abstract

This talk reviews some key developments that have taken place in hadron-collider jet finding over the past couple of years, including: technical advances such as the complete formulation of an infrared safe seedless cone algorithm and fast computational approaches to sequential recombination jet finders like the \(k_{\rm t}\) algorithm, together with universal methods for subtracting pileup; progress in understanding the sensitivity of jet algorithms to the underlying event and hadronisation; and work that exploits our knowledge of QCD divergences to better define and predict heavy-flavour jet cross sections.

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We study the correlation in azimuthal angle between Mueller–Navelet jets produced in hadron–hadron collisions. We argue that this observable would test the BFKL approach at next-to-leading logarithmic accuracy. In order to motivate such a measurement, we give predictions for jets separated by large rapidity intervals within the Tevatron and LHC ranges.

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We will discuss the new opportunities and experimental challenges of jet physics in Pb–Pb collisions at \(\sqrt {s_{NN}} = 5.5\) TeV at the LHC.

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Recent results on jet physics at the Fermilab Tevatron \(p\bar p\) collider from the CDF Collaboration are presented. The main focus is put on results for the inclusive jet and dijet, \(b\bar b\) dijet, \(W/Z+\)jets and \(W/Z+b\)-jets production.

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Recent results on dijet, inclusive jets, production at high \(p_{\rm T}\) in Deep Inelastic Scattering DIS and photoproduction \(\gamma p\) regimes using both the H1 and ZEUS detectors at HERA are presented. Also studies of integrated jet shape and jet radius dependencies in DIS performed by the ZEUS Collaborations are discussed. All the measurements are found to be well described by calculations at the next-to-leading order in perturbative QCD. A combined determination of the value of the strong coupling constant \(\alpha _{\rm s}(M_Z)\) from the H1 and ZEUS Collaborations using inclusive-jet cross-section measurements in neutral current DIS at high \(Q^2\) is shown.

abstract

Azimuthal anisotropy at low \(p_{\rm T}\) in heavy-ion collisions is studied in an approach that avoids the assumption of fast thermalization. What generates the asymmetry in momentum space is the ridge formation due to semi-hard scattering near the surface of the medium created in non-central collisions. Phenomenological input from ridge studies is used to derive analytical formulas for elliptic flow without using hydrodynamics. The result of this simple study is in accord with data for \(p_{\rm T}\lt 1.5\) GeV/\(c\).

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We present some improvements of our Monte Carlo implementation of Mueller’s dipole cascade model and apply it to inclusive, diffractive and elastic scattering in hadron collisions and deeply inelastic \(ep\) scattering. We obtain a Lorentz-frame invariant description of the total cross-section and, by considering all possible sources of fluctuations, also of diffractive and elastic cross-sections. In all cases we find reasonable agreement with experimental data.

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In this overview of heavy ion femtoscopy, we emphasize the dramatic progress during the last year in understanding the HBT puzzle.

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It is well known that perturbative saturation of small-\(x\) gluons modifies the transverse momentum distribution in high-energy heavy-ion collisions. Near the unitarity limit, their distribution in coordinate space also differs from the one predicted by leading-twist perturbative QCD or soft particle production models. This implies a different initial condition for the hydrodynamic expansion of the hot plasma formed in such collisions, and thus affects the equation of state and the transport coefficients extracted from RHIC flow data. Accurate data on relative flow fluctuations could help to constrain models for the initial state.

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Measurements of elliptic flow in high-energy nucleus–nucleus suggest that in these collisions a strongly interacting medium is formed. The expansion of this medium appears to be well described by ideal hydrodynamics. Further information about the properties of the medium and the hydrodynamic evolution can be obtained by studying not just the average strength of elliptic flow, \(\langle v_2 \rangle \), but also event-by-event fluctuations in the elliptic flow coefficient, \(v_2\). However, the quantitative interpretation of current measurements of \(v_2\) fluctuations is complicated by the presence of multi-particle correlations between final state hadrons. We will discuss the status of \(v_2\) fluctuation measurements, the influence of non-flow particle correlations and possible approaches to obtain the “true” \(v_2\) fluctuation strength.

