Search

The Large Hadron electron Collider (LHeC) is designed to move the field of deep inelastic scattering (DIS) to the energy and intensity frontier of particle physics. Exploiting energy recovery technology, it collides a novel, intense electron beam with a proton or ion beam from the High Luminosity--Large Hadron Collider (HL-LHC). The accelerator and interaction region are designed for concurrent electron-proton and proton-proton operation. This report represents an update of the Conceptual Design Report (CDR) of the LHeC, published in 2012. It comprises new results on parton structure of the proton and heavier nuclei, QCD dynamics, electroweak and top-quark physics. It is shown how the LHeC will open a new chapter of nuclear particle physics in extending the accessible kinematic range in lepton-nucleus scattering by several orders of magnitude. Due to enhanced luminosity, large energy and the cleanliness of the hadronic final states, the LHeC has a strong Higgs physics programme and its own discovery potential for new physics. Building on the 2012 CDR, the report represents a detailed updated design of the energy recovery electron linac (ERL) including new lattice, magnet, superconducting radio frequency technology and further components. Challenges of energy recovery are described and the lower energy, high current, 3-turn ERL facility, PERLE at Orsay, is presented which uses the LHeC characteristics serving as a development facility for the design and operation of the LHeC. An updated detector design is presented corresponding to the acceptance, resolution and calibration goals which arise from the Higgs and parton density function physics programmes. The paper also presents novel results on the Future Circular Collider in electron-hadron mode, FCC-eh, which utilises the same ERL technology to further extend the reach of DIS to even higher centre-of-mass energies., Comment: 373 pages, many figures, to be published by J. Phys. G

We consider forward inclusive production of several quarks in the high energy p-A collisions in the CGC formalism. For three particle production we provide a complete expression in terms of multipole scattering amplitudes on the nucleus and multi particle generalized TMD's of the proton. We then calculate all the terms that are not suppressed by the factor of the area in four particle production, and generalize this result up to terms of order $1/N_c^2$ for arbitrary number of produced particles. Our results include the contribution of quantum interference effects both in the final state radiation (HBT) and in the initial projectile wave function (Pauli blocking)., Comment: 20 pages

The Cherenkov Telescope Array, CTA, will be the major global observatory for very high energy gamma-ray astronomy over the next decade and beyond. The scientific potential of CTA is extremely broad: from understanding the role of relativistic cosmic particles to the search for dark matter. CTA is an explorer of the extreme universe, probing environments from the immediate neighbourhood of black holes to cosmic voids on the largest scales. Covering a huge range in photon energy from 20 GeV to 300 TeV, CTA will improve on all aspects of performance with respect to current instruments. The observatory will operate arrays on sites in both hemispheres to provide full sky coverage and will hence maximize the potential for the rarest phenomena such as very nearby supernovae, gamma-ray bursts or gravitational wave transients. With 99 telescopes on the southern site and 19 telescopes on the northern site, flexible operation will be possible, with sub-arrays available for specific tasks. CTA will have important synergies with many of the new generation of major astronomical and astroparticle observatories. Multi-wavelength and multi-messenger approaches combining CTA data with those from other instruments will lead to a deeper understanding of the broad-band non-thermal properties of target sources. The CTA Observatory will be operated as an open, proposal-driven observatory, with all data available on a public archive after a pre-defined proprietary period. Scientists from institutions worldwide have combined together to form the CTA Consortium. This Consortium has prepared a proposal for a Core Programme of highly motivated observations. The programme, encompassing approximately 40% of the available observing time over the first ten years of CTA operation, is made up of individual Key Science Projects (KSPs), which are presented in this document., Comment: 213 pages, including references and glossary. Version 2: credits and references updated, some figures updated, and author list updated

List of contributions from the Cherenkov Telescope Array Consortium presented at the 35th International Cosmic Ray Conference, July 12-20 2017, Busan, Korea., Comment: Index of Cherenkov Telescope Array conference proceedings at the ICRC2017, Busan, Korea

Predictions for cold nuclear matter effects on charged hadrons, identified light hadrons, quarkonium and heavy flavor hadrons, Drell-Yan dileptons, jets, photons, gauge bosons and top quarks produced in $p+$Pb collisions at $\sqrt{s_{_{NN}}} = 8.16$ TeV are compiled and, where possible, compared to each other. Predictions of the normalized ratios of $p+$Pb to $p+p$ cross sections are also presented for most of the observables, providing new insights into the expected role of cold nuclear matter effects. In particular, the role of nuclear parton distribution functions on particle production can now be probed over a wider range of phase space than ever before., Comment: 84 pages, 44 figures, version accepted for publication in Nuclear Physics A

We consider forward inclusive production of two quarks in the high energy p-A collisions in the CGC formalism. We demonstrate that the production cross-section is determined by the convolution of the proton generalized double transverse momentum-dependent distribution (2GTMD) functions with two independent eikonal scattering amplitudes: the product of two dipoles and a quadrupole. We explicitly demonstrate that the quadrupole amplitude term accounts for all the (initial and final state) effects of quantum statistics for identical fermions, and the correlations due to these effects. We also demonstrate that the effects due to quantum statistics (entirely encoded in the quadrupole) are parametrically leading contributions to the correlated particle production at large $N_c$. For non-identical quarks the quadrupole term also leads to correlated production which has characteristics similar to the HBT effect., Comment: 15 pages, 1 figure; v3: results unchanged, clarifying comments added. The version to appear in PRD

