Orateur
Prof.
Antoni Szczurek
(Rzeszow University and Institute of Nuclear Physics PAN)
Description
We discuss exclusive production of lepton-antilepton,
quark-antiquark, $\pi \pi$ and $\rho^0 \rho^0$ and $D \bar D$ meson
pairs in ultraperipheral, ultrarelativistic
heavy-ion collisions i.e. processes initiated by photon-photon
fusion which could be studied at RHIC and LHC.
The cross sections for exclusive muon pair production
in nucleus - nucleus collisions was calculated and
several differential distributions are shown.
Realistic (Fourier transform of charge density)
charge form factors of nuclei are used and the corresponding
results are compared with the cross sections calculated
with monopole charged form factor of a nucleus often used in the literature.
Absorption effects are discussed and quantified.
The cross sections obtained with realistic
form factors are significantly smaller than those obtained
with the monopole form factor. The effect is bigger for
large muon rapidities and/or large muon transverse momenta.
We show predictions for STAR and PHENIX collaborations
at RHIC as well as ALICE and CMS collaborations at LHC.
The cross section for exclusive heavy quark and heavy antiquark
pair ($Q \bar Q$) production in peripheral ultrarelativistic heavy
ion collisions was calculated for the LHC energy $\sqrt{s_{NN}}$ =
5.5 TeV. We present results in the impact parameter equivalent
photon approximation (EPA) and compare some of them with results obtained by
exact calculations of the Feynman diagrams in the momentum space.
We include both $Q \bar Q$, $Q \bar Q g$ and $Q \bar Q q \bar q$
final states as well as photon single-resolved components.
Realistic charge densities in nuclei were taken in the calculation.
The different components give contributions of the same order
of magnitude to the nuclear cross section.
We present for the first time cross section for exclusive production
of $\pi^+ \pi^-$ and $\pi^0 \pi^0$ pairs. The elementary process
$\gamma \gamma \to \pi \pi$ is discussed in detail.
We concentrate on high-$p_t$ processes. We consider
pQCD processes ala Brodsky-Lepage or alternatively hand-bag mechanism.
The nuclear cross section is calculated within b-space EPA for RHIC and
LHC.
Similar analysis is performed for $\rho^0 \rho^0$ production,
where the elementary cross section is less known.
Our analysis includes a low-energy phenomenon (close-to-threshold
enhancement of the cross section).
The cross section for the low-energy phenomenon is parametrized
and the high-energy cross section is calculated in a simple
Regge model. Predictions for heavy ion collisions are presented.
The cross sections for exclusive $D^+ D^-$ and $D^0 \bar {D^0}$ meson
pair production in peripheral nucleus - nucleus collisions are
calculated and several differential distributions are presented.
The calculation of the elementary $\gamma \gamma \to D \bar D$
cross section is done within the heavy-quark approximation and in
the Brodsky-Lapage formalism with distribution
amplitudes describing recent CLEO data on leptonic $D^+$ decay.
The cross sections of a few nb are predicted for RHIC and of a few
hundreds of nb for LHC with details depending on the approximation made
in calculating elementary $\gamma \gamma \to D \bar D$ cross sections.
The speaker will present these different results to domonstrate how
reach is the option of ultrarelativistic ultraperipheral collisions
at RHIC and LHC.
Literature:
\item M. K{\l}usek, W. Sch\"afer and A. Szczurek,
"Exlusive production of $\rho^0 \rho^0$ pairs
in $\gamma \gamma$ collisions at RHIC",
Phys. Lett. {\bf B674} (2009) 92.
\item K{\l}usek-Gawenda and A. Szczurek,
``Exclusive muon-pair production in utrarelativistic heavy-ion
collisions - realistic nucleus charge form factor and differential
distributions'',
Phys. Rev. {\bf C82} (2010) 014904.
\item M. K{\l}usek-Gawenda, A. Szczurek, M. Machado and V. Serbo,
``Double -- photon exclusive processes with heavy quark -- heavy
antiquark pairs in high-energy Pb-Pb collisions at LHC'',
Phys. Rev. {\bf C83} (2011) 024903.
\item M. {\L}uszczak and A. Szczurek,
``Exclusive $D \bar D$ meson pair production\\
in peripheral ultrarelativistic heavy ion collisions'',
arXiv:1103.4268, in print in Phys. Lett.B
\item M. K{\l}usek-Gawenda and A, Szczurek,
arXiv:1104.0571, in print in Phys. Lett.B
Auteur principal
Prof.
Antoni Szczurek
(Rzeszow University and Institute of Nuclear Physics PAN)
