Bruce Mellado - Academia.edu (original) (raw)
Papers by Bruce Mellado
The European Physical Journal C, 2006
The production of forward jets has been measured in deep inelastic ep collisions at HERA. The res... more The production of forward jets has been measured in deep inelastic ep collisions at HERA. The results are presented in terms of single differential cross sections as a function of the Bjorken scaling variable (x Bj) and as triple differential cross sections d 3 σ/dx Bj dQ 2 dp 2 t,jet , where Q 2 is the four momentum transfer squared and p 2 t,jet is the squared transverse momentum of the forward jet. Also cross sections for events with a di-jet system in addition to the forward jet are measured as a function of the rapidity separation between the forward jet and the two additional jets. The measurements are compared with next-to-leading order QCD calculations and with the predictions of various QCD-based models.
arXiv (Cornell University), Nov 21, 2017
Following a prediction made in Refs. [1-3], this paper focuses on multi-lepton signatures arising... more Following a prediction made in Refs. [1-3], this paper focuses on multi-lepton signatures arising from two new hypothetical scalar bosons, H and S, at the Large Hadron Collider (LHC). These two new bosons are an extension to the Standard Model (SM) and interact with the SM Higgs boson, h. We consider two production modes for H, one being gluon fusion and the other being in association with top quarks. The H → Sh decay mode is considered, where leptonic final states are studied. The CP properties of S are characterised by considering effective couplings derived from dimension six operators through SWW vertices. The nature of the S boson is considered in two separate contexts. Firstly in a simplified model, it is considered to have Higgs-like couplings. Secondly, we consider a heavy neutrino model and its interactions with the Z,W and S bosons. The predictions of the models are compared both to ATLAS and CMS results at √ s = 8 and 13 TeV, where appropriate. The data is interpreted using a simplified model where all the signal comes from H → Sh, assuming S to be Higgs-like, m H = 270 GeV and m S = 150 GeV. The combined result yields gives a best fit value for the parameter β g (the strength of the Yukawa coupling of H to top quarks), β 2 g = 1.38 ± 0.22. A number of regions of the phase space are suggested to the experiments for further exploration.
arXiv (Cornell University), Aug 11, 2016
The confirmation of the Higgs boson in Run I data at the Large Hadron Collider (LHC) and the exce... more The confirmation of the Higgs boson in Run I data at the Large Hadron Collider (LHC) and the excesses in recent Run II data suggest scenarios beyond the Standard Model (SM). We pursue a study in a minimal model which is an extension of a scalar doublet in the SM known as two-Higgs doublet model (THDM). Following earlier suggestions two real scalars χ and S have been introduced in the THDM where χ is treated as a candidate for dark matter. χ does not receive any vacuum expectation value (vev) in the model whereas the Higgs-like scalar S acquires vev. This allows small mixing between the CP-even scalars of the THDM, h, H and S. In this study the mass spectrum of new scalars is taken to be 2m h < mH < 2mt, mχ < m h /2, m h mS mH − m h , mA > 2mt and m ± H < mA, where m h and mt is masses of the SM Higgs and top-quark respectively, mH, mA and m H ± are the masses of the heavy CP-even scalar H, CP-odd scalar A, and charged Higgs H ± , respectively. A partial list of potential search channels at the LHC has been provided with possible phenomenological consequences. The expected phenomenology and constraints on parameters are also discussed in a model-independent approach .
The first measuremet of the differential cross section of the Higgs boson, performed in the dipho... more The first measuremet of the differential cross section of the Higgs boson, performed in the diphoton decay channel, is presented. The dataset used corresponds to 20.3 fb of protonproton collisions at the center of mass of 8 TeV, produced by the LHC and collected by the ATLAS detector in 2012. With its high signal selection efficiency the diphoton decay channel is well suited to probe the underlying kinematic properties of the signal production and decay. Measurements for several diphoton and jet distributions are made for isolated photons within the geometric acceptance of the detector and they are corrected for experimental acceptance and resolution. Results are compared to theoretical predictions at the particle level. Prospects for Run 2 are discussed.
In this presentation an account of the multi-lepton (electrons and muons) anomalies at the LHC is... more In this presentation an account of the multi-lepton (electrons and muons) anomalies at the LHC is given. These include the excess production of opposite sign leptons with and without b-quarks, including a corner of the phase-space with a full hadronic jet veto; same sign leptons with and without b-quarks; three leptons with and without b-quarks, including also the presence of a Z. Excesses emerge in corners of the phase space where a range of SM processes dominate, indicating that the potential mismodeling of a particular SM process is unlikely to explain them. A procedure is implemented that avoids parameter tuning or scanning the phase-space in order to nullify potential look-else-where effects or selection biases. The internal consistency of these anomalies and their interpretation in the framework of a simplified model are presented. Motivated by the multi-lepton anomalies, a search for narrow resonances with S → γγ, Zγ in association with light jets, b-jets or missing transvers...
