A
bstract
Charged lepton flavor violation is forbidden in the Standard Model but possible in several new physics scenarios. In many of these models, the radiative decays
τ
±
→
ℓ
±
γ
(
ℓ
=
e, μ
) are ...predicted to have a sizeable probability, making them particularly interesting channels to search at various experiments. An updated search via
τ
±
→
ℓ
±
γ
using full data of the Belle experiment, corresponding to an integrated luminosity of 988 fb
−
1
, is reported for charged lepton flavor violation. No significant excess over background predictions from the Standard Model is observed, and the upper limits on the branching fractions,
B
(
τ
±
→
μ
±
γ
) ≤ 4
.
2 × 10
−
8
and
B
(
τ
±
→
e
±
γ
) ≤ 5
.
6 × 10
−
8
, are set at 90% confidence level.
Using CLEO-c data, we confirm the observation of D0→ωη by BESIII. In the Dalitz plot of D0→KS0ηπ0, we find a background in the KS0(→π+π−)π0 projection with a m(π+π−π0) equal to the ω(782) mass. In a ...direct search for D0→ωη we find a clear signal and measure BFD0→ωη=(1.78±0.19±0.15)×10−3, in good agreement with BESIII.
A
bstract
We report a new measurement of the
e
+
e
−
→
ϒ(
nS
)
π
+
π
−
(
n
= 1
,
2
,
3) cross sections at energies from 10
.
52 to 11
.
02 GeV using data collected with the Belle detector at the KEKB ...asymmetric-energy
e
+
e
−
collider. We observe a new structure in the energy dependence of the cross sections; if described by a Breit-Wigner function its mass and width are found to be
M
=
10752.7
±
5.9
−
1.1
+
0.7
MeV
/
c
2
and
Γ
=
35.5
−
11.3
−
3.3
+
17.6
+
3.9
MeV, where the first error is statistical and the second is systematic. The global significance of the new structure including systematic uncertainty is 5.2 standard deviations. We also find evidence for the
e
+
e
−
→
ϒ (1
S
)
π
+
π
−
process at the energy 10
.
52 GeV, which is below the
B
B
¯
threshold.
First measurements of beam backgrounds at SuperKEKB Lewis, P.M.; Jaegle, I.; Nakayama, H. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
01/2019, Letnik:
914
Journal Article
Recenzirano
Odprti dostop
The high design luminosity of the SuperKEKB electron–positron collider is expected to result in challenging levels of beam-induced backgrounds in the interaction region. Properly simulating and ...mitigating these backgrounds is critical to the success of the Belle II experiment. We report on measurements performed with a suite of dedicated beam background detectors, collectively known as BEAST II, during the so-called Phase 1 commissioning run of SuperKEKB in 2016, which involved operation of both the high energy ring (HER) of 7 GeV electrons as well as the low energy ring (LER) of 4 GeV positrons. We describe the BEAST II detector systems, the simulation of beam backgrounds, and the measurements performed. The measurements include standard ones of dose rates versus accelerator conditions, and more novel investigations, such as bunch-by-bunch measurements of injection backgrounds and measurements sensitive to the energy spectrum and angular distribution of fast neutrons. We observe beam–gas, Touschek, beam–dust, and injection backgrounds. As there is no final focus of the beams in Phase 1, we do not observe significant synchrotron radiation, as expected. Measured LER beam–gas backgrounds and Touschek backgrounds in both rings are slightly elevated, on average three times larger than the levels predicted by simulation. HER beam–gas backgrounds are on average two orders of magnitude larger than predicted. Systematic uncertainties and channel-to-channel variations are large, so that these excesses constitute only 1–2 sigma level effects. Neutron background rates are higher than predicted and should be studied further. We will measure the remaining beam background processes, due to colliding beams, in the imminent commissioning Phase 2. These backgrounds are expected to be the most critical for Belle II, to the point of necessitating replacement of detector components during the Phase 3 (full-luminosity) operation of SuperKEB.
