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تسجيل مستخدم جديدDiscovery of the Odderon by TOTEM experiments and the FMO approach
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This paper is an extended version of the talk by B. Nicolescu at the XLVIII International Symposium on Multiparticle Dynamics (ISMD2018) at Singapore, 3-7 September, 2018. Theoretical basis and history of the Froissaron and Maximal Odderon (FMO) approach for elastic $pp$ and $bar pp$ scattering is presented. Precise formulation of the FMO model at any momentum transfer squared $t$ is given. The model is applied to description and analysis of the experimental data in a wide interval of energy $sqrt{s}$ and $t$. The special attention is given for the latest TOTEM data at 13 TeV, both at $t=0$ and at $t eq 0$ and to their interpretation in the FMO model. It is emphasized that the last TOTEM results can be considered as clear evidence for the first experimental observation of the Odderon, predicted theoretically about 50 years ago.
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Inspired by the recent TOTEM data for the elastic proton -- proton ($pp$) scattering at $sqrt{s} =$ 8 and 13 TeV, we update previous studies of the differential cross sections using the Phillips -- Barger (PB) model, which parametrizes the amplitude
in terms of a small number of free parameters. We demonstrate that this model is able to describe the recent $pp$ data on a statistically acceptable way. Additionally, we perform separate fits of the $pp$ data for each center - of - mass energy and propose a parametrization for the energy dependence of the parameters present in the PB model. As a consequence, we are able to present the PB predictions for the elastic proton - proton cross section at $sqrt{s} = 546$ GeV and $1.8$ TeV, which are compared with the existing antiproton -- proton ($bar{p}p$) data. We show that the PB predictions, constrained by the $pp$ data, are not able to describe the $bar{p}p$ data. In particular, the PB model predicts a dip in the differential cross section that is not present in the $bar{p}p$ data. Such result suggests the contribution of the Odderon exchange at high energies.
The recent data by the TOTEM Collaboration on $sigma_{tot}$ and $rho$ at 13 TeV, have shown agreement with a leading Odderon contribution at the highest energies, as demonstrated in the very recent analysis by Martynov and Nicolescu (MN). In order to
investigate the same dataset by means of Pomeron dominance, we introduce a general class of forward scattering amplitude, with leading contributions even under crossing, associated with simple, double and triple poles in the complex angular momentum plane. For the lower energy region, we consider the usual non-degenerated Regge trajectories, with even and odd symmetry. The analytic connection between $sigma_{tot}$ and $rho$ is obtained by means of dispersion relations and we carry out fits to $pp$ and $bar{p}p$ data in the interval $sqrt{s}=5$ GeV - 13 TeV; following MN we consider only the TOTEM data at the LHC energy region. From the fits, we conclude that the general analytic model, as well as some particular cases representing standard parameterizations, are not able to describe satisfactorily the $sigma_{tot}$ and $rho$ data at 13 TeV. Further analyses in course and some perspectives are outlined.
Inspired by the evidence of the odderon exchange recently observed by the D0 and TOTEM Collaborations, a QCD sum rule investigation is performed to study the odderon as a three-gluon bound state. There may exist six lowest-lying three-gluon odderons
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Very precise data on elastic proton-proton scattering at $sqrt{s}=7$, $8$ and $13$ TeV have been obtained by the TOTEM group at LHC in the near-forward region (momentum transfers down to $|t| = 6 times 10^{-4} {rm GeV}^2$ at $sqrt{s}=8$ TeV and to $|
t| = 8 times 10^{-4} {rm GeV}^2$ at $sqrt{s}=13$ TeV). The Coulomb-nuclear interference has been measured with sufficient accuracy for TOTEM to establish the falloff of the $rho$ parameter with increasing energy. The predictions from a previously studied model are shown to be in good agreement with the data and thus allow us to draw rather firm conclusions about the structure of the near-forward nuclear amplitude. We point out that due to a zero in the real part of the nuclear amplitude occurring at a very small momentum transfer--that can migrate into the Coulomb-nuclear interference (CNI) region at higher energies--much care is needed in extracting the numerical value of $rho$ for such energies. Thus, the true value of $rho$ would be higher than the TOTEM value for $rho$ found under the hypothesis that the real part of the elastic nuclear amplitude is devoid of such a zero in the CNI region.
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