Hadronic Width Research Articles

Minimal supersymmetry confronts Rb, and mh

We study the impact of the measurements of three sets of observables on the parameter space of the constrained minimal supersymmetric standard model (cMSSM), its slightly general variant, the non-universal scalar model (NUSM), and some selected benchmark points of the 19-parameter phenomenological MSSM (pMSSM): (i) the direct measurement of the Higgs boson mass mh ≈ 125 GeV at the CERN Large Hadron Collider (LHC); (ii) Z-boson decay width in the channel normalized to its hadronic width (Rb), and the forward–backward asymmetry on the Z-peak in the same channel ; and (iii) several B-physics observables, along with (g − 2) of muon. In addition, there are constraints from non-observation of superparticles from direct searches at the LHC. In view of the recently re-estimated standard model (SM) value of Rb with improved higher order corrections, the measured value of Rb has a 1.2σ discrepancy with its SM value, while the corresponding discrepancy in is 2.5σ. MSSM contributions from light superpartners improve the agreement of Rb but worsen that of . We project this (Rb–) tension vis-à-vis the constraints arising from other observables in the parameter space of cMSSM and NUSM. We also consider a few well-motivated pMSSM benchmark points and show that pMSSM does not fare any better than the SM.

Z-pole observables in an effective theory

There are two $Z$-peak observables related to the pair production of bottom quarks that show a deviation of about $2.5\ensuremath{\sigma}$ each from Standard Model expectations. While the discrepancy in the forward-backward asymmetry is a long-standing one, the tension for the second observable, namely the ratio of the partial width for a $Z$ decaying to a pair of bottom quarks to the total hadronic decay width of the $Z$, has recently gone up due to a full two-loop evaluation of the Standard Model contributions. We show how both these discrepancies may be explained in the framework of new physics that couples only to the third generation of quarks. In the paradigm of effective operators, the Wilson coefficients of some of the possible operators are already very tightly constrained by flavor physics data. However, there still remain certain operators, particularly those involving right-chiral quark fields, which can successfully explain the anomalies. We also show how the footprints of such operators may be observed at the upgraded LHC.

Hadron melting and QCD thermodynamics

We study in this paper mechanisms of hadron melting based on the spectral representation of hadronic quantum channels, and examine the hadron width dependence of the pressure. The findings are applied to a statistical hadron model of QCD thermodynamics, where hadron masses are distributed by the Hagedorn model and a uniform mechanism for producing hadron widths is assumed. According to this model the hadron - quark gluon plasma transition occurs at $T\approx 200$-250 MeV, the numerically observable $T_c=156$ MeV crossover temperature is relevant for the onset of the hadron melting process.

STRONG COUPLING FROM THE TAU HADRONIC WIDTH BY NON-POWER QCD PERTURBATION THEORY

Starting from the divergent character of the perturbative expansions in QCD and using the technique of series acceleration by the conformal mappings of the Borel plane, I define a novel, non-power perturbative expansion for the Adler function, which simultaneously implements renormalisation-group summation and has a tamed large-order behaviour. The new expansion functions, which replace the standard powers of the coupling, are singular at the origin of the coupling plane and have divergent perturbative expansions, resembling the expanded function itself. Confronting the new perturbative expansions with the standard ones on specific models investigated recently in the literature, I show that they approximate in an impressive way the exact Adler function and the spectral function moments. Applied to the τ hadronic width, the contour-improved and the renormalisation-group summed non-power expansions in the [Formula: see text] scheme lead to the prediction [Formula: see text], which translates to [Formula: see text].

DETERMINATION OF THE STRONG COUPLING FROM HADRONIC TAU DECAYS USING RENORMALIZATION GROUP SUMMED PERTURBATION THEORY

We determine the strong coupling constant αs from the τ hadronic width using a renormalization group summed (RGS) expansion of the QCD Adler function. The main theoretical uncertainty in the extraction of αs is due to the manner in which renormalization group invariance is implemented, and the as yet uncalculated higher order terms in the QCD perturbative series. We show that new expansion exhibits good renormalization group improvement and the behavior of the series is similar to that of the standard CIPT expansion. The value of the strong coupling in [Formula: see text] scheme obtained with the RGS expansion is [Formula: see text]. The convergence properties of the new expansion can be improved by Borel transformation and analytic continuation in the Borel plane. This is discussed elsewhere in these issues.

