Lepton Invariant Mass Research Articles

Search for Z′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Z^\\prime $$\\end{document} radiating from the dark matter at the LHC

We discuss a collider probe of a dark sector model in which the dark matter is charged under a new, hidden U(1) gauge group. In particular, we look for the so-called Darkstrahlung process, in which the final states dark matter radiates a new Z′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Z^\\prime $$\\end{document} gauge boson and it manifests as dilepton resonances. This work emphasizes the potential of dilepton final states with missing transverse energy in probing the darkstrahlung process. We recast the ATLAS Run 2 search for dilepton resonances in association with missing energy in addition to the ATLAS and CMS searches for sleptons. We find that the recasted searches put strong constraints on the coupling between the dark matter and the Z′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Z^\\prime $$\\end{document}. Moreover, we evaluate refined search strategies for Z′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Z^\\prime $$\\end{document} production and propose an analysis employing constraints on the lepton invariant mass and higher missing energy cut related to the darkstrahlung process. Simulation outcomes indicate substantial enhancements, particularly by a factor of 6 in regions featuring lower Z′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Z^\\prime $$\\end{document} masses. Finally, we also discuss the case when the Z′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Z^\\prime $$\\end{document} has a long lifetime, resulting in displaced decay of the boson.

NNLO QCD corrections to the q2 spectrum of inclusive semileptonic B-meson decays

We calculate the next-to-next-to-leading order QCD corrections to the leptonic invariant mass (q2) spectrum of semileptonic b → c inclusive decays, taking into account the mass of the charm quark and the charged lepton in the final state. We obtain analytic results in terms of generalized polylogarithms and present numerical studies of the O\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{O} $$\\end{document}(αs2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\alpha}_s^2 $$\\end{document}) corrections to the q2 spectrum of b → cℓν¯ℓ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ c\\ell {\\overline{\ u}}_{\\ell } $$\\end{document} decays, for ℓ = e, μ and τ, in the kinetic scheme. Our computation can be used to incorporate the recent measurements of q2 moments by Belle and Belle II into global fits of inclusive semileptonic B-decays.

QCD corrections to the Darwin coefficient in inclusive semileptonic B→Xuℓν¯ℓ decays

In this paper, we compute αs corrections to the matching coefficients of the dimension-six operators in the heavy quark expansion of the inclusive semileptonic heavy hadron decay rate and leptonic invariant mass spectrum with a massless quark and both a massive or massless lepton in the final state, analytically. The obtained results can be applied to the inclusive semileptonic B→Xuℓν¯ℓ (ℓ=e, μ, τ) and D→Xℓν¯ℓ (ℓ=e, μ) decays. The main application of our results is the background subtraction of the B→Xuℓν¯ℓ decay in the measurement of the B→Xcℓν¯ℓ decay, which is important for the precise extraction of Vcb and R(D(*)). They also play a role in the computation of lifetimes of heavy hadrons. Published by the American Physical Society 2024

New physics contributions to moments of inclusive b → c semileptonic decays

Inclusive semileptonic B → {X}_cell {overline{nu}}_{ell } decays, where ℓ = μ, e, are by now standard candles in the determination of the CKM element |Vcb|. These determinations rely on the heavy-quark expansion and use moments of decay spectra to extract the non-perturbative parameters directly from data under the standard model assumption.At the same time, new physics could influence the moments of the inclusive decay. In this paper, we compute power-corrections and next-to-leading order corrections in the strong coupling constant using the full basis of dimension-six new physics operators for the inclusive B → {X}_cell overline{nu} decay. We provide predictions for lepton energy, hadronic and leptonic invariant mass moments, and perform a phenomenological study to show the possible impact of new physics. Our results could be used to perform a global fit including new physics contributions.

Impact of the electromagnetic field on Z0 leptonic invariant mass in ultrarelativistic heavy ion collisions

The extraordinary strong magnetic field generated in ultrarelativistic heavy ion collisions makes it possible to investigate many novel effects in the hot QCD matter, and a direct probe of it thus becomes an urgent task in the field. Here we report a new way to probe it, where the leptonic invariant mass distribution of Z0 boson will be modified in the presence of the magnetic field due to the Lorentz force on the lepton pairs from the decay of Z0 boson. It is found that the magnetic field can decrease the mean value of Z0 leptonic invariant mass and increase its width, and both shifts approximately depend on the integral of the magnetic field over its time duration quadratically.

