524 research outputs found
Importance of mesons in light-by-light scattering in ultraperipheral lead-lead collisions at the LHC
Possibility of PbPbPbPb measurement at smaller (< 5 GeV)
diphoton invariant mass will be presented. Analysis focuses only on
ultraperipheral heavy-ion collisions. This estimate shows that the collisions can be measured at the LHC by ALICE and
LHCb experiments for diphoton invariant mass 2 GeV. Predictions for the
resonance scattering shows that
these resonances can be measured with rather good statistics. A~possible
observation of peaks related to intermediate , ,
, , mesons will be presented too.
Attempts of reduction of background which comes from dipion production will be
considered.Comment: 4 pages, 3 figures, 1 table, MESON2018 - the 15th International
Workshop on Meson Physic
Domains of doping in graphene on polycrystalline gold: first-principles and scanning tunneling spectroscopy studies
We have studied the graphene/gold interface by means of density functional
theory (DFT) and scanning tunneling spectroscopy (STS). Weak interaction
between graphene and the underlying gold surface leaves unperturbed Dirac cones
in the band-structure, but they can be shifted with respect to the Fermi level
of the whole system, which results in effective doping of graphene. DFT
calculations revealed that the interface is extremely sensitive to the
adsorption distance and to the structure of metal's surface, in particular
strong variation in doping can be attributed to the specific rearrangements of
substrate's atoms, such as the change in the crystallographic orientation,
relaxation or other modifications of the surface. On the other hand, STS
experiments have shown the presence of energetic heterogeneity in terms of the
changes in the local density of states (LDOS) measured at different places on
the sample. Randomly repeated regions of zero-doping and p-type doping have
been identified from parabolic shape characteristics and from well defined
Dirac points, respectively. The doping domains of graphene on gold seem to be
related to the presence of various types of the surface structure across the
sample. DFT simulations for graphene interacting with Au have shown large
differences in doping induced by considered structures of substrate, in
agreement with experimental findings. All these results demonstrate the
possibility of engineering the electronic properties of graphene, especially
tuning the doping across one flake which can be useful for applications of
graphene in electronic devices
scattering in ultrarelativistic UPC
We discuss diphoton semi(exclusive) production in ultraperipheral lead-lead
collisions at energy of = 5.5 TeV (LHC) and in proton-proton
collisions at = 7 TeV (LHC) and = 100 TeV
(FCC). The nuclear calculations are based on equivalent photon approximation in
the impact parameter space. The cross sections for elementary subprocess are calculated including three different mechanisms:
box diagrams with leptons and quarks in the loops, a VDM-Regge contribution
with virtual intermediate hadronic excitations of the photons and the two-gluon
exchange contribution. We get relatively high cross sections in heavy ion
collisions. This opens a possibility to study the light-by-light (quasi)elastic
scattering at the LHC. We find that the cross section for elastic
scattering could be measured in the lead-lead collisions for the
diphoton invariant mass up to 15 - 20 GeV. Our
Standard Model predictions are compared to a recent ATLAS experimental result.
We present differential distributions for PbPbPbPb and
pppp reaction.Comment: 5 pages, 3 figures, talk was given by Antoni Szczurek at European
Physical Society conference on High Energy Physics (EPS-HEP 2017), Venice,
Italy. Two references were added. arXiv admin note: text overlap with
arXiv:1610.08546, arXiv:1611.05601, arXiv:1606.0903
Photoproduction of vector mesons: from ultraperipheral to semi-central heavy ion collisions
We discuss nuclear cross sections for and
reactions with one or two vector mesons in the final state. Our analysis is
done in the impact parameter space equivalent photon approximation. This
approach allows to consider the above processes taking into account distance
between colliding nuclei. We consider both ultraperipheral and semi-central
collisions. We are a first group which undertook a study of single
photoproduction for different centrality bins. We show that one can describe
new ALICE experimental data by including geometrical effects of collisions in
the flux factor.
Next, total and differential cross section for double-scattering mechanism in
the exclusive reaction in ultrarelativistic ultraperipheral heavy
ion collisions is presented. In this context we consider double photoproduction
and photon-photon processes. Simultaneously, we get very good agreement of our
results with STAR (RHIC), CMS and ALICE (LHC) experimental data for single
and vector meson production. A comparison of our predictions
for exclusive four charged pions production is also presented.Comment: 6 pages, 6 figures, an invited talk presented by M. Klusek-Gawenda at
the 14th International Workshop on Meson Production, Properties and
Interaction, (Meson2016), Krakow, Poland, June 2-7, 201
Exclusive production of pairs in ultrarelativistic heavy ion collisions
We disuss exclusive electromagnetic production of two neutral ~mesons
and show the predictions for the reactions for
gold-gold collisions at the energy of = 200 GeV (RHIC) and for
lead-lead collisions at the energy of = 5.5 TeV (LHC). The
elementary cross section is calculated with the help of the
vector-dominance-model (VDM)-Regge approach which usually very well describes
the experimental data at large energy. The low-energy cross section is parametrized. The cross section for
nuclear process is calculated by means of the equivalent photon approximation
(EPA). We compare the results with realistic charge density with the results
for monopole form factor.Comment: 3 pages, 3 figures, talk by Mariola Klusek-Gawenda at Meson2010, June
2010, Krakow, Polan
Double scattering production of two positron-electron pairs in ultraperipheral heavy-ion collisions
We present first measurable predictions for electromagnetic (two-photon)
double scattering production of two positron-electron pairs in ultraperipheral
heavy-ion collisions at LHC. Measureable cross sections are obtained with
realistic cuts on electron/positron (pseudo)rapidities and transverse momenta
for the ALICE and ATLAS or CMS experiments. The predictions for total and
differential cross sections are presented. We show also two-dimensional
distributions in rapidities of the opposite-sign (from the same or different
subcollisions) and of the same-sign ( or ) electrons and in
rapidity distance between them. Expected number of events are presented and
discussed. Our calculations strongly suggest that relevant measurements with
the help of ATLAS, CMS and ALICE detectors are possible in a near future.Comment: 10 pages, 6 figure
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