Exclusive production of four charged pions at the ep collider HERA is studied at small photon virtualities $Q^2<2$ GeV${}^2$. The data were taken with the H1 detector in the years 2006 and 2007 at a centre-of-mass energy of $\sqrt{s}=319$ GeV and correspond to an integrated luminosity of 7.6 pb$^{-1}$. The cross section of the reaction $\gamma p \to 2(\pi^+\pi^-)Y$ is determined in the phase...
We study quantitatively [1] the importance of the recently derived NLO corrections [2,3,4] to the DIS structure functions at small x in the dipole formalism. We show that these corrections can be significant and depend on the factorization scheme used to resum large logarithms of energy into renormalization group evolution with the BK equation. This feature is similar to what has recently...
We report on a first NLO computation of inclusive photon production at small x in
e+A collisions. The computation is performed to next-to-leading-log x accuracy and resums all multiple scattering (higher twist) computations within the CGC effective theory. In the soft photon (Low) limit, we recover results the NLO results of Balitsky and Chirilli for inclusive DIS. We point to key technical...
A photon is a fundamental particle, instead of a nonperturbative composite like hadrons. However, an energetic photon can fluctuate into vector mesons in the kinematic region with a small Bjorken variable $x < 0.1$. Particularly at $x < 0.01$, the hadronic contribution to cross sections of the electron-photon deep inelastic scattering dominates, and a photon can be regarded as a hadron rather...
Calculations for dijet production in diffractive deep-inelastic scattering (DIS) at next-to-next-to-leading order accuracy (NNLO) are presented. The calculations are based on the antenna subtraction formalism and the hard coefficients are convoluted with currently available PDFs for diffractive scattering (DPDFs).
The NNLO predictions are compared to a large number of available measurements...
A correct modelling of the underlying event in proton-proton collisions is important for the proper simulation of kinematic distributions of high-energy collisions. The ATLAS collaboration extended previous studies at 7 TeV with a leading track or jet or Z boson by a new study at 13 TeV, measuring the number and transverse-momentum sum of charged particles as a function of pseudorapidity and...
We present results on the measurement of the underlying event at 13 TeV and recent results from Minimum Bias measurements with the CMS experiment.
New CMS PYTHIA 8 event tunes are presented. The new tunes are obtained using minimum bias and underlying event observables using Monte Carlo configurations with consistent parton distribution functions and strong coupling constant values in the matrix element and the parton shower. Validation and performance studies are presented by comparing the predictions of the new tune to various soft-...
Inclusive four-jet events produced in proton--proton collisions at a center-of-mass energy of 7 TeV have been analyzed for the presence of hard double parton scattering collected with the ATLAS detector. The contribution of hard double parton scattering to the production of four-jet events has been extracted using an artificial neural network. The assumption made was that hard double parton...
We present recent results on Double Parton Scattering (DPS) studies using data collected during Run 1 and Run 2 of the LHC with the CMS experiment. Double parton scattering is investigated in several final states including vector bosons and multi-jets. Measurements of observables designed to highlight the DPS contribution are shown and compared to MC predictions from models based on multiple...
We present recent results on forward energy flow and forward jet production measurements in CMS, including measurements with proton-proton collisions at 13 TeV, and proton-lead collisions at 5 TeV.
We improve the state-of-the-art description of the disappearance of the away-side peak in forward pA collisions at Relativistic Heavy Ion Collider (RHIC) energies in the framework of the Color Glass Condensate (CGC).
Using the recently proposed improved transverse momentum dependent (ITMD) factorization formula for two-particle production in the back-to-back limit, we derive a parameter-free...
Using the formalism of the light-cone wave function in perturbative QCD together with the hybrid factorization, we compute the cross-section for three particle production at forward rapidities in proton-nucleus collisions. In this picture, the three produced partons — a quark accompanied by a gluon pair, or two quarks plus one antiquark — are all generated via two successive splittings of a...
We calculate the transverse momentum dependent gluon-to-gluon splitting function within kT-factorization, generalizing the framework employed in the calculation of the quark splitting functions in [1205.1759, 1511.08439, 1607.01507] and demonstrate at the same time the consistency of the extended formalism with previous results. While existing versions of kT factorized evolution equations...
We discuss the \gamma \to \rho^0 impact factor, i.e., the transition amplitude of a photon to a neutral vector meson \rho^0, where the transition is mediated by the two t-channel gluons. The impact factor is a building block in the QCD descriptions of high-energy exclusive processes like $\gamma p \to V p$, and $\gamma\gamma \to V V$, with $V = \rho^0, \omega, \phi$, …. In the framework of QCD...
