We discuss the central exclusive production of Higgs boson
and $q\bar{q}$ pairs in proton-proton (proton-antiproton) collisions
at LHC and Tevatron.
The amplitude for both processes is derived within the $k_t$-factorization
approach and discussed in different kinematical asymptotia.
In particular, we consider important high-$p_t$ and massless quark
limits for $q \bar q$ production.
Rapidity distributions, quark jet $p_t$ distributions,
invariant $q\bar{q}$ mass distributions, angular azimuthal correlations
between outgoing protons and between ougoing jets are presented.
Exclusive $b \bar b$ production constitutes an
irreducible background for exclusive Higgs production
The $b{\bar b}$ background is analyzed in detail,
in particular we study how to impose cuts to maximize signal-to-background
ratio and show some solutions.
We consider also central exclusive production of $gg$ dijets.
The amplitude for the process is derived within the
$k_t$-factorization approach (with both the standard QCD and the
Lipatov's effective 3-gluon verticies) and is considered in various
kinematical asymptotia, in particular, in the important limit of
high-$p_t$ jets. Compared to earlier works we include emissions of
gluons from different gluonic $t$-channel lines.
Rapidity distributions, gluon jet $p_t$
distributions, invariant dijet mass distributions, angular azimuthal
correlations between outgoing protons and jets are presented. We
explore the competition of the standard diagram with both jets
emitted from a single $t$-channel gluon and the one with the
emission from both $t$-channel gluons. We find that the latter
contribution is much smaller than that known from the literature.
It becomes comparable only when the jet rapidity difference is large
or the gluon transverse momenta are very small. It can, therefore,
give contributions to the central diffractive production of mesons.
We compare our results with the Tevatron data for exclusive dijets.
\item R. Maciu{\l}a, R.S. Pasechnik and A. Szczurek,
"Exclusive double-diffractive production of open charm in
proton-proton and proton-antiproton collisions",
Phys. Lett. {\bf B685} (2010) 165.
\item R. Maciu{\l}a, R. Pasechnik and A. Szczurek,
``Exclusive $b \bar b$ pair production and irreducible background
to the exclusive Higgs boson production'',
Phys. Rev. {\bf D82} (2010) 114011.
\item R. Maciu{\}a, R. Pasechnik and A. Szczurek,
``Central exclusive quark-antiquark dijet and Standard Model
Higgs boson production in proton-(anti)proton collisions,
arXiv:1011.5842, to be published in Phys. Rev.D