We present an analysis of the static properties of heavy baryons at next-to-leading order in the perurbative expansion of QCD. We obtain analytical next-to-leading order three-loop results for the two-point correlators of baryonic currents with one finite mass quark field for a variety of quantum numbers of the baryonic currents. We consider both the massless limit and the HQET limit of the correlator as special cases of the general finite mass formula and find agreement with previous results. We present closed form expressions for the moments of the spectral density. We determine the residues of physical baryon states using sum rule techniques.
With the QCD sum rules approach, we study the newly discovered doubly heavy baryon $Ξ_{cc}^{++}$. We analytically calculate the next-to-leading order (NLO) contribution to the perturbative part of $J^{P} = \frac{1}{2}^{+}$ baryon current with two identical heavy quarks, and then reanalyze the mass of $Ξ_{cc}^{++}$ at the NLO level. We find that the NLO correction significantly improves both scheme dependence and scale dependence, whereas it is hard to control these theoretical uncertainties at leading order. With the NLO contribution, the baryon mass is estimated to be $m_{Ξ_{cc}^{++}} = 3.66_…
We give an overview of the calculation of the forward jet vertex associated to a rapidity gap (coupling of a hard pomeron to a jet) in the Balitsky-Fadin-Kuraev-Lipatov (BFKL) formalism at next-to-leading order (NLO). This result allows, together with the NLO non-forward gluon Green function, to perform NLO studies of jet production in diffractive events (Mueller-Tang dijets, as a well-known example)
The deep-inelastic neutrino-nucleon cross section is one of the components of few GeV neutrino interactions. We present here our results for neutrino-isoscalar nucleon charged current scattering including perturbative next-to-leading order QCD corrections, target mass corrections, charm mass and lepton mass corrections.
We present analytical next-to-leading order results for the correlator of baryonic currents at the three-loop level with one finite mass quark. We obtain the massless and the HQET limits of the correlator as particular cases from the general formula, we also give explicit expressions for the moments of the spectral density. Calculations have been performed with an extensive use of the symbolic manipulation programs MATHEMATICA and REDUCE.
The MC@NLO and MEPS@NLO methods, as implemented in the Monte-Carlo event generator framework Sherpa, are used to estimate the perturbative and non-perturbative uncertainties in various processes such as dijet production and the production of a W boson in association with (multiple) jets.
QCD sum-rule mass predictions for tetraquark states provide insights on the interpretations and internal structure of experimentally-observed exotic mesons. However, the overwhelming majority of tetraquark QCD sum-rule analyses have been performed at leading order (LO), which raises questions about the underlying theoretical uncertainties from higher-loop corrections. The impact of next-to-leading order (NLO) perturbative effects are systematically examined in scalar ($J^{PC}=0^{++}$) isoscalar light-quark tetraquark systems where comprehensive LO sum-rule analyses have been performed and NLO …
We study the triply heavy baryons $Ω_{QQQ}$ $(Q=c, b)$ in the QCD sum rules by performing the first calculation of the next-to-leading order (NLO) contribution to the perturbative QCD part of the correlation functions. Compared with the leading order (LO) result, the NLO contribution is found to be very important to the $Ω_{QQQ}$. This is because the NLO not only results in a large correction, but also reduces the parameter dependence, making the Borel platform more distinct, especially for the $Ω_{bbb}$ in the $\overline{\rm{MS}}$ scheme, where the platform appears only at NLO but not at LO. …
In this talk the application of the recently introduced methods to merge NLO calculations of successive jet multiplicities to the production of top pairs in association with jets will be discussed, in particular a fresh look is taken at the top quark forward-backward asymmetries. Emphasis will be put on the achieved theoretical accuracy and the associated perturbative and non-perturbative error estimates.
