arXiv subjects

Matthias Jamin

Publications and source records attributed to Matthias Jamin.

At least 55 records · Page 3Linked to original sources

arXiv2004

Extraction of m_s and |V_us| from Hadronic Tau Decays

We review recent work to determine the strange quark mass m_s as well as the proposal to determine |V_{us}| using hadronic tau decay data. The recent update of the strange spectral function by OPAL and their moments of the invariant mass distribution are employed. Our results are |V_us|=0.2208 +- 0.0034 and m_s (2 GeV)=81 +- 22 MeV. Our result is already competitive to the standard extraction of |V_us| from K_e3 decays and to the new proposals to determine it. The error on V_us is dominated by experiment and will be eventually much improved by the B-factories hadronic tau data. Ultimately, a simultaneous fit of both m_s and |V_us| to a set of moments of the hadronic tau decays invariant mass distribution will provide one of the most accurate determinations of these Standard Model parameters.

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arXiv2004

Order p^6 chiral couplings from the scalar K Pi form factor

Employing results from a recent determination of the scalar KPi form factor F_0^KPi within a coupled channel dispersion relation analysis \cite{JOP01}, in this work we calculate the slope and curvature of F_0^KPi(t) at zero momentum transfer. Knowledge of the slope and curvature of the scalar KPi form factor, together with a recently calculated expression for F_0^KPi(t) in chiral perturbation theory at order p^6, enable to estimate the O(p^6) chiral constants C_12^r=(0.3 +- 5.4)10^-7 and (C_12^r+C_34^r)=(3.2 +- 1.5)10^-6. Our findings also allow to estimate the contribution coming from the C_i to the vector form factor F_+^KPi(0) which is crucial for a precise determination of |V_us| from K_l3 decays. Our result F_+^KPi(0)|_C_i^r=-0.018 +- 0.009, though inflicted with large uncertainties, is in perfect agreement with a previous estimate by Leutwyler and Roos already made twenty years ago.

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arXiv2004

epsilon'/epsilon at the NLO: 10 Years Later

During the last four years several parameters relevant for the analysis of the CP-violating ratio epsilon'/epsilon improved and/or changed significantly. In particular, the experimental value of epsilon'/epsilon and the strange quark mass decreased, the uncertainty in the CKM factor has been reduced, and for a value of the hadronic matrix element of the dominant electroweak penguin operator Q_8, some consensus has been reached among several theory groups. In view of this situation, ten years after the first analyses of epsilon'/epsilon at the next-to-leading order, we reconsider the analysis of epsilon'/epsilon within the SM and investigate what can be said about the hadronic Q_6 matrix element of the dominant QCD penguin operator on the basis of the present experimental value of epsilon'/epsilon and todays values of all other parameters. Employing a conservative range for the reduced electroweak penguin matrix element R_8=1.0+-0.2 from lattice QCD, and present values for all other input parameters, on the basis of the current world average for epsilon'/epsilon, we obtain the reduced hadronic matrix element of the dominant QCD penguin operator R_6=1.23+-0.16 implying _0^NDR(m_c) ~ -0.8 _2^NDR(m_c). We compare these results with those obtained in large-N_c approaches in which generally R_6 ~ R_8 and _0^NDR(m_c) is chirally suppressed relatively to _2^NDR(m_c). We present the correlation between R_6 and R_8 that is implied by the data on epsilon'/epsilon provided new physics contributions to epsilon'/epsilon can be neglected.

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arXiv2003

Finite energy sum rules for the vector current: the strange quark mass

We determine the strange quark mass in the framework of finite energy sum rules from the vector current channel. The theoretical contributions are calculated in contour improved perturbation theory and a substantial difference to fixed order perturbation theory is found. In our phenomenological parametrisation we include recent experimental results from CMD-2.

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arXiv2003

A novel route to V_us

Already in the past, hadronic tau decays have served as an interesting source to obtain information on the parameters of the Standard Model, like the strong coupling alpha_s or the strange quark mass. Below it will be shown that the approach to obtain the strange mass from the hadronic tau-decay width can be turned into a determination of the CKM matrix element V_us, once the strange mass is used as an input from other sources. At present, we obtain V_us = 0.2179 +- 0.0045, where the error is completely dominated by the experimental uncertainty, and can be improved through an improved measurement of the hadronic tau-decay rate into strange particles R_tau,S.

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arXiv2002

Light quark masses from scalar sum rules

In this work, the mass of the strange quark is calculated from QCD sum rules for the divergence of the strangeness-changing vector current. The phenomenological scalar spectral function which enters the sum rule is determined from our previous work on strangeness-changing scalar form factors [1]. For the running strange mass in the MS_bar scheme, we find m_s(2 GeV) = 99 +- 16 MeV. Making use of this result and the light-quark mass ratios obtained from chiral perturbation theory, we are also able to extract the masses of the lighter quarks m_u and m_d. We then obtain m_u(2 GeV) = 2.9 +- 0.6 MeV and m_d(2 GeV) = 5.2 +- 0.9 MeV. In addition, we present an updated value for the light quark condensate.

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arXiv2002

Flavour-symmetry breaking of the quark condensate and chiral corrections to the Gell-Mann-Oakes-Renner relation

The relation between the chiral quark condensate in QCD sum rules and chiral perturbation theory is clarified with the help of a low-energy theorem for the scalar and pseudoscalar correlation functions. It is found that the quark condensate should be identified with the non-normal-ordered vacuum expectation value of quark-antiquark fields. Utilising results on flavour SU(3) breaking of the quark condensate from QCD sum rules, the unphysical low-energy constant H_2^r in the chiral Lagrangian, as well as next-to-leading order corrections to the Gell-Mann-Oakes-Renner relation are estimated.

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arXiv2001

f_B and f_B_s from QCD sum rules

The decay constants of the pseudoscalar mesons B and B_s are evaluated from QCD sum rules for the pseudoscalar two-point function. Recently calculated perturbative three-loop QCD corrections are incorporated into the sum rule. An analysis in terms of the bottom quark pole mass turns out to be unreliable due to large higher order radiative corrections. On the contrary, in the MS_bar scheme the higher order corrections are under good theoretical control and a reliable determination of f_B and f_{B_s} becomes feasible. Including variations of all input parameters within reasonable ranges, our final results for the pseudoscalar meson decay constants are f_B = 210 +- 19 MeV and f_B_s = 244 +- 21 MeV. Employing additional information on the product sqrt(B_B) f_B from global fits to the unitarity triangle, we are in a position to also extract the B-meson B-parameter B_B = 1.26 +- 0.45. Our results are well compatible with analogous determinations of the above quantities in lattice QCD.

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arXiv2001

Strangeness-changing scalar form factors

We derive expressions for strangeness-changing scalar form factors, which incorporate known theoretical constraints both at low and high energies. Their leading behaviour in the limit of a large number of colours is calculated from the resonance chiral Lagrangian. A set of short-distance constraints on the scalar resonance couplings is obtained, imposing the form factors to vanish at infinite momentum transfer. Making use of previous results on S-wave KPi scattering [1], and a coupled--channel dispersion-relation analysis, the KPi, KEta and KEta' scalar form factors are calculated up to 2 GeV. These scalar form factors are a key ingredient in the determination of the corresponding scalar spectral function which is important in the extraction of the mass of the strange quark from QCD sum rules as well as hadronic tau decays.

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arXiv2000

QCD sum rule analysis of the charmonium system: The charm quark mass

In this work, the charm quark mass is obtained from a QCD sum rule analysis of the charmonium system. In our investigation we include results from non-relativistic QCD at next-to-next-to-leading order. Using the pole mass scheme, we obtain a value of $M_c=1.70\pm 0.13$ GeV for the charm pole mass. The introduction of a potential-subtracted mass leads to an improved scale dependence. The running ${\rm \MSb}$-mass is then determined to be $m_{c}(m_{c}) = 1.23 \pm 0.09$ GeV.

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arXiv2000

S-wave Kpi scattering in chiral perturbation theory with resonances

We present a detailed analysis of S-wave Kpi scattering up to 2 GeV, making use of the resonance chiral Lagrangian predictions together with a suitable unitarisation method. Our approach incorporates known theoretical constraints at low and high energies. The present experimental status, with partly conflicting data from different experiments, is discussed. Our analysis allows to resolve some experimental ambiguities, but better data are needed in order to determine the cross-section in the higher-energy range. Our best fits are used to determine the masses and widths of the relevant scalar resonances in this energy region.

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arXiv1999

Theoretical status of epsilon'/epsilon

The present theoretical status of the parameter for direct CP violation epsilon'/epsilon in the Standard Model is reviewed and compared with most recent experimental measurements of the same quantity. After collecting the basic expressions for epsilon'/epsilon, the situation of hadronic matrix element calculations is summarised. The matrix elements constitute the dominant source of uncertainty for theoretical determinations of epsilon'/epsilon. For central values of the input parameters, the numerical analysis then yields results which are generally below the experimental data. Possible reasons for these findings are discussed.

