We study the process e + e − → e + e − η ′ in the double-tag mode and measure for the first time the γ * γ * → η ′ transition form factor F η′ ( Q 2 1 , Q 2 2 ) in the momentum-transfer range 2 < Q 2 ...1 , Q 2 2 < 60 GeV 2 . The analysis is based on a data sample corresponding to an integrated luminosity of around 469 fb − 1 collected at the PEP-II e + e − collider with the BABAR detector at center-of-mass energies near 10.6 GeV.
Observations of the Crab nebula with HESS Aharonian, F.; Akhperjanian, A. G.; Bazer-Bachi, A. R. ...
Astronomy and astrophysics (Berlin),
10/2006, Letnik:
457, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Context.The Crab nebula was observed with the HESS stereoscopic Cherenkov-telescope array between October 2003 and January 2005 for a total of 22.9 h (after data quality selection). This period of ...time partly overlapped with the commissioning phase of the experiment; observations were made with three operational telescopes in late 2003 and with the complete 4 telescope array in January–February 2004 and October 2004–January 2005. Aims.Observations of the Crab nebula are discussed and used as an example to detail the flux and spectral analysis procedures of HESS. The results are used to evaluate the systematic uncertainties in HESS flux measurements. Methods.The Crab nebula data are analysed using standard HESS analysis procedures, which are described in detail. The flux and spectrum of γ-rays from the source are calculated on run-by-run and monthly time-scales, and a correction is applied for long-term variations in the detector sensitivity. Comparisons of the measured flux and spectrum over the observation period, along with the results from a number of different analysis procedures are used to estimate systematic uncertainties in the measurements. Results.The data, taken at a range of zenith angles between $45^{\circ}$ and $65^{\circ}$, show a clear signal with over 7500 excess events. The energy spectrum is found to follow a power law with an exponential cutoff, with photon index $\Gamma = 2.39$ ± $0.03_{{\rm {stat}}}$ and cutoff energy $E_{\rm c} = (14.3 \pm 2.1_{{\rm {stat}}})~{\rm TeV}$ between 440 GeV and 40 TeV. The observed integral flux above 1 TeV is $(2.26 \pm 0.08_{{\rm {stat}}}) \times 10^{-11}~{{\rm cm}^{-2}~{\rm s}^{-1}}$. The estimated systematic error on the flux measurement is estimated to be 20%, while the estimated systematic error on the spectral slope is 0.1.
We present improved measurements of CP-violation parameters in the decays B super(0) arrow right pi super(+)pi super(-), B super(0) arrow right K super(+)pi super(-), and B super(0) arrow right pi ...super(0)pi super(0), and of the branching fractions for B super(0) arrow right pi super(0)pi super(0) and B super(0) arrow right K super(0)pi super(0). The results are obtained with the full data set collected at the Upsilon(4S) resonance by the BABAR experiment at the PEP-II asymmetric-energy B factory at the SLAC National Accelerator Laboratory, corresponding to (467 + or - 5) x 10 super(6) BB pairs. We find the CP-violation parameter values and branching fractions: S sub(pi+pi-) = -0.68 + or - 0.10 + or - 0.03, C sub(pi+pi-) = -0.25 + or - 0.08 + or - 0.02, (ProQuest: Formulae and/or non-USASCII text omitted), C sub(pi0pi0) = -0.43 + or - 0.26 + or - 0.05, Bernoulli(B super(0) arrow right pi super(0)pi super(0)) = (1.83 + or - 0.21 + or - 0.13) x 10 super(-6), Bernoulli(B super(0) arrow right K super(0)pi super(0)) = (10.1 + or - 0.6 + or - 0.4) x 10 super(-6), where in each case, the first uncertainties are statistical and the second are systematic. We observe CP violation with a significance of 6.7 standard deviations for B super(0) arrow right pi super(+)pi super(-) and 6.1 standard deviations for B super(0) arrow right K super(+)pi super(-), including systematic uncertainties. Constraints on the unitarity triangle angle alpha are determined from the isospin relations among the B arrow right pipi rates and asymmetries. Considering only the solution preferred by the Standard Model, we find alpha to be in the range 71degrees, 109degrees at the 68% confidence level.
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