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Register a new userMeasurement of cross sections of exclusive $e^+ e^- to VP$ processes at $sqrt{s}=10.58$ GeV
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The cross sections for the reactions $e^+e^- to phieta, quad phieta, quad rhoeta, quad rhoeta$ have been measured using a data sample of 516 fb$^{-1}$ collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. The corresponding values of the cross sections are: $1.4 pm 0.4 pm 0.1$ fb $(phieta)$, $5.3 pm 1.1 pm 0.4$ fb $(phieta)$, $3.1 pm 0.5 pm 0.1$ fb $(rhoeta)$ and $3.3 pm 0.6 pm 0.2$ fb $(rhoeta)$. The energy dependence of the cross sections is presented using Belle measurements together with those of CLEO and BaBar.
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We report the first double differential cross sections of two charged pions and kaons ($e^+e^- rightarrow hhX$) in electron-positron annihilation as a function of the fractional energies of the two hadrons for any charge and hadron combination. The dependence of these di-hadron cross sections on the topology (same, opposite-hemisphere or anywhere) is also studied with the help of the event shape variable thrust and its axis. The ratios of these di-hadron cross sections for different charges and hadron combinations directly shed light on the contributing fragmentation functions. For example, we find that the ratio of same-sign pion pairs over opposite-sign pion pairs drops toward higher fractional energies where disfavored fragmentation is expected to be suppressed. These di-hadron results are obtained from a $655,{rm fb}^{-1}$ data sample collected near the $Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. Extending the previously published single-pion and single-kaon cross sections, single-proton ($e^+e^- rightarrow pX$) cross sections are extracted from a $159,{rm fb}^{-1}$ data sub-sample.
We report measurements of the production cross sections of charged pions, kaons, and protons as a function of fractional energy, the event-shape variable called thrust, and the transverse momentum with respect to the thrust axis. These measurements access the transverse momenta created in the fragmentation process, which are of critical importance to the understanding of any transverse momentum dependent distribution and fragmentation functions. The low transverse momentum part of the cross sections can be well described by Gaussians in transverse momentum as is generally assumed but the fractional-energy dependence is non-trivial and different hadron types have varying Gaussian widths. The width of these Gaussians decreases with thrust and shows an initially rising, then decreasing fractional-energy dependence. The widths for pions and kaons are comparable within uncertainties, while those for protons are significantly narrower. These single-hadron cross sections and Gaussian widths are obtained from a $558,{rm fb}^{-1}$ data sample collected at the $Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider.
The Collins effect connects transverse quark spin with a measurable azimuthal asymmetry in the yield of hadronic fragments around the quarks momentum vector. Using two different reconstruction methods we measure statistically significant azimuthal asymmetries for charged pion pairs in e+e- annihilation at center-of-mass energies of 10.52 GeV and 10.58 GeV, which can be attributed to the fragmentation of primordial quarks with transverse spin components. The measurement was performed using a dataset of 547 fb^{-1} collected by the Belle detector at KEKB improving the statistics of the previously published results by nearly a factor of 20.
The cross section for the process $e^+e^- to omegaeta$ is measured in the center-of-mass energy range 1.34--2.00 GeV. The analysis is based on data collected with the SND detector at the VEPP-2000 $e^+e^-$ collider. The measured $e^+e^- to omegaeta$ cross section is the most accurate to date. A significant discrepancy is observed between our data and previous BABAR measurement.
The cross section of the process $e^{+} e^{-} rightarrow K^{+} K^{-}$ is measured at a number of center-of-mass energies $sqrt{s}$ from 2.00 to 3.08 GeV with the BESIII detector at the Beijing Electron Positron Collider (BEPCII). The results provide the best precision achieved so far. A resonant structure around 2.2 GeV is observed in the cross section line shape. A Breit-Wigner fit yields a mass of $M=2239.2 pm 7.1 pm 11.3$~and a width of $Gamma=139.8pm12.3pm20.6$ MeV, where the first uncertainties are statistical and the second ones are systematic. In addition, the time-like electromagnetic form factor of the kaon is determined at the individual center-of-mass energy points.
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