Close to one half of the LHC events are expected to be due to elastic or inelastic diffractive scattering. Still, predictions based on extrapolations of experimental data at lower energies differ by large factors in estimating the relative rate of diffractive event categories at the LHC energies. By identifying diffractive events, detailed studies on proton structure can be carried out.
The combined forward physics objects: rapidity gaps, forward multiplicity and transverse energy flows can be used to efficiently classify proton-proton collisions. Data samples recorded by the forward detectors, with a simple extension, will allow first estimates of the single diffractive (SD), double diffractive (DD), central diffractive (CD), and non-diffractive (ND) cross sections. The approach, which uses the measurement of inelastic activity in forward and central detector systems, is complementary to the detection and measurement of leading beam-like protons.
In this investigation, three different multivariate analysis approaches are assessed in classifying forward physics processes at the LHC. It is shown that with gene expression programming, neural networks and support vector machines, diffraction can be efficiently identified within a large sample of simulated proton-proton scattering events. The event characteristics are visualized by using the self-organizing map algorithm.
The PYTHIA 8 generator is used to estimate the percentage of non-diffractive and diffractive events at the LHC energies. It is shown that a simple condition of the absence of charged hadrons in the central pseudorapidity region is sufficient to remove almost all non-diffractive events. This opens the way to investigate diffraction without waiting for the future specialized detectors.
In this paper we study the photon production in single and double diffractive processes considering the Resolved Pomeron model. We estimate the rapidity and transverse momentum dependence of the cross section for the diffractive double photon and photon+jet production. A comparison with the inclusive production is presented. We predict large values for the total cross sections, which makes the experimental analysis of these observables feasible at LHC energies.
In this paper we present a detailed analysis of the contribution of the Light -- by -- Light (LbL), Durham and double diffractive processes for the diphoton production in ultraperipheral $PbPb$ collisions at the Large Hadron Collider (LHC), High -- Energy LHC (HE -- LHC) and Future Circular Collider (FCC). The acceptance of the central and forward LHC detectors is taken into account and predictions for the invariant mass, rapidity, transverse momentum and acoplanarity distributions are presented. Our results indicate that the contribution of the Durham and double diffractive processes can be s…
In this letter we estimate the contribution of the double diffractive processes for the diphoton production in $pp$ collisions at the Large Hadron Collider (LHC). The acceptance of the central and forward LHC detectors is taken into account and predictions for the invariant mass, rapidity and, transverse momentum distributions are presented. A comparison with the predictions for the Light -- by -- Light (LbL) scattering and exclusive diphoton production is performed. We demonstrate that the events associated to double diffractive processes can be separated and its study can be used to constrai…
We discuss the single diffractive production of $c \bar c$ pairs and charmed mesons at the LHC. For a first time we propose a $k_t$-factorization approach to the diffractive processes. The transverse momentum dependent diffractive parton distributions are obtained from standard (collinear) diffractive parton distributions used in the literature. In this calculation the transverse momentum of the pomeron is neglected with respect to transverse momentum of partons entering the hard process. We also perform the first evaluation of the cross sections at the LHC using the diffractive transverse mom…
In this paper we study the diffractive $Z$ boson pair production mediated by the Kaluza-Klein graviton in the large extra dimensions scenario at the CERN Large Hadron Collider energies. Considering the Durham model we estimate the total cross section for the central inclusive and exclusive diffractive production of a $Z$ boson pair in $pp/pPb/PbPb$ collisions. Our results indicate that the experimental analysis of the central inclusive production in $pp$ collisions is feasible at CERN LHC.
The implementation of exclusive diffractive production of Higgs boson and dijets in the FPMC (Forward Physics Monte Carlo) framework is presented following the models by Khoze, Martin, Ryskin and Cudell, Dechambre, Hernandez and Ivanov. The predictions of the models are compared to the CDF measurement of exclusive jets and the uncertainties on the Higgs boson and jet production cross sections at the LHC are discussed.
