We report the first observation of the decay Λ_{c}^{+}→pK^{+}π^{-} using a 980 fb^{-1} data sample collected by the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. This is the ...first observation of a doubly Cabibbo-suppressed decay of a charmed baryon. We measure the branching ratio of this decay with respect to its Cabibbo-favored counterpart to be B(Λ_{c}^{+}→pK^{+}π^{-})/B(Λ_{c}^{+}→pK^{-}π^{+})=(2.35±0.27±0.21)×10^{-3}, where the uncertainties are statistical and systematic, respectively.
Larvae of the androdioecious and endangered barnacle, Octolasmis unguisiformis, were cultured in the laboratory for the first time. The larvae passed through six free-swimming naupliar stages and a ...cyprid stage. The naupliar stages required a combined minimum of 44 days at 25°C, and the cyprid stage lasted up to 7 days. However, none of the cyprids settled, even if the host crab (Macrophthalmus milloti) was introduced. The morphological features of the naupliar stages are described and compared with other Octolasmis spp.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NMLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Cypris settlement and metamorphosis into dwarf males were studied in the androdioecious barnacle Scalpellum scalpellum using field collected samples from the North Sea, and experiments with ...laboratory reared larvae, observed with video. In the field sample, dwarf males were always situated on the rim of the mantle aperture and almost invariably confined to two areas (receptacles) located along the scutal plates near their contact to the terga. In the laboratory experiments, cyprids settling on the mantle rim always developed into males. Those settling elsewhere, whether on the external surfaces of the adults, or on their hydroid substratum, always developed into hermaphrodites. The numbers settling as males did not differ significantly from those settling as hermaphrodites, suggesting that genetic sex determination may operate in S. scalpellum. The N. Sea sample comprised 52 adult hermaphrodites. Of these 15 (29%) lacked males altogether, while 37 (71%) carried males with an average of 4.7 per hermaphrodite. On the hermaphrodite, a thin lamella along the mantle rim protects the settling and metamorphosing male from accidental damage or dislocation by the beating cirri. The cyprid gains additional protection by starting almost immediately after settlement to penetrate into the receptacle tissue. After 12–24h the developing dwarf male can be almost completely buried. It appears that the cyprid does not use any preformed burrow, but actively descends into the hermaphrodite integument.
► Hermaphrodites of S. scalpellum can carry 0–13 dwarf males. ► In field populations males are invariably located in two confined receptacle areas. ► Experiments show that cyprids developing into males settle in these areas. ► Settled cyprids penetrate into the hermaphrodite tissue within 12h after settlement. ► These events are documented by video observations.
A
bstract
We present a search for the dark photon
A
′ in the
B
0
→
A
′
A
′ decays, where
A
′ subsequently decays to
e
+
e
−
,
μ
+
μ
−
, and
π
+
π
−
. The search is performed by analyzing 772 × 10
6
B
...B
¯
events collected by the Belle detector at the KEKB
e
+
e
−
energy-asymmetric collider at the ϒ(4
S
) resonance. No signal is found in the dark photon mass range 0
.
01 GeV
/c
2
≤
m
A
′
≤ 2
.
62 GeV
/c
2
, and we set upper limits of the branching fraction of
B
0
→
A
′
A
′ at the 90% confidence level. The products of branching fractions,
ℬ
B
0
→
A
′
A
′
×
ℬ
A
′
→
e
+
e
−
2
and
ℬ
B
0
→
A
′
A
′
×
ℬ
A
′
→
μ
+
μ
−
2
, have limits of the order of 10
−
8
depending on the
A
′ mass. Furthermore, considering
A
′ decay rate to each pair of charged particles, the upper limits of
ℬ
B
0
→
A
′
A
′
are of the order of 10
−
8
–10
−
5
. From the upper limits of
ℬ
B
0
→
A
′
A
′
, we obtain the Higgs portal coupling for each assumed dark photon and dark Higgs mass. The Higgs portal couplings are of the order of 10
−
2
–10
−
1
at
m
h
′
≃
m
B
0
± 40 MeV
/c
2
and 10
−
1
–1 at
m
h
′
≃
m
B
0
± 3 GeV
/c
2
.
