Interpretation of charged-particle spectra inp+pandp+Pbcollisions at energies available at the CERN Large Hadron Collider using an improved hijing code with a collective cascade

Abstract

We supplement the Heavy Ion Jet Interaction Generator (hijing) code with a collective cascade recipe and updated Martin-Stirling-Thorne-Watt (MSTW2009) parton distribution functions (PDFs) to describe nonsingle diffractive (NSD) $p+p$ and Pb collisions at CERN Large Hadron Collider energies. The collective cascade, developed in the space of an impact parameter, is used to induce nuclear modification of nucleons, that are involved in primary interactions, inside the dense nuclear medium. It is found that the improved hijing (Imhijing) code (that with MSTW2009 PDFs) reproduces rather well the pseudorapidity density, the multiplicity, and the transverse momentum distributions of charged particles within the pseudorapidity interval $|{\ensuremath{\eta}}_{\mathrm{c}.\mathrm{m}.\mathrm{system}}|<2.4$ in NSD $p+p$ collisions at $\sqrt{{s}_{\mathrm{NN}}}=0.9$, 2.36, and 7 TeV. The Imhijing with collective cascade calculations is also shown to be a good fit to the pseudorapidity density (in the laboratory system) and transverse momentum $({p}_{T})$ dependence of the nuclear modification of charged particles in NSD $p+\mathrm{Pb}$ collisions at $\sqrt{{s}_{\mathrm{NN}}}=5.02\phantom{\rule{4pt}{0ex}}\mathrm{TeV}$. The effects of the collective cascade are clearly seen in the target $(3<{\ensuremath{\eta}}_{\mathrm{lab}}<4)$ and central (within $|{\ensuremath{\eta}}_{\mathrm{c}.\mathrm{m}.\mathrm{system}}|<0.3$ at $1<{p}_{T}<8\phantom{\rule{0.28em}{0ex}}\mathrm{GeV}/\phantom{\rule{0.0pt}{0ex}}c)$ interaction regions when studying the pseudorapidity density and transverse momentum dependence of the nuclear modification factor of the charged particles, respectively.