Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userMeasurement of eta meson decays into lepton-antilepton pairs
221
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
A search for rare lepton decays of the eta meson was performed using the WASA detector at CELSIUS. Two candidates for double Dalitz decay eta->e+e-e+e- events are reported with a background of 1.3+/-0.2 events. This allows to set an upper limit to the branching ratio of 9.7E-5 (90% CL). The branching ratio for the decay eta->e+e-gamma is determined to (7.8+/-0.5 stat+/-0.8 syst)E-3. An upper limit (90% CL) for the branching ratio for the eta->e+e- decay is 2.7E-5 and a limit for the sum of the eta->mu+mu-mu+mu- and eta->pi+pi-mu+mu- decays is 3.6E-4.
rate research
Read More
In this work, we calculate the branching ratios for the $eta(eta)rightarrowbar{ell}ell$ decays, where $ell = e,mu$. These processes have tiny rates in the standard model due to spin flip, loop, and electromagnetic suppression, for what they could be sensitive to New Physics effects. In order to provide a reliable input for the Standard Model, we exploit the general analytical properties of the amplitude. For that purpose, we invoke the machinery of Canterbury approximants, which provides a systematic description of the underlying hadronic physics in a data-driven fashion. Given the current experimental discrepancies, we discuss in detail the role of the resonant region and comment on the reliability of $chi$PT calculations. Finally, we discuss the kind of new physics which we think would be relevant to account for them.
We present our model-independent and data-driven method to describe pseudoscalar meson transition form factors in the space- and (low-energy) time-like regions. The method is general and conforms a toolkit applicable to any other form factor, of one and two variables, with the potential to include both high- and low-energy QCD constraints altogether. The method makes use of analyticity and unitary properties of form factors, it is simple, systematic and can be improved upon by including new data. In the present discussion, the method is used to show the impact of experimental data for precision calculations in the low-energy sector of the Standard Model. In particular, due to its relevance for New Physics searches, we have considered the hadronic light-by-light scattering contribution to the anomalous magnetic moment of the muon (the pseudoscalar exchange contribution), the pseudoscalar decays into lepton pairs, and the determination of the mixing parameters of the $eta$ and $eta$ system. For all of them we provide the most updated results in a data-driven manner.
Decays of $chi_{c1}$ to vector meson pairs $phiphi$, $omegaomega$ and $omegaphi$ are observed for the first time using $(106pm4)times 10^6$ $psip$ events accumulated at the BESIII detector at the BEPCII $e^+e^-$ collider. The branching fractions are measured to be $(4.4pm 0.3pm 0.5)times 10^{-4}$, $(6.0pm 0.3pm 0.7)times 10^{-4}$, and $(2.2pm 0.6pm 0.2)times 10^{-5}$, for $chi_{c1}to phiphi$, $omegaomega$, and $omegaphi$, respectively. The observation of $chi_{c1}$ decays into a pair of vector mesons $phiphi$, $omegaomega$ and $omegaphi$ indicates that the hadron helicity selection rule is significantly violated in $chi_{cJ}$ decays. In addition, the measurement of $chi_{cJ}to omegaphi$ gives the rate of doubly OZI-suppressed decay. Branching fractions for $chi_{c0}$ and $chi_{c2}$ decays into other vector meson pairs are also measured with improved precision.
The open-charm strong decays of higher charmonium states up to the mass of the $6P$ multiplet are systematically studied in the $^3P_0$ model. The wave functions of the initial charmonium states are calculated in the linear potential (LP) and screened potential (SP) quark model. The decay widths for most of the well-established charmonium states above the open-charm thresholds can be reasonably described. By comparing our quark model calculations with the experimental observations we also discuss the nature of some of the newly observed charmonium-like states. It is found that (i) the $psi(4415)$ may favor the $psi(4S)$ or $psi_1(3D)$ assignment. There may exist two highly overlapping vector charmonium states around 4.4 GeV; (ii) In the LP model the $J^{PC}=1^{--}$ $Y(4660)$ resonance and the $J^{PC}=0^{++}$ $X(4500)$ resonance may be assigned as the $psi(5S)$ and $chi_{c0}(4P)$, respectively; (iii) The newly observed state $X^*(3860)$ can be assigned as the $chi_{c0}(2P)$ state with a narrow width of about $30$ MeV; (iv) It seems to be difficult to accommodate the $X(4140)$ and $X(4274)$ states in the same potential model as excited $chi_{c1}$ states. (v) The $X(3940)$ resonance can be assigned as the $eta_c(3S)$ state; (vi) The vector charmonium-like states $Y(4230/4260,4360)$ and scalar $X(4700)$ cannot be described by any conventional charmonium states self-consistently in our model.
Working at a $phi$-factory, KLOE/KLOE-2 has collected a very large and clean sample of $eta$ decays, which allow to perform a variety of precision measurements. This report presents the recent results on the $eta$-meson decays from KLOE/KLOE-2 experiments, including the search of the $C$-violating decay $etarightarrowgammagammagamma$, the determination of the $CP$ asymmetry in $etarightarrowpi^+pi^-e^+e^-$, the precision measurement of the $etarightarrowpi^+pi^-pi^0$ Dalitz plot distribution, the search for the $CP$-violating decay $etarightarrowpi^+pi^-$ and the precision measurement of ${cal O}(p^6)$ dominated decay $etarightarrowgammagammapi^0$.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
