0000000000140069
AUTHOR
S. Bussino
Search for an Invisibly Decaying Z′ Boson at Belle II in e+e−→μ+μ−(e±μ∓) Plus Missing Energy Final States
Theories beyond the standard model often predict the existence of an additional neutral boson, the Z′. Using data collected by the Belle II experiment during 2018 at the SuperKEKB collider, we perform the first searches for the invisible decay of a Z′ in the process e+e-→μ+μ-Z′ and of a lepton-flavor-violating Z′ in e+e-→e±μZ′. 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 Lμ-Lτ theory, into upper limits on the Z′ coupling constant at the level of 5×10-2-1 for MZ′≤6 GeV/c2.
Search for Axionlike Particles Produced in e+e− Collisions at Belle II
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-→γa, a→γγ in the mass range 0.2<ma<9.7 GeV/c2 using data corresponding to an integrated luminosity of (445±3) pb-1. Light pseudoscalars interacting predominantly with standard model gauge bosons (so-called axionlike 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 gaγγ of ALPs to photons at the level of 10-3 GeV-1. The limits are the most restrictive to date for 0.2<ma<1 GeV/c2.
Optimization of the JUNO liquid scintillator composition using a Daya Bay antineutrino detector
To maximize the light yield of the liquid scintillator (LS) for the Jiangmen Underground Neutrino Observatory (JUNO), a 20 t LS sample was produced in a pilot plant at Daya Bay. The optical properties of the new LS in various compositions were studied by replacing the gadolinium-loaded LS in one antineutrino detector. The concentrations of the fluor, PPO, and the wavelength shifter, bis-MSB, were increased in 12 steps from 0.5 g/L and <0.01 mg/L to 4 g/L and 13 mg/L, respectively. The numbers of total detected photoelectrons suggest that, with the optically purified solvent, the bis-MSB concentration does not need to be more than 4 mg/L. To bridge the one order of magnitude in the detect…
Gamma-Ray Flares from Mrk421 in 2008 observed with the ARGO-YBJ detector
In 2008 the blazar Markarian 421 entered a very active phase and was one of the brightest sources in the sky at TeV energies, showing frequent flaring episodes. Using the data of ARGO-YBJ, a full coverage air shower detector located at Yangbajing (4300 m a.s.l., Tibet, China), we monitored the source at gamma ray energies E > 0.3 TeV during the whole year. The observed flux was variable, with the strongest flares in March and June, in correlation with X-ray enhanced activity. While during specific episodes the TeV flux could be several times larger than the Crab Nebula one, the average emission from day 41 to 180 was almost twice the Crab level, with an integral flux of (3.6 +-0.6) 10^-1…
Precise Measurement of the D0 and D+ Lifetimes at Belle II
We report a measurement of the D^{0} and D^{+} lifetimes using D^{0}→K^{-}π^{+} and D^{+}→K^{-}π^{+}π^{+} decays reconstructed in e^{+}e^{-}→cc[over ¯] data recorded by the Belle II experiment at the SuperKEKB asymmetric-energy e^{+}e^{-} collider. The data, collected at center-of-mass energies at or near the ϒ(4S) resonance, correspond to an integrated luminosity of 72 fb^{-1}. The results, τ(D^{0})=410.5±1.1(stat)±0.8(syst) fs and τ(D^{+})=1030.4±4.7(stat)±3.1(syst) fs, are the most precise to date and are consistent with previous determinations.
The Status of the ARGO Experiment at YBJ
The ARGO-YBJ experiment, located at Yangbajing, Tibet, China, performed by a wide Sino-Italian collaboration, is designed to study cosmic rays, sub-TeV gamma ray sources and GeV Gamma Ray Burst (GRB) emission in the northern hemisphere, by means of detecting small size EAS (Extensive Air Shower) using a full coverage RPC (Resistive Plate Chamber) carpet. The central carpet of the detector is installed and put into operation to date, with 1900 m^2 of the carpet already operating since December 2004. With a trigger multiplicity of ≥60 hits, corresponding to a primary mode energy of 2 TeV, the angular resolution of EAS measurements is < 1 degree for showers with more than 500 recorded hits. We…
Search for B+→K+νν¯ Decays Using an Inclusive Tagging Method at Belle II
A search for the flavor-changing neutral-current decay B^{+}→K^{+}νν[over ¯] is performed at the Belle II experiment at the SuperKEKB asymmetric energy electron-positron collider. The data sample corresponds to an integrated luminosity of 63 fb^{-1} collected at the ϒ(4S) resonance and a sample of 9 fb^{-1} collected at an energy 60 MeV below the resonance. Because the measurable decay signature involves only a single charged kaon, a novel measurement approach is used that exploits not only the properties of the B^{+}→K^{+}νν[over ¯] decay, but also the inclusive properties of the other B meson in the ϒ(4S)→BB[over ¯] event, to suppress the background from other B meson decays and light-qua…
Scaler mode technique for the ARGO-YBJ detector
The ARGO-YBJ experiment has been designed to study the Extensive Air Showers with an energy threshold lower than that of the existing arrays by exploiting the high altitude location(4300 m a.s.l. in Tibet, P.R. China) and the full ground plane coverage. The lower energy limit of the detector (E $\sim$ 1 GeV) is reached by the scaler mode technique, i.e. recording the counting rate at fixed time intervals. At these energies, transient signals due to local (e.g. Forbush Decreases) and cosmological (e.g. Gamma Ray Bursts) phenomena are expected as a significant variation of the counting rate compared to the background. In this paper the performance of the ARGO-YBJ detector operating in scaler …
The Belle II Physics Book
cd. autorów: L. Cao48,‡, G. Caria145,‡, G. Casarosa57,‡, C. Cecchi56,‡,D. Cˇ ervenkov10,‡,M.-C. Chang22,‡, P. Chang92,‡, R. Cheaib146,‡, V. Chekelian83,‡, Y. Chen154,‡, B. G. Cheon28,‡, K. Chilikin77,‡, K. Cho70,‡, J. Choi14,‡, S.-K. Choi27,‡, S. Choudhury35,‡, D. Cinabro170,‡, L. M. Cremaldi146,‡, D. Cuesta47,‡, S. Cunliffe16,‡, N. Dash33,‡, E. de la Cruz Burelo9,‡, E. de Lucia52,‡, G. De Nardo54,‡, †Editor. ‡Belle II Collaborator. §Theory or external contributing author. M. De Nuccio16,‡, G. De Pietro59,‡, A. De Yta Hernandez9,‡, B. Deschamps129,‡, M. Destefanis60,‡, S. Dey116,‡, F.Di Capua54,‡, S.Di Carlo75,‡, J. Dingfelder129,‡, Z. Doležal10,‡, I. Domínguez Jiménez125,‡, T.V. Dong30,26,…
Distillation and stripping pilot plants for the JUNO neutrino detector: Design, operations and reliability
Abstract This paper describes the design, construction principles and operations of the distillation and stripping pilot plants tested at the Daya Bay Neutrino Laboratory, with the perspective to adapt these processes, system cleanliness and leak-tightness standards to the final full scale plants to be used for the purification of the liquid scintillator of the JUNO neutrino detector. The main goal of these plants is to remove radio impurities from the liquid scintillator while increasing its optical attenuation length. Purification of liquid scintillator will be performed with a system combining alumina oxide, distillation, water extraction and steam (or N 2 gas) stripping. Such a combined…