Regular Series


Vol. 40 (2009), No. 7, pp. 1765 – 2187

Cracow Epiphany Conference Hadron Interactions at the Dawn of the LHC

Kraków, Poland; January 5–7, 2009

Special Address in Honour of Jan Kwieciński


Cross-Sections at HERA

abstract

The energy dependence of cross-sections is discussed as a way to learn about the dynamics of photon induced interactions at HERA. The question of determining the scale of exclusive electroproduction of vector mesons is addressed.


The HERA Challenges for LHC

abstract

Over the last two decades, the HERA collider has provided a large amount of new information about QCD dynamics at high energy. While the most appreciated are the measurements of the proton structure functions in a wide range of parton momentum \(x\) and virtuality \(Q^2\), it is hard to believe that some of the observations at HERA which do not fit the simple picture of DGLAP dynamics would not get amplified at the LHC, possibly rendering certain approaches to searches beyond the Standard Model inadequate.


The Nucleon Spin in Perspective

abstract

In the twentieth anniversary of the “proton spin crisis”, a review of the nucleon spin structure is presented.


Diffraction at HERA, Tevatron and LHC

abstract

In this short review, we describe some of the results on diffraction from the Tevatron and give some prospects for the LHC. In particular, we discuss the search for exclusive events at the Tevatron and their importance for the LHC program. We finish by presenting the project of installing forward detectors in the ATLAS Collaboration at 220 and 420 m.


Forward Physics at the LHC

abstract

We review two inter-related topics. First, we consider the behaviour of “soft” scattering observables, such as \(\sigma _{\rm tot}\), \(d\sigma _{\,\rm el}\) / \(dt\), \(d\sigma _{\rm SD}\) / \(dtdM^{\,2}\), particle multiplicities etc., at high-energy proton-(anti)proton colliders. We emphasize the sizeable effects of absorption on high-energy ‘soft’ processes, and, hence, the necessity to include multi-Pomeron–Pomeron interactions in the usual multi-channel eikonal description. We describe a multi-component model which has been tuned to the available data for soft processes in the CERN-ISR to Tevatron energy range, and which therefore allows predictions to be made for ‘soft’ observables at the LHC. The second topic concerns the calculation of the rate of exclusive processes of the form \(pp \to p+A+p\) at high energy colliders, where \(A\) is a heavy system. In particular, we discuss the survival probability of the rapidity gaps (denoted by the \(+\) signs) to both eikonal and enhanced soft rescattering effects. At the LHC energy, the most topical case is when \(A\) is a Higgs boson. At the Tevatron, measurements have been made for the exclusive diffractive production of various systems: \(A\) being either \(\gamma \gamma \), dijet, or a \(\chi _c\) meson. We compare the observed rates with the expectations. Finally, we describe how predictions for exclusive processes may be checked in the early runs of the LHC.


Central Exclusive Production at High Energies

abstract

I briefly review several mechanisms of central exclusive production of mesons at high energies. Some illustrative examples for the BNL RHIC, FNAL Tevatron and CERN LHC as well as for lower energies are discussed. Some differential distributions are shown.


Physics with Tagged Forward Protons at RHIC

abstract

We describe past, current and future physics program based on triggering (tagging) on forward protons at the Relativistic Heavy Ion Collider (RHIC). This program includes measuring spin dependence in proton–proton elastic scattering, diffractive processes and central production processes. The very forward protons, which remain intact after the scattering of polarized proton–proton collisions at RHIC are detected by detectors placed in the Roman Pots, thus selecting processes, for which the exchange is dominated by one with the quantum numbers of the vacuum, thus enhancing the probability of measuring reactions where colorless gluonic matter dominates the exchange. We present the results obtained by the \(pp2pp\) experiment in polarized proton–proton scattering [S. Bültmann et al., Phys. Lett. B579, 245 (2004), Nucl. Instrum. Methods A535, 415 (2004), W. Guryn et al., RHIC Proposal R7 (1994)] and future physics plans, which are based on using Roman Pots of the \(pp2pp\) experiment and the STAR detector K.H. Ackermann et al., Nucl. Instrum. Methods A499, 624 (2003) at RHIC. The capabilities of the setup to detect Glueballs and Exotics in central production mechanism are described.


Prospect for the Higgs Searches with the ATLAS Detector

abstract

The investigation of the electroweak symmetry breaking is one of the primary tasks of the experiments at the CERN Large Hadron Collider (LHC). The potential of the ATLAS experiment for the discovery of the Higgs boson(s) in Standard Model and Minimal Supersymmetric Standard Model is presented, with emphasis on studies which have been completed recently.


New Physics in the First Year of the LHC

abstract

In 2009 the LHC will start its long awaited operation to explore the Tera-scale energy region. The opportunities for new physics discoveries at the LHC are reviewed.


all authors

S.Y. Choi, M. Drees, J. Kalinowski, J.M. Kim, E. Popenda, P.M. Zerwas

Color-Octet Scalars at the LHC

abstract

Elements of the phenomenology of color-octet scalars (sgluons), as predicted in the hybrid \(N=1\)/\(N=2\) supersymmetric model, are discussed in the light of forthcoming experiments at the CERN Large Hadron Collider.


