Precision identified-hadron spectrum analysis for 5 TeV $\bf p$-$\bf Pb$ collisions -- Part I

Abstract

The $p$-Pb collision system occupies a unique position regarding physical interpretation of high-energy particle data. More-peripheral $p$-Pb is indistinguishable from $p$-$p$ collision while more-central $p$-Pb overlaps an interval of Pb-Pb centrality wherein it has been claimed that quark-gluon plasma (QGP) formation is achieved. One basis for such claims is certain features and centrality trends of identified-hadron (PID) $p_t$ spectra, including similarities between $p$-Pb and Pb-Pb spectra. In order to verify or falsify such claims it is essential that PID spectra for $p$-Pb collisions (as a control experiment) be understood in terms of fundamental QCD principles. This article (Part I of a two-part report) presents application of a two-component (soft + hard) model (TCM) to PID spectra from 5 TeV $p$-Pb collisions. Certain issues remaining from a preliminary PID TCM analysis (e.g. proton detection inefficiency) are resolved. Coefficients for TCM model functions previously assumed independent of $p$-Pb centrality are obtained directly from spectra. Jet-related spectrum hard components are precisely isolated and their shape evolution with centrality determined relative to a fixed TCM as reference. In Part II the TCM is further elaborated to describe varying spectrum hard components (and therefore entire spectra) within data statistical uncertainties. The completed PID TCM is then used to investigate properties of spectrum and yield ratios (e.g. $p/\pi$) and $\bar p_t$ data.