Cross section and analyzing power of pol{p}p -> pn pi+ near threshold

The cross section and analyzing power of the pol{p}p -> pn pi+ reaction near threshold are estimated in terms of data obtained from the pol{p}p -> d pi+ and pp -> pp pi0 reactions. A simple final state interaction theory is developed which depends weakly upon the form of the pion-production operator and includes some Coulomb corrections. Within the uncertainties of the model and the input data, the approach reproduces well the measured energy dependence of the total cross section and the proton analyzing power at a fixed pion c.m. angle of 90deg, from threshold to T_p = 330 MeV. The variation of the differential cross section with pion angle is also very encouraging.Comment: 20 pages, Latex including 4 eps figure

Chiral Perturbation Theory and the pp -> pp pi0 Reaction Near Threshold

A chiral-perturbative consideration of the near-threshold pp -> pp pi0 reaction indicates that the pion-rescattering term has a substantial energy and momentum dependence. The existing calculations that incorporate this dependence give pion rescattering contributions significantly larger than those of the conventional treatment, and this enhanced rescattering term interferes destructively with the one-body impulse term, leading to theoretical cross sections that are much smaller than the observed values. However, since the existing calculations are based on coordinate-space representation, they involve a number of simplifying assumptions about the energy-momentum flow in the rescattering diagram, even though the delicate interplay between the one-body and two-body terms makes it desirable to avoid these kinematical assumptions. We carry out here a momentum-space calculation that retains the energy-momentum dependence of the vertices as predicted by chiral perturbation theory. Our improved treatment increases the rescattering amplitude by a factor of 3 over the value obtained in the r-space calculations. The pp -> pp pi0 transition amplitude, which is now dominated by the rescattering term, leads to the cross section much larger than what was reported in the approximate r-space calculations. Thus, the extremely small cross sections obtained in the previous chiral perturbative treatments of this reaction should be considered as an accidental consequence of the approximations employed rather than a general feature.Comment: 25 pages,REVTEX, 5 ps figure

Virtual-pion and two-photon production in pp scattering

Two-photon production in pp scattering is proposed as a means of studying virtual-pion emission. Such a process is complementary to real-pion emission in pp scattering. The virtual-pion signal is embedded in a background of double-photon bremsstrahlung. We have developed a model to describe this background process and show that in certain parts of phase space the virtual-pion signal gives significant contribution. In addition, through interference with the two-photon bremsstrahlung background, one can determine the relative phase of the virtual-pion process

Evidence for CP Violation in B0 -> D+D- Decays

We report measurements of the branching fraction and CP violation parameters in B0 -> D+D- decays. The results are based on a data sample that contains 535 x 10^6 BBbar pairs collected at the Upsilon(4S) resonance, with the Belle detector at the KEKB asymmetric-energy e+e- collider. We obtain [1.97 +- 0.20 (stat) +- 0.20 (syst)] x 10^(-4) for the branching fraction of B0 -> D+D-. The measured values of the CP violation parameters are: S = -1.13 +- 0.37 +- 0.09, A = 0.91 +- 0.23 +- 0.06, where the first error is statistical and the second is systematic. We find evidence of CP violation in B0 -> D+D- at the 4.1 sigma confidence level. While the value of S is consistent with expectations from other measurements, the value of the parameter A favors large direct CP violation at the 3.2 sigma confidence level, in contradiction to Standard Model expectations.Comment: 12 pages, 3 figures, submitted to PR

First results on light readout from the 1-ton ArDM liquid argon detector for dark matter searches

ArDM-1t is the prototype for a next generation WIMP detector measuring both the scintillation light and the ionization charge from nuclear recoils in a 1-ton liquid argon target. The goal is to reach a minimum recoil energy of 30\,keVr to detect recoiling nuclei. In this paper we describe the experimental concept and present results on the light detection system, tested for the first time in ArDM on the surface at CERN. With a preliminary and incomplete set of PMTs, the light yield at zero electric field is found to be between 0.3-0.5 phe/keVee depending on the position within the detector volume, confirming our expectations based on smaller detector setups.Comment: 14 pages, 10 figures, v2 accepted for publication in JINS

