[Brahms-l] Ionut's QM08 abstract

         Dear collaborator,

       Bellow find my draft for the QM08 abstract. I am grateful for
comments and criticism.

                  Regards,
                        Ionut


Title:
"Strangeness production in Au+Au collisions at $\sqrt{s_{NN}}=62.4 GeV$"

BRAHMS experiment has taken data from the short RHIC run for Au+Au
collisions at c.m. energy of 62.4 AGeV. Due to its special setup, BRAHMS
was able to measure and identify charged particles over the widest
rapidity range at RHIC.
This feature enabled us to shed some light on one of the
predicted signals of quark gluon plasma (QGP), strangeness enhancement.
    Experimentally, we have a limited set of observables. BRAHMS can only
measure charged pions, charged kaons, protons and anti-protons so the
strange quarks that we can see are contained in the charged kaons. The
majority of the produced strange quarks form negative kaons and
$\Lambda$ baryons in comparable quantities so $K^{-}$ is not a good
tool for strangeness estimation when we don't control the $\Lambda$
yield. The anti-strange quarks however form mostly positive kaons and
$K^0$s in equal quantities. The other species
containing anti-strange quarks are in a very limited number and this makes
the number of positive kaons approximately proportional to the total
strangeness created during the collision.
    From the AGS energies up to the highest RHIC energy we observed
experimentally that the $K^{+}/\pi^{+}$ ratio is higher than the same
ratio in p+p collisions at the same collision energy. This fact was
interpreted to happen
due to the final state effects (rescatterings) taking place in a
nucleus-nucleus collision. We also observed that the difference between
the strangeness ratio in nucleus-nucleus collisions and the one in p+p
collisions is varying. By looking at older SPS data in mid-rapidity,
together with BRAHMS data in different rapidity slices, we observed that
there is a scaling of the $K^{+}/\pi^{+}$ ratio with the $\bar{p}/p$
ratio. Our conclusion is that in nucleus-nucleus collisions where the
formed medium is baryon rich (e.g. AGS energies, low SPS energies, forward
rapidity in Au+Au collisions at 62.4GeV in RHIC), the additional
strangeness created trough rescatterings is higher than in the collisions
where the medium created is highly deconfined and baryon poor (e.g. RHIC
at 200GeV). A posible explanation might be the evolution time which is
longer in low energy collisions and allows for multiple rescatterings
before the chemical freezeout.
    In this work we will show measured yields and ratios of identified
particles from the 10\% most central Au+Au collisions at 62.4 GeV
together with comparisons with results from other experiments and from
theoretical models.

-- 
Ionut Cristian Arsene
PhD student at Physics Department, University of Oslo, Norway
Phone: +47 22856456 (Office)
Phone: +47 94214593 (Mobile)

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