Soft Gluon Effects in Supersymmetric Particle Production at the LHC

abstract

We report on recent results A. Kulesza, L. Motyka, Phys. Rev. Lett. 102, 111802 (2009) on soft gluon effects in the production of squark–antisquark and gluino–gluino pairs at the LHC. The soft gluon corrections are resummed at the next-to-leading logarithmic (NLL) accuracy and matched with the known next-to-leading (NLO) order estimates of the cross-sections. The one-loop soft anomalous dimension matrices controlling the colour evolution of the gluino pair production are presented. We show that the resummation of soft gluon effects reduces substantially the theoretical uncertainty for gluino pair-production at the LHC.


Fundamental Problems with Hadronic and Leptonic Interactions

abstract

Common beliefs about unitarity are not reliable, and we do not know how to apply DGLAP evolution at small \(x\). Together with the big discrepancy between the measurements of the total cross-section at the Tevatron, a consequence is that the cross-section at the LHC could be anywhere between 90 and 160 mb.


Multiple Interactions, Saturation and Final States in \(pp\) Collisions and DIS

abstract

In high energy collisions saturation and multiple collisions are most easily accounted for in transverse coordinate space, while analyses in momentum space have been more suitable for calculating properties of exclusive final states. In this paper I describe an extension of Mueller’s dipole cascade model, which attempts to combine the good features of both these descriptions. Besides saturation it also includes effects of correlations and fluctuations, which have been difficult to account for in previous approaches. The model reproduces successfully total, elastic, and diffractive cross-sections in \(pp\) collisions and DIS, and a description of final states will be ready soon.


Initial Conditions of Heavy Ion Collisions and High Energy Factorization

abstract

The Color Glass Condensate is an effective theory description for the small momentum fraction \(x\) degrees of freedom in a high energy hadron or nucleus, which can be understood in terms of strong classical gluon fields. We discuss the resulting picture of the initial conditions in a relativistic heavy ion collision. We describe recent work to show that the leading logarithms of the collision energy can be factorized into the renormalization group evolution of the small \(x\) wavefunction. We will then show how this framework can be used to understand the long range rapidity correlations observed by the RHIC experiments.


The First Three Yoctoseconds of Relativistic Heavy-Ion Collisions

abstract

The recent results of the hydrodynamic calculations describing consistently one- and two-particle observables in relativistic heavy-ion collisions suggest that interesting phenomena may take place at the very early stages of the collisions. Firstly, the successful hydrodynamic fits indicate that the initial conditions for the hydrodynamic equations may differ from those obtained from the Glauber model. This may hint to yet unrecognized mechanisms of the particle production and thermalization which are responsible for such modified initial conditions. Secondly, the thermalization processes may be preceded by the free-streaming stage. It is also plausible, that the full three-dimensional hydrodynamic expansion is preceded by the purely transverse, two-dimensional hydrodynamic evolution. Such observations emphasize the importance of the proper matching between the microscopic models of early stages and the hydrodynamic evolution. In this respect, physics of the first 1 fm/\(c\) or, equivalently, of the first three yoctoseconds becomes an exciting subject of present and future investigations.


Transverse Hydrodynamics in Relativistic Heavy-Ion Collisions

abstract

General features of the formalism describing hydrodynamic evolution of transversally thermalized matter possibly produced at the very early stages of ultra-relativistic heavy-ion collisions are presented. Thermodynamical consistency of the model is emphasized. The covariant formulas for the moments of the phase-space distribution function are derived. The simple model for the transition from purely transverse to standard perfect-fluid hydrodynamics is proposed.


Forward–Backward Multiplicity Correlations in AuAu Collisions

abstract

We investigate the wounded nucleon model contribution to the forward–backward multiplicity correlation coefficient measured by the STAR Collaboration in AuAu collisions at \(\sqrt {s}=200\) GeV.


Traveling Waves and Impact-Parameter Correlations in High Energy QCD

abstract

We report on a numerical check of one of the main assumptions that underly the recent conjecture that high-energy scattering may be a reaction-diffusion like process in the universality class of the FKPP equation, namely the fact that the QCD evolution is local in impact-parameter space.


Exact Kinematics in Gluon Cascade on the Light-Front

abstract

In this talk we discuss the problem of kinematic effects in the development of the gluon cascade at high energies. The modification to the original dipole kernel for the dipole evolution at small \(x\) is proposed which accommodates important kinematical corrections. The techniques presented in this talk utilize the perturbation theory on the light-front. Using these techniques we construct recurrence relations for the wave-functions of gluons with arbitrary number of gluon components and with exact kinematics. In some special cases the recurrence relations can be solved exactly. By combining similar techniques for the fragmentation amplitudes one can derive the Parke–Taylor scattering amplitudes.


