Central Pp Collisions Research Articles

The small-x gluon distribution in centrality biased pA and pp collisions

The nuclear modification factor RpA(pT) provides information on the small-x gluon distribution of a nucleus at hadron colliders. Several experiments have recently measured the nuclear modification factor not only in minimum bias but also for central pA collisions. In this paper we analyze the bias on the configurations of soft gluon fields introduced by a centrality selection via the number of hard particles. Such bias can be viewed as reweighting of configurations of small-x gluons. We find that the biased nuclear modification factor QpA(pT) for central collisions is above RpA(pT) for minimum bias events, and that it may redevelop a “Cronin peak” even at small x. The magnitude of the peak is predicted to increase approximately like 1/A⊥ν, ν∼0.6±0.1, if one is able to select more compact configurations of the projectile proton where its gluons occupy a smaller transverse area A⊥. We predict an enhanced Qpp(pT)−1∼1/(pT2)ν and a Cronin peak even for central pp collisions.

Large elliptic flow in low multiplicity pp collisions at LHC energy [formula omitted

We explore the possibility of observing elliptic flow in low multiplicity events in central pp collisions at LHC energy, s=14 TeV. It is assumed that the initial interactions produce a number of hot spots. Hydrodynamical evolution of two or more hot spots can generate sufficiently large elliptic flow to be accessible experimentally in 4th order cumulant analysis.

Experimental and theoretical indications for an intermediate σ-dressed dibaryon in the NN interaction

Numerous theoretical and experimental arguments in favor of the generation of intermediate σ-dressed dibaryon in NN interaction at middle and short distances are presented. We argue that this intermediate dibaryon should be responsible for the strong middle-range attraction and the short-range repulsion in the NN interaction, and also for the short-range correlations in nuclei. The suggested mechanism for the σ-dressing of the dibaryon is identical to that which explains the Roper-resonance structure, its dominant decay mode and its extraordinary low mass. It is arguing that the (partial) chiral symmetry restoration effects, common for the Roper resonance and dressed dibaryon, are responsible for strong renormalizing of their masses and widths and the observed σ-meson mass and decay width as well. The new experimental data on 2 π-production in the scalar–isoscalar channel produced in pn- and pd-collisions and recent data on γγ correlations in pC and dC scattering in the GeV region seems to corroborate the existence of the σ-dressed dibaryon in two- and three-nucleon interactions. A similar transformation mechanism from the glue to the scalar field can be valid also in some J/ Ψ decays and in enormous σ-meson production in central pp collisions at high energies.

Resonance production in central pp collisions at the CERN Omega Spectrometer

A study of resonance production in central pp collisions is presented as a function of several kinematical variables. In particular the difference in the transverse momentum ( dP T ) of the exchanged particles shows that undisputed q q ̄ mesons are suppressed at small dP T whereas glueball candidates are enhanced and in addition, the azimuthal angle φ gives information on the nature of the Pomeron.

The ηη systems produced in 450 GeV/c central pp collisions

New data on the ηη systems produced in the central pp collisions at 450 GeV/c proton beam momentum are presented. The data are obtained with the improved version of GAMS NA12/2 set-up with identification and vector momentum measurements of all particles in the final state. The tensor glueball candidate f2(2175) is confirmed. A structure in the 1.6 GeV mass region is compatible with f′2 (1525) and f0 (1590) contribution.

Inelastic diffraction in the quark-glue model

Diffractive dissociation of hadrons is related to the quark-glue picture of their structure. It is shown that the quark-glue model can produce sufficiently large variations of opacities for diffractive eigenstates to account for the experimental value of diffractive cross sections if unitarity is saturated in central glue-glue collisions. This requirement simplifies the collision picture and provides a natural explanation for the observed energy independence of proton opacity in central pp collisions.