We have measured the cross section of the radiative process e+e- -> pi+pi-gamma with the KLOE detector at the Frascati phi-factory DAPHNE, from events taken at a CM energy W=1 GeV. Initial state radiation allows us to obtain the cross section for e+e- -> pi+pi-, the pion form factor |F_pi|^2 and the dipion contribution to the muon magnetic moment anomaly, Delta a_mu^{pipi} = (478.5+-2.0_{stat}+-5.0_{syst}+-4.5_{th}) x 10^{-10} in the range 0.1 < M_{pipi}^2 < 0.85 GeV^2, where the theoretical error includes a SU(3) ChPT estimate of the uncertainty on photon radiation from the final pions. The discrepancy between the Standard Model evaluation of a_mu and the value measured by the Muon g-2 collaboration at BNL is confirmed.
Differential cross section for $e^+e^-\rightarrow\pi^+\pi^-\gamma$, with $50^o<\theta_\gamma<130^o$
Statistical covariance matrix for differential cross section for $e^+e^-\rightarrow\pi^+\pi^-\gamma$, with $50^o<\theta_\gamma<130^o$
Inverse statistical covariance matrix for differential cross section for $e^+e^-\rightarrow\pi^+\pi^-\gamma$, with $50^o<\theta_\gamma<130^o$
A study of the inclusive charged hadron production in two-photon collisions is described. The data were collected with the DELPHI detector at LEP II. Results on the inclusive single-particle p_T distribution and the differential charged hadrons dsigma/dp_T cross-section are presented and compared to the predictions of perturbative NLO QCD calculations and to published results.
Differential inclusive DSIG/DPT distribution of charged particles produced in GAMMA* GAMMA* interaction with two pseudorapidity cut offs.
The cross sections for the reactions $e^+e^- \to \phi\eta, \quad \phi\eta', \quad \rho\eta, \quad \rho\eta'$ 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 $(\phi\eta)$, $5.3 \pm 1.1 \pm 0.4$ fb $(\phi\eta')$, $3.1 \pm 0.5 \pm 0.1$ fb $(\rho\eta)$ and $3.3 \pm 0.6 \pm 0.2$ fb $(\rho\eta')$. The energy dependence of the cross sections is presented using Belle measurements together with those of CLEO and BaBar.
Radiativity corrected cross section.
The differential cross section for the process $\gamma \gamma \to \eta \pi^0$ has been measured in the kinematic range $0.84 \GeV < W < 4.0 \GeV$, $|\cos \theta^*|<0.8$, where $W$ and $\theta^*$ are the energy and $\pi^0$ (or $\eta$) scattering angle, respectively, in the $\gamma\gamma$ center-of-mass system. The results are based on a 223 fb$^{-1}$ data sample collected with the Belle detector at the KEKB $e^+ e^-$ collider. Clear peaks due to the $a_0(980)$ and $a_2(1320)$ are visible. The differential cross sections are fitted in the energy region $0.9 \GeV < W < 1.46 \GeV$ to obtain the parameters of the $a_0(980)$. Its mass, width and $\Gamma_{\gamma \gamma} \B (\eta \pi^0)$ are measured to be $982.3 ^{+0.6}_{-0.7} ^{+3.1}_{-4.7} \MeV/c^2$, $75.6 \pm 1.6 ^{+17.4}_{-10.0} \MeV$ and $128 ^{+3}_{-2} ^{+502}_{-43} \eV$, respectively. The energy and angular dependences above 3.1 GeV are compared with those measured in the $\pi^0 \pi^0$ channel. The integrated cross section over $|\cos \theta^*|<0.8$ has a $W^{-n}$ dependence with $n = 10.5 \pm 1.2 \pm 0.5$, which is slightly larger than that for $\pi^0 \pi^0$. The differential cross sections show a $\sin^{-4} \theta^*$ dependence similar to $\gamma \gamma \to \pi^0 \pi^0$. The measured cross section ratio, $\sigma(\eta \pi^0)/\sigma(\pi^0 \pi^0) = 0.48 \pm 0.05 \pm 0.04$, is consistent with a QCD-based prediction.
The total cross section integrated over ABS(COS(THETA*)) < 0.8.
The differential cross section as a function of angle for W = 0.85 GeV.