Saturation Effects in Final States Due to CCFM Equation with Absorptive Boundary

abstract

We apply the absorptive boundary prescription to include saturation effects in the CCFM evolution equation. We are in particular interested in saturation effects in exclusive processes which can be studied using the Monte Carlo event generator CASCADE. We calculate the cross section for three-jet production and the distribution of charged hadrons.


NLO QCD Evolution in the Fully Unintegrated Form

abstract

The next-to-leading order (NLO) evolution of the parton distribution functions (PDF’s) in QCD is the “industry standard” in the lepton–hadron and hadron–hadron collider data analysis. The standard NLO DGLAP evolution is formulated for inclusive (integrated) PDFs and is done using inclusive NLO kernels. We report here on the ongoing project, called KRKMC, in which NLO DGLAP evolution is performed for the exclusive multiparton (fully unintegrated) distributions (ePDF’s) with the help of the exclusive kernels. These kernels are calculated within the two-parton phase space for bremsstrahlung subset of the Feynman diagrams of the non-singlet evolution, using Curci–Furmanski–Petronzio factorization scheme. The multiparton distribution with multiple use of the exclusive NLO kernels is implemented in the Monte Carlo program simulating multi-gluon emission from single quark emitter. With high statistics tests (\(\sim 10^{9}\) events) it is shown that the new scheme works perfectly well in practice and is equivalent at the inclusive level with the traditional inclusive NLO DGLAP evolution. Once completed, this Monte Carlo module is aimed as a building block for the NLO parton shower Monte Carlo, for \(W/Z\) production at LHC and for \(ep\) scattering, as well as a starting point for other perturbative QCD based Monte Carlo projects.


Non-Abelian Infra-Red Cancellations in the Unintegrated NLO Kernel

abstract

We investigate the infrared singularity structure of Feynman diagrams entering the next-to-leading-order (NLO) DGLAP kernel (non-singlet). We examine cancellations between diagrams for two gluon emission contributing to NLO kernels. We observe the crucial role of colour coherence effects in cancellations of infra-red singularities. Numerical calculations are explained using analytical formulas for the singular contributions.


Non-Perturbative Effects in the Transverse Momentum Distribution of Electroweak Bosons at the LHC

abstract

The transverse momentum of electroweak bosons in a Drell–Yan process is an important quantity for the experimental program at the LHC. The new model of non-perturbative gluon emission in an initial state parton shower presented in this note gives a good description of this quantity for the data taken in previous experiments over a wide range of CM energy. The model’s prediction for the transverse momentum distribution of \(Z\) bosons for the LHC is presented and used for a comparison with other approaches.


QCD Factorization at Fixed \(Q^2(1-x)\)

abstract

Amplitudes of hard exclusive processes such as \(\gamma ^*(Q^2) N \to \gamma Y\), where \(Y=N\) (DVCS) or any other state with a limited mass (\(M_Y^2 \ll Q^2\)), factorize into a hard subprocess amplitude and a target (transition) GPD. The corresponding inclusive cross-section, summed over all states \(Y\) of a given (limited) mass, is then given by the discontinuity of a forward multiparton distribution. An application to the Drell–Yan process \(\pi ^+ N \to \gamma ^*(x_{\rm F},Q^2)+Y\) allows to explain the observed longitudinal polarization of the virtual photon at high \(x_{\rm F}\).


QCD Factorization Beyond Leading Twist in Exclusive \(\rho _{\rm T}\)-Meson Production

abstract

We describe hard exclusive processes involving a transversally polarized \(\rho \) meson in the twist 3 approximation, in a framework based on the Taylor expansion of the amplitude around the dominant light-cone direction.


Unintegrated Parton Distributions and Applications to Jet Physics

abstract

We give a concise overview on unintegrated parton distributions and discuss applications to the physics of parton showers and hadronic jets.


From Chiral Quark Models to High-Energy Processes

abstract

We show the results of low-energy chiral quark models for soft matrix elements involving pions and photons. Such soft elements, upon convolution with the hard matrix elements, are relevant in various high-energy processes. We focus on quantities related to the generalized parton distributions of the pion: the parton distribution functions, the parton distribution amplitudes, and the generalized form factors. Wherever possible, the model predictions are confronted with the data or lattice simulations, where surprisingly good agreement is achieved. The QCD evolution from the low quark model scale up to the scale of the data is crucial for this agreement.


Limiting Fragmentation in \(e^+e^-\) Annihilation and \(ep\) Deep Inelastic Scattering

abstract

The subject of this paper is hadron production in the limiting fragmentation region. The density of particles per unit of rapidity for \(e^+e^-\) annihilation is investigated at different energies of the colliding beams using data collected at the PETRA and LEP accelerators. This is compared with \(p\bar {p}\) interactions and predictions for \(ep\) deep inelastic scattering. The investigation was inspired by a model of hadron production proposed by Bialas and Jezabek. This model describes hadron production via radiation from the colour charges.


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