Nuclear modification of hadron production in deep inelastic lepton-nucleus scattering can be applied to study the parton propagation mechanism in cold nuclear matter. By means of the analytic parameterization of quenching weight based on BDMPS formalism with the target nuclear geometry effect, the leading-order computations for hadron multiplicity ratios are performed with comparison to the HERMES charged pions production data on the quarks hadronization occurring outside the nucleus. The relation is discovered between quark transport coefficient and the measurable kinematic variables in deep inelastic scattering. Four models are proposed on the quark transport coefficient. The constant model, the power-law model and the double power-law model can be ruled out because of the experimental fact that the transverse momentum broadening increases as a function of the photon virtuality $Q^2$. The quark transport coefficient is determined as a function of the Bjorken variable $x$ and scale $Q^2$. The trend of quark transport coefficient in respect of Bjorken variable $x$ and scale $Q^2$ is qualitatively in partial agreement with HERMES experimental data on transverse momentum broadening. It is hoped that our effort is conducive to understanding of jet quenching phenomenon in relativistic heavy ion collisions.
We revisit high energy factorization for gluon mediated inclusive Deep Inelastic Scattering (DIS) for which we propose a new semi-classical approach that accounts systematically for the longitudinal extent of the target in contrast with the shockwave limit. In this framework, based on a partial twist expansion, we derive a factorization formula that involves a new gauge invariant unintegrated gluon distribution which depends explicitly on the Feynman $x$ variable. It is shown that both the Regge and Bjorken limits are recovered in this approach. We reproduce in particular the full one loop inc…
A detailed study of inclusive deep inelastic scattering from mirror A = 3 nuclei at large values of Bjorken-x is presented. The main purpose is to estimate the theoretical uncertainties on the extraction of F2n from such measurements. Within the convolution approach we confirm the cancellation of nuclear effects at the level of ~1 % for x < 0.75 in overall agreement with previous findings. However, within models in which modifications of the bound nucleon structure functions are accounted for to describe the EMC effect in nuclei, we find that the nuclear effects may be canceled at a level of ~…
It is proposed the modification of the Jacobi polynomial expansion method (MJEM) which is based on the application of the truncated moments instead of the full ones. This allows to reconstruct with a high precision the local quark helicity distributions even for the narrow accessible for measurement Bjorken $x$ region using as an input only four first moments extracted from the data in NLO QCD. It is also proposed the variational (extrapolation) procedure allowing to reconstruct the distributions outside the accessible Bjorken $x$ region using the distributions obtained with MJEM in the access…
We re-analyze data on deep inelastic polarized lepton-nucleon scattering, with particular attention to testing the Bjorken sum rule and estimating the quark contributions to the nucleon spin. Since only structure function data at fixed $Q^2$ can be used to test sum rules, we use E142 asymmetry measurements and unpolarized structure function data to extract $g_1^n$ at fixed $Q^2$ = 2 GeV$^2$. When higher-twist effects, which are important at low $Q^2$, are included, both the E142 and SMC data are compatible with the Bjorken sum rule within one standard deviation. Assuming validity of the Bjorke…
A detailed study of inclusive deep inelastic scattering (DIS) from mirror A = 3 nuclei at large values of the Bjorken variable x is presented. The main purpose is to estimate the theoretical uncertainties on the extraction of the neutron DIS structure function from such nuclear measurements. On one hand, within models in which no modification of the bound nucleon structure functions is taken into account, we have investigated the possible uncertainties arising from: i) charge symmetry breaking terms in the nucleon-nucleon interaction, ii) finite Q**2 effects neglected in the Bjorken limit, iii…
In this talk, we review the QCD calculation of the lepton spectrum from inclusive semileptonic $B$ decay. We compare this prediction to that of the ACCMM model. This latter work was done in collaboration with Csaba Csaki.
We study the heavy-quark contributions to the proton structure functions $F_2^i(x,Q^2)$ and $F_L^i(x,Q^2)$, with $i=c,b$, for small values of Bjorken's $x$ variable and provide compact formulas for their ratios $R_i=F_L^i/F_2^i$ that are useful to extract $F_2^i(x,Q^2)$ from measurements of the doubly differential cross section of inclusive deep-inelastic scattering at DESY HERA. Our approach naturally explains why $R_i$ is approximately independent of $x$ and the details of the parton distribution functions in the low-$x$ regime.
