ترغب بنشر مسار تعليمي؟ اضغط هنا

Power Corrections in Electron-Positron Annihilation: Experimental Review

51   0   0.0 ( 0 )
 نشر من قبل Stefan Kluth
 تاريخ النشر 2006
  مجال البحث
والبحث باللغة English
 تأليف Stefan Kluth




اسأل ChatGPT حول البحث

Experimental studies of power corrections with e+e- data are reviewed. An overview of the available data for jet and event shape observables is given and recent analyses based on the Dokshitzer-Marchesini-Webber (DMW) model of power corrections are summarised. The studies involve both distributions of the observables and their mean values. The agreement between perturbative QCD combined with DMW power corrections and the data is generally good, and the few exceptions are discussed. The use of low energy data sets highlights deficiencies in the existing calculations for some observables. A study of the finiteness of the physical strong coupling at low energies using hadronic $tau$ decays is shown.

قيم البحث

اقرأ أيضاً

We calculate the cross section for the exclusive production of J^{PC}=0^{++} glueballs G_0 in association with the J/psi in e^+e^- annihilation using the pQCD factorization formalism. The required long-distance matrix element for the glueball is boun ded by CUSB data from a search for resonances in radiative Upsilon decay. The cross section for e^+e^- -> J/psi+ G_0 at sqrt{s}=10.6 GeV is similar to exclusive charmonium-pair production e^+e^- -> J/psi+h for h=eta_c and chi_{c0}, and is larger by a factor 2 than that for h=eta_{c}(2S). As the subprocesses gamma^* -> (c c-bar) (c c-bar) and gamma^* -> (c c-bar) (g g) are of the same nominal order in perturbative QCD, it is possible that some portion of the anomalously large signal observed by Belle in e^+ e^- -> J/psi X may actually be due to the production of charmonium-glueball J/psi G_J pairs.
Using a sample of $1.31times 10^9$ $J/psi$ events collected with the BESIII detector, we report the first observation of spin polarization of $Lambda$ and $barLambda$ hyperons from the coherent production in the $J/psitoLambdabarLambda$ decay. We mea sure the phase between the hadronic form factors to be $DeltaPhi=(42.4pm0.6pm0.5)^circ$. The decay parameters for $Lambdato ppi^-$ ($alpha_-$), $barLambdatobar ppi^+$ ($alpha_+$) and $barLambdatobar npi^0$ ($baralpha_0$) are measured to be $alpha_-=0.750pm0.009pm0.004$, $alpha_+=-0.758pm0.010pm0.007$ and $baralpha_0=-0.692pm0.016pm0.006$, respectively. The obtained value of $alpha_-$ is higher by $(17pm 3)%$ than the current world average. In addition, the $CP$ asymmetry of $-0.006pm0.012pm0.007$ is extracted with substantially improved precision. The ratio $bar{alpha}_0/alpha_{+} = 0.913pm 0.028 pm 0.012$ is also measured.
In this work we study the e^{+}e^{-}tophi K^{+}K^{-} reaction. The leading order electromagnetic contributions to this process involve the gamma*phi K^{+}K^{-} vertex function with a highly virtual photon. We calculate this function at low energies u sing Rchi PT supplemented with the anomalous term for the VVP interactions. Tree level contributions involve the kaon form factors and the K*K transition form factors. We improve this result, valid for low photon virtualities, replacing the lowest order terms in the kaon form factors and K*K transition form factors by the form factors as obtained in Uchi PT in the former case and the ones extracted from recent data on e^{+}e^{-}to KK* in the latter case. We calculate rescattering effects which involve meson-meson amplitudes. The corresponding result is improved using the unitarized meson-meson amplitudes containing the scalar poles instead of the lowest order terms. Using the BABAR value for BR(Xto phi f_{0})Gamma (Xto e^{+} e^{-}), we calculate the contribution from intermediate X(2175). A good description of data is obtained in the case of destructive interference between this contribution and the previous ones, but more accurate data on the isovector K*K transition form factor is required in order to exclude contributions from an intermediate isovector resonance to e^{+}e^{-}to phi K^{+}K^{-} around 2.2 GeV.
Radiative corrections to the annihilation of proton--antiproton into electron--positron are revisited, including virtual and real (soft and hard) photon emission. This issue is relevant for the time-like form factors measurements planned at the PANDA experiment at the FAIR facility, in next future. The relevant formulas are given. A stand-alone Monte-Carlo integrator is developed on the basis of the calculated radiative cross section and its application to the PANDA experiment is illustrated.
60 - Y. Yan , C. Kobdaj , P. Suebka 2004
The reactions of electron-positron to nucleon-antinucleon pairs are studied in a non-perturbative quark model. The work suggests that the two-step process, in which the primary quark-antiquark pair forms first a vector meson which in turn decays into a hadron pair, is dominant over the one-step process in which the primary quark-antiquark pair is directly dressed by additional quark-antiquark pairs to form a hadron pair. To reproduce the experimental data of the reactions of electron-positron to proton-antiproton and electron-positron to neutron-antineutron a D-wave omega-like vector meson with a mass of around 2 GeV has to be introduced.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا