Azimuth quadrupole component spectra on transverse rapidity ${\bf y_t}$ for identified hadrons from Au-Au collisions at $\sqrt{s_{NN}} =$ 200 GeV

TL;DR

This paper isolates and analyzes the azimuth quadrupole component spectra from identified hadrons in Au-Au collisions at 200 GeV, revealing that it originates from a common boosted source and challenges hydrodynamic interpretations.

Contribution

It presents the first extraction of azimuth quadrupole spectra on transverse rapidity for identified hadrons, showing they are emitted from a common boosted source and are a small fraction of total yield.

Findings

Quadrupole spectra have a Levy form similar to the soft component of single-particle spectra.

Quadrupole component constitutes less than 5% of total hadron yield.

The $v_2(p_t)$ form is dominated by the hard component of the spectrum above 0.5 GeV/c.

Abstract

I present the first isolation of azimuth quadrupole components from published $v_2(p_t)$ data (called elliptic flow) as spectra on transverse rapidity $y_t$ for identified pions, kaons and lambdas/protons from minimum-bias Au-Au collisions at 200 GeV. The form of the spectra on $y_t$ indicates that the three hadron species are emitted from a common boosted source with boost $\Delta y_{t0} \sim 0.6$. The quadrupole spectra have a L\'evy form similar to the soft component of the single-particle spectrum, but with significantly reduced ($\sim 0.7\times$) slope parameters $T$. Comparison of quadrupole spectra with single-particle spectra suggests that the quadrupole component comprises a small fraction ($< 5$%) of the total hadron yield, contradicting the hydrodynamic picture of a thermalized, flowing bulk medium. The form of $v_2(p_t)$ is, within a constant factor, the product of $p'_t$ ($p_t$ in the boost frame) times the ratio of quadrupole spectrum to single-particle spectrum. That ratio in turn implies that above 0.5 GeV/c the form of $v_2(p_t)$ is dominated by the hard component of the single-particle spectrum (interpreted as due to minijets). It is therefore unlikely that so-called {\em constituent-quark scaling} attributed to $v_2$ is relevant to soft hadron production mechanisms (e.g., chemical freezeout).