We discuss the open charm production in peripheral reactions
$\bar pp\to \bar Y_cY_c$ and $\bar pp\to M_c\bar M_c$, where
$Y_c$ and $M_c$ stand for $Λ_c^+,Σ_c^+$ and
$D,D^*$, respectively, at $\sqrt{s}\lesssim 15$ GeV, which corresponds to the energy range of FAIR. Our consideration is based on the topological decomposition of the planar quark and diquark diagrams which allows to estimate consistently meson and baryon exchange trajectories and energy scale parameters as well. The spin dependence is determined by the effective interaction of lowest exchanged resonance. Unknown parameters are fixed by an independent analysis of open strangeness production in $\bar pp\to \bar YY$ and $\bar pp\to \bar KK$ reactions and of SU(4) symmetry. We present the corresponding cross sections and longitudinal double-spin asymmetries for exclusive binary reactions with open charm mesons and baryons in the final state. The polarization observables have a non-trivial $t$ and $s$ dependence which is sensitive to details of the open charm production mechanism.
The cross sections for the charmonium production processes p pbar -> m Psi, where m is a light meson and Psi is a charmonium state, are of great interest for the planned p-pbar experiment PANDA. In this paper we estimate these cross sections using known results for the decays Psi -> m p pbar which are related to these reactions by crossing. In lieu of detailed experimental data on the decay Dalitz plots, we assume a constant amplitude as a first approximation; this implies a simple relation between the cross sections and decay widths. The single measured exclusive cross section of this type is…
We examine the possibility to extract information about the DN and DbarN interactions from the pbar d to D Dbar N reaction. We utilize the notion that the open-charm mesons are first produced in the annihilation of the antiproton on one nucleon in the deuteron and subsequently rescatter on the other (the spectator) nucleon. The latter process is then exploited for investigating the DN and DbarN interactions. We study different methods for isolating the contributions from the D^0p and D^-p rescattering terms.
Motivated by recent data on B-> p pbar K decay, we study various charmless three-body baryonic B decay modes, including Lambda pbar pi, Sigma0 pbar pi, p pbar pi, p pbar Kbar0, in a factorization approach. These modes have rates of order 10^{-6}. There are two mechanisms for the baryon pair production, current-produced and transition. The behavior of decay spectra from these baryon production mechanisms can be understood by using QCD counting rules. Predictions on rates and decay spectra can be checked in the near future.
We propose to investigate various charmonium states using their common decay channel to p pbar at LHC. Having the branching ratios for charmonium decaying into the p pbar final state measured or calculated, we propose to measure the charmonium production rate for both hadroproduction including soft-diffraction and inclusive production from b-hadron decays. We discuss the theoretical impacts in QCD of measuring different charmonium production rates and also the experimental prospects at LHCb, in particular, those for yet unmeasured eta_c and h_c.
Exclusive proton-antiproton annihilation into two photons at large s (~10 GeV^2) and |t|,|u| ~ s can be described by a generalized parton picture analogous to the 'soft mechanism' in wide-angle real Compton scattering. The two photons are emitted in the annihilation of a single fast quark and antiquark. The matrix element describing the transition of the p-pbar system to a q-qbar pair can be related to the timelike proton elastic form factors as well as to the quark/antiquark distributions measured in inclusive deep-inelastic scattering. The reaction could be studied with the proposed 1.5-15 G…
In this paper we summarize our recent results for low energy associated charmonium production cross sections, using 1) crossing symmetry, and 2) an explicit hadronic model. These predictions are of relevance to the planned charmonium and charmonium hybrid production experiment PANDA at GSI.