The Standard Model, SM, of electro-weak and strong interactions successfully describes collider d... more The Standard Model, SM, of electro-weak and strong interactions successfully describes collider data. However, weak bosons, quarks and leptons are massive. The mechanism of spontaneous electro-weak symmetry breaking is introduced in the SM in order to reconcile weak boson and fermion masses with gauge invariance of the theory. In its minimal expression this mechanism leads to a new physical state, a scalar boson, usually referred to as the Higgs boson. The ATLAS and CMS collaborations at the Large Hadron Collider have observed a new particle consistent with a scalar boson and with a mass of about 125GeV.
Chinese Physics C, 2020
In a previous paper by several of the authors a number of predictions were made in a study pertai... more In a previous paper by several of the authors a number of predictions were made in a study pertaining to the anomalous production of multiple leptons at the Large Hadron Collider (LHC). Discrepancies in multi-lepton final states have become statistically compelling with the available Run 2 data. These could be connected with a heavy boson, H, which predominantly decays into a standard model Higgs boson, h, and a singlet scalar, S, where GeV and GeV. These can then be embedded into a scenario where a two-Higgs-doublet is considered with an additional singlet scalar, 2HDM+S. The long-standing discrepancy in the muon anomalous magnetic moment, , is interpreted in the context of the 2HDM+S type-II and type-X, along with additional fermionic degrees of freedom. The 2HDM+S model alone, with constraints from the LHC data, does not seem to explain the anomaly. However, adding fermions with mass of order GeV can explain the discrepancy for sufficiently low values of fermion-scalar couplings.
Proceedings of International Conference on the Structure and the Interactions of the Photon including the 20th International Workshop on Photon-Photon Collisions and the International Workshop on High Energy Photon Linear Colliders — PoS(Photon 2013), Apr 22, 2014
Journal of Physics: Conference Series, 2017
The Madala hypothesis postulates a new heavy scalar, H, which explains several independent anomal... more The Madala hypothesis postulates a new heavy scalar, H, which explains several independent anomalous features seen in ATLAS and CMS data simultaneously. It has already been discussed and constrained in the literature by Run 1 results, and its underlying theory has been explored under the interpretation of a two Higgs doublet model coupled with a scalar singlet, S. When applying the hypothesis to Run 2 results, it can be shown that the constraints from the data are compatible with those obtained using Run 1 results.
Journal of Physics: Conference Series, 2017
In this study we consider an effective model by introducing two hypothetical real scalars, H and ... more In this study we consider an effective model by introducing two hypothetical real scalars, H and χ-a dark matter candidate, where the masses of these scalars are 2m h < mH < 2mt and mχ ≈ m h /2 with m h and mt being the Standard Model Higgs boson and top quark masses, respectively. A distortion in the transverse momentum distributions of h in the intermediate region of the spectrum through the processes pp → H → hχχ could be observed in this model. An additional scalar, S, has been postulated to explain large H → hχχ branching ratios, assuming m h mS mH − m h and mS > 2mχ. Furthermore, a scenario of a two Higgs doublet model (2HDM) is introduced and a detailed proposal at the present energies of the Large Hadron Collider to study the extra CP-even (h, H), CP-odd (A) and charged (H ±) scalars has been pursued. With possible phenomenological implications, production and decay modes for these scalars are discussed. Based on the mass spectrum of H, A and H ± , the production of multi-leptons and Z+jets+missing-energy events are predicted. A specific, Type-II 2HDM model is discussed in detail.
The study of Higgs production in e + e − collisions presents us with an avenue for studying Higgs... more The study of Higgs production in e + e − collisions presents us with an avenue for studying Higgs to W W coupling in the t-channel. Our understanding of the tensor structure of the Higgs boson is furthered by learning the phenomenology of how it couples to the W W pair in these reactions. This can be done by applying effective coupling strength constants to an effective Lagrangian as beyond standard model (BSM) terms and performing Monte Carlo studies with these terms present. The investigation includes a two dimensional analysis of the polar angle and the Higgs boson momentum, such that the correlation between these variables can lead to enhanced sensitivity to new dynamics. We also present an energy scan of cross sections for the processes. A likelihood analysis is performed to show that an electron positron collider operating with an integrated luminosity of 5fb −1 would be enough to fully realise an admixture of BSM effects. 1. Introduction With the July 2012 discovery of what a...
