Attenuation ofωmesons in cold nuclear matter

Abstract

The attenuation of ω mesons in cold nuclear matter has been investigated via the time-dependent multiplescattering Monte Carlo multicollisional (MCMC) intranuclear cascade model. The inelastic ω width deduced from CBELSA/TAPS Collaboration data of meson transparency in complex nuclei ( * 30 MeV/c 2 ) is approximately 5 times lower than the value obtained with recent theoretical models and consistent with an in-medium total ωN cross section within 25-30 mb for an average meson momentum of 1.1 GeV/c . The momentum-dependent transparency ratios suggest an elastic/total cross-section ratio around 40%. For the case of CLAS Collaboration data a much higher width is deduced ( * 120 MeV/c 2 ), with the MCMC model providing a consistent interpretation of the data, assuming a much higher meson absorption (σ * ωN 100 mb) for p ω ∼ 1.7 GeV/c. Medium modifications of vector meson properties (masses/widths) in heated and/or dense nuclear matter can provide evidence for a partial restoration of chiral symmetry [1][2][3][4][5][6][7]. Photon-induced nuclear reactions [8][9][10][11][12][13][14][15] have been recently used for this purpose and represent some advantages in comparison with heavy-ion collisions, since the nucleus is close to equilibrium and the nuclear cross section (σ A ) is expected to scale with the nucleon cross section (σ N ) for the case of incoherent photoproduction.Recent data from the E01-112 experiment at the Thomas Jefferson Laboratory (JLab) [14] indicate a much stronger ω absorption in nuclei than the one deduced from the CBELSA/TAPS Collaboration results [11]. Both experiments extracted the in-medium ω width via measurement of the nuclear transparencies normalized to carbon (T A /T C ).Three different models were used for the analyses of the data of Refs. [11,14]: a Glauber approach [16-18], a Boltzmann-Uehling-Uhlenbeck (BUU) transport model [18], and a calculation by the Valencia theory group [19]. For CBELSA/TAPS results the hadronic decay channel ω → π 0 γ was detected and all the models found a width ∼30 times higher than the vacuum value (225 − 260 MeV/c 2 in the ω rest frame) and an average ωN inelastic cross section of ∼70 mb. For CLAS Collaboration data the leptonic decay ω → e + e − was used and none of the recent theoretical models explained the huge ω absorption, which suggested an in-medium width greater than 200 MeV/c 2 in the nuclear rest frame (∼480 MeV/c 2 in the ω rest frame). As reported in [14], the discrepancy between CLAS and CBELSA/TAPS could be due to the different average ω momentum and/or decay modes. Furthermore, since the ρ meson also decays into e + e − , a destructive ρ − ω interference could play an important role in [14].Consequently, the aim of this Rapid Communication is to investigate the strong absorptions observed for the ω mesons [11,14] in terms of the ωN interaction (elastic or inelastic) without further assumptions about the influence of QCD condensates [20] and/or ω mass shifts (lowering) at finite densities [2]. Our strategy is to determine the in-medium ωN cros...

Investigating in-medium properties of the $ω$ meson via the $ω\rightarrowπ^0γ$ decay

“…More recently, it was claimed in [25] that the CBELSA/TAPS data can be described by a much lower total ωN cross section on the order of 30 mb. However, we note that the treatment presented there assumed a fixed photon energy of 1.5 GeV for comparison with the CBELSA/TAPS data, instead of the full bremsstrahlung energy spectrum of E γ = 1.2−2.2 GeV used in the experiment.…”

The πρ cloud contribution to the ω width in nuclear matter

“…For both φ and ω, large in-medium widths have been deduced, e.g., Γ med ω ≃ 130-150 MeV [16], or even above 200 MeV [15], for the ω at normal nuclear matter density. These values exceed the free ω width by a factor of ∼20, posing a challenge for theoretical models [17][18][19][20][21][22][23][24][25].…”

Anderson localization and multifractal spectrum at the transition point in a two-dimensional non-Hermitian AII† system

“…They found only a crossover in the 2D TME model. But in the 3D system, the Anderson localization transition (ALT) happens as in the Hermitian situation, but the critical disorder W c reduces from 16.5 to 6.0 due to the introduction of non-Hermiticity [5,11]. According to the single-parameter scaling hypothesis [2,5], they gave an estimate of the critical exponent ν as 1.5 ± 0.2, which is close to that of the AI orthogonal class, ν = 1.57 ± 0.01, although the symmetric class is changed from AI to AI † .…”