Hot and Cold QCD White Paper from ALICE-USA: Input for 2023 U.S. Long Range Plan for Nuclear Science
The ALICE-USA collaboration presents its plans for the 2023 U.S. Long Range Plan for Nuclear Science.
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arXiv subjects
J. E. Seger
Publications and source records attributed to J. E. Seger.
Photoproduction in Ultra-Peripheral Relativistic Heavy Ion Collisions with STAR
We present a summary of recent photoproduction results in ultra peripheral relativistic heavy ions collisions with STAR. These collisions have impact parameters larger then twice the nuclear radius; the nuclei do not physically collide, but interact via long-range electromagnetic fields. We observe exclusive $ρ^0$ production as well as $AuAu\to Au^*Au^* ρ^0$ with accompanying mutual nuclear excitation at $\sqrt{s_{NN}}=200$ GeV. We report the $ρ^0$ production cross section for both coherent and incoherent coupling accompanied by mutual nuclear excitation. We have studied the cross section as a function of $p_T$, $y_{ρ^0}$ and $M_{ππ}$ and compared it to theoretical models. In addition, we measured the $ρ^0$ helicity matrix elements. They are found to be consistent with s-channel helicity conservation. The ratio of coherent $ρ^0$ and direct $π^+π^-$ pair photoproduction has been measured and found to be consistent with earlier measurements. The 4-pion final state $AuAu \to π^+π^-π^+π^-$ state has also been observed.
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Fermion Pair Production From an Electric Field Varying in Two Dimensions
The Hamiltonian describing fermion pair production from an arbitrarily time-varying electric field in two dimensions is studied using a group-theoretic approach. We show that this Hamiltonian can be encompassed by two, commuting SU(2) algebras, and that the two-dimensional problem can therefore be reduced to two one-dimensional problems. We compare the group structure for the two-dimensional problem with that previously derived for the one-dimensional problem, and verify that the Schwinger result is obtained under the appropriate conditions.
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