arXiv subjects
Publications and source records attributed to V. A. Khoze.
We consider photon-initiated events with large rapidity gaps in proton-proton collisions, where one or both protons may break up. We formulate a modified photon PDF that accounts for the specific experimental rapidity gap veto, and demonstrate how the soft survival probability for these gaps may be implemented consistently. Finally, we present some phenomenological results for the two-photon induced production of lepton and $W$ boson pairs.
Motivated by the recent LHC observation of an excess of diphoton events around an invariant mass of 750 GeV, we discuss the possibility that this is due to the decay of a new scalar or pseudoscalar resonance dominantly produced via photon-photon fusion. We present a precise calculation of the corresponding photon-photon luminosity in the inclusive and exclusive scenarios, and demonstrate that the theoretical uncertainties associated with these are small. In the inclusive channel, we show how simple cuts on the final state may help to isolate the photon-photon induced cross section from any gluon-gluon or vector boson fusion induced contribution. In the exclusive case, that is where both protons remain intact after the collision, we present a precise cross section evaluation and show how this mode is sensitive to the parity of the object, as well as potential $CP$-violating effects. We also comment on the case of heavy-ion collisions and consider the production of new heavy colourless fermions, which may couple to such a resonance.
We present a range of physics results for central exclusive production processes at the LHC, using the new SuperChic 2 Monte Carlo event generator. This includes significant theoretical improvements and updates, most importantly a fully differential treatment of the soft survival factor, as well as a greater number of generated processes. We provide an overview of the latest theoretical framework, and consider in detail a selection of final states, namely exclusive 2 and 3 jets, photoproduced vector mesons, two-photon initiated muon and $W$ boson pairs and heavy $χ_{c,b}$ quarkonia.
We argue that the secondaries produced in high energy hadron collisions are emitted by small size sources distributed over a much larger area in impact parameter space occupied by the interaction amplitude. That is, Bose-Einstein correlation of two emitted identical particles should be described by a `two-radii' parametrization ansatz. We discuss the expected energy, charged multiplicity and transverse momentum of the pair (that is, $\sqrt{s},~N_{\rm ch}, k_t$) behaviour of both the small and large size components.
We study the prompt production of the $χ_c(1^+)$ and $χ_b(1^+)$ mesons at high energies. Unlike $χ(0^+,2^+)$ production, $χ(1^+)$ mesons cannot be created at LO via the fusion of two on-mass-shell gluons, that is $gg\toχ_{c,b}(1^+)$ are not allowed. However, the available experimental data show that the cross sections for $χ_c(1^+)$ and $χ_c(2^+)$ are comparable. We therefore investigate four other $χ(1^+)$ production mechanisms: namely, (i) the standard NLO process $gg\toχ_{c,b}(1^+)+g$, (ii) via gluon virtuality, (iii) via gluon reggeization and, finally, (iv) the possibility to form $χ_{c,b}(1^+)$ by the fusion of three gluons, where one extra gluon comes from another parton cascade, as in the Double Parton Scattering processes.
We review recent results within the Durham model of central exclusive production. We discuss the theoretical aspects of this approach and consider the phenomenological implications in a variety of processes, comparing to existing collider data and addressing the possibilities for the future.
We present the first calculation of exclusive double $J/ψ$ production in hadronic collisions. We analyse in detail the form of the Born-level $gg \to J/ψJ/ψ$ amplitudes within the non-relativistic quarkonium approximation and discuss the implications of this for the central exclusive production channel, within the `Durham' perturbative model. In addition we show that this direct single parton scattering contribution is expected to be strongly dominant in the exclusive case. We present predictions for the LHC and show that the expected cross sections are in reasonable agreement with the LHCb Run-I measurement of exclusive double $J/ψ$ production, with the measured invariant mass distribution described well by the theory. Motivated by this encouraging result we present predictions for observables that may be measured in LHC Run-II, and estimate the size of the expected cross sections in the $ψ(2S)$ and $χ_{c}$ cases.
We consider the main factors which cause the variation of the value of the local slope of the elastic pp cross section B(t)=d[\ln(dσ_el(pp)/dt]/dt with t. Namely, we discuss the role of the pion-loop insertion in the pomeron trajectory, the t-dependence of the pomeron-nucleon coupling and the role of the eikonalization of the proton-proton amplitude in both the one- and two-channel eikonal models.
In the light of LHC data, we discuss the global description of all high energy elastic and diffractive data, using a one-pomeron model, but including multi-pomeron interactions. The LHC data indicate the need of a $k_t(s)$ behaviour, where $k_t$ is the gluon transverse momentum along the partonic ladder structure which describes the pomeron. We also discuss tensions in the data, as well as the $t$ dependence of the slope of $dσ_{el}/dt$ in the small $t$ domain.