In this paper we study the double $J/ψ$ production in central diffractive processes considering the Resolved Pomeron model. Based on the nonrelativistic QCD (NRQCD) factorization formalism for the quarkonium production mechanism we estimate the rapidity and transverse momentum dependence of the cross section for the double $J/ψ$ production in diffractive processes at LHC energies. The contributions of the color-singlet and color-octet channels are estimated and predictions for the total cross sections in the kinematical regions of the LHC experiments are also presented. Our results demonstrate…
The double quarkonium production in single and double diffractive processes is investigated considering $pp$ collisions at the Run 2 LHC energy. Using the nonrelativistic QCD (NRQCD) factorization formalism for the quarkonium production and the Resolved Pomeron model to describe the diffractive processes, we estimate the rapidity and transverse momentum dependencies of the cross sections for the $J/ΨJ/Ψ$ and $ΥΥ$ production. The contributions of the color-singlet and color-octet channels are estimated and predictions for the total cross sections in the kinematical regions of the LHC experiment…
Diffractive events at hadron colliders are typically characterised by a region of the detector without particles, known as a rapidity gap. In order to observe diffractive events in this way, we consider the pseudorapidity acceptance in the forward region of the ATLAS and CMS detectors at the Large Hadron Collider (LHC) and discuss the methods to select soft diffractive dissociation for pp collisions at sqrt(s) = 7 TeV. We showed that in the limited detector rapidity acceptance, it is possible to select diffractive dissociated events by requiring a rapidity gap in the event, however, it is not …
We report on the spin and diffractive physics at a future multi-purpose fixed-target experiment with proton and lead LHC beams extracted by a bent crystal. The LHC multi-TeV beams allow for the most energetic fixed-target experiments ever performed, opening new domains of particle and nuclear physics and complementing that of collider physics, in particular that of RHIC and the EIC projects. The luminosity achievable with AFTER using typical targets would surpass that of RHIC by more than 3 orders of magnitude. The fixed-target mode has the advantage to allow for measurements of single-spin as…
The central diffractive production of mesons f0(980) and f2(1270) at the energy of CERN-LHC experiment on proton-proton collisions is investigated. The processes initiated by quasi-real photon-photon collisions and by central diffraction processes are considered. The role played by the photon-Odderon production channel is also studied. The cross sections for these distinct production channels are compared and analyzed.
The inclusive diffractive quarkonium photoproduction in $pp$ and $pA$ collisions is investigated considering the Resolved Pomeron Model to describe the diffractive interaction. We estimate the rapidity and transverse momentum distributions for the $J/Ψ$, $Ψ(2S)$ and $Υ$ photoproduction in hadronic collisions at the LHC and present our estimate for the total cross sections at the Run 2 energies. A comparison with the predictions associated to the exclusive production also is presented. Our results indicate that the inclusive diffractive production is a factor $\gtrsim 10$ smaller than the exclu…
The production of a quarkonium -- pair in exclusive and diffractive processes in $pp$ collisions at the LHC and FCC energies is investigated. We consider the $J/ΨJ/Ψ$ and $ΥΥ$ production in these processes and present predictions for the transverse momentum and rapidity distributions considering the kinematical ranges expected to be covered by central and forward detectors. Results for the cross sections are also presented. Our results indicate that the double $J/Ψ$ production is dominated by the exclusive process, while the double $Υ$ production receive a large contribution of the diffractive…
Elastic diffractive scattering of nucleons is described in terms of Regge-eikonal approach. It is demonstrated that, in a wide kinematic region (starting from the U-70 energies), the eikonal of proton-proton scattering can be approximated by the sum of two Reggeon exchange terms (namely, the so-called soft Pomeron and $f$-Reggeon contributions). The range of applicability of the considered approximation is determined. The predictive value of the proposed phenomenological scheme is verified.
In this paper we estimate the production of dimuons ($μ^+ μ^-$) in exclusive photon -- photon ($γγ$) and diffractive Pomeron - Pomeron $(I\!P I\!P)$, Pomeron - Reggeon $(I\!P I\!R)$ and Reggeon - Reggeon $(I\!R I\!R)$ interactions in $pp$ collisions at the LHC energy. The invariant mass, rapidity and tranverse momentum distributions are calculated using the Forward Physics Monte Carlo (FPMC), which allows to obtain realistic predictions for the dimuon production with two leading intact hadrons. In particular, predictions taking into account the CMS and LHCb acceptances are presented. Moreover,…
We discuss the high-energy dependencies of diffractive and non-diffractive inelastic cross-sections in view of the recent LHC data which revealed a presence of the reflective scattering mode.
