ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cardillo, F., Castillo, F. L., et al. (2021). Search for bottom-squark pair production in pp collision events at root s=13 TeV with hadronically decaying tau-leptons, b-jets, and missing transverse momentum using the ATLAS detector. Phys. Rev. D, 104(3), 032014–31pp.
Abstract: A search for pair production of bottom squarks in events with hadronically decaying t-leptons, b-tagged jets, and large missing transverse momentum is presented. The analyzed dataset is based on proton-proton collisions at root s = 13 TeV delivered by the Large Hadron Collider and recorded by the ATLAS detector from 2015 to 2018, and corresponds to an integrated luminosity of 139 fb(-1). The observed data are compatible with the expected Standard Model background. Results are interpreted in a simplified model where each bottom squark is assumed to decay into the second-lightest neutralino (chi) over tilde (0)(2) and a bottom quark, with (chi) over tilde (0)(2) decaying into a Higgs boson and the lightest neutralino (chi) over tilde1(0). The search focuses on final states where at least one Higgs boson decays into a pair of hadronically decaying t-leptons. This allows the acceptance and thus the sensitivity to be significantly improved relative to the previous results at low masses of the (chi) over tilde (0)(2), where bottom-squark masses up to 850 GeV are excluded at the 95% confidence level, assuming a mass difference of 130 GeV between (chi) over tilde (0)(2) and (chi) over tilde (0)(1). Model-independent upper limits are also set on the cross section of processes beyond the Standard Model.
|
BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., & Oyanguren, A. (2019). Search for B- -> Lambda(p)over-bar nu(nu)over-bar with the BABAR experiment. Phys. Rev. D, 100(11), 111101–8pp.
Abstract: A search for the rare flavor-changing neutral current process B- -> Lambda(p) over bar nu(nu) over bar using data from the BABAR experiment has been performed. A total of 424 fb(-1) of e(+) e(-) collision data collected at the center-of-mass energy of the Upsilon(4S) resonance is used in this study, corresponding to a sample of (471 +/- 3) x 10(6) B (B) over bar pairs. Signal B- -> Lambda(p) over bar nu(nu) over bar candidates arc identified by fast fully reconstructing a B+ decay in one of many possible exclusive decays to hadronic final states, then examining detector activity that is not associated with this reconstructed B+ decay for evidence of a signal B- -> Lambda(p) over bar nu(nu) over bar decay. The data yield is found to be consistent with the expected background contribution under a null signal hypothesis, resulting in an upper limit of B(B- -> Lambda(p) over bar nu(nu) over bar) < 3.0 x 10(-5) at the 90% confidence level.
|
BABAR Collaboration(del Amo Sanchez, P. et al), Lopez-March, N., Martinez-Vidal, F., Milanes, D. A., & Oyanguren, A. (2010). Search for B+ meson decay to a(1)(+)(1260)K*(0)(892). Phys. Rev. D, 82(9), 091101–8pp.
Abstract: We present a search for the decay B+ -> a(1)(+)(1260)K*(0)(892). The data, collected with the BABAR detector at the SLAC National Accelerator Laboratory, represent 465 X 10(6)B (B) over bar pairs produced in e(+)e(-) annihilation at the energy of the gamma(4S). We find no significant signal and set an upper limit at 90% confidence level on the product of branching fractions B(B+ -> a(1)(+) (1260)K*(0)(892)) X B(a(1)(+)(1260) -> pi(+) pi(-) pi(+)) of 1.8 X 10(-6).
|
BABAR Collaboration(Aubert, B. et al), Azzolini, V., Lopez-March, N., Martinez-Vidal, F., Milanes, D. A., & Oyanguren, A. (2010). Search for B+ -> l(+)nu(l) recoiling against B- -> D(0)l(-)(nu)over-barX. Phys. Rev. D, 81(5), 051101–9pp.
Abstract: We present a search for the decay B+ -> l(+)nu(l) (l = tau, mu, or e) in (458.9 +/- 5.1) x 10(6) B (B) over bar pairs recorded with the BABAR detector at the PEP-II B-factory. We search for these B decays in a sample of B+B- events where one B- meson is reconstructed as B- -> D(0)l(-)(nu) over barX. Using the method of Feldman and Cousins, we obtain B(B+ -> tau(+)nu(tau)) = (1.7 +/- 0.8 +/- 0.2) x 10(-4), which excludes zero at 2.3 sigma. We interpret the central value in the context of the standard model and find the B meson decay constant to be f(B)(2) = (62 +/- 31) x 10(3) MeV2. We find no evidence for B+ -> e(+)nu(e) and B+ -> mu(+)nu(mu) and set upper limits at the 90% C. L. B(B+ -> e(+)nu(e)) < 0.8 x 10(-5) and B(B+ -> mu(+)nu(mu)) < 1.1 x 10(-5).
|
BABAR Collaboration(del Amo Sanchez, P. et al), Lopez-March, N., Martinez-Vidal, F., Milanes, D. A., & Oyanguren, A. (2010). Search for B+ -> (D+K0) and B+ -> (D+K0) decays. Phys. Rev. D, 82(9), 092006–11pp.
