arXiv subjects

S. Titard

Publications and source records attributed to S. Titard.

4 recordsLinked to original sources

arXiv1995

Heavy quarkonium Systems and Nonperturbative Field Correlators

Bound states of heavy quarks are considered. Using the path integral formalism we are able to rederive, in a gauge invariant way, the Leutwyler-Voloshin short distance analysis as well as a long distance linear potential. At all distances we describe the states in terms of nonperturbative field correlators, and we include radiative corrections at short and intermediate distances. For intermediate distance states (particularly $b\bar {b}$ with $n=2$) our results improve, qualitatively and quantitatively, standard analyses, thanks mostly to being able to take into account the finiteness of the correlation time.

hep-ph↗

arXiv1995

The $l=1$ Hyperfine Splitting in Bottomium as a Precise Probe of the QCD Vacuum.

By relating fine and hyperfine spittings for l=1 states in bottomium we can factor out the less tractable part of the perturbative and nonperturbative effects. Reliable predictions for one of the fine splittings and the hyperfine splitting can then be made calculating in terms of the remaining fine splitting, which is then taken from experiment; perturbative and nonperturbative corrections to these relations are under full control. The method (which produces reasonable results even for the $c{\bar c}$ system) predicts a value of 1.5 MeV for the $(s=1)-(s=0)$ splitting in $b{\bar b}$, opposite in sign to that in $c{\bar c}$. For this result the contribution of the gluon condensate $<α_s G^2>$ is essential, as any model (in particular potential models) which neglects this would give a negative $b{\bar b}$ hyperfine splitting.

hep-ph↗

arXiv1994

Rigourous QCD Evaluation of Spectrum and Other Properties of Heavy Quarkonium Systems; II Bottomium with n=2, l=0,1

We calculate the Lamb, fine and hyperfine shifts in $b\bar b$ with $n=2$, $l=0,1$. Radiative corrections as well as leading nonperturbative corrections (known to be due to the gluon condensate) are taken into account. The calculation is parameter-free, as we take $Λ$, ${\langle α_s G^2 \rangle}$ from independent sources. Agreement with experiment is found at the expected level $\sim 30\%$. Particularly interesting is a prediction for the hyperfine splitting, $M_{\rm average}(2^3P)-M(2^1P_1) = 1.7 \pm 0.9\, {\rm MeV}$, opposite in sign to the $c\bar c$ one ($\approx -0.9\, {\rm MeV}$), and where the nonzero value of ${\langle α_s G^2 \rangle}$ plays a leading role.

hep-ph↗

arXiv1993

Rigourous QCD Evaluation of Spectrum and Ground State Properties of Heavy Quarkonium Systems; with a Precision Determination of the bottom quark mass and of the eta-b mass

We present an evaluation of heavy quarkonium states (bottomium and charmonium) from first principles. We use tree-level QCD (including relativistic corrections) and the full one-loop potential; nonperturbative effects are taken into account at the leading order through the contribution of the gluon condensate . We use the values Lambda_QCD= 200 (+80/-60) MeV and = 0.042 +/- 0.020 GeV^4, but we trade the value of the quark mass by the masses of J/psi, Upsilon as input. We get good agreement in what is essentially a zero parameter evaluation for the masses of the 1S, 2S, 2P states of bottomium, the 1S state for charmonium, and the decay Upsilon --> e^+ e^-. As outstanding result we obtain the precise determination of the bottom quark mass (m_b) as well as an estimate of the hyperfine splitting M(Upsilon)-M(eta_b): m_b(m_b^2) = 4387 (+7/-2) (-3/+4) (+16/-32)(systematic) MeV, M(Upsilon)-M(eta_b) = 36 (+13/-7)(+3/-6) (+11/-5)(syst.) MeV, the first error due to that in Lambda_QCD, the second to that in (varied independently). For the c quark, we find m_c(m_c^2)= 1306 (+21/-34)(-6/+6) MeV (up to systematic errors).

hep-ph↗