Nuclear dependence of light neutral meson production in p–A collisions at 400 GeV with NA60

Abstract

The NA60 experiment has studied low-mass muon pair production in proton-nucleus collisions with a system of Be, Cu, In, W, Pb and U targets, using a 400 GeV proton beam at the CERN SPS. The transverse momentum spectra of the ρ/ω and φ mesons are measured in the full p T range accessible, from p T = 0 up to 2 GeV/c. The nuclear dependence of the production cross sections of the η, ω and φ mesons has been found to be consistent with the power law σ pA ∝ A α , with the α parameter increasing as a function of p T for all the particles, and an approximate hierarchy α η ≈ α φ > α ω . The cross section ratios σ η /σ ω , σ ρ /σ ω and σ φ /σ ω have been studied as a function of the size A of the production target, and an increase of the η and φ yields relative to the ω is observed from p-Be to p-U collisions. a

Energy dependence of $$\phi $$ meson production at forward rapidity in pp collisions at the LHC

“…The reconstructed opposite-sign dimuon mass spectrum is then fitted with a superposition of the hadronic cocktail and the regularized continuum discussed above: the procedure is applied independently for each of the three options considered for the empirical function describing the continuum. The free parameters of the fit are the normalization of the continuum and the η → μμγ , ω → μμ, and φ → μμ contributions, while the other processes are fixed according to the relative branching ratios or cross sections known from existing measurements [14,[19][20][21]. The mass shapes of the processes included in the hadronic cocktail are extracted through full Monte Carlo (MC) simulations that include the resolution effects induced by the apparatus.…”

“…The third contribution to the systematic uncertainty on the signal extraction was determined by varying the normalization of the ρ → μμ, η → μμγ , η → μμ and ω → μμπ 0 processes relative to the main contributions to the hadronic cocktail (η → μμγ , ω → μμ and φ → μμ), by modi-fying the relative branching ratios or cross sections. To test the sensitivity of the fit results on the normalization of the first two processes, the σ ρ /σ ω ratio was varied by 10% [21], while the σ η /σ η ratio was varied by 50%, according to the differences between σ η /σ φ obtained with calculations performed with PHOJET and with the PYTHIA 6 tunes D6T [27], ATLAS-CSC [28], Perugia 0 and Perugia 11 [29]. To account for the variation of the other two processes, the relative branching ratios of the 2-body and Dalitz decay channels of η and ω mesons were varied by one standard deviation, taking into account the values and the uncertainties reported in Ref.…”