The QCD mechanisms underlying the exclusive strong decays and hadronic production amplitudes of charmonium remain poorly understood, despite decades of study and an increasingly detaled body of experimental information. One set of hadronic channels of special interest are those that include baryon-antibaryon states. These are being investigated experimentally at BES and CLEO-c in terms of their baryon resonance content, and are also of interest for the future PANDA experiment, in which charmonium and charmonium hybrids will be produced in p-pbar annihilation in association with light mesons. I…
The forward photoproduction amplitude for gamma p to Upsilon p is calculated in a pQCD k_t-factorization approach with an unintegrated gluon distribution constrained by inclusive deep-inelastic structure functions. The total cross section for diffractive Upsilons is compared with a recent HERA data. We also discuss the 2S/1S ratio in diffractive Upsilon-production. The amplitude is used to predict the cross section for exclusive Upsilon production in hadronic reactions. Differential distributions for the exclusive p pbar to p Upsilon pbar process are calculated for Tevatron energies. We also s…
Recent data on B->p pbar K, K0 pi pi and K Kbar K hint at a $\sim 2.3$ GeV object recoiling against a kaon. This could be the narrow state observed in J/ψ-> gamma xi. Nonobservation in p pbar annihilation implies ${\cal B}(ξ\to p\bar p) \sim$ few $\times 10^{-3}$, consistent with eta_c and J/ψdecays, but there are actual hints in p pbar -> phi phi and p p-> p pi^+ pi^- pi^+ pi^- p. Simple modeling shows ${\cal B}(B \to ξK){\cal B}(ξ\to p\bar p) \sim 1\times 10^{-6}$, appearing as a spike in the $p\bar p$ spectrum, with $\sim$ 30 events per 100 fb$^{-1}$; modes such as K K_s K_s, K phi phi, K4 …
We study the production of charmed mesons (D, D_s) in antiproton-proton annihilation close to the reaction thresholds. The elementary charm production process is described by baryon exchange and in the constituent quark model, respectively. Effects of the interactions in the initial and final states are taken into account rigorously. The calculations are performed in close analogy to our earlier study on pbarp to KbarK by connecting the processes via SU(4) flavor symmetry. Our predictions for the DDbar production cross section are in the order of 10^{-2} -- 10^{-1} mu b. They turned out to be …
In this paper we consider a sequential "meson emission" mechanism for charmonium decays of the type Psi -> N Nbar m, where Psi is a generic charmonium state, N is a nucleon and m is a light meson. This decay mechanism, which may not be dominant in general, assumes that an NNbar pair is created during charmonium annihilation, and the light meson m is emitted from the outgoing nucleon or antinucleon line. A straightforward generalization of this model can incorporate intermediate N* resonances. We derive Dalitz plot event densities for the cases Psi = eta_c, J/psi, chi_c0, chi_c1} and psi' and m…
The exclusive gamma-met signal has a small standard model cross-section and is thus a good channel in which to look for signs of new physics. This signature is predicted by models with a superlight gravitino or with large extra spatial dimensions. We search for such signals at the CDF detector at the Tevatron, using 87 pb^-1 of data at sqrt(s) = 1.8 TeV, and extract 95% C.L. limits on these processes. A limit of 221 GeV is set on the scale |F|^{1/2} in supersymmetry models. For 4, 6, and 8 extra dimensions, limits on the fundamental mass scale M_D of 549, 581, and 602 GeV, respectively, are fo…
We review the current theoretical situation with regard to the anomalously large cross section for exclusive J/psi + eta_c production in e^+ e^- annihilation, as measured by BELLE Collaboration.
We calculate differential cross sections for exclusive double diffractive (EDD) production of open charm in proton-proton and proton-antiproton collisions. Sizeable cross sections are found. The EDD contribution constitutes about 1 % of the total inclusive cross section for open charm production. A few differential distributions are shown and discussed. The EDD contribution falls faster both with transverse momentum of the $c$ quark/antiquark and the $c \bar c$ invariant mass than in the inclusive case.
