Cms Data Demonstrates 50% Correlation Between Initial Shape and Charm Quark Flow in QGP

The behaviour of charm quarks offers a unique window into the extreme conditions created during heavy-ion collisions, allowing scientists to probe the properties of the quark-gluon plasma, a state of matter thought to have existed shortly after the Big Bang. Soumik Chandra from Purdue University, alongside collaborators including A. M. Sickles and R. Reed, investigate how charm quarks interact with this plasma by analysing the production and flow of mesons, particles containing a charm quark, at the CMS experiment. This research presents a comprehensive study of meson behaviour across a broad range of energies and collision centralities, utilising a technique called event-shape engineering to correlate the initial shape of the collision with the resulting particle flow. The team’s findings, achieved with the widest energy range explored to date using this method, provide crucial insights into the mechanisms governing heavy quark interactions within the quark-gluon plasma and refine our understanding of this fundamental state of matter.

The team’s findings, achieved with the widest energy range explored to date using this method, provide crucial insights into the mechanisms governing heavy quark interactions within the quark-gluon plasma and refine our understanding of this fundamental state of matter.

The study focuses on the effect of the initial collision system shape on the elliptic flow of promptly produced D0 mesons, utilising event-shape engineering in lead-lead collisions. A correlation between initial shape anisotropy and the D0 flow would indicate that the flow originates from interactions between the charm quark and the quark-gluon plasma. Comparison with theoretical predictions aims to elucidate the mechanism generating this flow, and the anisotropic flow of nonprompt D0 production is also investigated.

Charm Quark Behaviour in Quark-Gluon Plasma

Scientists at the CMS experiment have achieved a detailed understanding of how charm quarks behave within the quark-gluon plasma (QGP), a state of matter created in heavy-ion collisions. The team studied the production and flow of D0 mesons, the lightest particles containing charm quarks, in lead-lead collisions, focusing on a transverse momentum range of 1 to 30 GeV/c. Measurements reveal a strong dependence of the nuclear modification factor on momentum, with a minimum around 10 GeV/c, indicating energy loss of the charm quark within the QGP medium, and enhancement at low momentum suggests hadronization via coalescence.

Experiments demonstrate a significant momentum dependence for both the elliptic flow and triangular flow of promptly produced D0 mesons, with a measurable triangular flow observed for low momentum values. Analysis of nonprompt D0 mesons, originating from the decay of bottom quarks, shows lower flow values compared to their prompt counterparts, and a nonzero triangular flow is observed for nonprompt D0 mesons in a specific momentum range.

A key breakthrough involves correlating the D0 flow with the flow of charged particles, utilising event-shape engineering to control the initial collision geometry. Measurements confirm a linear trend between normalized D0 flow and normalized charged-particle flow, independent of collision centrality and momentum. The measured slopes consistently align with unity, strongly suggesting that the D0 elliptic flow originates primarily from the initial eccentricity of the collision system.

Charm Quark Flow Mirrors Collision Geometry

Researchers at the CMS experiment have demonstrated a strong link between the initial geometry of heavy-ion collisions and the collective flow of charm quarks, observed through the production of D0 mesons. By systematically altering the initial conditions of these collisions using an event-shape technique, the team established that the observed flow of D0 mesons correlates directly with the eccentricity of the initial collision geometry across a wide range of collision centralities and momentum values. This finding supports the idea that the interactions between charm quarks and the quark-gluon plasma are a primary driver of the observed flow patterns.

Further investigations into the flow of D0 mesons originating from bottom quark decays, alongside measurements of nuclear modification factors, provide additional insights into how heavy quarks interact within the quark-gluon plasma. The data suggest that energy loss experienced by charm quarks within the plasma may be dependent on the path length they travel through the medium, particularly at higher momenta.