Exclusive top production at a Linear Collider at and off the threshold
Jürgen Reuter, Fabian Bach, Bijan Chokoufé Nejad, Andre Hoang, Wolfgang Kilian, Jonas Lindert, Stefano Pozzorini, Maximilian Stahlhofen, Thomas Teubner, Christian Weiss
备注：
Talk presented at the International Workshop on Future Linear Colliders (LCWS2017), Strasbourg, France, 23-27 October 2017. C17-10-23.2
We review exclusive top pair production including decays at a future high-energy lepton collider, both in the threshold region and for higher energies. For the continuum process, we take complete QCD next-to-leading order matrix elements for the $2\to 6$ process with leptonic W decays into account. At threshold, we match the fixed-order relativistic QCD-NLO cross section to a nonrelativistic cross section with next-to-leading logarithmic (NLL) threshold resummation implemented via a form factor.
The next generation of $e^+e^-$ colliders will offer a possibility of clean testing of QCD dynamics. Recent progress in the theoretical description of exclusive processes permits for many of them a consistent use of the perturbative QCD methods. We find that already on the basis of Born approximation, the exclusive diffractive production of two $ρ$ mesons from virtual photons at very high energies should be measurable at the linear collider (LC).
A few examples of exclusive processes at high energy are discussed. Several mechanisms are presented. The differential distributions are shown. The possibilities to measure the processes are discussed.
The cross section for exclusive $Υ$ ultraperipheral photoproduction at present and future colliders is determined using the low $x$ gluon PDF extracted from an analysis of exclusive $J/ψ$ measurements performed at HERA and the LHC. Predictions are given at next-to-leading order in collinear factorisation over a wide $γp$ centre-of-mass energy range, calculated assuming the non-relativistic approximation for the $Υ$ wave function, and with skewing corrections incorporated.
Groundbreaking studies of exclusive physics processes at the Tevatron have demonstrated that proton-(anti)proton colliders are not only quark-antiquark but also gluon-gluon colliders, photon-photon and photon - gluon colliders. These studies are briefly reviewed in this paper.
Calculations of central exclusive diffractive di-pion continuum production are presented in the Regge-eikonal approach. Data from ISR, STAR, CDF and CMS were analyzed and compared with theoretical description. We also consider theoretical predictions for LHC, possible nuances and problems of calculations and prospects of investigations at present and future hadron colliders.
We critically re-examine the calculation of central production of dijets in quasi-elastic hadronic collisions. We find that the process is not dominated by the perturbative contribution, and discuss several sources of uncertainties in the calculation.
We review the subject of central exclusive particle production at high energy hadron colliders. In particular we consider reactions of the type A + B -> A + X + B, where X is a fully specified system of particles that is well separated in rapidity from the outgoing beam particles. We focus on the case where the colliding particles are strongly interacting and mainly they will be protons (or antiprotons) as at the ISR, SppS, Tevatron and LHC. The data are surveyed and placed within the context of theoretical developments.
The theoretical and experimental aspects of particle production from the strong equivalent photon fluxes present at high energy hadron colliders are reviewed. The goal is to show how photons at hadron colliders can improve what we have learnt from experiments with lepton beams. Experiments during the last 5-10 years have shown the feasibility of studying photoproduction in proton-proton and heavy-ion collisions. The experimental and theoretical development has revealed new opportunities as well as challenges.
