arXiv subjects
Publications and source records attributed to I. M. Dremin.
It is shown that the impact parameter profile of inelastic hadron collisions is robust to admissible variations of the shape of the diffraction cone of elastic scattering. This conclusion is obtained using the unitarity condition and experimental data only with no phenomenological model inputs.
Experimental findings of CMS on properties of jets and underlying events at high multiplicities in proton-proton interactions at 7 TeV are interpreted as an indication of increasing role of central collisions with small impact parameters. We find an indication that the rates of different hard processes observed by CMS and ALICE universally depend on underlying event charged-particles multiplicity until it becomes four times more than average. It is shown that the increase of the overlap area of colliding protons is not sufficient for explanation of the rate of jet production in events with charged-particle multiplicity three times higher than average and some new mechanisms are necessary like interaction of protons in rare configurations of higher than average gluon density. Such mechanisms are not included in the present Monte Carlo event generators. Further studies are proposed
We show that the interaction region of colliding protons looks completely absorptive (black) at the impact parameters up to 0.4 - 0.5 fm at the LHC energy 7 TeV. It is governed by the ratio of the elastic diffraction peak slope to the total cross section. The corresponding parameter is approximately equal to 1 at the LHC. The behavior of this ratio at higher energies will show if this region will evolve to the black disk or to the black torus. Recent fits at 7 TeV can not distinguish between these possibilities within the limits of experimental indefiniteness and of extrapolations in the regions of unmeasured transferred momenta.
It is shown that the darkness of the interaction region of protons is governed by the ratio of the slope of the diffraction cone to the total cross section. At LHC energies, it becomes completely absorptive at small impact parameters. The lower limit of the ratio is determined. That imposes some restrictions on its energy behavior. It is argued that the black disk terminology should be replaced by the black torus.
When colliding, the high energy hadrons can either produce new particles or scatter elastically without change of their quantum numbers and other particles produced. Namely elastic scatterings of hadrons are considered in this paper. The general machinery of their theoretical treatment is described. Some new experimental data are presented and confronted to phenomenological approaches. The internal structure of hadrons is the main subject of these studies. Its impact on properties of their interactions is reviewed. It is shown that protons become larger and darker with increase of their collision energy and reveal some substructure. The violation of the geometric scaling in the diffraction cone and new problems of description of differential cross sections outside it are described.
Three main statements are advocated in this talk: 1. Protons become more active at the periphery with increase of their collision energy as follows from comparison of ISR and LHC data. 2. The geometric scaling is violated even in the diffraction region as follows from comparison of lower energy and LHC data. 3. The problem of the ratio of real to imaginary parts of the elastic scattering amplitude at non-zero transferred momenta is very crucial. The talk is based on arXiv:1206.5474 (review), 1202.2016, 1204.1914, 1204.4866, 1208.3073, 1209.1935, 1212.3313, 1304.5345, 1306.5384. All papers have been published already.
It is shown that protons become more active at the periphery with increase of their collision energy. By computing the impact parameter distribution of the proton-proton overlap function at LHC energies and comparing it with ISR (and S$p\bar p$S for $p\bar p$) data, we conclude that the peripheral region of protons plays an increasing role in the rise of total cross sections through multiparticle dynamics. The size of the proton as well as its blackness increase with energy. The protons become more black both in the central region and, especially, at the periphery. This effect can be related to the ridge phenomenon and to the inelastic diffraction processes at LHC energies.
A short review of the two recently analyzed collective effects in dense non-Abelian matter, the photon and dilepton production in nonequilibrium glasma and polarization properties of turbulent Abelian and non-Abelian plasmas, is given.
The impact of different assumptions about high energy behavior of the total cross section of proton-proton interactions on the ratio of the real to imaginary part of the forward elastic scattering amplitude is analyzed. It is shown how experimental data about this ratio at LHC energies can help in the proper choice of the asymptotic dependence of the total cross section.
