Exclusive Dijet Production Research Articles

Revisiting azimuthal angular asymmetries in diffractive di-jet production

We explore the impact of initial state soft gluon radiations on the azimuthal angle asymmetries in photo-production of hard di-jet via coherent diffraction in ultraperipheral heavy ion collisions, as well as in electron-proton (ep) and electron-nucleus (eA) collisions. The primary production mechanism is identified as the diffractive production of two hard jets, accompanied by a collinear gluon emission along the beam direction. In contrast, the diffractive exclusive di-jet production, where the initial state radiation is absent, is suppressed due to color transparency. Our analysis shows that azimuthal asymmetries, traditionally attributed to final state gluon emissions, are reduced by the presence of initial state radiations. The sensitivity of azimuthal asymmetries to both initial and final state radiations suggests that they could provide novel insights into the mechanisms of di-jet production in diffractive processes.

Probing gluon saturation via diffractive jets in ultra-peripheral nucleus-nucleus collisions

We argue that semi-inclusive photo-production of a pair of hard jets via coherent diffraction in nucleus-nucleus ultra-peripheral collisions at high energy is a golden channel to study gluon saturation. The dominant contribution is the diffractive production of three jets in an asymmetric configuration. Two of the jets are hard and propagate at nearly central pseudo-rapidities. The third jet is semi-hard, with transverse momentum comparable to the nuclear saturation momentum, and is well separated in pseudo-rapidity from the hard dijets. The emission of the semi-hard jet allows for strong scattering, thus avoiding the “higher-twist” suppression of the exclusive dijet production due to colour transparency. We compute the trijet cross-section using the diffractive TMD factorisation which emerges from the CGC effective theory at high energy. The cross-section is controlled by gluon saturation, which leaves its imprints on the structure of the final state, notably on the rapidity distribution.

Gluon dipole factorisation for diffractive dijets

Within the colour dipole picture for deep inelastic scattering at small Bjorken x, we study the production of a pair of relatively hard jets via coherent diffraction. By “relatively hard” we mean that the transverse momenta of the two jets — the quark (q) and the antiquark ( overline{q} ) generated by the decay of the virtual photon — are much larger than the target saturation momentum Qs(Yℙ) evaluated at the rapidity gap Yℙ. We argue that the typical final-state configurations are such that the hard qoverline{q} dijets are accompanied by a semi-hard gluon jet, with a transverse momentum of the order of Qs(Yℙ). The presence of this third jet ensures that the scattering is strong and thus avoids the strong suppression of exclusive (hard) dijet production due to colour transparency. For such “2+1” jet configurations, we demonstrate that both the emission of the semi-hard gluon and its scattering with the hadronic target can be factorised in terms of an effective gluon-gluon dipole. This effective description, originally proposed in [1–7], builds a bridge between the colour dipole picture and the transverse-momentum dependent (TMD) version of the collinear factorisation: the cross-section for diffractive 2+1 jets can be written as the product between a hard factor describing the qoverline{q} dijets and a semi-hard factor expressing the unintegrated gluon distribution of the Pomeron. The latter is controlled by gluon dipole scattering in the black disk limit and hence is strongly sensitive to gluon saturation. By integrating out the kinematics of the 3 jets, we obtain the qoverline{q}g contribution to the diffractive structure function in collinearly-factorised form.

Signature of the Gluon Orbital Angular Momentum.

We propose a novel observable for the experimental detection of the gluon orbital angular momentum (OAM) that constitutes the proton spin sum rule. We consider longitudinal double spin asymmetry in exclusive dijet production in electron-proton scattering and demonstrate that the cosϕ azimuthal angle correlation between the scattered electron and proton is a sensitive probe of the gluon OAM at small x and its interplay with the gluon helicity. We also present a numerical estimate of the cross section for the kinematics of the Electron-Ion Collider.

On the one loop γ ∗ → q q ¯ $$ {\gamma}^{\left(\ast \right)}\to q\overline{q} $$ impact factor and the exclusive diffractive cross sections for the production of two or three jets

We present the calculation of the impact factor for the $\gamma^{(*)}\to q\bar{q}$ transition with one loop accuracy in arbitrary kinematics. The calculation was done within Balitsky's high energy operator expansion. Together with our previous result for the $\gamma^{(*)}\to q\bar{q} g$ Born impact factor it allows one to derive cross-sections for 2- (one loop) and 3-jet (Born) difractive electroproduction. We write such cross sections for the 2 and 3 jet exclusive diffractive electroproduction off a proton in terms of hadronic matrix elements of Wilson lines. For the 2-jet cross section we demonstrate the cancellation of IR, collinear and rapidity singularities. Our result can be directly exploited to describe the recently analyzed data on exclusive dijet production at HERA and used for the study of jet photoproduction in ultraperipheral proton or nuclear scattering.