We propose to investigate a largely unexplored sector that is unique to the formulation of hard exclusive processes in terms of GPDs, namely the electroproduction of strange and charmed mesons in the kinematical ranges of Jefferson Lab's 12 GeV upgrade, and of the proposed Electron Ion Collider (EIC). In this contribution we focus on charmed meson production that is unique to the EIC. Exclusive strange and charmed meson production provides new insights in the connection of the quark/gluon degrees of freedom with the meson-baryon description, both in the unpolarized and polarized sectors. Howev…
{We investigate the photoproduction process $ p γ\rightarrow Λ_{c}^{+} \overline{D^{0}}$ within the handbag approach, which we assume to be the dominant mechanism at energies well above the production threshold and in the forward scattering hemisphere.
Exclusive nonleptonic decays of bottom baryons to charm baryons and pseudoscalar light mesons are analyzed within a relativistic three-quark model. We include factorizing as well as nonfactorizing contributions to the decay amplitudes. The total contribution of the nonfactorizing diagrams amount up to 30% of the factorizing contributions in amplitude. We present detailed predictions for rates and asymmetry parameters.
This paper is devoted to the leading twist exclusive bottomonia decays with double charmonium in the final state. Using models of the twist-2 charmonia distribution amplitudes the widths of these decays are calculated within light cone formalism. In addition, the processes under consideration are studied within nonrelativistic QCD. In our analysis we have found that the production of some of the $P$-wave charmonia mesons with $L_z \neq 0$ is allowed already at the leading twist approximation. This means that the selection rules which predict the suppression of such decays are violated. The mec…
The role of higher Fock-state contributions to exclusive charmonium decays will be discussed. It will be argued that the J/Psi (Psi') decays into baryon-antibaryon pairs are dominated by the valence Fock-state contributions. P-wave charmonium decays, on the other hand, receive strong contributions from the c cbar g Fock states since the valence Fock-state contributions are suppressed in these reactions. Numerical results for the decay widths of J/Psi (Psi') into baryon-antibaryon and chi(J) into pairs of pseudoscalar mesons will be also presented and compared to data.
We apply the newly developed NRQCD factorization formula to analyze the exclusive production of the fully-charmed tetraquark $T_{4c}$ plus a hard photon at $B$ factory. For simplicity, in this work we have concentrated on the associated production of the $0^{++}$ and $2^{++}$ tetraquarks with a photon. With some rough estimates about the size of the unknown nonperturbative NRQCD matrix elements, we predict the production rates of these types of exclusive channels at $\sqrt{s}=10.6$ GeV and also assess their observation prospect at {\tt Belle 2} experiment.
In the framework of QCD factorization, we study the $B$ meson exclusive decays $B\to χ_{cJ}K$ where the spin-triplet P-wave charmonium states $χ_{cJ}(J=0,1,2)$ are described by the color-singlet non-relativistic wave functions. We find that for these decays (except $χ_{c1}$) there are infrared divergences arising from nonfactorizable vertex corrections as well as logarithmic end-point singularities arising from nonfactorizable spectator interactions at leading-twist order. The infrared divergences due to vertex corrections will explicitly break down QCD factorization within the color-singlet m…
It is argued that colour octet contribution in exclusive charmonium decays is very important even though the same infrared divergence found in P-wave colour singlet inclusive decay is absent. This comes about because of the suppression at the level of the wavefunction of P-wave quarkonia. Using the modified hard scattering approach of Brodsky, Lepage, Botts, Li and Sterman, we use charmonium decay into baryon-antibaryon pair as an example and show that the colour singlet contribution alone is clearly insufficient to explain the experimental decay widths.
