Search

Understanding the formation of topological defects in connected magnetic nanowires such as in artificial spin ices (ASIs) is critical to controlling their behavior. Moreover, emergent frustration behavior of these defects can be expected due to complex underlying lattice geometry of the ASIs. We have explored in situ thermalization and quenching of quasicrystalline ASIs, which exhibit additional frustration due to aperiodicity from near the Curie temperature, and we observe the formation of two sets of topological vortex defects: within the magnetic bars and within the vertices at which the bars meet. By varying the laser fluence, we show that the number of defects in the vertices varies as the quenching rate changes following a power law relation, which we interpret as being related to the ferromagnetic-to-paramagnetic phase transition. Conversely, the defects formed within the bars are metastable states related to the spontaneous magnetization reversal of the magnetic bars and are therefore strongly dependent on underlying lattice geometry. These results provide insight into the emergence and control of topological defects in confined frustrated magnetic systems.

We search for decays of a $B$ meson into a neutral $D$ meson and a charged kaon, with the $D$ meson decaying into a charged kaon, a charged pion, and a neutral pion. This final state can be reached through the $b\to c$ transition $B^{-}\to D^0{K}^{-}$ followed by the doubly Cabibbo-suppressed $D^0\to K^{+}{\pi }^{-}{\pi }^0$, or the $b\to u$ transition $B^{-}\to {\overline{D}}^0{K}^{-}$ followed by the Cabibbo-favored ${\overline{D}}^0\to K^{+}{\pi }^{-}{\pi }^0$. The interference of these two amplitudes is sensitive to the angle $\gamma$ of the unitarity triangle. We present results based on $226\times {10}^6$ $e^{+}{e}^{-}\to {\rm Y}(4S)\to B\overline{B}$ events collected with the BABAR detector at SLAC. We find no significant evidence for these decays and we set a limit $R_{\mathrm{ADS}}\equiv \frac{\Gamma ([K^{+}{\pi }^{-}{\pi }^0{]}_D{K}^{-})+\Gamma ([K^{-}{\pi }^{+}{\pi }^0{]}_D{K}^{+})}{\Gamma ([K^{+}{\pi }^{-}{\pi }^0{]}_D{K}^{+})+\Gamma ([K^{-}{\pi }^{+}{\pi }^0{]}_D{K}^{-})}<0.039$ at 95% confidence level, which we translate with a Bayesian approach into $r_B\equiv |A(B^{-}\to {\overline{D}}^0{K}^{-})/A(B^{-}\to D^0{K}^{-})|<0.19$ at 95% confidence level.

We present a search for Higgs bosons in multilepton final states in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ recorded with the D0 detector at the Fermilab Tevatron Collider, using the full Run II data set with integrated luminosities of up to $9.7{\mathrm{fb}}^{-1}$. The multilepton states considered are $ee\mu$, $e\mu \mu$, $\mu {\tau }_h{\tau }_h$, and like-charge $e^{\pm }{\mu }^{\pm }$ pairs. These channels directly probe the HVV ($V=W$, $Z$) coupling of the Higgs boson in production and decay. The $\mu {\tau }_h{\tau }_h$ channel is also sensitive to $H\to {\tau }^{+}{\tau }^{-}$ decays. Upper limits at the 95% C.L on the rate of standard model Higgs boson production are derived in the mass range $100\le M_H\le 200\mathrm{GeV}$. The expected and observed limits are a factor of 6.3 and 8.4 above the predicted standard model cross section at $M_H=125\mathrm{GeV}$. We also interpret the data in a fermiophobic Higgs boson model.

A search for resonant diboson production using a data sample corresponding to $4.7{\mathrm{fb}}^{-1}$ of integrated luminosity collected by the ATLAS experiment at the Large Hadron Collider in $pp$ collisions at $\sqrt{s}=7\mathrm{TeV}$ is presented. The search for a narrow resonance in the $WW$ or $WZ$ mass distribution is conducted in a final state with an electron or a muon, missing transverse momentum, and at least two jets. No significant excess is observed and limits are set using three benchmark models: $WW$ resonance masses below 940 and 710 GeV are excluded at 95% confidence level for spin-2 Randall–Sundrum and bulk Randall–Sundrum gravitons, respectively; $WZ$ resonance masses below 950 GeV are excluded at 95% confidence level for a spin-1 extended gauge model $W^{\prime }$ boson.