For ultrarelativistic proton-proton and proton-nucleus collisions, we perform an exploratory study of the contribution to the elliptic flow $v_2$ coming from the orientation of the momentum of the produced particles with respect to the reaction plane. Via the CGC factorization valid at high energies, this contribution is related to the orientation of a color dipole with respect to its impact parameter, which in turn probes the transverse inhomogeneity in the target. Using the McLerran-Venugopalan model (with impact-parameter dependence) as an effective description for the soft gluon distribution in the (proton or nuclear) target, we present a semi-analytic calculation of the dipole scattering amplitude, including its angular dependence. We find that the angular dependence is controlled by soft gluon exchanges and hence is genuinely non-perturbative. The effects of multiple scattering turn out to be essential (in particular, they change the sign of $v_2$). We find that sizable values for $v_2$, comparable to those observed in the LHC data and having a similar dependence upon the transverse momenta of the produced particles, can be easily generated via peripheral collisions. In particular, $v_2$ develops a peak at a transverse momentum which scales with the saturation momentum in the target., Comment: 28 pages, 22 figures; v2: extended version, new discussion about the relation between elliptic flow and eccentricity, 8 new plots and some additional references added

We introduce a technique to study double parton scattering (DPS) in the Color-Glass-Condensate (CGC) approach. We show that the cross-section of the DPS in the CGC approach is calculable in terms of new nonperturbative objects, generalized double transverse momentum-dependent parton distribution (2GTMD) functions. We investigate the production of pairs of prompt photons from two partons in the projectile hadron in high-energy proton-nucleus collisions. We show that even for independent partons in the projectile, the prompt photon correlation function exhibits Hanbury Brown and Twiss (HBT) correlations. The width of the HBT peak is controlled by the transverse distance between the parton of the pair, which is of the order of the proton size. Thus, the HBT measurements in two-particle production such as prompt photon pairs provide useful information about the nonperturbative 2GTMDs., Comment: 14 pages, 3 figures; v2: results unchanged, notation clarified and corrected, references added. The version to appear in PRD

Predictions made in Albacete {\it et al} prior to the LHC $p+$Pb run at $\sqrt{s_{NN}} = 5$ TeV are compared to currently available data. Some predictions shown here have been updated by including the same experimental cuts as the data. Some additional predictions are also presented, especially for quarkonia, that were provided to the experiments before the data were made public but were too late for the original publication are also shown here., Comment: 55 pages 35 figures

The Future Circular Collider (FCC) Study is aimed at assessing the physics potential and the technical feasibility of a new collider with centre-of-mass energies, in the hadron-hadron collision mode, seven times larger than the nominal LHC energies. Operating such machine with heavy ions is an option that is being considered in the accelerator design studies. It would provide, for example, Pb-Pb and p-Pb collisions at sqrt{s_NN} = 39 and 63 TeV, respectively, per nucleon-nucleon collision, with integrated luminosities above 30 nb^-1 per month for Pb-Pb. This is a report by the working group on heavy-ion physics of the FCC Study. First ideas on the physics opportunities with heavy ions at the FCC are presented, covering the physics of the Quark-Gluon Plasma, of gluon saturation, of photon-induced collisions, as well as connections with other fields of high-energy physics., Comment: 57 pages, 28 figures. This document will be part of a CERN Yellow Report on Physics at FCC-hh

We investigate long range rapidity correlations of pairs of prompt photon and jet in the Color Glass Condensate (CGC) framework in proton-proton and proton-nucleus collisions at RHIC and the LHC. We show that photon-jet correlations exhibit long-range azimuthal collimation at near-side for low transverse momenta of the produced photon and jet in high-multiplicity events. These ridge-like features are strikingly similar to the observed ridge effect for di-hadron correlations at RHIC and the LHC. We show that correlations in the relative rapidity and the relative azimuthal angle between pairs of prompt photon and jet strongly depend on the gluon saturation dynamics at small-x kinematics and such measurements can help to understand the true origin of the observed di-hadron ridge in p+A collisions, and address whether the ridge is a universal phenomenon for all two particle correlations at high energy and high multiplicity events. We also investigate if there is a ridge-like structure for photon-hadron pair correlations at RHIC and the LHC. We found that the hadronization of jet has non-trivial effects on the photon-jet correlations., Comment: 15 pages, 12 figures; v2: results unchanged, presentation improved, typos corrected. The version to appear in PRD. arXiv admin note: text overlap with arXiv:1209.0478

We study exclusive dijet production in coherent diffractive processes in deep inelastic scattering and real (and virtual) photon-hadron ($\gamma^{(*)}$-h) collisions in the Color Glass Condensate formalism at leading order. We show that the diffractive dijet cross section is sensitive to the color-dipole orientation in the transverse plane, and is a good probe of possible correlations between the $q\bar{q}$-dipole transverse separation vector $\r$ and the dipole impact parameter $\b$. We also investigate the diffractive dijet azimuthal angle correlations and $t$-distributions in $\gamma^{(*)}$-h collisions and show that they are sensitive to gluon saturation effects in the small-$x$ region. In particular, we show that the $t$-distribution of diffractive dijet photo-production off a proton target exhibits a dip-type structure in the saturation region. This effect is similar to diffractive vector meson production. Besides, at variance with the inclusive case, the effect of saturation leads to stronger azimuthal correlations between the jets., Comment: 15 pages, 10 figures; v2: a clarifying Appendix added, 3 new plots added, references added. The version to appear in PLB

We provide a detailed study of prompt double $J/\psi$ production within the non-relativistic QCD (NRQCD) framework in proton-proton collisions at the LHC. We confront the recent LHC data with the results obtained at leading-order (LO) in the NRQCD framework within two approaches of the collinear factorization and the $k_T$-factorization. We show that the LHCb data are consistent with the $k_T$-factorized LO NRQCD results. We show that the full LO NRQCD formalism cannot describe the recent CMS data, with about one order of magnitude discrepancy. If the CMS data are confirmed, this indicates rather large higher-order corrections for prompt double $J/\psi$ production. We provide various predictions which can further test the NRQCD-based approach at the LHC in a kinematic region that LO contributions dominate. We also investigate long-range in rapidity double $J/\psi$ correlations. We found no evidence of a ridge-like structure for double $J/\psi$ production in proton-proton collisions at the LHC up to subleading $\alpha_s^6$ accuracy., Comment: 10 pages, 14 figures; v2: version includes a complete LO NRQCD calculation in the kT-factorization approach, Color-Octet contributions added, 5 new plots added. The version to appear in PRD

We obtain prompt di-photon cross-section in proton-nucleus collisions in Hamiltonian light-cone approach within a hybrid approximation, treating the projectile proton in the parton model and the target nucleus in the Color-Glass-Condensate approach. We study in details the di-photon correlations in quark-nucleus and proton-nucleus collisions at RHIC and the LHC. We show that the single fragmentation di-photon produces the away side correlations peak, and the double fragmentation component of prompt di-photon is responsible for the near-side peak, and the long-range in rapidity near-side azimuthal collimation, the so-called "ridge" structure. We study the transverse momentum, density and energy dependence of the di-photon ridge and show that it strongly depends on the kinematics and saturation dynamics. We show that while di-photon ridge exists at the LHC in quark-nucleus collisions, the effect disappears in proton-nucleus collisions at the LHC. At RHIC the ridge-type structure persists at low transverse momenta of di-photon even in proton-nucleus collisions. We argue that di-photon correlation measurments in p+A collisions can help to discriminate among models and understand the true origin of the observed di-hadron ridge in p+A collisions. We also show that in addition to the ridge structure, prompt di-photon correlation also exhibits some distinct novel features, including the emergence of away side double-peak structure at intermediate transverse momenta., Comment: 23 pages, 11 figures; v2: results unchanged, a clarifying Appendix added. The version to appear in PRD

We confront saturation-based results for diffractive $\psi(2s)$ and $\rho$ production at HERA and $J/\psi$ photoproduction with all available data including recent ones from HERA, ALICE and LHCb, finding a good agreement. We show that the $t$-distribution of differential cross-section of photoproduction of vector mesons offers a unique opportunity to discriminate among saturation and non-saturation models. This is due to emergence of a pronounced dip (or multiple dips) in the $t$-distribution of diffractive photoproduction of vector mesons at relatively large, but potentially accessible $|t|$ that can be traced back to the unitarity features of colour dipole amplitude in the saturation regime. We provide various predictions for exclusive (photo)-production of different vector mesons including the ratio of $\psi(2s)/J/\psi$ at HERA, the LHC and at future colliders., Comment: 7 pages, 9 figures, to appear in proceedings of DIS 2014, XXII. International Workshop on Deep-Inelastic Scattering and Related Subjects, 28 April - 2 May 2014, Warsaw, Poland

The Impact-Parameter dependent Color Glass Condensate (b-CGC) and Saturation (IP-Sat) dipole models incorporate key features of small-x physics properties and match smoothly to the perturbative QCD regime at large $Q^2$ for a given $x$. Although both models include saturation effects and depend on impact-parameter, the former is based on the non-linear BK equation, while the latter is based on DGLAP evolution. After confronting the models to the recently released high precision combined HERA data, we show that in both models, the typical impact-parameter probed in the total $\gamma^{*}p$ cross-section is about $b\approx 2\div 3\,\text{GeV}^{-1}$ and the proton saturation scale is $Q_S<1$ GeV in HERA kinematics. We show that most features of inclusive DIS and exclusive diffractive data at HERA are correctly reproduced in both models. Nevertheless, the b-CGC and the IP-Sat models give significantly different predictions beyond the current HERA kinematics for the structure functions at very low x and high virtualities $Q^2$, and for the exclusive diffractive vector meson and DVCS production at high $t$., Comment: 7 pages, 10 figures. To appear in proceedings of DIS 2014, XXII. International Workshop on Deep-Inelastic Scattering and Related Subjects, 28 April - 2 May 2014, Warsaw, Poland

We consider semi-inclusive diphoton+jet and inclusive diphoton production in high-energy proton-nucleus collisions, treating the target nucleus as a Color-Glass-Condensate and the projectile proton in the parton model. We obtain the prompt diphoton production cross-section in terms of fragmentation and direct contributions. The fragmentation part is given in terms of single-photon and double-photon fragmentation functions. We study prompt, direct and fragmentation diphoton correlations in p+p and p+A collisions at the LHC, and show that at low values of transverse momenta of the produced photon pair, these correlations are sensitive to saturation effects. We show that back-to-back (de)-correlations in prompt diphoton production are stronger in fragmentation part than in the direct one., Comment: 17 pages, 8 figures; v2: results unchanged, a clarifying footnote added. The version to appear in PRD

We systematically study exclusive diffractive (photo) production of vector mesons ($J/\psi$, $\psi(2s)$, $\phi$ and $\rho$) off protons in high-energy collisions and investigate whether the production is a sensitive probe of gluon saturation. We confront saturation-based results for diffractive $\psi(2s)$ and $\rho$ production at HERA and $J/\psi$ photoproduction with all available data including recent ones from HERA, ALICE and LHCb, finding good agreement. In particular, we show that the $t$-distribution of differential cross sections of photoproduction of vector mesons offers a unique opportunity to discriminate among saturation and non-saturation models. This is due to the emergence of a pronounced dip (or multiple dips) in the $t$-distribution of diffractive photoproduction of vector mesons at relatively large, but potentially accessible $|t|$ that can be traced back to the unitarity features of colour dipole amplitude in the saturation regime. We show that in saturation models the dips in $t$-distribution recede towards lower $|t|$ with decreasing mass of the vector meson, increasing energy or decreasing Bjorken-$x$, and decreasing virtuality $Q$. We provide various predictions for exclusive (photo) production of different vector mesons including the ratio of $\psi(2s)/J/\psi$ at HERA, the LHC, and future colliders., Comment: 20 pages, 24 figures; v3: the old LHCb data replaced with updated 2014 data, ALICE preliminary data added for the comparison, all results and predictions unchanged, 10 new plots added, more predictions, discussions and references added. The version to appear in PRD

The first moment of the charged-particle transverse momentum spectrum and its correlation with the charged-particle multiplicity N_{ch} provide vital information about the underlying particle production mechanism. The ALICE collaboration recently reported that versus N_{ch} in Pb+Pb collisions is smaller than in p+p and p+Pb collisions. Other interesting features of data is rather flatness of at high N_{ch} in Pb+Pb and p+Pb collisions in seemingly striking contrast to the case of p+p collisions. With a detailed calculation, we show all these peculiar features in a wide range of energies and system sizes can be well described by the idea of gluon saturation within the Color Glass Condensate framework using the k_T-factorization. This establishes an important fact that the bulk of the produced particles in heavy-ion collisions at the LHC carries signature of the initial stage of collisions. We also show that the recent scaling property seen by the CMS collaboration between the number of tracks in p+p and p+Pb collisions may provide a strong evidence in favor of geometric-scaling phenomenon and gluon saturation, indicating that the underlying dynamics of high multiplicity events in p+p and p+Pb collisions should be similar., Comment: 11 pages, 9 figures; v2: predictions are extended to large N_ch, two new plots added. The version to appear in PLB

The Impact-Parameter dependent Color Glass Condensate (b-CGC) dipole model is based on the Balitsky-Kovchegov non-linear evolution equation and improves the Iancu-Itakura-Munier dipole model by incorporating the impact-parameter dependence of the saturation scale. Here we confront the model to the recently released high precision combined HERA data and obtain its parameters. The b-CGC results are then compared to data at small-x for the structure function, the longitudinal structure function, the charm structure function, exclusive vector meson (J/\psi, \phi, \rho) production and Deeply Virtual Compton Scattering (DVCS). We also compare our results with the Impact-Parameter dependent Saturation model (IP-Sat). We show that most features of inclusive DIS and exclusive diffractive data, including the Q^2, W, |t| and x dependence are correctly reproduced in both models. Nevertheless, the b-CGC and the IP-Sat models give different predictions beyond the current HERA kinematics, namely for the structure functions at very low x and high virtualities Q^2, and for the exclusive diffractive vector meson and DVCS production at high t. This can be traced back to the different power-law behavior of the saturation scale in x, and to a different impact-parameter b dependence of the saturation scale in these models. Nevertheless, both models give approximately similar saturation scale Q_S<1 GeV for the proton in HERA kinematics, and also both models lead to the same conclusion that the typical impact-parameter probed in the total \gamma^{*}p cross-section is about b\approx 2\div 3 GeV^{-1}. Our results provide a benchmark for further investigation of QCD at small-x in heavy ion collisions at RHIC and the LHC and also at future experiments such as an Electron-Ion Collider and the LHeC., Comment: 21 pages, 31 figures; v3: results unchanged, more comparison with HERA data added, one plot and references added. The version to appear in PRD

In this talk, we present a global analysis of available small-x data on inclusive DIS and exclusive diffractive processes, including the latest data from the combined HERA analysis on reduced cross sections within the Impact-Parameter dependent Saturation (IP-Sat) Model. The impact-parameter dependence of dipole amplitude is crucial in order to have a unified description of both inclusive and exclusive diffractive processes. With the parameters of model fixed via a fit to the high-precision reduced cross-section, we compare model predictions to data for the structure functions, the longitudinal structure function, the charm structure function, exclusive vector mesons production and Deeply Virtual Compton Scattering (DVCS). Excellent agreement is obtained for the processes considered at small x in a wide range of Q^2., Comment: 7 pages, 5 figures, talk given by A.R. at the XXI International Workshop on Deep-Inelastic Scattering and Related Subjects (DIS2013), Marseille, 22-26 April 2013

