We compute the O(α_s^2) corrections to the differential rate of the semileptonic decay b -> clv at the "intermediate recoil" point, where the c-quark mass and the invariant mass of the leptons are equal. The calculation is based on an expansion around two opposite limits of the quark masses m_{b,c}: m_c ~ m_b and m_c << m_b. The former case was previously studied; we correct and extend that result. The latter case is new. The smooth matching of both expansions provides a check of both. We clarify the discrepancy between the recent determinations of the full NNLO QCD correction to the semileptonic b -> c rate, and its earlier estimate.
We present complete O(alpha_s^2) corrections to the decay b-->c+l+nu at the point where the invariant mass of the leptons sqrt{q^2} equals the c quark mass. We use this result, together with previously obtained corrections at the ends of the q^2 spectrum, to estimate the total width of the semileptonic b-->c decay with O(alpha_s^2) accuracy, essential for the |V_{cb}| determination.
The Cabibbo-Kobayashi-Maskawa matrix element |V_ub| can be extracted from the rate for the semi-leptonic decay B -> pi + l + antineutrino_l, with little theoretical uncertainty, provided the hadronic form factor for the B -> pi transition can be measured from some other B decay. In here, we suggest using the decay B -> pi Jψ. This is a color suppressed decay, and it cannot be properly described within the usual factorization approximation; we use instead a simple and very general phenomenological model for the b d Jψvertex. In order to relate the hadronic form factors in the B -> pi Jψand B ->…
We consider the transverse-momentum ($q_T$) distribution of Drell-Yan lepton pairs produced, via $W$ and $Z/γ^*$ decay, in hadronic collisions. At small values of $q_T$, we resum the logarithmically-enhanced perturbative QCD contributions up to next-to-next-to-leading logarithmic accuracy. Resummed results are consistently combined with the known ${\mathcal O}(α_S^2)$ fixed-order results at intermediate and large values of $q_T$. Our calculation includes the leptonic decay of the vector boson with the corresponding spin correlations, the finite-width effects and the full dependence on the fina…
The model--independent QED radiative corrections to polarization observables in elastic scattering of unpolarized and longitudinally--polarized electron beam by the deuteron target have been calculated in leptonic variables. The experimental setup when the deuteron target is arbitrarily polarized is considered and the procedure for applying derived results to the vector or tensor polarization of the recoil deuteron is discussed. The basis of the calculations consists of the account for all essential Feynman diagrams which results in the form of the Drell-Yan representation for the cross-sectio…
We examine the applicability of perturbative QCD to $B$ meson decays into $D$ mesons. We find that the perturbative QCD formalism, which includes Sudakov effects at intermediate energy scales, is applicable to the semi-leptonic decay $B\to D lν$, when the $D$ meson recoils fast. Following this conclusion, we analyze the two-body non-leptonic decays $B\to Dπ$ and $B\to DD_s$. By comparing our predictions with experimental data, we extract the matrix element $|V_{cb}|=0.044$.
TeV Higgsino Interpretation of the LZ High-Recoil Event with Intermediate-Scale Electroweak Gauginos
Institute of Physics, Henan Academy of Sciences（中国科学院河南分院物理研究所）；Centre for Theoretical Physics, Henan Normal University（河南师范大学理论物理中心）；School of Physics, Zhengzhou University（郑州大学物理学院）
Leptonic flavor-changing $H^0$ decays with branching ratios of the order of $10^{-5}-10^{-6}$ may constitute an interesting framework when looking for large $CP$-violating effects. We show that leptonic $CP$~asymmetries of an intermediate $H^0$ boson can be fairly large in natural scenarios of the minimal Standard Model ($SM$) with right-handed neutrinos, at a level that may be probed at future $H^0$~factories.
