Nuclear Physics Seminar

Within the next two years the LHC will commence a heavy ion program starting with Pb
+Pb collisions at a nucleon-nucleon center of mass energy of 5.5 TeV. Such collisions
are expected to produce quark gluon plasma at initial energy densities an order of
magnitude larger than those achieved at RHIC with copious production of high-pT jets,
prompt photons, and other hard observables. The increased energy density of Pb+Pb
collisions at the LHC will provide an essential test of the strongly coupled QGP (sQGP)
interpretation of elliptic flow measurements at RHIC. The high rate for production of jets
with (e.g.) ET > 50 GeV will make it possible to carry out high-statistics measurements
of jet quenching using direct measurement of jet energies, fragmentation functions, and
jet shapes. The large LHC collision energy will also allow tests of saturation at x values
as low as 10-7 in A+A and p+A collisions.
The ATLAS detector at the LHC was designed primarily for Higgs and/or beyond the
standard model measurements in p-p collisions. However, the large acceptance of the
ATLAS detector, the high granularity electromagnetic and hadronic calorimetry, and
precision silicon tracking and the large acceptance muon spectrometers also make
ATLAS an excellent Pb+Pb detector. ATLAS is well-suited to make day-1 measurements
of bulk observables such as charged particle dN/dη, dET/dη, and photon and charged
particle v2. ATLAS will carry out high-resolution single jet and multi-jet measurements
over |η|<5 and will measure jet charge particle fragmentation functions and JT
distributions over |η|<2.5. Heavy flavor jets will be tagged using semi-leptonic decay
muons and displaced vertices. using the fine segmentation of the ATLAS
electromagnetic calorimeters to efficiently rejection photons from neutral hadron decay
ATLAS will be able to statistically measure direct and jet fragmentation photon
production in Pb + Pb and cleanly measure γ-jet pairs.