Coherent photoproduction of vector mesons is sensitive to the shape of the target nucleus, as probed at Q^2 ~ (M_V/2)^2. Previously STAR presented a high-statistics measurement of d\sigma/dt for rho^0 photoproduction in ultra-peripheral Au+Au collisions, and made a two-dimensional Fourier-Bessel (Hanckel) transformation to give the distribution of targets in the nucleus. Here, we study the Q^2...
The electromagnetic field of a fast moving lead ion at the LHC is an intense source of quasi-real photons. This makes it possible to study J/Psi exclusive photoproduction off protons in p-Pb collisions at the LHC. This process is sensitive to the gluon content of the target. Measuring the scattering angle of the produced vector meson one can compute the centre-of-mass energy (W) of the...
We present recent results on the exclusive production of the Upsilon and rho mesons with the CMS experiment in proton-lead collisions at 5 TeV. And measurements of dipion production in proton-proton collisions at 5, 7, and 13 TeV.
In this contribution we present a comprehensive analysis of exclusive vector-meson photoproduction in $pp$, $pPb$ and $PbPb$ collisions at Run 2 LHC energies using the color dipole formalism. The rapidity distributions and total cross sections for the $\rho$, $\phi$, $J/\Psi$ and $\Upsilon$ production are estimated considering the more recent phenomenological models for the dipole-proton...
We present a model of coherent and incoherent photoproduction of vector mesons off proton and off nuclear targets. The computations are perfomed within the color-dipole formalism. The targets are described by a profile, in the impact parameter space, including subnucelon degrees of freedom, so-called hot spots. Their positions change event by event. The key aspect of our model is that the...
In the absence of forward proton tagging, exclusive processes can be distinguished in the central part of the ATLAS detector exploiting the large rapidity gap in the central region and the absence of charged particles reconstructed in the inner tracking detector. This strategy has been exploited to study the exclusive production of dilepton pairs in the data taken at centre-of-mass energies of...
The CT-PPS (CMS-TOTEM Precision Proton Spectrometer) detector system consists of silicon tracking stations as well as timing detectors to measure both the position and direction of protons and their time-of-flight with high precision. They are located at around 200 m from the interaction point in the very forward region on both sides of the CMS experiment. CT-PPS is built to study Central...
The TOTEM experiment at the interaction point 5 of the LHC has measured the total, elastic and inelastic proton-proton cross sections in a centre-of-mass energy range from 2.76 to 13 TeV, in dedicated fills with special beam optics.
Most recently, TOTEM has performed the first measurement of the ρ parameter at $\sqrt{s} = 13$ TeV, where rho is the ratio between the real and the imaginary...
The dynamics of gluons in high energy proton and nuclei interactions remain an elusive process. Gluon interactions can be accessed via both light and heavy flavor hadron production at the PHENIX experiment at RHIC. In particular, via systematically measuring the nuclear modification in light hadron production in p+A and light-ion-A collisions at $\sqrt{s_{NN}} = 200$ GeV, we observed a...
The unique acceptance of the LHCb experiment at the LHC offers the ability to make studies of QCD that are complementary to those made at the other LHC experiments.
A selection of recent results will be presented, including production measurements, inelastic cross-section measurements, and studies of correlations in particle production.
Heavy quark pair production in minimum bias p+p and p+A collisions has been studied extensively in the CGC framework and compared successfully to both the RHIC and LHC data on $J/\psi$ production [1, 2], $\psi(2S)$ production [3] and $D$-meson production [4]. We first present an update in this framework based on comparisons to the latest LHC and RHIC data on p+p and light-heavy ion collisions....
We report on a recent computation of the NLO inclusive photon cross section using the Color Glass Condensate framework at the RHIC and LHC energies. Our result is appropriate for collisions where a dilute projectile (proton) hits a dense target (a proton or a heavy ion). We will briefly elucidate the main analytic NLO formula obtained in [1], while the main focus of this contribution are the...
The ridge structure in two-particle correlations produced in high multiplicity collisions at the LHC have been examined in the Color Glass Condensate formalism. In this formalism it was found that in the dilute-dilute nucleus limit, corresponding to glasma graphs, the ridge structure was due to the Bose enhancement associated with two-gluon production, with a successful phenomenology developed...
We present recent results on diffraction with the CMS and TOTEM experiments.
Light-by-light (LbyL) scattering ($\gamma\gamma \rightarrow \gamma\gamma$) is a fundamental quantum-mechanical process with tiny cross sections. Studies of LbyL scattering, using the large photon fluxes from ultraperipheral PbPb collisions at sqrt(s_N) = 5.02 TeV at the LHC, will be reported based on the evidence of a signal corresponding to an integrated luminosity of 391 $\mu b^{-1}$. The...