We study the penguin-dominated B -> PV decays, with P (V) representing a pseudo-scalar (vector) meson, in the next-to-leading-order (NLO) perturbative QCD (PQCD) formalism, concentrating on the B -> K phi, pi K^*, rho K, and omega K modes. It is found that the NLO corrections dramatically enhance the B -> rho K, omega K branching ratios, which were estimated to be small under the naive factorization assumption. The patterns of the direct CP asymmetries A_{CP}(B^0 -> rho^\mp K^\pm) \approx A_{CP}(B^\pm -> rho^0 K^\pm) and |A_{CP}(B^0 -> pi^\mp K^{*\pm})| > |A_{CP}(B^\pm -> pi^0 K^{*\pm})| are p…
Fragmentation functions for D mesons, based on the convolution of a perturbative part, related to the heavy quark perturbative showering, and a non-perturbative model for its hadronization into the meson, are used to describe D^* production in e^+e^- and ep collisions. The non-perturbative part is determined by fitting the e^+e^- data taken by ARGUS and OPAL at 10.6 and 91.2 GeV respectively. When fitting with a non perturbative Peterson fragmentation function and using next-to-leading evolution for the perturbative part, we find an epsilon parameter sensibly different from the one commonly us…
A dedicated test of the perturbative QCD NLO parton evolution in the very small-$x$ region is performed. We find a good agreement with recent precision HERA-data for $F_2^p(x,Q^2)$, as well as with the present determination of the curvature of $F_2^p$. Characteristically, perturbative QCD evolutions result in a positive curvature which increases as $x$ decreases. Future precision measurements in the very small $x$-region, $x<10^{-4}$, could provide a sensitive test of the range of validity of perturbative QCD
We study predictions from perturbative Quantum Chromodynamics (QCD) for the process pp -> H -> gamma gamma + X. In particular, we compare fully differential calculations at next-to-leading (NLO) and next-to-next-to-leading order (NNLO) in the strong coupling constant to the results obtained with the MC@NLO Monte Carlo (MC) generator, which combines QCD matrix elements at NLO with a parton shower algorithm. Estimates for the systematic uncertainties in the various predictions due to the choice of the renormalization scale and the parton distribution functions are given for the inclusive and acc…
We compute in next-to-leading order (NLO) perturbative QCD the transverse energy carried into the central rapidity unit of hadron or nuclear collisions by the partons freed in the few-GeV subcollisions. The formulation is based on a rapidity window and a measurement function of a new type. The behaviour of the NLO results as a function of the minimum transverse momentum and as a function of the scale choice is studied. The NLO results are found to be stable relative to the leading-order ones even in the few-GeV domain.
In this paper we firstly demonstrate step by step that the factorization hypothesis is valid at the next-to-leading order (NLO) for the exclusive process $ργ^{\star} \to ρ$ by employing the collinear factorization approach, and then extend this proof to the case of the $k_T$ factorization by taking into account the transversal momentum of the light external quark (anti-quark) lines in the $ρ$ meson. At the NLO level, we then show that the soft divergences from different sub-diagrams will be canceled each other in the quark level, while the remaining collinear divergences can be absorbed into t…
We propose a perturbative evaluation for the next-to-leading-order (NLO) $O(1/Q^4)$ power correction to the photon-pion transition form factor. The effects of the NLO power correction are analyzed.
Compatibility of the Reggeized form of QCD multi-particle amplitudes with the s-channel unitarity requires fulfilment of an infinite number of the "bootstrap" relations. On the other hand, it turns out that fulfillment of all these relations ensures the Reggeized form of energy dependent radiative corrections order by order in perturbation theory. It is extremely nontrivial, that all these relations are fulfilled if the Reggeon vertices and trajectory satisfy several bootstrap conditions. The full set of these conditions in the next-to-leading order was derived in the last year and the ultimat…
In this paper, we calculated the $B \to (\jpsi, η_c) K$ decays in the perturbative QCD approach with the inclusion of the partial next-to-leading order (NLO) contributions. We found that (a) when the large enhancements from the known NLO contributions are taken into account, the NLO pQCD predictions for the branching ratios are the following: $Br(B^0 \to \jpsi K^0) = 5.2^{+3.5}_{-2.8}\times 10^{-4}$, $Br(B^+ \to \jpsi K^+) = 5.6^{+3.7}_{-2.9}\times 10^{-4}$, $Br(B^0 \to η_c K^0) = 5.5^{+2.3}_{-2.0}\times 10^{-4}$, $Br(B^+ \to η_c K^+) = 5.9^{+2.5}_{-2.1}\times 10^{-4}$, which are roughly 40% s…
It is shown that the previously noted extreme perturbative NNLO/NLO instability of the longitudinal structure function F_L(x,Q^2) is a mere artefact of the commonly utilized `standard' gluon distributions. In particular it is demonstrated that using the appropriate -- dynamically generated -- parton distributions at NLO and NNLO, F_L(x,Q^2) turns out to be perturbatively rather stable already for Q^2 $\geq$ O(2-3 GeV^2).