We use the new Type Ia supernovae discovered by the Sloan Digital Sky Survey-II supernova survey, together with additional supernova data sets as well as observations of the cosmic microwave ...background and baryon acoustic oscillations to constrain cosmological models. This complements the standard cosmology analysis presented by Kessler et al. in that we discuss and rank a number of the most popular nonstandard cosmology scenarios. When this combined data set is analyzed using the MLCS2k2 light-curve fitter, we find that more exotic models for cosmic acceleration provide a better fit to the data than the Delta *LCDM model. For example, the flat Dvali-Gabadadze-Porrati model is ranked higher by our information-criteria (IC) tests than the standard model with a flat universe and a cosmological constant. When the supernova data set is instead analyzed using the SALT-II light-curve fitter, the standard cosmological-constant model fares best. This investigation of how sensitive cosmological model selection is to assumptions about, and within, the light-curve fitters thereby highlights the need for an improved understanding of these unresolved systematic effects. Our investigation also includes inhomogeneous Lemaitre-Tolman-Bondi (LTB) models. While our LTB models can be made to fit the supernova data as well as any other model, the extra parameters they require are not supported by our IC analysis. Finally, we explore more model-independent ways to investigate the cosmic expansion based on this new data set.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted) We report results of a study of doubly charmed baryons and charmed strange baryons. The analysis is performed using a 980 fb super(-1) ...data sample collected with the Belle detector at the KEKB asymmetric-energy e super(+)e super(-) collider. We search for doubly charmed baryons ... with the ... and ... final states. No significant signal is observed. We also search for two excited charmed strange baryons, Xi sub(c)(3055) super(+) and Xi sub(c)(3123) super(+) with the ... and ... final states. The Xi sub(c)(3055) super(+) signal is observed with a significance of 6.6 standard deviations including systematic uncertainty, while no signature of the Xi sub(c)(3123) super(+) is seen. We also study properties of the Xi sub(c)(2645) super(+) and measure a width of 2.6 + or - 0.2(stat) + or - 0.4(syst) MeV /c super(2), which is the first significant determination.
Abstract We present a measurement of the Cabibbo-Kobayashi-Maskawa unitarity triangle angle ϕ 3 (also known as γ) using a model-independent Dalitz plot analysis of B + → D ( K S 0 $$ {K}_S^0 $$ h + h ...− )h +, where D is either a D 0 or D ¯ $$ \overline{D} $$ 0 meson and h is either a π or K. This is the first measurement that simultaneously uses Belle and Belle II data, combining samples corresponding to integrated luminosities of 711 fb −1 and 128 fb −1, respectively. All data were accumulated from energy-asymmetric e + e − collisions at a centre-of-mass energy corresponding to the mass of the Υ(4S) resonance. We measure ϕ 3 = (78.4 ± 11.4 ± 0.5 ± 1.0)°, where the first uncertainty is statistical, the second is the experimental systematic uncertainty and the third is from the uncertainties on external measurements of the D-decay strong-phase parameters.
The dark photon A^{'} and the dark Higgs boson h^{'} are hypothetical constituents featured in a number of recently proposed dark sector models. Assuming prompt decays of both dark particles, we ...search for their production in the so-called Higgstrahlung channel e^{+}e^{-}→A^{'}h^{'}, with h^{'}→A^{'}A^{'}. We investigate ten exclusive final states with A^{'}→e^{+}e^{-}, μ^{+}μ^{-}, or π^{+}π^{-} in the mass ranges 0.1 GeV/c^{2} <m_{A^{'}}<3.5 GeV/c^{2} and 0.2 GeV/c^{2} <m_{h^{'}}<10.5 GeV/c^{2}. We also investigate three inclusive final states 2(e^{+}e^{-})X, 2(μ^{+}μ^{-})X, and (e^{+}e^{-})(μ^{+}μ^{-})X, where X denotes a dark photon candidate detected via missing mass, in the mass ranges 1.1 GeV/c^{2} <m_{A^{'}}<3.5 GeV/c^{2} and 2.2 GeV/c^{2} <m_{h^{'}}<10.5 GeV/c^{2}. Using the entire 977 fb^{-1} data set collected by Belle, we observe no significant signal. We obtain individual and combined 90% credibility level upper limits on the branching fraction times the Born cross section, B×σ_{Born}, on the Born cross section σ_{Born}, and on the dark photon coupling to the dark Higgs boson times the kinetic mixing between the standard model photon and the dark photon, α_{D}×ε^{2}. These limits improve upon and cover wider mass ranges than previous experiments. The limits from the final states 3(π^{+}π^{-}) and 2(e^{+}e^{-})X are the first placed by any experiment. For α_{D} equal to 1/137, m_{h^{'}}< 8 GeV/c^{2}, and m_{A^{'}}<1 GeV/c^{2}, we exclude values of the mixing parameter ε above ∼8×10^{-4}.
We report the analysis of the three-body e^{+}e^{-}→BBover ¯π^{±}, BBover ¯^{*}π^{±}, and B^{*}Bover ¯^{*}π^{±} processes, including the first observations of the Z_{b}^{±}(10610)→BBover ...¯^{*}+c.c.^{±} and Z_{b}^{±}(10650)→B^{*}Bover ¯^{*}^{±} transitions that are found to dominate the corresponding final states. We measure Born cross sections for the three-body production of σ(e^{+}e^{-}→BBover ¯^{*}+c.c.^{±}π^{∓})=17.4±1.6(stat)±1.9(syst) pb and σ(e^{+}e^{-}→B^{*}Bover ¯^{*}^{±}π^{∓})=8.75±1.15(stat)±1.04(syst) pb and set a 90% C.L. upper limit of σ(e^{+}e^{-}→BBover ¯^{±}π^{∓})<2.9 pb. The results are based on a 121.4 fb^{-1} data sample collected with the Belle detector at a center-of-mass energy near the ϒ(10860) peak.
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