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arXiv2012

Search for anomalous production of multiple leptons in association with W and Z bosons at CDF

This paper presents a search for anomalous production of multiple low-energy leptons in association with a W or Z boson using events collected at the CDF experiment corresponding to 5.1 fb$^{-1}$ of integrated luminosity. This search is sensitive to a wide range of topologies with low-momentum leptons, including those with the leptons near one another. The observed rates of production of additional electrons and muons are compared with the standard model predictions. No indications of phenomena beyond the standard model are found. A 95% confidence level limit is presented on the production cross section for a benchmark model of supersymmetric hidden-valley Higgs production. Particle identification efficiencies are also provided to enable the calculation of limits on additional models.

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arXiv2012

Phase Difference Between the Electromagnetic and Strong Amplitudes for psi(2S) and J/psi Decays into Pairs of Pseudoscalar Mesons

Using the data for 24.5x10^6 psi(2S) produced in e^+e^- annihilations at sqrt{s}=3686 MeV at the CESR-c e^+e^- collider and 8.6x10^6 J/psi produced in the decay psi(2S)->pi^+pi^-J/psi, the branching fractions for psi(2S) and J/psi decays to pairs of pseudoscalar mesons, pi^+pi^-, K^+K^-, and K_S K_L, have been measured using the CLEO-c detector. We obtain branching fractions Br(psi(2S)->pi^+pi^-)=(7.6+-2.5+-0.6)x10^-6, Br(psi(2S)->K^+K^-)=(74.8+-2.3+-3.9)x10^-6, Br(psi(2S)->K_S K_L)=(52.8+-2.5+-3.4)x10^-6, and Br(J/psi->pi^+pi^-)=(1.47+-0.13+-0.13)x10^-4, Br(J/psi->K^+K^-)=(2.86+-0.09+-0.19)x10^-4, Br(J/psi+-K_S K_L)=(2.62+-0.15+-0.14)x10^-4, where the first errors are statistical and the second errors are systematic. The phase differences between the amplitudes for electromagnetic and strong decays of psi(2S) and J/psi to 0^{-+} pseudoscalar pairs are determined by a Monte Carlo method to be δ(psi(2S)_{PP}=(110.5^{+16.0}_{-9.5})^o and δ(J/psi)_{PP}=(73.5^{+5.0}_{-4.5})^o. The difference between the two is Δδ= δ(psi(2S))_{PP}-δ(J/psi)_{PP} =(37.0^{+16.5}_{-10.5})^o.

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arXiv2011

Revisiting the 'LSND anomaly' I: impact of new data

This paper, together with a subsequent paper, questions the so-called 'LSND anomaly': a 3.8 σ excess of anti-electronneutrino interactions over standard backgrounds, observed by the LSND Collaboration in a beam dump experiment with 800 MeV protons. That excess has been interpreted as evidence for the anti-muonneutrino{\to} anti-electronneutrino oscillation in the Δm2 range from 0.2 eV2 to 2 eV2. Such a Δm2 range is incompatible with the widely accepted model of oscillations between three light neutrino species and would require the existence of at least one light 'sterile' neutrino. In this paper, new data on pion production by protons on nuclei are presented, and four decades old data on pion production by neutrons on nuclei are recalled, that together increase significantly the estimates of standard backgrounds in the LSND experiment, and decrease the significance of the 'LSND anomaly' from 3.8 σ to 2.9 σ. In a subsequent paper, in addition the LSND Collaboration's data analysis will be questioned, rendering a further reduction of the significance of the 'LSND anomaly'.

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arXiv2011

Revisiting the 'LSND anomaly' II: critique of the data analysis

This paper, together with a preceding paper, questions the so-called 'LSND anomaly': a 3.8 sigma excess of antielectronneutrino interactions over standard backgrounds, observed by the LSND Collaboration in a beam dump experiment with 800 MeV protons. That excess has been interpreted as evidence for the antimuonneutrino to antielectronneutrino oscillation in the \Deltam2 range from 0.2 eV2 to 2 eV2. Such a \Deltam2 range is incompatible with the widely accepted model of oscillations between three light neutrino species and would require the existence of at least one light 'sterile' neutrino. In a preceding paper, it was concluded that the estimates of standard backgrounds must be significantly increased. In this paper, the LSND Collaboration's estimate of the number of antielectronneutrino interactions followed by neutron capture, and of its error, is questioned. The overall conclusion is that the significance of the 'LSND anomaly' is not larger than 2.3 sigma.