In this paper, the semileptonic decays of heavy mesons are treated fully relativistically. By means of an effective vertex, the effect of Fermi momentum are included both at the inclusive and at the exclusive levels, and the spin of both parent and daughter particles are taken into account. The differential decay rates with respect to the lepton energy and momentum transfer are compared with data from ARGUS and CLEO.
The detailed proof of cancellation of topologically unfactorized infrared divergences in the inclusive production of lepton pair close to the threshold of heavy quarkonia is presented. To make the effects of transition between states containing heavy quark pairs, which is important in such cancellation, the final detected states are constrained to be lepton pair near the threshold of the heavy quarkonia instead of heavy quarkonia themselves. Such cancellation is crucial for the NRQCD factorization of these processes.
We give a systematic way to compute higher orders in the 1/m_b expansion in inclusive semi-leptonic decays at tree level. We reproduce the known 1/m_b^3 terms and compute the 1/m_b^4 terms at tree level. The appearing non-perturbative parameters and the impact on the determination of V_{cb} are discussed.
Theoretical description of inclusive tau lepton hadronic decay is performed in the framework of Dispersive approach to QCD. The significance of effects due to hadronization is demonstrated. The approach on hand is capable of describing experimental data on tau lepton decay in vector and axial-vector channels. The vicinity of values of QCD scale parameter obtained in both channels testifies to the self-consistency of developed approach.
Perturbative corrections of the order of $α_s$ to inclusive double differential lepton distribution from $b$ quark decay are considered. A perturbative correction to the charged lepton energy spectrum has been calculated for an arbitrary charged lepton mass. The perturbative contribution suppresses the partial rate but almost does not change the shape of energy distribution. Applications of our result to semileptonic B meson decays are briefly discussed.
Starting from an Operator Product Expansion in the Heavy Quark Effective Theory up to order 1/m_b^2 we calculate the inclusive semileptonic decays of unpolarized bottom hadrons including lepton mass effects. We calculate the differential decay spectra dΓ/(dE_τ), and the total decay rate for B meson decays to final states containing a τlepton.
The contribution of lepton and photon pair production in ep-scattering to the cross section of semi-inclusive deep inelastic scattering ep-> e'p'X has been calculated. The numerical results showed a large contribution of this processes at $ϕ_h=180^o$, in a good agreement with preliminary experimental data.
We analize semi-inclusive electron-nucleus processes e+A->e'+h+X at moderate Q**2 and energy transfer nu. Our results show that nucleons bound in the nuclear medium are distributed according to a function f_A that reduces to the standard light-cone distribution in the Bjorken limit and exhibits a sizeable Q**2-dependence at lower Q**2, particular Q**2 is order of nu**2.
Nonperturbative corrections up to $m_b^{-2}$ to the heavy lepton energy distributions are investigated in the inclusive semileptonic weak decays of heavy flavors in QCD. In the case of $B$-meson decays, for $b \ra uτ\bnu$ transitions they decrease the decay rate by 6\% of its perturbative value, while for $b \ra cτ\bnu$ they decrease it by 10\%.
We present Standard Model predictions for lepton flavour universality ratios of inclusive $B\to X_{(c)} \ell \barν_\ell$. For the $\ell=μ,e$, these ratios are very close to unity as expected. For the $τ$ mode, we update the SM prediction for the branching ratio including power-corrections in the heavy-quark expansion up to $1/m_b^3$. These inclusive ratios serve as an important cross-check of the exclusive $B\to D^{(*)}\ell\barν_\ell$ modes, in which tensions exists between the predictions and measurements in those modes.
We calculate the single spin asymmetry in the inclusive pion production in proton-proton collisions. We generate the asymmetry at the level of fragmentation function (Collins effect) by the Lund coloured string mechanism. We compare our results with the Fermilab E704 data from polarized proton-proton collisions at 200 GeV. We show that the transversely polarized quark densities at high Bjorken x strongly differ from these predicted by the SU(6) proton wave function.
