Generalised Known Kinematics (GKK) An Approach for Kinematic Observables in Pair Production Events with Decays Involving Invisible Particles

Many analyses in high energy physics are limited due to missing kinematic information of known invisible particles in the detector, for example neutrinos. The undetected particle carries away momentum and energy information, preventing the full reconstruction of such an event. In this paper, we present a method to handle this missing information, referred to as the Generalised Known Kinematics (GKK) approach. It is based on constructing event-by-event probability density distributions that describe the physically allowed kinematics of an event. For GKK we take into account the available kinematic information and constraints given by the assumed final state. Summing these event-wise distributions over large data sets allows the determination of parameters that influence the event kinematics, such as particle masses, which are otherwise obscured by the missing information on the invisible final-state particles. The method is demonstrated in simulation studies with $\tau^+ \tau^-$ events in $e^+ e^-$ collisions at the $\Upsilon$(4S) resonance, presenting a new, promising approach for the measurement of the $\tau$ lepton mass.Comment: Second Versio

Snowmass 2021 White Paper: Charged lepton flavor violation in the tau sector

Charged lepton flavor violation has long been recognized as unambiguous signature of New Physics. Here we describe the physics capabilities and discovery potential of New Physics models with charged lepton flavor violation in the tau sector as its experimental signature. Current experimental status from the B-Factory experiments BaBar, Belle and Belle II, and future prospects at Super Tau Charm Factory, LHC, EIC and FCC-ee experiments to discover New Physics via charged lepton flavor violation in the tau sector are discussed in detail. Submitted to the Proceedings of the US Community Study on the Future of Particle Physics (Snowmass 2021)Comment: Contribution to Snowmass 202

Evidence of Υ(1S)→J/ψ+χc1\Upsilon(1S) \to J/\psi+\chi_{c1} and search for double-charmonium production in Υ(1S)\Upsilon(1S) and Υ(2S)\Upsilon(2S) decays

Using data samples of $102\times10^6$ $\Upsilon(1S)$ and $158\times10^6$ $\Upsilon(2S)$ events collected with the Belle detector, a first experimental search has been made for double-charmonium production in the exclusive decays $\Upsilon(1S,2S)\rightarrow J/\psi(\psi')+X$, where $X=\eta_c$, $\chi_{cJ} (J=~0,~1,~2)$, $\eta_c(2S)$, $X(3940)$, and $X(4160)$. No significant signal is observed in the spectra of the mass recoiling against the reconstructed $J/\psi$ or $\psi'$ except for the evidence of $\chi_{c1}$ production with a significance of $4.6\sigma$ for $\Upsilon(1S)\rightarrow J/\psi+\chi_{c1}$. The measured branching fraction \BR(\Upsilon(1S)\rightarrow J/\psi+\chi_{c1}) is $(3.90\pm1.21(\rm stat.)\pm0.23 (\rm syst.))\times10^{-6}$. The $90\%$ confidence level upper limits on the branching fractions of the other modes having a significance of less than $3\sigma$ are determined. These results are consistent with theoretical calculations using the nonrelativistic QCD factorization approach.Comment: 12 pages, 4 figures, 1 table. The fit range was extended to include X(4160) signal according to referee's suggestions. Other results unchanged. Paper was accepted for publication as a regular article in Physical Review

Observation of e+e−→π+π−π0χbJe^+e^- \to \pi^+ \pi^- \pi^0 \chi_{bJ} and search for Xb→ωΥ(1S)X_b \to \omega \Upsilon(1S) at s∼10.867\sqrt{s}\sim 10.867 GeV

The $e^+e^- \to \pi^+ \pi^- \pi^0 \chi_{bJ}$ ($J=0,~1,~2$) processes are studied using a 118~fb$^{-1}$ data sample collected at a center-of-mass energy of 10.867 GeV, in the $\Upsilon(10860)$ energy range, with the Belle detector. The $\pi^+ \pi^- \pi^0 \chi_{b1}$, $\pi^+\pi^-\pi^0\chi_{b2}$, $\omega\chi_{b1}$ signals and the evidence of $\omega\chi_{b2}$ are observed for the first time and the cross sections are measured. No significant $\pi^+\pi^-\pi^0\chi_{b0}$ or $\omega\chi_{b0}$ signal is observed and 90\% confidence level upper limits on the cross sections for these two processes are obtained. In the $\pi^+\pi^-\pi^0$ invariant mass spectrum, significant non-$\omega$ signals are also observed. We search for the $X(3872)$-like state with a hidden $b\bar{b}$ component (named $X_b$) decaying into $\omega \Upsilon(1S)$; no significant signal is observed with a mass between $10.55$ and $10.65$ GeV/$c^2$.Comment: 7 pages, 3 figures, accepted for publication as a Letter in Physical Review Letter

Fragmentation and Monte Carloe generators at Belle II

The Belle II experiment at the SuperKEKB collider is a major upgrade of the KEK “B factory” facility in Tsukuba, Japan aiming at an increase of the peak luminosity by a factor of 40. Commissioning of the SuperKEKB main ring took place in the first half of 2016. Phase 2 of the commissioning will start beginning of 2018 after the installation of the final focus system in the IR but still without the vertex detector system. Once machine operation in the nano-beam scheme is established, the goal is to accumulate data for early physics analyses at different center-of-mass energies. In this talk we describe the Belle II physics program in the QCD sector focusing on the tuning of the fragmentation process of quarks in PYTHIA8 Monte Carlo generator

Future directions on tau physics with Belle II

Future directions on tau physics with Belle I