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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., Fiorini, L., et al. (2012). Search for Magnetic Monopoles in root s=7 TeV pp Collisions with the ATLAS Detector. Phys. Rev. Lett., 109(26), 261803–18pp.
Abstract: This Letter presents a search for magnetic monopoles with the ATLAS detector at the CERN Large Hadron Collider using an integrated luminosity of 2.0 fb(-1) of pp collisions recorded at a center-of-mass energy root s = 7 TeV. No event is found in the signal region, leading to an upper limit on the production cross section at 95% confidence level of 1.6/epsilon fb for Dirac magnetic monopoles with the minimum unit magnetic charge and with mass between 200 GeV and 1500 GeV, where epsilon is the monopole reconstruction efficiency. The efficiency epsilon is high and uniform in the fiducial region given by pseudorapidity vertical bar eta vertical bar < 1: 37 and transverse kinetic energy 600-700<E-kin sin theta< 1400 GeV. The minimum value of 700 GeV is for monopoles of mass 200 GeV, whereas the minimum value of 600 GeV is applicable for higher mass monopoles. Therefore, the upper limit on the production cross section at 95% confidence level is 2 fb in this fiducial region. Assuming the kinematic distributions from Drell-Yan pair production of spin-1= 2 Dirac magnetic monopoles, the efficiency is in the range 1%-10%, leading to an upper limit on the cross section at 95% confidence level that varies from 145 fb to 16 fb for monopoles with mass between 200 GeV and 1200 GeV. This limit is weaker than the fiducial limit because most of these monopoles lie outside the fiducial region.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2012). Search for a Supersymmetric Partner to the Top Quark in Final States with Jets and Missing Transverse Momentum at root s=7 TeV with the ATLAS Detector. Phys. Rev. Lett., 109(21), 211802–18pp.
Abstract: A search for direct pair production of supersymmetric top squarks ((t) over tilde (1)) is presented, assuming the (t) over tilde (1) decays into a top quark and the lightest supersymmetric particle, (chi) over tilde (0)(1), and that both top quarks decay to purely hadronic final states. A total of 16 (4) events are observed compared to a predicted standard model background of 13.5(-3.6)(+3.7) (4.4(-1.3)(+1.7)) events in two signal regions based on integral Ldt = 4.7 fb(-1) of pp collision data taken at root s = 7 TeV with the ATLAS detector at the LHC. An exclusion region in the (t) over tilde (1) versus (chi) over tilde (0)(1) mass plane is evaluated: 370 < m(<(t)over tilde>1) < 465 GeV is excluded for m(<(chi)over tilde>10) similar to 0 GeV while m((t) over tilde1) = 445 GeV is excluded for m((chi) over tilde 10) <= 50 GeV.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2013). Search for Dark Matter Candidates and Large Extra Dimensions in Events with a Photon and Missing Transverse Momentum in pp Collision Data at root s=7 TeV with the ATLAS Detector. Phys. Rev. Lett., 110(1), 011802–18pp.
Abstract: Results of a search for new phenomena in events with an energetic photon and large missing transverse momentum in proton-proton collisions at root s = 7 TeV are reported. Data collected by the ATLAS experiment at the LHC corresponding to an integrated luminosity of 4.6 fb(-1) are used. Good agreement is observed between the data and the standard model predictions. The results are translated into exclusion limits on models with large extra spatial dimensions and on pair production of weakly interacting dark matter candidates.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2013). Measurement of Z Boson Production in Pb-Pb Collisions at root s(NN)=2.76 TeV with the ATLAS Detector. Phys. Rev. Lett., 110(2), 022301–18pp.
Abstract: The ATLAS experiment has observed 1995 Z boson candidates in data corresponding to 0.15 nb(-1) of integrated luminosity obtained in the 2011 LHC Pb + Pb run at root s(NN) = 2.76 TeV. The Z bosons are reconstructed via dielectron and dimuon decay channels, with a background contamination of less than 3%. Results from the two channels are consistent and are combined. Within the statistical and systematic uncertainties, the per-event Z boson yield is proportional to the number of binary collisions estimated by the Glauber model. The elliptic anisotropy of the azimuthal distribution of the Z boson with respect to the event plane is found to be consistent with zero.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2013). Observation of Associated Near-Side and Away-Side Long-Range Correlations in root S-NN=5.02 TeV Proton-Lead Collisions with the ATLAS Detector. Phys. Rev. Lett., 110(18), 182302–18pp.
Abstract: Two-particle correlations in relative azimuthal angle (Delta phi) and pseudorapidity (Delta eta) are measured in root S-NN = 5.02 TeV p + Pb collisions using the ATLAS detector at the LHC. The measurements are performed using approximately 1 μb(-1) of data as a function of transverse momentum (p(T)) and the transverse energy (Sigma E-T(Pb)) summed over 3.1 < eta < 4.9 in the direction of the Pb beam. The correlation function, constructed from charged particles, exhibits a long-range (2 < vertical bar Delta eta vertical bar < 5) “near-side” (Delta phi similar to 0) correlation that grows rapidly with increasing Sigma E-T(Pb). A long-range “away-side” (Delta phi similar to pi) correlation, obtained by subtracting the expected contributions from recoiling dijets and other sources estimated using events with small Sigma E-T(Pb), is found to match the near-side correlation in magnitude, shape (in Delta eta and Delta phi) and Sigma E-T(Pb) dependence. The resultant Delta phi correlation is approximately symmetric about pi/2, and is consistent with a dominant cos2 Delta phi modulation for all Sigma E-T(Pb) ranges and particle p(T).