We extend previous computations of the second order QCD corrections to semileptonic b \to c inclusive transitions, to the case where the charged lepton in the final state is massive. This allows accurate description of b \to c τ\bar ν_τdecays. We review techniques used in the computation of O(α_s^2) corrections to inclusive semileptonic b \to c transitions and present extensive numerical studies of O(α_s^2) QCD corrections to b \to c l \bar ν_l decays, for l =e, τ.
We calculate the next-to-leading order QCD corrections to the `direct' part of the spin-dependent cross section for single-inclusive charged-hadron photoproduction. This process could be studied experimentally in future polarized fixed-target lepton-nucleon experiments, but also at the HERA ep collider after an upgrade to both beams being polarized. We present a brief numerical evaluation of our results by studying the K-factors and the scale dependence of the NLO cross section.
In the framework of the QCD parton model, we study unpolarized scattering of high energy real photons from a proton target into lepton pairs and a system of hadrons. For a given parametrization of parton distributions in the proton, we calculate the cross section of this process and show the cancellation of the interference terms.
The dispersive approach to QCD, which properly embodies the intrinsically nonperturbative constraints originating in the kinematic restrictions on relevant physical processes and extends the applicability range of perturbation theory towards the infrared domain, is briefly overviewed. The study of OPAL (update 2012) and ALEPH (update 2014) experimental data on inclusive tau lepton hadronic decay in vector and axial-vector channels within dispersive approach is presented.
We argue that there is strong experimental evidence in the data of b- and c-decays that the pattern of power suppressed corrections predicted by the short distance expansion, the heavy quark effective theory and the assumption of local duality is not correct for the non-leptonic inclusive widths. The data indicate instead the presence of 1/m corrections that should be absent in the above theoretical framework. These corrections can be simply described by replacing the heavy quark mass by the mass of the decaying hadron in the m^5 factor in front of all the non-leptonic widths.
The inclusion of heavy neutral leptons to the Standard Model particle content could provide solutions to many open questions in particle physics and cosmology. The modification of the charged and neutral currents from active-sterile mixing of neutral leptons can provide novel signatures in Standard Model processes. We revisit the displaced vertex signature that could occur in collisions at the LHC via the decay of heavy neutral leptons with masses of a few GeV emphasizing the implications of flavor, kinematics, inclusive production and number of these extra neutral fermions. We study in partic…
The dispersive approach to QCD is applied to the study of the inclusive tau lepton hadronic decay. This approach provides the unified integral representations for the hadronic vacuum polarization function, related R function, and Adler function. These representations account for the intrinsically nonperturbative constraints, which originate in the kinematic restrictions on the functions on hand, and retain the effects due to hadronization, which play a valuable role in the analysis of the strong interaction processes at low energies. The dispersive approach proves to be capable of describing r…
We derive a general framework for describing semi-inclusive deep-inelastic lepton-nucleon scattering in terms of the unintegrated parton distributions and other higher twist parton correlations. Such a framework provides a consistent approach to the calculation of inclusive and semi-inclusive cross sections including higher twist effects. As an example, we calculate the azimuthal asymmetries to the order of 1/Q in semi-inclusive process with transversely polarized target. A non-vanishing single-spin asymmetry in the ``triggered inclusive process'' is predicted to be 1/Q suppressed with a part …
We present all-order expressions for the leading double-logarithmic threshold contributions to the quark-gluon coefficient functions for inclusive Higgs-boson production in the heavy top-quark limit and for Drell-Yan lepton-pair production. These results have been derived using the structure of the unfactorized cross sections in dimensional regularization and the large-x resummation of the gluon-quark and quark-gluon splitting functions. The resummed coefficient functions, which are identical up to colour factor replacements, are similar to their counterparts in deep-inelastic scattering but s…
We apply the operator product expansion to resum the leading nonperturbative corrections to the endpoint region of the lepton spectrum in inclusive semileptonic $B\to X_q\,\ell\,\barν$ decays, taking into account a finite quark mass $m_q$ in the final state. We show that both for $b\to c$ and $b\to u$ transitions, it is consistent to describe these effects by a convolution of the parton model spectrum with a fundamental light-cone structure function. The moments of this function are proportional to forward matrix elements of higher-dimension operators. The prospects for an extraction of the st…
Bauer, Ligeti and Luke have recently proposed a new method for measuring |V_{ub}| in inclusive semileptonic B decays, using a cut on the lepton invariant mass to discriminate against b->c transitions. We investigate the structure of the heavy-quark expansion for this case and show that to all orders the magnitude of the leading perturbative and nonperturbative corrections is controlled by a hadronic scale mu_c=O(m_c) depending on the minimal value of q^2. These corrections can be analyzed using a modified version of the heavy-quark expansion (``hybrid expansion''). We find that the theoretical…
We propose a method for a QCD based calculation of one-particle inclusive decays of the form B \to \bar D X or B \to \bar D^* X. It is based on the heavy mass limit and a short distance expansion of the amplitudes, which yield a power series in the parameter 1/M^2_X for the spectra and in Λ_QCD m_b/(m_b - m_c)^2 for the rates. We study the leading term of this expansion for the case of the semi--leptonic decays B \to \bar D X l^+ ν.