NLO QCD corrections to inclusive semitauonic weak decays of heavy hadrons up to 1/mb3

This paper presents ${\ensuremath{\alpha}}_{s}$ corrections to the inclusive semitauonic $B\ensuremath{\rightarrow}{X}_{c}\ensuremath{\tau}{\overline{\ensuremath{\nu}}}_{\ensuremath{\tau}}$ decay width and leptonic invariant mass spectrum up to order $1/{m}_{b}^{3}$ in the heavy quark expansion. Analytical results with full dependence on the final-state quark and tau lepton masses are obtained. The results up to $1/{m}_{b}^{2}$ can be extrapolated to the $B\ensuremath{\rightarrow}{X}_{u}\ensuremath{\tau}{\overline{\ensuremath{\nu}}}_{\ensuremath{\tau}}$ decay by taking the limit of vanishing final-state quark mass.

A first glance to the kinematic moments of B → Xcℓν at third order

We study the impact of third-order QCD corrections for several kinematic moments of the inclusive semileptonic B decays, to first order in the 1/mb expansion. We consider the first four moments of the charged-lepton energy ER spectrum, the total leptonic invariant mass q2 and the hadronic invariant mass {M}_X^2 . No experimental cuts are applied. Our analytic results are obtained via an asymptotic expansion around the limit mb ~ mc. After converting the scheme for the bottom mass to the kinetic scheme we compare the size of higher QCD corrections to the contributions from 1/ {m}_b^2 and 1/ {m}_b^3 power corrections and to the relative uncertainties.

NLO QCD corrections to inclusive b→cℓν¯ decay spectra up to 1/mQ3

We present analytical results for higher order corrections to the decay spectra of inclusive semileptonic heavy hadron weak decays, using the heavy quark expansion (HQE). We compute analytically the spectrum of the leptonic invariant mass for $B\ensuremath{\rightarrow}{X}_{c}\ensuremath{\ell}\overline{\ensuremath{\nu}}$ up to and including terms of order $1/{m}_{Q}^{3}$ within the HQE at next-to-leading order in ${\ensuremath{\alpha}}_{s}$. The full dependence of the differential rate on the mass of the final-state quark is taken into account. We discuss the implications of our results for the precision determination of the Cabbibo-Kobayashi-Maskawa matrix element $|{V}_{cb}|$.

Modification of Z0 leptonic invariant mass in ultrarelativistic heavy ion collisions as a measure of the electromagnetic field

An extraordinary strong magnetic field, eB0≈1018 Gauss, is expected to be generated in non-central ultrarelativistic heavy ion collisions and it is envisaged to induce several effects on hot QCD matter including the possibility of local parity and local charge conjugation and parity symmetry violations. A direct signature of such e.m. fields and a first quantitative measurement of its strength and lifetime are still missing. We point out that both the mean value of leptonic invariant mass of Z0 boson, reconstructed by its decaying lepton pairs, and the relative width are modified in relativistic heavy ion collisions due to the presence of strong initial e.m. fields. We propose a measurement of the leptonic invariant mass of Z0 as a novel probe of the strength of the By. Both shifts could be up to about few hundred MeV and are found to depend on the integral of By over the time duration quadratically (approximate). Hence it provides a novel and clear probe of electromagnetic fields, which can be tested experimentally.

Master integrals for inclusive weak decays of heavy flavors at next-to-leading order

We present analytical results for master integrals emerging in the computation of differential rates for inclusive weak decays of heavy flavors at next-to-leading order (NLO) in QCD. As an immediate physical application, these master integrals allow for a calculation of the spectra of the leptonic invariant mass in inclusive semileptonic decays in the framework of the heavy quark expansion, including the NLO QCD corrections to power suppressed terms.

A closer look at observables from exclusive semileptonic B \u2192 (\u03c0, \u03c1)\u2113\u03bd\u2113 decays

This article analyses the available inputs in B → πℓνℓ and B → ρℓνℓ decays which include the measured values of differential rate in different q2-bins (lepton invariant mass spectrum), lattice, and the newly available inputs on the relevant form-factors from the light-cone sum rules (LCSR) approach. We define different fit scenarios, and in each of these scenarios, we predict a few observables in the standard model (SM). For example, R(M)=frac{mathcal{B}left(Bto M{ell}_i{nu}_{ell_i}right)}{mathcal{B}left(Bto M{ell}_j{nu}_{ell_j}right)},{R}_{ell_j}^{ell_i}(M)=frac{mathcal{B}left(Bto {ell}_i{nu}_{ell_i}right)}{mathcal{B}left(Bto M{ell}_j{nu}_{ell_j}right)} with M = π or ρ and ℓi,j = e, μ or τ. We also discuss the new physics (NP) sensitivities of all these observables and obtain bounds on a few NP Wilson coefficients in b → uτντ decays using the available data. We have noted that the data at present allows sizeable NP contributions in this mode. Also, we have predicted a few angular observables relevant to these decay modes.

