Central Diffractive Processes Research Articles

Hard diffractive ηc,b hadroproduction at the LHC

In this paper, we investigate the inclusive diffractive hadroproduction for $\rm \eta_{c}$ and $\rm \eta_{b}$ at the LHC energies. Based on the NRQCD factorization formalism and the resolved-Pomeron model for the quarkonium production mechanism, we estimate the rapidity, momentum fraction loss dependence of the cross section. We give prediction ratios for single and central diffractive processes with respect to non diffractive process. These inclusive processes are sensitive to gluon content of Pomeron for small-$x$ and Reggeon for large-$x$, useful to study small and large-$x$ physics and good to test different mechanism for $\rm \eta_{c}$ and $\rm \eta_{b}$ production at the LHC. They also serve as the background to related exclusive processes thus should be predicted. Our results demonstrate that the Reggeon contribution of diffractive processes can be sizable, even sometimes dominant over Pomeron, and that its study can be useful to better constrain the Reggeon parton content. The experimental study of Reggeon can be carried out in certain kinematic windows.

Resonance production in Pomeron–Pomeron collisions at the LHC

A Regge pole model for Pomeron-Pomeron total cross section in the resonance region $\sqrt{M^2}\le$ 5 GeV is presented. The cross section is saturated by direct-channel contributions from the Pomeron as well as from two different $f$ trajectories, accompanied by the isolated f$_0(500)$ resonance which dominates the $\sqrt{M^{2}}\lesssim 1$ GeV region. A slowly varying background is taken into account. The calculated Pomeron-Pomeron total cross section cannot be measured directly, but is an essential part of central diffractive processes. In preparation of future calculations of central resonance production at the hadron level, and corresponding measurements at the LHC, we normalize the Pomeron-Pomeron cross section at large masses $\sigma_{t}^{PP} (\sqrt{M^2}\rightarrow \infty) \approx$ 1 mb as suggested by QCD-motivated estimates.

DoubleJ/ψproduction in central diffractive processes at the LHC

In this paper we study the double $J/\ensuremath{\psi}$ production in central diffractive processes considering the resolved Pomeron model. Based on the nonrelativistic QCD factorization formalism for the quarkonium production mechanism we estimate the rapidity and transverse momentum dependence of the cross section for the double $J/\ensuremath{\psi}$ production in diffractive processes at LHC energies. The contributions of the color-singlet and color-octet channels are estimated and predictions for the total cross sections in the kinematical regions of the LHC experiments are also presented. Our results demonstrate that the contribution of central diffractive processes is not negligible and that its study can be useful to test the resolved Pomeron model.

Predictions for diffraction at the LHC compared to experimental results

Diffractive proton-proton cross sections at the lhc, as well as the total and total-inelastic proton-proton cross sections, are predicted in a simple model obeying all unitarity constraints. The model has been implemented in the pythia8-mbr event genera- tor for single diffraction, double diffraction, and central diffraction processes. Predictions of the model are compared to recent LHC results. The pythia8-mbr option includes a full simulation of the hadronization of the implemented diffrac- tion dissociation processes: single, double, and central diffraction. In the original mbr simulation used in cdf, the hadronization of the final state(s) was based on a data-driven phenomenological model of multiplicities and pt distributions calibrated using S ¯ ppS and Fermilab fixed-target results. Later, the model was successfully tested against Tevatron mb and diffraction data. However, only π ± and π 0 particles were produced in the final state, with multiplicities obeying a statistical model of a modified Gamma distribution function that provided good fits to experimental data (8). This model could not be used to predict specific-particle final states. In the pythia8-mbr implementation, hadronization is performed by PYTHIA8 tuned to reproduce final-state distributions in agreement with mbr's, with hadronization done in the pythia8 framework. Thus, all final-state particles are now automatically produced, greatly enhancing the horizon of applicability of tpythia8-mbr.

A Study of Diffractive Production in ALICE

The ALICE collaboration is investigating single, double and central diffractive processes in pp interactions. The single and double diffractive cross-sections are presented at 900 GeV 2.76 TeV and 7 TeV using an analysis method based on the classification of diffractive gaps. Promising early results on central diffractive processes have motivated the use of additional diffractive counters, which are currently being installed.

Investigating the central diffractivef0(980)andf2(1270)meson production at the LHC

The central diffractive production of mesons ${f}_{0}(980)$ and ${f}_{2}(1270)$ at the energy of CERN-Large Hadron Collider experiment on proton-proton collisions is investigated. The processes initiated by quasireal photon-photon collisions and by central diffraction processes are considered. The role played by the photon-Odderon production channel is also studied. The cross sections for these distinct production channels are compared and analyzed.

Subdominant terms in the production ofcc¯pairs in proton-proton collisions

At high-energies the gluon-gluon fusion is the dominant mechanism of $c \bar c$ production. This process was calculated in the NLO collinear as well as in the k$_t$-factorization approaches in the past. We show that the present knowledge of gluon distributions does not allow to make a precise predictions for $c \bar c$ production at LHC, in particular at forward rapidities. In this paper we study production of $c \bar c$ pairs including several subleading mechanisms. This includes: $gg \to Q \bar Q$, $\gamma g \to Q \bar Q$, $g \gamma \to Q \bar Q$, $\gamma \gamma \to Q \bar Q$. In this context we use MRST-QED parton distributions which include photon as a parton in the proton as well as elastic photon distributions calculated in the equivalent photon approximation. We present distributions in the $c$ quark ($\bar c$ antiquark) rapidity and transverse momenta and compare them to the dominant gluon-gluon fusion contribution. We discuss also inclusive single and central diffractive processes using diffractive parton distribution found from the analysis of HERA diffractive data. As in the previous case we present distribution in $c$ ($\bar c$) rapidity and transverse momentum. Finally we present results for exclusive central diffractive mechanism discussed recently in the literature. We show corresponding differential distributions and compare them with corresponding distributions for single and central diffractive components.

