Search for Exclusive Events Using the Dijet Mass Fraction at the Tevatron

Double pomeron exchange (DPE) processes are expected to extend the physics program at the LHC not only due to the possible Higgs boson detection but also because of the possibility to study broader range of QCD physics and diffraction [1, 2, 3, 4, 5, 6, 7, 8]. The processes are theoreticaly characterized by large rapidity gap regions devoid of particles between centrally produced heavy object and the scattered hadrons which leave the interaction intact. This is attributed to the exchange of a colorless object, the pomeron (or the reggeon). In the LHC environment, however, the rapidity gap signature will not appear because of the high number of multiple interactions occuring at the same time, and the diffractive events will be identified tagging the escaping protons in the beam pipe. One generally considers two classes of DPE processes, namely, exclusive DPE events if the central object is produced alone carrying away the total available diffractive energy and inclusive events when the total energy is used to produce the central object and in addition the pomeron remnants. Exclusive events allow a precise reconstruction of the mass and kinematical properties of the central object using the central detector or even more precisely using very forward detectors installed far downstream from the interaction point. The most appealing exclusive process to be studied at the LHC is the Higgs boson production but since it cannot be observed at the Tevatron due to the low production cross section, one should find other ways to look for exclusive events at the Tevatron, for example in dijet, diphoton channels. It is needed to mention that until recently, there was not a decisive measurement that would provide enough evidence for the existence of exclusive production. Although exclusive production yields kinematically well constrained final state objects, their experimental detection is non-trivial due to the overlap with the inclusive DPE events. In those events, the colliding pomerons are usualy viewed as an object with partonic sub-structure. A parton emitted from the pomeron takes part in the hard interaction and pomeron remnants accompanying the central object are distributed uniformly in rapidity. Exclusive events usually appear as a small deviation from the inclusive model predictions which need to be studied precisely before accepting a new kind of production. In particular, the structure of the pomeron as obtained from HERA is not precisely known at high momentum fraction, and specifically, the gluon in the pomeron is not well constrained. It is not clear if such uncertainty could not lead to mis-identifying observed processes as exclusive. This would for instance preclude the spin analysis of the produced object. In this paper, we aim to investigate the observation of exclusive production at the Tevatron. Indeed, we use the dijet mass fraction distribution measured by the CDF collaboration and show that even taking into account uncertainties associated with the pomeron structure, one is unable to give a satisfactory description of the data without the existence of exclusive events. We also include other approach to explain diffraction in our study, the so called Soft color interaction model (the properties of all the models are discussed later). As an outlook, we apply current models for the DPE production for LHC energies and demonstrate the possible appereance of exclusive events through the dijet mass fraction. The paper is organized as follows: in the second section we give a brief description of the inclusive, exclusive, and Soft color interaction models. The third section discusses how well the various models can explain the preliminary