Recent measurements for F_2(x,Q^2) have been analyzed in terms of the `dynamical' and `standard' parton model approach at NLO and NNLO of perturbative QCD. Having fixed the relevant NLO and NNLO parton distributions, the implications and predictions for the longitudinal structure function F_L(x,Q^2) are presented. It is shown that the previously noted extreme perturbative NNLO/NLO instability of F_L(x,Q^2) is an artifact of the commonly utilized `standard' gluon distributions. In particular it is demonstrated that using the appropriate -- dynamically generated -- parton distributions at NLO an…
Existing calculations of heavy quark hadroproduction in perturbative QCD are either based on the approximate conventional zero-mass perturbative QCD theory or on next-to-leading order (NLO) fixed-flavor-number (FFN) scheme which is inadequate at high energies. We formulate this problem in the general mass variable-flavor-number scheme which incorporates initial/final state heavy quark parton distribution/fragmentation functions as well as exact mass dependence in the hard cross-section. This formalism has the built-in feature of reducing to the FFN scheme near threshold, and to the conventiona…
We report the first complete leading-twist next-to-leading-order perturbative QCD predictions for the two-photon exclusive channels gamma gamma -> M+ M- (M=pi,K) at large momentum transfer. The asymptotic distribution amplitude is utilized as a candidate form for the nonperturbative dynamical input. Comparison of the obtained results with the existing experimental data does not provide sufficiently clear evidence to support the applicability of the hard-scattering approach at currently accessible energies.
We compute the next-to-leading order perturbative QCD corrections to the correlators of nucleon interpolating currents in relativistic nuclear matter. The main new result is the calculation of the O(alpha_s) perturbative corrections to the coefficient functions of the vector quark condensate in matter. This condensate appears in matter due to the violation of Lorentz invariance. The NLO perturbative QCD corrections turn out to be large which implies that the NLO corrections must be included in a sum rule analysis of the properties of both bound nucleons and relativistic nuclear matter.
We present the first next-to-leading-order (NLO) perturbative QCD (pQCD) study of rapidity-differential cross sections of coherent exclusive photoproduction of $J/ψ$ mesons in heavy-ion ultraperipheral collisions (UPCs) at the LHC, $dσ/dy(\text{Pb} + \text{Pb} \rightarrow \text{Pb} + J/ψ+ \text{Pb})$. For this, we account for the photon-nucleon NLO cross sections at the forward limit, the $t$ dependence using a standard nuclear form factor, and the photon fluxes of the colliding nuclei. Approximating the generalized parton distributions with their forward-limit parton distribution functions (P…
We apply the method of perturbative fragmentation to study bottom fragmentation in top decay. We present the energy spectrum of b-quarks and b-flavoured hadrons in top decay
The highest exclusive jet multiplicity studied at LEP experiments is five. In this paper we compute the next-to-leading order QCD corrections to e+e- annihilation to five jets, essentially closing the (pure) perturbative QCD studies of exclusive jetty final states at LEP. We compare fixed-order perturbative results with ALEPH data. We estimate hadronization corrections to five-jet observables using the event generator SHERPA, which employs the CKKW procedure to combine a reliable perturbative treatment of high-multiplicity jet final states with parton showers. We show that a competitive value …
The amplitude for the forward electroproduction of two light vector mesons can be written completely within perturbative QCD in the Regge limit with next-to-leading accuracy, thus providing the first example of a physical application of the BFKL approach at the next-to-leading order. Recently, a numerical determination of the amplitude has been obtained in the case of equal photon virtualities, by using a definite representation for the amplitude and a definite optimization method for the perturbative series. Here, we study the main systematic effects in the previous determination, by consider…
The possibility of an improvement of current NLO Monte Carlo event generators by means of choosing a suitable factorization scheme is studied. The optimal factorization scheme for combining initial state parton showers and NLO hard scattering cross-sections is the ZERO factorization scheme, in which all NLO splitting functions vanish. However, it has turned out that the ZERO factorization scheme has a limited range of practical applicability. Hence, this paper is focused on searching for a factorization scheme which is applicable at the NLO in the full range of x relevant for QCD phenomenology…
