We observe a signal for the doubly charmed baryon Xi(+)(cc) in the charged decay mode Xi(+)(cc)-->Lambda(+)(c)K-pi(+) in data from SELEX, the charm hadroproduction experiment at Fermilab. We observe an excess of 15.9 events over an expected background of 6.1+/-0.5 events, a statistical significance of 6.3sigma. The observed mass of this state is 3519+/-1 MeV/c(2). The Gaussian mass width of this state is 3 MeV/c(2), consistent with resolution; its lifetime is less than 33 fs at 90% confidence.

We show that by combining high precision measurements of the atmospheric δm 2 in both the electron and muon neutrino (or anti-neutrino) disappearance channels one can determine the neutrino mass hierarchy. The required precision is a very challenging fraction of one per cent for both measurements. At even higher precision, sensitivity to the cosine of the CP violating phase is also possible. This method for determining the mass hierarchy of the neutrino sector does not depend on matter effects. Typeset by REVT E XNeutrino flavor transitions have been observed in atmospheric, solar, reactor and accelerator neutrino experiments. Transitions for at least two different E/L's (neutrino energy divided by baseline) are seen. To explain these transitions, extensions to the Standard Model of particle physics are required. The simplest and most widely accepted extension is to allow the neutrinos to have masses and mixings, similar to the quark sector, then these flavor transitions can be explained by neutrino oscillations. This picture of neutrino masses and mixings has recently come into sharper focus with the latest salt data presented by the SNO collaboration[1]. When combined with the latest KamLAND experiment[2] and other solar neutrino experiments[4, 5] the range of allowed values for the solar mass squared difference, δm 2 21 , and the mixing angle, θ 12 , are 1 + 7.3 × 10 −5 eV 2 < δm 2 21

We present a novel framework that provides an explanation to the long-standing excess of electronlike events in the MiniBooNE experiment at Fermilab. We suggest a new dark sector containing a dark neutrino and a dark gauge boson, both with masses between a few tens and a few hundreds of MeV. Dark neutrinos are produced via neutrino-nucleus scattering, followed by their decay to the dark gauge boson, which in turn gives rise to electron-like events. This mechanism provides an excellent fit to MiniBooNE energy spectra and angular distributions.

Flavor changing (FC) neutrino-matter interactions can account for the zenith-angle-dependent deficit of atmospheric neutrinos observed in the SuperKamiokande experiment, without directly invoking either neutrino mass or mixing. We find that FC n m -matter interactions provide a good fit to the observed zenith angle distributions, comparable in quality to the neutrino oscillation hypothesis. The required FC interactions arise naturally in many attractive extensions of the standard model. [S0031-9007(99) PACS numbers: 14.60. Pq, 14.60.St, 25.30.Pt, 96.40.Tv Neutrinos produced as decay products in hadronic showers from cosmic ray collisions with nuclei in the upper atmosphere [1] have been observed by several detectors [2][3][4][5][6][7]. Although the absolute fluxes of atmospheric neutrinos are largely uncertain, the expected ratio ͑m͞e͒ of the muon neutrino flux ͑n m 1n m ͒ over the electron neutrino flux ͑n e 1n e ͒ is robust, since it largely cancels out the uncertainties associated with the absolute flux. In fact, this ratio has been calculated [1] with an uncertainty of less than 5% over energies varying from 0.1 to 100 GeV. In this resides our confidence in the longstanding atmospheric neutrino anomaly.Although the first iron-calorimeter detectors in Fréjus [2] and NUSEX [3] reported a value of the double ratio, R͑m͞e͒ ͑m͞e͒ data ͑͞m͞e͒ MC , consistent with one, all of the water Cherenkov detectors, Kamiokande [4], IMB [5], and SuperKamiokande [6], have measured R͑m͞e͒ significantly smaller than one. Moreover, not long ago, the Soudan-2 Collaboration, also using an iron calorimeter, reported a small value of R͑m͞e͒ [7], showing that the so-called atmospheric neutrino anomaly was not a feature of water Cherenkov detectors.Recent SuperKamiokande high statistics observations [6] indicate that the deficit in the total ratio R͑m͞e͒ is due to the number of neutrinos arriving in the detector at large zenith angles. Although e-like events do not present any compelling evidence of a zenith angle dependence, the m-like event rates are substantially suppressed at large zenith angles.The n m ! n t [6,8], as well as the n m ! n s [8,9], oscillation hypothesis provides an appealing explanation for this smaller-than-expected ratio, as they are simple and well motivated theoretically. This led the SuperKamiokande Collaboration to conclude that their data provide good evidence for neutrino oscillations and neutrino masses.In this Letter we give an alternative explanation of the atmospheric neutrino data in terms of flavor changing (FC) neutrino-matter interactions [10][11][12][13][14]. We show that, even if neutrinos have vanishing masses and/or the vacuum mixing angle is negligible, FC neutrino-matter interactions can still explain the SuperKamiokande data.There are attractive theories beyond the standard model (SM), where neutrinos are naturally massless [15] as a result of a protecting symmetry, such as B-L in the case of supersymmetric SU͑5͒ models [16] and the model proposed in [17], or chiral symmetry in theories w...