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We analyse charged particle ratio fluctuations and charge transfer fluctuations within samples of central Au+Au events at \(\sqrt {s_{NN}}=200\) GeV simulated using a dynamical recombination approach including an explicit transition from quark to hadronic matter (quark Molecular Dynamics, qMD). In previous papers, we argued that the recombination-hadronization procedure implemented in the qMD model is responsible for the vanishing of the initial QGP fluctuations for both observables. In this investigation, the rapidity window size dependence (critical in fluctuation analyses) of charged particle ratio fluctuations within qMD is calculated and found to be compatible with the hadronic values. Charge transfer fluctuations are studied as a function of rapidity for a fixed rapidity window. This observable turns out to be insensitive to the quark stage of the qMD model, even in the midrapidity region. These results might indicate a drastic effect of (recombination-)hadronization on fluctuation observables and might explain the compatibility of the available experimental results on charged particle ratio fluctuations with hadronic expectations.

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Model-independent, three-dimensional source functions for pion pairs have been extracted from heavy ion collisions from SPS to RHIC energies. The source functions exhibit long-range non-Gaussian tails in the direction of the pion pair transverse momentum and in the beam. Comparison with the Therminator model allows extraction of the pion source proper breakup time and emission duration from SPS to RHIC.

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A simple model based on relativistic geometry and final-state hadronic rescattering is used to predict pion source parameters extracted in two-pion correlation studies of proton–proton collisions at \(\sqrt s=14\) TeV. By comparing the results of these model studies with data, it might be possible to obtain information on the hadronization time in these collisions. As a test of this model, comparisons between existing two-pion correlation data at \(\sqrt {s}= 1.8\) TeV and results from the model are made. It is found at this lower energy that using a short hadronization time in the model best describes the trends of the data.

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We argue that fragmentation at hadronisation is likely scenario in ultrarelativistic nuclear collisions. In case of crossover phase transition it is driven by a singularity of the bulk viscosity. We claim that such a scenario can explain the “HBT puzzle” and can be identified by non-statistical differences between event-wise rapidity distributions and by proton–proton rapidity correlations.

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Using the hydrodynamic code NeXSPheRIO, Au+Au and Cu+Cu collisions at 200 AGeV are studied. By fixing the model parameters adequately, data on pseudo-rapidity and transverse momentum distributions for charge particles are reproduced in the various centrality windows. Reasonable agreement of elliptic flow of these particles is obtained as function of pseudo-rapidity, transverse momentum and centrality. In addition, elliptic flow fluctuations are in agreement with Au+Au data.

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In this paper we summarize the ellipsoidally symmetric Buda–Lund model’s results on HBT radii. We calculate the Bose–Einstein correlation function from the model and derive formulas for the transverse momentum dependence of the correlation radii in the Bertsch–Pratt system of out, side and longitudinal directions. We show a comparison to \(\sqrt {s_{NN}}=200\) GeV RHIC PHENIX two-pion correlation data and make prediction on the same observable for different particles.

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Recent results on forward jet and multijet production at low Bjorken \(x\) at HERA are reviewed. The measured cross sections and jet correlations are compared to predictions from DGLAP-based fixed order calculations. Further comparisons are made to DGLAP-based and CCFM-based leading-order Monte Carlo (MC) predictions as well as to colour dipole model (CDM) predictions. Recent results on multijet production in photoproduction are also presented.

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Inelastic and elastic (exclusive) cross-section measurements of vector meson production at HERA are discussed.

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In this paper the review of our understanding of diffraction in framework of high density QCD is presented in a collections of pictures.

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The Color Glass Condensate has become an important tool to understand saturation phenomena in high energy collisions involving large nuclei. Until recently, the underlying JIMWLK and BK evolution equations have been known only to one loop accuracy. Here I summarize results of the first calculations to step beyond leading order and provide running coupling corrections to both equations.