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LHCb Collaboration(Aaij, R. et al), Oyanguren, A., & Ruiz Valls, P. (2013). Determination of the X(3872) Meson Quantum Numbers. Phys. Rev. Lett., 110(22), 222001–8pp.
Abstract: The quantum numbers of the X(3872) meson are determined to be J(PC) = 1(++) based on angular correlations in B+ -> X(3872)K+ decays, where X(3872) -> pi(+) pi(-) j/psi and J/psi -> pi(+) mu(-). The data correspond to 1.0 fb(-1) of pp collisions collected by the LHCb detector. The only alternative assignment allowed by previous measurements J(PC) = 2(-+) is rejected with a confidence level equivalent to more than 8 Gaussian standard deviations using a likelihood-ratio test in the full angular phase space. This result favors exotic explanations of the X(3872) state.
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LHCb Collaboration(Aaij, R. et al), Oyanguren, A., & Ruiz Valls, P. (2013). First Measurement of the CP-Violating Phase in B-s(0) -> phi phi Decays. Phys. Rev. Lett., 110(24), 241802–8pp.
Abstract: A first flavor-tagged measurement of the time-dependent CP-violating asymmetry in B-s(0) -> phi phi decays is presented. In this decay channel, the CP-violating weak phase arises due to CP violation in the interference between B-s(0)-(B) over bar (0)(s) mixing and the b -> s (s) over bars gluonic penguin decay amplitude. Using a sample of pp collision data corresponding to an integrated luminosity of 1.0 fb(-1) and collected at a center-of-mass energy of 7 TeV with the LHCb detector, 880 B-s(0) -> phi phi signal decays are obtained. The CP-violating phase is measured to be in the interval [-2.46, -0.76] rad at a 68% confidence level. The p value of the standard model prediction is 16%.
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., Oyanguren, A., & Villanueva-Perez, P. (2013). Measurement of the D*(2010)(+) Meson Width and the D*(2010)(+) – D-0 Mass Difference. Phys. Rev. Lett., 111(11), 111801–8pp.
Abstract: We measure the mass difference Delta m(0) between the D*(2010)(+) and the D-0 and the natural linewidth Gamma of the transition D*(2010)(+) -> D-0 pi(+). The data were recorded with the BABAR detector at center-of-mass energies at and near the gamma(4S) resonance, and correspond to an integrated luminosity of approximately 477 fb(-1). The D-0 is reconstructed in the decay modes D-0 -> K-pi(+) and D-0 -> K-pi(+) and D-0 -> K-pi(+)pi(-)pi(+). For the decay mode D-0 -> K-pi(+) we obtain Gamma = (83.4 +/- 1.7 +/- 1.5) keV and Delta m(0) = (145425.6 +/- 0.6 +/- 18) keV, where the quoted errors are statistical and systematic, respectively. For the D-0 -> K-pi(+)pi(-)pi(+) mode we obtain Gamma = (83.2 +/- 1.5 +/- 2.6) keV and Delta m(0) = (145426.6 +/- 0.5 +/- 2.0) keV. The combined measurements yield Gamma = (83.3 +/- 1.2 +/- 1.4) keV and Delta m(0) (145425.9 +/- 0.4 +/- 1.7) keV; the width is a factor of approximately 12 times more precise than the previous value, while the mass difference is a factor of approximately 6 times more precise.
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LHCb Collaboration(Aaij, R. et al), Oyanguren, A., & Ruiz Valls, P. (2013). First Observation of CP Violation in the Decays of B-s(0) Mesons. Phys. Rev. Lett., 110(22), 221601–9pp.
Abstract: Using pp collision data corresponding to an integrated luminosity of 1.0 fb(-1) and collected by LHCb in 2011 at a center-of-mass energy of 7 TeV, we report the measurement of direct CP violation in B-s(0) -> K-pi(+) decays, A(CP) (B-s(0) -> K-pi(+)) = 0.27 +/- 0.04(stat) +/- 0.01(syst), with significance exceeding 5 standard deviations. This is the first observation of CP violation in the decays of B-s(0) mesons. Furthermore, we provide an improved determination of direct CP violation in B-0 -> K+pi(-) decays, A(CP)(B-0 -> K+pi(-) ) = -0.080 +/- 0.007(stat) +/- 0.003(syst), which is the most precise measurement of this quantity to date.
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., Oyanguren, A., & Villanueva-Perez, P. (2013). Search for CP Violation in B-0-<(B-0)over bar> mixing using partial reconstruction of B-0 -> D*(-)Xl(+)nu(l) and a kaon tag. Phys. Rev. Lett., 111(10), 101802–7pp.
Abstract: We present results of a search for CP violation in B-0-(B) over bar (0) mixing with the BABAR detector. We select a sample of B0 -> D*-Xl(+)nu decays with a partial reconstruction method and use kaon tagging to assess the flavor of the other B meson in the event. We determine the CP violating asymmetryA(CP) [N((BB0)-B-0) – N((B-0) over bar (B-0) over bar)]/[N((B-0) over bar (B-0) over bar) + N((BB0)-B-0)] = (0.06 +/- 0.17 +/- 0.38-0.32)%, corresponding to Delta(CP) = 1- vertical bar q/p vertical bar = (0.29 +/- 0.84+1.88-1.61) X 10(-3).
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