We observe a signal for the doubly charmed baryon Ξ + cc in the decay mode Ξ + cc → pD + K − to complement the previous reported decay Ξ + cc → Λ + c K − π + in data from SELEX, the charm hadroproduction experiment at Fermilab. In this new decay mode we observe an excess of 5.62 events over a combinatoric background estimated by event mixing to be 1.38 ± 0.13 events. The mixed background has Gaussian statistics, giving a signal significance of 4.8σ. The Poisson probability that a background fluctuation can produce the apparent signal is less than 6.4 × 10 −4. The observed mass of this state is 3518 ± 3 MeV/c 2 , consistent with the published result. Averaging the two results gives a mass of 3518.7 ± 1.7 MeV/c 2. The observation of this new weak decay mode confirms the previous SELEX suggestion that this state is a double charm baryon. The relative branching ratio for these two modes is 0.36 ± 0.21.

We examine various scenarios that involve a light O(1 TeV) leptoquark state and select those which are compatible with the current experimental values for B(B s → µµ), B(B → Kµµ) large−q 2 , R K = B (B → Kµµ)/B (B → Kee), and which lead to predictions consistent with other experimental data. We show that two such scenarios are phenomenologically plausible, namely the one with a doublet of scalar leptoquarks of hypercharge 1/6, and the one with a triplet of vector leptoquarks of hypercharge 2/3. We also argue that a model with a singlet scalar leptoquark of hypercharge 1/3 is not viable. Using the present experimental data as constraints, it is shown that the exclusive lepton flavor violating decays, B(B s → µτ ), B(B → Kµτ ) and B(B → K * µτ ), can be as large as O(10 −5 ).

Mixing of active neutrinos with sterile ones generate "induced" contributions to the mass matrix of active neutrinos ∼ m S sin 2 θ aS , where m S is the Majorana mass of the sterile neutrino and θ aS is the active-sterile mixing angle. We study possible effects of the induced matrix which can modify substantially the implications of neutrino oscillation results. We have identified the regions of m S and sin 2 θ aS where the induced matrix (i) provides the dominant structures, (ii) gives the sub-dominant effects and (iii) where its effects can be neglected. The induced matrix can be responsible for peculiar properties of the lepton mixing and neutrino mass spectrum, in particular, it can generate the tri-bimaximal mixing. We update and discuss bounds on the induced masses from laboratory measurements, astrophysics and cosmology. We find that substantial impact of the induced matrix is possible if m S ∼ (0.1 − 0.3) eV and sin 2 θ aS ∼ 10 −3 − 10 −2 or m S ≥ 300 MeV and sin 2 θ aS ≤ 10 −9 . The bounds can be relaxed in cosmological scenarios with low reheating temperature, if sterile neutrinos decay sufficiently fast, or their masses change with time.

Starting from the general effective hamiltonian relevant to the b → s transitions, we derive the expressions for the full angular distributions of the B → K ( * ) 1 2 decay modes, as well as for B(B s → 1 2 ) ( 1 = 2 ). We point out the differences in the treatment of the lepton flavor violating modes with respect to the lepton flavor conserving ones. The relevant Wilson coefficients we evaluate in two different scenarios: (i) The (pseudo-)scalar coefficients are obtained using the (pseudo-)scalar coupling extracted from the experimental non-zero value of B(h → μτ ), (ii) we revisit a Z model in which the flavor changing neutral couplings are allowed. We provide the numerical estimates of the branching fractions of the above-mentioned modes in both scenarios.