Predictions for charged hadron, identified light hadron, quarkonium, photon, jet and gauge bosons in p+Pb collisions at sqrt s_NN = 5 TeV are compiled and compared. When test run data are available, they are compared to the model predictions., Comment: 84 pages

The Impact-Parameter dependent Saturation Model (IP-Sat) is a simple dipole model that incorporates key features of the physics of gluon saturation and matches smoothly to the perturbative QCD dipole expression at large Q^2 for a given x. It was previously shown that the model gives a good description of HERA data suggesting evidence for gluon saturation effects at small x. The model has also been applied to proton-proton and proton-nucleus collisions and provides the basis for the IP-Glasma model of initial conditions in heavy ion collisions. Here we present a reanalysis of available data in electron-proton collisions at small Bjorken-x, including the recently released combined data from the ZEUS and H1 collaborations. We first confront the model to the high precision combined data for the reduced cross-section and obtain its parameters. With these parameters fixed, we compare model results to data for the structure function F_2, the longitudinal structure function F_L, the charm structure function F_2^{c\bar{c}}, exclusive vector meson (J/\psi, \phi and \rho) production and Deeply Virtual Compton Scattering (DVCS). Excellent agreement is obtained for the processes considered at small x in a wide range of Q^2. Our results strongly hint at universality of the IP-Sat dipole amplitude and the extracted impact-parameter distribution of the proton. They also provide a benchmark for further refinements in studies of QCD saturation at colliders., Comment: 17 pages, 18 figures

We present various predictions for the upcoming p+Pb collisions at \sqrt{S}=5 TeV within the color glass condensate (CGC) formalism, including single inclusive charged hadron production, single inclusive prompt photon production, direct photon production, charged hadron multiplicity distribution and photon-hadron azimuthal correlations. Using the running-coupling Balitsky-Kovchegov evolution equation for calculating various observables, we show that the main source of uncertainties is due to less constrained initial nuclear saturation scale. This gives rise to rather large theoretical uncertainties for nuclear modification factor R_{pA} at the LHC. Nevertheless, we propose a simple scheme in which one can still test the main dynamics of the CGC/saturation in p+A collisions at the LHC., Comment: 16 pages, 17 figures; v2: predictions/results unchanged, typos corrected, references added, predictions for charged hadron multiplicity distribution at various centralities in p+Pb collisions at 5.02 TeV added, a note with comparison to the p+Pb data from the ALICE Collaboration added. The version to appear in PLB

We investigate semi-inclusive photon-hadron production in the color glass condensate (CGC) framework at RHIC and the LHC energies in proton-proton (pp) and proton-nucleus (pA) collisions. We calculate the coincidence probability for azimuthal correlation of pairs of photon-hadron and show that the away-side correlations have a double-peak or a single-peak structure depending on trigger particle selection and kinematics. This novel feature is unique for semi-inclusive photon-hadron production compared to a similar measurement for double inclusive dihadron production in pA collisions. We obtain necessary conditions between kinematics variables for the appearance of a double-peak or a single peak structure for the away-side photon-hadron correlations in pp and pA collisions at forward rapidities and show that this feature is mainly controlled by the ratio p_T^hadron/p_T^photon. Decorrelation of away-side photon-hadron production by increasing the energy, rapidity and density, and appearance of double-peak structure can be understood by QCD saturation physics. We also provide predictions for the ratio of single inclusive prompt photon to hadron production, and two-dimensional nuclear modification factor for the semi-inclusive photon-hadron pair production at RHIC and the LHC at forward rapidities., Comment: 16 pages, 20 figures; v2: latex Compilation problem in Figs. 3,4 corrected

The forthcoming LHC measurements in proton-nucleus (pA) collisions at forward rapidities can discriminate between the color glass condensate (CGC) and alternative approaches including standard collinear factorization one. We report some of our recent predictions based on gluon saturation/CGC formalism for pA collisions at the LHC including the charged hadron multiplicity distribution, the nuclear modification factor for single inclusive hadron and prompt photon production, and the azimuthal angle correlation of the semi-inclusive hadron-photon production., Comment: 4 pages, 8 figures; v2: a typo corrected. Talk given at "Hard Probes 2012", 27 May - 1 June, 2012, Cagliari, Italy

We investigate inclusive prompt photon and semi-inclusive prompt photon-hadron production in high energy proton-nucleus collisions using the Color Glass Condensate (CGC) formalism which incorporates non-linear dynamics of gluon saturation at small x via Balitsky-Kovchegov equation with running coupling. For inclusive prompt photon production, we rewrite the cross-section in terms of direct and fragmentation contributions and show that the direct photon (and isolated prompt photon) production is more sensitive to gluon saturation effects. We then analyze azimuthal correlations in photon-hadron production in high energy proton-nucleus collisions and obtain a strong suppression of the away-side peak in photon-hadron correlations at forward rapidities, similar to the observed mono-jet production in deuteron-gold collisions at forward rapidity at RHIC. We make predictions for the nuclear modification factor R_{p(d)A} and photon-hadron azimuthal correlations in proton(deuteron)-nucleus collisions at RHIC and the LHC at various rapidities., Comment: 18 pages, 16 figures; v2: 3 plots added. The version to appear in PRD

