421 research outputs found
Thermal enhancement of the antiferromagnetic exchange coupling between Fe epilayers separated by a crystalline ZnSe spacer
We have put into evidence the existence of an antiferromagnetic coupling
between iron epilayers separated by a ZnSe crystalline semiconductor. The
effect has been observed for ZnSe spacers thinner than 4 nm at
room-temperature. The coupling constant increases linearly with temperature
with a constant slope of ~5.5x 10-9 J/m2K. The mechanisms that may explain such
exchange interaction are discussed in the manuscript. It results that
thermally-induced effective exchange coupling mediated by spin-dependent on and
off resonant tunnelling of electrons via localized mid-gap defect states in the
ZnSe spacer layer appears to be the most plausible mechanism to induce the
antiferromagnetic coupling.Comment: 29 pages, 8 figure
Inclusive Measure of |V_ub| with the Analytic Coupling Model
By analyzing B -> X_u l nu_l spectra with a model based on soft-gluon
resummation and an analytic time-like QCD coupling, we obtain |V_ub| = (3.76
+-0.13 +- 0.22)*10^(-3), where the first and the second error refers to
experimental and theoretical errors, respectively. The V_ub value is obtained
from the available measured semileptonic branching fractions in limited regions
of the phase-space. The distributions in the lepton energy E_l, the hadron
invariant mass m_X, the light-cone momentum P_+ = E_X - p_X, together with the
double distributions in (m_X,q^2) and (E_l,s_h^max), are used to select the
phase-space regions. The q^2 is the dilepton squared momentum and s_h^max is
the maximal m_X^2 at fixed q^2 and E_l. The V_ub value obtained is in complete
agreement with the value coming from exclusive B decays and from an over-all
fit to the Standard Model parameters. We show that the slight disagreement (up
to +2 sigma) with respect to previous inclusive measurements is not related to
different choices for the b (and c) masses but to a different modelling of the
threshold (Sudakov) region.Comment: 19 pages, 2 figures, revised version accepted in Eur.Phys.J.
Measurements of Charmless Hadronic b->s Penguin Decays in the pi+pi-K+pi- Final State and First Observation of B0 -> rho0K+pi-
We report measurements of charmless hadronic B^0 decays into the pi+pi-K+pi+
final state. The analysis uses a sample of 657x10^6 BBbar pairs collected with
the Belle detector at the KEKB asymmetric-energy e+e- collider at the Y(4S)
resonance. The decay B^0 -> rho0 Kpi is observed for the first time; the
significance is 5.0sigma and the corresponding partial branching fraction for
M_Kpi in (0.75,1.20) GeV/c^2 is [2.8 +- 0.5(stat) +-0.5(syst)] x 10^{-6}. We
also obtain the first evidence for B^0 -> f0Kpi with 3.5sigma significance and
for B^0 -> pi+pi-K*0 with 4.5sigma significance. For the two-body decays B^0 ->
rho0K*0 and B^0 -> f0K*0, the significances are 2.7sigma and 2.5sigma,
respectively, and the upper limits on the branching fractions are 3.4x10^{-6}
and 2.2x10^{-6} at 90% confidence level.Comment: 6 pages, 3 figures. accepted by PRD(RC
Measurement of Decays and Search for
We report on a search for the decay and other charmless
modes with a final state, including
, non-resonant ,
, and . These results are obtained from a data sample containing
657 million pairs collected with the Belle detector at the KEKB
asymmetric-energy collider. We set an upper limit on
of at the 90% confidence
level (C.L.). From our measurement and an isospin
analysis, we determine the Cabibbo-Kobayashi-Maskawa phase to be degrees. We find excesses in and
non-resonant with 1.3 and 2.5 significance,
respectively. The corresponding branching fractions are less than and at the 90% C.L. In addition, we set 90% C.L.
upper limits as follows: , , and
.Comment: 6 pages, 2 figures. Submitted to PRD(RC
Measurement of Time-Dependent CP-Violating Parameters in B0 -> K0S K0S decays
We report a measurement of the CP-violating parameters in B0->K0S K0S decays
based on a data sample of 657 million BBbar pairs collected at the Y(4S)
resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider.
