Search for the dark photon in pi0 decays

Abstract A sample of 1.69 7 10 7 fully reconstructed \u3c0 0 \u2192 \u3b3 e + e 12 decay candidates collected by the NA48/2 experiment at \{CERN\} in 2003\u20132004 is analyzed to search for the dark photon ( A \u2032 ) production in the \u3c0 0 \u2192 \u3b3 A \u2032 decay followed by the prompt A \u2032 \u2192 e + e 12 decay. No signal is observed, and an exclusion region in the plane of the dark photon mass m A \u2032 and mixing parameter \u3b5 2 is established. The obtained upper limits on \u3b5 2 are more stringent than the previous limits in the mass range 9 \ua0 MeV / c 2 < m A \u2032 < 70 \ua0 MeV / c 2 . The NA48/2 sensitivity to the dark photon production in the K \ub1 \u2192 \u3c0 \ub1 A \u2032 decay is also evaluated

Precise tests of low energy QCD from Ke4 decay properties

We report results from the analysis of the K\ub1 \u2192 pi+ pi 12 e\ub1 \u3bd (Ke4 ) decay by the NA48/2 collaboration at the CERN SPS, based on the total statistics of 1.13 million decays collected in 2003\u20132004. The hadronic form factors in the S- and P-wave and their variation with energy are obtained. The phase difference between the S- and P-wave states of the pion pion system is accurately measured and allows a precise determination of a00 and a02 , the I = 0 and I = 2 S-wave pion pion scattering lengths: a00 = 0.2220 \ub1 0.0128stat \ub1 0.0050syst \ub1 0.0037th , a02 = 120.0432 \ub1 0.0086stat \ub1 0.0034syst \ub1 0.0028th . Combination of this result with the other NA48/2 measurement obtained in the study of K\ub1 \u2192 pi0 pi0 pi\ub1 decays brings an improved determination of a00 and the first precise experimental measurement of a02, providing a stringent test ofChiral Perturbation Theory predictions and lattice QCD calculations. Using constraints based on analyticity and chiral symmetry, even more precise values are obtained: a00 = 0.2196 \ub1 0.0028stat \ub1 0.0020syst and a02 = 120.0444 \ub10.0007stat \ub1 0.0005syst \ub1 0.0008ChPT

Precision measurements of charmonium states formed in pp\uaf annihilation

ermilab experiment E-760 studies the resonant formation of charmonium states in proton-antiproton interactions using a hydrogen gas-jet target in the Antiproton Accumulator ring at Fermilab. Precision measurements of the mass and width of the charmonium states \u3c7c1,\u3c7c2, a direct measurement of the \u3c8\u2019 width, and a new precision measurement of the J/\u3c8 mass are presented

Study of the \u3c71 and \u3c72 charmonium states formed in p annihilations

We report on a study of the \u3c7 1( 3P 1) and \u3c7 2( 3P 1) states of charmonium formed in antiproton-proton annihilations. An energy scan through the resonances, performed with a very narrow momentum-band beam of antiprotons intersecting a hydrogen jet target, enables us to perform very precise measurements of the mass and the total width of the two resonances. From a sample of 513 \u3c7 1 and 585 \u3c7 2 events we find M \u3c71 = (3510.53 \ub1 0.13) MeV/c 2, M \u3c72 = (3556.15 \ub1 0.14) MeV/c 2, \u393 \u3c71 = (0.88 \ub1 0.14) MeV and \u393 \u3c72 = (1.98 \ub1 0.18) MeV. From our measurement of the quantity \u393(R \u2192 p\u304p) 7 BR(R \u2192 J/\u3c8\u3b3) 7 BR(J/\u3c8/ \u2192 e + e -), using known branching ratios, we obtain \u393(\u3c7 1 \u2192 p\u304p) = (69 \ub1 13) eV and \u393(\u3c7 2 \u2192 p\u304p) = (180 \ub1 31) eV

Detailed study of the K\ub1 \u2192 \u3c0 0\u3c00e\ub1\u3bd (Ke4 00) decay properties

A sample of 65210 K\ub1 \u2192 \u3c00\u3c00e\ub1\u3bd (Ke4 00) decay candidates with 1% background contamination has been collected in 2003-2004 by the NA48/2 collaboration at the CERN SPS. A study of the differential rate provides the first measurement of the hadronic form factor variation in the plane (M\u3c0\u3c0 2, Me\u3bd 2) and brings evidence for a cusp-like structure in the distribution of the squared \u3c00\u3c00 invariant mass around (Formula Presented). Exploiting a model independent description of this form factor, the branching ratio, inclusive of radiative decays, is obtained using the K\ub1 \u2192 \u3c00\u3c00\u3c0\ub1 decay mode as normalization. It is measured to be BR(Ke4 00) = (2.552 \ub1 0.010stat \ub1 0.010syst \ub1 0.032ext) 7 10 125, which improves the current world average precision by an order of magnitude while the 1.4% relative precision is dominated by the external uncertainty from the normalization mode. A comparison with the properties of the corresponding mode involving a \u3c0+\u3c0 12 pair (Ke4 + 12) is also presented