Interactions of charmed mesons with light pseudoscalar mesons from lattice QCD and implications on the nature of theDs0*(2317)

We study the scattering of light pseudoscalar mesons $(\ensuremath{\pi},K)$ off charmed mesons $(D,{D}_{s})$ in full lattice QCD. The $S$-wave scattering lengths are calculated using L\"uscher's finite volume technique. We use a relativistic formulation for the charm quark. For the light quark, we use domain-wall fermions in the valence sector and improved Kogut-Susskind sea quarks. We calculate the scattering lengths of isospin-$3/2\text{ }D\ensuremath{\pi}$, ${D}_{s}\ensuremath{\pi}$, ${D}_{s}K$, isospin-0 $D\overline{K}$ and isospin-1 $D\overline{K}$ channels on the lattice. For the chiral extrapolation, we use a chiral unitary approach to next-to-leading order, which at the same time allows us to give predictions for other channels. It turns out that our results support the interpretation of the ${D}_{s0}^{*}(2317)$ as a $DK$ molecule. At the same time, we also update a prediction for the isospin breaking hadronic decay width $\ensuremath{\Gamma}({D}_{s0}^{*}(2317)\ensuremath{\rightarrow}{D}_{s}\ensuremath{\pi})$ to $(133\ifmmode\pm\else\textpm\fi{}22)\text{ }\text{ }\mathrm{keV}$.

Perturbative expansion of the QCD Adler function improved by renormalization-group summation and analytic continuation in the Borel plane

We examine the large-order behaviour of a recently proposed renormalization-group-improved expansion of the Adler function in perturbative QCD, which sums in an analytically closed form the leading logarithms accessible from renormalization-group invariance. The expansion is first written as aneffective series in powers of the one-loop coupling, and its leading singularities in the Borel plane are shown to be identical to those of the standard "contour-improved" expansion. Applying the technique of conformal mappings for the analytic continuation in the Borel plane, we define a class of improved expansions, which implement both the renormalization-group invariance and the knowledge about the large-order behaviour of the series. Detailed numerical studies of specific models for the Adler function indicate that the new expansions have remarkable convergence properties up to high orders. Using these expansions for the determination of the strong coupling from the the hadronic width of the $\tau$ lepton we obtain, with a conservative estimate of the uncertainty due to the nonperturbative corrections, $\alpha_s(M_\tau^2)= 0.3189^{+ 0.0173}_{-0.0151}$, which translates to $\alpha_s(M_Z^2)= 0.1184^{+0.0021}_{-0.0018}$.

The case for three-body decaying dark matter

Fermi-LAT has confirmed the excess in cosmic positron fraction observed by PAMELA, which could be explained by dark matter annihilating or decaying in the center of the galaxy. Most existing models postulate that the dark matter annihilates or decays into final states with two or four leptons, which would produce diffuse gamma ray emissions that are in tension with data measured by Fermi-LAT. We point out that the tension could be alleviated if the dark matter decays into three-body final states with a pair of leptons and a missing particle. Using the goldstino decay in a certain class of supersymmetric theories as a prime example, we demonstrate that simultaneous fits to the total e++e− and the fractional e+/e− fluxes from Fermi-LAT and PAMELA could be achieved for a 2 TeV parent particle and a 1 TeV missing particle, without being constrained by gamma-ray measurements. By studying different effective operators giving rise to the dark matter decay, we show that this feature is generic for three-body decaying dark matter containing a missing particle. Constraints on the hadronic decay widths from the cosmic anti-proton spectra are also discussed.

Perturbative expansion of τ hadronic spectral function moments and α s extractions

Various moments of the hadronic spectral functions have been employed in the determination of the strong coupling α s from tau decays. In this work we study the behaviour of their perturbative series under different assumptions for the large-order behaviour of the Adler function, extending previous work on the tau hadronic width. We find that the moments can be divided into a small number of classes, whose characteristics depend only on generic features of the moment weight function and Adler function series. Some moments that are commonly employed in α s analyses from τ decays should be avoided because of their perturbative instability. This conclusion is corroborated by a simplified α s extraction from individual moments. Furthermore, under reasonable assumptions for the higher-order behaviour of the perturbative series, fixed-order perturbation theory (FOPT) provides the preferred framework for the renormalization group improvement of all moments that show good perturbative behaviour. Finally, we provide further evidence for the plausibility of the description of the Adler function in terms of a small number of leading renormalon singularities.