The forthcoming LHC measurement of hadron multiplicity in proton-nucleus collisions is a crucial test of the k_t factorization and gluon saturation based models. Here, we provide quantitative predictions for the pseudorapidity distribution of charged particles produced in minimum bias proton-nucleus collisions at the LHC based on the idea of gluon saturation in the color-glass condensate framework. Our formulation gives good descriptions of the LHC and RHIC data for the charged-hadron multiplicities in both proton-proton and nucleus-nucleus collisions, and also the deep inelastic scattering at HERA at small Bjorken-x., Comment: 5 pages, 3 figures; v2: version improved. The version to appear in PRD

We extract the energy-dependence of the gluon-jet decay cascade from e^+e^- annihilation data and show that this energy-dependence has power-low behavior for the average transverse momentum of jet bigger than 1 GeV. We show that the observed different power-law energy-dependence of hadron multiplicity in AA compared to pp collisions at the LHC is due to the enhanced gluon-decay effect before hadronization. This effect is more important for AA collisions where the saturation scale is larger than 1 GeV. Here we confront our published predictions in arXiv:1102.2385 for the rapidity distribution of the charged hadron production with the recently released data from the CMS collaboration in AA collisions and show that our predictions is in perfect agreement with the data., Comment: 8 pages, 7 figures, contribution to the proceedings of "Low-x 2011", Santiago de Compostela (Spain), June 3-7, 2011

We investigate the contribution of inelastic and elastic processes to single inclusive hadron production in proton-proton and proton (deuteron)-nucleus collisions at RHIC and the LHC. Using the hybrid formulation which includes both elastic and inelastic contributions, supplemented with the running-coupling Balitsky-Kovchegov equation, we get a good description of RHIC data. It is shown that inclusion of the inelastic terms makes the transverse momentum dependence of the production cross section steeper in the mid-rapidity region but does not affect the cross section in the very forward region. The inelastic processes also lead to a sharper increase of the nuclear modification factor R_{pA} with increasing p_T. We also make predictions for the nuclear modification factor in proton-nucleus collisions at the LHC (\sqrt{s}=4.4 and 8.8 TeV) at various rapidities using the Color Glass Condensate framework., Comment: 11 pages, 12 figures; v3: references added. The version to appear in PRD

We show that the long-range rapidity correlations between the produced charged-hadron pairs from two BFKL parton showers generate considerable azimuthal angle correlations. These correlations have no 1/N_c suppression. The effect of gluon saturation on these correlations are discussed and we show that it is important. We show that a pronounced ridge-like structure emerges by going from the BFKL to the saturation region. We show that the ridge structure at high-energy proton-proton and nucleus-nucleus collisions has the same origin and its main feature can be understood due to initial-state effects. Although the effects of final-state interactions in the latter case can be non-negligible., Comment: 12 pages, 6 figures; v2: version improved. The version to appear in Phys. Rev. D

The recent results in \sqrt{s}=2.76 TeV Pb+Pb collisions at the Large Hadron Collider (LHC) reported by the ALICE collaboration shows that the power-law energy-dependence of charged hadron multiplicity in Pb+Pb collisions is significantly different from p+p collisions. We show that this different energy-dependence can be explained by inclusion of a strong angular-ordering in the gluon-decay cascade within the Color-Glass-Condensate (or gluon saturation) approach. This effect is more important in nucleus-nucleus collisions where the saturation scale is larger than 1 GeV. Our prescription gives a good description of the LHC data both in p+p and Pb+Pb collisions., Comment: 11 pages, 8 figures; v2: references added, results unchanged, discussion added about the centrality dependence of average transverse momentum over the charged-particle multiplicity at RHIC and the LHC. The version to appear in Phys. Rev. D

We confront soft Pomeron and gluon saturation models with the first LHC data on inclusive hadron production. We claim that while the first type of models are not able to describe some part of the LHC data, the Colour-Glass-Condensate (gluon saturation) approach gives an adequate description of the data. Here, we compare our published predictions with the recently available 7 TeV data. We firmly believe that if further experimental measurements confirm that the gluon saturation works, it will be a major discovery., Comment: 8 pages, 12 figure, Based on two talks given by authors at Diffraction 2010, Otranto (Lecce), Italy, September 10-15, 2010

We show that pQCD factorization incorporated with pre-haronization energy-loss effect naturally leads to flatness of the nuclear modification factor R_{AA} for produced hadrons at high transverse momentum p_T. We consider two possible scenarios for the pre-hadronization: In scenario 1, the produced gluon propagates through dense QCD medium and loses energy. In scenario 2, all gluons first decay to quark-antiquark pairs and then each pair loses energy as propagating through the medium. We show that the estimates of the energy-loss in these two different models lead to very close values and is able to explain the suppression of high-p_T hadrons in nucleus-nucleus collisions at RHIC. We show that the onset of the flatness of R_{AA} for the produced hadron in central collisions at midrapidity is about p_T\approx 15 and 25 GeV at RHIC and the LHC energies, respectively. We show that the smallness (R_{AA}<0.5) and the high-p_T flatness of R_{AA} obtained from the k_T factorization supplemented with the Balitsky-Kovchegov (BK) equation is rather generic and it does not strongly depend on the details of the BK solutions. We show that energy-loss effect reduces the nuclear modification factor obtained from the k_T factorization about 30\div 50% at moderate p_T., Comment: 14 pages, 10 figures; v2: results unchanged, more discussion and references added. The version to appear in Nucl. Phys. A

