Cross Section For Diffractive Dissociation Research Articles

Core destruction in knockout reactions

A model is presented to calculate projectile core destruction in knockout reactions. It incorporates physics arguments similar to the formulation of the state of the art theory to calculate stripping and diffraction dissociation cross sections in heavy ion collisions with bombarding energies around 100 MeV/nucleon and larger. It is shown that secondary collisions between the incoming and struck nucleons with the projectile core decrease the core survival probability by as much as 9.5%. However, no clear evidence is found for reduction of the cross section with increasing binding energy of the removed nucleon.

Low-mass Diffraction Dissociation at the LHC. Role of the Background

A dual model with a nonlinear proton Regge trajectory in the missing mass (M2X) channel is constructed. A background based on a direct-channel exotic trajectory, developed and applied earlier for the inclusive electron-proton cross section description in the nucleon resonance region, is used. The parameters of the model are determined from the extrapolations to earlier experiments. Predictions for the low-mass (2 < M2X < 8 GeV2) diffraction dissociation cross sections at the LHC energies are given.

Measurement of differential cross sections for single diffractive dissociation in sqrt{s} = 8 TeV pp collisions using the ATLAS ALFA spectrometer

A dedicated sample of Large Hadron Collider proton-proton collision data at centre-of-mass energy sqrt{s} = 8 TeV is used to study inclusive single diffractive dissociation, pp → X p. The intact final-state proton is reconstructed in the ATLAS ALFA forward spectrometer, while charged particles from the dissociated system X are measured in the central detector components. The fiducial range of the measurement is −4.0 < log10ξ < −1.6 and 0.016 < |t| < 0.43 GeV2, where ξ is the proton fractional energy loss and t is the squared four-momentum transfer. The total cross section integrated across the fiducial range is 1.59 ± 0.13 mb. Cross sections are also measured differentially as functions of ξ, t, and ∆η, a variable that characterises the rapidity gap separating the proton and the system X . The data are consistent with an exponential t dependence, dσ/dt ∝ eBt with slope parameter B = 7.65 ± 0.34 GeV−2. Interpreted in the framework of triple Regge phenomenology, the ξ dependence leads to a pomeron intercept of α(0) = 1.07 ± 0.09.

Measurement of differential cross sections for Single Diffractive Dissociation in [formula omitted] pp collisions using the ATLAS detector

Preliminary LHC results on proton-tagged measurements of Single Diffractive Dissociation (pp → pX) are presented from ATLAS using s=8 TeV data. The central ATLAS detector is used to reconstruct the dissociative X system, and the forward spectrometer ALFA is used to tag the intact proton. Differential cross sections are measured as a function of ξ, the fractional energy loss of the intact proton; |t|, the squared four-momentum exchanged and Δη, the observable rapidity gap. The unfolded t differential cross section is consistent with an exponential dependence dσ/dt ∝ eBt with a slope parameter B = 7.60 ± 0.32 GeV−2. The unfolded ξ differential cross section is interpreted in the framework of Regge phenomenology to extract a Pomeron intercept of α(0) = 1.07 ± 0.09.

Semiexclusive production of J/ψ mesons in proton–proton collisions with electromagnetic and diffractive dissociation of one of the protons

We calculate the cross sections for both electromagnetic and diffractive dissociation of protons for the semiexclusive production of J/ψ mesons in proton–proton collisions at the LHC. Several differential distributions in missing mass (MX), or single-particle variables related exclusively to the J/ψ meson are calculated for s=7and13 TeV. The cross sections and distributions are compared to the cross section of the purely exclusive reaction pp→ppJ/ψ. We show the corresponding ratio as a function of J/ψ meson rapidity. We compare the distributions for purely electromagnetic and purely diffractive proton excitations/dissociation. We predict cross sections for electromagnetic and diffractive excitations of similar order of magnitude.