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 2012
The ATLAS experiment at the LHC has measured the centrality dependence of charged particle pseudo... more The ATLAS experiment at the LHC has measured the centrality dependence of charged particle pseudorapidity distributions over |η| < 2 in lead-lead collisions at a nucleon-nucleon centre-of-mass energy of √ s NN = 2.76 TeV. In order to include particles with transverse momentum as low as 30 MeV, the data were recorded with the central solenoid magnet off. Charged particles were reconstructed with two algorithms (2-point "tracklets" and full tracks) using information from the pixel detector only. The lead-lead collision centrality was characterized by the total transverse energy in the forward calorimeter in the range 3.2 < |η| < 4.9. Measurements are presented of the per-event charged particle pseudorapidity distribution, dN ch /dη, and the average charged particle multiplicity in the pseudorapidity interval |η| < 0.5 in several intervals of collision centrality. The results are compared to previous midrapidity measurements at the LHC and RHIC. The variation of the mid-rapidity charged particle yield per colliding nucleon pair with the number of participants is consistent with lower √ s NN results. The shape of the dN ch /dη distribution is found to be independent of centrality within the systematic uncertainties of the measurement.
Physics Letters B, 2011
A search for long-lived charged particles reaching the muon spectrometer is performed using a dat... more A search for long-lived charged particles reaching the muon spectrometer is performed using a data sample of 37 pb −1 from pp collisions at √ s = 7 TeV collected by the ATLAS detector at the LHC in 2010. No excess is observed above the estimated background. Stableτ sleptons are excluded at 95% CL up to a mass of 136 GeV, in GMSB models with N 5 = 3, m messenger = 250 TeV, sign(μ) = 1 and tanβ = 5. Electroweak production of sleptons is excluded up to a mass of 110 GeV. Gluino R-hadrons in a generic interaction model are excluded up to masses of 530 GeV to 544 GeV depending on the fraction of Rhadrons produced asg-balls.
Physical Review Letters, 2006
![Research paper thumbnail of Erratum: Measurement of Branching Fractions and Mass Spectra ofB→Kππγ[Phys. Rev. Lett.98, 211804 (2007)]](https://attachments.academia-assets.com/114622253/thumbnails/1.jpg)
](Physical Review Letters, 2008
Physical Review Letters, 2006
Physical Review Letters, 2006
We present the first measurement of Υ (4S) decays to π + π − Υ (1S) and π + π − Υ (2S) based on a... more We present the first measurement of Υ (4S) decays to π + π − Υ (1S) and π + π − Υ (2S) based on a sample of 230×10 6 Υ (4S) mesons collected with the BABAR detector. We measure the product branching fractions B(Υ (4S) → π + π − Υ (1S))×B(Υ (1S) → µ + µ −) = (2.23±0.25stat ±0.27sys)×10 −6 and B(Υ (4S) → π + π − Υ (2S))×B(Υ (2S) → µ + µ −) = (1.69±0.26stat ±0.20sys)×10 −6 , from which we derive the partial widths Γ(Υ (4S) → π + π − Υ (1S)) = (1.8±0.4) keV and Γ(Υ (4S) → π + π − Υ (2S)) = (2.7 ± 0.8) keV.
Physical Review Letters, 2005
We present evidence for the b → d penguin-dominated decays B + → K 0 K + and B 0 → K 0 K 0 with s... more We present evidence for the b → d penguin-dominated decays B + → K 0 K + and B 0 → K 0 K 0 with significances of 3.5 and 4.5 standard deviations, respectively. The results are based on a sample of 227 million Υ (4S) → BB decays collected with the BABAR detector at the PEP-II asymmetricenergy e + e − collider at SLAC. We measure the branching fractions B(B + → K 0 K +) = (1.5 ± 0.5 ± 0.1) × 10 −6 (< 2.4 × 10 −6) and B(B 0 → K 0 K 0) = (1.19 +0.40 −0.35 ± 0.13) × 10 −6 , where the uncertainties are statistical and systematic, respectively, and the upper limit on the branching fraction for K 0 K + is at the 90% confidence level. We also present improved measurements of the charge-averaged branching fraction B(B + → K 0 π +) = (26.0 ± 1.3 ± 1.0) × 10 −6 and CP-violating charge asymmetry ACP (K 0 π +) = −0.09 ± 0.05 ± 0.01, where the uncertainties are statistical and systematic, respectively.
