Neutral meson production in p-Be and p-Au collisions at 450 GeV beam energy

Abstract

In a joint experiment the TAPS and CERES collaborations have studied the production of the neutral mesons and in 450 GeV p-Be and p-Au collisions at the CERN SPS. The mesons were identified by their , , and decay modes. The cross sections were measured down to very low ( 20 MeV/c) near mid-rapidity (). The and cross sections are smaller than expected from extrapolations of earlier data to low . Integrated over all , the ratios and / are lower by about 25% compared to previously published values. The reduction may be attributed to the large number of low pions from decays of heavier mesons. In addition, we have studied the dependence of neutral meson production on the mass of the nuclear target and find it in good agreement with previous measurements of charged mesons

Low-mass e+e− pair production in 158 A GeV Pb-Au collisions at the CERN SPS, its dependence on multiplicity and transverse momentum

“…The data are compared to the expected e + e − pair yield from decays of π 0 , η, η ′ , ρ, ω, and φ, in line with ref. [6,7] where a more detailed description can be found. The relative meson abundances are assumed to be independent of the collision system.…”

Dileptons and Direct Photons at SPS

“…± 0.7(stat) ± 2. (syst)) LMR excess in e + e − production in S-Au collision [8] with respect to the "cocktail" of hadronic decays [9], well describing the p-Be and p-Au spectra [9]. The triggered theoretical activity, trying to describe these data, was not successful until the appearence of calculations involving in-medium ππ annihilation via a modified ρ spectral function.…”

Constraints on sub-GeV hidden sector gauge bosons from a search for heavy neutrino decays

“…The total η and η ′ production cross sections in p-Cu collisions were calculated from its linear extrapolation to the target atomic number. The B-G p T distributions at low transverse momenta were corrected by taking into account the measurements results of π 0 's and η's production in 450 GeV p-Be and p-Au collisions down to very low p T ( 20 MeV/c) obtained by a joint experiment of the TAPS and CERES Collaborations at the CERN SPS [58]. In this experiment precise measurement data on η-production at low p T , revealed a lower cross section than expected from extrapolating data at higher p T .…”

“…This observation results in decrease of the acceptance of the CHARM DD for A ′ 's produced in η(η ′ ) → γA ′ decays and, hence has to be taken into account. To achieve a better description of the low-p T -region, a parameterization suggested by [58,59] was used:…”

“…where m T is the transverse mass, x T = 2m T / √ s, and parameters β = 0.15, b = 6.5 GeV −1 , α = 0.011, c = 7.9 and normalization factors B η(η ′ ) were determined in Ref. [58] by fitting the precise low p T experimental data in the rapidity range 3 < y < 4. The results of fitting were also in good agreement with other meson production data obtained for different rapidity intervals.…”