Formula omitted] pair production in proton-proton collisions including subdominant terms

For the c c ¯ production at high-energies the gluon-gluon fusion is the dominant mechanism. This process was calculated in the NLO collinear as well as in the k t -factorisation approaches in the past. We show that the present knowledge of gluon distributions does not allow to make precise predictions for c c ¯ production at LHC. Next, we study production of c c ¯ pairs including following subprocesses: g g → Q Q ¯ , γ g → Q Q ¯ , g γ → Q Q ¯ , γ γ → Q Q ¯ . In this context we use MRST-QED (Martin, Roberts, Stirling, Thorne) parton distributions which include photon as a parton in the proton. We include also elastic contributions (single proton in the final state) within the equivalent photon approximation. We present distributions in c ( c ¯ ) rapidity and transverse momenta and compare them with the dominant gluon-gluon fusion contribution. We discuss also single and central diffractive processes using diffractive parton distribution found from the analysis of HERA data. As in the previous case we present distribution in c ( c ¯ ) rapidity and transverse momentum.

Inclusive and exclusive diffractive production of dilepton pairs in proton-proton collisions at high energies

We calculate for the first time cross sections for single and central diffractive as well as exclusive diffractive production of dilepton pairs in proton-proton collisions. Several differential distributions are shown. The inclusive diffractive processes are calculated using diffractive parton distributions extracted from the analysis of diffractive structure function and dijet production at HERA. We find that the inclusive single-diffractive Drell-Yan process is by about 2 orders of magnitude smaller than ordinary Drell-Yan process. The central-diffractive processes are smaller by one order of magnitude compared to single-diffractive ones. We consider also exclusive production of dilepton pairs. The exclusive photon-pomeron (pomeron-photon) process constitutes a background to the QED photon-photon process proposed to be used for controlling luminosity at LHC. Both processes are compared then in several differential distributions. We find a region of the phase space where the photon-pomeron or pomeron-photon contributions can be larger than the photon-photon one.

Central diffraction at ALICE

The ALICE experiment is shown to be well suited for studies of exclusive final states from central diffractive reactions. The gluon-rich environment of the central system allows detailed QCD studies and searches for exotic meson states, such as glueballs, hybrids and new charmonium-like states. It would also provide a good testing ground for detailed studies of heavy quarkonia. Due to its central barrel performance, ALICE can accurately measure the low-mass central systems with good purity. The efficiency of the Forward Multiplicity Detector (FMD) and the Forward Shower Counter (FSC) system for detecting rapidity gaps is shown to be adequate for the proposed studies. With this detector arrangement, valuable new data can be obtained by tagging central diffractive processes.

Exclusive glueball production in high-energy nucleus-nucleus collisions

The cross sections for the glueball candidates production in quasi-real photon-photon collisions and on central diffraction processes, i.e. double Pomeron exchange, in heavy ion interactions at RHIC and LHC are computed. The rates for these distinct production channels are compared and they may be a fruitful approach to the investigation of glueballs.

Central diffraction at the LHCb

The LHCb experiment is shown to be ideal for studies of exclusive final states from central diffractive reactions. The gluon-rich environment of the central system allows detailed QCD studies and searches for exotic meson states, such as glueballs, hybrids and new charmonium-like states. It would also provide a good testing ground for detailed studies of heavy quarkonia. Due to its distinct design features, the LHCb can accurately measure the low-mass central systems with good purity. The efficiency of the Forward Shower Counter (FSC) system for detecting rapidity gaps is shown to be adequate for the proposed studies. With this detector arrangement, valuable new data can be obtained by tagging central diffractive processes.

Proton-Proton Collisions

At high-energies the gluon-gluon fusion is the dominant mechanism of c� c production. This process was calculated in the NLO collinear as well as in the kt-factorization approaches in the past. We show that the present knowledge of gluon distributions does not allow to make a precise predictions for cproduction at LHC, in particular at forward rapidities. In this paper we study production of c� c pairs including several subleading mechanisms. This includes: gg → Q � Q, g → Q � Q, g → Q � Q, → Q � Q. In this context we use MRST-QED parton distributions which include photon as a parton in the proton as well as elastic photon distributions calculated in the equivalent photon approximation. We present distributions in the c quark (�c antiquark) rapidity and transverse momenta and compare them to the dominant gluon-gluon fusion contribution. We discuss also inclusive single and central diffractive processes using diffractive parton distribution found from the analysis of HERA diffractive data. As in the previous case we present distribution in c (�c) rapidity and transverse momentum. Finally we present results for exclusive central diffractive mechanism discussed recently in the literature. We show corresponding differential distributions and compare them with corresponding distributions for single and central diffractive components.