Double Pomeron Exchange Processes Research Articles

Central Exclusive Production in pp collisions at LHCb

Central Exclusive Production (CEP) is a unique process at hadron machines in which particles are produced via colourless propagators, and several measurements at the LHC are directly comparable with past and future electron-ion colliders. LHCb have measured the cross-sections for the CEP of vector mesons, J /ψ,ψ (2S ),ϒ(1S ), ϒ(2S ) and ϒ(3S ), which are photo-produced. In the double Pomeron exchange process, preliminary measurements have been made of χ c 0 , χ c 1 , χ c 2 meson production while the first observations of the CEP of pairs of charmonia, J /ψJ /ψ and J/ψψ (2S ), have been made and limits obtained on the pair production of other charmonia.

Central Exclusive Production in Proton-Proton Collisions with the STAR Experiment at RHIC

We shall describe the physics program with tagged forward protons, focusing on Central Exclusive Production in polarized proton-proton collisions at the Relativistic Heavy Ion Collider (RHIC), with the STAR detector at √ s = 200 GeV. Preliminary results in CEP of two oppositely charged pions and kaons produced in the processes pp → ppπ + π − and pp → ppK + K − shall be presented. Those Double Pomeron Exchange (DPE) processes, allow the final states to be dominated by gluonic exchanges. Silicon strip detectors placed in Roman Pots were used for measuring forward protons. The preliminary results are based on the measurement of the recoil system of charged particles in the STAR experiment’s Time Projection Chamber (TPC). Ionization energy loss, dE/dx, of charged particles was used for particle identification (PID).

A review of central production experiments at the CERN Omega spectrometer

The non-Abelian nature of QCD suggests that particles that have a gluon constituent, such as glueballs or hybrids, should exist. This paper presents a study of central meson production in the fixed target experiments WA76, WA91 and WA102 at the CERN Omega spectrometer at centre-of-mass energies of [Formula: see text], 23.8 and 29 GeV. A study of the resonance production cross-section as a function of [Formula: see text] shows which states are compatible with being produced by Double Pomeron Exchange (DPE). In these DPE processes, the difference in the transverse momentum between the exchange particles (dPT) can be used to select out known [Formula: see text] states from non-[Formula: see text] candidates. The distribution of the azimuthal angle (ϕ) between the two exchange particles suggests that the Pomeron transforms like a nonconserved vector current. Finally there is evidence from an analysis of the decay modes of the scalar states observed, that the lightest scalar glueball manifests itself through the mixing with nearby [Formula: see text] states.

Central exclusive production at RHIC

The present status and future plans of the physics program of Central Exclusive Production (CEP) at RHIC are described. The measurements are based on the detection of the forward protons from the Double Pomeron Exchange (DPE) process in the Roman Pot system and of the recoil system of charged particles from the DPE process measured in the STAR experiment's Time Projection Chamber (TPC). The data described here were taken using polarized proton–proton collisions at [Formula: see text]. The preliminary spectra of two-pion mass reconstructed by STAR TPC in central region of pseudorapidity |η| < 1, are presented. Near future plans to take data with the current system at center-of-mass energy [Formula: see text] and plans to upgrade the forward proton tagging system are presented. Also a possible addition of the RPs to the sPHENIX detector is discussed.

Probing the Pomeron structure using dijets andγ+jetevents at the LHC

We consider hard diffractive events in proton-proton collisions at the LHC, in which both protons escape the collision intact. In such double Pomeron exchange processes, we propose to measure dijets and photon-jet final states, and we show that it has the potential to pin down the Pomeron quark and gluon contents, a crucial ingredient in the standard QCD description of hard diffraction. By comparing with predictions of the soft color interaction approach, we also show that more generally, the measurement of the photon-jet to dijet cross section ratio can put a stringent test on the QCD dynamics at play in diffractive processes in hadronic collisions.

PRESENT AND FUTURE OF CENTRAL PRODUCTION WITH STAR DETECTOR AT RHIC

The present status and future physics program of Central Production using the STAR detector at RHIC will be described. The program focuses on particle production resulting from the Double Pomeron Exchange (DPE) process. Forward protons from the DPE interaction are detected in the Roman Pot system installed at 55.5 m and 58.5 m on both sides of the STAR interaction point. The recoil system of charged particles from the DPE process is measured in the STAR Time Projection Chamber (TPC). The first data were taken in 2009 during the RHIC-Run 9 using polarized proton-proton collisions at [Formula: see text]. The preliminary spectra of two pion and four pion invariant mass reconstructed by STAR TPC in central region of pseudo-rapidity |η| < 1, are presented. Plans to take data with the current system at [Formula: see text] and plans to upgrade the forward proton tagging system, so that it can reach higher masses and obtain large data samples in searching for glueballs that could be produced in the DPE process, are also discussed.