The differential cross section as a function of angle for W = 0.87 GeV.
Using a data sample with a total integrated luminosity of 10.0 pb$^{-1}$ collected at center-of-mass energies of 2.6, 3.07 and 3.65 GeV with BESII, cross sections for $e^+e^-$ annihilation into hadronic final states ($R$ values) are measured with statistical errors that are smaller than 1%, and systematic errors that are about 3.5%. The running strong interaction coupling constants $\alpha_s^{(3)}(s)$ and $\alpha_s^{(5)}(M_Z^2)$ are determined from the $R$ values.
R values.
The ZZ production cross section is measured from a data sample corresponding to a total integrated luminosity of 452 pb(-')(1), collected by the ALEPH experiment at LEP at centre-of-mass energies from 192 to 209 GeV. Individual cross sections, ext racted at six centre-of-mass energies, are found to be in agreement with Standard Model calculations. The results are used to set limits on anomalous neutral gauge couplings.
Measured E+ E- --> Z0 Z0 cross sections.
By analyzing the data sets of 17.3 pb$^{-1}$ taken at $\sqrt s= 3.773$ GeV and of 6.5 pb$^{-1}$ taken at $\sqrt s= 3.650$ GeV with the BES-II detector at the BEPC collider, we measure the observed cross sections for the exclusive light hadron final states of $K_S^0K^-\pi^+$, $K_S^0K^-\pi^+\pi^0$, $K_S^0K^-\pi^+\pi^+\pi^-$, $K_S^0K^-\pi^+\pi^+\pi^-\pi^0$, $K_S^0K^-\pi^+\pi^+\pi^+\pi^-\pi^-$ and $K_S^0K^-\pi^+\pi^0\pi^0$ produced in $e^+ e^-$ annihilation at the two energy points. We set the upper limits on the observed cross sections and the branching fractions for $\psi(3770)$ decay to these final states at 90% C.L..
Observed cross sections.
By analyzing the data sets of 17.3, 6.5 and 1.0 pb$^{-1}$ taken, respectively, at $\sqrt s= 3.773$, 3.650 and 3.6648 GeV with the BES-II detector at the BEPC collider, we measure the observed cross sections for $e^+e^-\to \pi^+\pi^-\pi^0\pi^0$, $K^+K^-\pi^0\pi^0$, $2(\pi^+\pi^-\pi^0)$, $K^+K^-\pi^+\pi^-\pi^0\pi^0$ and $3(\pi^+\pi^-)\pi^0\pi^0$ at the three energy points. Based on these cross sections we set the upper limits on the observed cross sections and the branching fractions for $\psi(3770)$ decay into these final states at 90% C.L..
Observed cross sections.
We report e+e- --> b anti-b cross section measurements by the BABAR experiment performed during an energy scan in the range of 10.54 to 11.20 GeV at the PEP-II e+e- collider. A total relative error of about 5% is reached in more than three hundred center-of-mass energy steps, separated by about 5 MeV. These measurements can be used to derive precise information on the parameters of the Y(10860) and Y(11020) resonances. In particular we show that their widths may be smaller than previously measured.
Measured values of R(b) from the detailed scan in SQRT(S),. where R(b) is the ratio between the number of observed E+ E- --> B BBAR(GAMMA) normalized to luminosity divided to the bare dimuon cross-section.
We have measured the cross section $\sigma(e^+e^-\to\pi^+\pi^-\gamma(\gamma))$ at DA$\Phi$NE, the Frascati \phi-factory, using events with initial state radiation photons emitted at small angle and inclusive of final state radiation. We present the analysis of a new data set corresponding to an integrated luminosity of 240 pb$^{-1}$. We have achieved a reduced systematic uncertainty with respect to previously published KLOE results. From the cross section we obtain the pion form factor and the contribution to the muon magnetic anomaly from two pion states in the mass range $0.592 < M_{\pi\pi} < 0.975$ GeV. For the latter we find $\Delta a^{\pi\pi}_\mu = (387.2\pm0.5_{\rm stat}\pm2.4_{\rm exp}\pm2.3_{\rm th})\times 10^{-10}$
Differential cross section for E+ E- --> PI+ PI- GAMMA (GAMMA).
Total cross section for E+ E- --> PI+ PI-.
Pion form factor.
Forum