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The small \(x\) deep inelastic scattering in the saturation region is governed by the non-linear evolution of Wilson-line operators. In the leading logarithmic approximation it is given by the BK equation for the evolution of color dipoles. In the next-to-leading order the BK equation gets contributions from quark and gluon loops as well as from the tree gluon diagrams with quadratic and cubic nonlinearities.

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We discuss the beginning of the unitarization program for high energy scattering based on String/Gauge duality.

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We present an overview of cross-section measurements at BaBar. In \(e^\pm \to \) few-body processes at a center-of-mass energy \(E_{\rm CM}=10.6\) GeV we make new QCD tests and the first observation of two-virtual-photon annihilations into hadrons. Studies at lower \(\sqrt {s}\), using radiative return, yield new/improved data on spectroscopy, form factors and the total hadronic cross section, an important input to calculations of \(g_\mu - 2\) and \(\alpha (M_Z)\). We also present an inclusive measurement of the running of \(\alpha \).

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A review of recent particle production and fragmentation results from H1 and ZEUS are presented for deep inelastic scattering (DIS) and photoproduction (\(\gamma p\)) at HERA on a wide range of topics.

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The Large Hadron Collider at CERN will provide Pb–Pb collisions at energies up to \(\sqrt {\mathrm {s}_{_{{NN}}}} = 5.5\) TeV. We speculate on global observables, i.e. the charged particle density at mid-rapidity, chemical freeze-out conditions and collective parameters for transverse radial an elliptic flow. Finally, we present an idea how to address the important issue of thermalization by measuring the correlated production of heavy-quark hadrons.

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Current status of a study for dynamics of relativistic heavy ion collisions is reported by focusing on hadronic rescattering effects on elliptic flow. We show mass splitting behavior of differential elliptic flow for non-strange hadrons is generated mainly during the late hadronic rescattering stage. \(\phi \) mesons which undergo less scattering due to small cross-section do not follow mass ordering of differential elliptic flow predicted by ideal hydrodynamics.

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Recent results of experiment NA49 from Pb+Pb collisions at the CERN SPS are shown on light nuclei production, on the Balance Function and on the energy dependence of multiplicity and mean transverse momentum fluctuations.

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Relativistic covariance of a Langevin type equation is discussed. The requirement of Lorentz invariance generates an entanglement between the force and noise terms so that the noise itself should not be a covariant quantity.

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Strong interactions which lead to quark confinement are analyzed from the point of view of quantum information theory. It is shown how states with nontrivial colour charge can be transformed into white mixed states described by density matrices and how the information about colour states of quarks is lost due to interactions with non-Abelian quantum gauge fields. For mixed state of a single quark the entropy growth rate is found to be proportional to the tension of QCD string.

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The multiparticle production problems are analyzed in the high multiplicity region. Some collective phenomena can be revealed in this region. The results obtained on Thermalization project are reported.

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HiRes measurements of the highest energy cosmic rays lead to the observation of the GZK cutoff. HiRes consequently puts new limits on the resulting flux of cosmogenic neutrinos.

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We present the status and the recent measurements from the Pierre Auger Observatory. The energy spectrum will be described and its steepening discussed. The mass composition is addressed with the measurements of the variation of the depth of shower maximum with energy. We also report on upper limits in the primary photon fraction. And finally, searches for anisotropies of cosmic rays arrival directions are reported.

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A new generation of observatories have revolutionized the study of the very high energy gamma-ray sky. The recently-commissioned VERITAS observatory, an array of four 12 m diameter imaging atmospheric Cherenkov telescopes designed to search for gamma-ray sources in the energy band between 100 GeV and 50 TeV, is one of these new instruments. VERITAS has been taking scientific data with three or more telescopes since November 2006. We discuss the thrust of the VERITAS observation program and present results from these early observations, including new results on the sources IC433, LSI+61 303, 1ES 1218+304 and M87.