A generic search is presented for a heavy particle decaying to $WZ\to \ell \nu {\ell }^{\prime }{\ell }^{\prime }$ ($\ell$, ${\ell }^{\prime }=e$, $\mu$) final states. The data were recorded by the ATLAS detector in $\sqrt{s}=7\mathrm{TeV}$ $pp$ collisions at the Large Hadron Collider and correspond to an integrated luminosity of $1.02{\mathrm{fb}}^{-1}$. The transverse mass distribution of the selected $WZ$ candidates is found to be consistent with the standard model expectation. Upper limits on the production cross section times branching ratio are derived using two benchmark models predicting a heavy particle decaying to a $WZ$ pair.

First measurements of the azimuthal anisotropy of neutral pions produced in Pb-Pb collisions at a center-of-mass energy of $\sqrt{s_{NN}}=2.76\mathrm{TeV}$ are presented. The amplitudes of the second Fourier component ($v_2$) of the ${\pi }^0$ azimuthal distributions are extracted using an event-plane technique. The values of $v_2$ are studied as a function of the neutral pion transverse momentum ($p_T$) for different classes of collision centrality in the kinematic range $1.6<p_T<8.0\mathrm{GeV}/c$, within the pseudorapidity interval $|\eta |<0.8$. The CMS measurements of $v_2(p_T)$ are similar to previously reported ${\pi }^0$ azimuthal anisotropy results from $\sqrt{s_{NN}}=200\mathrm{GeV}$ Au-Au collisions at RHIC, despite a factor of $\sim 14$ increase in the center-of-mass energy. In the momentum range $2.5<p_T<5.0\mathrm{GeV}/c$, the neutral pion anisotropies are found to be smaller than those observed by CMS for inclusive charged particles.

This paper presents a search for a new heavy particle produced in association with a top or antitop quark. Two models in which the new heavy particle is a color singlet or a color triplet are considered, decaying, respectively, to $\overline{t}q$ or $tq$, leading to a resonance within the $t\overline{t}+\mathrm{\text{jets}}$ signature. The full 2011 ATLAS $pp$ collision data set from the LHC ($4.7{\mathrm{fb}}^{-1}$) is used to search for $t\overline{t}$ events produced in association with jets, in which one of the $W$ bosons from the top quarks decays leptonically and the other decays hadronically. The data are consistent with the Standard Model expectation, and a new particle with mass below 430 Gev for both $W^{\prime }$ boson and color triplet models is excluded at 95% confidence level, assuming unit right-handed coupling.

This report describes a search for associated production of $W$ and Higgs bosons based on data corresponding to an integrated luminosity of $\mathcal{L}\approx 5.3\mathrm{f}{\mathrm{b}}^{-1}$ collected with the D0 detector at the Fermilab Tevatron $p\overline{p}$ Collider. Events containing a $W\to \ell \nu$ candidate (with $\ell$ corresponding to $e$ or $\mu$) are selected in association with two or three reconstructed jets. One or two of the jets are required to be consistent with having evolved from a $b$ quark. A multivariate discriminant technique is used to improve the separation of signal and backgrounds. Expected and observed upper limits are obtained for the product of the $WH$ production cross section and branching ratios and reported in terms of ratios relative to the prediction of the standard model as a function of the mass of the Higgs boson ($M_H$). The observed and expected 95% C.L. upper limits obtained for an assumed $M_H=115\mathrm{GeV}$ are, respectively, factors of 4.5 and 4.8 larger than the value predicted by the standard model.

We report on a search for a dijet resonance in events with only two or three jets and a large imbalance in the total event transverse momentum. This search is sensitive to the possible production of a new particle in association with a $W$ or $Z$ boson, where the boson decays leptonically with one or more neutrinos in the final state. We use the full data set collected by the CDF II detector at the Tevatron collider at a proton-antiproton center-of-mass energy of 1.96 TeV. These data correspond to an integrated luminosity of $9.1{\mathrm{fb}}^{-1}$. We study the invariant mass distribution of the two jets with highest transverse energy. We find good agreement between data and standard model background expectations and measure the combined cross section for $WW$, $WZ$, and $ZZ$ production to be ${13.8}_{-2.7}^{+3.0}\mathrm{pb}$. No significant anomalies are observed in the mass spectrum, and 95% credibility level upper limits are set on the production rates of a potential new particle in association with a $W$ or $Z$ boson.