This is the introductory part of my PhD thesis which consists of two parts, the separate introduction and four published articles. The introduction begins by a technically detailed description of the DGLAP evolution and the fast numerical solving method for the DGLAP equations, which has been used in the numerical works of the published articles of this thesis. A write-up of the next-to-leading order (NLO) calculations for the deeply inelastic scattering (DIS) and the Drell-Yan (DY) dilepton production cross-sections is also included. The formalism of the inclusive single hadron production at …
Precision background predictions with well-defined uncertainty estimates are important for interpreting collider-physics measurements and for planning future high-energy collider experiments. It is especially important to estimate the perturbative uncertainties in predictions of inclusive measurements of jet observables, that are designed to be largely insensitive to non-perturbative effects such as the structure of beam-remnants, multi-parton scattering or hadronization. In this study, we discuss possible pit-falls in defining the perturbative uncertainty of unitarized next-to-leading order m…
The chiral $SU(3)$ Lagrangian with charmed baryons of spin $J^P=1/2^+$ and $J^P=3/2^+$ is analyzed. We consider all counter terms that are relevant at next-to-next-to-next-to-leading order (N$^3$LO) in a chiral extrapolation of the charmed baryon masses. At N$^2$LO we find 16 low-energy parameters. There are 3 mass parameters for the anti-triplet and the two sextet baryons, 6 parameters describing the meson-baryon vertices and 7 symmetry breaking parameters. The heavy-quark spin symmetry predicts four sum rules for the meson-baryon vertices and degenerate masses for the two baryon sextet field…
We present predictions for the rapidity-differential cross sections of exclusive $Υ$ photoproduction in ultraperipheral collisions (UPCs) of lead ions at the Large Hadron Collider (LHC). We work in the framework of collinear factorization at next-to-leading order (NLO) in perturbative QCD, modeling the generalized parton distributions (GPDs) through the Shuvaev transform of nuclear parton distribution functions (nPDFs). While the effects due to the GPD modeling turn out to be small, the direct NLO predictions still carry significant nPDF-originating uncertainties and depend strongly on the cho…
We present a study of the $S=-1$ meson-baryon interaction, employing a chiral SU(3) Lagrangian up to next-to-leading order (NLO) and implementing unitarization in coupled channels. The parameters of the model have been fitted to a large set of experimental scattering data in different two-body channels, to threshold branching ratios, and to the precise SIDDHARTA value of the energy shift and width of kaonic hidrogen. In contrast to other groups, we have taken into consideration the $K^- p\to K^+Ξ^-, K^0Ξ^0$ reaction data, since we found in a previous work to be especially sensitive to the NLO …
We apply the so-called conformal subtraction scheme to predict perturbatively exclusive processes beyond leading order. Taking into account evolution effects, we study the scheme dependence for the photon-to-pion transition form factor and the electromagnetic pion form factor at next-to-leading order for different pion distribution amplitudes. Relying on the conformally covariant operator product expansion and using the known higher order results for polarized deep inelastic scattering, we are able to predict perturbative corrections to the hard-scattering amplitude of the photon-to-pion trans…
We present the results of a complete leading-twist next-to-leading order (NLO) QCD analysis of the spacelike pion electromagnetic form factor at large momentum transfer Q. We have studied their dependence on the form of the pion distribution amplitude. For a given distribution amplitude, we have examined the sensitivity of the predictions to the choice of the renormalization and factorization scales. Theoretical uncertainty of the LO results related to the renormalization scale ambiguity has been significantly reduced by including the NLO corrections. Adopting the criteria according to which a…
We have constructed a heavy baryon effective field theory with photon as an external field in accordance with the symmetry requirements similar to the heavy quark effective field theory. By treating the heavy baryon and anti-baryon equally on the same footing in the effective field theory, we have calculated the spin polarisabilities $γ_i, i=1...4$ of the nucleon at third order and at fourth-order of the spin-dependent Compton scattering. At leading order (LO), our results agree with the corresponding results of the heavy baryon chiral perturbation theory, at the next-to-leading order(NLO) the…
We search for deviations from next-to-leading order QCD evolution in HERA structure function data. We compare to data predictions for structure functions in the small x region, obtained by evolving backwards to low Q^2 the results of a parton fit performed in the large Q^2 region, where fixed-order perturbative QCD is certainly reliable. We find evidence for deviations which are qualitatively consistent with the behaviour predicted by small x perturbative resummation, and possibly also by nonlinear evolution effects, but incompatible with next-to-next-to leading order corrections.
