c}.\mathrm{c}.)=(1.52\pm 0.08\pm 0.16)\times {10}^{-3}$.

Using $2.93{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ collision data collected at a center-of-mass energy of 3.773 GeV with the BESIII detector, we present a measurement of the branching fraction of the doubly Cabibbo-suppressed (DCS) decay $D^0\to K^{+}{\pi }^{-}{\pi }^0$ and a search for the DCS decay $D^0\to K^{+}{\pi }^{-}{\pi }^0{\pi }^0$. The branching fraction of $D^0\to K^{+}{\pi }^{-}{\pi }^0$ is determined to be $[3.13_{-0.56}^{+0.60}(\mathrm{stat})\pm 0.15(\mathrm{syst})]\times {10}^{-4}$. No signal is observed for $D^0\to K^{+}{\pi }^{-}{\pi }^0{\pi }^0$, and an upper limit of $3.6\times {10}^{-4}$ is set on the branching fraction at the 90% CL. We combine these results with the world-average branching fractions of their counterpart Cabibbo-favored decays to determine the ratios of the DCS over the Cabibbo-favored branching fractions, $\mathcal{B}(D^0\to K^{+}{\pi }^{-}{\pi }^0)/\mathcal{B}(D^0\to K^{-}{\pi }^{+}{\pi }^0)=(0.22\pm 0.04)\%$ and $\mathcal{B}(D^0\to K^{+}{\pi }^{-}{\pi }^0{\pi }^0)/\mathcal{B}(D^0\to K^{-}{\pi }^{+}{\pi }^0{\pi }^0)<0.40\%$ at the 90% CL which correspond to $(0.75\pm 0.14){\tan }^4{\theta }_C$ and $1.37\times {\tan }^4{\theta }_C$, respectively, where ${\theta }_C$ is the Cabibbo mixing angle.

Using data samples collected at center-of-mass energies of $\sqrt{s}=4.009$, 4.226, 4.257, 4.358, 4.416, and 4.599 GeV with the BESIII detector operating at the BEPCII storage ring, we search for the isospin violating decay $Y(4260)\to J/\psi \eta {\pi }^0$. No signal is observed, and upper limits on the cross section $\sigma (e^{+}{e}^{-}\to J/\psi \eta {\pi }^0)$ at the 90% confidence level are determined to be 3.6, 1.7, 2.4, 1.4, 0.9, and 1.9 pb, respectively.

Using a sample of 1.31 billion $J/\psi$ events accumulated with the BESIII detector at the BEPCII collider, we report the observation of the decay $J/\psi \to \varphi {\pi }^0$, which is the first evidence for a doubly Okubo–Zweig–Iizuka suppressed electromagnetic $J/\psi$ decay. A clear structure is observed in the $K^{+}{K}^{-}$ mass spectrum around $1.02\mathrm{GeV}/c^2$, which can be attributed to interference between $J/\psi \to \varphi {\pi }^0$ and $J/\psi \to K^{+}{K}^{-}{\pi }^0$ decays. Due to this interference, two possible solutions are found. The corresponding measured values of the branching fraction of $J/\psi \to \varphi {\pi }^0$ are $[2.94\pm 0.16(\mathrm{stat})\pm 0.16(\mathrm{syst})]\times 10^{-6}$ and $[1.24\pm 0.33(\mathrm{stat})\pm 0.30(\mathrm{syst})]\times 10^{-7}$.

Using a data sample of $4.48\times {10}^8$ $\psi (3686)$ events collected with the BESIII detector, we present a first observation of $\psi (3686)\to p\overline{p}\varphi$, and we measure its branching fraction to be $[6.06\pm 0.38(\mathrm{stat})\pm 0.48(\mathrm{syst})]\times {10}^{-6}$. In contrast to the earlier discovery of a threshold enhancement in the $p\overline{p}$-mass spectrum of the channel $J/\psi \to \gamma p\overline{p}$, denoted as $X(p\overline{p})$, we do not find a similar enhancement in $\psi (3686)\to p\overline{p}\varphi$. An upper limit of $1.82\times {10}^{-7}$ at the 90% confidence level on the branching fraction of $\psi (3686)\to X(p\overline{p})\varphi \to p\overline{p}\varphi$ is obtained.