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arXiv2011

Measurement of the $W \to e ν$ and $Z/γ^* \to e^+e^-$ Production Cross Sections at Mid-rapidity in Proton-Proton Collisions at $\sqrt{s}$ = 500 GeV

We report measurements of the charge-separated $W^{+(-)} \to e^{+(-)} + ν_e(\barν_e)$ and $Z/γ^* \to e^+e^-$ production cross sections at mid-rapidity in proton-proton collisions at $\sqrt{s}$ = 500 GeV. These results are based on 13.2 pb$^{-1}$ of data recorded in 2009 by the STAR detector at RHIC. Production cross sections for W bosons that decay via the $e ν$ channel were measured to be $σ(pp \to W^+ X) \cdot BR(W^+ \to e^+ ν_e)$ = 117.3 \pm 5.9(stat) \pm 6.2(syst) \pm 15.2(lumi) pb, and $σ(pp \to W^- X) \cdot BR(W^- \to e^- \barν_e)$ = 43.3 \pm 4.6(stat) \pm 3.4(syst) \pm 5.6(lumi) pb. For $Z/γ^*$ production, $σ(pp \to Z/γ^* X) \cdot BR(Z/γ^* \to e^+ e^-)$ = 7.7 \pm 2.1(stat) $^{+0.5}_{-0.9}$(syst) \pm 1.0(lumi) pb for di-lepton invariant masses $m_{e^+e^-}$ between 70 and 110 GeV/$c^2$. First measurements of the W cross section ratio, $σ(pp \to W^+ X) / σ(pp \to W^- X)$, at $\sqrt{s}$ = 500 GeV are also reported. Theoretical predictions, calculated using recent parton distribution functions, are found to agree with the measured cross sections.

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arXiv2012

Neutrino energy reconstruction problems and neutrino oscillations

We discuss the accuracy of the usual procedure for neutrino energy reconstruction which is based on the quasielastic kinematics. Our results are described in terms of a probability distribution for a real neutrino energy value. Several factors are responsible of the deviations from the reconstructed value. The main one is the multinucleon component of the neutrino interaction which in the case of Cherenkov detectors enters as a quasielastic cross section, increasing the mean neutrino energy which can differ appreciably from the reconstructed value. As an application we derive, for excess electron events attributed to the conversion of muon neutrinos, the true neutrino energy distribution based on the experimental one which is given in terms of the reconstructed value. The result is a reshaping effect. For MiniBooNE the low energy peak is suppressed and shifted at higher energies, which may influence the interpretation in terms of oscillation. For T2K at the Super Kamiokande far detector the reshaping translates into a narrowing of the energy distribution.

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arXiv2012

An updated determination of α_s from tau decays

Employing our previous framework to treat non-perturbative effects self-consistently, including duality violations, we update the determination of the strong coupling, α_s, using a modified version of the 1998 OPAL data, updated to reflect current values of exclusive mode hadronic τdecay branching fractions. Our best n_f=3 values from the updated OPAL data are α_s(m^2_τ)=0.325+-0.018 and α_s(m^2_τ)=0.347+-0.025 in fixed-order and contour-improved perturbation theory, respectively. To account for non-perturbative effects, non-linear, multi-parameter fits are necessary. We have, therefore, investigated the posterior probability distribution of the model parameters underlying our fits in more detail. We find that OPAL data alone provide only weak constraints on some of the parameters needed to model duality violations, especially in the case of fits involving axial vector channel data, making additional prior assumptions on the expected size of these parameters necessary at present. We provide evidence that this situation could be greatly improved if hadronic spectral functions based on the high-statistics BaBar and Belle data were to be made available.