The European Physical Journal C, 2006
The production of forward jets has been measured in deep inelastic ep collisions at HERA. The res... more The production of forward jets has been measured in deep inelastic ep collisions at HERA. The results are presented in terms of single differential cross sections as a function of the Bjorken scaling variable (x Bj) and as triple differential cross sections d 3 σ/dx Bj dQ 2 dp 2 t,jet , where Q 2 is the four momentum transfer squared and p 2 t,jet is the squared transverse momentum of the forward jet. Also cross sections for events with a di-jet system in addition to the forward jet are measured as a function of the rapidity separation between the forward jet and the two additional jets. The measurements are compared with next-to-leading order QCD calculations and with the predictions of various QCD-based models.
arXiv (Cornell University), Nov 21, 2017
Following a prediction made in Refs. [1-3], this paper focuses on multi-lepton signatures arising... more Following a prediction made in Refs. [1-3], this paper focuses on multi-lepton signatures arising from two new hypothetical scalar bosons, H and S, at the Large Hadron Collider (LHC). These two new bosons are an extension to the Standard Model (SM) and interact with the SM Higgs boson, h. We consider two production modes for H, one being gluon fusion and the other being in association with top quarks. The H → Sh decay mode is considered, where leptonic final states are studied. The CP properties of S are characterised by considering effective couplings derived from dimension six operators through SWW vertices. The nature of the S boson is considered in two separate contexts. Firstly in a simplified model, it is considered to have Higgs-like couplings. Secondly, we consider a heavy neutrino model and its interactions with the Z,W and S bosons. The predictions of the models are compared both to ATLAS and CMS results at √ s = 8 and 13 TeV, where appropriate. The data is interpreted using a simplified model where all the signal comes from H → Sh, assuming S to be Higgs-like, m H = 270 GeV and m S = 150 GeV. The combined result yields gives a best fit value for the parameter β g (the strength of the Yukawa coupling of H to top quarks), β 2 g = 1.38 ± 0.22. A number of regions of the phase space are suggested to the experiments for further exploration.
arXiv (Cornell University), Aug 11, 2016
The confirmation of the Higgs boson in Run I data at the Large Hadron Collider (LHC) and the exce... more The confirmation of the Higgs boson in Run I data at the Large Hadron Collider (LHC) and the excesses in recent Run II data suggest scenarios beyond the Standard Model (SM). We pursue a study in a minimal model which is an extension of a scalar doublet in the SM known as two-Higgs doublet model (THDM). Following earlier suggestions two real scalars χ and S have been introduced in the THDM where χ is treated as a candidate for dark matter. χ does not receive any vacuum expectation value (vev) in the model whereas the Higgs-like scalar S acquires vev. This allows small mixing between the CP-even scalars of the THDM, h, H and S. In this study the mass spectrum of new scalars is taken to be 2m h < mH < 2mt, mχ < m h /2, m h mS mH − m h , mA > 2mt and m ± H < mA, where m h and mt is masses of the SM Higgs and top-quark respectively, mH, mA and m H ± are the masses of the heavy CP-even scalar H, CP-odd scalar A, and charged Higgs H ± , respectively. A partial list of potential search channels at the LHC has been provided with possible phenomenological consequences. The expected phenomenology and constraints on parameters are also discussed in a model-independent approach .
The first measuremet of the differential cross section of the Higgs boson, performed in the dipho... more The first measuremet of the differential cross section of the Higgs boson, performed in the diphoton decay channel, is presented. The dataset used corresponds to 20.3 fb of protonproton collisions at the center of mass of 8 TeV, produced by the LHC and collected by the ATLAS detector in 2012. With its high signal selection efficiency the diphoton decay channel is well suited to probe the underlying kinematic properties of the signal production and decay. Measurements for several diphoton and jet distributions are made for isolated photons within the geometric acceptance of the detector and they are corrected for experimental acceptance and resolution. Results are compared to theoretical predictions at the particle level. Prospects for Run 2 are discussed.