Diffractive dijet production in deep inelastic scattering and photon-hadron collisions in the color glass condensate

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.

Exlusive diffraction at HERA

The cross section of the diffractive process γπ+→ρ0π+ was measured first time in ep scattering. Elastic and proton-dissociative photoproduction of J/Ψ were measured as a function of the four-momentum transfer squared and of the photon-proton centre-of-mass energy. The energy dependence is consistent with a model prediction assuming a two-gluon exchange. The ratio of cross sections of the elastic production of Ψ(2S) and J/Ψ was measured with inproved precision in Deep Inelastic Scattering (DIS). The diffractive exchange was studied in a measurement of exclusive dijet production in DIS. The data are consistent with a model prediction assuming a two-gluon exchange.

Recent diffractive results from HERA

The diffractive dijet cross sections for photoproduction and deep inelastic scattering were studied and compared with theoretical NLO QCD predictions. The results of exclusive dijet production were compared to predictions from models which are based on different assumptions about the nature of diffractive exchange. Isolated prompt photons in diffractive photoproduction produced inclusively or together with a jet were studied for the first time.

Central exclusive dijet production at the Tevatron

We present a review of central exclusive dijet production in [Formula: see text] collisions, where the proton and antiproton emerge intact, and only two jets of transverse energy above a certain threshold are present in the final state. The results are published in two papers by the Collider Detector at Fermilab (CDF) Collaboration, a PRL (2000) and a PRD (2008), based on data collected at [Formula: see text] and 1.96 TeV, respectively, and a D0 Collaboration paper from studies at 1.96 TeV. In all three cases predictions for the cross-section of Higgs boson production are discussed, a process that proceeds via a similar mechanism as dijet production. Roman Pot Spectrometers equipped with tracking detectors are used to measure the outgoing antiproton (CDF and D0) and proton (D0), and special forward detectors are employed to help reduce backgrounds and enrich the data in diffractive and exclusive dijet events.

New contributions to central exclusive production of dijets in proton-(anti)proton collisions

We consider central exclusive production of $gg$ dijets in proton-proton (proton-antiproton) collisions at LHC and Tevatron for different intermediate and final gluon polarizations. The amplitude for the process is derived within the ${k}_{\ensuremath{\perp}}$-factorization approach (with both the standard QCD and the Lipatov's effective three-gluon vertices) and is considered in various kinematical asymptotia, in particular, in the important limit of high-${p}_{\ensuremath{\perp}}$ jets. Compared to earlier works we include emissions of gluons from different gluonic $t$-channel lines as well as emission of quark-antiquark dijets. Rapidity distributions, gluon jet ${p}_{\ensuremath{\perp}}$ distributions and invariant dijet mass distributions are presented. We explore the competition of the standard diagram with both jets emitted from a single $t$-channel gluon and the one with the emission from both $t$-channel gluons. The second mechanism requires a special treatment. We propose two different approaches. Including special kinematics and using properties of off-diagonal gluons at small $x$ and $\ensuremath{\xi}$, we arrive to correlations in two-dimensional distributions in rapidity of one and second jet. We find that the second contribution is much smaller than that known from the literature. The digluon production constitutes an important background to exclusive Higgs production.

High mass exclusive diffractive dijet production in [formula omitted] collisions at [formula omitted

We present evidence for diffractive exclusive dijet production with an invariant dijet mass greater than 100 GeV in data collected with the D0 experiment at the Fermilab Tevatron Collider. A discriminant based on calorimeter information is used to measure a significant number of events with little energy (typically less than 10 GeV) outside the dijet system, consistent with the diffractive exclusive dijet production topology. The probability for these events to be explained by other dijet production processes is 2×10−6, corresponding to a 4.7 standard deviation significance.

Survival probability of large rapidity gaps in the QCD and N=4 SYM motivated model

In this paper we present a self-consistent theoretical approach for the calculation of the Survival Probability for central dijet production. These calculations are performed in a model of high energy soft interactions based on two ingredients: (i) compatibility with the results of N=4 SYM, which at the moment is the only theory that is able to deal with a large coupling constant; and (ii) the required matching with high energy QCD. Assuming, in accordance with these prerequisites, that the soft Pomeron intercept is rather large and the slope of the Pomeron trajectory is equal to zero, we derive analytical formulae that sum both enhanced and semi-enhanced diagrams for elastic and diffractive amplitudes. Using parameters obtained from a fit to the available experimental data, we calculate the Survival Probability for exclusive central dijet production at energies accessible at the LHC. The results presented here, which include the contribution of semi-enhanced and net diagrams, are considerably larger than our previous estimates.

