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star physics results: High-pT phenomena

Note: Click on a figure for a larger version.

Figure. The measured azimuthal anisotropy parameter divided by the number of quark constituents in the hadron as a function of transverse momentum divided by the number of quark constituents for K0s, and Lambda+anti-Lambda for Au-Au collisions at 200 GeV. The error bars are statistical only.

Apparent scaling for the azimuthal anisotropy of Lambda and K0s

In Au-Au collisions at RHIC one of the first measurements was the observation of collective harmonic flow for charged hadrons and that this flow showed a strong pt dependence. This observation has since been extended to that the identified particles. The K0s and Lambda+anti-Lambda also show a strong pt dependence in the measured v2. However, they also show that the value of v2 at a given pt is mass dependent. This mass dependence is predicted hydrodynamical models and the magnitude is in agreement with the STAR measured results up to pt ~2 GeV/c . Above this transverse momentum the measured v2 seems to saturate, this is in contradiction with hydrodynamic predictions. For pt /n > 0.8 GeV/c, where n is the number of constituent quarks in the hadron, it is interesting to note that the measured v2/n of the K0s and Lambda+anti-Lambda is equal. If hadrons at intermediate pt are created via coalescence of co-moving quarks from bulk partonic matter it is predicted that the v2 /n of the measured particles would behave in such a fashion. In such a scenario this measurement reveals that the partons develop an momentum-space azimuthal anisotropy created by the ellipsoidal shape of the initial collision.

Related STAR papers

Particle-type dependence of azimuthal anisotropy and nuclear modification of particle production in Au+Au collisions at sqrt(snn) = 200 GeV
Phys. Rev. Lett. 92 (2004) 052302
e-Print Archives (nucl-ex/0306007): Abstract | PS | PDF
Journal article: Phys. Rev. Lett. server

Azimuthal anisotropy of K0s and Lambda + Lambdabar production at mid-rapidity from Au+Au collisions at sqrt(snn) = 130 GeV
Phys. Rev. Lett. 89 (2002) 132301
e-Print Archives (hep-ex/0205072): Abstract | PS | PDF
Journal article: Phys. Rev. Lett. server

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