In this presentation an account of the multi-lepton (electrons and muons) anomalies at the LHC is... more In this presentation an account of the multi-lepton (electrons and muons) anomalies at the LHC is given. These include the excess production of opposite sign leptons with and without b-quarks, including a corner of the phase-space with a full hadronic jet veto; same sign leptons with and without b-quarks; three leptons with and without b-quarks, including also the presence of a Z. Excesses emerge in corners of the phase space where a range of SM processes dominate, indicating that the potential mismodeling of a particular SM process is unlikely to explain them. A procedure is implemented that avoids parameter tuning or scanning the phase-space in order to nullify potential look-else-where effects or selection biases. The internal consistency of these anomalies and their interpretation in the framework of a simplified model are presented. Motivated by the multi-lepton anomalies, a search for narrow resonances with S → γγ, Zγ in association with light jets, b-jets or missing transvers...
The Standard Model, SM, of electro-weak and strong interactions successfully describes collider d... more The Standard Model, SM, of electro-weak and strong interactions successfully describes collider data. However, weak bosons, quarks and leptons are massive. The mechanism of spontaneous electro-weak symmetry breaking is introduced in the SM in order to reconcile weak boson and fermion masses with gauge invariance of the theory. In its minimal expression this mechanism leads to a new physical state, a scalar boson, usually referred to as the Higgs boson. The ATLAS and CMS collaborations at the Large Hadron Collider have observed a new particle consistent with a scalar boson and with a mass of about 125GeV.
Chinese Physics C, 2020
In a previous paper by several of the authors a number of predictions were made in a study pertai... more In a previous paper by several of the authors a number of predictions were made in a study pertaining to the anomalous production of multiple leptons at the Large Hadron Collider (LHC). Discrepancies in multi-lepton final states have become statistically compelling with the available Run 2 data. These could be connected with a heavy boson, H, which predominantly decays into a standard model Higgs boson, h, and a singlet scalar, S, where GeV and GeV. These can then be embedded into a scenario where a two-Higgs-doublet is considered with an additional singlet scalar, 2HDM+S. The long-standing discrepancy in the muon anomalous magnetic moment, , is interpreted in the context of the 2HDM+S type-II and type-X, along with additional fermionic degrees of freedom. The 2HDM+S model alone, with constraints from the LHC data, does not seem to explain the anomaly. However, adding fermions with mass of order GeV can explain the discrepancy for sufficiently low values of fermion-scalar couplings.
Proceedings of International Conference on the Structure and the Interactions of the Photon including the 20th International Workshop on Photon-Photon Collisions and the International Workshop on High Energy Photon Linear Colliders — PoS(Photon 2013), Apr 22, 2014
Journal of Physics: Conference Series, 2017
The Madala hypothesis postulates a new heavy scalar, H, which explains several independent anomal... more The Madala hypothesis postulates a new heavy scalar, H, which explains several independent anomalous features seen in ATLAS and CMS data simultaneously. It has already been discussed and constrained in the literature by Run 1 results, and its underlying theory has been explored under the interpretation of a two Higgs doublet model coupled with a scalar singlet, S. When applying the hypothesis to Run 2 results, it can be shown that the constraints from the data are compatible with those obtained using Run 1 results.
Journal of Physics: Conference Series, 2017
In this study we consider an effective model by introducing two hypothetical real scalars, H and ... more In this study we consider an effective model by introducing two hypothetical real scalars, H and χ-a dark matter candidate, where the masses of these scalars are 2m h < mH < 2mt and mχ ≈ m h /2 with m h and mt being the Standard Model Higgs boson and top quark masses, respectively. A distortion in the transverse momentum distributions of h in the intermediate region of the spectrum through the processes pp → H → hχχ could be observed in this model. An additional scalar, S, has been postulated to explain large H → hχχ branching ratios, assuming m h mS mH − m h and mS > 2mχ. Furthermore, a scenario of a two Higgs doublet model (2HDM) is introduced and a detailed proposal at the present energies of the Large Hadron Collider to study the extra CP-even (h, H), CP-odd (A) and charged (H ±) scalars has been pursued. With possible phenomenological implications, production and decay modes for these scalars are discussed. Based on the mass spectrum of H, A and H ± , the production of multi-leptons and Z+jets+missing-energy events are predicted. A specific, Type-II 2HDM model is discussed in detail.
The study of Higgs production in e + e − collisions presents us with an avenue for studying Higgs... more The study of Higgs production in e + e − collisions presents us with an avenue for studying Higgs to W W coupling in the t-channel. Our understanding of the tensor structure of the Higgs boson is furthered by learning the phenomenology of how it couples to the W W pair in these reactions. This can be done by applying effective coupling strength constants to an effective Lagrangian as beyond standard model (BSM) terms and performing Monte Carlo studies with these terms present. The investigation includes a two dimensional analysis of the polar angle and the Higgs boson momentum, such that the correlation between these variables can lead to enhanced sensitivity to new dynamics. We also present an energy scan of cross sections for the processes. A likelihood analysis is performed to show that an electron positron collider operating with an integrated luminosity of 5fb −1 would be enough to fully realise an admixture of BSM effects. 1. Introduction With the July 2012 discovery of what a...