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arXiv2012

A Sterile Neutrino Search with Kaon Decay-at-rest

Monoenergetic muon neutrinos (235.5 MeV) from positive kaon decay-at-rest are considered as a source for an electron neutrino appearance search. In combination with a liquid argon time projection chamber based detector, such a source could provide discovery-level sensitivity to the neutrino oscillation parameter space indicative of a sterile neutrino. Current and future intense >3 GeV kinetic energy proton facilities around the world can be employed for this experimental concept.

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arXiv2012

Revisiting the pure annihilation decays $B_s\to π^+ π^-$ and $B^0 \to K^+ K^-$: the data and the pQCD predictions

In this work, we recalculate the charmless pure annihilation decays $B_s\to π^+ π^-$ and $B^0 \to K^+ K^-$ by using the perturbative QCD (pQCD) factorization approach, and compare the pQCD predictions with currently available experimental measurements. We used the same set of relevant input parameters and wave functions to make the calculations for the considered decay modes and found the following results: (a) one can provide a consistent pQCD interpretation for both the measured $Br(B_s^0 \to π^+ π^-)$ and $Br(B_d^0 \to K^+ K^-)$ simultaneously; (b) the pQCD predictions for $Br(B_s^0 \to π^+π^-)$ obtained by different authors are well consistent with each other; (c) our new pQCD prediction for $Br(B_d^0 \to K^+K^-)$ agree very well with the measured values from CDF and LHCb Collaboration; and (d) the CP-violating asymmetry ${\cal A}_{CP}(B_d^0 \to K^+K^-) \approx 16%$, which is large and may be detected at the LHCb experiment.

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arXiv2012

Pure Gravity Mediation with m_{3/2} = 10-100TeV

Recently, the ATLAS and CMS collaborations reported exciting hints of a Standard Model-like Higgs boson with a mass around 125GeV. Such a Higgs boson mass can be easily obtained in the minimal supersymmetric Standard Model based on the "pure gravity mediation model" where the sfermion masses and the Higgs mass parameters are in tens to hundreds TeV range while the gauginos are in the hundreds GeV to TeV range. In this paper, we discuss detalis of the gaugino mass spectrum in the pure gravity mediation model. We also discuss the signals of the model at the current and future experiments such as cosmic ray observations and the LHC experiments. In particular, we show that the parameter space which is consistent with the thermal leptogenesis can be fully surveyed experimentally in the foreseeable future.

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arXiv2012

Prospective Constraints on Neutrino Masses from a Core-Collapse Supernova

We discuss the prospects for improved upper limits on neutrino masses that may be provided by a core-collapse supernova explosion in our galaxy, if it exhibits time variations in the neutrino emissions on the scale of a few milliseconds as suggested by recent two-dimensional simulations. Analyzing simulations of such neutrino emissions using the wavelet technique adopted in [1], we find that an upper limit m_nu ~ 0.14 eV could be established at the 95% confidence level if the time variations in emissions were to be preserved during neutrino propagation to the Earth.

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arXiv2012

Initial-State Radiation Measurement of the e+e- -> pi+pi-pi+pi- Cross Section

We study the process e+e- -> pi+pi-pi+pi-gamma, with a photon emitted from the initial-state electron or positron, using 454.3 fb^-1 of data collected with the BABAR detector at SLAC, corresponding to approximately 260,000 signal events. We use these data to extract the non-radiative sigma(e+e- ->pi+pi-pi+pi-) cross section in the energy range from 0.6 to 4.5 Gev. The total uncertainty of the cross section measurement in the peak region is less than 3%, higher in precision than the corresponding results obtained from energy scan data.

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arXiv2012

Optimization of a Very Low Energy Neutrino Factory for the Disappearance Into Sterile Neutrinos

We discuss short-baseline electron and muon neutrino disappearance searches into sterile neutrinos at a Very Low Energy Neutrino Factory (VLENF) with a muon energy between about two and four GeV. A lesson learned from reactor experiments, such as Double Chooz and Daya Bay, is to use near and far detectors with identical technologies to reduce the systematical errors. We therefore derive the physics results from a combined near-far detector fit and illustrate that uncertainties on cross sections x efficiencies can be eliminated in a self-consistent way. We also include the geometry of the setup, i.e., the extension of the decay straight and the muon decay kinematics relevant at the near detector, and we demonstrate that these affect the sensitivities for Delta m^2 > 30 eV^2, where oscillations take place already in the near detector. Compared to appearance searches, we find that the sensitivity depends on the locations of both detectors and the muon energy, where the near detector should be as close as possible to the source, and the far detector at about 500 to 800m. In order to exclude the currently preferred parameter region, at least 10^19 useful muon decays per polarity are needed for E_mu=2 GeV, or, alternatively, a higher muon energy can be used.

