Landau-Pomeranchuk-Midgal effect and charm production in $pp$ collisions at energies available at the CERN Large Hadron Collider using the parton cascade model

We study the impact of the Landau-Pomeranchuk-Midgal (LPM) effect on the dynamics of parton interactions in proton-proton collisions at energies available at the CERN Large Hadron Collider. For our investigation we utilize a microscopic kinetic theory based on the Boltzmann equation. The calculation traces the space-time evolution of the cascading partons interacting via semihard pQCD scatterings and fragmentations. We focus on the impact of the LPM effect on the production of charm quarks, since their production is exclusively governed by processes well described in our kinetic theory. The LPM effect is found to become more prominent as the collision energy rises and at central rapidities, and may significantly affect the model's predicted charm distributions at low momenta.

Figure 1

Number of collisions (a), number of fragmentations (b), and number of charm quarks produced per event (c) for minimum-bias $pp$ interactions as a function of center-of-mass energy. The three calculations involve multiple collisions among partons by neglecting and including the LPM effect and collisions only among primary partons with radiations off the scattered partons.

Figure 2

Number of collisions (a), number of fragmentations (b), and number of charm quarks produced per event (c) for $pp$ interactions as a function of center-of-mass energy at impact parameter equal to zero fm. The three calculations involve multiple collisions among partons by neglecting and including the LPM effect and collisions only among primary partons with radiations off the scattered partons.

Figure 3

The transverse momentum spectra of charm quarks in $pp$ collisions at 200 GeV (a) and 2.76 TeV (b) due to multiple collisions among partons and fragmentations off final state quarks, with and without inclusion of LPM effect.

Figure 4

The transverse momentum spectra of charm quarks in $pp$ collisions at 200 GeV, with $p_T^{\mathrm{cutoff}}=0.77\mathrm{GeV}$ and ${\mu }_0=1\mathrm{GeV}$ (a) and with $p_T^{\mathrm{cutoff}}=0.77\mathrm{GeV}$ and ${\mu }_0=0.5\mathrm{GeV}$ (b) due to multiple collisions among partons and fragmentations off final state quarks, with and without inclusion of LPM effect.

Figure 5

The transverse momentum spectra of charm quarks in $pp$ collisions at 5.02 TeV due to multiple collisions among partons and fragmentations off final state quarks, with and without inclusion of the LPM effect.

Figure 6

The transverse momentum spectra of charm quarks in $pp$ collisions at 7.00 TeV due to multiple collisions among partons and fragmentations off final state quarks, with and without inclusion of LPM effect.

Figure 7

The transverse momentum spectra of charm quarks in $pp$ collisions at 13.00 TeV due to multiple collisions among partons and fragmentations off final state quarks, with and without inclusion of LPM effect.