The analysis of hyperon semi-leptonic decay data is re-examined in the light of a recent suggestion that SU(3) symmetry breaking effects may be taken into account by applying a correction to the $F/D$ ratio obtained via naive linear extrapolation in the hyperon masses. Comparison is made with the physically better motivated approach of applying so-called centre-of-mass corrections. This study (including all available data) reveals certain short-comings of the former of the above treatments, highlights some interesting aspects of this type of analysis and attempts to pinpoint the decay data tha…
We propose a novel type of interpolating field operators, which manifests the hybrid-like configuration that the charm quark-antiquark pair recoils against gluonic degrees of freedom. A heavy vector charmonium-like state with a mass of $4.33(2)\,{\rm GeV}$ is disentangled from the conventional charmonium states in the quenched approximation. This state has affinity for the hybrid-like operators but couples less to the relevant quark bilinear operator. We also try to extract its leptonic decay constant and give a tentative upper limit that it is less than one tenth of that of $J/ψ$, which corre…
Perturbative corrections to b->c transitions at zero recoil are considered in the two-step matching scheme. The matching coefficient for the b->c currents from the intermediate effective theory (between the scales m_b and m_c) to the low-energy effective theory (scales below m_c) has been found with two-loop accuracy. The next-to-next-to-leading logarithms has been summed in the leading order in m_c/m_b. Higher-order corrections are estimated in the large-beta_0 limit.
We study the gluon fusion into pairs of off-shell Z bosons and their subsequent decay into charged lepton pairs at hadron colliders. We do not restrict the intermediate state Z bosons to the narrow width approximation but allow for arbitrary invariant masses. We compare the strength of this process with the known leading order results for q q_bar -> Z Z -> 4 l and for g g -> H -> Z Z -> 4 l .
We propose a method to non-perturbatively calculate the forward-scattering matrix elements relevant to inclusive semi-leptonic B meson decays. Corresponding hadronic structure functions at unphysical kinematics are accessible through lattice QCD calculation of four-point correlation functions. The unphysical kinematical point may be reached by analytic continuation from the physical differential decay rate. A numerical test is performed for the B_s -> X_c l nu mode in the zero-recoil limit. We use lattice ensembles generated with 2+1 dynamical quark flavors. The valence charm quark mass is tun…
We compute the O(alpha_s) QCD corrections to charged triple vector boson production at a hadron collider, i.e. the processes pp -> ZZW + X and pp -> WWW + X. Intermediate Higgs boson exchange effects, spin correlations from leptonic vector boson decays, and off-shell contributions are all taken into account. Results are implemented in a fully flexible Monte Carlo program that allows for an easy customization of kinematical cuts and variation of the factorization and renormalization scales. We analyze the dependence of the differential cross sections under scale variations and present distribut…
In this work we use the heavy-quark-light-diquark picture to study the semileptonic decay $Λ_b \to Λ_c+l+\barν_l$ in the so-called hybrid scheme. Namely, we apply the heavy quark effective theory (HQET) for larger $q^2$ (corresponding to small recoil), which is the invariant mass square of $l+\barν$, whereas the perturbative QCD approach for smaller $q^2$ to calculate the form factors. The turning point where we require the form factors derived in the two approaches to be connected, is chosen near $ρ_{cut}=1.1$. It is noted that the kinematic parameter $ρ$ which is usually adopted in the pertu…
Two important sources of systematic errors in lattice QCD calculations of radiative leptonic decays are unwanted exponentials in the sum over intermediate states and unwanted excited states created by the meson interpolating field. Performing the calculation using a 3d sequential propagator allows for better control over the systematic uncertainties from intermediate states, while using a 4d sequential propagator allows for better control over the systematic uncertainties from excited states. We calculate form factors using both methods and compare how reliably each controls these systematic e…
