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C. Royon
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In this short report, we discuss the Jet Physics results and perspectives at HERA, Tevatron and LHC.
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Jet production in electron-proton collisions at HERA provides a unique testing ground for Quantum Chromodynamics (QCD). Apart from the determination of the strong coupling constant $alpha_s$, ep jet data may especially be used to gain insight into the dynamics of the exchanged parton cascade, whose structure is probed by the high-$E_T$ dijet system; thus information on the parton content of the proton and (quasi-)-real and virtual photons is obtained. This report touches some of these aspects revealed in recent jet data from the HERA experiments which are testing perturbative QCD at the limits of applicability.
We demonstrate that in the back-to-back kinematics the production of four jets in the collision of two partons is suppressed in the leading log approximation of pQCD, compared to the hard processes involving the collision of four partons. We derive the basic equation for four-jet production in QCD in terms of the convolution of generalized two-parton distributions of colliding hadrons in the momentum space representation. Our derivation leads to geometrical approach in the impact parameter space close to that suggested within the parton model and used before to describe the four-jet production. We develop the independent parton approximation to the light-cone wave function of the proton. Comparison with the CDF and D0 data shows that the independent parton approximation to the light-cone wave function of the proton is insufficient to explain the data. We argue that the data indicate the presence of significant multiparton correlations in the light-cone wave functions of colliding protons.
The proton diffractive structure function $F_2^{D(3)}$ measured in the H1 and ZEUS experiments at HERA are analysed in terms of perturbative QCD in the perspective of the QCD extrapolation to the Tevatron and the LHC. It is shown that both data sets can be well described by a QCD analysis in which point-like parton distributions, evolving according to the next-leading DGLAP equations, are assigned to the leading and sub-leading Regge exchanges. For present data from H1 and ZEUS the gluon distributions are found to be quite different and we give the corresponding sets of quark and gluon parton distributions for the Pomeron, extracted from the two experiments. An extrapolation to the Tevatron range is compared with CDF data on single diffraction. Conclusions on factorization breaking between HERA and Tevatron critically depend on whether H1 (strong violation) or ZEUS (compatibility at low $beta$) fits are taken into account. Using the double Pomeron formulation in central diffractive dijet production we show that the Tevatron mass fraction is much sensitive to the high $beta$ tail of the gluon in the Pomeron, suggesting a new way of handling the otherwise badly known gluon distribution in the Pomeron. Extrapolation of the fits to very high $Q^2$ are given since they will be relevant for QCD and diffraction studies at the LHC.
The Fermilab Tevatron offers unique opportunities to perform measurements of the heavier b-hadrons that are not accessible at the Y(4S) resonance. In this summary, we describe most important heavy flavor results from DO and CDF collaborations and we discuss prospects for future measurements, that could reveal New Physics before the start-up of the Large Hadron Collider (LHC).
The CDF and DO experiments at the Tevatron $pbar{p}$ collider established that extensive and detailed exploration of the $b$--quark dynamics is possible in hadron collisions, with results competitive and supplementary to those from $e^+e^-$ colliders. This provides a rich, and highly rewarding program that is currently reaching full maturity. I report a few recent world-leading results on rare decays, CP-violation in $B^0_s$ mixing, $bto s$ penguin decays, and charm physics.
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