Abstract: We report a search for the rare decays B+ -> (D+K0) and B+ -> D+K*(0) in an event sample of approximately 465 x 10(6) B (B) over bar pairs collected with the BABAR detector at the PEP-II asymmetric-energy e(+)e(-) collider at SLAC National Accelerator Laboratory. We find no significant evidence for either mode and we set 90% probability upper limits on the branching fractions of B(B+ -> (D+K0)) < 2.9 x 10(-6) and B(B+ -> D+K*(0)) < 3.0 x 10(-6)
|
BABAR Collaboration(del Amo Sanchez, P. et al), Lopez-March, N., Martinez-Vidal, F., Milanes, D. A., & Oyanguren, A. (2010). Search for b -> u transitions in B- -> DK- and D*K- decays. Phys. Rev. D, 82(7), 072006–18pp.
Abstract: We report results from an updated study of the suppressed decays We report results from an updated study of the suppressed decays B- -> DK- and B- -> D*K- followed by D -> K+ pi(-), where D-(*()0) indicates a D-(*()0)or a (D) over bar (()*()0) meson, and D* -> D pi(0) or D* -> D gamma. These decays are sensitive to the Cabibbo-Kobayashi-Maskawa unitarity triangle angle gamma due to interference between the b -> c transition B- -> D-(*K-)0(-) followed by the doubly Cabibbo-suppressed decay D-0 -> K+ pi(-), and the b -> u transition B- -> (D) over bar (()*()0) K- followed by the Cabibbo-favored decay (D) over bar (0) -> K+ pi(-). We also report an analysis of the decay B- -> D-(*())pi(-) with the D decaying into the doubly Cabibbo-suppressed mode D -> K+ pi(-). Our results are based on 467 x 10(6) Gamma(4S) -> BB- decays collected with the BABAR detector at SLAC. We measure the ratios R-(*()) of the suppressed ([K+ pi(-)](D)K- / pi(-)) to favored ([K+ pi(-)](D)K- / pi(-)) branching fractions as well as the CP asymmetries A(()*()) of those modes. We see indications of signals for the B- -> DK- and B- -> D-D pi 0(()*()) K- suppressed modes, with statistical significances of 2.1 and 2.2 sigma, respectively, and we measure: R-DK = (1.1 +/- 0: 6 +/- 0.2) x 10(-2); A(DK) = -0.86 +/- 0: 47(-0.16)(+0.12), R-(D pi 0)K* = (1.8 +/- 0: 9 +/- 0: 4) x 10(-2); A ((D pi 0)K)* = +0.77 +/- 0: 35 +/- 0.12; R-(D gamma)K* = (1.3 +/- 1.4 +/- 0.8) x 10(-2); A((D gamma)K)* = +0.36 +/- 0: 94(-0.41)(+0.25), where the first uncertainty is statistical and the second is systematic. We use a frequentist approach to obtain the magnitude of the ratio r(B) equivalent to vertical bar A(B- -> (D) over bar 0K(-))/A(B- -> (DK-)-K-0)vertical bar = (9.5(-4.1)(+5.1))%, with r(B) < 16: 7% at 90% confidence level. In the case of B- -> D*K- we find r(B) equivalent to vertical bar A(B- -> <(D)over bar>0K(-))/A(B- -> (DK-)-K-0)vertical bar = (9.6(-5.1)(+3.5))%, with r(B)* < 15.0% at 90% confidence level.
|
BABAR Collaboration(Lees, J. P. et al), Lopez-March, N., Martinez-Vidal, F., & Oyanguren, A. (2011). Search for b -> u transitions in B(+/-) -> [K(-/+)pi(+/-)pi(0)](D)K(+/-) decays. Phys. Rev. D, 84(1), 012002–10pp.