Measurement of diffractive dissociation cross sections inppcollisions ats=7 TeV

Measurements of diffractive dissociation cross sections in pp collisions at sqrt(s) = 7 TeV are presented in kinematic regions defined by the masses M[X] and M[Y] of the two final-state hadronic systems separated by the largest rapidity gap in the event. Differential cross sections are measured as a function of xi[X]= M[X]^2/s in the region -5.5 < log[10]xi[X] < -2.5, for log[10]M[Y] < 0.5, dominated by single dissociation (SD), and 0.5 < log[10]M[Y] < 1.1, dominated by double dissociation (DD), where M[X] and M[Y] are given in GeV. The inclusive pp cross section is also measured as a function of the width of the central pseudorapidity gap Delta eta for Delta eta > 3, log[10]M[X] > 1.1, and log[10]M[Y] > 1.1, a region dominated by DD. The cross sections integrated over these regions are found to be, respectively, 2.99 +/- 0.02 (stat) +0.32 -0.29 (syst) mb, 1.18 +/- 0.02 (stat) +/- 0.13 (syst) mb, and 0.58 +/- 0.01 (stat) +0.13 -0.11 (syst) mb, and are used to extract total SD and DD cross sections. In addition, the inclusive differential cross section, d sigma /d Delta eta[F], for events with a pseudorapidity gap adjacent to the edge of the detector, is measured over Delta eta[F] = 8.4 units of pseudorapidity. The results are compared to those of other experiments and to theoretical predictions, and found compatible with slowly-rising diffractive cross sections as a function of center-of-mass energy.

A-Dependence of diffraction dissociation phenomenon in neutrino interactions with nuclei

We present results on A-dependence of diffraction dissociation (DD) phenomenon in interactions of muonic neutrino with nuclei at various values of momentum transfer. Calculations were done within the two-gluon exchange model by Nikolaev-Zakharov-Zoller(NZZ). Comparison with experimental data obtained in interactions of muonic neutrino with photoemulsion nuclei is carried out. All data are presented as ratio of the DD cross section to the deep inelastic cross section.

Diffractive dissociation in proton-nucleus collisions at collider energies

The cross section for the nuclear diffractive dissociation in proton-lead collisions at the LHC is estimated. Based on the current theoretical uncertainties for the single (target) diffactive cross section in hadron-hadron reactions one obtains $ \sigma^{pA\rightarrow pX}_{SD}(\sqrt{s}= 5.02 TeV)=19.67\pm 5.41$ mb and $ \sigma^{pA\rightarrow pX}_{SD} (\sqrt{s}=8.8 TeV) = 18.76\pm 5.77$ mb, respectively. The invariant mass MX for the reaction $ p Pb \rightarrow pX$ is also analyzed. Discussion is performed on the main theoretical uncertainties associated to the calculations.

Small-xnuclear shadowing from diffractive scattering

We calculate nuclear shadowing ratios at small Bjorken-$x$ for nuclei in the mass range $3lAl239$ in the framework of a generalized form of the Gribov theory. The diffractive dissociation cross sections needed as inputs are taken from the FNAL (Fermi National Laboratory) and HERA (Hadron-Electron Ring Accelerator) experiments. Our calculations cover a wide range of energies between 12.8 and 231 GeV. The effects of the inclusion of subleading Reggeons on nuclear shadowing are investigated. At lower energies our results are compared to available data from the New Muon Collaboration (NMC) and E665 Collaboration (E665) experiments at $x\ensuremath{\simeq}{10}^{\ensuremath{-}4}$. At higher energies subleading Reggeons are found to contribute significantly to nuclear shadowing.

Mass dependence of nuclear shadowing at small Bjorken-xfrom diffractive scattering

We calculate the nuclear shadowing ratio for a wide range of nuclei at small Bjorken-x in the framework of Gribov theory. The coherent contribution to the (virtual) photon-nucleon cross section is obtained in terms of the diffractive dissociation cross section. Information on diffraction from FNAL and HERA is used. Our results are compared to available data from the New Muon Collaboration and E665 Collaboration experiments at x{approx_equal}10{sup -4}.

The partonic interpretation of reggeon theory models

We review the physical content of the two simplest models of reggeon field theory: namely the eikonal and the Schwimmer models. The AGK cutting rules are used to obtain the inclusive, the inelastic and the diffractive cross sections. The system of non-linear equations for these cross sections is written down and analytic expressions for its solution are obtained. We derive the rapidity gap dependence of the differential cross sections for diffractive dissociation in the Schwimmer model and in its eikonalized extension. The results are interpreted from the partonic viewpoint of the interaction at high energies.

Towards the theory of coherent hard dijet production on hadrons and nuclei

We carry out a detailed calculation of the cross section of pion diffraction dissociation into two jets with large transverse momenta, originating from a hard gluon exchange between the pion constituents. Both the quark and the gluon contribution are considered and in the latter case we present calculations both in covariant and in axial gauges. We find that the standard collinear factorization does not hold in this reaction. The structure of non-factorizable contributions is discussed and the results are compared with the experimental data. Our conclusion is that the existing theoretical uncertainties do not allow, for the time being, for a quantitative extraction of the pion distribution amplitude.

