Large Rapidity Gap Research Articles

Three-jet production in diffractive deep inelastic scattering at HERA

Three-jet production in the reaction ep --> eXp has been studied with the ZEUS detector at HERA using an integrated luminosity of 42.74 pb^-1. The data were measured in the kinematic region 5 < Q^2 < 100 GeV^2, 200 < W < 250 GeV and 23 < M_X < 40 GeV. The diffractive signal was selected by requiring a large rapidity gap in the outgoing proton direction. Jets were reconstructed in the centre-of-mass system of X using the exclusive k_T-algorithm. A sample of three-jet events in diffraction has been identified. Differential cross sections were measured as a function of the jet pseudorapidity and jet transverse momentum with respect to the virtual photon-Pomeron axis. The jets going in the Pomeron direction are broader than those going in the virtual-photon direction. This is consistent with models predicting that gluons are predominantly produced in the Pomeron direction and quarks in the virtual-photon direction.

High $p_T$ Higgs signal for the LHC

We show that the broad transverse momentum distribution of the Higgs boson produced by WW fusion can provide a viable way to identify H --> b anti-b decays at the LHC, if particular kinematical configurations with large rapidity gaps are selected. We estimate the event rate of the signal and of the QCD b anti-b background. We also discuss Higgs boson detection via the H --> tau tau and H --> WW* decay modes.

Survival probability of large rapidity gaps inp¯p, pp, γp,andγγcollisions

Using an eikonal analysis, we simultaneously fit a QCD-inspired parametrization of all accelerator data on forward proton-proton and antiproton-proton scattering amplitudes, together with cosmic ray data (using Glauber theory), to predict proton-air and proton-proton cross sections at energies near $\sqrt{s}\ensuremath{\approx}30 \mathrm{TeV}.$ The p-air cosmic ray measurements greatly reduce the errors in the high energy proton-proton and proton-air cross section predictions---in turn, greatly reducing the errors in the fit parameters. From this analysis, we can then compute the survival probability of rapidity gaps in high energy $\overline{p}p$ and $\mathrm{pp}$ collisions, with high accuracy in a quasi-model-free environment. Using an additive quark model and vector meson dominance, we note that the survival probabilities are identical, at the same energy, for $\ensuremath{\gamma}p$ and $\ensuremath{\gamma}\ensuremath{\gamma}$ collisions, as well as for nucleon-nucleon collisions. Significantly, our analysis finds large values for gap survival probabilities: $\ensuremath{\approx}30%$ at $\sqrt{s}=200 \mathrm{GeV},$ $\ensuremath{\approx}21%$ at $\sqrt{s}=1.8 \mathrm{TeV}$ and $\ensuremath{\approx}13%$ at $\sqrt{s}=14 \mathrm{TeV}.$

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.

Diffractive jet production in deep-inelastic $e^+p$ collisions at HERA

A measurement is presented of dijet and 3-jet cross sections in low-\(|t|\) diffractive deep-inelastic scattering interactions of the type \(ep \rightarrow eXY\), where the system X is separated by a large rapidity gap from a low-mass baryonic system Y. Data taken with the H1 detector at HERA, corresponding to an integrated luminosity of 18.0 pb\(^{-1}\), are used to measure hadron level single and double differential cross sections for \(4 4 \rm GeV\). The energy flow not attributed to jets is also investigated. The measurements are consistent with a factorising diffractive exchange with trajectory intercept close to 1.2 and tightly constrain the dominating diffractive gluon distribution. Viewed in terms of the diffractive scattering of partonic fluctuations of the photon, the data require the dominance of \(q\overline{q}g\) over \(q\overline{q}\) states. Soft colour neutralisation models in their present form cannot simultaneously reproduce the shapes and the normalisations of the differential cross sections. Models based on 2-gluon exchange are able to reproduce the shapes of the cross sections at low \(x_\mathbb{P}\) values.

Dijet Production by Double Pomeron Exchange at the Fermilab Tevatron

We report the first observation of dijet events with a double Pomeron exchange topology produced in &pmacr;p collisions at sqrt[s] = 1800 GeV. The events are characterized by a leading antiproton, two jets in the central pseudorapidity region, and a large rapidity gap on the outgoing proton side. We present results on jet kinematics and production rates, compare them with corresponding results from single diffractive and inclusive dijet production, and test factorization.

Gluon fragmentation into glueballs and hybrid mesons

The constituent nature of candidate gluonic mesons can be studied by comparing their production in quark and gluon jets. The production rate for such mesons depends on the colour confinement processes at the end of the perturbative evolution. Whereas we expect enhanced production of hybrids in the fragmentation region of a gluon jet, the rate for glueballs depends on the relative importance of colour triplet and colour octet neutralization. These neutralization processes can be studied independently in events with large rapidity gaps. If octet processes turn out important the recently suggested lightest J PC =0 ++ glueball with mass around 1000 MeV should become visible already in the spectrum of the leading charged particle pairs.

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.

Soft colour interactions in non-perturbative QCD

Improved understanding of non-perturbative QCD dynamics can be obtained in terms of soft colour exchange models. Their essence is the variation of colour string-field topologies giving a unified description of final states in high energy interactions. In particular, both events with and without large rapidity gaps are obtained in agreement with data from ep at HERA and ppbar at the Tevatron, where also the surprisingly large production rate of high-p_T charmonium and bottomonium is reproduced.

