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Register a new userConstraints on New Physics in the Electron g-2 from a Search for Invisible Decays of a Scalar, Pseudoscalar, Vector, and Axial Vector
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We performed a search for a new generic $X$ boson, which could be a scalar ($S$), pseudoscalar ($P$), vector ($V$) or an axial vector ($A$) particle produced in the 100 GeV electron scattering off nuclei, $e^- Z to e^- Z X$, followed by its invisible decay in the NA64 experiment at CERN. No evidence for such process was found in the full NA64 data set of $2.84times 10^{11}$ electrons on target. We place new bounds on the $S, P, V, A$ coupling strengths to electrons, and set constraints on their contributions to the electron anomalous magnetic moment $a_e$, $|Delta a_{X}| lesssim 10^{-15} - 10^{-13}$ for the $X$ mass region $m_Xlesssim 1$ GeV. These results are an order of magnitude more sensitive compared to the current accuracy on $a_e$ from the electron $g-2$ experiments and recent high-precision determination of the fine structure constant.
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A previous formal derivation of the effective chiral Lagrangian for low-lying pseudoscalar mesons from first-principles QCD without approximations [Wang et al., Phys. Rev. D61, (2000) 54011] is generalized to further include scalar, vector, and axial-vector mesons. In the large Nc limit and with an Abelian approximation, we show that the properties of the newly added mesons in our formalism are determined by the corresponding underlying fundamental homogeneous Bethe--Salpeter equation in the ladder approximation, which yields the equations of motion for the scalar, vector, and axial-vector meson fields at the level of an effective chiral Lagrangian. The masses appearing in the equations of motion of the meson fields are those determined by the corresponding Bethe--Salpeter equation.
A search is performed for a new sub-GeV vector boson ($A$) mediated production of Dark Matter ($chi$) in the fixed-target experiment, NA64, at the CERN SPS. The $A$, called dark photon, could be generated in the reaction $ e^- Z to e^- Z A$ of 100 GeV electrons dumped against an active target which is followed by the prompt invisible decay $A to chi overline{chi}$. The experimental signature of this process would be an event with an isolated electron and large missing energy in the detector. From the analysis of the data sample collected in 2016 corresponding to $4.3times10^{10}$ electrons on target no evidence of such a process has been found. New stringent constraints on the $A$ mixing strength with photons, $10^{-5}lesssim epsilon lesssim 10^{-2}$, for the $A$ mass range $m_{A} lesssim 1$ GeV are derived. For models considering scalar and fermionic thermal Dark Matter interacting with the visible sector through the vector portal the 90% C.L. limits $10^{-11}lesssim y lesssim 10^{-6}$ on the dark-matter parameter $y = epsilon^2 alpha_D (frac{m_chi}{m_{A}})^4 $ are obtained for the dark coupling constant $alpha_D = 0.5$ and dark-matter masses $0.001 lesssim m_chi lesssim 0.5 $ GeV. The lower limits $alpha_D gtrsim 10^{-3} $ for pseudo-Dirac Dark Matter in the mass region $m_chi lesssim 0.05 $ GeV are more stringent than the corresponding bounds from beam dump experiments. The results are obtained by using tree level, exact calculations of the $A$ production cross-sections, which turn out to be significantly smaller compared to the one obtained in the Weizs{a}cker-Williams approximation for the mass region $m_{A} gtrsim 0.1$ GeV.
We evaluate ratios of the $chi_{c1}$ decay rates to $eta$ ($eta, K^-$) and one of the $f_0(1370)$, $f_0(1710)$, $f_2(1270)$, $f_2(1525)$, $K^{*}_2(1430)$ resonances, which in the local hidden gauge approach are dynamically generated from the vector-vector interaction. With the simple assumption that the $chi_{c1}$ is a singlet of SU(3), and the input from the study of these resonances as vector-vector molecular states, we describe the experimental ratio $mathcal{B}(chi_{c1} rightarrow eta f_2(1270))/ mathcal{B}(chi_{c1} rightarrow eta f_2(1525))$ and make predictions for six more ratios that can be tested in future experiments.
Neutrino-electron scattering is a purely leptonic fundamental interaction and therefore provides an important channel to test the Standard Model, especially at the low energy-momentum transfer regime. We derived constraints on neutrino nonstardard interaction couplings depending on model-independent approaches which are described by a four-Fermi pointlike interaction and unparticle physics model with tensorial components. Data on $bar{ u}_{e}-e$ and $ u_{e}-e$ scattering from the TEXONO and LSND experiments, respectively, are used. The upper limits and the allowed regions of scalar, pseudoscalar, and tensorial nonstandard interaction couplings of neutrinos are derived at 90% confidence level in both one-parameter and two-parameter analysis. New upper limits for tensorial unparticle physics coupling constants and mass parameters are also placed.
Using samples of 102 million $Upsilon(1S)$ and 158 million $Upsilon(2S)$ events collected with the Belle detector, we study exclusive hadronic decays of these two bottomonium resonances to $ks K^+ pi^-$ and charge-conjugate (c.c.) states, $pi^+ pi^- pi^0 pi^0$, and $pi^+ pi^- pi^0$, and to the two-body Vector-Pseudoscalar ($K^{ast}(892)^0bar{K}^0+ {rm c.c.}$, $K^{ast}(892)^-K^+ + {rm c.c.}$, $omegapi^0$, and $rhopi$) final states. For the first time, signals are observed in the modes $Upsilon(1S) to ks K^+ pi^- + {rm c.c.}$, $pi^+ pi^- pi^0 pi^0$, and $Upsilon(2S) to pi^+ pi^- pi^0 pi^0$, and evidence is found for the modes $Upsilon(1S)to pi^+ pi^- pi^0$, $K^{ast}(892)^0 bar{K}^0+ {rm c.c.}$, and $Upsilon(2S) to ks K^+ pi^- + {rm c.c.}$ Branching fractions are measured for all the processes, while 90% confidence level upper limits on the branching fractions are also set for the modes with a statistical significance of less than $3sigma$. The ratios of the branching fractions of $Upsilon(2S)$ and $Upsilon(1S)$ decays into the same final state are used to test a perturbative QCD prediction for OZI-suppressed bottomonium decays.
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