Experimental estimate of the diffractive-dissociation phenomenon following neutrino interaction with photoemulsion nuclei

The first experimental estimate of the diffractive-dissociation (DD) cross section for muon-neutrino interaction with nuclei is presented. Eleven events that satisfy the DD criteria (xB 2) are found among 207 events induced by neutrino interactions with Ag and Br nuclei of nuclear photoemulsion and borrowed from the database of the E-564 experiment (FNAL). The ratio of the DD cross section to the total deep-inelastic cross section for the charged current is 0.29±0.09. Four of the 11 events proved to be candidates for events of coherent DD.

Calculation of the cross section for the pion diffractive dissociation into two jets

Contribution of the gluon distribution in the nucleon to the cross section for the pion diffractive dissociation into two jets has been calculated recently. In addition, we present here calculation of contribution of the quark distributions to this process. It is expected usually that the quark contributions are much smaller than the gluon one at high energies. We show that, under the conditions of the E791 experiment, the quark contributions are as significant as the gluon one, so that the total cross section exceeds several times those with only gluon contribution. Nevertheless, the distribution of jets in longitudinal momentum fractions does not change significantly and remains qualitatively the same. We compare our results with the data from the E791 experiment.

QCD factorization for the pion diffractive dissociation to two jets

We calculate the cross section of a pion diffraction dissociation in two jets with large transverse momenta originating from a hard gluon exchange between the pion constituents. To the leading logarithmic accuracy (in energy), the contribution coming from small transverse separations between the quark and the antiquark in the pion acquires the expected factorized form, the longitudinal momentum distribution of the jets being proportional to the pion distribution amplitude. The hard gluon exchange can in this case be considered as a part of the unintegrated gluon distribution. Beyond the leading logarithms (in energy) this proportionality does not hold. Moreover, the collinear factorization appears to be broken by the end-point singularities. Remarkably enough, the longitudinal momentum distribution of the jets for the non-factorizable contribution is calculable, and turns out to be the same as for the factorizable contribution with the asymptotic pion distribution amplitude.

A pomeron approach to hadron–nucleus and nucleus–nucleus “soft” interaction at high energy

We formulate a generalization of the Glauber formalism for hadron–nucleus and nucleus–nucleus collisions based on the pomeron approach to high-energy interaction. Our treatment is based on two physical assumptions (i.e. two small parameters): (i) that only sufficiently small distances contribute to the pomeron structure; and (ii) the triple-pomeron vertex G3P/gPN≪1 (where gPN is the pomeron–nucleon vertex) is small. A systematic method is developed for calculating the total, elastic and diffractive dissociation cross sections as well as the survival probability of large rapidity gap processes and inclusive observables, both for hadron–nucleus and nucleus–nucleus collisions. Our approach suggests saturation of the density of the produced hadrons in nucleus–nucleus collisions, the value of the saturation density turns out to be large.

Shadowing corrections and diffractive production in DIS on nuclei

We calculate, in the Glauber–Mueller approach, the ratio of the diffractive dissociation cross section to the total cross section for nuclei. We observe that shadowing corrections (SC) in the calculated σ diff/ σ tot ratio are significant, but they do not lead to a smooth energy dependence of the ratio for a proton target as was observed at HERA.

Diffractive dissociation including multiple pomeron exchanges in high parton density QCD

We derive an evolution equation describing the high energy behavior of the cross section for the single diffractive dissociation in deep inelastic scattering on a hadron or a nucleus. The evolution equation resums multiple BFKL pomeron exchanges contributing to the cross section of the events with large rapidity gaps. Analyzing the properties of an approximate solution of the proposed equation we point out that at very high energies there is a possibility that for a fixed center of mass energy the cross section will reach a local maximum at a certain intermediate size of the rapidity gap, or, equivalently, at some non-zero value of the invariant mass of the produced particles.

Introduction to session C: Total cross sections and diffraction

A brief introduction to total, elastic, and diffraction dissociation cross sections is given. Data measured in pp p , γp, and γγ scattering are reviewed and their phenomenological interpretation in terms of geometrical models is discussed.

Unitarized model of hadronic diffractive dissociation.

It is shown that in a supercritical Pomeron model the contribution of the triple-Pomeron diagrams violates the unitarity bound for the cross section even when taking into account the multiple Pomeron exchanges between the initial hadrons. The asymptotic behavior of the single diffractive dissociation cross section is calculated in the approximation where every Pomeron in the $3P$ diagram is eikonalized as well as an elastic interaction of initial hadrons is taken into account. In this approximation $\frac{{\ensuremath{\sigma}}^{\mathrm{SD}}}{{\ensuremath{\sigma}}_{\mathrm{tot}}}\ensuremath{\rightarrow}0$, at $s\ensuremath{\rightarrow}\ensuremath{\infty}$.