Higgs couplings and precision electroweak data

In light of the discovery of a Higgs-like particle at the LHC, we revisit the status of the precision electroweak data, focusing on two discrepant observables: 1) the long-standing 2.4 sigma deviation in the forward-backward asymmetry of the bottom quark A_{FB}^b, and 2) the 2.3 sigma deviation in R_b, the ratio of the Z \rightarrow b \bar b partial width to the inclusive hadronic width, which is now in tension after a recent calculation including new two-loop electroweak corrections. We consider possible resolutions of these discrepancies. Taking the data at face value, the most compelling scenario is that new physics directly affects A_{FB}^b and R_b, bringing the prediction into accord with the measured values. We propose a modified `Beautiful Mirrors' scenario which contains new vector-like quarks that mix with the b quark, modifying the Z b\bar b vertex and thus correcting A_{FB}^b and R_b. We show that this scenario can lead to modifications to the production rates of the Higgs boson in certain channels, and in particular a sizable enhancement in the diphoton channel. We also describe additional collider tests of this scenario.

2++glueball

The mixing between the ${f}_{2}(1270)$, the ${f}_{2}^{\ensuremath{'}}(1525)$, and the ${2}^{++}$ glueball is determined and tested. The mass and the hadronic decay widths of two bodies of the ${G}_{2}$ are predicted. The search for the ${G}_{2}$ state in the radiative decay of the $J/\ensuremath{\psi}$ is discussed.

Determination ofαs(Mτ2)from improved fixed order perturbation theory

We revisit the extraction of ${\ensuremath{\alpha}}_{s}({M}_{\ensuremath{\tau}}^{2})$ from the QCD perturbative corrections to the hadronic $\ensuremath{\tau}$ branching ratio, using an improved fixed-order perturbation theory based on the explicit summation of all renormalization-group accessible logarithms, proposed some time ago in the literature. In this approach, the powers of the coupling in the expansion of the QCD Adler function are multiplied by a set of functions ${D}_{n}$, which depend themselves on the coupling and can be written in a closed form by iteratively solving a sequence of differential equations. We find that the new expansion has an improved behavior in the complex energy plane compared to that of the standard fixed-order perturbation theory (FOPT), and is similar but not identical to the contour-improved perturbation theory (CIPT). With five terms in the perturbative expansion we obtain in the $\overline{\mathrm{MS}}$ scheme ${\ensuremath{\alpha}}_{s}({M}_{\ensuremath{\tau}}^{2})=0.338\ifmmode\pm\else\textpm\fi{}0.010$, using as input a precise value for the perturbative contribution to the hadronic width of the $\ensuremath{\tau}$ lepton reported recently in the literature.

In-medium hadronic spectral functions through the soft-wall holographic model of QCD

We study the scalar glueball and vector meson spectral functions in a hot and dense medium by means of the soft-wall holographic model of QCD. Finite temperature and density effects are implemented through the AdS/RN metric. We analyse the behaviour of the hadron masses and widths in the $(T,\mu)$ plane, and compare our results with the experimental ones and with other theoretical determinations.

New hadronic currents in TAUOLA: for confrontation with the experimental data

The status of implementation of new hadronic currents into the Monte Carlo system for simulation of τ -lepton production and decay in high-energy accelerator experiments is reviewed. Since the τ -lepton conference in 2010 substantial progress was achieved: (i) For the TAUOLA Monte Carlo generator of τ -lepton decays, automated and simultaneous use of many versions of form factors for the calculation of optional weights for fits was developed and checked to work in the Belle and BaBar software environment. Alternative parameterizations of hadronic currents based on the Resonance Chiral approach are available now. This was achieved for more than 88% of the total τ hadronic width. (ii) the TAUOLA universal interface based on HepMC (the C++ event record) is available. This is the case for C++ users of PHOTOS Monte Carlo for radiative corrections in decays, as well. An algorithm for weighted events to explore spin effects in analysis of hard processes was prepared. (iii) Kernels featuring a complete first-order matrix element are available now for PHOTOS users interested in decays of Z and W bosons. New tests with different options of matrix elements for those and for K l 3 decays are available as well. Presented results illustrate the status of the projects performed in collaboration with Zofia Czyczula, Nadia Davidson, Tomasz Przedziński, Olga Shekhovtsova, Elżbieta Richter-Wąs, Pablo Roig, Qingjun Xu and others.

PROPERTIES OF $b\bar{b}$ MESONS IN CONSTITUENT QUARK MODELS

The properties of bottomonia are investigated in detail in the constituent quark model. The wave functions of bottomonia are obtained by solving Dirac equation and Schrödinger equation. The potentials between quark and antiquark include color confinement (linear and quadratic) and one-gluon-exchange. Based on the obtained wave functions, the electromagnetic and two-photon decay, electric dipole transition, and hadronic width of bottomonia are calculated. The calculated results are in a good agreement with the experimental data. The results also show that the nonrelativistic and relativistic version of quark model can all describe the properties of bottomonia.