The radiative and leptonic decays of $η_c\to γγ$ and $η_c\to l^+l^-$ are studied. For $η_c\to γγ$ decay, the second-order electromagnetic tree-level diagram gives the leading contribution. The decay rate of $η_c\to γγ$ is calculated, the prediction is in good agreement with the experimental data. For $η_c\to l^+ł^-$, both the tree and loop diagrams are calculated. The analysis shows that the loop contribution dominates, the contribution of tree diagram with $Z^0$ intermediate state can only modifies the decay rate by less than 1%. The prediction of the branching ratios of $η_c\to e^+e^-$ and $…
Using dispersion relations, we derive the complete virtual QED contributions to Bhabha scattering due to vacuum polarization effects in photon propagation. We apply our result to hadronic corrections and to heavy lepton and top quark loop insertions. We give the first complete estimate of their net numerical effects for both small and large angle scattering at typical beam energies of meson factories, LEP, and the ILC. The effects turn out to be smaller, in most cases, than those corresponding to electron loop insertions, but stay, with amounts of typically one per mille, of relevance for prec…
We compute the chiral corrections to octet baryon axial currents through ${\cal O}(p^3)$ in heavy baryon chiral perturbation theory, including both octet and decuplet baryon intermediate states. We include the latter in a consistent way by using the small scale expansion. We find that, in contrast to the situation at ${\cal O}(p^2)$, there exist no cancellations between octet and decuplet contributions at ${\cal O}(p^3)$. Consequently, the ${\cal O}(p^3)$ corrections spoil the expected scaling behavior of the chiral expansion. We discuss this result in terms of the $1/N_c$ expansion. We also c…
The extension of Majorana neutrino mass mechanism of the neutrinoless double-beta decay ($0νββ$) with the inclusion of right-handed leptonic and hadronic currents is revisited. While only the exchange of light neutrinos is assumed, the $s_{1/2}$ and $p_{1/2}$-states of emitted electrons as well as recoil corrections to the nucleon currents are taken into account. Within the standard approximations the decay rate is factorized into a sum of products of kinematical phase-space factors, nuclear matrix elements and the fundamental parameters that characterize the lepton number violation. Unlike in…
In this work we examine the possible existence of new physics beyond the standard model which could modify the branching fractions of the leptonic (mainly tauonic) decays of bottomonium vector resonances below the $B\bar{B}$ threshold. The decay width is factorized as the product of two pieces: a) the probability of an intermediate pseudoscalar color-singlet $b\bar{b}$ state (coupling to the dominant Fock state of the Upsilon via a magnetic dipole transition) and a soft (undetected) photon; b) the annihilation width of the $b\bar{b}$ pair into two leptons, mediated by a non-standard CP-odd Hig…
The recent discovery of the B_c meson by the CDF collaboration and proposed new experiments at Fermilab and CERN motivate new theoretical studies of the B_c system. Here we investigate the radiative leptonic decay B_c -> gamma l nu. This process is an important background to the annihilation process B_c -> l nu, which will be used to extract the B_c decay constant. We perform a model-independent calculation, based on QCD, of the partial width and various kinematic distributions. We also examine the decay within the framework of NRQCD, an effective field theory of nonrelativistic quarks, genera…
Neutron stars harbour matter under extreme conditions, providing a unique testing ground for fundamental interactions. We recently developed an improved treatment of dark matter (DM) capture in neutron stars that properly incorporates many of the important physical effects, and outlined useful analytic approximations that are valid when the scattering amplitude is independent of the centre of mass energy. We now extend that analysis to all interaction types. We also discuss the effect of going beyond the zero-temperature approximation, which provides a boost to the capture rate of low mass dar…
We treat 0+ -> 2+ neutrinoless double beta decays taking into account recoil corrections to the nuclear currents. The decay probability can be written as a quadratic form of the effective coupling constants of the right-handed leptonic currents and the effective neutrino mass. We calculate the nuclear matrix elements for the 0+ -> 2+ neutrinoless double beta decays of 76Ge and 100Mo, and demonstrate that the relative sensitivities of 0+ -> 2+ decays to the neutrino mass and the right-handed currents are comparable to those of 0+ -> 0+ decays.