This article is devoted to systematic analysis of double charmonium production in exclusive $Z$ boson decays in the framework of Nonrelativistic Quantum Chromodynamic (NRQCD) and leading twist light-cone (LC) models. Theoretical predictions for branching fractions of all considered decays are presented. According to obtained results in the case of allowed by helicity suppression rule processes the effect of internal quark motion increases the branching fraction by a factor 1.5, while for forbidden reactions LC predictions are strictly zero, while NRQCD ones are significantly smaller than for a…
The presented paper is devoted to theoretical analysis of charmonium mesons $η_c$, $J/ψ$, $χ_{c0,1,2}$, and $h_c$ production in exclusive radiative $Z$ boson decays in the frameworks of Nonrelativistic Chromodynamic and amplitude expansion on the light-cone. In the framework of light-cone expansion amplitudes and widths of all processes are described with one universal relation. It is interesting to note that from this relation it follows automatically which component of $Z$ boson (either vector or axial) gives contribution to the width of the particular decay. It is shown that the effect of i…
We summarize what is known about the transverse spatial distribution of gluons in the nucleon and its x-dependence from exclusive J/psi photo/electroproduction in e-p fixed-target and collider experiments (HERA H1 and ZEUS). This information can be used to predict the impact parameter dependence of the cross section for certain hard QCD processes (dijet production) in pbar-p and p-p collisions at the Tevatron and LHC.
Exclusive nonleptonic decays of bottom and charm baryons are studied within a relativistic three-quark model with a Gaussian shape for the momentum dependence of the baryon-three-quark vertex. We include factorizing as well as nonfactorizing contributions to the decay amplitudes. For heavy-to-light transitions Q -> q u d the total contribution of the nonfactorizing diagrams amount up to approximately 60% of the factorizing contributions in amplitude, and up to approximately 30% for b -> c u d transitions. We calculate the rates and the polarization asymmetry parameters for various nonleptonic …
In the wake of recent measurements of ratios of semileptonic branching fractions: ${\cal R}_{J/ψ}, {\cal R}_D$ and ${\cal R}_{D^*}$ reported by the LHCb, BELLE and HFLAV Collaborations, we calculate invariant form factors for the exclusive semileptonic $B_c$-meson decays to radially excited charmonium and charm meson states in the full kinematical region within the framework of relativistic independent quark (RIQ)model. We evaluate the lepton mass effect in the decay processes induced by $b\to c,u$ transition at the quark level. Our predictions on branching fractions for $B_c\to η_c/ψ(nS)$ are…
We study the exclusive decays of $B$ meson into P-wave charmonium states $χ_{cJ}(J=0,1)$ in the QCD factorization approach with light-cone distribution functions describing the mesons in the processes. For $B \to χ_{c1} K$ decay, we find that there are logarithmic divergences arising from nonfactorizable spectator interactions even at twist-2 order and the decay rate is too small to accommodate the experimental data. For $B\to χ_{c0} K$ decay, we find that aside from the logarithmic divergences arising from spectator interactions at leading-twist order, more importantly, the factorization will…
We develop a framework to study the exclusive two-body decays of bottomonium into two charmed mesons and apply it to study the decays of the C-even bottomonia. Using a sequence of effective field theories, we take advantage of the separation between the scales contributing to the decay processes, 2m_b >> m_c >> Λ_{QCD}. We prove that, at leading order in the EFT power counting, the decay rate factorizes into the convolution of two perturbative matching coefficients and three non-perturbative matrix elements, one for each hadron. We calculate the relations between the decay rate and non-perturb…
In this paper, we calculate the next-to-leading order (NLO) quantum chromodynamics (QCD) corrections to the exclusive processes $B_c^+\to χ_{cJ}(h_c)π^+$ in the framework of the nonrelativistic QCD (NRQCD) factorization formalism. The results show that NLO QCD corrections markedly enhance the branching ratios with $K$ factors of about 2.5. In combination with the study of $B_c^+\to J/ψπ^+$, we find that the NLO NRQCD prediction for the ratio of branching fractions $\frac{\mathcal{B}(B_c^+\to χ_{c0}π^+)}{\mathcal{B}(B_c^+\to J/ψπ^+)}$ is then compatible with the experimental measurement.