Bd,s \u2192 gamma mathrm{ell}overline{mathrm{ell}} decay with an energetic photon

We calculate the differential branching fraction, lepton forward-backward asymmetry and direct CP asymmetry for Bd,s → gamma mathrm{ell}overline{mathrm{ell}} decays with an energetic photon. We employ factorization methods, which result in rigorous next-to-leading order predic- tions in the strong coupling at leading power in the large-energy/heavy-quark expansion, together with estimates of power corrections and a resonance parameterization of sub- leading power form factors in the region of small lepton invariant mass q2. The Bd,s → gamma mathrm{ell}overline{mathrm{ell}} decay shares features of the charged-current decay Bu → gamma mathrm{ell}{overline{nu}}_{mathrm{ell}} ., and the FCNC decays B → {K}^{left(ast right)}mathrm{ell}overline{mathrm{ell}} . As in the former, the leading-power decay rates can be expressed in terms of the B-meson light-cone distribution amplitude and short-distance factors. However, similar to B → {K}^{left(ast right)}mathrm{ell}overline{mathrm{ell}} , four-quark and dipole operators contribute to the Bd,s → gamma mathrm{ell}overline{mathrm{ell}} decay in an essential way, limiting the calculation to q2 ≲ 6 GeV2 below the charmonium resonances in the lepton invariant mass spectrum. A detailed analysis of the main observables and theoretical uncertainties is presented.

Vcb determination from inclusive b \u2192 c decays: an alternative method

The determination of Vcb relies on the Heavy-Quark Expansion and the extraction of the non-perturbative matrix elements from inclusive b → c decays. The proliferation of these matrix elements complicates their extraction at 1/mb4 and higher, thereby limiting the Vcb extraction. Reparametrization invariance links different operators in the Heavy-Quark expansion thus reducing the number of independent operators at 1/mb4 to eight for the total rate. We show that this reduction also holds for spectral moments as long as they are defined by reparametrization invariant weight-functions. This is valid in particular for the leptonic invariant mass spectrum (q2), i.e. the differential rate and its moments. Currently, Vcb is determined by fitting the energy and hadronic mass moments, which do not manifest this parameter reduction and depend on the full set of 13 matrix elements up to 1/mb4. In light of this, we propose an experimental analysis of the q2 moments to open the possibility of a model-independent Vcb extraction from semileptonic decays including the 1/mb4 terms in a fully data-driven way.

Leptoquark effects on and decay processes

We study the rare semileptonic decays of B mesons induced by as well as transitions in the scalar leptoquark (LQ) model, where the LQs have the representation (3, 2, 7/6) and (3, 2, 1/6) under the standard model gauge group. The LQ parameter space is constrained using the most recent experimental results on and processes. Considering only the baryon number conserving LQ interactions, we estimate the branching ratios for the exclusive and inclusive decay processes by using the constraint parameters. We also obtain the low recoil (large lepton invariant mass, i.e., ) predictions for the angular distribution of process and several other observables including the flat term and lepton flavour non-universality factor in this model.

Two-loop QCD corrections to semileptonicb-quark decays near maximum recoil

Two-gluon radiative corrections to the $b\ensuremath{\rightarrow}c\ensuremath{\ell}{\overline{\ensuremath{\nu}}}_{\ensuremath{\ell}}$ decay width have been computed analytically as an expansion in terms of $\frac{{m}_{c}}{{m}_{b}}\ensuremath{\ll}1$ in the kinematical limit of zero lepton invariant mass. The obtained results match smoothly with a previously known expansion around $(1\ensuremath{-}\frac{{m}_{c}}{{m}_{b}})\ensuremath{\ll}1$. Together they describe the process $b\ensuremath{\rightarrow}c\ensuremath{\ell}{\overline{\ensuremath{\nu}}}_{\ensuremath{\ell}}$ for all mass ratios $\frac{{m}_{c}}{{m}_{b}}$.