Central exclusive Higgs boson production, pp -> p + H + p, at the LHC and s-channel resonant Higgs production in the photon-collider option of the ILC can provide a very important contribution to the comprehensive study of the Higgs sector. Especially attractive is the b bbar Higgs decay mode, which for certain MSSM scenarios may become the discovery channel in exclusive Higgs production at the LHC and the Photon Collider (PC). Strongly suppressed and controllable backgrounds is an obvious requirement for the success of these exclusive measurements. One of the main sources of background comes …
The central exclusive production (CEP) of heavy resonance states that subsequently decay into meson pairs, MMbar, is an important signature for such processes at hadron colliders. However there is a potentially important background from the direct QCD production of meson pairs, as mediated for example by the exclusive gg --> MMbar hard scattering subprocess. This is in fact an interesting process in its own right, testing novel aspects of perturbative QCD technology. We explicitly calculate the gg --> MMbar helicity amplitudes for different meson states within the hard exclusive formalism, and…
Central exclusive production (CEP) processes in high-energy hadron-hadron collisions provide an especially clean environment in which to measure the nature and quantum numbers (in particular, the spin and parity) of new resonance states. Encouraged by the broad agreement between experimental measurements and theoretical predictions based on the Durham approach, we perform a detailed phenomenological analysis of diphoton and meson pair CEP final states, paying particular attention to the theoretical uncertainties in the predictions, including those from parton distribution functions, higher-ord…
We present the next-to-leading order QCD corrected rate for the production of a scalar Higgs boson with a pair of high p_T bottom and anti-bottom quarks at the Tevatron and at the Large Hadron Collider. Results are given for both the Standard Model and the Minimal Supersymmetric Standard Model. The exclusive b-bbar-h production rate is small in the Standard Model, but it can be greatly enhanced in the Minimal Supersymmetric Standard Model for large tan(beta), making b-bbar-h an important discovery mode. We find that the next-to-leading order QCD results are much less sensitive to the renormali…
Within the framework of the perturbative QCD approach, we calculate the time-like $B_cB_c(B_c^*)$ form factors $F(Q^2)$ and $A_2(Q^2)$. We include relativistic corrections and QCD corrections, either of which can give about $20\%$ correction to the leading-order contribution, but there are cancellation effects between them. We calculate the cross sections of the $e^+e^-\to B_c^-B_c^+(B_c^{*+})$ processes. The cross sections are enhanced at the $Z$ pole to be $σ^{PP}(Q=m_Z) \sim 1.3\times10^{-5}\text{pb}$ and $σ^{PV}(Q=m_Z) \sim 2.5\times10^{-5}\text{pb}$, which are still too small to be detect…
Central exclusive double diffractive Higgs boson production, p p \to p + H + p, is now recognised as an important search scenario for the LHC. We consider the case when the Higgs boson decays to two W bosons, one of which may be off-mass-shell, that subsequently decay to the q qbar l nu final state. An important background to this is from the QCD process g g \to W q qbar, where the two gluons are required to be in a J_z=0, colour-singlet state. We perform an explicit calculation and investigate the salient properties of this potentially important background process.
In this work we investigate the coherent photoproduction of psi(1S), psi(2S) and Upsilon (1S) states in the proton-nucleus collisions in the LHC energies. Predictions for the rapidity distributions are presented using the color dipole formalism and including saturation effects that are expected to be relevant at high energies. Calculations are done at the energy 5.02 TeV and also for the next LHC run at 8.8 TeV in proton-lead mode. Discussion is performed on the main theoretical uncertainties associated to the calculations.
The threshold scan at future lepton colliders is the most precise known method to determine the top quark mass (well below 100 MeV), a fundamental parameter of the Standard Model that co-determines the stability properties of the electroweak vacuum. We present a new method to match the continuum next-to-leading order QCD corrections with the next-to-leading logarithmic resummation of the Coulomb singularities of the quasi-toponium bound state at threshold where fixed-order perturbation theory is invalid. This matching is performed at the level of the fully exclusive $W^+bW^-\bar{b}$ final stat…
We consider QCD radiative corrections to the production of W and Z bosons in hadron collisions. We present a fully exclusive calculation up to next-to-next-to-leading order (NNLO) in QCD perturbation theory. To perform this NNLO computation, we use a recently proposed version of the subtraction formalism. The calculation includes the gamma-Z interference, finite-width effects, the leptonic decay of the vector bosons and the corresponding spin correlations. Our calculation is implemented in a parton level Monte Carlo program. The program allows the user to apply arbitrary kinematical cuts on th…
We compute the cross section for exclusive double-diffractive gamma-gamma production at the Tevatron, $p{\bar p} \to p + γγ+ {\bar p}$, and the LHC. We evaluate both the gluon-gluon and quark-antiquark t-channel exchange contributions to the process. The observation of exclusive gamma-gamma production at the Tevatron will provide a check on the model predictions, and offer an opportunity to confirm the expectations for exclusive double-diffractive Higgs production at the LHC.
The two-photon exclusive production of lepton pairs at the Electron-Ion Collider will open interesting research directions thanks to a very high luminosity and clean experimental conditions. A survey of the scientific potential of such studies is reported. In particular, we consider unique measurements of the proton elastic electromagnetic form-factors and a possibility of studying the anomalous electromagnetic dipole moments of $τ$ leptons.