Recent progress in hadronic τ decays

The determination of alpha_s from hadronic tau decays is impeded by the fact that two choices for the renormalisation group resummation, namely fixed-order (FOPT) and contour-improved perturbation theory (CIPT), yield systematically differing results. On the basis of a model for higher-order terms in the perturbative series, which incorporates well-known structure from renormalons, it is found that FOPT smoothly approaches the Borel sum for the tau hadronic width, while CIPT is unable to account for the resummed series. An example for the behaviour of QCD spectral function moments, displaying a similar behaviour, is presented as well.

QCD description of hadronic tau decays

The QCD analysis of hadronic tau decays is reviewed and a summary of the present phenomenological status is presented. The following topics are discussed: the determination of alpha_s(m_tau) = 0.338 +- 0.012 from the inclusive tau hadronic width, the measurement of |V_us| through the Cabibbo-suppressed decays of the tau, and the extraction of chiral-perturbation-theory couplings from the spectral tau data.

O(αsv2)corrections to hadronic and electromagnetic decays ofS01heavy quarkonium

We study $O({\ensuremath{\alpha}}_{s}{v}^{2})$ corrections to decays of $^{1}S_{0}$ heavy quarkonium into light hadrons and two photons within the framework of nonrelativistic QCD and find these $O({\ensuremath{\alpha}}_{s}{v}^{2})$ corrections to have significant contributions especially for the decay into light hadrons. With these new results, experimental measurements of the hadronic width and the $\ensuremath{\gamma}\ensuremath{\gamma}$ width of ${\ensuremath{\eta}}_{c}$ can be described more consistently. By fitting experimental data, we find the long-distance matrix elements of ${\ensuremath{\eta}}_{c}$ to be $|{\mathcal{R}}_{{\ensuremath{\eta}}_{c}}(0){|}^{2}={0.834}_{\ensuremath{-}0.197}^{+0.281}\text{ }\text{ }{\mathrm{GeV}}^{3}$ and $⟨{\mathbit{v}}^{2}{⟩}_{{\ensuremath{\eta}}_{c}}={0.232}_{\ensuremath{-}0.098}^{+0.121}$. Moreover, ${\ensuremath{\eta}}_{c}(2S)$ is also discussed and the $\ensuremath{\gamma}\ensuremath{\gamma}$ decay width is predicted to be ${3.34}_{\ensuremath{-}2.10}^{+2.06}\text{ }\text{ }\mathrm{KeV}$.

Erratum: Hadronic quarkonium decays at orderv7[Phys. Rev. D79, 074002 (2009)

We compute the complete imaginary part of the NRQCD Lagrangian at order 1/M^4 in the heavy-quark mass expansion, which includes center of mass operators, and at order alpha_s^2 in the matching coefficients. We also compute the imaginary part of the NRQCD Lagrangian at order 1/M^6 and at order alpha_s^2 that contributes to the S-wave and P-wave inclusive decay widths of heavy quarkonium into light hadrons at order v^7 in the heavy-quark velocity expansion. If we count alpha_s(M) ~ v^2, the calculation provides the complete next-to-leading order corrections to the P-wave hadronic widths, and in the original NRQCD power counting, the complete next-to-leading order corrections to the vector S-wave widths, and part of the next-to-next-to leading order corrections to the pseudoscalar S-wave widths. In the S-wave case, we confirm previous findings and add new terms in a more conservative power counting. In the P-wave case, our results are in disagreement with previous ones. Constraints induced by Poincare' invariance on the NRQCD four-fermion sector are studied for the first time and provide an additional check of the calculation. Perspectives for phenomenological applications are discussed.

Asymptotic Regge trajectories of non-strange mesons

We analyze the asymptotic behavior of Regge trajectories of non-strange mesons. In contrast to an existing belief, it is demonstrated that for the asymptotically linear Regge trajectories the width of heavy hadrons cannot linearly depend on their mass. Using the data on masses and widths of rho_J, omega_J, a_J and f_J mesons for the spin values J \leq 6, we extract the parameters of the asymptotically linear Regge trajectory predicted by the finite width model of quark gluon bags. As it is shown the obtained parameters for the data set B correspond to the cross-over temperature lying in the interval 170.9-175.3 MeV which is consistent with the kinetic freeze-out temperature of early hadronizing particles found in relativistic heavy ion collisions at and above the highest SPS energy.