The partonic transverse momentum, k_t distribution plays a crucial role in driving high-energy hadron interactions. If k_t is limited we have old fashioned Regge Theory. If k_t increases with energy the interaction may be described by perturbative QCD. We use BFKL diffusion in ln k_t, supplemented by a stronger absorption of low k_t partons, to estimate the growth of the mean transverse momenta with energy. This growth reveals itself in the distribution of secondaries produced at the collider energies. We present a simple, BFKL-based, model to demonstrate the possible size of the effect. Moreover, we propose a way to evaluate experimentally the shape of the parton transverse momenta distribution by studying the spectra of the (D or B) mesons which contain one heavy quark.
We present a study of the central exclusive production of light meson pairs, concentrating on the region of lower invariant masses of the central system and/or meson transverse momentum, where perturbative QCD cannot be reliably applied. We describe in detail a phenomenological model, using the tools of Regge theory, that may be applied with some success in this regime, and we present the new, publicly available, Dime Monte Carlo (MC) implementation of this for $ππ$, $KK$ and $ρρ$ production. The MC includes a fully differential treatment of the survival factor, which in general depends on all kinematic variables, as well as allowing for the so far reasonably unconstrained model parameters to be set by the user. We present predictions for the Tevatron and LHC and show how future measurements may further test this Regge--based approach, as well as the soft hadronic model required to calculate the survival factor, in particular in the presence of tagged protons.
We study the behaviour of elastic and diffractive proton dissociation cross sections at high energy. First, we describe what would be expected to be observed at the LHC based on conventional Regge theory. We emphasize the tension between these expectations and the recent LHC measurements, and we discuss the possibilty to modify the classic Reggeon Field Theory in a physically-motivated way so as to accommodate the tendencies observed at the LHC. As a result, we show that we are able to achieve a `global' description of the wide variety of high energy elastic and diffractive data that are presently available, particularly from the LHC experiments. The model is based on only one pomeron pole, but includes multi-pomeron interactions and, significantly, includes the transverse momentum dependence of intermediate partons as a function of their rapidity, which provides the rapidity dependence of the multi-pomeron vertices. We give predictions for diffractive observables at LHC, and higher, energies.
We present a `global' description of the wide variety of high energy elastic and diffractive data that are presently available, particularly from the LHC experiments. The model is based on only one pomeron pole, but includes multi-pomeron interactions and, significantly, includes the transverse momentum dependence of intermediate partons as a function of their rapidity, which provides the rapidity dependence of the multi-pomeron vertices. We give predictions for diffractive observables at LHC energies.
We present the results of recent work on the central exclusive production of meson pairs. We concentrate on the case of flavour-singlet pseudoscalar mesons eta, eta' and show that the central exclusive process, as modelled using a recent novel application of the 'hard exclusive' perturbative formalism, is potentially highly sensitive to the size of the gluon content of these states. We also discuss the exclusive production of meson pairs in the lower mass region, and present the first results of the new Dime Monte Carlo.
We present the results of a recent novel application of the `hard exclusive' perturbative formalism to the process gg --> MMbar at large angles, where M (Mbar) is a light meson (anti-meson). As well as discussing the important theoretical features of the relevant leading-order gg --> qqbar(gg) qqbar(gg) 6-parton amplitudes, we also comment on their phenomenological implications. In particular, we consider the central exclusive production of meson pairs at comparatively large transverse momentum k_t, which is expected to proceed via this mechanism. We show that this leads to various non-trivial predictions for a range of exclusive processes, and that the cross sections for the eta' and eta mesons display significant sensitivity to any valence gg component of the meson wavefunctions.
We show that the diffractive pp (and p\bar{p}) data (on σ_tot, dσ_el/dt, proton dissociation into low-mass systems, σ^D(low M), and high-mass dissociation, dσ/d(Δη)) in a wide energy range from CERN-ISR to LHC energies, may be described in a two-channel eikonal model with only one `effective' pomeron. By allowing the pomeron coupling to the diffractive eigenstates to depend on the collider energy (as is expected theoretically) we are able to explain the low value of σ^D(low M) measured at the LHC. We calculate the survival probability, S^2, of a rapidity gap to survive `soft rescattering'. We emphasize that the values found for S^2 are particularly sensitive to the detailed structure of the diffractive eigenstates.
Currently, the long-standing issue concerning the size of the gluonic content of the eta' and eta mesons remains unsettled. With this in mind we consider the central exclusive production (CEP) of eta', eta meson pairs in the perturbative regime, applying the Durham pQCD-based model of CEP and the `hard exclusive' formalism to evaluate the meson production subprocess. We calculate for the first time the relevant parton-level processes gg --> qqbar gg and gg --> gggg, where the final-state gg and qqbar pairs form a pseudoscalar flavour-singlet state. We observe that these amplitudes display some non-trivial and interesting theoretical properties, and we comment on how this can be understood in a MHV framework. Finally, we present a phenomenological study, and show that the cross sections for the CEP of eta', eta meson pairs are strongly sensitive to the size of the gluon content of these mesons. The observation of these processes could therefore provide important and novel insight into this problem.
Selected new results in central exclusive production (CEP) processes within the pQCD-based Durham model are discussed. Topics covered include the CEP of SM and BSM Higgs-like particles, meson pair CEP and the gap survival probability.