Exclusive quarkonium pair production in electron-positron collisions is studied in non-relativistic QCD. The obtained cross section for J/ψ+ η_c production in the leading order is confronted against the recent measurements by the Belle Collaboration at KEKB. It is shown that a large renormalization K-factor is necessary to explain the experimental data. We point out that the J^{PC}=0^{-+} nature of the hadronic systems that are assigned to be η_c should be tested by the triple angular distributions in terms of the scattering angle, and, polar and azimuthal angles of J/ψinto leptons. We further…
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.
We study the exclusive, double--diffractive production of the Standard Model Higgs particle in hadronic collisions at LHC and FNAL (upgraded) energies. Such a mechanism would provide an exceptionally clean signal for experimental detection in which the usual penalty for triggering on the rare decays of the Higgs could be avoided. In addition, because of the color singlet nature of the hard interaction, factorization is expected to be preserved, allowing the cross--section to be related to similar hard--diffractive events at HERA. Starting from a Fock state expansion in perturbative QCD, we obt…
Exploring the nucleon's sea quark and gluon structure is a prime objective of a future electron-ion collider (EIC). Many of the key questions require accurate differential semi-inclusive (spin/flavor decomposition, orbital motion) and exclusive (spatial distributions of quarks/gluons) DIS measurements in the region 0.01 < x < 0.3 and Q^2 ~ few 10 GeV^2. Such measurements could ideally be performed with a high-luminosity collider of moderate CM energy, s ~ 10^3 GeV^2, and relatively symmetric configuration, e.g. E_e/E_p = 5/30-60 GeV. Specific examples are presented, showing the advantages of t…
Investigation of the $l^{-}l^{+}ν\overlineν$ final state at multi-TeV muon colliders through the exclusive decay of ZZ/WW gauge bosons in the Randall-Sundrum model
Hanoi National University of Education（河内国家师范大学）；Faculty of Applied Sciences, University of Economics - Technology for Industries（工业经济与技术大学应用科学学院）
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…
We consider QCD radiative corrections to Standard Model Higgs boson production in association with a W boson in hadron collisions. We present a fully exclusive calculation up to next-to-next-to-leading order (NNLO) in QCD perturbation theory. To perform this NNLO computation, we use a recently proposed version of the subtraction formalism. Our calculation includes finite-width effects, the leptonic decay of the W boson with its spin correlations, and the decay of the Higgs boson into a bbbar pair. We present selected numerical results at the Tevatron and the LHC.
We report on numerical studies of the NLO corrections to exclusive meson electroproduction, both in collider and fixed-target kinematics. Corrections are found to be huge at small xB and sizeable at intermediate or large xB.
QED radiative effects are considered in the case of measurement of spin-density matrix elements of diffractive $ρ$-meson electroproduction. Large radiative correction for $r^5_{00}$ is found in the kinematics of collider experiments at HERA.
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 upgrade of the coherent exclusive (CEEX) exponentiation realization of the Yennie-Frautschi-Suura (YFS) theory used in our Monte Carlo ({\cal KK} MC) to the processes f\bar{f}\rightarrow f'\bar{f'}, f=μ,τ,q,ν_\ell, f'=e,μ,τ,q,ν_\ell, q=u,d,s,c,b,t, \ell=e,μ,τwith f\ne f', with an eye toward the precision physics of the LHC and possible high energy muon colliders. We give a brief summary of the CEEX theory in comparison to the older (EEX) exclusive exponentiation theory and illustrate theoretical results relevant to the LHC and possible muon collider physics programs.
Exclusive dijet production at the Tevatron can be used as a benchmark to establish predictions on exclusive diffractive Higgs production, a process with a much smaller cross section. Exclusive dijet production in Double Pomeron Exchange processes, including diffractive Higgs production with measurements at the Tevatron and predictions for the Large Hadron Collider are presented. Using new data from the Tevatron and dedicated diffractive triggers, no excess over a smooth falling distribution for exclusive dijet events could be found. Upper limits on the exclusive dijet production cross section …
The exclusive vector meson production in electron-ion collisions for the energies of the future colliders is investigated. We present predictions for the coherent and incoherent $ϕ$ and $J/ψ$ production in $eAu$ collisions considering the possible states of nucleon configurations in the nuclear wave function and taking into account of the non-linear corrections to the QCD dynamics. The cross sections and transverse momentum distributions are estimated assuming the energies of the Electron-Ion Collider (EIC), Large Hadron Electron Collider (LHeC) and Future Circular Collider (FCC-$eh$). Our res…
In this paper we study leading neutron production in photon - hadron interactions which take place in $pp$ and $pA$ collisions at large impact parameters. Using a model that describes the recent leading neutron data at HERA, we consider exclusive vector meson production in association with a leading neutron in $pp/pA$ collisions at RHIC and LHC energies. The total cross sections and rapidity distributions of $ρ$, $ϕ$ and $J/Ψ$ produced together with a leading neutron are computed. Our results indicate that the study of these processes is feasible and that it can be used to improve the understa…
We consider higher-order QCD corrections for vector boson production at hadron colliders. We present recent results on transverse-momentum resummation for Z production. Moreover we show numerical results from a new fully exclusive next-to-next-to-leading order (NNLO) calculation.