The Belle II experiment is a new generation B factory experiment at the SuperKEKB electron–positron collider. The main purpose of the experiment is to search for new physics with a large sample of B ...meson decays. The proximity-focusing Aerogel Ring-Imaging Cherenkov detector (ARICH) has been designed to identify kaons and pions in the forward end-cap of the Belle II spectrometer. Using aerogel as radiator with specialized photon sensors called HAPD, the K/π separation is expected to reach more than 4 σ in the momentum range from 0.5 GeV/c to 4.0 GeV/c. ARICH detector was constructed in summer 2017 and was installed in the Belle II spectrometer in the beam line of the SuperKEKB collider. The test of the ARICH detector is performed using both cosmic rays and the beam collisions during the accelerator commissioning. We observe Cherenkov rings in the ARICH detector associated with charged tracks detected by the tracking system. The reconstructed Cherenkov angle distribution has a clear and reasonable peak. The ARICH K∕π separation performance is evaluated using Bhabha events in beam runs; the separation power achieve the design value.
Equal amounts of matter and antimatter are predicted to have been produced in the Big Bang, but our observable Universe is clearly matter-dominated. One of the prerequisites for understanding this ...elimination of antimatter is the nonconservation of charge-parity (CP) symmetry. So far, two types of CP violation have been observed in the neutral K meson (K0) and B meson (B0) systems: CP violation involving the mixing between K0 and its antiparticle (and likewise for B0 and ), and direct CP violation in the decay of each meson. The observed effects for both types of CP violation are substantially larger for the B0 meson system. However, they are still consistent with the standard model of particle physics, which has a unique source of CP violation that is known to be too small to account for the matter-dominated Universe. Here we report that the direct CP violation in charged B±→K± 0 decay is different from that in the neutral B0 counterpart. The direct CP-violating decay rate asymmetry, (that is, the difference between the number of observed B-→K- 0 event versus B+→K+ 0 events, normalized to the sum of these events) is measured to be about +7%, with an uncertainty that is reduced by a factor of 1.7 from a previous measurement. However, the asymmetry for versus B0→K+ - is at the -10% level. Although it is susceptible to strong interaction effects that need further clarification, this large deviation in direct CP violation between charged and neutral B meson decays could be an indication of new sources of CP violation-which would help to explain the dominance of matter in the Universe.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
28.
Aerogel RICH for the Belle II forward PID Nishida, S.; Adachi, I.; Hamada, N. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2014, Letnik:
766
Journal Article
Recenzirano
The Belle II spectrometer, a follow up of the very successful Belle experiment, is under construction at the SuperKEKB electron-positron collider at KEK in Japan. For the PID system in the forward ...region of the spectrometer, a proximity focusing ring-imaging Cherenkov (RICH) counter with an aerogel radiator is being developed. The counter will provide a 4 sigma separation of pions and kaons up to momenta of 4 GeV/c. For the position sensitive photon sensor, a 144-channel Hybrid Avalanche Photo-Detector (HAPD) has been developed with Hamamatsu Photonics K.K. The readout electronics is based on the custom developed ASIC. The design of the components is currently being finalized and part of their mass production have already started. Herein, we report the final design of the counter and a prototype test conducted with test beams at DESY.
Front-end electronics of the Belle II aerogel ring imaging detector Pestotnik, R.; Adachi, I.; Burmistrov, L. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2020, Letnik:
952
Journal Article
Recenzirano
A proximity focusing RICH detector with an aerogel radiator is used for charged particle identification in the forward end-cap of the Belle II spectrometer. The detector, consisting of a 4 cm aerogel ...radiator, a 16 cm expansion volume and a photon detector with 420 Hybrid Avalanche Photo Detectors, is mounted in a very confined space between Central Drift Chamber and Electromagnetic Calorimeter, allowing only 5 cm of space for the readout electronics. In our solution, low power front-end read-out boards are mounted at the back side of each of the HAPD photosensors. These boards have each been tested individually before their installation onto the photosensors and into the spectrometer. Most important design issues and first experiences with the aforementioned front-end read-out boards are presented in this contribution.
We have developed a RICH counter as a new forward particle identification device for the Belle II experiment. As a Cherenkov radiator in this counter, a dual aerogel layer combination consisting of ...two refractive indicies, n=1.045 and 1.055, is employed. Mass production of these aerogel tiles has been done during 2013–2014 with new method improved by Chiba group. Optical qualities for them have been examined. The refractive indices of the obtained tiles were found to be in good agreement with our expectations, and the transparencies were high enough to be used for the RICH radiator.
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