Effects of overlapping strings in pp collisions

Abstract

In models for hadron collisions based on string hadronization, the strings are usually treated as independent, allowing no interaction between the confined colour fields. In studies of nucleus collisions it has been suggested that strings close in space can fuse to form "colour ropes". Such ropes are expected to give more strange particles and baryons, which also has been suggested as a signal for plasma formation. Overlapping strings can also be expected in pp collisions, where usually no phase transition is expected. In particular at the high LHC energies the expected density of strings is quite high. To investigate possible effects of rope formation, we present a model in which strings are allowed to combine into higher multiplets, giving rise to increased production of baryons and strangeness, or recombine into singlet structures and vanish. Also a crude model for strings recombining into junction structures is considered, again giving rise to increased baryon production. The models are implemented in the DIPSY MC event generator, using PYTHIA8 for hadronization, and comparison to pp minimum bias data, reveals improvement in the description of identified particle spectra.1 String interaction effects in pp collisions have also earlier been included in the event generator DTU-JET [17], formulated in momentum space. This was generalized to nucleus collisions, including a geometric distribution of nucleons within a nucleus [18]. Rope effects are also included, together with hadron rescattering, in the RQMD model, with applications in the SPS fixed target and RHIC energy ranges [19][20][21].2 For a review of the Lund hadronization model see ref.[24], or a more recent summary in ref. [25].

Systematics of quark/gluon tagging

“…Swing refers to color reconnections performed during the perturbative cascade, where dipoles in the same color state are allowed to reconnect in a way which prefers low-mass dipoles [46,119]. Turning off swing has an effect already at parton level, which is amplified at hadron level, leading to improved quark/gluon separation.…”

Baryon production from cluster hadronisation

“…These ideas have been advocated in some way e.g. in the Dipsy rope model [8] where many overlapping strings are combined into a colour field of a higher representation. Thermodynamical string fragmentation in Pythia also addresses this issue where shifts of the transverse momentum of heavier particles to higher values are the main result a e-mail: kirchgaesser@gmail.com [9].…”

Nuclear and quark matter at high temperature

“…The details of the latter process are still unresolved; phenomenologybased fragmentation functions and modeling level stringor rope-decay scenarios are in use [26][27][28][29][30]. For the early phase, when nevertheless most of the final state entropy is supposed to be produced already, pictures utilizing the concept of coherent, nearly classical color fields dominate, describing color rope formation and more recently a colored glass condensate (CGC) [31][32][33][34].…”