[Paper Review] Toward UrQMD Model Description of pp and pC Interactions at High Energies

V. Uzhinsky|arXiv (Cornell University)|Aug 3, 2013

High-Energy Particle Collisions Research4 references3 citations

TL;DR

This paper investigates discrepancies between UrQMD model version 3.3 and high-energy pp and pC interaction data from NA61/SHINE and NA49 Collaborations. Despite including η-meson decays, the model underestimates pion production at 20–80 GeV, indicating that a new tuning of model parameters and inclusion of low-mass diffraction dissociation are essential for accurate description of experimental data.

ABSTRACT

It is found that UrQMD model version 3.3 does not describe NA61/SHINE Collaboration data on π-meson production in pp interactions at energies 20 - 80 GeV. At the same time, it describes quite well the NA49 Collaboration data on the meson production in pp and pC interactions at 158 GeV. The Collaborations do not consider feedback of η-meson decays. All versions of the UrQMD model assume that η-mesons are "stable". An inclusion of the decays into calculations leads to 2--3 % increase of the meson production which is not enough for description of the data. Possible ways of the model improvements are considered. Conclusions of the paper are: accounting of η-meson decays is not essential for a description of experimental data; a new tuning of the UrQMD model parameters is needed for a successful description of pp and pC interactions at high energies; inclusion of the low mass diffraction dissociation in the UrQMD model would be desirable.

Motivation & Objective

• To identify shortcomings in UrQMD model version 3.3 in describing high-energy pp and pC interactions.
• To assess the impact of η-meson decays on meson production spectra in the model.
• To evaluate whether modifications to binary reaction cross sections or inclusion of low-mass diffraction dissociation can improve agreement with experimental data.
• To guide future model tuning and implementation for accurate simulation of hadronic interactions at FAIR and NICA facilities.

Proposed method

• Comparison of UrQMD 3.3 simulations with experimental data from NA61/SHINE and NA49 Collaborations on pion, kaon, and proton spectra in pp and pC interactions.
• Implementation of η-meson decays in the UrQMD code by modifying decay branching ratios and forcing decay via event loop logic.
• Systematic reduction of binary reaction cross sections by a factor of 3 to test sensitivity of central rapidity spectra.
• Introduction of a fixed 50% probability for single diffraction dissociation to counteract energy-dependent suppression in the Fritiof model.
• Simulation of proton spectra in pp and pC interactions to analyze structure in the target and projectile fragmentation regions.
• Replotting data in rapidity space to clarify contributions from different kinematic regions (projectile vs. target fragmentation).

Experimental results

Research questions

• RQ1 Does accounting for η-meson decays significantly improve the UrQMD model's description of pion production in pp and pC interactions at 20–80 GeV?
• RQ2 Why does the UrQMD 3.3 model fail to describe NA61/SHINE data on π⁻ production at 20–80 GeV despite good agreement with NA49 data at 158 GeV?
• RQ3 Can reducing binary reaction cross sections in UrQMD improve agreement with mid-rapidity pion spectra at lower energies?
• RQ4 Is the inclusion of low-mass diffraction dissociation necessary to correctly describe proton and pion spectra in pp and pC interactions?
• RQ5 How do the model's predictions for proton spectra in pp vs. pC interactions reflect the influence of binary reactions and diffraction processes?

Key findings

• Including η-meson decays increases meson production by 2–3%, but this is insufficient to resolve discrepancies with NA61/SHINE data at 20–80 GeV.
• The UrQMD 3.3 model with default parameters fails to describe NA61/SHINE data on π⁻ production at 20–80 GeV, though it agrees well with NA49 data at 158 GeV/c.
• Reducing binary reaction cross sections by a factor of 3 improves agreement with data at 20–80 GeV, but leads to overestimation at 158 GeV/c.
• Fixing the single diffraction dissociation probability at 50% improves agreement with NA49 data at 158 GeV/c, suggesting the Fritiof model's energy-dependent suppression is unphysical at high energies.
• The model predicts a broad proton peak at low angles and ~2 GeV/c in pp interactions due to binary reactions or low-mass diffraction, but this feature is suppressed in pC interactions due to equal contributions from pp and pn collisions.
• Replotting data in rapidity space reveals that low-angle pion data (θ < 60 mrad) originate from the projectile fragmentation region, while higher-angle data reflect central production.