The available data on $|ΔB| = |ΔS| = 1$ decays are in good agreement with the Standard Model when permitting subleading power corrections of about 15% at large hadronic recoil. Constraining new-physics effects in $\mathcal{C}_7$, $\mathcal{C}_9$, $\mathcal{C}_{10}$, the data still demand the same size of power corrections as in the Standard Model. In the presence of chirality-flipped operators, all but one of the power corrections reduce substantially. The Bayes factors are in favor of the Standard Model. Using new lattice inputs for $B\to K^*$ form factors, the evidence of models with chirali…
We consider electron-deuteron deep-inelastic scattering (DIS) with detection of a proton in the nuclear fragmentation region ("spectator tagging") as a method for extracting the free neutron structure functions and studying their nuclear modifications. Such measurements could be performed at a future Electron-Ion Collider (EIC) with suitable forward detectors. The measured proton recoil momentum (~< 100 MeV in the deuteron rest frame) specifies the deuteron configuration during the high-energy process and permits a controlled theoretical treatment of nuclear effects. Nuclear and nucleonic stru…
We calculate the amplitude of the rare flavour-changing neutral-current decay $B\to π\ell^+\ell^-$ at large recoil of the pion. The nonlocal contributions in which the weak effective operators are combined with the electromagnetic lepton-pair emission are systematically taken into account. These amplitudes are calculated at off-shell values of the lepton-pair mass squared, $q^2<0$, employing the operator-product expansion, QCD factorization and light-cone sum rules. The results are fitted to hadronic dispersion relations in $q^2$, including the intermediate vector meson contributions. The disp…
A general formalism for calculating the bulk viscosity of strange quark matter is developed. Contrary to the common belief that the non-leptonic processes alone give the dominant contribution to the bulk viscosity, the inclusion of the Urca processes is shown to play an important role at intermediate densities when the characteristic r-mode oscillation frequencies are not too high. The interplay of non-leptonic and Urca processes is analyzed in detail
We have addressed the study of non-leptonic weak decays of heavy hadrons ($Λ_b, Λ_c, B$ and $D$), with external and internal emission to give two final hadrons, taking into account the spin-angular momentum structure of the mesons and baryons produced. A detailed angular momentum formulation is developed which leads to easy final formulas. By means of them we have made predictions for a large amount of reactions, up to a global factor, common to many of them, that we take from some particular data. Comparing the theoretical predictions with the experimental data, the agreement found is quite g…
We review recent progress in techniques for searching for the Standard Model light `Intermediate Mass' Higgs Boson ($80 \GeV \lsim M_H \lsim 140\GeV$). We pay particular attention to associated production at the SSC and LHC where we search for the Higgs produced in association with either a $W$ boson or a $t$ quark. This production mode can be detected cleanly when the Higgs decays into two isolated photons, and the associated heavy particle decays semi-leptonically. We discuss the possibility that radiative corrections may significantly enhance the $W γγ$ background, decreasing the significan…
In Carrasco et al. we have recently proposed a method to calculate $O(e^2)$ electromagnetic corrections to leptonic decay widths of pseudoscalar mesons. The method is based on the observation that the infrared divergent contributions (that appear at intermediate stages of the calculation and that cancel in physical quantities thanks to the Bloch-Nordsieck mechanism) are universal, i.e. depend on the charge and the mass of the meson but not on its internal structure. In this talk we perform a detailed analysis of the finite-volume effects associated with our method. In particular we show that a…
The next-to-leading-order electroweak corrections to $pp\to l^+l^-/\barνν+γ+X$ production, including all off-shell effects of intermediate Z bosons in the complex-mass scheme, are calculated for LHC energies, revealing the typically expected large corrections of tens of percent in the TeV range. Contributions from quark-photon and photon-photon initial states are taken into account as well, but their impact is found to be moderate or small. Moreover, the known next-to-leading-order QCD corrections are reproduced. In order to separate hard photons from jets, both a quark-to-photon fragmentation…