In this paper we propose the study of the diffractive quarkonium photoproduction in $pp$ collisions at LHC energies to probe the photon flux associated to a ultrarelativistic proton. The total photon distribution is expected to be given in terms of the elastic and inelastic components. Distinctly from the elastic photon component which can be determined from the elastic form factors, the magnitude of the inelastic component still is an open question. We consider the current parametrizations for the photon distribution of a proton and estimate the rapidity distributions and total cross sections…
The expected resonance structure for the low-mass single diffractive states from a Regge-dual model elaborated paper by the present authors in a previous is predicted. Estimates for the observable low-mass single diffraction dissociation (SDD) cross sections and efficiencies for single diffractive events simulated by PYTHIA 6.2 as a function of the diffractive mass are given.
We have discussed single and central diffractive production of $c \bar c$ pairs in the Ingelman-Schlein model. In these calculations we have included diffractive parton distributions obtained by the H1 collaboration at HERA and absorption effects neglected in some early calculations in the literature. The absorption effects which are responsible for the naive Regge factorization breaking cause that the cross section for diffractive processes is much smaller than that for the fully inclusive case, but could be measured at RHIC and LHC by imposing special condition on rapidity gaps. We discuss a…
The diffractive vector meson photoproduction with hadron dissociation in coherent hadron-hadron interactions at LHC energies is studied assuming that the color singlet $t$-channel exchange carries large momentum transfer. We estimate the rapidity distribution and total cross section for the processes $pp \rightarrow p V X$ and $PbPb \rightarrow Pb V X$ ($V = ρ$ or $Υ$) considering the non-forward solution of the BFKL equation at high energy and large momentum transfer. Our results indicate that the experimental identification of these processes can be feasible at the LHC.
We make predictions for the cross sections of diffractive dijet photoproduction in $pp$, $pA$ and $AA$ ultraperipheral collisions (UPCs) at the LHC during Runs 1 and 2 using next-to-leading perturbative QCD. We find that the resulting cross sections are sufficiently large and, compared to lepton-proton scattering at HERA, have an enhanced sensitivity to small observed momentum fractions in the diffractive exchange, commonly denoted $z_{P}^{\rm jets}$, and an unprecedented reach in the invariant mass of the photon-nucleon system $W$. We examine two competing schemes of diffractive QCD factoriza…
We describe recent results from CMS and TOTEM on hard diffraction, diffractive jets and jet gap jet events. We also give the first sensitivities and limits on quartic anomalous couplings and axion-like particles at high mass using the LHC as a $γγ$ collider. The predicted sensitivities with 300 fb$^{-1}$ are better by two or three orders of magnitude compared to the more standard methods at the LHC without measuring intact protons after collision
Feasibility studies of an observation of the exclusive diffractive bremsstrahlung in proton-proton scattering at the LHC are reported. A simplified approach to the photon and the scattered proton energy reconstruction is used. The background influence is discussed.
A complete list of operators contributing at the lowest order to Quartic Neutral Gauge Boson Couplings involving photons and Z-bosons, is presented. We show that, for the couplings we consider, the lowest order contribution is from dimension 8 operators in the case when a light Higgs is present and from dimension 6 operators in the higgsless case where electroweak symmetry is non-linearly realized. We also show that these operators are generated by exchange of the Kaluza-Klein partners of the graviton in extra-dimensional models. We then explore the possibility of probing these couplings in th…
The gauge boson production at forward rapidities in single diffractive events at the LHC is investigated considering $pp$ collisions at $\sqrt{s} =$ 8 and 13 TeV. The impact of gap survival effects is analysed using two different models for the soft rescattering contributions. We demonstrate that using the Forward Shower Counter Project at LHCb -- HERSCHEL, together with the Vertex Locator -- VELO, it is possible to discriminate diffractive production of the gauge bosons $W$ and $Z$ from the non-diffractive processes and studies of the Pomeron structure and diffraction phenomenology are feasib…
The measurement of diffractively scattered protons in the ATLAS Forward Physics detector system placed 220 m away from the ATLAS interaction point is studied. A parameterisation of the scattered proton transport through the LHC magnet lattice is presented. The proton energy unfolding and its impact on the centrally produced scalar particle mass resolution are discussed.
We calculate the cross section of inclusive dijet photoproduction in ultraperipheral collisions (UPCs) of heavy ions at the CERN Large Hadron Collider using next-to-leading order perturbative QCD and demonstrate that it provides a good description of the ATLAS data. We study the role of this data in constraining nuclear parton distribution functions (nPDFs) using the Bayesian reweighting technique and find that it can reduce current uncertainties of nPDFs at small $x$ by a factor of 2. We also make predictions for diffractive dijet photoproduction in UPCs and examine its potential to shed ligh…
Proton-proton collisions at the LHC can be classified as elastic, non-diffractive, and diffractive. In this paper we discuss various measurements of these above processes at various LHC experiments. We report about the total proton-proton cross-section measurements, about the analysis of diffractive events and also about the pseudorapidity distribution in inelastic events.
