-
Particle Data Group,
S. Eidelman,
K. G. Hayes,
K. A. Olive,
M. Aguilar-Benitez,
C. Amsler,
D. Asner,
K. S. Babu,
R. M. Barnett,
J. Beringer, [......],
K. van Bibber,
M. G. Vincter,
D. R. Ward,
B. R. Webber,
M. Whalley,
L. Wolfenstein,
J. Womersley,
C. L. Woody,
O. V. Zenin,
R.-Y. Zhu
Physics Letters B 06/2004; 592:31-88. · 3.95 Impact Factor
-
Nucl.Phys. 01/2004; B693:103-133.
-
[show abstract]
[hide abstract]
ABSTRACT: We present a study of the finite-volume two-pion matrix elements and correlation functions of the I=0 scalar operator, in full and partially quenched QCD, at one-loop order in chiral perturbation theory. In partially quenched QCD, when the sea and valence light quark masses are not equal, the lack of unitarity leads to the same inconsistencies as in quenched QCD and the matrix elements cannot be determined. It is possible, however, to overcome this problem by requiring the masses of the valence and sea quarks to be equal for the u and d quarks while keeping the strange quark (s) quenched (or partially quenched), but only in the kinematic region where the two-pion energy is below the two-kaon threshold. Although our results are obtained at NLO in chiral perturbation theory, they are more general and are also valid for non-leptonic kaon decays (we also study the matrix elements of (8,1) operators, such as the QCD penguin operator Q6). We point out that even in full QCD, where any problems caused by the lack of unitarity are clearly absent, there are practical difficulties in general, caused by the fact that finite-volume energy eigenstates are linear combination of two-pion, two-kaon and two-η states. Our Letter implies that extracting ΔI=1/2, K→ππ decay amplitudes from simulations with ms=md,u is not possible in partially quenched QCD (and is very difficult in full QCD).
Physics Letters B. 09/2003;
-
[show abstract]
[hide abstract]
ABSTRACT: We perform a calculation in one-loop chiral perturbation theory of the two-pion matrix elements and correlation functions of an I=0 scalar operator, in finite and infinite volumes for both full and quenched QCD. We show that major difficulties arise in the quenched theory due to the lack of unitarity. Similar problems are expected for quenched lattice calculations of K→ππ amplitudes with ΔI=1/2. Our results raise the important question of whether it is consistent to study K→ππ amplitudes beyond leading order in chiral perturbation theory in quenched or partially quenched QCD.
Physics Letters B. 12/2002;
-
[show abstract]
[hide abstract]
ABSTRACT: We demonstrate, by an explicit one-loop calculation, that at leading twist the nonperturbative effects in B→γℓνℓ, B→γγ and B→γℓ+ℓ− radiative decays are contained in a common multiplicative factor (ΛB(Eγ), where Eγ is the energy of the photon). We argue that this result holds also at higher orders. Ratios of the amplitudes for these processes do not depend on scales below the mass of the B-meson (MB), and can be calculated as perturbative series in αs(MB).
Physics Letters B. 12/2002;
-
[show abstract]
[hide abstract]
ABSTRACT: We present results of several numerical studies with Wilson fermions relevant for kaon physics. We compute theBk parameter by using two different methods and extrapolate to the continuum limit. Our preliminary result isBKMS(2GeV) = 0.66(7).ΔI =3/2K → ππ matrix elements (MEs) are obtained by using the next-to-leading order (NLO) expressions derived in chiral perturbation theory (ChPT) in which the low energy constants (LECs) are determined by the lattice results computed at unphysical kinematics. From the simulation at β = 6.0 our (preliminary) results read: 〈gpπ O7¦MS¯(2GeV)¦K〉I=2=0.14(1)(1)GeV3 and 〈gpπ O8¦MS¯(2GeV)¦K〉I=2=0.69(6)(6)GeV3.
Nuclear Physics B - Proceedings Supplements. 09/2002;
-
[show abstract]
[hide abstract]
ABSTRACT: We provide a rigorous basis for factorization for a large class of non-leptonic two-body B-meson decays in the heavy-quark limit. The resulting factorization formula incorporates elements of the naive factorization approach and the hard-scattering approach, but allows us to compute systematically radiative (“non-factorizable”) corrections to naive factorization for decays such as B→Dπ and B→ππ. We first discuss the factorization formula from a general point of view. We then consider factorization for decays into heavy-light final states (such as B→Dπ) in more detail, including a proof of the factorization formula at two-loop order. Explicit results for the leading QCD corrections to factorization are presented and compared to existing measurements of branching fractions and final-state interaction phases.