In this paper, we make a detailed discussion on the $η$ and $η'$-meson leading-twist light-cone distribution amplitude $ϕ_{2;η^{(\prime)}}(u,μ)$ by using QCD sum rules approach under the background field theory. Taking both the non-perturbative condensates up to dimension-six and NLO QCD corrections to the perturbative part, its first three moments $\langleξ^n_{2;η^{(\prime)}}\rangle|_{μ_0} $ with $n = (2,4,6)$ at initial scale $μ_0 = 1$ GeV can be determined. e.g. $\langleξ_{2;η}^2\rangle|_{μ_0} =0.231_{-0.013}^{+0.010}$, $\langleξ_{2;η}^4 \rangle|_{μ_0} =0.109_{-0.007}^{+0.007}$, and $\langl…
The study on the charmed scalar meson spectroscopy has become a hot topic both experimentally and theoretically. The $B_{(s)}$ decays provide an ideal place to study their property. We employ the $B$-meson light-cone sum rules to compute the $\bar B_s^0\to D_s^{*+}(2317)$ and $B^-\to D_0^{*0}(2400)$ transition form factors at large recoil, assuming $D_s^{*+}(2317)$ and $D_0^{*0}(2400)$ being scalar quark-anti-quark states. The results are extrapolated to the whole momentum region with the help of HQET. Considering large uncertainties, our results can be consistent with the previous studies, wh…
We present details of a calculation of the cross section for hadronic top-antitop production in next-to-leading order (NLO) QCD, including the decays of the top and antitop into bottom quarks and leptons. This calculation is based on matrix elements for νe e+ μ- \barν_μb\bar{b} production and includes all non-resonant diagrams, interferences, and off-shell effects of the top quarks. Such contributions are formally suppressed by the top-quark width and turn out to be small in the inclusive cross section. However, they can be strongly enhanced in exclusive observables that play an important role…
The detection of an intermediate mass charged Higgs boson at $\gamgam$ colliders via the modes $\gamgam \to H^+ H^- \to ντ^+ \barν τ^-,~ c \bar{s} \bar{c} s,~$ and $ ντ^+ \bar{c}s + c \bar{s} \barν τ^-$ is considered. $W^+ W^-$ boson pair production is the dominant background for these modes. The three modes may be used in a complementary fashion to detect a charged Higgs boson. The mixed leptonic-hadronic mode may be used to determine the charged Higgs mass by reconstructing the invariant hadronic mass. The sensitivity of Br$(H^+ \rightarrow c\bar s,\,ντ^+)$ on the discovery limit of the char…
In these lectures, I present several important applications of QCD sum rules to the decay processes involving heavy-flavour hadrons. The first lecture is introductory. As a study case, the sum rules for decay constants of the heavy-light mesons are considered. They are relevant for the leptonic decays of $B$-mesons. In the second lecture I describe the method of QCD light-cone sum rules used to calculate the heavy-to-light form factors at large hadronic recoil, such as the $B\to π\ell ν_\ell$ form factors. In the third lecture, the nonlocal hadronic amplitudes in the flavour-changing neutral c…
The production of the \sm\ Higgs $ϕ$ with intermediate mass at the proposed CERN LEP$\otimes$LHC $ep$ collider in $γq(\bar q)\rightarrow W^\pmϕq'(\bar q')$, $γq(\bar q)\rightarrow Z^0ϕq(\bar q)$ and $gγ\rightarrow q\bar qϕ$ events is studied. This is done for all possible (massive) flavours of the quarks $q(q')$ and using photons generated via Compton back--scattering of laser light. We study signatures in which the Higgs decays to $b\bar b$--pairs and the electroweak vector bosons $W^\pm$ and $Z^0$ decay either hadronically or leptonically. All possible backgrounds to these signals are also c…
We reconsider observables for discovering a heavy Higgs boson (with m_h > 2m_W) via its di-leptonic decays h -> WW -> l nu l nu. We show that observables generalizing the transverse mass that take into account the fact that both of the intermediate W bosons are likely to be on-shell give a significant improvement over the variables used in existing searches. We also comment on the application of these observables to other decays which proceed via narrow-width intermediates.
We study the feasibility and advantages of investigating the $c\to s$ decay channel of the $B_c$ meson through the cascade decay $B_c\to B_sπ$, $B_s\to D_s\ellν$. We take into account possible contaminations coming from the vector excitations (like $B_s^*$, $D_s^*$ or $ρ$ in the intermediate stages of the cascade) too, as well as the opposite cascade $B_c\to B_s\ellν$, $B_s\to D_sπ$. We show how the $p_T$ distribution of the pion and the lepton can possibly help to differentiate between various form factor models, for which we either need more integrated luminosity at the LHC, or a high-lumino…
We evaluate the non leptonic decays $B \to D^* ππ$ and $B \to D^* ρπ$ in the limit of infinitely heavy quarks, assuming the dominance of intermediate positive parity charmed resonances. We find that the branching ratios are of the order $10^(-3)$.