By analyzing $482{\mathrm{pb}}^{-1}$ of $e^{+}{e}^{-}$ collision data collected at $\sqrt{s}=4.009\mathrm{GeV}$ with the BESIII detector at the BEPCII collider, we measure the absolute branching fractions for the semileptonic decays $D_s^{+}\to \eta e^{+}{\nu }_e$ and $D_s^{+}\to {\eta }^{\prime }{e}^{+}{\nu }_e$ to be $B(D_s^{+}\to \eta e^{+}{\nu }_e)=(2.30\pm 0.31\pm 0.08)\%$ and $B(D_s^{+}\to {\eta }^{\prime }{e}^{+}{\nu }_e)=(0.93\pm 0.30\pm 0.05)\%$, respectively, and their ratio $\frac{B(D_s^{+}\to {\eta }^{\prime }{e}^{+}{\nu }_e)}{B(D_s^{+}\to \eta e^{+}{\nu }_e)}=0.40\pm 0.14\pm 0.02$, where the first uncertainties are statistical and the second ones are systematic. The results are in good agreement with previous measurements within uncertainties; they can be used to determine the $\eta -{\eta }^{\prime }$ mixing angle and improve upon the $D_s^{+}$ semileptonic branching ratio precision.

Using $482{\mathrm{pb}}^{-1}$ of $e^{+}{e}^{-}$ collision data collected at a center-of-mass energy of $\sqrt{s}=4.009\mathrm{GeV}$ with the BESIII detector, we measure the branching fractions of the decays $D_s^{+}\to {\mu }^{+}{\nu }_{\mu }$ and $D_s^{+}\to {\tau }^{+}{\nu }_{\tau }$. By constraining the ratio of decay rates of $D_s^{+}$ to ${\tau }^{+}{\nu }_{\tau }$ and to ${\mu }^{+}{\nu }_{\mu }$ to the Standard Model prediction, the branching fractions are determined to be $\mathcal{B}(D_s^{+}\to {\mu }^{+}{\nu }_{\mu })=(0.495\pm 0.067\pm 0.026)\%$ and $\mathcal{B}(D_s^{+}\to {\tau }^{+}{\nu }_{\tau })=(4.83\pm 0.65\pm 0.26)\%$. Using these branching fractions, we obtain a value for the decay constant $f_{D_s^{+}}$ of $(241.0\pm 16.3\pm 6.5)\mathrm{MeV}$, where the first error is statistical and the second systematic.

A search for three-jet hadronic resonance production in $pp$ collisions at a center-of-mass energy of 7 TeV has been conducted by the CMS Collaboration at the LHC, using a data sample corresponding to an integrated luminosity of $35{\mathrm{pb}}^{-1}$. Events with high jet multiplicity and a large scalar sum of jet transverse momenta are analyzed using a signature-based approach. The number of expected standard model background events is found to be in good agreement with the observed events. Limits on the cross section times branching ratio are set in a model of gluino pair production with an $R$-parity-violating decay to three quarks, and the data rule out such particles within the mass range of 200 to $280\mathrm{GeV}/c^2$.

A search for the rare decays of $J/\psi \to D_s^{-}{\rho }^{+}+\mathrm{c}.\mathrm{c}.$ and $J/\psi \to {\overline{D}}^0{\overline{K}}^{*0}+\mathrm{c}.\mathrm{c}.$ is performed with a data sample of 225.3-million $J/\psi$ events collected with the Beijing Spectrometer III detector. No evident signal is observed. Upper limits on the branching fractions are determined to be $\mathcal{B}(J/\psi \to D_s^{-}{\rho }^{+}+\mathrm{c}.\mathrm{c}.)<1.3\times {10}^{-5}$ and $\mathcal{B}(J/\psi \to {\overline{D}}^0{\overline{K}}^{*0}+\mathrm{c}.\mathrm{c}.)<2.5\times {10}^{-6}$ at the 90% confidence level.