Direct measurement of the in-medium ${\eta }^{\prime }$ mass spectrum through the $\gamma \gamma$ decay channel

Abstract

We measured the invariant mass of the ${\eta }^{\prime }(958)$ meson through the ${\eta }^{\prime }\to \gamma \gamma$ decay channel to search for possible character change of ${\eta }^{\prime }$ in a nuclear medium. The measured invariant-mass spectra were analyzed by fitting realistic spectral functions. An enhancement was observed in the lower tail of the ${\eta }^{\prime }$ mass peak for low-momentum ($P_{\gamma \gamma }<1$~$GeV/c$) events. Three statistical methods were applied to assess the significance of the enhancement. All methods yield a statistical significance above 3.7$\sigma$. The spectral fitting indicates a mass reduction of $57.5_{-27.8}^{+5.7}$~${MeV/c}^2$. Our result provides the first evidence for an in-medium spectral modification of the ${\eta }^{\prime }$ meson obtained through a direct measurement of its invariant mass.

References in corpus (26)

• Hadron properties in the nuclear medium
• Nucleon and hadron structure changes in the nuclear medium and impact on observables
• Evidence for in-medium modification of the $\varphi$ meson at normal nuclear density
• Hadrons in strongly interacting matter
• Meson-nucleus potentials and the search for meson-nucleus bound states
• Differential cross sections for the reactions gamma p-> p eta and gamma p -> p eta-prime
• Eta bound states in nuclei: a probe of flavour-singlet dynamics
• η- and η'-mesic nuclei and U_A(1) anomaly at finite density
• Transparency ratio in γA -> η' A' and the in-medium η' width
• $U_A(1)$ symmetry restoration in QCD with $N_f$ flavors
• Determination of the η'-nucleus optical potential
• Nuclear bound state of eta'(958) and partial restoration of chiral symmetry in the eta' mass
• Pseudoscalar neutral mesons in hot and dense matter
• Analysis of U${}_A$(1) symmetry-breaking and restoration effects on the scalar-pseudoscalar spectrum
• Indirect observation of an in-medium eta' mass reduction in sqrt(s_{NN})=200 GeV Au+Au collisions
• Determination of the eta'-proton scattering length in free space
• In medium eta' mass and eta' N interaction based on chiral effective theory
• Development of High Intensity Laser-Electron Photon Beams up to 2.9 GeV at the SPring-8 LEPS Beamline
• Determination of the real part of the η'-Nb optical potential
• Missing-mass spectroscopy of the ${}^{12}\mathrm{C}(p,d)$ reaction near the ${\eta }^{\prime }$-meson production threshold
• Significant in-medium eta' mass reduction in sqrt(s(NN))=200 GeV Au+Au collisions at the BNL Relativistic Heavy Ion Collider
• Search for ${\eta }^{\prime }$ bound nuclei in the ${}^{12}\mathrm{C}(\gamma ,p)$ reaction with simultaneous detection of decay products
• The η'-carbon potential at low meson momenta
• Pion properties at finite nuclear density based on in-medium chiral perturbation theory
• Differential cross sections and photon beam asymmetries of $\eta$ photoproduction on the proton at $E_{\gamma }$ = 1.3-2.4 GeV
• Role of U${}_A$(1) breaking term in dynamical chiral symmetry breaking of chiral effective theories