We provide quantitative predictions for the rapidity, centrality and energy dependencies of inclusive charged-hadron productions for the forthcoming LHC measurements in nucleus-nucleus collisions based on the idea of gluon saturation in the color-glass condensate framework. Our formulation gives very good descriptions of the first data from the LHC for the inclusive charged-hadron production in proton-proton collisions, the deep inelastic scattering at HERA at small Bjorken-x, and the hadron multiplicities in nucleus-nucleus collisions at RHIC., Comment: 7 pages, 8 figures; v3: minor changes, one reference added, results unchanged, the version to appear in Phys. Rev. D

In high density QCD the hadron production stems from decay of mini-jets that have the transverse momenta of the order of the saturation scale. It is shown in this paper that this idea is able to describe in a unique fashion both the inclusive hadron production for \sqrt{s} \geq 546 GeV including the first data from LHC and the deep inelastic scattering at HERA. Recently reported data from ALICE, CMS and ATLAS including inclusive charged-hadron transverse-momentum and multiplicity distribution in pp collisions are well described in our approach. We provide predictions for the upcoming LHC measurements., Comment: 14 pages, 9 figures; v2: version improved, more discussion and references added, results unchanged, version accepted to Phys. Rev. D

We investigate hadrons and direct photon production in pp collisions at the LHC energy within the color-dipole approach. We show that greatest sensitivity to gluon saturation effects is reached at very forward rapidities in pp collisions at LHC (\sqrt{s}=14 TeV). The discrepancies among various saturation models (fitted to HERA data) results can be about a factor of 2-3 at forward rapidities. We found that the ratio of direct-photon to pion production can be about 20-10 at forward rapidities \eta=7-8. Therefore, direct photon production at forward rapidities should provide a rather clean probe as the background from radiative hadronic decays is significantly suppressed., Comment: 4 pages, 6 figures, Contributed to "Lepton-Photon 2009 (LP09)", Hamburg, Germany

We provide predictions for the nuclear modification factor R_{pA} for pions and direct photon production in p+A collisions at LHC energy at midrapidity within different saturation models fitted to HERA data. In our approach we have no free parameters to adjust and all model parameters are fitted to other reactions. Our approach gives a rather good description of PHENIX data for R_{pA} for pions. We show that, in various saturation models, the pion Cronin enhancement is replaced by a moderate suppression at LHC energy at midrapidity due to gluon shadowing effects. However, Cronin enhancement of direct photons can survive at LHC energy in models with a larger saturation scale. We show that both shadowing and saturation effects are important at LHC in p+A collisions and give rise to a rather sizable effect in the nuclear modification factor R_{pA}. Therefore, a precise measurement of p+A collisions at LHC is crucial in order to understand the underlying dynamics of heavy ion collisions., Comment: 4 pages, 3 figures, talk given at "The 2009 Europhysics Conference on High Energy Physics", 16-22 July 2009, Krakow, Poland

We investigate hadrons and direct photon production in pp and pA collisions at the energies of RHIC and LHC within the color-dipole approach employing various saturation models. We show that greatest sensitivity to saturation effects is reached at very forward rapidities for pp collisions at LHC (\sqrt{s}=14 TeV). The ratio of direct-photon to pion production can be about 20-10 (at \eta=7-8). Therefore, direct photon production at forward rapidities should provide a rather clean probe. We calculate the rapidity dependence of the invariant cross-section and find some peculiar enhancement at forward rapidities which is more pronounced for direct photon production. We show that this peak is further enhanced by saturation effects. We provide predictions for the nuclear modification factor R_{pA} for pions and direct photon production in pA collisions at LHC energy at midrapidity. We show within various saturation models that the pion Cronin enhancement at RHIC is replaced by a moderate suppression at LHC energy at midrapidity due to gluon shadowing effects. Cronin enhancement of direct photons can survive at LHC energy within models with a larger saturation scale., Comment: 21 pages, 23 figures; v2: version improved, more discussion and references added, version accepted to Phys. Rev. D

We show that HERA data for the inclusive structure function F_2(x,Q^2) at small Bjorken-x and Q^2 can be reasonably well described by a color-dipole model with an AdS/CFT-inspired dipole-proton cross section. The model contains only three free parameters fitted to data. In our AdS/CFT-based parameterization the saturation scale varies in the range of 1-3 GeV becoming independent of energy/Bjorken-x at very small x. This leads to the prediction of x-independence of the F_2 and F_L structure functions at very small x. We provide predictions for F_2 and F_L in the kinematic regions of future experiments. We discuss the limitations of our approach and its applicability region, and argue that our AdS/CFT-based model of non-perturbative physics could be viewed as complimentary to the perturbative description of data based on saturation/Color Glass Condensate physics., Comment: 23 pages, 10 figures; v3: new plots added showing our model predictions for charm and longitudinal structure functions and photoproduction cross-section, discussion extended. The version to appear in PRD

We investigate direct photon production in pp collisions at the energies of RHIC, CDF and LHC, at different rapidities employing various color-dipole models. The cross section peaks at forward rapidities due to the abelian dynamics of photon radiation. This opens new opportunities for measurement of direct photons at forward rapidities, where the background from radiative hadronic decays is strongly suppressed. Our model calculations show that photon production is sensitive to the gluon saturation effects, and strongly depends on the value of the anomalous dimension., Comment: 7 pages, 8 figures, minor clarifications added. The version to appear in PLB

