We report the first direct measurement of the inclusive branching fraction ${mathcal B}(B_s rightarrow D_s X)$ via $B_s$ tagging in $e^+e^-toUpsilon$(5S) events. Tagging is accomplished through a partial reconstruction of semileptonic decays $B_s rig
htarrow D_s X ell u$, where $X$ denotes unreconstructed additional hadrons or photons and $ell$ is an electron or muon. With 121.4 fb$^{-1}$ of data collected at the $Upsilon$(5S) resonance by the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider, we obtain ${mathcal B}(B_s rightarrow D_s X)$ = $(61.6 pm 5.3 pm 2.1)$%, where the first uncertainty is statistical and the second is systematic.
For the first time the scientific community in Latin America working at the forefront of research in high energy, cosmology and astroparticle physics (HECAP) have come together to discuss and provide scientific input towards the development of a regi
onal strategy. The present document, the Latin American HECAP Physics Briefing Book, is the result of this ambitious bottom-up effort. This report contains the work performed by the Preparatory Group to synthesize the main contributions and discussions for each of the topical working groups. This briefing book discusses the relevant emerging projects developing in the region and considers potentially impactful future initiatives and participation of the Latin American HECAP community in international flagship projects to provide the essential input for the creation of a long-term HECAP strategy in the region.
We report the first search for the penguin-dominated process $B_{s}^{0} rightarrow eta^{prime} X_{sbar{s}}$ using a semi-inclusive method. A 121.4 $mathrm{fb}^{-1}$ integrated luminosity $Upsilon(5S)$ data set collected by the Belle experiment, at th
e KEKB asymmetric-energy $e^+e^-$ collider, is used. We observe no statistically significant signal and including all uncertainties, we set a 90% confidence level upper limit on the partial branching fraction at 1.4 $times$ 10$^{-3}$ for $M(X_{sbar{s}})$ $leq$ 2.4 GeV/$c^{2}$.
Core-collapse supernovae are among the most magnificent events in the observable universe. They produce many of the chemical elements necessary for life to exist and their remnants -- neutron stars and black holes -- are interesting astrophysical obj
ects in their own right. However, despite millennia of observations and almost a century of astrophysical study, the explosion mechanism of core-collapse supernovae is not yet well understood. Hyper-Kamiokande is a next-generation neutrino detector that will be able to observe the neutrino flux from the next galactic core-collapse supernova in unprecedented detail. We focus on the first 500 ms of the neutrino burst, corresponding to the accretion phase, and use a newly-developed, high-precision supernova event generator to simulate Hyper-Kamiokandes response to five different supernova models. We show that Hyper-Kamiokande will be able to distinguish between these models with high accuracy for a supernova at a distance of up to 100 kpc. Once the next galactic supernova happens, this ability will be a powerful tool for guiding simulations towards a precise reproduction of the explosion mechanism observed in nature.
Using data collected in the Belle experiment at the KEKB asymmetric-energy $e^+e^-$ collider we search for transitions $Upsilon(4S) rightarrow eta_b(1S)omega$, $Upsilon(5S) rightarrow eta_b(1S)omega$ and $Upsilon(5S) rightarrow eta_b(2S)omega$. No si
gnificant signals are observed and we set 90% confidence level upper limits on the corresponding visible cross sections: $0.2 ~textrm{pb}, 0.4 ~textrm{pb}$ and $1.9 ~textrm{pb}$, respectively.
Hyper-Kamiokande is the next generation underground water Cherenkov detector that builds on the highly successful Super-Kamiokande experiment. The detector which has an 8.4~times larger effective volume than its predecessor will be located along the
T2K neutrino beamline and utilize an upgraded J-PARC beam with 2.6~times beam power. Hyper-Ks low energy threshold combined with the very large fiducial volume make the detector unique, that is expected to acquire an unprecedented exposure of 3.8~Mton$cdot$year over a period of 20~years of operation. Hyper-Kamiokande combines an extremely diverse science program including nucleon decays, long-baseline neutrino oscillations, atmospheric neutrinos, and neutrinos from astrophysical origins. The scientific scope of this program is highly complementary to liquid-argon detectors for example in sensitivity to nucleon decay channels or supernova detection modes. Hyper-Kamiokande construction has started in early 2020 and the experiment is expected to start operations in 2027. The Hyper-Kamiokande collaboration is presently being formed amongst groups from 19 countries including the United States, whose community has a long history of making significant contributions to the neutrino physics program in Japan. US physicists have played leading roles in the Kamiokande, Super-Kamiokande, EGADS, K2K, and T2K programs.