Feasibility studies of the measurement of the exclusive diffractive bremsstrahlung cross-section in proton-proton scattering at the centre of mass energy of 13 TeV at the LHC are reported. Present studies were performed for the low luminosity LHC running with the betatron function value of 90~m using the ATLAS associated forward detectors ALFA and ZDC. A simplified approach to the event simulation and reconstruction is used. The background influence is also discussed.
Multivariate machine learning techniques provide an alternative to the rapidity gap method for event-by-event identification and classification of diffraction in hadron-hadron collisions. Traditionally, such methods assign each event exclusively to a single class producing classification errors in overlap regions of data space. As an alternative to this so called hard classification approach, we propose estimating posterior probabilities of each diffractive class and using these estimates to weigh event contributions to physical observables. It is shown with a Monte Carlo study that such a sof…
In this work we investigate the photoproduction of radially excited vector mesons off nuclei in heavy ion relativistic collisions. In particular, we analyze the exclusive photoproduction of psi(2S) off nuclei, evaluating the coherent and the incoherent contributions to that process. The theoretical framework used in the present analysis is the light-cone dipole formalism and predictions are done for PbPb collisions at the CERN-LHC energy of 2.76 TeV. The theoretical uncertainties are analyzed and comparison is also done to the recent ALICE Collaboration data for the psi(1S) state photoproducti…
Central exclusive production of $η$ and $η'$ mesons in diffractive proton-proton collisions at the LHC
Institute of Nuclear Physics Polish Academy of Sciences（波兰科学院核物理研究所）；Institut für Theoretische Physik, Universität Heidelberg（海德堡大学理论物理研究所）；University of Rzeszów（热舒夫大学）
The vector meson production in coherent hadron-hadron interactions at LHC energies is studied assuming that the color singlet $t$-channel exchange carries large momentum transfer. We consider the non-forward solution of the BFKL equation at high energy and large momentum transfer and estimate the rapidity distribution and total cross section for the process $h_1 h_2 \to h_1 J/ΨX$, where $h_i$ can be a proton or a nucleus. We predict large rates, which implies that the experimental identification can be feasible at the LHC.
The main parts of the LHC diffractive physics programme possible to be measured using a proton tagging technique are presented. The geometric acceptance of the ATLAS forward proton detectors: ALFA and AFP for various LHC optics settings are shown. The probabilities of observing a proton originating from a minimum-bias event in ALFA and AFP stations are given. The main properties of single diffractive and double Pomeron exchange production of dijets, photon+jet, jet-gap-jet and W/Z bosons are discussed. The possibility of measuring the jet production in exclusive (double proton tag) and semi-ex…
We present a next-to-leading order QCD calculation of inclusive dijet photoproduction in ultraperipheral Pb-Pb collisions at the LHC and show that the results agree very well with various kinematic distributions measured by the ATLAS collaboration. The effect of including these data in nCTEQ or EPPS16 nuclear parton density functions (nPDFs) is then studied using the Bayesian reweighting technique. For an assumed total error of 5\% on the final data, its inclusion would lead to a significant reduction of the nPDF uncertainties of up to a factor of two at small values of the parton momentum fra…
In this paper we consider the Good - Walker approach for the diffractive excitation and updated the Miettinen -- Pumplin (MP) model for $pp/\bar{p}p$ collisions considering the recent LHC data for the total and elastic $pp$ cross sections. The behavior of the total, elastic and diffractive cross sections is analyzed and predictions for the energies of Run 3 of the LHC and those of the Cosmic Rays experiments are derived. Our results demonstrate that the MP model is able to describe the current data and that it implies that the cross section for the diffraction excitation in $pp$ collisions is …
A rapidity gap program with great potential can be realized at the Large Hadron Collider, LHC, by adding a few simple forward shower counters (FSCs) along the beam line on both sides of the main central detectors, such as CMS. Measurements of single diffractive cross sections down to the lowest masses can be made with an efficient level-1 trigger. Exceptionally, the detectors also make feasible the study of Central Diffractive Excitation, and in particular the reaction g + g to g + g, in the color singlet channel, effectively using the LHC as a gluon-gluon collider.