Nuclear Physics B. 06/2000;
-
[show abstract]
[hide abstract]
ABSTRACT: We compute the two-loop term in the perturbation series for the quark-mass in the lattice Heavy Quark Effective Theory (HQET). This is an ingredient in the matching factor required to obtain the b-quark mass from lattice simulations of the HQET at first-order in the Heavy Quark Expansion. Combining our calculation with numerical results from quenched simulations by the APE collaboration, we find, at two-loop order, . It was expected that the two-loop term would have a significant effect, and this is indeed what we find. Depending on the choice of “reasonable” coupling constant in the one-loop estimates, the result for can change by several hundred MeV when the two-loop terms are included.
Nuclear Physics B. 12/1998;
-
[show abstract]
[hide abstract]
ABSTRACT: We discuss the evaluation of power corrections to hard scattering and decay processes for which an operator product expansion is applicable. The Wilson coefficient of the leading-twist operator is the difference of two perturbative series, each of which has a renirmalon ambiguity of the same order as the power corrections themselves, but which cancel in the difference. We stress the necessity of calculating this coefficient function to sufficiently high orders in perturbation theory so as to make the uncertainty of the same order of or smaller than the relevant power corrections. We investigate in some simple examples whether this can be achieved. Our conclusion is that in most of the theoretical calculations which include power corrections, the uncertainties are at least comparable to the power corrections themselves, and that it will be a very difficult task to improve the situation.
Nuclear Physics B. 05/1996;
-
[show abstract]
[hide abstract]
ABSTRACT: We present the first lattice calculation of the B-meson binding energy and of the kinetic energy −λ1/2mQ of the heavy-quark inside the pseudoscalar B-meson. This calculation has required the non-perturbative subtraction of the power divergences present in matrix elements of the Lagrangian operator and of the kinetic energy operator . The non-perturbative renormalisation of the relevant operators has been implemented by imposing suitable renormalisation conditions on quark matrix elements, in the Landau gauge. Our numerical results have been obtained from several independent numerical simulations at β = 6.0 and 6.2, and using, for the meson correlators, the results obtained by the APE group at the same values of β. Our best estimate, obtained by combining results at different values of β, is . For the MS running mass, we obtain , in reasonable agreement with previous determinations. From a subset of 36 configurations, we were only able to establish a loose upper bound on the b-quark kinetic energy in a B-meson, . This shows that a much larger statistical sample is needed to determine this important parameter.
Nuclear Physics B. 06/1995;
-
[show abstract]
[hide abstract]
ABSTRACT: We propose a general renormalization method, which avoids completely the use of lattice perturbation theory. We present the results from its numerical applications to two-fermion operators on a 163 × 32 lattice, at β = 6.0.
Nuclear Physics B - Proceedings Supplements. 12/1994;
-
[show abstract]
[hide abstract]
ABSTRACT: We present the first lattice calculation of the B-meson binding energy and of the kinetic energy λ1/2mQ of the heavy-quark inside the pseudoscalar B-meson. In order to cancel the ambiguities due to the ultraviolet renormalons present in the operator matrix elements, this calculation has required the non-perturbative subtraction of the power divergences present in the Lagrangian operator and in the kinetic energy operator . The non-perturbative renormalization of the relevant operators has been implemented by imposing suitable renormalization conditions on quark matrix elements in the Landau gauge.
Nuclear Physics B - Proceedings Supplements. 12/1994;
-
[show abstract]
[hide abstract]
ABSTRACT: We propose a non-perturbative method for computing the renormalization constants of generic composite operators. This method is intended to reduce some systematic errors, which are present when one tries to obtain physical predictions from the matrix elements of lattice operators. We also present the results of a calculation of the renormalization constants of several two-fermion operators, obtained, with our method, by numerical simulation of QCD, on a 163x 32 lattice, at β = 6.0. The results of this simulation are encouraging, and further applications to four-fermion operators and to the heavy quark effective theory are proposed.
