Two-photon Mass Spectra Research Articles

Search for Resonances in the Mass Spectrum of Two-Photon Events Produced in π+A-Interactions in the Hyperon-M Experiment at the U-70 Accelerator Complex

Studies at the Nuclotron in JINR indicate the presence of a previously unknown resonance-like structure in the two-photon mass spectrum in the region of 300–400 MeV/c2, observed in nucleus–nucleus interactions. The goal of this work is to search for such structures in the two-photon mass spectrum in meson–nuclear interactions at a momentum of 7 GeV/cat the Hyperon-M experiment of the U-70 accelerator complex. An upper limit has been established on the ratio of the cross section for the formation of unknown resonance structures to the cross section for the production ofη-mesonρ(R→2γ/η→2γ)3.2×10−3at the 95% confidence level.

Study of two-photon decays of pseudoscalar mesons via J/ψ radiative decays

Using a sample of $4.48\times10^{8}$ $\psi(3686)$ events collected with the BESIII detector at the BEPCII collider, we study the two-photon decays of the pseudoscalar mesons $\pi^0$, $\eta$, $\eta^\prime$, $\eta(1405)$, $\eta(1475)$, $\eta(1760)$, and $X(1835)$ in $J/\psi$ radiative decays using $\psi(3686)\to\pi^{+}\pi^{-}J/\psi$ events. The $\pi^0$, $\eta$ and $\eta^\prime$ mesons are clearly observed in the two-photon mass spectra, and the branching fractions are determined to be $B(J/\psi\to\gamma\pi^{0}\to3\gamma)=(3.57\pm0.12\pm0.16)\times10^{-5}$, $B(J/\psi\to\gamma\eta\to3\gamma)=(4.42\pm0.04\pm0.18)\times10^{-4}$, and $B(J/\psi\to\gamma\eta'\to3\gamma)=(1.26\pm0.02\pm0.05)\times10^{-4}$, where the first errors are statistical and the second systematic. No clear signal for $\eta(1405)$, $\eta(1475)$, $\eta(1760)$ or $X(1835)$ is observed in the two-photon mass spectra, and upper limits at the $90\%$ confidence level on the product branching fractions are obtained.

Cross-sections for low-energy πgamma; reactions

We review the cross-sections for low-energy π-γ reactions in the framework of chiral perturbation theory. Charged-pion Compton scattering, π-γ → π-γ , is considered up to one-loop order where the pion's internal structure enters through the difference of the electric and magnetic pion polarizability, απ - βπ . The ongoing COMPASS experiment aims at measuring this important structure constant with high statistics using the Primakoff effect. In the same way, the reaction π-γ → π-π0 serves as a test of the QCD chiral anomaly (via the γ3π -coupling constant F γ3π . Furthermore, we calculate the total cross-sections for neutral and charged pion-pair production, π-γ → π-π0π0 and π-γ → π-π+π- , which are governed by the chiral ππ -interaction. Finally, we investigate the radiative (correction) process π-γ → π-γγ and calculate the corresponding two-photon mass spectrum. This information will be useful for analyzing the π- Primakoff scattering events with photons in the final state.

Reducing systematic errors in the selection of signals from two-photon mass spectra

When selecting signals from two-photon invariant mass spectra the signal significance can be optimised by selecting signal candidates from a narrow mass window around the signal peak. However, such tight cuts can lead to large systematic errors. In this study systematic errors due to inaccuracies in the Monte Carlo simulation of the peak width are studied for three selection methods. It is shown that in the presence of such inaccuracies a wider selection window is required to reduce systematic errors. The Ranking selection method is found to be much less sensitive to systematic errors of this type.

Analysis of K0 s K0 s and π+ π– π0 final states in two photon collisions at LEP

The K0 s K0 s and π+ π– π0 final states in two-photon collisions are studied with the L3 detector at LEP. A full energy dependent partial wave analysis demonstrates that the two-photon mass spectra are dominated by the formation of tensor mesons. Their masses, widths and two-photon partial widths are determined.

Rate and spectrum of η→π0γγ

The rate and invariant two-photon mass spectrum are calculated for the decay η→π0γγ. Contributions from internal vector mesons and kaon loop are considered, with the latter having a small but noticeable effect. We find Γ(η→ →π0γγ)≈(0.3÷0.4)eV, significantly lower than the latest experimental result.

Two-photon mass spectra produced in p-p collision at √s = 52 GeV

In this paper we repor t on the resul ts obta ined at t i le ISR for ~Js--52 GeV on the react ion p-p -+ 2 y + a n y t h i n g , where the two photons are emi t t ed on opposite sides a round 90 ~ wi th respect to the c i rcula t ing beams. The lay-out of the exper imenta l set up, main ly consist ing of two matr ices of lead glasses (SP, S X ) , has been described in a previous paper (1) on the produc t ion cross-section of the J / ~ observed in the e+e decay mode. The da ta repor ted here correspond to an in tegra ted luminos i ty of 1.15.1037 em 2 and have been obta ined wi th the same t r igger described in ref. (~), i.e. at least one lead glass in each of the two matr ices wi th a deposi ted energy ~ 600 MeV. In the analysis, we look for lead glasses showing re la t ive m a x i m a of the deposi ted energy > 100 MeV, and define as ( the sum of the energies deposi ted in this counter and in the ad jacent lead glasses. A (~ y-ray ,) is defined as an energy cluster wi thou t signal in the scint i l la tor counter in f ront of it. 0 n l y those events have been analyses tha t show in the S P as well as in the S X units at least one (, y-ray ,) wi th energy larger t han 900 MeV. A single cluster somet imes is due to unresolved ~0. Fo r reducing this cont r ibut ion we have in t roduced the following selection requ i rements :