Hadronic Diffraction Research Articles

Unitarity and the Finkelstein-Kajantie problem in diffractive hadron production

The diffraction production of many hadron showers separated by large rapidity gaps, when calculated within the standard pomeron approach, lead to cross sections rising much faster than Froissart-Martin bound. This is the point of Finkelstein-Kajantie problem. We consider the unitarization procedure based on Dyson-Schwinger equations with input froissaron propagators and 3-froissaron vertex (3f-vertex) depending on angular momenta of froissarons in it. The developed diffraction production model allows to resolve Finkelstein-Kajantie problem.

Hard hadronic diffraction is not hard

Hadronic diffractive processes characterized by a hard scale (hard diffraction) contain a nontrivial interplay of hard and soft, nonperturbative interactions, which breaks down factorization of short and long distances. On the contrary to the expectations based on the factorization hypothesis, assuming that hard diffraction is a higher twist, these processes should be classified as a leading twist. We overview various implications of this important observation for diffractive radiation of Abelian (Drell–Yan, gauge bosons, Higgs boson) and non-Abelian (heavy flavors) particles, as well as direct coalescence into the Higgs boson of the nonperturbative intrinsic heavy flavor component of the hadronic wave function.

A new timing detector for the CT-PPS project

The CT-PPS detector will be installed close to the beam line on both sides of CMS, 200m downstream the interaction point. This detector will measure forward scattered protons, allowing detailed studies of diffractive hadron physics and Central Exclusive Production. The main components of the CT-PPS detector are a silicon tracking system and a timing system. In this contribution we present the proposal of an innovative solution for the timing system, based on Ultra-Fast Silicon Detectors (UFSD). UFSD are a novel concept of silicon detectors potentially able to obtain the necessary time resolution (∼20ps on the proton arrival time). The use of UFSD has also other attractive features as its material budget is small and the pixel geometries can be tailored to the precise physics distribution of protons. UFSD prototypes for CT-PPS have been designed by CNM (Barcelona) and FBK (Trento): we will present the status of the sensor productions and of the low-noise front-end electronics currently under development and test.

Hadron Diffraction: Results and Problems

This is a cursory review of diffractive studies ( mostly elastic scattering)at the LHC with physical interpretation of the experimental data and comments to related problems of theory.

Diffractive hadron production at ultrahigh energies

Diffractive production is considered in the ultrahigh energy region where pomeron exchange amplitudes are transformed into black disk ones due to rescattering corrections. The corresponding corrections in hadron reactions h1 + h3 → h1 + h2 + h3 with small momenta transferred [Formula: see text] are calculated in terms of the K-matrix technique modified for ultrahigh energies. Small values of the momenta transferred are crucial for introducing equations for amplitudes. The three-body equation for hadron diffractive production reaction h1 + h3 → h1 + h2 + h3 is written and solved precisely in the eikonal approach. In the black disk regime final state scattering processes do not change the shapes of amplitudes principally but dump amplitudes by a factor ~ ¼; initial state rescatterings result in additional factor ~ ½. In the resonant disk regime initial and final state scatterings damp strongly the production amplitude that corresponds to σ inel /σ tot → 0 at [Formula: see text] in this mode.

Double pomeron exchange at the CERN Intersecting Storage Rings and $Sp\bar{p}S$ Collider

The CERN Intersecting Storage Rings, with [Formula: see text] from 22 GeV to 63 GeV and [Formula: see text], allowed the first observations of p + p → p + X + p with two leading protons (xF > 0.95) or two rapidity gaps Δy > 3. Studies of the central hadronic system (X) were made to search for glueballs, finding f0 and f2 resonances, and to advance our understanding of hadronic diffraction. I review the experiments, not including those at the Split Field Magnet (SFM) facility covered elsewhere in this volume. Some double pomeron exchange studies at the CERN [Formula: see text] Collider are also covered.

Forward physics of hadronic colliders

These lectures were given at the Baikal Summer School on Physics of Elementary Particles and Astrophysics in July 2012. They can be viewed as a concise introduction to hadronic diffraction, to the physics of the Pomeron and related topics.