We measure the polarization of $W$ bosons from top-quark ($t$) decays into final states with a charged lepton and jets, $t\overline{t}\to W^{+}b{W}^{-}\overline{b}\to \ell \nu bq{\overline{q}}^{\prime }\overline{b}$, using the full Run II data set collected by the CDF II detector, corresponding to an integrated luminosity of $8.7{\mathrm{fb}}^{-1}$. A model-independent method simultaneously determines the fraction of longitudinal ($f_0$) and right-handed ($f_{+}$) $W$ bosons to yield $f_0=0.726\pm 0.066(\mathrm{stat})\pm 0.067(\mathrm{syst})$ and $f_{+}=-0.045\pm 0.044(\mathrm{stat})\pm 0.058(\mathrm{syst})$ with a correlation coefficient of $-0.69$. Additional results are presented under various standard model assumptions. No significant discrepancies with the standard model are observed.

We present a search for new particles in an extension to the standard model that includes a heavy Higgs boson ($H^0$), a lighter charged Higgs boson ($H^{\pm }$), and an even lighter Higgs boson $h^0$, with decays leading to a $W$-boson pair and a bottom-antibottom quark pair in the final state. We use events with exactly one lepton, missing transverse momentum, and at least four jets in data corresponding to an integrated luminosity of $8.7{\mathrm{fb}}^{-1}$ collected by the CDF II detector in proton-antiproton collisions at $\sqrt{s}=1.96\mathrm{TeV}$. We find the data to be consistent with standard model predictions and report the results in terms of a simplified Higgs-cascade-decay model, setting 95% confidence level upper limits on the product of cross section and branching fraction from 1.3 pb to 15 fb as a function of $H^0$ and $H^{\pm }$ masses for $m_h^0=126\mathrm{GeV}/c^2$.

We present the first signature-based search for delayed photons using an exclusive photon plus missing transverse energy final state. Events are reconstructed in a data sample from the CDF II detector corresponding to $6.3{\mathrm{fb}}^{-1}$ of integrated luminosity from $\sqrt{s}=1.96\mathrm{TeV}$ proton-antiproton collisions. Candidate events are selected if they contain a photon with an arrival time in the detector larger than expected from a promptly produced photon. The mean number of events from standard model sources predicted by the data-driven background model based on the photon timing distribution is $286\pm 24$. A total of 322 events are observed. A $p$ value of 12% is obtained, showing consistency of the data with standard model predictions.

A search is performed for heavy particle pairs produced in $\sqrt{s}=7\mathrm{TeV}$ proton-proton collisions with $35{\mathrm{pb}}^{-1}$ of data collected by the CMS experiment at the LHC. The search is sensitive to squarks and gluinos of generic supersymmetry models, provided they are kinematically accessible, with minimal assumptions on properties of the lightest superpartner particle. The kinematic consistency of the selected events is tested against the hypothesis of heavy particle pair production using the dimensionless razor variable $R$, related to the missing transverse energy $E_{\mathrm{T}}^{\mathrm{miss}}$. The new physics signal is characterized by a broad peak in the distribution of $M_R$, an event-by-event indicator of the heavy particle mass scale. This new approach is complementary to $E_{\mathrm{T}}^{\mathrm{miss}}$-based searches. After background modeling based on data, and background rejection based on $R$ and $M_R$, no significant excess of events is found beyond the standard model expectations. The results are interpreted in the context of the constrained minimal supersymmetric standard model as well as two simplified supersymmetry models.

A search is presented for gluinos decaying via the supersymmetric partner of the top quark using events with two same-sign leptons, jets, and missing transverse momentum. The analysis is performed with $2.05{\mathrm{fb}}^{-1}$ of integrated luminosity from $pp$ collisions at $\sqrt{s}=7\mathrm{TeV}$ collected by the ATLAS detector at the LHC. No excess beyond the standard model expectation is observed, and exclusion limits are derived for simplified models where the gluino decays via the supersymmetric partner of the top quark and in the minimal supergravity and constrained minimal supersymmetric standard model framework. In those scenarios, gluino masses below 550 GeV are excluded at 95% C.L. within the parameter space considered, significantly extending the coverage with respect to existing limits. Depending on the model parameters, gluino masses up to 750 GeV can also be excluded at 95% C.L.