Some estimates for the transverse single spin asymmetry, A_N, in the inclusive processes l p(transv. pol.) -> h X are compared with new experimental data. The calculations are based on the Sivers and Collins functions as extracted from SIDIS azimuthal asymmetries, within a transverse momentum dependent factorization approach. The values of A_N thus obtained agree in sign and shape with the data. Predictions for future experiments are also given.
We discuss hadron mass corrections and threshold resummation for deep-inelastic scattering $\ell N\rightarrow\ell' X$ and semi-inclusive annihilation $e^+e^-\rightarrow h X$ processes, and provide a prescription how to consistently combine these two corrections respecting all kinematic thresholds. We find an interesting interplay between threshold resummation and target mass corrections for deep-inelastic scattering at large values of Bjorken $x_B$. In semi-inclusive annihilation, on the contrary, the two considered corrections are relevant in different kinematic regions and do not affect each…
We employ OPE techniques within HQET to calculate the inclusive semileptonic decays of polarized $Λ_b$ baryons. Lepton mass effects are included which enables us to also discuss rates into polarized $τ$-leptons. We present explicit results for the longitudinal polarization of the $τ$ in the $Λ_b$ rest frame as well as in the $(τ^-, \bar ν_τ)$ c.m. frame. In both cases we make use of novel calculational techniques which considerably simplify the calculations. The transverse polarization components of the $τ$ are calculated in the $(τ^-,\barν_τ)$ c.m. frame. We delineate how to measure the full …
In connection with the semi-inclusive polarized DIS, it is proposed to consider the first Melin moments $Δq$ of the polarized quark and antiquark densities, instead of the respective variables $δq(x)$, local in Bjorken x themselves. This gives rise to a very essential simplification of the next to leading order (NLO) QCD and, besides, allows one to use the respective QCD sum rules. An expression for $Δ\bar{u}-Δ\bar{d}$ in NLO is obtained which is just a simple combination of the directly measured asymmetries and of the quantities taken from the unpolarized data.