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 2012
The ATLAS experiment at the LHC has measured the centrality dependence of charged particle pseudo... more The ATLAS experiment at the LHC has measured the centrality dependence of charged particle pseudorapidity distributions over |η| < 2 in lead-lead collisions at a nucleon-nucleon centre-of-mass energy of √ s NN = 2.76 TeV. In order to include particles with transverse momentum as low as 30 MeV, the data were recorded with the central solenoid magnet off. Charged particles were reconstructed with two algorithms (2-point "tracklets" and full tracks) using information from the pixel detector only. The lead-lead collision centrality was characterized by the total transverse energy in the forward calorimeter in the range 3.2 < |η| < 4.9. Measurements are presented of the per-event charged particle pseudorapidity distribution, dN ch /dη, and the average charged particle multiplicity in the pseudorapidity interval |η| < 0.5 in several intervals of collision centrality. The results are compared to previous midrapidity measurements at the LHC and RHIC. The variation of the mid-rapidity charged particle yield per colliding nucleon pair with the number of participants is consistent with lower √ s NN results. The shape of the dN ch /dη distribution is found to be independent of centrality within the systematic uncertainties of the measurement.
Physics Letters B, 2011
A search for long-lived charged particles reaching the muon spectrometer is performed using a dat... more A search for long-lived charged particles reaching the muon spectrometer is performed using a data sample of 37 pb −1 from pp collisions at √ s = 7 TeV collected by the ATLAS detector at the LHC in 2010. No excess is observed above the estimated background. Stableτ sleptons are excluded at 95% CL up to a mass of 136 GeV, in GMSB models with N 5 = 3, m messenger = 250 TeV, sign(μ) = 1 and tanβ = 5. Electroweak production of sleptons is excluded up to a mass of 110 GeV. Gluino R-hadrons in a generic interaction model are excluded up to masses of 530 GeV to 544 GeV depending on the fraction of Rhadrons produced asg-balls.
Physical Review Letters, 2006
Physical Review Letters, 2008
Physical Review Letters, 2006
Physical Review Letters, 2006
We present the first measurement of Υ (4S) decays to π + π − Υ (1S) and π + π − Υ (2S) based on a... more We present the first measurement of Υ (4S) decays to π + π − Υ (1S) and π + π − Υ (2S) based on a sample of 230×10 6 Υ (4S) mesons collected with the BABAR detector. We measure the product branching fractions B(Υ (4S) → π + π − Υ (1S))×B(Υ (1S) → µ + µ −) = (2.23±0.25stat ±0.27sys)×10 −6 and B(Υ (4S) → π + π − Υ (2S))×B(Υ (2S) → µ + µ −) = (1.69±0.26stat ±0.20sys)×10 −6 , from which we derive the partial widths Γ(Υ (4S) → π + π − Υ (1S)) = (1.8±0.4) keV and Γ(Υ (4S) → π + π − Υ (2S)) = (2.7 ± 0.8) keV.
Physical Review Letters, 2005
We present evidence for the b → d penguin-dominated decays B + → K 0 K + and B 0 → K 0 K 0 with s... more We present evidence for the b → d penguin-dominated decays B + → K 0 K + and B 0 → K 0 K 0 with significances of 3.5 and 4.5 standard deviations, respectively. The results are based on a sample of 227 million Υ (4S) → BB decays collected with the BABAR detector at the PEP-II asymmetricenergy e + e − collider at SLAC. We measure the branching fractions B(B + → K 0 K +) = (1.5 ± 0.5 ± 0.1) × 10 −6 (< 2.4 × 10 −6) and B(B 0 → K 0 K 0) = (1.19 +0.40 −0.35 ± 0.13) × 10 −6 , where the uncertainties are statistical and systematic, respectively, and the upper limit on the branching fraction for K 0 K + is at the 90% confidence level. We also present improved measurements of the charge-averaged branching fraction B(B + → K 0 π +) = (26.0 ± 1.3 ± 1.0) × 10 −6 and CP-violating charge asymmetry ACP (K 0 π +) = −0.09 ± 0.05 ± 0.01, where the uncertainties are statistical and systematic, respectively.