We calculate differential distributions for the $p p \to p p γ$ reaction at the LHC energy $\sqrt{s} = 14$ TeV. We consider diffractive classical bremsstrahlung mechanisms including effects of non point-like nature of protons. In addition, we take into account (vector meson)-pomeron, photon-pion as well as photon-pomeron exchange processes for the first time in the literature. Predictions for the total cross section and several observables related to these processes e.g. differential distributions in pseudorapidities and transverse momenta of photons or protons are shown and discussed. The int…
Using next-to-leading order (NLO) perturbative QCD, we calculate the diffractive contribution to inclusive dijet photoproduction in Pb-Pb ultraperipheral collisions (UPCs) at the LHC and find that it does not exceed $5-10$% in small-$x_A$ bins in the ATLAS kinematics at $\sqrt{s_{NN}}=5.02$ TeV. Its smallness is a result of the restricted kinematics ($p_{T1} > 20$ GeV and $x_A > 0.001$), the large nuclear suppression of nuclear diffractive parton distribution functions predicted in the leading twist model of nuclear shadowing, and additional suppression due to QCD factorization breaking in dif…
The measurement of the total $pp$ cross section and its various sub-components (elastic, inelastic and diffractive) is a very powerful tool to understand the proton macro structure and fundamental QCD dynamics. In this contribution I first provide a theoretical introduction to the topic, then a summary of the experimental techniques and finally I review the new results from AUGER and LHC experiments.
The differential cross section measurement for dijet production at proton-proton collisions at $\sqrt{s}=7$ TeV is presented as a function of an approximation for the fractional momentum loss of the scattered proton ($\tildeξ$), an useful observable to distinguish model predictions of diffractive and nondiffractive components. The data was collected by the CMS detector at low instantaneous luminosity runs at LHC, corresponding to an integrated luminosity of $2.7 {\rm nb}^{-1}$. This is the first observation of single diffractive dijets at LHC.
HERA data on diffractive DIS show deviations from twist 2 DGLAP predictions below $Q^2\sim 5$ GeV$^2$ at low pomeron $ξ$, which may reach up to 100%. These deviations are consistent with higher twists effects extracted from the saturation model. It is a first direct evidence for the higher twists in DIS. This finding affects determination of the diffractive parton densities that are used for the predictions at the LHC.
The first double diffractive cross-section measurement in the very forward region has been carried out by the TOTEM experiment at the LHC with center-of-mass energy of sqrt(s)=7 TeV. By utilizing the very forward TOTEM tracking detectors T1 and T2, which extend up to |eta|=6.5, a clean sample of double diffractive pp events was extracted. From these events, we measured the cross-section sigma_DD =(116 +- 25) mub for events where both diffractive systems have 4.7 <|eta|_min < 6.5 .
In the Randall-Sundrum (RS) scenario the compactification radius of the extra dimension is stabilized by the radion, which is a scalar field lighter than the graviton Kaluza-Klein states. It implies that the detection of the radion will be the first signature of the stabilized RS model. In this paper we study the exclusive production of the radion in electromagnetic and diffractive hadron - hadron collisions at the LHC. Our results demonstrate that the diffractive production of radion is dominant and should be feasible of study at CERN LHC.
The cross section for dijet production in pp collisions at sqrt(s) = 7 TeV is presented as a function of xi, a variable that approximates the fractional momentum loss of the scattered proton in single-diffractive events. The analysis is based on an integrated luminosity of 2.7 inverse nanobarns collected with the CMS detector at the LHC at low instantaneous luminosities, and uses events with jet transverse momentum of at least 20 GeV. The dijet cross section results are compared to the predictions of diffractive and nondiffractive models. The low-xi data show a significant contribution from di…
A double-gap topology is used for filtering central-diffractive events from a proton-proton minimum-bias data sample at a centre-of-mass energy {$\sqrt{s}=7$\,TeV}. This topology is defined by particle activity in the ALICE central barrel and absence of particle activity outside. The fraction of events satisfying the double-gap requirement $R_{DG}$ is found to be {$7.63\pm0.02(stat.)\pm0.87(syst.)\times 10^{-4}$}. The background of this double-gap fraction is estimated by studying the contributions of non-diffractive, single- and double-diffractive dissociation processes as modelled by Monte C…