We calculate the polarizations for different octet hyperons produced in the current fragmentation regions of the deeply inelastic lepton-nucleon scatterings $μ^-N \to μ^- HX$ and $ν_μ N \to μ^- HX$ at high energy using different models for spin transfer in fragmentation processes. The results show that measurements of those hyperon polarizations should provide useful information to distinguish between different models in particular the SU(6) and the DIS pictures used frequently in the literature. We found, in particular, that measuring the polarization of $Σ^+$ produced in these processes can …
We estimate the sensitivity of single lepton CP violation measurements with respect to that of traditional di-lepton measurements. We find that the sensitivity of the single lepton method is better than that of the di-lepton method. The achievable sensitivity with the currently available data is already in the range relevant to standard model predictions. We also give general expressions for inclusive decay time distributions on $Υ4S$ where the other $B$ is not measured, which will be used to obtain time dependent asymmetries. The expression is of general use whenever one deals with inclusive …
We present a QCD-based approach to the endpoint region of the lepton spectrum in $\bar B\to X_u\,\ell\,\barν$ decays. We introduce a genuinely nonperturbative form factor, the shape function, which describes the fall-off of the spectrum close to the endpoint. The moments of this function are related to forward scattering matrix elements of local, higher-dimension operators. We find that nonperturbative effects are dominant over a finite region in the lepton energy spectrum, the width of which is related to the kinetic energy of the $b$-quark inside the $B$ meson. Applications of our method to …
The one-particle inclusive cross section in deeply inelastic lepton--nucleon scattering, expressed in terms of parton densities and fragmentation functions being differential in the invariant mass of the observed hadron and of the incoming nucleon, diverges if this invariant mass vanishes. This divergence can be traced back to the kinematical configuration where the parent parton of the observed hadron is emitted collinearly from the incoming parton of the QCD subprocess. By using the concept of ``fracture functions'', which has recently been introduced by Trentadue and Veneziano, it is possib…
We derive the lepton spectrum in semileptonic beauty decays from a nonperturbative treatment of QCD; it is based on an expansion in $1/m_Q$ with $m_Q$ being the heavy flavour quark mass. The leading corrections arising on the $1/m_Q$ level are completely expressed in terms of the difference in the mass of the heavy hadron and the quark. Nontrivial effects appear in $1/m_Q^2$ terms affecting mainly the endpoint region; they are different for meson and baryon decays as well as for beauty and charm decays.
We establish the relationship between distribution and fragmentation functions and the structure functions appearing in the cross section of polarized 1-particle inclusive deep-inelastic scattering. We present spectator model evaluations of these structure functions focusing on the case of an outgoing spin-1/2 baryon. Distribution functions obtained in the spectator model are known to fairly agree at low energy scales with global parameterizations extracted, for instance, from totally inclusive DIS data. Therefore, we expect it to give good hints on the functional dependence of the structure f…
Compact analytic expressions have been obtained for the first order perturbative QCD corrections to the inclusive spectra of the leptons in the semileptonic decays of polarised heavy quarks. Charmed and beautiful $Λ$ baryons from $Z^0$ decays can be viewed as sources of highly polarised charm and bottom quarks. Charged leptons and neutrinos from $Λ_b$ and $Λ_c$ decays can be used in the polarisation studies for the corresponding heavy quarks. Thus our results are applicable for the b quark polarisation measurements at LEP. Short lifetime enables polarisation studies for the top quark. The angu…
We summarize a new analysis of the distribution $ϕ_η^{*}$ of charged leptons produced in decays of $Z$ and $γ^{*}$ bosons in the Collins-Soper-Sterman (CSS) formalism for transverse momentum resummation. By comparing the $ϕ_η^{*}$ distribution measured at the Tevatron with the resummed CSS cross section with approximate ${\cal O}(α_{s}^{2})$ Wilson coefficients, we constrain the magnitude of the nonperturbative Gaussian smearing factor and analyze its uncertainty caused by variations in scale parameters. We find excellent agreement between the $ϕ_η^{*}$ data and our theoretical prediction, pro…
We discuss the close relation between shadowing in deep-inelastic lepton-nucleus scattering and diffractive photo- and leptoproduction of hadrons from free nucleons. We show that the magnitude of nuclear shadowing at small Bjorken-x, as measured by the E665 and NMC collaborations, is directly related to HERA data on the amount of diffraction in the scattering from free nucleons.
The annihilation of the $B_c$ meson to leptons and inclusive light hadrons is analyzed in the framework of nonrelativistic QCD (NRQCD) factorization. We find that the decay mode, which escapes from the helicity suppression, contributes a sizable fraction width. According to the analysis, the branching ratio due to the contribution from the color-singlet component of the meson $B_c$ can be of order (10^{-2}). We also estimate the contributions from the color-octet components. With the velocity scaling rule of NRQCD, we find that the color-octet contributions are sizable too, especially, in cert…
Hadron production in lepton-nucleus deep inelastic scattering is studied in a quark energy loss model. The leading-order computations for hadron multiplicity ratios are presented and compared with the selected HERMES pions production data with the quark hadronization occurring outside the nucleus by means of the hadron formation time. It is found that the obtained energy loss per unit length is $0.440 \pm 0.013$ GeV/fm for an outgoing quark by the global fit. It is confirmed that the atomic mass number dependence of hadron attenuation is theoretically and experimentally in good agreement with …
Hadron production in lepton-nucleus deep inelastic scattering is studied in a model including quark energy loss and nuclear absorption. The leading-order computations for hadron multiplicity ratios are presented and compared with the selected HERMES experimental data with the quark hadronization occurring inside the nucleus by means of the hadron formation time. It is shown that with increase of the energy fraction carried by the hadron, the nuclear suppression on hadron multiplicity ratio from nuclear absorption gets bigger. It is found that when hadronization occurs inside the nucleus, the n…
The dispersive approach to QCD and its applications to inclusive tau lepton hadronic decay and hadronic vacuum polarization function are briefly discussed.