We study the potential of the exclusive $pp\to p\ell^-\ell^+p$ process to probe excited leptons at the LHC which is known to be one of the most clean channel at the hadron colliders. The sensitivity of the model parameters is obtained 95% confidence level by considering three forward detector acceptances; $0.0015< ξ< 0.5$, $0.0015< ξ<0.15$ and $0.1< ξ< 0.5$.
In this talk estimates are presented of the odderon contributions to the exclusive J/psi and Upsilon production cross-sections at the Tevatron and the Large Hadron Collider. The obtained cross-sections are compared to cross-sections of the dominant background subprocesses mediated by the photon exchange. Possible experimental cuts are proposed that reduce the photon background.
The central exclusive production of $χ_{c}$ and $χ_{b}$ at the LHC, RHIC and Tevatron energies is analyzed, using the recent unintegrated parton distribution (UGDs) functions available in the package TMDlib. Comparison with data is performed, which tests the underlying assumptions basing the theoretical approach and it can constrain the unintegrated gluon distribution function at the small-$x$ region. Predictions for LHC energies using recent UGDs based in CCFM formalism are provided. It is explored the underlying uncertainties on this production as the choice for the unintegrated gluon distri…
We argue that the proton multiplicities measured in Roman pot detectors at an electron ion collider can be used to determine centrality classes in incoherent diffractive scattering. Incoherent diffraction probes the fluctuations in the interaction strengths of multi-parton Fock states in the nuclear wavefunctions. In particular, the saturation scale that characterizes this multi-parton dynamics is significantly larger in central events relative to minimum bias events. As an application, we study the centrality dependence of incoherent diffractive vector meson production. We identify an observa…
Coherent exclusive vector meson electroproduction is a key physics channel at an electron-ion collider. It probes the gluon structure of nuclei over a wide range of $Q^2$, and can be used to measure nuclear shadowing and to search for gluon saturation and/or the colored glass condensate. In this paper, we present calculations of the kinematic distributions for a variety of exclusive vector meson final states: the $ρ$, $ϕ$, J/$ψ$, $ψ'$ and the $Υ$ states. The cross-sections for light and $c\overline c$ mesons are large, while $Υ$ states should be produced in moderate numbers at a medium energy …
In the present work, $k_T$-factorization formalism is applied to compute the exclusive dilepton production by timelike Compton scattering (TCS) in $eA$, $pA$ and $AA$ collisions. The nuclear effects are investigated considering heavy and light ions. The production cross section in terms of invariant mass and rapidity distribution of the lepton pair is shown. The analysis is done for electron-ion collisions at the Large Hadron-Electron Collider (LHeC), its high-energy upgrade (HE-LHeC) and at the Future Circular Collider (FCC) in lepton-hadron mode. Additionally, ultraperipheral heavy ion colli…
We investigate the implication of uncertainties in the unintegrated gluon distribution for the predictions for central exclusive production of scalars at hadron colliders. We use parameterizations of the kT-unintegrated gluon density obtained from the Linked Dipole Chain model, applying different options for the treatment of non-leading terms. We find that the luminosity function for central exclusive production is very sensitive to details of the transverse momentum distribution of the gluon which, contrary to the kT-integrated distribution, is not very well constrained experimentally.
We calculate the exclusive process gamma* gamma* ->rho rho at high energy. The Born order estimate and the leading (LLA) and next to leading order (NLLA) BFKL resummation effects show the feasibility of experimental detection in a quite large range of Q2 values at future high energy e+e- linear colliders.
