arXiv subjects

U. Nierste

Publications and source records attributed to U. Nierste.

23 records · Page 2Linked to original sources

arXiv1998

Determination of the CKM angle gamma and |V_{ub}/V_{cb}| from inclusive direct CP asymmetries and branching ratios in charmless B decays

We have calculated inclusive direct CP-asymmetries for charmless B^{+/-} -decays. After summing large logarithms to all orders the CP-asymmetries in Delta S=0 and Delta S=1 decays are found as a_{CP} (Delta S=0) = (2.0 +1.2/-1.0)% and a_{CP} (Delta S=1) = ( -1.0 +/- 0.5)%. These results are much larger than previous estimates based on a work without summation of large logarithms. We further show that the dominant contribution to a_{CP} (ΔS=0 ) is proportional to (sin gamma) times |V_{cb}/V_{ub}|. The constraints on the apex (rho-bar,eta-bar) of the unitarity triangle obtained from these two CP-asymmetries define circles in the (rho-bar,eta-bar)-plane. We have likewise analyzed the information on the unitarity triangle obtainable from a measurement of the average non-leptonic branching ratios Br(Delta S=0), Br(Delta S=1) and their sum Br_{NL} (B --> no charm). These CP-conserving quantities define circles centered on the rho-bar--axis of the (rho-bar,eta-bar)-plane. We expect a determination of |V_{ub}/V_{cb}| from Br_{NL} (B --> no charm) to be promising. Our results contain some new QCD corrections enhancing Br(Delta S=1), which now exceeds Br(Delta S=0) by roughly a factor of two.

hep-ph↗

arXiv1998

Inclusive direct CP-asymmetries in charmless B^{+/-}-decays

Direct CP-asymmetries in inclusive decay modes can be cleanly calculated by exploiting quark-hadron duality. This is in sharp contrast to CP-asymmetries in exclusive channels, where unknown strong phases prevent a clean extraction of CKM parameters from measured CP-asymmetries. We have calculated the inclusive CP-asymmetries in B^{+/-}-decays into charmless final states with strangeness one or strangeness zero. In our results large logarithms are properly summed to all orders. We find a_{CP} ( Delta S=0 ) = ( 2.0 +1.2 / -1.0) % and a_{CP} ( Delta S=1 ) = (-1.0 +/- 0.5 ) % . The constraints on the apex (rho-bar,eta-bar) of the unitarity triangle obtained from these two CP-asymmetries define circles in the (rho-bar,eta-bar)-plane. a_{CP} ( Delta S=0 ) measures sin(gamma) times |V_{cb}/V_{ub}|. The presented work has been done in collaboration with Gaby Ostermaier and Alexander Lenz.

hep-ph↗

arXiv1994

The determination of $|V_{cb}|$ from semileptonic inclusive decay rates

We report on the determination of $|V_{cb}|$ from the comparison of the semileptonic inclusive decay rates of B-- and D--mesons using the heavy quark symmetry of QCD. While the renormalization scale ambiguity does not allow for a reliable estimate of the quark masses, it almost cancels in the prediction for $|V_{cb}|$, which reads $|V_{cb}|(τ_B/1.49\,{\rm ps})^{1/2} = 0.036\pm 0.005$, where the error stems from the uncertainty in the kinetic energy of the heavy quark inside the meson, in the experimental branching ratios, in QCD input parameters, and from scale uncertainties. This talk is based on research work done in collaboration with Patricia Ball.

hep-ph↗

arXiv1994

The Mass Definition in Hqet and a New Determination of V$_{\text{cb}}$

Positive powers of the mass parameter in a physical quantity calculated with the help of heavy quark effective theory originate from a Wilson coefficient in the matching of QCD and HQET Green function. We show that this mass parameter enters the calculation as a well--defined running current mass. We further argue that the recently found ill--definition of the pole mass, which is the natural expansion parameter of HQET, does not affect a phenomenological analysis which uses truncated perturbative series. We reanalyse inclusive semileptonic decays of heavy mesons and obtain the $c$ quark mass $m_c^{\overline{\text{MS}}}(m_c) = (1.35\pm 0.20)\,\text{GeV}$ where the error is almost entirely due to scale--uncertainties. We also obtain $m_b^{\overline{\text{MS}}}(m_b) = (4.6\pm 0.3)\,\text{GeV}$ and $|V_{cb}|(τ_B/1.49\,\text{ps})^{1/2} = 0.036\pm 0.005$ where the errors come from the uncertainty in the kinetic energy of the heavy quark inside the meson, in the experimental branching ratios, in QCD input parameters, and scale--uncertainties.

hep-ph↗

arXiv1993

Enhancement of the $K_L$ -- $K_S$ Mass Difference by Short Distance QCD Corrections Beyond Leading Logarithms

We calculate the next-to-leading order short distance QCD corrections to the coefficient $η_1$ of the effective $ΔS = 2$ hamiltonian in the standard model. This part dominates the short distance contribution $(Δm_K)^{\rm SD}$ to the $K_L$ -- $K_S$ mass difference. The next-to-leading order result enhances $η_1$ and $(Δm_K)^{\rm SD}$ by 20\% compared to the leading order estimate. Taking $0.200 \gev \le \laMSb \le 0.350 \gev$ and $1.35 \gev \le m_c(m_c) \le 1.45 \gev$ we obtain $0.922 \le η_1^{\rm NLO} \le 1.419$ compared to $0.834 \le η_1^{\rm LO} \le 1.138$. For $B_K = 0.7$ this corresponds to 48 -- 75 \% of the experimentally observed mass difference. The inclusion of next-to- leading order corrections to $η_1$ reduces considerably the theoretical uncertainty related to the choice of renormalization scales.

hep-ph↗