We present a complete next-to-leading order QCD calculation for single-inclusive large-pT hadron production in longitudinally polarized lepton-nucleon collisions, consistently including ``direct'' and ``resolved'' photon contributions. This process could be studied experimentally at a future polarized lepton-proton collider like eRHIC at BNL. We examine the sensitivity of such measurements to the so far completely unknown parton content of circularly polarized photons.
We evaluate the differential cross section for the electroproduction of lepton pairs off a polarized nucleon target in the generalized Bjorken region to leading power accuracy in hard momentum. We discuss the importance of this process for phenomenology of generalized parton distributions. A special attention is given to the sensitivity of physical observables, i.e., diverse asymmetries, to their dependence on scaling variables that allows to map directly the functional two-dimensional surface of generalized parton distributions.
We calculate shadowing in the process of deep inelastic interactions of leptons with nuclei in the perturbative regime of QCD. We find appreciable shadowing for heavy nuclei (e.g. Pb) in the region of small Bjorken scaling variable $10^{-5}\leq x \leq 10^{-3}$. This shadowing depends weakly on $Q^2$, but it may be strongly influenced, especially at $x \geq 10^{-3}$, by the existence of real parts of the forward scattering amplitudes.
We present an analysis of nonperturbative contributions to the transverse momentum distribution of $Z/γ^*$ bosons produced at hadron colliders. The new data on the angular distribution $ϕ^*_η$ of Drell-Yan pairs measured at the Tevatron is shown to be in excellent agreement with a perturbative QCD prediction based on the Collins-Soper-Sterman (CSS) resummation formalism at NNLL accuracy. Using these data, we determine the nonperturbative component of the CSS resummed cross section and estimate its dependence on arbitrary resummation scales and other factors. With the scale dependence included …
We construct a semi-inclusive Lepton Flavour Universality (LFU) ratio, $R_Σ$, to test $μ/e$ universality in $b\to s\ell^+\ell^-$ transitions at $e^+e^-$ $B$-meson factories. Combining different decay channels, this observable maximises the sensitivity to possible LFU violations of short distance origin, yet preserving a clean theoretical interpretation in case of a deviation from its Standard Model prediction, $R_Σ^{\rm SM}=1$.
Semi-inclusive deep inelastic scattering on nuclear targets is an ideal tool to study the energy loss effect of an outgoing quark in a nuclear medium. By means of the short hadron formation time, the experimental data with quark hadronization occurring outside the nucleus are picked out. A leading-order analysis is performed for the hadron multiplicity ratios as a function of the energy fraction on helium, neon, and copper nuclei relative to deuteron for the various identified hadrons. It is shown that the nuclear effects on parton distribution functions can be neglected. It is found that the …
We demonstrate that a measurement of the Bjorken process $e^+e^-, μ^+μ^-\to ZH$ in the threshold region can yield a precise determination of the Higgs boson mass. With an integrated luminosity of $100 fb^{-1}$, it is possible to measure the Higgs mass to within 60 MeV (100 MeV) for m_H=100 GeV (150 GeV).
We present predictions for the inclusive production of leptons ($e^{\pm},μ^{\pm}$) originating from charm and bottom-hadrons at the CERN LHC in the general-mass variable-flavor-number scheme at next-to-leading order. Detailed numerical results are compared to data of the CMS, ATLAS and ALICE collaborations.