The vanishing of the Higgs quartic coupling at a high energy scale may be explained by Intermediate Scale Supersymmetry, where supersymmetry breaks at $(10^9$-$10^{12})$ GeV. The possible range of supersymmetry breaking scales can be narrowed down by precise measurements of the top quark mass and the strong coupling constant. On the other hand, nuclear recoil experiments can probe Higgsino or sneutrino dark matter up to a mass of $10^{12}$ GeV. We derive the correlation between the dark matter mass and precision measurements of standard model parameters, including supersymmetric threshold corr…
Light-cone sum rules analysis of the semi-leptonic $D^+_s\to f_0(980)(\toπ^+π^-)e^+ν_e$ decay incorporating $f_0(980)$ mixing state twist-2 distribution amplitudes
We reconsider the complete set of four-quark operators in the Weak Effective Theory (WET) for non-leptonic $ΔF=1$ decays that govern $s\to d$ and $b\to d, s$ transitions in the Standard Model (SM) and beyond, at the Next-to-Leading Order (NLO) in QCD. We discuss cases with different numbers $N_f$ of active flavours, intermediate threshold corrections, as well as the issue of transformations between operator bases beyond leading order to facilitate the matching to high-energy completions or the Standard Model Effective Field Theory (SMEFT) at the electroweak scale. As a first step towards a SME…
A future e+e- collider, such as the ILC or CLIC, would allow the Higgs sector to be probed with a precision significantly beyond that achievable at the High-Luminosity LHC. A central part of the Higgs programme at an e+e- collider is the model-independent determination of the absolute Higgs couplings to fermions and to gauge bosons. Here the measurement of the e+e-->HZ Higgsstrahlung cross section, using the recoil mass technique, sets the absolute scale for all Higgs coupling measurements. Previous studies have considered e+e- ->ZH with Z->l+l-, where l = electron or muon. In this paper it is…
We present results for different observables in weak decays of pseudoscalar and vector mesons with a heavy $c$ or $b$ quark. The calculations are done in a nonrelativistic constituent quark model improved at some instances by heavy quark effective theory constraints. We determine pseudoscalar and vector meson decay constants that within a few per cent satisfy $f_V M_V/f_P M_P=1$, a result expected in heavy quark symmetry when the heavy quark masses tend to infinity. We also analyze the semileptonic $B\to D$ and $B\to D^*$ decays for which we evaluate the different form factors. Here we impose …
We study the cross sections for the production of intermediate mass Higgs bosons via the reactions $e^-γ\rightarrow ν_eW^-Φ^0$, $e^-γ\rightarrow ν_eH^-Φ^0$, $e^-γ\rightarrow e^-Z^0Φ^0$ and $e^-γ\rightarrow e^-H^+H^-$ in the Minimal Supersymmetric Standard Model (with $Φ^0=H^0,h^0$ and, where possible, $A^0$) at TeV energies, taking into account $b$--tagging capabilities. We find that the rates for $e^-γ\rightarrow ν_eW^-Φ^0$ are large enough to permit the discovery of at least one between $h^0$ and $H^0$ over the whole intermediate mass range of $M_{A^0}$, at all $\tanβ$, using the $(jj)(b\bar…
We study lepton number violating and lepton number conserving semi-leptonic decays of heavy baryons $Λ_b^0$ to three charged leptons and a neutrino. The decays occur through two intermediate quasi-degenerate GeV-scale sterile neutrinos of either Majorana or Dirac type that can be on-shell. Interference between the intermediate heavy neutrinos leads to CP violation in the final states. Effect of neutrino oscillations between the heavy states are also considered in observables of interests, \emph{i.e.,} branching ratio, and the CP-asymmetry. Given the present constraints on the heavy-to-light mi…
We study the impact of the multi-lepton searches at the LHC on supersymmetric models with compressed mass spectra. For such models the acceptances of the usual search strategies are significantly reduced due to requirement of large effective mass and missing E_T. On the other hand, lepton searches do have much lower thresholds for missing E_T and p_T of the final state objects. Therefore, if a model with a compressed mass spectrum allows for multi-lepton final states, one could derive constraints using multi-lepton searches. For a class of simplified models we study the exclusion limits using …
We calculate the rates and lepton (l) invariant mass distributions for decays of the form 0^{-+}->l^+l^-γ, which are important radiative corrections to the purely leptonic decays 0^{-+}->l^+l^-. Our approach uses the loop diagrams which arise by including the two photon intermediate state and we retain the imaginary parts of the loops - a radiative extension of the `unitarity bound' for the process. These results are compared which those obtained using a model in which the meson couples directly to the leptons.
