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Description
Measure v2(pt) is interpreted to estimate the amplitude of an azimuth component of particle pt spectra arising from transverse (elliptic) flow of a dense QCD medium. Comparisons of v2 data with hydrodynamic (hydro) theory seem to indicate very low medium viscosity leading to attribution of a "perfect liquid." As defined v2(pt) is a ratio, with a single-particle spectrum appearing in its denominator. Its numerator represents a Fourier component -- an azimuth cylindrical quadrupole -- arising from a boosted (on transverse rapidity) particle source. The Cooper-Frye (CF) formalism may be used to describe emission from a boosted source based on relativistic kinematics. CF analysis reveals that the v2(pt) numerator includes pt in the transverse boost frame as a factor, which has major consequences for data interpretation. A unique quadrupole pt spectrum may be isolated from v2(pt) data and compared directly with the single-particle spectrum in the v2 denominator and with hydro theory. A monopole boost (aka radial flow) value may be estimated from v2(pt) data. Certain conjectured data trends such as meson vs baryon segregation and NCQ scaling may also be tested. Several novel results emerge via the Cooper-Frye analysis.