Nuclear Physics B. 11/1994;
-
[show abstract]
[hide abstract]
ABSTRACT: We propose a method for evaluating the slope (and higher derivatives) of the Isgur-Wise function at the zero recoil point using lattice simulations. These derivatives are required for the extrapolation of the experimental data for B→D∗l⦶v decays to the zero recoil point, from which the Vcb element of the CKM-matrix can be determined.
Physics Letters B. 01/1994;
-
Nuclear Physics B - Proceedings Supplements 03/1989; 7:228-254. · 0.88 Impact Factor
-
A. Abada,
C.R. Allton,
Ph. Boucaud,
D.B. Carpenter,
M. Crisafulli,
J. Galand,
S. Güsken,
G. Martinelli,
O. Péne, C.T. Sachrajda,
R. Sarno,
K. Schilling,
R. Sommer
[show abstract]
[hide abstract]
ABSTRACT: We present an extensive lattice study of the physical properties of mesons, composed of a heavy, H, and a light, q, quark, at β = 6.4 on a 243 × 60 lattice, using the Wilson action in the quenched approximation. We have studied the mass spectrum and the decay constants of vector and pseudoscalar mesons. We find significant violations of the mass scaling law fP√MP = const. ( ∼ 50% for D-mesons and ∼ 20% for B-mesons). The results using quenched but propagating quarks are remarkably consistent with the static results when the scale is taken from the pion decay constant. Combining the results obtained by several calculations of the pseudoscalar decay constants as a function of the meson mass, at different values of the lattice spacing, we obtain by extrapolation fB√BB = (220 ± 40) MeV (fB = (205 ± 40) MeV and BB = 1.16 ± 0.07), where BB is the renormalization group invariant B-parameter relevant for mixing. We also find . This last result is relevant in experimental studies of mixing. The vector-pseudoscalar mass splittings do not follow the predicted behaviour, MV2 - MP2 ∼ const., which is expected (and found experimentally) in the limit of large heavy quark masses (i.e. when mQ ⪢ ΛQCD).
Nuclear Physics B - Proceedings Supplements 26:344-346. · 0.88 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We calculate the anomalous dimensions of the lowest twist, flavour non-singlet operators in the Wilson expansion to two loops. The calculation is performed using dimensional regularization and the minimal subtraction renormalization scheme. The physical relevance of our results in deep inelastic scattering is discussed.
Nuclear Physics B.
-
[show abstract]
[hide abstract]
ABSTRACT: We complete the calculation of all parameters needed to discuss deep inelastic scattering in QCD to subleading order by calculating the anomalous dimensions of the twist-two flavour singlet operators in the Wilson expansion to two loops and the coefficient functions to order . The calculation is performed in the dimensional regularization scheme with the minimal subtraction renormalization prescription. The application of the results to deep inelastic scattering is discussed.
Nuclear Physics B.
-
[show abstract]
[hide abstract]
ABSTRACT: We show that knowledge of the valence quark distribution of a proton at one value of q2, enables one to calculate a contribution to the difference between the distribution of anti-up quarks and anti-down quarks in the sea of the proton at higher values of q2. This difference can be expressed as a linear combination of the structure functions F1, for νp → νX and e−p → e−p (for which one knows the q2 behaviour of the moments) and for (for which one knows the q2 behaviour of the odd moments). The calculable contribution involves a non-trivial continuation of the even (odd) moments of the neutral (charged) current structure functions to odd (even) moments. We calculate this contribution and although we find that its sign is negative we point out that this cannot be interpreted as a consequences of the Pauli exclusion principle. We discuss the constraints our results impose on antiquark distributions.
Nuclear Physics B.
-
[show abstract]
[hide abstract]
ABSTRACT: We discuss finite-volume computations of two-body hadronic decays below the inelastic threshold (e.g., K→ππ decays). The relation between finite-volume matrix elements and physical amplitudes, recently derived by Lellouch and Lüscher, is extended to all elastic states under the inelastic threshold. We present a detailed comparison of our approach with that of Lellouch and Lüscher and discuss the possible limitations of the method which could arise due to the presence of inelastic thresholds. We also examine a standard alternative method which can be used to extract the real part of the decay amplitude from correlators of the form . We show that in this case there are finite-volume corrections which vanish as inverse powers of the volume, which cannot be removed by a multiplicative factor.
Nuclear Physics B.