In this study, one neutral B meson is fully reconstructed in the B0->K0S K0S
decay mode, and the flavor of the accompanying B meson is identified by its
decay products. The CP-violating parameters are measured from the asymmetry in
the distributions of the proper-time interval between the two B decays: S =
-0.38 +0.69-0.77(stat) +-0.09(syst) and A = -0.38 +-0.38(stat) +-0.05(syst).Comment: 5pages, 2figures, submitted to PR
Measurement of D0 -> pilnu (Klnu) Form Factors and Absolute Branching Fractions
Using a 282 1/fb data sample collected by the Belle experiment at the KEKB
e+e- collider, we study D0 decays to K-l+nu and pi-l+nu final states. The D0
flavor and momentum are tagged through a full reconstruction of the recoiling
charm meson and additional mesons from fragmentation. The reconstruction method
provides very good resolution in neutrino momentum and in q^2 = (p_l+p_nu)^2.
Normalizing to the total number of D0 tags, we measure the absolute branching
fractions to be B(D0 -> Klnu) =(3.45 +- 0.07stat +- 0.20syst)% and B(D0 ->
pilnu) = (0.255 +- 0.019stat +- 0.016syst)% and the semi-leptonic form factors
(within the modified pole model) f+^K(0) = 0.695 +- 0.007stat +- 0.022syst and
f+^pi(0) = 0.624 +- 0.020stat +- 0.030syst.Comment: 9 pages, 2 figures, submitted to Phys. Rev. Let
Search for short baseline nu(e) disappearance with the T2K near detector
8 pages, 6 figures, submitted to PRD rapid communication8 pages, 6 figures, submitted to PRD rapid communicationWe thank the J-PARC staff for superb accelerator performance and the CERN NA61 collaboration for providing valuable particle production data. We acknowledge the support of MEXT, Japan; NSERC, NRC and CFI, Canada; Commissariat `a l’Energie Atomique and Centre National de la Recherche Scientifique–Institut National de Physique Nucle´aire et de Physique des Particules, France; DFG, Germany; INFN, Italy; National Science Centre (NCN), Poland; Russian Science Foundation, RFBR and Ministry of Education and Science, Russia; MINECO and European Regional Development Fund, Spain; Swiss National Science Foundation and State Secretariat for Education, Research and Innovation, Switzerland; STFC, UK; and DOE, USA. We also thank CERN for the UA1/NOMAD magnet, DESY for the HERA-B magnet mover system, NII for SINET4, the WestGrid and SciNet consortia in Compute Canada, GridPP, UK. In addition participation of individual researchers and institutions has been further supported by funds from ERC (FP7), EU; JSPS, Japan; Royal Society, UK; DOE Early Career program, USA
Observation of Large CP Violation in the Neutral B Meson System
We present a measurement of the Standard Model CP violation parameter sin
2phi_1 based on a 29.1 fb^{-1} data sample collected at the Upsilon(4S)
resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider.
One neutral B meson is fully reconstructed as a J/psi Ks, psi(2S) Ks, chi_c1
Ks, eta_c Ks, J/psi K_L or J/psi K^{*0} decay and the flavor of the
accompanying B meson is identified from its decay products. From the asymmetry
in the distribution of the time intervals between the two B meson decay points,
we determine sin 2phi_1 = 0.99 +- 0.14(stat) +- 0.06(syst). We conclude that we
have observed CP violation in the neutral B meson system.Comment: 4 figures, to appear in Phys. Rev. Letter
Belle II Technical Design Report
The Belle detector at the KEKB electron-positron collider has collected
almost 1 billion Y(4S) events in its decade of operation. Super-KEKB, an
upgrade of KEKB is under construction, to increase the luminosity by two orders
of magnitude during a three-year shutdown, with an ultimate goal of 8E35 /cm^2
/s luminosity. To exploit the increased luminosity, an upgrade of the Belle
detector has been proposed. A new international collaboration Belle-II, is
being formed. The Technical Design Report presents physics motivation, basic
methods of the accelerator upgrade, as well as key improvements of the
detector.Comment: Edited by: Z. Dole\v{z}al and S. Un
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