We calculate the exclusive cross sections for e^+ e^- annihilation into two charmonium states through a virtual photon. Purely electromagnetic contributions are surprisingly large, changing the cross sections by as much as 21%. The predicted cross section for J/psi + eta_c is about an order of magnitude smaller than a recent measurement by the BELLE Collaboration, although part of the discrepancy can be attributed to large relativistic corrections. The cross sections for S-wave + P-wave, P-wave + P-wave, and S-wave + D-wave charmonium states are also calculated. It may be possible to discover …
We revisit the calculation of nonfactorizable corrections induced by charm-quark loops in exclusive FCNC $B$-decays. For the sake of clarity, we make use of a field theory with scalar particles: this allows us to focus on the conceptual issues and to avoid technical complications related to particle spins in QCD. We perform a straightforward calculation of the appropriate correlation function and show that it requires the knowledge of the full generic three-particle distribution amplitude with non-aligned arguments, $\langle 0|\bar s(y)G_{μν}(x)b(0)|B(p)\rangle$. Moreover, the dependence of th…
Within the Standard Model, CP rate asymmetries for $B\to K^-π^{+,0}$ could reach 10%. With strong final state phases, they could go up to 20--30%, even for $\bar K^0π^-$ mode which would have opposite sign. We can account for $K^-π^{+}$, $\bar K^0π^-$ and $ϕK$ rate data with new physics enhanced color dipole coupling and destructive interference. Asymmetries could reach 40--60% for $Kπ$ and $ϕK$ modes and are all of the same sign. We are unable to account for $K^-π^0$ rate. Our inclusive study supports our exclusive results.
We calculate the contributions from QED processes involving two virtual photons to the cross sections for e^+ e^- annihilation into two charmonium states with the same C-parity. Generically, the cross sections are three orders of magnitude smaller than those for charmonia with opposite C-parity because they are suppressed by a factor of alpha^2/alpha_s^2. However, if both charmonia have quantum numbers J^{PC} = 1^{--}, then there is a contribution to the cross section that involves the fragmentation of each photon into a charmonium. The fragmentation contribution is enhanced by powers of E_{be…
The spin structure of the matrix element for the reactions $γ+ N\to Y_c +{D}^*$, where $Y_c=Λ_c^+(2285)$, $Σ_c(2455)$ are charmed baryons with spin 1/2, and $D^*(2010)$ is the vector charmed meson, can be parametrized, in collinear regime, in terms of three independent scalar amplitudes, which are functions of the photon energy $E_γ$, only. In framework of an effective Lagrangian approach generalized to charm photoproduction, we calculate the energy dependence of the differential cross section, the density matrix element of $\bar{D}^*$, $ρ_{11}$, the asymmetry $A_z$ in the collision of circula…
In this paper, we preformed a further research on the exclusive productions of double charmonium via $Z$-boson decay by using nonrelativistic QCD factorizations approach, where the single-photon fragmentation topologies of the QED diagrams, the interference terms between the QCD and full QED diagrams, the next-to-leading-order calculations of the interference terms are preformed. For the production of $J/ψ+J/ψ$ in $Z$-boson decay, the interference terms show a significantly phenomenological effect due to the addition of the newly calculated NLO QCD corrections. After adding together all contri…
In this paper the cross sections of the processes $e^+ e^- \to H+γ, H=η_c, η_c', χ_{c0}, χ_{c1}, χ_{c2}$ are calculated. The calculation is carried out at the leading twist approximation of light cone formalism. Within this approach the leading logarithmic radiative and relativistic corrections to the amplitudes are resumed. For the processes $e^+ e^- \to η_c, η_c'+γ$ one loop radiative corrections are taken into account. It is also shown that one loop leading logarithmic radiative corrections calculated within light cone formalism for the processes under study coincide with that obtained by d…
It is generally assumed that due to factorization of long- and short-distance dynamics perturbative QCD can be applied to exclusive hadronic reactions at large momentum transfers. Within such a perturbative approach diquarks turn out to be a useful phenomenological device to model non-perturbative effects still observable in the kinematic range accessible by present-days experiments. The basic ingredients of the perturbative formalism with diquarks, i.e. Feynman rules for diquarks and quark-diquark wave functions of baryons, are briefly summarized. Applications of the diquark model to the elec…
We calculate the cross section and the beam asymmetry for exclusive photoproduction of charmed particles near threshold ($γ+p\to Λ_c^+ +\bar{D^0}$), in the framework of an effective Lagrangian model. We discuss the sensitivity of these observables to the magnetic moment of the $Λ_c$ baryon and of the coupling constant in the $pΛ_c D$ vertex. We show that exclusive measurements allow, in principle, to determine the magnetic moments of charmed baryons.
