No Arabic abstract
We examine the intrinsic spin-dependence of the dominant $gg rightarrow gggg$ subprocess contribution to four-jet production in polarized proton-proton collisions using helicity amplitude techniques. We find that the partonic level, longitudinal spin-spin asymmetry, $hat{a}_{LL}$, is intrinsically large in the kinematic regions probed in experiments detecting four isolated jets. Such events may provide another qualitative or semi-quantitative test of the spin-structure of QCD in planned polarized $pp$ collisions at RHIC.
We present the full next-to-next-to-leading order (NNLO) coefficient functions for the polarized cross section $dDelta sigma/dQ$ for the Drell-Yan process $p + pto l^+l^- + X$. Here $X$ denotes any inclusive hadronic state and $Q$ represents the invariant mass of the lepton pair. All QCD partonic subprocesses have been included provided the lepton pair is created by a virtual photon, which is a valid approximation for $Q<50$ GeV. Unlike the differential distribution w.r.t. transverse momentum the dominant subprocess for the integrated cross section is given by $q+bar q to gamma^* + X$ and its higher order corrections so that massive lepton pair production provides us with an excellent tool to measure the polarized anti-quark densities. Our calculations are carried out using the method of $n$-dimensional regularization by making a special choice for the $gamma_5$ matrix. We give predictions for double longitudinal spin asymmetry measurements at the RHIC.
The two-pion production reaction $vec{p}pto pppi^+pi^-$ was measured with a polarized proton beam at $T_p approx$ 750 and 800 MeV using the short version of the COSY-TOF spectrometer. The implementation of a delayed pulse technique for Quirl and central calorimeter provided positive $pi^+$ identification in addition to the standard particle identification, energy determination as well as time-of-flight and angle measurements. Thus all four-momenta of the emerging particles could be determined with 1-4 overconstraints. Total and differential cross sections as well as angular distributions of the vector analyzing power have been obtained. They are compared to previous data and theoretical calculations. In contrast to predictions we find significant analyzing power values up to $A_y$ = 0.3.
We establish some signatures of the extra bilepton boson ${X^0}$ predicted in the ${SU (3)_C times SU (3)_L times U (1)_X}$ model with right-handed neutrinos. We analyze the process $p + p longrightarrow X^0 +X^{0*} + {hbox {anything}}$, for center of mass energy regime of the Large Hadron Collider. The main contributions for the neutral bilepton production in $q bar q$ process come from the $s-$channel ($Z$ and $Z^prime$ exchanges), when the initial quarks have charge 2/3, and from an additional $t-$channel (heavy quark exchange) when they have -1/3 of the positron electric charge. We calculate some distributions of the final bileptons and from these results we conclude that LHC can show a clear signature for the existence of the $X^0$ predicted in the 3-3-1 model.
In this article, we investigate the contribution of the higher twist Feynman diagrams to the large-$p_T$ inclusive pion production cross section in proton-proton collisions and present the general formulae for the higher twist differential cross sections in the case of the running coupling and frozen coupling approaches. The structure of infrared renormalon singularities of the higher twist subprocess cross section and the resummed expression (the Borel sum) for it are found. We compared the resummed higher twist cross sections with the ones obtained in the framework of the frozen coupling approximation and leading twist cross section. We obtain, that ratio $R$ for all values of the transverse momentum $p_{T}$ of the pion identical equivalent to ratio $r$. It is shown that the resummed result depends on the choice of the meson wave functions used in calculation. Phenomenological effects of the obtained results are discussed.
A micro-canonical treatment is used to study particle production in pp collisions. First this micro-canonical treatment is compared to some canonical ones. Then proton, antiproton and pion 4(pi) multiplicities from proton-proton collisions at various center of mass energies are used to fix the micro-canonical parameters (E) and (V). The dependences of the micro-canonical parameters on the collision energy are parameterised for the further study of pp reactions with this micro-canonical treatment.