THE POMERON AND ODDERON IN ELASTIC, INELASTIC AND TOTAL CROSS-SECTIONS AT THE LHC

A simple model for elastic diffractive hadron scattering, reproducing the dip-bump structure is used to analyze pp and [Formula: see text] scattering. The main emphasis is on the delicate and nontrivial dynamics in the dip-bump region, near t = -1 GeV 2. The simplicity of the model and the expected smallness of the absorption corrections enables one the control of various contributions to the scattering amplitude, in particular the interplay between the C-even and C-odd components of the amplitude, as well as their relative contribution, changing with s and t. The role of the nonlinearity of the Regge trajectories is scrutinized. The ratio of the real to imaginary parts of the forward amplitude, the ratio of elastic to total cross-sections and the inelastic cross-section are calculated. Predictions for the LHC energy region, where most of the existing models will be either confirmed or ruled out, are presented.

Diffractive hadron production in deep inelastic scattering off heavy nuclei and gluon saturation

We calculate the cross section for diffractive hadron production in deep inelastic scattering off heavy nuclei in the framework of gluon saturation/color glass condensate. We analyze the kinematic region of the future Electron-Ion Collider. We argue that coherent and incoherent diffractive channels are very sensitive to the structure of the nuclear matter at low $x$. This expresses itself in a characteristic dependence of the cross sections on rapidity and transverse momentum of the produced hadron and on the nuclear weight. We also discuss dependence on the scattering angle and argue that both coherent and incoherent cross sections may be within experimental reach at Electron-Ion Collider.

Radion production in exclusive processes at CERN LHC

In the Randall-Sundrum (RS) scenario the compactification radius of the extra dimension is stabilized by the radion, which is a scalar field lighter than the graviton Kaluza-Klein states. It implies that the detection of the radion will be the first signature of the stabilized RS model. In this paper we study the exclusive production of the radion in electromagnetic and diffractive hadron - hadron collisions at the LHC. Our results demonstrate that the diffractive production of radion is dominant and should be feasible of study at CERN LHC.

Coherent and incoherent diffractive hadron production inpAcollisions and gluon saturation

We study coherent and incoherent diffractive hadron production in high-energy quarkonium―heavy nucleus collisions as a probe of the gluon saturation regime of quantum chromodynamics. Taking this process as a model for pA collisions, we argue that the coherent diffractive gluon production, in which the target nucleus stays intact, exhibits a remarkable sensitivity to the energy, rapidity, and atomic number dependence. The incoherent diffractive gluon production is less sensitive to the details of the low-x dynamics but can serve as a probe of fluctuations in the color glass condensate. As a quantitative measure of the nuclear effects on diffractive hadron production we introduce a new observable―the diffractive nuclear modification factor. We discuss possible signatures of gluon saturation in diffractive gluon production at the Relativistic Heavy Ion Collider, the Large Hadron Collider, and Electron Ion Collider.

Probing the low-xstructure of nuclear matter with diffractive hadron production inpAcollisions

We argue that hadron production in coherent diffraction of protons on a heavy nucleus provides a very sensitive probe of the low-$x$ QCD dynamics. This process probes the BFKL dynamics in protons and the nonlinear gluon evolution in nuclei. We calculate the diffractive hadron production cross sections in the BNL Relativistic Heavy Ion Collider (RHIC) and CERN Large Hadron Collider (LHC) kinematic regions. To study the nuclear effects we introduce the diffractive nuclear modification factor. We show that, unlike the nuclear modification factor for inclusive hadron production that has very interesting dynamics at RHIC but is expected to be almost completely saturated at the LHC, the nuclear modification factor for diffractive production exhibits a nontrivial behavior at both RHIC and LHC.

Double parton scattering, diffraction, and effective cross section

The rates of multiparton collisions in high energy hadronic interactions provide information on the typical transverse distances between partons in the hadron structure. The different configurations of the hadron in transverse space are, on the other hand, at the origin of hadron diffraction. The relation between the two phenomena is explored in an eikonal model of hadronic interactions.