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The gamma-ray emission from the galaxy as visible from the Northern Hemisphere — Galactic latitude \(|b|\lt 10^\circ \) and Galactic longitude \(l\in [30^\circ ,216^\circ ]\) — is measured at TeV energies by the Milagro Gamma-Ray Observatory. The Milagro experiment performed a survey of this region of the Galaxy and observed eight sources or source candidates with a pre-trials significance of 4.5 standard deviations above the isotropic background. The contribution of these sources is subtracted from the total emission in the studied Galactic plane region to calculate the diffuse flux near the Galactic equator. The flux and position of the eight excess locations, as well as the diffuse emission profiles will be reported.

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We summarize the dihadron correlation results from RHIC, focusing on the high \(p_{\rm T}\) region and lower \(p_{\rm T}\) region for the away-side. The former is consistent with fragmentation of jets that surviving the medium, while the latter suggests the redistribution of the energy from the quenched jets. We also discuss the role of the jet in the intermediate \(p_{\rm T}\).

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Results on dihadron correlations at near-side at RHIC (\(\sqrt {s_{NN}}\!=\!200\) GeV) are presented. In addition to the jet-like component, long-range pseudo-rapidity (\(\Delta \eta \)) correlations, the ridge, are observed in Au+Au collisions. Properties of the jet- and ridge-like correlations are discussed as a function of collision centrality, transverse momentum and particle composition. The results are confronted with recent model predictions.

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We propose a new implementation of medium effects in jet structures in which a modification of the splitting function is included at every step in the typical final state parton shower. Although the main application of this new formalism will be at the LHC, it is interesting that, in the presence of a trigger bias to small number of splittings, non-trivial angular dependences could appear with shapes similar to those measured experimentally at RHIC in high-\(p_{\rm T}\) particle correlations.

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The use of jet modification to study the properties of dense matter is reviewed. Different sets of jet correlations measurements which may be used to obtain both the space-time and momentum space structure of the produced matter are outlined.

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We report on azimuthal correlations of high-\(p_{\rm t}\) charged particles in Pb–Au collisions at 158 AGeV, recorded with the CERES spectrometer at the CERN-SPS. We observe a significant dependence of the extracted associated yield on the charges of the particles. The correlation functions exhibit a very broad away-side structure in central collisions. The results of a three-particle correlation analysis are consistent with cone-like emission of jet-correlated hadrons.

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Two-particle jet-like correlations have shown medium modification in central Au+Au collisions. This modification can be explained by different physics mechanisms such as: large angle gluon radiation [2], jets deflected by radial flow [3] or path-length dependent energy loss [4], Mach-cone shock waves [5], and Čerenkov gluon radiation [6]. Three-particle correlations can be used to distinguish the mechanisms with conical emission, Mach-cone shock waves and Čerenkov radiation. This paper reviews three 3-particle correlation analyses at RHIC and discuss the physics extracted from them.

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We calculate the stress energy tensor of an \(\mathcal {N}=4\) super-Yang–Mills plasma due to a heavy quark moving through it at constant velocity. We observe a Mach cone and a wake, and discuss these results in the context of dijet correlations.

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The coherent hadron production analogous to Čerenkov radiation of photons gives rise to the ring-like events. Being projected on the ring diameter they produce the two-bump structure recently observed for the away-side jets at RHIC. The position of the peaks and their height determine such properties of the hadronic medium as its nuclear index of refraction, the parton density, the free path length and the energy loss of Čerenkov gluons. Beside comparatively low energy gluons observed at RHIC, there could be high energy gluons at LHC, related to the high energy region of positive real part of the forward scattering amplitude and possessing different characteristics.