Exclusive decays of B and D mesons are discussed with the focus on the theoretical problem how to calculate the relevant hadronic matrix elements of weak operators in the framework of QCD sum rules. The three lectures are devoted to 1. leptonic decays and decay constants 2. semileptonic decays and form factors 3. nonleptonic decays and nonfactorizable amplitudes. I shall introduce some of the basic concepts, describe various calculational techniques, and illustrate the numerical results. The latter are compared with lattice and quark model predictions and, where possible, with experimental dat…
We have fully reconstructed decays of both B0 and B- Mesons into final states containing either D, D*, D**, Psi, Psi', or Chi_{c1} mesons. This allows us to obtain new results on many physics topics including branching ratios, tests of the factorization hypothesis, color suppression, resonant substructure, and the B- - B0 mass difference.
We discuss exclusive charmless B decays within the Standard Model of particle physics. In particular, we consider hadronic two-body decays as B -> pi pi and perform a conceptual analysis of heavy-to-light form factors which encode the strong interaction effects in semi-leptonic decays as B -> pi l nu. Concerning the hadronic decays we compute NNLO QCD corrections which are particularly important with respect to strong interaction phases and hence direct CP asymmetries. We present results for the imaginary part of the topological tree amplitudes and a partial calculation of the real part of the…
We study exclusive production of scalar $χ_{c0}\equiv χ_c(0^{++})$ and pseudoscalar $η_c$ charmonia states in proton-proton collisions at the LHC energies. The amplitudes for $gg \to χ_{c0}$ as well as for $gg \to η_c$ mechanisms are derived in the $k_{T}$-factorization approach. The $p p \to p p η_c$ reaction is discussed for the first time. We have calculated rapidity, transverse momentum distributions as well as such correlation observables as the distribution in relative azimuthal angle and $(t_1,t_2)$ distributions. The latter two observables are very different for $χ_{c0}$ and $η_c$ case…
A narrow resonance in D*- p and D*+ pbar invariant mass combinations is observed in inelastic electron-proton collisions at centre-of-mass energies of 300 GeV and 320 GeV at HERA. The resonance has a mass of 3099 \pm 3 (stat.) \pm 5 (syst.) MeV and a measured Gaussian width of 12 \pm 3 (stat.) MeV, compatible with the experimental resolution. The resonance is interpreted as an anti-charmed baryon with a minimal constituent quark composition of uuddcbar, together with the charge conjugate.
We evaluate exclusive semileptonic decays of ground-state spin-1/2 doubly heavy charmed baryons driven by a $c\to s,d$ transition at the quark level. Our results for the form factors are consistent with heavy quark spin symmetry constraints which are valid in the limit of an infinitely massive charm quark and near zero recoil. Only a few exclusive semileptonic decay channels have been theoretically analyzed before. For those cases we find that our results are in a reasonable agreement with previous calculations.
Recent data on charmonium production in B-meson decays suggest that charmonium hybrid mesons with mass ~4 GeV may be produced in B-decay via c\bar{c} colour octet operators. Some of these states are likely to be narrow with clean signatures to J/ψpi^+ pi^- final states. Experimental signatures and search strategies for existing B-factories are described.