Determination of|Vub|from Measurements of the Inclusive Charmless Semileptonic Partial Rates ofBMesons using Full Reconstruction Tags

We present a measurement of the Cabibbo-Kobayashi-Maskawa matrix element /Vub/, based on 253 fb(-1) of data collected by the Belle detector at the KEKB e+ e- asymmetric collider. Events are tagged by fully reconstructing one of the B mesons, produced in pairs from Gamma(4S). The signal for b --> u semileptonic decay is distinguished from the b --> c background using the hadronic mass Mx, the leptonic invariant mass squared q2 and the variable P+ [triple bond] Ex - /px/. The results are obtained for events with p(l)* > or = 1 GeV/c, in three kinematic regions (1) Mx < 1.7 GeV/c2, (2) Mx < 1.7 GeV/c2 combined with q2 > 8 GeV2/c2, and by (3) P+ < 0.66 GeV/c. The matrix element /Vub/ is found to be (4.09 +/- 0.19 +/- 0.20(+0.14) -0.15 +/- 0.18) x 10(-3), where the errors are statistical, systematic including Monte Carlo modeling, theoretical, and from shape function parameter determination, respectively.

Theory of charmless inclusiveBdecays and the extraction ofVub

We present ``state-of-the-art'' theoretical expressions for the triple differential B->X_u l^- nu decay rate and for the B->X_s gamma photon spectrum, which incorporate all known contributions and smoothly interpolate between the ``shape-function region'' of large hadronic energy and small invariant mass, and the ``OPE region'' in which all hadronic kinematical variables scale with M_B. The differential rates are given in a form which has no explicit reference to the mass of the b quark, avoiding the associated uncertainties. Dependence on m_b enters indirectly through the properties of the leading shape function, which can be determined by fitting the B->X_s gamma photon spectrum. This eliminates the dominant theoretical uncertainties from predictions for B->X_u l^- nu decay distributions, allowing for a precise determination of |V_{ub}|. In the shape-function region, short-distance and long-distance contributions are factorized at next-to-leading order in renormalization-group improved perturbation theory. Higher-order power corrections include effects from subleading shape functions where they are known. When integrated over sufficiently large portions in phase space, our results reduce to standard OPE expressions up to yet unknown O(alpha_s^2) terms. Predictions are presented for partial B->X_u l^- nu decay rates with various experimental cuts. An elaborate error analysis is performed that contains all significant theoretical uncertainties, including weak annihilation effects. We suggest that the latter can be eliminated by imposing a cut on high lepton invariant mass.

Exclusive radiative and electroweak $b\to d$ and $b\to s$ penguin decays at NLO

We provide Standard Model expectations for the rare radiative decays B->K^* gamma, B->rho gamma and B-> omega gamma, and the electroweak penguin decays B->K^* l^+ l^- and B->rho l^+ l^- at the next-to-leading order (NLO), extending our previous results to b->d transitions. We consider branching fractions, isospin asymmetries and direct CP asymmetries. For the electroweak penguin decays, the lepton-invariant mass spectrum and forward-backward asymmetry is also included. Radiative and electroweak penguin transitions in b->d are mainly interesting in the search for new flavour-changing neutral current interactions, but in addition the B->rho gamma decays provide constraints on the CKM parameters (\bar\rho,\bar\eta). The potential impact of these constraints is discussed.

Exclusive rareB→K*ℓ+ℓ−decays at low recoil: Controlling the long-distance effects

We present a model-independent description of the exclusive rare decays $\overline{B}\ensuremath{\rightarrow}{K}^{*}{e}^{+}{e}^{\ensuremath{-}}$ in the low recoil region (large lepton invariant mass ${q}^{2}\ensuremath{\sim}{m}_{b}^{2}$). In this region the long-distance effects from quark loops can be computed with the help of an operator product expansion in $1/Q$, with $Q={{m}_{b},\sqrt{{q}^{2}}}$. Nonperturbative effects up to and including terms suppressed by $\ensuremath{\Lambda}/Q$ and ${m}_{c}^{2}/{m}_{b}^{2}$ relative to the short-distance amplitude can be included in a model-independent way. Based on these results, we propose an improved method for determining the Cabibbo-Kobayashi-Maskawa matrix element $|{V}_{ub}|$ from a combination of rare and semileptonic $B$ and $D$ decays near the zero recoil point. The residual theoretical uncertainty from long-distance effects in this $|{V}_{ub}|$ determination comes from terms in the operator product expansion of order ${\ensuremath{\alpha}}_{s}(Q)\ensuremath{\Lambda}/{m}_{b}$, ${\ensuremath{\alpha}}_{s}^{2}(Q)$, ${m}_{c}^{4}/{m}_{b}^{4}$, and duality violations, and is estimated to be below 10%.

Heavy-to-light-quark decays with two-loop accuracy.

We present a determination of a new class of three-loop Feynman diagrams describing heavy-to-light transitions. We apply it to find the O(alpha2(s)) corrections to the top quark decay t --> bW and to the distribution of lepton invariant mass in the semileptonic b quark decay b --> ulnu. We also confirm the previously determined total rate of that process as well as the O(alpha2) corrections to the muon lifetime.