Central exclusive production of dijets at hadronic colliders

In view of the recent diffractive dijet data from CDF run II, we critically re-evaluate the standard approach to the calculation of central production of dijets in quasi-elastic hadronic collisions. We find that the process is dominated by the non-perturbative region, and that even perturbative ingredients, such as the Sudakov form factor, are not under theoretical control. Comparison with data allows us to fix some of the uncertainties. Although we focus on dijets, our arguments apply to other high-mass central systems, such as the Higgs boson.

Observation of exclusive dijet production at the Fermilab Tevatronp¯pcollider

We present the first observation and cross section measurement of exclusive dijet production in pbar-p interactions, pbar + p --> pbar + dijet + p. Using a data sample of 310 pb-1 collected by the Run II Collider Detector at Fermilab at sqrt{s}=1.96 TeV, exclusive cross sections for events with two jets of transverse energy ET >= 10 GeV have been measured as a function of minimum ET(jet). The exclusive signal is extracted from fits to data distributions based on Monte Carlo simulations of expected dijet signal and background shapes. The simulated background distribution shapes are checked in a study of a largely independent data sample of 200 pb-1 of b-tagged jet events, where exclusive dijet production is expected to be suppressed by the Jz=0 total angular momentum selection rule. Results obtained are compared with theoretical expectations, and implications for exclusive Higgs boson production at the pp Large Hadron Collider at sqrt{s}=14 TeV are discussed.

New CDF results on diffraction

We report new diffraction results obtained by the CDF collaboration in proton-antiproton collisions at the Fermilab Tevatron collider at <FONT FACE=Symbol>Ö</FONT>s = 1.96 TeV. The first experimental evidence of exclusive dijet and diphoton production is presented. The exclusive results are discussed in context of the exclusive Higgs production at LHC. We also present the measurement of the Q² and t dependence of the diffractive structure function.

Central jet production as a probe of the perturbative formalism for exclusive diffraction

We propose a new variable, Rj, in order to identify exclusive double-diffractive high ET di-jet production. The variable Rj is calculated using the transverse energy ET and pseudorapidity of the jet with the largest ET. For a purely exclusive event the value of Rj→1, if we were to neglect hadronisaton and the detector resolution effects. To illustrate the expected Rj distribution we also compute exclusive three-jet production; and, moreover, we include jet smearing effects. By studying the predictions as a function of the size of the rapidity interval, δη, which allows for additional gluon radiation, one can probe the QCD radiation effects which are responsible for the Sudakov suppression of the exclusive amplitude. In this way we may check and improve the formalism used to predict the cross sections of exclusive double-diffractive Higgs boson (and/or other new physics) production.

Central exclusive dijet production at the Fermilab Tevatron

We perform a phenomenological analysis of dijet production in double pomeron exchange at the Tevatron. We find that the CDF Run I results do not rule out the presence of an exclusive dijet component, as predicted by Khoze, Martin and Ryskin (KMR). With the high statistics CDF Run II data, we predict that an exclusive component at the level predicted by KMR may be visible, although the observation will depend on accurate modelling of the inclusive double pomeron exchange process. We also compare to the predictions of the DPEMC Monte Carlo, which contains a non-perturbative model for the central exclusive process. We show that the perturbative model of KMR gives different predictions for the di-jet ET dependence in the high di-jet mass fraction region than non-perturbative models.

Diffraction at CDF

The results of the diffractive measurements at CDF experiment at the Tevatron pp¯ collider are presented. Diffractive structure functions are studied in single diffractive dijet production. The exclusive dijet and low-mass state production in double pomeron exchange are discussed in context of the exclusive Higgs production at LHC.

Exclusive Higgs and dijet production by double pomeron exchange. The CDF upper limits

We use as a starting point the original, central inclusive Bialas–Landshoff model for Higgs and dijet production by double pomeron exchange in pp(pp¯) collisions. Next, we propose the simple extension of this model to the exclusive processes. We find the extended model to be consistent with the CDF Run I, II upper limits for double diffractive exclusive dijet production. The predictions for the exclusive Higgs boson production cross sections at the Tevatron and the LHC energies are also presented.

Exclusive production of dijets in QCD

We study in a framework of QCD collinear factorization the processes of a pion and a photon diffraction dissociation into two jets. The structure of non-factorizable contributions is discussed. We argue that coherent production of hard dijets by linearly polarized real photons can provide direct evidence for chirality violation in hard processes, the first measurement of the magnetic susceptibility of the quark condensate and the photon distribution amplitude.