The perturbatively-stable scheme of Next-to-Leading order (NLO) calculations of cross-sections for multi-scale hard-processes in DIS-like kinematics is developed in the framework of High-Energy Factorization. The evolution equation for unintegrated PDF, which resums $\log 1/z$-corrections to the coefficient function in the Leading Logarithmic approximation together with a certain subset of Next-to-Leading Logarithmic and Next-to-Leading Power corrections, necessary for the perturbative stability of the formalism, is formulated and solved in the Doubly-Logarithmic approximation. An example of D…
We review standard applications of perturbative QCD to baryon production, and argue by examining data that it is generally relevant at high but experimentally feasible momentum transfers. Then we consider some new initiatives, particularly meson photoproduction off baryons and the seeming quagmire of Delta(1232) electroproduction.
In this paper we compare the experimental HERA data with the next-to-leading order approach (NLO) of Ref.[C.~Contreras, E.~Levin, R.~Meneses and M.~Sanhueza,Eur. Phys. J. C 80 (2020) no.11, 1029). This approach includes the re-summed NLO corrections to the kernel of the evolution equation, the correct asymptotic behaviour in the NLO at $τ= r^2 Q^2_s \,\gg\,1$; the impact parameter dependence of the saturation scale in accord with the Froissarrt theorem as well as the non-linear corrections. In this paper, we successfully describe the experimental data with the quality, which is not worse, than…
In these proceedings we present results from a recent calculation for the production of a W boson in conjunction with five jets at next-to-leading order in perturbative QCD. We also use results at lower multiplicities to extrapolate the cross section to the same process with six jets.
Presently available perturbative QCD calculations combining hard process matrix element with the Parton Shower Monte Carlo programs feature hard process matrix element calculated often beyond the leading order (LO), that is including complete next-to-leading-order (NLO), or even next-to-next-to-leading-order (NNLO) corrections, while Parton Shower is only at the leading order (LO). We report here on a work in progress which demonstrate feasibility of constructing Parton Shower Monte Carlo (PSMC) featuring complete NLO corrections to QCD evolution with respect to the logarithm of the factorizat…
In this paper, we firstly varify that the factorization hypothesis is valid for the exclusive process $ργ^{\star} \to π$ at the next-to-leading order (NLO) with the collinear factorization approach, and then extend this proof to the case of the $k_T$ factorization approach. We particularly show that at the NLO level, the soft divergences in the full quark level calculation could be canceled completely as for the $πγ^{\star} \to π$ process where only the pseudoscalar $π$ meson involved, and the remaining collinear divergences can be absorbed into the NLO hadron wave functions. The full amplitud…
The aim of this thesis is to calculate field-theoretically as rigorously as possible the initial state of partonic matter produced in ultrarelativistic heavy-ion collisions at CERN-LHC and BNL-RHIC colliders. The computed minijet initial conditions are then used in the initialization of the relativistic hydrodynamical modeling of these collisions. In the theoretical introduction part the computation of parton production cross section at next-to-leading order (NLO) perturbative QCD (pQCD) is discussed. Furthermore, the full analytical calculation for the squared quark-quark scattering matrix el…
Seven next-to-leading order QCD evolution programs are compared. The deviations of the results due to different theoretical prescriptions for truncating the perturbative series are clarified, and a numerical agreement between five codes of better than 0.1% is achieved. Reference results for further comparison are provided.
We apply the perturbative chiral quark model at one loop to analyze the electromagnetic form factors of the baryon octet. The analytic expressions for baryon form factors, which are given in terms of fundamental parameters of low-energy pion-nucleon physics (weak pion decay constant, axial nucleon coupling, strong pion-nucleon form factor), and the numerical results for baryon magnetic moments, charge and magnetic radii are presented. Our results are in good agreement with experimental data.