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arXiv1997

QCD field strength correlator at the next-to-leading order

The gauge invariant two-point correlation function of the gauge field strength tensor is calculated in perturbation theory at the next-to-leading order. Besides a direct calculation in perturbative QCD we also present a derivation of the correlation function in the heavy quark effective theory. Our results are briefly compared with recent determinations of the field strength correlator on the lattice.

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arXiv1997

Bottom quark mass and alpha_s from the Upsilon system

The mass of the bottom quark and the strong coupling constant alpha_s are determined from QCD moment sum rules for the Upsilon system. Two analyses are performed using both the pole mass M_b as well as the mass m_b in the $\MSb$ scheme. In the pole-mass scheme large perturbative corrections resulting from coulombic contributions have to be resummed. In the $\MSb$ scheme this can be avoided by an appropriate choice for the renormalization scale. For the bottom quark mass we obtain M_b = 4.60 +- 0.02 GeV and m_b(m_b) = 4.13 +- 0.06 GeV. Our combined result from both determinations for the strong coupling is alpha_s(M_Z) = 0.119 +- 0.008.

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arXiv1994

The Strange Quark Mass from QCD Sum Rules

The strange quark mass is calculated from QCD sum rules for the divergence of the vector as well as axial-vector current in the next-next-to-leading logarithmic approximation. The determination for the divergence of the axial-vector current is found to be unreliable due to large uncertainties in the hadronic parametrisation of the two-point function. From the sum rule for the divergence of the vector current, we obtain a value of $m_s\equiv\mb_s(1\,\gev)=189\pm32\,\mev$, where the error is dominated by the unknown perturbative ${\cal O}(α_s^3)$ correction. Assuming a continued geometric growth of the perturbation series, we find $m_s=178\pm18\,\mev$. Using both determinations of $m_s$, together with quark-mass ratios from chiral perturbation theory, we also give estimates of the light quark masses $m_u$ and $m_d$.

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arXiv1994

QCD corrections to inclusive $ΔS=1,2$ transitions

The talk summarises a calculation of the two-point functions for $ΔS=1$ current-current and QCD-penguin operators, as well as for the $ΔS=2$ operator, at the next-to-leading order. The size of the gluonic corrections to current-current operators is large, providing a qualitative understanding of the observed enhancement in $ΔI=1/2$ transitions. In the $ΔS=2$ sector the QCD corrections are quite moderate ($\approx -20\%$). This work has been done in collaboration with Antonio Pich.

hep-ph↗

arXiv1994

QCD corrections to inclusive $ΔS=1,2$ transitions at the next-to-leading order

The 2--point functions for $ΔS=1$ current-current and QCD-penguin operators, as well as for the $\ds$ operator, are calculated at the next-to-leading order. The calculation is performed in two different renormalization schemes for $γ_5$, and the compatibility of the results obtained in the two schemes is verified. The scale- and scheme-invariant combinations of spectral 2--point functions and corresponding Wilson-coefficients are constructed and analyzed. For $ΔS=1$, the QCD corrections to the CP-conserving part, dominated by current-current operators, are 40\%--120\% at $q^2=\left(1-3\,\mbox{\rm GeV}\right)^2$, whereas the correction to the imaginary part, mainly coming from the penguin operator $Q_6$, are 100\%--240\%. The large size of the gluonic corrections to current-current operators provides a qualitative understanding of the observed enhancement of $ΔI=1/2$ transitions. In the $ΔS=2$ sector the QCD corrections are quite moderate ($\approx -20\%$).

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arXiv1993

The Anatomy of eps'/eps Beyond Leading Logarithms with Improved Hadronic Matrix Elements

Results of a recent calculation of the effective $\dS$ Hamiltonian at the next-to-leading order will be presented\footnote{Work done in collaboration with A. J. Buras and M. E. Lautenbacher.}. These, together with an improved treatment of hadronic matrix elements, are used to evaluate the measure for direct CP-violation, $\epe$, at the next-to-leading order. Taking $\mt=130\,GeV$, $\Lms=300\,MeV$ and calculating $\langle Q_6 \rangle$ and $\langle Q_8 \rangle$ in the $1/N$ approach, we find in the NDR scheme $\epe = (6.7 \pm 2.6)\times 10^{-4}$ in agreement with the experimental findings of E731. We point out however that the increase of $\langle Q_6 \rangle$ by only a factor of two gives $\epe = (20.0 \pm 6.5)\times 10^{-4}$ in agreement with the result of NA31. The dependencies of $\epe$ on $\Lms$, $\mt$, and some $B$-parameters, parameterizing hadronic matrix elements, are briefly discussed.

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