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arXiv2012

First extraction of Interference Fragmentation Functions from e+e- data

We report on the first extraction of interference fragmentation functions from the semi-inclusive production of two hadron pairs in back-to-back jets in e+e- annihilation. A nonzero asymmetry in the correlation of azimuthal orientations of opposite π+π- pairs is related to the transverse polarization of fragmenting quarks through a significant polarized dihadron fragmentation function. Extraction of the latter requires the knowledge of its unpolarized counterpart, the probability density for a quark to fragment in a π+π- pair. Since data for the unpolarized cross section are missing, we extract the unpolarized dihadron fragmentation function from a Monte Carlo simulation of the cross section.

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arXiv2012

Probing higher-order corrections in dijet production at the LHC

Both the ATLAS and CMS Collaborations have sought for effects beyond pure next-to-leading order in dijet observables, with the goal to distinguish between the perturbative descriptions provided by a next-to-leading order plus collinear-resummation calculation and by the resummation of wide-angle, hard emissions. In this paper we identify regions of phase space in dijet production where some observables receive large corrections beyond next-to-leading order and study their theoretical description with two tools that perform these two different resummations: the POWHEG BOX and HEJ. Furthermore, we suggest analyses where the predictions from POWHEG and HEJ can be clearly distinguished experimentally.

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arXiv2012

Top forward-backward asymmetry and the CDF Wjj excess in leptophobic U(1)' flavor models

We construct anomaly-free leptophobic U(1)' flavor models with light Z'(~ 145 GeV). In order to allow renormalizable Yukawa interactions for the standard model chiral fermions, new Higgs doublets with nonzero U(1)' charges are introduced. Then the neutral (pseudo)scalar Higgs bosons as well as Z' contribute to the t\bar{t} and the same sign top pair productions [σ(t\bar{t}]) and σ(tt)], and one can evade the strong constraint from σ(tt). The top forward-backward asymmetry (A_{FB}) and Wjj excess at CDF could be accommodated by A_{FB}^{New} = 0.084 ~ 0.12 and σ(W j j) \lesssim O(10) pb \times \sin^2 2 β.

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arXiv2012

Search for Proton Decay into Muon plus Neutral Kaon in Super-Kamiokande I, II, and III

We have searched for proton into muon plus neutral kaon using data from a 91.7 kiloton-year exposure of Super-Kamiokande-I, a 49.2 kiloton-year exposure of Super-Kamiokande-II, and a 31.9 kiloton-year exposure of Super-Kamiokande-III. The number of candidate events in the data was consistent with the atmospheric neutrino background expectation and no evidence for proton decay in this mode was found. We set a partial lifetime lower limit of 1.6x10^33 years at the 90% confidence level.

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arXiv2012

Measurement of the differential cross section dσ/dt in elastic $p\bar{p}$ scattering at sqrt(s)=1.96 TeV

We present a measurement of the elastic differential cross section $dσ(p\bar{p}\rightarrow p\bar{p})/dt$ as a function of the four-momentum-transfer squared t. The data sample corresponds to an integrated luminosity of $\approx 31 nb^{-1}$ collected with the D0 detector using dedicated Tevatron $p\bar{p} $ Collider operating conditions at sqrt(s) = 1.96 TeV and covers the range $0.26 <|t|< 1.2 GeV^2$. For $|t|<0.6 GeV^2$, dσ/dt is described by an exponential function of the form $Ae^{-b|t|}$ with a slope parameter $ b = 16.86 \pm 0.10(stat) \pm 0.20(syst) GeV^{-2}$. A change in slope is observed at $|t| \approx 0.6 GeV^2$, followed by a more gradual |t| dependence with increasing values of |t|.

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