We study the exclusive two-body nonleptonic $B_c\to X_{c\bar{c}}M$ decays, where $X_{c\bar{c}}$ is either a ground(1S) or a radially excited (2S or 3S) charmonium and $M$ is a pseudoscalar $(P)$ or a vector $(V)$ meson. We consider here three categories of decays: $B_c \to PP, PV, VP$ decays within the framework of relativistic independent quark(RIQ) model based on a flavor-independent interaction potential in scalar-vector harmonic form. Using the factorization approximation, we calculate the weak form factors from the overlapping integrals of meson wave functions obtained in the RIQ model an…
We make a comparative and comprehensive study on the charmonium exclusive productions at the $e^+e^-$ collider with the collision energy either round the $Z^0$-boson mass for a super $Z$ factory or equals to 10.6 GeV for the $B$ factories as Belle and BABAR. We study the total cross sections for the charmonium production via the exclusive processes $e^+e^- \to γ^*/Z^0 \to H_{1}+H_{2}$ and $e^+e^- \to γ^*/Z^0 \to H_{1} +γ$, where $H_{1}$ and $H_{2}$ represent the dominant color-singlet $S$-wave and $P$-wave charmonium states respectively. Total cross sections versus the $e^+e^-$ collision energ…
We outline the proofs of the factorization theorems for exclusive two-body charmonium production in B-meson decay and e^+e^- annihilation to all orders in perturbation theory in quantum chromodynamics. We find that factorized expressions hold up to corrections of order m_c/m_b in B-meson decay and corrections of order m_c^2/s in e^+e^- annihilation, where m_c is the charm-quark mass, m_b is the bottom-quark mass, and root-s is the e^+e^- center-of-momentum energy.
We present the main results of our recent analyses of exclusive production of vector charmonia ($J/ψ$ and $ψ'$) in $k_t$-factorization approach and for $γγ$ production of charged dilepton pairs in exclusive and semiinclusive processes in a new approach, similar in spirit to $k_t$-factorization. The results for charmonia are compared with recent results of the LHCb collaboration. We include some helicity flip contributions and quantify the effect of absorption correction. The effect of $c \bar c$ wave function is illustrated. We present uncertainties related to $F_2$ structure function which ar…
Confinement indicates an asymptotic quark state not observable except its energy is zero. Unitarity indicates that the total probability of a definite state of quark system to transit to any final state is exactly one. This talk reviews some important conclusions/predictions from the basic properties like unitarity of the combination model, as addressed by the title. We also in the Postscript section address the bottom quark energy loss. In the discussions around the dinner table in the Rencontre, the author combined the large transverse momentum J/Psi suppression and the contribution to J/Psi…
The proton form factor, two-photon annihilations into $p\bar{p}$ as well as exclusive charmonium decays are critically examined. It will be argued that the standard perturbative QCD analysis of these reactions fails, i.e. the need for additional contributions can convincingly be demonstrated. Possible dynamical mechanisms such as colour-octet admixtures to the charmonium states or diquarks inside baryons, will be discussed and compared to the data.
The exclusive decay of $Υ$ to a vector plus pseudoscalar charmonium is studied in perturbative QCD. The corresponding branching ratios are predicted to be of order $10^{-6}$ for first three $Υ$ resonances, and we expect these decay modes should be discovered in the prospective high-luminosity $e^+e^-$ facilities such as super $B$ experiment. As a manifestation of the short-distance loop contribution, the relative phases among strong, electromagnetic and radiative decay amplitudes can be deduced. It is particularly interesting to find that the relative phase between strong and electromagnetic a…
We study baryon pair production in two-photon collisions, gamma gamma -> B Bbar, within perturbative quantum chromodynamics, treating baryons as quark-diquark systems. We extend previous work within the same approach by treating constituent-mass effects systematically by means of an expansion in the small parameter (mass/photon energy). Our approach enables us to give a consistent description of the cross sections for all octet baryon channels. Adopting the model parameters from foregoing work, we are able to reproduce the most recent large-momentum-transfer data from LEP for the p pbar, Lambd…