Glue drops inside hadrons

We present experimental evidences for the existence of a semi-hard scale in light hadrons. This includes the suppression of gluon radiation that is seen in high mass hadron diffraction; the weak energy dependence of hadronic total cross sections; the small value of the Pomeron trajectory slope measured in photoproduction of J / Ψ ; the weakness of gluon shadowing in nuclei; shortage of gluons in the proton revealed by an unusual behavior of the proton structure function in the soft limit, and the enhanced intrinsic transverse momentum of quarks and gluons, which considerably exceeds the inverse hadronic size. All these observations suggest that gluons in hadrons are located within spots of a small size relative to the confinement radius.

Survival probability of large rapidity gaps in a QCD model with a dynamical infrared mass scale

Abstract We compute the survival probability 〈 | S | 2 〉 of large rapidity gaps (LRG) in a QCD based eikonal model with a dynamical gluon mass, where this dynamical infrared mass scale represents the onset of nonperturbative contributions to the diffractive hadron–hadron scattering. Since rapidity gaps can occur in the case of Higgs boson production via fusion of electroweak bosons, we focus on W W → H fusion processes and show that the resulting 〈 | S | 2 〉 decreases with the increase of the energy of the incoming hadrons, in line with the available experimental data for LRG. We obtain 〈 | S | 2 〉 = 27.6 ± 7.8 % ( 18.2 ± 7.0 % ) at Tevatron (CERN-LHC) energy for a dynamical gluon mass m g = 400 MeV .

QCD ASPECTS OF HADRONIC DIFFRACTION

Experimental results on soft and hard diffractive processes obtained by the CDF Collaboration in [Formula: see text] interactions are examined with emphasis on regularities that point to QCD aspects of hadronic diffraction. Data are interpreted in a phenomenological approach in which diffractive cross sections are related to the underlying inclusive parton distribution functions of the nucleon. In this approach, diffraction appears to be mediated by the exchange of low-x partons subject to color constraints.

Inclusive inelastic hadron diffraction

We show that angular distributions of the inclusive hadron inelastic diffraction at small momentum transfers are determined by elastic scattering in the transition region between the forward peak and the diffractive minimum. This is due to a multi-channel correction, accounting for intermediate transitions inside an equivalence class of diffractive states,which factorizes in the form N Δ t to be taken in the Bjorken-like limit: N → ∞ , Δ t → 0 such that N Δ t is finite.

Diffractive hadroproduction of dijets andW’s at the Fermilab Tevatron collider and the Pomeron structure function

Results from a phenomenological analysis of dijet and W hard diffractive hadroproduction at Fermilab Tevatron energies are reported. The theoretical framework employed here is a modified version of the Ingelman-Schlein approach which includes DGLAP-evolved structure functions. Different from what has been achieved by the DESY ep HERA reactions, a reasonable overall description of such diffractive hadron processes is obtained only when a complex, quark-rich Pomeron structure function is employed in the calculation.

Coulomb induced diffraction of energetic hadrons into jets

The electromagnetic (e.m.) current conservation and renormalizability of QCD are used to calculate the amplitude of energetic hadron(photon) diffraction into several jets with large relative transverse momenta off the nucleon(nucleus) Coulomb field. Numerical estimates of the ratio of e.m. and strong amplitudes show that within the kinematic range where the leading twist approximation for the strong amplitude is applicable, the e.m. contribution can be neglected. In pA scattering at LHC and in the fragmentation of a photon into two jets in ultraperipheral AA collisions in the black limit (which maybe realistic at LHC) e.m. contribution may win.

Transverse spin effects in diffractive hadron leptoproduction

We consider double spin asymmetries for longitudinally polarized leptons and transversely polarized protons in diffractive vector meson and $Q \bar Q$ production at high energies within the two-gluon model. The asymmetry predicted for meson production is quite small. The $A_{lT}$ asymmetry for $Q \bar Q$ production contains two independent terms which are large and can be used to obtain information on the polarized gluon distributions in the proton.