The momentum and helicity density distributions of the strange quark sea in the nucleon are obtained in leading order from charged-kaon production in deep-inelastic scattering on the deuteron. The ...distributions are extracted from spin-averaged K± multiplicities, and from K± and inclusive double-spin asymmetries for scattering of polarized positrons by a polarized deuterium target. The shape of the momentum distribution is softer than that of the average of the u¯ and d¯ quarks. In the region of measurement 0.02<x<0.6 and Q2>1.0 GeV2, the helicity distribution is zero within experimental uncertainties.
We report the results of a search for the B→Y(4260)K, Y(4260)→J/ψπ+π− decays. This study is based on a data sample corresponding to an integrated luminosity of 711 fb−1, collected at the ϒ(4S) ...resonance with the Belle detector at the KEKB asymmetric-energy e+e− collider. We investigate the J/ψπ+π− invariant mass distribution in the range 4.0 to 4.6 GeV/c2 using both B+→J/ψπ+π−K+ and B0→J/ψπ+π−KS0 decays. We find excesses of events above the background levels, with significances of 2.1 and 0.9 standard deviations for charged and neutral B→Y(4260)K decays, respectively, taking into account the systematic uncertainties. These correspond to upper limits on the product of branching fractions, B(B+→Y(4260)K+)×B(Y(4260)→J/ψπ+π−)<1.4×10−5 and B(B0→Y(4260)K0)×B(Y(4260)→J/ψπ+π−)<1.7×10−5 at the 90% confidence level.
We report searches for the processes e+e−→π+π−π0χbJ and e+e−→ϕχbJ (J=1, 2) based on data samples collected by the Belle experiment at the KEKB collider. We report the first observation of the process ...e+e−→(π+π−π0)non−ωχb1 and first evidence for e+e−→ωχbJ in the vicinity of the ϒ(11020) resonance, with center-of-mass energies from 10.96 to 11.05 GeV. The significances for (π+π−π0)non−ωχb1 and ωχbJ are greater than 5.3σ and 4.0σ, respectively. We also investigate the energy dependence of the e+e−→π+π−π0χbJ cross section, but we cannot determine whether the contributions are from the ϒ(10860) and ϒ(11020) resonances or nonresonant continuum processes. The signals for e+e−→ϕχbJ are not significant, and the upper limits of the Born cross sections at the 90% confidence level are 0.7 and 1.0 pb for e+e−→ϕχb1 and ϕχb2, respectively, for center-of-mass energies from 10.96 to 11.05 GeV.
Study of B → p¯pππ Chu, K
Physical review. D,
03/2020, Letnik:
101, Številka:
5
Journal Article
Recenzirano
Using a data sample of 772 × 106 B¯B pairs collected on the Υ(4S) resonance with the Belle detector at the KEKB asymmetric energy e+e− collider, we report the observation of B0 → p¯pπ+π− and the ...first observation of B+ → p¯pπ+π0. We measure a decay branching fraction of (0.83 ± 0.17 ± 0.17) × 10−6 in B0 → p¯pπ+π− for Mπ+π− < 1.22 GeV/c2 with a significance of 5.5 standard deviations. The contribution from B0 → p¯pK0 is excluded. We measure a decay branching fraction of (4.58 ± 1.17 ± 0.67) × 10−6 for B+ → p¯pπ+π0 with Mπ+π0 < 1.3 GeV/c2 with a significance of 5.4 standard deviations. We study the difference of the Mp¯p distributions in B0 → p¯pπ+π− and B+ → p¯pπ+π0.
Exclusive electroproduction of
ω
mesons on unpolarized hydrogen and deuterium targets is studied in the kinematic region of
Q
2
>
1.0
GeV
2
, 3.0 GeV
<
W
<
6.3 GeV, and
-
t
′
<
0.2
GeV
2
. ...Results on the angular distribution of the
ω
meson, including its decay products, are presented. The data were accumulated with the HERMES forward spectrometer during the 1996–2007 running period using the 27.6 GeV longitudinally polarized electron or positron beam of HERA. The determination of the virtual-photon longitudinal-to-transverse cross-section ratio reveals that a considerable part of the cross section arises from transversely polarized photons. Spin density matrix elements are presented in projections of
Q
2
or
-
t
′
. Violation of
s
-channel helicity conservation is observed for some of these elements. A sizable contribution from unnatural-parity-exchange amplitudes is found and the phase shift between those amplitudes that describe transverse
ω
production by longitudinal and transverse virtual photons,
γ
L
∗
→
ω
T
and
γ
T
∗
→
ω
T
, is determined for the first time. A hierarchy of helicity amplitudes is established, which mainly means that the unnatural-parity-exchange amplitude describing the
γ
T
∗
→
ω
T
transition dominates over the two natural-parity-exchange amplitudes describing the
γ
L
∗
→
ω
L
and
γ
T
∗
→
ω
T
transitions, with the latter two being of similar magnitude. Good agreement is found between the HERMES proton data and results of a pQCD-inspired phenomenological model that includes pion-pole contributions, which are of unnatural parity.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A special arrangement of Bonse–Hart X‐ray interferometers, which uses the Bragg geometry of X‐ray diffraction for the beam splitter, mirrors and the analyser (so‐called BBB interferometers), has been ...designed and characterized both computationally and experimentally in different versions. The design includes wavelength‐dependent optimization of transmission through the lamella, which is used both for beam splitting and for recombination. For characterization of the function of the instrument, interference patterns were evaluated from BBB interferograms, as well as from LLL (employing the Laue geometry for coherent beam splitting, reflecting and analysing) topograms and from interferograms resulting from a new combined geometrical layout. The influence of gravitation on the horizontally running diffraction planes was visible as a system of fringes in the interferograms, resulting from bending of the lamella under its own weight.
Search for the decay B0 → Φγ King, Z.; Pal, B.; Schwartz, A. J. ...
Physical review. D,
06/2016, Letnik:
93, Številka:
11
Journal Article
Recenzirano
Odprti dostop
We have searched for the decay B0 → Φγ using the full Belle data set of 772 × 106 BB¯ pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB e+e– collider. No signal is observed, ...and we set an upper limit on the branching fraction of B(B0 → Φγ) < 1.0 × 10–7 at the 90% confidence level. Here, this is the most stringent limit on this decay mode to date.
The branching fractions of the Υ(1S) inclusive decays into final states with a J/ψ or a ψ(2S) are measured with improved precision to be B(Υ(1S)→J/ψ+anything)=(5.25±0.13(stat)±0.25(syst))×10-4 and ...B(Υ(1S)→ψ(2S)+anything)=(1.23±0.17(stat)±0.11(syst))×10-4. The first search for Υ(1S) decays into XYZ states that decay into a J/ψ or a ψ(2S) plus one or two charged tracks yields no significant signals for XYZ states in any of the examined decay modes, and upper limits on their production rates in Υ(1S) inclusive decays are determined.
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