We present a search for the direct production of a light pseudoscalar $a$ decaying into two photons with the Belle II detector at the SuperKEKB collider. We search for the process ${e^+e^-togamma a, a togammagamma}$ in the mass range ${0.2} ,< m_a <
{9.7},{text{GeV/$c$}^2}$ using data corresponding to an integrated luminosity of $(445pm 3),text{pb}^{-1}$. Light pseudoscalars interacting predominantly with standard model gauge bosons (so-called axion-like particles or ALPs) are frequently postulated in extensions of the standard model. We find no evidence for ALPs and set 95% confidence level upper limits on the coupling strength $g_{agammagamma}$ of ALPs to photons at the level of $10^{-3},{text{GeV}^{-1}}$. The limits are the most restrictive to date for $0.2,<,m_a,<,1,{text{GeV/$c$}^2}$.
The first dedicated search for the $eta_{c2}(1D)$ is carried out using the decays $B^+ rightarrow eta_{c2}(1D) K^+$, $B^0 rightarrow eta_{c2}(1D) K^0_S$, $B^0 rightarrow eta_{c2}(1D) pi^- K^+$, and $B^+ rightarrow eta_{c2}(1D) pi^+ K^0_S$ with $eta_{
c2}(1D) to h_c gamma$. No significant signal is found. For the $eta_{c2}(1D)$ mass range between $3795$ and $3845 mathrm{MeV}/c^2$, the branching-fraction upper limits are determined to be $mathcal{B}(B^+ rightarrow eta_{c2}(1D) K^+) times mathcal{B}(eta_{c2}(1D) to h_c gamma) < 3.7 times 10^{-5}$, $mathcal{B}(B^0 rightarrow eta_{c2}(1D) K^0_S) times mathcal{B}(eta_{c2}(1D) to h_c gamma) < 3.5 times 10^{-5}$, $mathcal{B}(B^0 rightarrow eta_{c2}(1D) pi^- K^+) times mathcal{B}(eta_{c2}(1D) to h_c gamma) < 1.0 times 10^{-4}$, and $mathcal{B}(B^+ rightarrow eta_{c2}(1D) pi^+ K^0_S) times mathcal{B}(eta_{c2}(1D) to h_c gamma) < 1.1 times 10^{-4}$ at 90% C. L. The analysis is based on the 711 $mathrm{fb}^{-1}$ data sample collected on the $Upsilon(4S)$ resonance by the Belle detector, which operated at the KEKB asymmetric-energy $e^+ e^-$ collider.
We report new measurements of the production cross sections of pairs of charged pions and kaons as a function of their fractional energies using various fractional-energy definitions. Two different fractional-energy definitions were used and compared
to the conventional fractional-energy definition reported previously. The new variables aim at either identifying dihadron cross sections in terms of single-hadron fragmentation functions, or to provide a means of characterizing the transverse momentum created in the fragmentation process. The results were obtained applying the updated initial-state radiation correction used in other recent Belle publications on light-hadron production cross sections. In addition, production cross sections of single charged pions, kaons, and protons were also updated using this initial-state radiation correction. The cross sections are obtained from a $558,{rm fb}^{-1}$ data sample collected at the $Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider.
Theories beyond the standard model often predict the existence of an additional neutral boson, the $Z^{prime}$. Using data collected by the Belle II experiment during 2018 at the SuperKEKB collider, we perform the first searches for the invisible dec
ay of a $Z^{prime}$ in the process $e^+ e^- to mu^+ mu^- Z^{prime}$ and of a lepton-flavor-violating $Z^{prime}$ in $e^+ e^- to e^{pm} mu^{mp} Z^{prime}$. We do not find any excess of events and set 90% credibility level upper limits on the cross sections of these processes. We translate the former, in the framework of an $L_{mu}-L_{tau}$ theory, into upper limits on the $Z^{prime}$ coupling constant at the level of $5 times 10^{-2}$ -- $1$ $M_{Z^prime}leq 6$ GeV/$c^2$.