Abstract: We present a study of the decays B(+) -> DK(+) with D mesons reconstructed in the K(+)pi(-)pi(0) or K(-)pi(+)pi(0) final states, where D indicates a D(0) or a (D) over bar (0) meson. Using a sample of 474 x 10(6) B (B) over bar pairs collected with the BABAR detector at the PEP- II asymmetric- energy e(+)e(-) collider at SLAC, we measure the ratios R +/- equivalent to Gamma(B(+)->[K(-/+)pi(+)pi(0)](D)K(+))/Gamma(B(+)->[K(+)pi(-/+)pi(0)](D) K(+)). We obtain R+ = (5(-10)(+12)(stat)(4)(2)(syst)) X 10(-3) and R(-) = (12(-10)(+12)(stat)(-5)(+3)(syst)) X 10(-3), from which we extract the upper limits at 90% probability: R(+) < 23 X 10(-3) and R- < 29 X 10(-3). Using these measurements, we obtain an upper limit for the ratio r(B) of the magnitudes of the b -> u and b -> c amplitudes r(B) < 0.13 at 90% probability.
|
BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., Oyanguren, A., & Villanueva-Perez, P. (2013). Search for B -> K-(*()) v(v)over-bar and invisible quarkonium decays. Phys. Rev. D, 87(11), 112005–13pp.
Abstract: We search for the flavor-changing neutral-current decays B -> K-(*()) v (v) over bar, and the invisible decays J/psi -> v (v) over bar and psi(2S) -> v (v) over bar via B -> K-(*())J/psi and B -> K-(*()) psi(2S), respectively, using a data sample of 471 x 10(6) B (B) over bar pairs collected by the BABAR experiment. We fully reconstruct the hadronBic decay of one of the B mesons in the Y(4S) -> B (B) over bar decay, and search for the B -> K-(*()) v (v) over bar decay in the rest of the event. We observe no significant excess of signal decays over background and report branching fraction upper limits of B(B+ -> K+ v (v) over bar) < 3.7 x 10(-5), B(B-0 -> K-0 v<(v)over bar>) < 8.1 x 10(-5), B(B+ -> K*(+) v<(v)over bar>) < 11.6 x 10(-5), B(B-0 -> K*(0) v<(v)over bar>), < 9.3 x 10(-5), and combined upper limits of B(B -> K v<(v)over bar>) < 3.2 x 10(-5) and B(B -> K* v<(v)over bar>) < 7.9 x 10(-5), all at the 90% confidence level. For the invisible quarkonium decays, we report branching fraction upper limits of B(J/psi -> v<(v)over bar>) < 3.9 x 10(-3) and B(psi(2S) -> v<(v)over bar> < 15.5 x 10(-3) at the 90% confidence level. Using the improved kinematic resolution achieved from hadronic reconstruction, we also provide partial branching fraction limits for the B -> K-(*()) v<(v)over bar> decays over the full kinematic spectrum.
|
ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2018). Search for B – L R-parity-violating top squarks in root s=13 TeV pp collisions with the ATLAS experiment. Phys. Rev. D, 97(3), 032003–28pp.
Abstract: A search is presented for the direct pair production of the stop, the supersymmetric partner of the top quark, that decays through an R-parity-violating coupling to a final state with two leptons and two jets, at least one of which is identified as a b-jet. The data set corresponds to an integrated luminosity of 36.1 fb(-1) of proton-proton collisions at a center-of-mass energy of root s = 13 TeV, collected in 2015 and 2016 by the ATLAS detector at the LHC. No significant excess is observed over the Standard Model background, and exclusion limits are set on stop pair production at a 95% confidence level. Lower limits on the stop mass are set between 600 GeV and 1.5 TeV for branching ratios above 10% for decays to an electron or muon and a b-quark.
|
ATLAS Collaboration(Aad, G. et al), Amoros, G., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., et al. (2012). Search for anomalous production of prompt like-sign muon pairs and constraints on physics beyond the standard model with the ATLAS detector. Phys. Rev. D, 85(3), 032004–23pp.
Abstract: An inclusive search for anomalous production of two prompt, isolated muons with the same electric charge is presented. The search is performed in a data sample corresponding to 1.6 fb(-1) of integrated luminosity collected in 2011 at root s = 7 TeV with the ATLAS detector at the LHC. Muon pairs are selected by requiring two isolated muons of the same electric charge with p(T) > 20 GeV and vertical bar eta vertical bar < 2.5. Minimal requirements are placed on the rest of the event activity. The distribution of the invariant mass of the muon pair m(mu mu) is found to agree well with the background expectation. Upper limits on the cross section for anomalous production of two muons with the same electric charge are placed as a function of m(mu mu) within a fiducial region defined by the event selection. The fiducial cross-section limit constrains the like-sign top-quark pair-production cross section to be below 3.7 pb at 95% confidence level. The data are also analyzed to search for a narrow like-sign dimuon resonance as predicted for e. g. doubly charged Higgs bosons (H-+/-+/-). Assuming pair production of H-+/-+/- bosons and a branching ratio to muons of 100% (33%), this analysis excludes masses below 355 (244) GeV and 251 (209) GeV for H-+/-+/- bosons coupling to left-handed and right-handed fermions, respectively.
|