It is well-known that the dominant mechanism to produce hadronic bound states with large transverse momentum is fragmentation. This mechanism is described by the fragmentation functions (FFs) which are the universal and process-independent functions. Here, we review the perturbative FFs formalism as an appropriate tool for studying these hadronization processes and detail the extension of this formalism at next-to-leading order (NLO). Using the Suzuki's model, we calculate the perturbative QCD FF for a heavy quark to fragment into a S-wave heavy meson at NLO. As an example, we study the LO and…
We compute the QCD corrections to the production of a top quark pair in association with one hard jet at the Tevatron and the LHC, using the method of generalized D-dimensional unitarity. Top quark decays are included at leading order in perturbative QCD. We present kinematic distributions of top quark decay products in lepton plus jets and dilepton final states at the Tevatron and the LHC, using realistic selection cuts. We confirm a strong reduction of the top quark forward-backward asymmetry for the process ttbar+jet at the Tevatron at next-to-leading order, first observed by Dittmaier, Uwe…
We present the results of a calculation of the perturbative QCD corrections for the semileptonic inclusive width of a heavy flavored meson. Within the Heavy Quark Expansion we analytically compute the QCD correction to the coefficient of power suppressed contribution of the chromo-magnetic operator in the limit of vanishing mass of the final state quark. The important phenomenological applications are decays of bottom mesons, and to the less extend, charmed mesons.
We evaluate in perturbative QCD the semi-inclusive Drell-Yan cross-section for the production of a single hadron accompaining the lepton pair. We demonstrate to one loop level a collinear factorization formula within the fracture functions approach. We propose such a process as a factorization analyzer in hadronic collisions. Phenomenological implications at the hadron colliders are briefly discussed.
We present new NLO sets of parton distributions in real photons based on a scheme invariant definition of the non-perturbative input. We compare the theoretical predictions with LEP data and a best fit allows us to constrain the parameters of the distributions. The shape of the gluon distribution is poorly constrained and we consider the possibility to measure it in photoproduction experiments. Three parametrizations which aim to take into account the scattering of LEP data are proposed. They are compared to other NLO parametrizations.
We analyze the perturbative and parametric stability of the QCD predictions for the Callan-Gross ratio $R(x,Q^2)=F_L/F_T$ in heavy-quark leptoproduction. We consider the radiative corrections to the dominant photon-gluon fusion mechanism. In various kinematic regions, the following contributions are investigated: exact NLO results at low and moderate $Q^2\lesssim m^2$, asymptotic NLO predictions at high $Q^2\gg m^2$, and both NLO and NNLO soft-gluon (or threshold) corrections at large Bjorken $x$. Our analysis shows that large radiative corrections to the structure functions $F_T(x,Q^2)$ and $…
Three-jet event-shape distributions can be exploited to investigate the dependence of hadronisation effects on the colour and the geometry of the underlying hard event. We present here the first comparison of data in e+e- annihilation and state-of-the-art theoretical predictions, including resummation of large logarithms at next-to-leading logarithmic accuracy matched to exact next-to-leading order and leading non-perturbative power corrections.
In these proceedings we discuss next-to-leading order (NLO) perturbative-QCD calculations of the cross section for the process $\ell N\to h X$. We briefly present the main features of the calculation and in particular analyze the role of quasi-real photons that enter the processes because the scattered lepton is not observed. We find that the NLO corrections are sizable for the spin-averaged cross section. In order to quantify this statement we present the K-factors of the cross sections for fixed target experiments HERMES, JLab12 and COMPASS.
We make predictions for the cross section of coherent $J/ψ$ photoproduction in Pb-Pb and O-O ultraperipheral collisions (UPCs) at the LHC as a function of the $J/ψ$ rapidity $y$ in the framework of collinear factorization and next-to-leading order (NLO) perturbative QCD. We quantify the strong scale dependence and significant uncertainties due to nuclear PDFs and show that our approach provides a reasonable description of the LHC data on coherent $J/ψ$ photoproduction in Pb-Pb UPCs. We demonstrate that these uncertainties are reduced by approximately a factor of 10 in the scaled ratio of the O…
In light of recent tension between theory and experiment for the process ttW in the 3l channel, we present a phenomenological study of carefully chosen observables. We employ the full off-shell results at NLO QCD for ttW+ and ttW- to build the cross section ratio, an observable which is expected to exhibit enhanced perturbative stability. Furthermore, we also revisit the charge asymmetries of the top and its decay products at the fiducial integrated level. The impact of modelling is investigated for all observables.