Colliding high energy hadrons either produce new particles or scatter elastically with their quantum numbers conserved and no other particles produced. We consider the latter case here. Although inelastic processes dominate at high energies, elastic scattering contributes considerably (18-25%) to the total cross section. Its share first decreases and then increases at higher energies. Small-angle scattering prevails at all energies. Some characteristic features are seen that provide informationon the geometrical structure of the colliding particles and the relevant dynamical mechanisms. The steep Gaussian peak at small angles is followed by the exponential (Orear) regime with some shoulders and dips, and then by a power-law drop. Results from various theoretical approaches are compared with experimental data. Phenomenological models claiming to describe this process are reviewed. The unitarity condition predicts an exponential fall for the differential cross section with an additional substructure to occur exactly between the low momentum transfer diffraction cone and a power-law, hard parton scattering regime under high momentum transfer. Data on the interference of the Coulomb and nuclear parts of amplitudes at extremely small angles provide the value of the real part of the forward scattering nuclear amplitude. The real part of the elastic scattering amplitude and the contribution of inelastic processes to the imaginary part of this amplitude (the so-called overlap function) at nonforward transferred momenta are also discussed. Problems related to the scaling behavior of the differential cross section are considered. The power-law regime at highest momentum transfer is briefly described.
Theoretical proposals of scaling laws for the differential elastic scattering cross sections of protons are confronted with experimental data over a wide energy range. Different combinations of the transferred momentum and energy resulting from the solution of the definite partial differential equation are attempted as scaling variables. Reasonable scaling of the differential cross sections in the diffraction cone has been shown for one of these variables. The violation of the geometrical scaling is ascribed to the increase of the proton blackness with energy. The origin of high-t region violations of scaling laws is discussed.
The partial differential equation for the imaginary part of the elastic scattering amplitude is derived. It is solved in the black disk limit. The asymptotical scaling behavior of the amplitude coinciding with the geometrical scaling is proved. Its extension to preasymptotical region and modifications of scaling laws for the differential cross section are considered.
The s-channel unitarity condition for the imaginary part of the hadronic elastic scattering amplitude outside the diffraction peak is studied within different assumptions about the behavior of its real part. The integral equation for the imaginary part is derived with the asymptotical expression for the real part inserted in the unitarity condition. The conclusions about the asymptotical approach to the black disk limit and possible zeros of the imaginary part of the amplitude are obtained. Their relation to the present day experiments is discussed.
It is argued that the very first signatures of the approach to the black disk asymptotical limit in hadron collisions may be observed in the differential cross section of elastic scattering. The exponentially decreasing with the angle (or $\sqrt {|t|}$) regime beyond the diffraction peak will become replaced by an oscillatory behavior or by the power-like falloff. Some estimates of energies where this can happen are presented.
The model-independent solution of the s-channel unitarity condition for the imaginary part of the hadronic elastic scattering amplitude outside the diffraction peak allows to make conclusions about its real part at nonzero transferred momenta. The asymptotical properties of the ratio of the real to imaginary part of the amplitude are discussed. In particular, it is explicitly shown that the ratio changes its sign at a defnite value of the transferred momentum. Some comments concerning the present day experimental results about the behavior of the differential cross-section of elastic scattering outside the diffraction cone are given.
The unitarity condition unambigously requires the Orear region to appear in between the diffraction cone at low transferred momenta and hard parton scattering regime at high transferred momenta in hadron elastic scattering. It originates from rescattering of the diffraction cone processes. It is shown that such region has been observed in the differential cross section of the elastic pp-scattering at \sqrt s=7 TeV. The Orear region is described by exponential decrease with the scattering angle and imposed on it damped oscillations. They explain the steepening at the end of the diffraction cone as well as the dip and the subsequent maximum observed in TOTEM data. The failure of several models to describe the data in this region can be understood as improper account of the unitarity condition. It is shown that the real part of the amplitude can be as large as the imaginary part in this region. The overlap function is calculated and shown to be small outside the diffraction peak. Its negative sign there indicates the important role of phases in the amplitudes of inelastic processes.
We analyse the multiplicity distributions of charged particles at Tevatron (p\bar p) and LHC (pp) energies in the framework of the independent pair parton interactions (IPPI) model. It is shown that the number of soft pair parton interactions (and therefore the density of the partonic medium) is large and increases with energy. The mean multiplicity at each parton interaction grows also with energy. This growth depends on the width of the rapidity window. The similar conclusions are obtained in the multiladder exchange model (QGSM).
It is shown that the soft mechanism of multiparticle production by Lund hadronic strings formed by colliding constituent degrees of freedom generates a shape of angular correlations similar to the ridge structure observed in the pp collisions at 7 TeV at the LHC.