We analyze the reach of Linear Colliders (LC)s for models of dynamical electroweak symmetry breaking. We show that LCs can efficiently test the compositeness scale, identified with the mass of the new spin-one resonances, till the maximum energy in the center-of-mass of the colliding leptons. In particular we analyze the Drell-Yan processes involving spin-one intermediate heavy bosons decaying either leptonically or into two Standard Model (SM) gauge bosons. We also analyze the light Higgs production in association with a SM gauge boson stemming also from an intermediate spin-one heavy vector.
We study the purely leptonic decays of $W^\pm \to e^\pm e^\pm μ^\mp ν$ and $μ^\pm μ^\pm e^\mp ν$ produced at the LHC, induced by sterile neutrinos with mass $m_N$ below $M_W$ in the intermediate state. Since the final state neutrino escapes detection, one cannot tell whether this process violates lepton number, what would indicate a Majorana character for the intermediate sterile neutrino. Our study shows that when the sterile neutrino mixings with electrons and muons are different enough, one can still discriminate between the Dirac and Majorana character of this intermediate neutrino by simp…
Results for next-to-leading order QCD corrections to the pp(p\bar{p}) -> t \bar{t} -> W^+W^- b\bar{b} -> e^{+} ν_{e} μ^{-} \barν_μ b \bar{b} +X processes with complete off-shell effects are presented for the first time. Double-, single- and non-resonant top contributions of the order {\cal{O}}(α_{s}^3 α^4) are consistently taken into account, which requires the introduction of a complex-mass scheme for unstable top quarks. Moreover, the intermediate W bosons are treated off-shell. Comparison to the narrow width approximation for top quarks, where non-factorizable corrections are not accounted …
We consider Drell-Yan production $pp\to V^* X \to L X$ at small $q_T \ll Q$. Experimental measurements require fiducial cuts on the leptonic state $L$, which introduce enhanced, linear power corrections in $q_T/Q$. We show that they can be unambiguously predicted from factorization, and resummed to the same order as the leading-power contribution. We thus obtain predictions for the fiducial $q_T$ spectrum to N3LL and next-to-leading-power in $q_T/Q$. Matching to full NNLO ($α_s^2$), we find that the linear power corrections are indeed the dominant ones, and the remaining fixed-order correction…
In this paper, for the first time a method is proposed to compute electromagnetic effects in hadronic processes using lattice simulations. The method can be applied, for example, to the leptonic and semileptonic decays of light or heavy pseudoscalar mesons. For these quantities the presence of infrared divergences in intermediate stages of the calculation makes the procedure much more complicated than is the case for the hadronic spectrum, for which calculations already exist. In order to compute the physical widths, diagrams with virtual photons must be combined with those corresponding to th…
We reconsider observables for discovering and measuring the mass of a Higgs boson via its di-leptonic decays: H --> WW* --> l nu l nu. We define an observable generalizing the transverse mass that takes into account the fact that one of the intermediate W-bosons is likely to be on-shell. We compare this new variable with existing ones and argue that it gives a significant improvement for discovery in the region m_h < 2 m_W.
