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Register a new userProbing the Pomeron structure using dijets and $gamma$+jet events at the LHC
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We consider hard diffractive events in proton-proton collisions at the LHC, in which both protons escape the collision intact. In such double Pomeron exchange processes, we propose to measure dijets and photon-jet final states, and we show that it has the potential to pin down the Pomeron quark and gluon contents, a crucial ingredient in the standard QCD description of hard diffraction. By comparing with predictions of the soft color interaction approach, we also show that more generally, the measurement of the photon-jet to di-jet cross section ratio can put stringent test on the QCD dynamics at play in diffractive processes in hadronic collisions.
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Within the resolved Pomeron model of hard diffractive scattering, we compute prompt photon production in double-Pomeron-exchange events in proton-proton collisions. Using specific kinematical constraints chosen according to the acceptances of the forward proton detectors of experiments at the Large Hadron Collider, we provide estimates for inclusive and isolated photon production. This is done using the JetPhox program. We find that next-to-leading order corrections to the hard process are important and must be included in order to correctly constrain the quark and gluon content of the Pomeron from such processes at the LHC.
A Regge pole model for Pomeron-Pomeron total cross section in the resonance region $sqrt{M^2}le$ 5 GeV is presented. The cross section is saturated by direct-channel contributions from the Pomeron as well as from two different $f$ trajectories, accompanied by the isolated f$_0(500)$ resonance which dominates the $sqrt{M^{2}}lesssim 1$ GeV region. A slowly varying background is taken into account. The calculated Pomeron-Pomeron total cross section cannot be measured directly, but is an essential part of central diffractive processes. In preparation of future calculations of central resonance production at the hadron level, and corresponding measurements at the LHC, we normalize the Pomeron-Pomeron cross section at large masses $sigma_{t}^{PP} (sqrt{M^2}rightarrow infty) approx$ 1 mb as suggested by QCD-motivated estimates.
A model for Pomeron-Pomeron total cross section in the resonance region $sqrt{M^{2}} le$ 5 GeV is presented. This model is based on Regge poles from the Pomeron and two different $f$ trajectories, and includes the isolated f$_{0}(500)$ resonance in the region $sqrt{M^{2}}lesssim 1$ GeV. A slowly varying background is included. The presented Pomeron-Pomeron cross section is not directly measurable, but is an essential ingredient for calculating exclusive resonance production at the LHC.
The production of $X(4350)$ in the $gamma gamma$ interactions that occur in proton-proton, proton-nucleus and nucleus-nucleus collisions at the CERN Large Hadron Collider (LHC) is investigated and predictions for the kinematical ranges probed by the ALICE and LHCb Collaborations are presented. We focus on the $gamma gamma rightarrow phi J/Psi$ process, which have been measured by the Belle Collaboration, and present parameter free predictions for the total cross sections at the LHC energies. Our results demonstrate that the experimental study of this process is feasible and can be used to confirm or not the existence of the $X(4350)$ state. Finally, for completeness, we present predictions for the production of the $X(3915)$ state in the $gamma gamma rightarrow omega J/Psi$ process and show that this exotic state can also be probed in $gamma gamma$ interactions at the LHC.
The 13 TeV run of the LHC has provided a unique opportunity to explore multi-jet final states with unprecedented accuracy. An interesting region for study is that of events where one jet is tagged in the forward direction and another one in the backward direction and a plethora of low energy mini-jets populate the possibly large rapidity span in between them. Since the number of these events is very high, it is possible to introduce stringent constraints on the transverse momentum of the two leading jets which can be kept in small windows not very different from each other, defining what we call twin jets. The associated crowd of mini-jets can also have a restricted span in transverse momentum. The study of these events for a fixed multiplicity is an ideal playground to investigate different models of multi-particle production in hadron-hadron collisions. We set up an exploratory analysis by using an ancient model of Chew and Pignotti to describe the gross features one can expect for the structure of single and double differential-in-rapidity cross sections and for particle-particle rapidity correlations when the longitudinal phase space completely decouples from the transverse degrees of freedom.
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