The diffractive program of the CDF Collaboration at the Fermilab Tevatron p-pbar collider is reviewed with emphasis on recent results from Run II at a c.m.s. energy of 1.96 TeV. Results are presented on the x-Bjorken and Q^2 dependence of the diffractive structure function obtained from di-jet production, on the slope parameter of the t-distribution of diffractive events as a function of Q^2 in the range 1 GeV^2<Q^2<10^4 GeV^2, and on cross sections for exclusive di-jet, e+e-, and di-photon production. The exclusive di-jet and di-photon production rates are used to check theoretical estimates …
We investigate the potentialities offered by the study of J/psi exclusive photo-production in ultra-peripheral collisions at a fixed-target experiment using the proton and lead LHC beams (generically denoted as AFTER@LHC) on hydrogen targets and at RHIC in the collider mode. We compare the expected counting rates in both set-ups. Studying Single-Transverse-Spin Asymmetries (A_N) in such a process provides a direct path to the proton Generalised Parton Distribution (GPD) E_g(x,xi,t). We evaluate the expected precision on A_N for realistic conditions with the LHCb detector in pH(pol) and PbH(pol…
Exclusive vector meson photoproduction associated with a leading baryon ($B = n, Δ^+, Δ^0$) in $pp$ and $pA$ collisions at RHIC and LHC energies is investigated using the color dipole formalism and taking into account nonlinear effects in the QCD dynamics. In particular, we compute the cross sections for $ρ$, $ϕ$ and $J/Ψ$ production together with a $Δ$ and compare the predictions with those obtained for a leading neutron. Our results show that the $V + Δ$ cross section is almost 30 % of the $V + n$ one. Our results also show that a future experimental analysis of these processes is, in princi…
The exclusive process e+ e- -> e+ e- rho^0_L rho^0_L allows to study various dynamics and factorization properties of perturbative QCD. At moderate energy, we demonstrate how collinear QCD factorization emerges, involving generalized distribution amplitudes (GDA) and transition distribution amplitudes (TDA). At higher energies, in the Regge limit of QCD, we show that it offers a promising probe of the BFKL resummation effects to be studied at the International Linear Collider (ILC).
The next generation of $e^+e^-$-colliders will offer a possibility of clean testing of QCD dynamics in the Regge limit. Recent progress in the theoretical description of exclusive processes permits for many of them a consistent use of the perturbative QCD methods. We advocate that the exclusive diffractive production of two $ρ$ mesons from virtual photons at very high energies should be measurable at the future linear collider (LC).
Central exclusive production (CEP) processes in high-energy proton -- (anti)proton collisions offer a very promising framework within which to study both novel aspects of QCD and new physics signals. Among the many interesting processes that can be studied in this way, those involving the production of heavy (c,b) quarkonia and gamma gamma states have sufficiently well understood theoretical properties and sufficiently large cross sections that they can serve as `standard candle' processes with which we can benchmark predictions for new physics CEP at the CERN Large Hadron Collider. Motivated …
The exclusive $π^0$ electroproduction is analyzed within the handbag approach based on Generalized Parton Distributions (GPDs) factorization. We consider the leading-twist contribution together with the transversity effects. It is shown that the transversity, $H_T$ and $\bar E_T$ GPDs are essential in the description of $π^0$ cross section. Predictions for future Electron-Ion Collider of China (EicC) energy range are done. It is found that transversity dominance $σ_T\ggσ_L$, observed at low energies is valid up to EicC energy range.
In this work the $k_{\perp}$-factorization formalism is applied to compute the exclusive $Z^0$ boson photoproduction in $ep$ and $eA$ collisions. The study is also extended to $pp$ and $AA$ processes. The nuclear effects are investigated considering heavy and light ions. Analytical models for the unintegrated gluon distribution are taken into account and the corresponding theoretical uncertainty is quantified. The analysis is done for electron-ion collisions at the Large Hadron-Electron Collider (LHeC), its high-energy upgrade (HE-LHeC) and at the Future Circular Collider (FCC) in lepton-hadro…
The process of exclusive vector meson production (gamma gamma to J/psi rho^0) is studied for almost real photons. This process may be reduced to photoproduction of J/psi off the rho^0 meson. We discuss the possibility of extracting the gluon distribution of rho^0 and of the photon from such measurement. Predictions are also given for the reaction (e+e- to e+ e- J/psi rho^0) for various e+e- cms energies typical for LEP and for the future linear colliders.
In a previous report we used the Linked Dipole Chain model unintegrated gluon densities to investigate the uncertainties in the predictions for central exclusive production of scalars at hadron colliders. Here we expand this investigation by also looking at other parameterizations of the unintegrated gluon density, and look in more detail on the behavior of these at small k_T. We confirm our conclusions that the luminosity function for central exclusive production is very sensitive to this behavior. However, we also conclude that the available densities based on the CCFM and LDC evolutions are…