These lectures stress the theoretical elements that underlie a wide range of phenomenological studies of high-energy QCD, which include both soft and hard processes. After a brief introduction to the basics of QCD, various aspects of QCD-based phenomenology are covered: colour transparency, hadronization of colour charges, Regge phenomenology, parton model, Bjorken scaling and its violation, DGLAP evolution equation, BFKL formalism, GLR-MQ evolution equation and saturation. In the last part of the lecture, we employ the light-cone dipole formalism to describe deep inelastic lepton scattering, Drell-Yan processes, direct photon production, diffraction, quark and gluon shadowing in nuclei, the Cronin effect and nuclear broadening., Comment: 66 pages, 51 figures, Based on lectures given by B.K. at the 4th CERN-CLAF School of High-Energy Physics, Vina del Mar, Chile, 18 February - 3 March 2007, v.2: minor changes. The version to appear in Int. J. Mod. Phys. E

Pions and protons production cross-sections are analyzed in proton-proton and proton-nucleus collisions at the RHIC energy at midrapidity. We employ the pQCD factorization scheme supplemented with the color-dipole formalism to investigate the Cronin effect. We calculate the broadening in the color-dipole approach for different centralities. Our main goal is to investigate, in a parameter-free manner within a unified framework, how much of the cronin effect for both pions and baryons comes from the transverse momentum broadening due to initial partons multi-scatterings. We conclude that final-state effects in pA collisions are important. Uncertainties in nuclear shadowing of various parton distributions and parton fragmentation functions are also discussed., Comment: 7 pages, 8 figures

We investigate the azimuthal asymmetry v2 of produced pions in pp and pA collisions at both RHIC and SPS energies. In our approach, based on the pQCD parton model and the light-cone QCD-dipole formalism, the azimuthal asymmetry results from a correlation between the color-dipole orientation and the impact parameter of the collision. We introduce the color-dipole orientation within an improved Born approximation and the saturation model which satisfies available DIS data, showing that the azimuthal asymmetry of partons and pions is very sensitive to the choice of the model, and that it is reduced in the saturation model. We find that v2 of quarks and gluons in parton-nucleus collisions have very different patterns. The azimuthal asymmetry of gluons in gluon-nucleus collisions can be negative at small transverse momentum, changes the sign and becomes positive at high transverse momentum. The azimuthal asymmetry of quarks in quark-nucleus collisions is positive at all values of transverse momentum. We find that the azimuthal anisotropy v2 of produced pions in both pp and pA collisions is positive, albeit rather small., Comment: 17 pages, 11 figures, minor typos corrected, references added. The version to appear in Phys. Rev. D

The azimuthal asymmetry of direct photons originating from primary hard scatterings between partons is calculated. This can be accounted for by the inclusion of the color dipole orientation, which is sensitive to the rapid variation of the nuclear profile. To this end we introduce the dipole orientation within the saturation model of Golec-Biernat and W\"usthoff, while preserving all its features at the cross-section level. We show that the direct photon elliptic anisotropy v2 coming from this mechanism changes sign and becomes negative for peripheral collisions, albeit it is quite small for nuclear collisions at the RHIC energy., Comment: 6 pages, 6 figures, Based on talk given by A.H.R. at II LAWHEP, Sao Miguel das Missoes, Brazil, December 3-7, 2007

The azimuthal elliptic asymmetry v2 observed in heavy ion collisions, is usually associated with properties of the medium created in the final state. We compute the azimuthal asymmetry which is due to multiple interactions of partons at the initial stage of nuclear collisions, and which is also present in $pA$ collisions. In our approach the main source of azimuthal asymmetry is the combination of parton multiple interactions with the steep variation of the nuclear density at the edge of nuclei. We apply the light-cone dipole formalism to compute the azimuthal asymmetry of prompt photons yield from parton-nucleus, proton-nucleus and nucleus-nucleus collisions at the RHIC energy., Comment: 13 pages, 4 figures, Eq.(4) corrected, figures and references updated. The version to appear in Nucl. Phys. A

The electromagnetic bremsstrahlung produced by a quark interacting with nucleons or nuclei is azimuthally asymmetric. In the light-cone dipole approach this effect is related to the orientation dependent dipole cross section. Such a radiation anisotropy is expected to contribute to the azimuthal asymmetry of direct photons in pA and AA collisions, as well as in DIS and in the production of dileptons., Comment: Equations (23), (26) and the figures are corrected, references added. The version to appear in Phys. Rev. D

This writeup is a compilation of the predictions for the forthcoming Heavy Ion Program at the Large Hadron Collider, as presented at the CERN Theory Institute 'Heavy Ion Collisions at the LHC - Last Call for Predictions', held from May 14th to June 10th 2007., Comment: LaTeX, 185 pages, uses iop styles; writeup of the CERN Theory Institute 'Heavy Ion Collisions at the LHC - Last Call for Predictions', held from May 14th to June 10th 2007

The DGLAP improved color dipole approach provides a good description of data for inclusive direct photon spectra at the energies of RHIC and Tevatron. Within the same framework we predict the transverse momentum distribution of direct photons at the CERN LHC energies., Comment: 2 pages, 2 figures. Contributed to Workshop on Heavy Ion Collisions at the LHC: Last Call for Predictions, Geneva, Switzerland, 14 May - 8 Jun 2007