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Azimuthal angle two particle correlations have been shown to be a powerful probe for extracting novel features of jet induced correlations produced in Au+Au collisions at RHIC. At intermediate \(p_{\rm T}\), 2–5GeV/\(c\), the jets have been shown to be significantly modified in both their particle composition and their angular distribution compared to \(p\)+\(p\) collisions. Two-particle angular correlations with identified particles provide sensitive probes of both the interactions between hard scattered partons and the medium. The systematics of these correlations are essential to understanding the physics of intermediate \(p_{\rm T}\) in heavy ion collisions.

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We calculate the probability of large rapidity gaps in high energy hadronic collisions using a model based on QCD minijets and soft gluon emission down into the infrared region. Comparing with other models we find a remarkable agreement among most predictions.

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We analyze recent data on the electroproduction of hadrons on nuclei using the Lund model for electroproduction on nucleons and a simple geometrical model for the absorption effects. We show that the model seems to overestimate the \(A\)-dependence of the absorption effects, although it described the earlier data of the same HERMES experiment reasonably well. We trace the origin of this discrepancy to the surprising difference between the data for nitrogen and neon.

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A short overview of recent results on charm and beauty production from the H1 and ZEUS Collaborations at the \(ep\) collider HERA is presented. The heavy quark contribution to the proton structure function \(F_2\) as well as differential cross-sections are shown. Results on the charm fragmentation are compared to measurements at \(e^+e^-\) colliders.

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We compute the momentum broadening of a heavy probe in \(\mathcal {N}=4\) super-symmetric Yang–Mills in the large number of colors limit and strong coupling. The mean momentum transferred squared per unit length, \(\kappa \), is expressed in terms of derivatives of a Wilson line. This definition is used to compute \(\kappa \) via the AdS/CFT correspondence.

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I briefly review the recent experimental progress on the open charm production in proton–proton and nucleus–nucleus collisions at RHIC. Comparisons with theoretical predictions leave some unsettle issues, which call for precise measurements on directly reconstructed open charm hadrons.

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Quarkonia provide a direct probe of hard parton interactions that occur in nucleon–nucleon collisions. Because the heavy quark pairs interact with the medium produced in heavy ion collisions, information regarding the properties of the collision environment is accessible through the quarkonia that escape. Quarkonia are useful probes of the collision medium because they are sensitive to the modification of the QCD confining potential. Measurements of quarkonia produced in \(p+p\), \(p+A\) and \(d+A\) collision systems provide reference information necessary for understanding their production mechanisms and for disentangling cold nuclear matter effects present in heavy ion data. Studies of heavy ion collisions can be used to quantify in-medium modifications. Experimental results from both the SPS and RHIC are presented in the context of the available theoretical interpretations.

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While the charmonium model has been effective in describing \(c\overline {c}\) bound mesons, there have been many recently discovered charmonium-like states it cannot accommodate. Here I provide a review of recent results from the \(B\)-factories including the \(X(3872)\), three new particles in the mass range near \(3.93\) GeV\(/c^{2}\), and four new resonances in initial state radiation (ISR) decays.

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We report results from our recent study on charm and anticharm quark pair production in the next-to-leading order in QCD from the quark-gluon formed in heavy ion collisions at the Large Hadron Collider (LHC) and its dependence on the number of charm quark pairs produced from initial hard scattering, the charm quark mass, and the temperature and formation time of the quark-gluon plasma.

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We discuss the energy dependence of the total charm cross-section and some of its theoretical uncertainties including the quark mass, scale choice and the parton densities. We compare the next-to-leading order calculation of the total cross-section with results obtained using PYTHIA.

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New analysis of high-\(p_{\rm T}\) hadron spectra obtained at RHIC is performed in \(z\)-scaling scheme. The energy, angular, and multiplicity independence of the scaling function \(\psi (z)\) is demonstrated. Universality of the shape of the scaling function for various types of produced hadrons (\(\pi , K, \bar p, {\mit \Lambda }\)) is shown. Results of analysis of experimental data are compared with the NLO QCD calculations in \(z\)-presentation.