We present a search for a standard model Higgs boson decaying to two $W$ bosons that decay to leptons using the full data set collected with the CDF II detector in $\sqrt{s}=1.96\mathrm{TeV}$ $p\overline{p}$ collisions at the Fermilab Tevatron, corresponding to an integrated luminosity of $9.7{\mathrm{fb}}^{-1}$. We obtain no evidence for production of a standard model Higgs boson with mass between 110 and $200\mathrm{GeV}/c^2$, and place upper limits on the production cross section within this range. We exclude standard model Higgs boson production at the 95% confidence level in the mass range between 149 and $172\mathrm{GeV}/c^2$, while expecting to exclude, in the absence of signal, the range between 155 and $175\mathrm{GeV}/c^2$. We also interpret the search in terms of standard model Higgs boson production in the presence of a fourth generation of fermions and within the context of a fermiophobic Higgs boson model. For the specific case of a standard-model-like Higgs boson in the presence of fourth-generation fermions, we exclude at the 95% confidence level Higgs boson production in the mass range between 124 and $200\mathrm{GeV}/c^2$, while expecting to exclude, in the absence of signal, the range between 124 and $221\mathrm{GeV}/c^2$.

We present a search for a Higgs boson decaying into a pair of photons based on $9.6{\mathrm{fb}}^{-1}$ of $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ collected with the D0 detector at the Fermilab Tevatron Collider. The search employs multivariate techniques to discriminate signal from the nonresonant background and is separately optimized for a standard model and a fermiophobic Higgs boson. No significant excess of data above the background prediction is observed and upper limits on the product of the cross section and branching fraction are derived at the 95% confidence level as a function of Higgs boson mass. For a standard model Higgs boson with mass of 125 GeV, the observed (expected) upper limits are a factor of 12.8 (8.7) above the standard model prediction. The existence of a fermiophobic Higgs boson with mass in the 100–113 GeV range is excluded at the 95% confidence level.

We search for high-mass resonances decaying into $Z$ boson pairs using data corresponding to $6{\mathrm{fb}}^{-1}$ collected by the CDF experiment in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$. The search is performed in three distinct final states: $ZZ\to {\ell }^{+}{\ell }^{-}{\ell }^{+}{\ell }^{-}$, $ZZ\to {\ell }^{+}{\ell }^{-}\nu \nu$, and $ZZ\to {\ell }^{+}{\ell }^{-}jj$. For a Randall-Sundrum graviton $G^{*}$, the 95% CL upper limits on the production cross section times branching ratio to $ZZ$, $\sigma (p\overline{p}\to G^{*}\to ZZ)$, vary between 0.26 pb and 0.045 pb in the mass range $300<M_{G^{*}}<1000\mathrm{GeV}/c^2$.

We search for $B^0$ meson decays into two-body combinations of $K^0$, $\eta$, ${\eta }^{\prime }$, and $\varphi$ mesons in $324\times {10}^6$ $B\overline{B}$ pairs collected with the BABAR detector at the PEP-II asymmetric-energy $e^{+}{e}^{-}$ collider at SLAC. We measure the following branching fractions (upper limits at 90% confidence level) in units of ${10}^{-6}$: $\mathcal{B}(B^0\to \eta K^0)={1.8}_{-0.6}^{+0.7}\pm 0.1(<2.9)$, $\mathcal{B}(B^0\to \eta \eta )={1.1}_{-0.4}^{+0.5}\pm 0.1(<1.8)$, $\mathcal{B}(B^0\to \eta \varphi )=0.1\pm 0.2\pm 0.1(<0.6)$, $\mathcal{B}(B^0\to {\eta }^{\prime }\varphi )={0.2}_{-0.3}^{+0.4}\pm 0.1(<1.0)$, and $\mathcal{B}(B^0\to {\eta }^{\prime }{\eta }^{\prime })={1.0}_{-0.6}^{+0.8}\pm 0.1(<2.4)$, where the first error is statistical and the second systematic.

An inclusive search for the standard model Higgs boson using the four-lepton final state in proton-antiproton collisions produced by the Tevatron at $\sqrt{s}=1.96\mathrm{TeV}$ is conducted. The data are recorded by the CDF II detector and correspond to an integrated luminosity of $9.7{\mathrm{fb}}^{-1}$. Three distinct Higgs decay modes, namely $ZZ$, $WW$, and $\tau \tau$, are simultaneously probed. Nine potential signal events are selected and found to be consistent with the background expectation. We set a 95% credibility limit on the production cross section times the branching ratio and subsequent decay to the four-lepton final state for hypothetical Higgs boson masses between $120\mathrm{GeV}/c^2$ and $300\mathrm{GeV}/c^2$.