Hard colour singlet exchange at the Tevatron

We have performed a detailed phenomenological investigation of the hard colour singlet exchange process which is observed at the Tevatron in events which have a large rapidity gap between outgoing jets. We include the effects of multiple interactions to obtain a prediction for the gap survival factor. Comparing the data on the fraction of gap events with the prediction from BFKL pomeron exchange we find agreement provided that a constant value of alpha_s is used in the BFKL calculation. Moreover, the value of alpha_s is in line with that extracted from measurements made at HERA.

Survival probability of large rapidity gaps in a three channel model

The values and energy dependence for the survival probability $ $ of large rapidity gaps (LRG) are calculated in a three channel model. This model includes single and double diffractive production, as well as elastic rescattering. It is shown that $ $ decreases with increasing energy, in line with recent results for LRG dijet production at the Tevatron. This is in spite of the weak dependence on energy of the ratio $ (\sigma_{el}+ \sigma_{SD})/\sigma_{tot}$.

High-t diffraction at HERA

The double dissociation photoproduction cross section for the process γp → XY, in which the systems X and Y are separated by a large rapidity gap, is measured at large 4-momentum transfer squared φtφ > 20GeV 2 by the H1 Collaboration at HERA. This measurement provides for the first time a direct measurement of the energy dependence of the gap production process at high φtφ.

Diffractive dijet production at HERA

Cross sections for events of the type ep → eXY, where the systems X and Y are separated by a large rapidity gap and X contains two jets, are presented for both deep inelastic scattering and photoproduction, measured using data from the H1 experiment at HERA. The corrected cross sections are described by a resolved pomeron model with parton densities for the pomeron which were obtained from a QCD analysis of F 2 D(3) from H1.

Survival probability in hadron-hadron interactions

The values and energy dependence for the survival probability < | S| 2 > of large rapidity gaps (LRG) are calculated in a three channel model. We find that < | S| 2 > decreases with increasing energy, in line with recent results for LRG dijet production at the Tevatron.

Diffractive [formula omitted](2010) production in deep inelastic scattering from ZEUS

Measurements of diffractive D ∗± production in deep inelastic scattering using the 1995–1997 ZEUS data are presented. Diffractive e + p → e + X N interactions are identified by the presence of a large rapidity gap in the final state. D ∗± candidates are identified from the D ∗ → D ∗ → D 0π decay mode, where the D 0 subsequently decays either to K − π + + (c.c.) or K − π + π − π + (c.c.). The integrated D ∗± cross section along with differential D ∗± cross sections as a function of Q 2, W, x p, p T (D ∗±) and ν(D ∗±) have been measured in a limited kinematic region. The fraction of D ∗± events produced diffractively has also been measured.

Analysis of rapidity gap cuts in diffractive DIS

The requirement of a large pseudo-rapidity gap to select diffractive DIS events at HERA restricts the kinematically accessible region of phase space for a significant range of Q 2, β and x p . Consequences of this include a breakdown of x p -factorization in large rapidity gap diffractive samples and an enhancement in the relative contribution of quark-antiquark-gluon processes over dijet processes in the diffractive DIS sample.

Semi-exclusive processes: new probes of hadron structure

We define and study hard “semi-exclusive” processes of the form A+ B→ C+ Y which are characterized by a large momentum transfer between the particles A and C and a large rapidity gap between the final state particle C and the inclusive system Y. Such reactions are in effect generalizations of deep inelastic lepton scattering, providing novel currents which probe specific quark distributions of the target B at fixed momentum fraction. We give explicit expressions for photo- and leptoproduction cross sections such as γp→ πY in terms of parton distributions in the proton and the pion distribution amplitude. Semi-exclusive processes provide opportunities to study fundamental issues in QCD, including odderon exchange and color transparency, and suggest new ways to measure spin-dependent parton distributions.

Hunting a light U(1) B gauge boson coupled to baryon number in collider experiments

We analyze several signals at HERA and the Tevatron of a light U(1) B gauge boson ( γ B ) coupling to baryon number. We show that the study of the production of b b ̄ pairs at the (upgraded) Tevatron can exclude γ B with masses ( m B ) in the range 40≲ m B ≲300 GeV for γ B couplings ( α B ) greater than 2×10 −2 (3×10 −3). We also show that the HERA experiments cannot improve the present bounds on γ B . Moreover, we demonstrate that the production at HERA and the Tevatron of di-jet events with large rapidity gaps between the jets cannot be explained by the existence of a light γ B .

Survival probability of large rapidity gaps

We summarize the discussions on the value of the survival probabilities of the large rapidity gap processes at Durham Workshop '98.

Energy dependence of the survival probability of large rapidity gaps

The energy dependence for the survival probability of large rapidity gaps (LRG) <∣ S∣ 2>, is calculated in an Eikonal model assuming a Gaussian opacity. The parameters determining <∣ S∣ 2> are evaluated directly from experimental data, without further recourse to models. We find that <∣ S∣ 2> decreases with increasing energy, in line with recent results for LRG dijet production at the Tevatron.