REFLECTIVE SCATTERING EFFECTS IN DOUBLE-POMERON EXCHANGE PROCESSES

We discuss energy dependence of rapidity gap survival probability in the double-pomeron exchange processes with account of the reflective scattering effects.

Central exclusive dijet production at the Fermilab Tevatron

We perform a phenomenological analysis of dijet production in double pomeron exchange at the Tevatron. We find that the CDF Run I results do not rule out the presence of an exclusive dijet component, as predicted by Khoze, Martin and Ryskin (KMR). With the high statistics CDF Run II data, we predict that an exclusive component at the level predicted by KMR may be visible, although the observation will depend on accurate modelling of the inclusive double pomeron exchange process. We also compare to the predictions of the DPEMC Monte Carlo, which contains a non-perturbative model for the central exclusive process. We show that the perturbative model of KMR gives different predictions for the di-jet ET dependence in the high di-jet mass fraction region than non-perturbative models.

Diffractive production of dijets by double Pomeron exchange processes

A phenomenological description of diffractive dijet hadroproduction via double Pomeron exchange is presented. This description is based on a modified version of the Ingelman-Schlein model which includes the evolution of the Pomeron structure function and corrections regarding rapidity gap suppression effects. The same quark-dominant Pomeron structure function employed in a previous report to describe diffractive dijet and W production via single Pomeron processes is shown here to yield results consistent with the available data for double Pomeron processes as well.

Heavy quarkonium production in double pomeron exchange processes in perturbative QCD

We calculate the heavy quarkonium production in double pomeron exchange processes in perturbative QCD by using two-gluon exchange model. For the $P$-wave $\chi_J$ productions, we find $\chi_1$ and $\chi_2$ production amplitudes which vanish in the forward scattering limit. We also calculate direct $J/\psi(\Upsilon)+\gamma$ production in the same approach, and these direct contributions are much smaller than the feeddown contributions from the $P$-wave states.

Large pT J/ production in double pomeron exchangeprocesses

Presented here is a study of the large pT J/ production in double pomeron exchange processes via gluon fragmentation at hadron colliders. We use three sets of parametrization (hard gluon, hard quark, and soft gluon) for the parton distribution in the pomeron to estimate the production cross section. We find that the J/ production rate is sensitive to the gluon component of the pomeron. Especially, at the LHC the soft gluon parametrization gives the J/ production rate two order of magnitude larger than that hard gluon parametrization gives.

Two-gluon exchange model predictions for double Pomeron jet production.

I extend the two-gluon exchange picture of elastic scattering, known as the Low-Nussinov or subtractive quark model, to predict cross sections for double Pomeron exchange processes. In particular, I calculate pp\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\rightarrow}pp\ifmmode\bar\else\textasciimacron\fi{}qq\ifmmode\bar\else\textasciimacron\fi{} where the qq\ifmmode\bar\else\textasciimacron\fi{} partons will appear as jets separated from the final p and p\ifmmode\bar\else\textasciimacron\fi{} by large gaps in rapidity. The predicted cross section is large enough that this process should be observable at the Fermilab Tevatron and at the CERN Large Hadron Collider. It can be distinguished from the background of ordinary jet production by an absence of particles produced in the gap regions.

Effects of shadowing in double Pomeron exchange processes

The effect of shadowing in double Pomeron exchange processes is investigated within an eikonal approach assuming a Gaussian input. Damping factors due to screening are calculated for the above process and compared with results obtained for total, elastic and single diffraction cross sections. Our main conclusion is that counting rate calculations, of various double Pomeron exchange processes (without screening corrections) such as heavy quark and Higgs production are reduced by a factor of 5 in the LHC energy range, when screening corrections are applied.

Evidence for double Pomeron exchange at the CERN ISR

We have observed events at the CERN Intersecting Storage Rings (ISR) which are consistent with the double Pomeron exchange process p + p → p + X + p, where X represents a system of particles in the central region of the rapidity distribution separated by at least two units from the outgoing protons in the forward directions. The observed low charge multiplicity of the central cluster X indicates that this process is dominated by the formation of a low-mass system in the central region. In particular, we find that the differential cross-section for the process p + p → p + h + + h - + p, where h represents a charged particle, shows no correlation between t A and t B and has an exponential slope of 9.9 ± 1.8 GeV −2 independent of energy. The cross-section for this process is found to be approximately 20 μb over the ISR energy range.

Double-Pomeron-Exchange Contribution to the Reactionpp→ppπ+π−at 205 GeV/c

The reaction $\mathrm{pp}\ensuremath{\rightarrow}\mathrm{pp}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ at 205 GeV/c is analyzed in terms of the rapidities of the secondary particles to measure the contribution of the double-Pomeron exchange process. Using a sample of 191 events, we estimate the maximum possible contribution for this process to be 44 \ensuremath{\mu}b for the region of $\ensuremath{\pi}p$ effective mass greater than 2.0 GeV in a total cross section of 680 \ifmmode\pm\else\textpm\fi{} 140 \ensuremath{\mu}b.