Abstract: We study the processes e(+)e(-) -> K+K-pi(+)pi(-)gamma, K+K-pi(0)pi(0)gamma, and K+K-K+K-gamma, where the photon is radiated from the initial state. About 84000, 8000, and 4200 fully reconstructed events, respectively, are selected from 454 fb(-1) of BABAR data. The invariantmass of the hadronic final state defines the e(+)e(-) center-of- mass energy, so that the K+K-pi(+)pi(-)gamma data can be compared with direct measurements of the e(+)e(-) -> K+K-pi(+)pi(-) reaction. No directmeasurements exist for the e(+)e(-) -> K+K-pi(0)pi(0) or e(+)e(-) -> K+K-K+K- reactions, andwe present an update of our previous result based on a data sample that is twice as large. Studying the structure of these events, we find contributions froma number of intermediate states and extract their cross sections. In particular, we perform a more detailed study of the e(+)e(-) -> phi(1020)pi pi gamma reaction and confirm the presence of the Y(2175) resonance in the phi(1020)integral(0)(980) and K+K-integral(0)(980) modes. In the charmonium region, we observe the J/psi in all three final states and in several intermediate states, as well as the psi(2S) in some modes, and measure the corresponding products of branching fraction and electron width.

Abstract: We present evidence of non-excimer-based secondary scintillation in gaseous xenon, obtained using both the NEXT-White time projection chamber (TPC) and a dedicated setup. Detailed comparison with first-principle calculations allows us to assign this scintillation mechanism to neutral bremsstrahlung (NBrS), a process that is postulated to exist in xenon that has been largely overlooked. For photon emission below 1000 nm, the NBrS yield increases from about 10(-2) photon/e(-) cm(-1) bar(-1) at pressure-reduced electric field values of 50 V cm(-1) bar(-1) to above 3 x 10(-1) photon/e(-) cm(-1) bar(-1) at 500 V cm(-1) bar(-1). Above 1.5 kV cm(-1) bar(-1), values that are typically employed for electroluminescence, it is estimated that NBrS is present with an intensity around 1 photon/e(-) cm(-1) bar(-1), which is about 2 orders of magnitude lower than conventional, excimer-based electroluminescence. Despite being fainter than its excimeric counterpart, our calculations reveal that NBrS causes luminous backgrounds that can interfere, in either gas or liquid phase, with the ability to distinguish and/or to precisely measure low primary-scintillation signals (S1). In particular, we show this to be the case in the "buffer region, where keeping the electric field below the electroluminescence threshold does not suffice to extinguish secondary scintillation. The electric field leakage in this region should be mitigated to avoid intolerable levels of NBrS emission. Furthermore, we show that this new source of light emission opens up a viable path toward obtaining S2 signals for discrimination purposes in future single-phase liquid TPCs for neutrino and dark matter physics, with estimated yields up to 20-50 photons/e(-) cm(-1).

Abstract: We search for single-photon decays of the Gamma(1S) resonance, Gamma -> gamma + invisible, where the invisible state is either a particle of definite mass, such as a light Higgs boson A(0), or a pair of dark matter particles, chi(chi) over bar. Both A(0) and chi are assumed to have zero spin. We tag Gamma(1S) decays with a dipion transition Gamma(1S) -> pi(+)pi(-)Y(1S) and look for events with a single energetic photon and significant missing energy. We find no evidence for such processes in the mass range m(A0) <= 9.2 GeV and m(chi) <= 4.5 GeV in the sample of 98 x 10(6) Gamma(2S) decays collected with the BABAR detector and set stringent limits on new physics models that contain light dark matter states.