Measurements of Branching Fractions and Polarization in B > K^* rho Decays

We present results of a study of the charmless vector-vector decays B^0 -> K^{*0} rho^0 and B^+ ->K^{*0} rho^+. The results are based on a 140 fb^{-1} data sample collected by the Belle detector at the KEKB asymmetric e^+e^- collider. We obtain the branching fraction B(B^+ -> K^{*0} rho^+)=(6.6 +- 2.2(stat.) +- 0.8 (syst.)) x 10^{-6}, and set upper limits on the branching fractions B(B^0 -> K^{*0} rho^0) f_0(980) K^{*0})<5.2 x 10^{-6}. We also perform a helicity analysis of the rho and K^* vector mesons in the decay B^+ -> K^{*0} rho^+, and obtain the longitudinal polarization fraction R_0(B^+ -> K^{*0} rho^+)=0.50 +- 0.19(stat.)+0.05-0.07}(syst.).Comment: 11 pages, 4 figures, submitted to ICHEP04, Beijing, Chin

Observation of B+->Lambda_c+Lambda_c-K+ and B0->Lambda_c+Lambda_c^-K0 decays

We report first measurements of the doubly charmed baryonic B decays B->Lambda_c+Lambda_c-K. The B+->Lambda_c+Lambda_c-K+ decay is observed with a branching fraction of (6.5+1.0-0.9+-1.1+-3.4)x10^{-4} and a statistical significance of 15.4sigma. The B0->Lambda_c+Lambda_c-K0 decay is observed with a branching fraction of (7.9+2.9-2.3+-1.2+-4.2)x10^{-4} and a statistical significance of 6.6sigma. The branching fraction errors are statistical, systematic, and the error resulting from the uncertainty of Lambda_c+->pK-pi+ decay branching fraction. The analysis is based on 357fb-1 of data accumulated at the Y(4S) resonance with the Belle detector at the KEKB asymmetric e+e- collider.Comment: 10 pages, 3 figure

Observation of b --> d gamma and Determination of |V_td/V_ts|

We report the observation of the flavor-changing neutral current process b --> d gamma using a sample of 386*10^6 B meson pairs accumulated by the Belle detector at the KEKB e+ e- collider. We measure branching fractions for the exclusive modes B- --> rho- gamma, B0bar --> rho0 gammaand B0bar --> omega gamma. Assuming that these three modes are related by isospin, we find Br(B --> (rho,omega) gamma) = (1.32 +0.34-0.31(stat.) +0.10-0.09(syst.)) * 10^-6 with a significance of 5.1 sigma. This result is used to determine the ratio of CKM matrix elements |V_td/V_ts| to be 0.199 +0.026-0.025(exp.) +0.018-0.015(theo.).Comment: 5 pages, 2 figures, submitted to Physical Review Letter

Time-Dependent CP Asymmetries in B0 -> Ks pi0 gamma transitions

We report measurements of CP violation parameters in B0->Ks pi0 gamma transitions based on a data sample of 535x10^6 BB pairs collected with the Belle detector at the KEKB asymmetric-energy e+ e- collider. One neutral B meson is fully reconstructed in the B0->Ks pi0 gamma mode. The flavor of the accompanying B meson is identified from its decay products. For a Ks pi0 invariant mass up to 1.8 GeV/c^2, we obtain S = -0.10 +- 0.31 +- 0.07 and A = -0.20 +- 0.20 +- 0.06. For a Ks pi0 invariant mass near the K*0(892) resonance, we obtain S = -0.32 +0.36-0.33 +-0.05 and A=-0.20 +-0.24 +-0.05.Comment: 6 pages, 3 figures, accepted by PR