Highly-parallelized simulation of a pixelated LArTPC on a GPU

The rapid development of general-purpose computing on graphics processing units (GPGPU) is allowing the implementation of highly-parallelized Monte Carlo simulation chains for particle physics experiments. This technique is particularly suitable for the simulation of a pixelated charge readout for time projection chambers, given the large number of channels that this technology employs. Here we present the first implementation of a full microphysical simulator of a liquid argon time projection chamber (LArTPC) equipped with light readout and pixelated charge readout, developed for the DUNE Near Detector. The software is implemented with an end-to-end set of GPU-optimized algorithms. The algorithms have been written in Python and translated into CUDA kernels using Numba, a just-in-time compiler for a subset of Python and NumPy instructions. The GPU implementation achieves a speed up of four orders of magnitude compared with the equivalent CPU version. The simulation of the current induced on 10^3 pixels takes around 1 ms on the GPU, compared with approximately 10 s on the CPU. The results of the simulation are compared against data from a pixel-readout LArTPC prototype

A study of time-dependent CP-violating asymmetries in B0→J/ψKS0B^{0} \to J/\psi K^{0}_{S} and B0→ψ(2S)KS0B^{0} \to \psi(2S) K^{0}_{S} decays

We present a preliminary measurement of time-dependent CP-violating asymmetries in B0 -> J/psi K0S and B0 -> psi(2S) K0S decays recorded by the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC. The data sample consists of 9.0 fb-1 collected at the Y(4S) resonance and 0.8 fb-1 off-resonance. One of the neutral B mesons, produced in pairs at the Y(4S), is fully reconstructed. The flavor of the other neutral B meson is tagged at the time of its decay, mainly with the charge of identified leptons and kaons. A neural network tagging algorithm is used to recover events without a clear lepton or kaon tag. The time difference between the decays is determined by measuring the distance between the decay vertices. Wrong-tag probabilities and the time resolution function are measured with samples of fully-reconstructed semileptonic and hadronic neutral B final states. The value of the asymmetry amplitude, sin2beta, is determined from a maximum likelihood fit to the time distribution of 120 tagged B0 -> J/psi K0S and B0 -> psi(2S) K0S candidates to be sin2beta = 0.12+/-0.37 (stat) +/- 0.09 (syst) (preliminary)

Measurement of the B0B^{0} meson properties using partially reconstructed B0→D∗−π+B^{0} \to D^{*-}\pi^{+} and B0→D∗−l+νB^{0} \to D^{*-}l^{+}\nu decay with the BABAR detector

The two B^0 decay processes B^0 --> D^{*-}pi^+ and B^0 --> D^{*-}l^+nu have been studied by means of a partial reconstruction technique using a data sample collected with the BABAR detector at the PEP-II storage ring. To increase statistics, only the soft pi^- from the decay D^{*-} --> pi^-D^0 was used in association with either an oppositely-charged high-momentum pion or lepton. Events were then identified by exploiting the constraints from the simple kinematics of Y(4S) decays. A clear signature is obtained in each case. The position of the B^0 decay point was obtained from the reconstructed pi^+(l^+)pi^- vertex. The position of the other anti-B^0 in the event was also determined. Taking advantage of the boost given to the Y(4S) system by the asymmetric beam energies of PEP-II, the lifetime of the B^0 meson has been measured from the separation distance between the two vertices along the beam direction. The preliminary results are tau_B0 = 1.55+/-0.05+/-0.07 ps, tau_B0 = 1.62+/-0.02+/-0.09 ps, respectively for the B^0 --> D^{*-}pi^+ and B^0 --> D^{*-}l^+nu channels

Search for B+→K+l+l−B^{+} \to K^{+}l^{+}l^{-} and B0→K∗0l+l−B^{0} \to K^{*0}l^{+}l^{-}

Using a sample of 3.7 x 10^{6} Y(4S) --> B-anti-B events collected with the BABAR detector at the PEP-II storage ring, we search for the electroweak penguin decays B^+ --> K^+e^+e^-, B^+ --> K^+mu^+mu^-, B^0 --> K^{*0)e^+e^-, and B^0 --> K^{*0)mu^+mu^-. We observe no significant signals for these modes and set preliminary 90% C.L. upper limits of B(B^+ --> K^+e^+e^-) 12.5 x 10^{-6}, B(B^+ --> K^+mu^+mu^-) 8.3 x 10^{-6}, B(B^0 --> K^{*0)e^+e^-) 24.1 x 10^{-6}, B(B^0 --> K^{*0)mu^+mu^-) 24.5 x 10^{-6}

Study of inclusive DS(∗)+/−D_S^{(*)+/-} production in B decays and measurement of B0→D∗−DS(∗)+B^0 \to D^{*-}D_S^{(*)+} decays using a partial reconstruction technique

Electron-positron annihilation data collected by the BABAR detector near the Y(4S) resonance are used to study the inclusive decay of B mesons to D_S^(+/-) and D_S^(*+/-) mesons, where the D_S^(+/-) is reconstructed using the decay D_S^(+/-) --> phi pi^(+/-). The production fraction of inclusive D_S^((*)+/-) and the corresponding momentum spectra have been determined. The exclusive decays B^0 --> D^(*-)D_S^((*)+) are observed with a partial reconstruction technique which uses the soft pion from the D^(*+/-) decay in association with the reconstructed D_S^((*)+/-). The beam energy constraint is used to determine the missing mass recoiling against the D_S^(+/-) system, showing a clear signal for this process. From the observed rates, preliminary results for the corresponding branching fractions have been obtained

A measurement of the charged and neutral B meson lifetimes using fully reconstructed decays

Data collected with the BABAR detector at the PEP-II asymmetric B Factory at SLAC are used to study the lifetimes of the B^0 and B^+ mesons. The data sample consists of 7.4 fb-1 collected near the Y(4S) resonance. B^0 and B^+ mesons are fully reconstructed in several exclusive hadronic decay modes to charm and charmonium final states. The B lifetimes are determined from the flight length difference between the two B mesons which are pair-produced in the Y(4S) decay. The preliminary measurements of the lifetimes are tau_B0 = 1.506+/-0.052(stat)+/-0.029(syst) ps, tau_B+ = 1.602+/-0.049(stat)+/-0.035(syst) ps, and of their ratio is tau_B+/tau_B0 = 1.065+/-0.044(stat)+/-0.021(syst

Measurement of branching fractions for two-body charmless B decays to charged pions and kaons at BABAR

We present preliminary results of a search for charmless two-body B decays to charged pions and kaons using data collected by the BABAR detector at the Stanford Linear Accelerator Center's PEP-II storage ring. In a sample of 8.8 million produced B-anti-B pairs we measure the branching fractions B(B^0 --> pi^+pi^-) = (9.3^{+2.6}_{-2.3}^{+1.2}_{-1.4}) x 10^{-6} and B(B^0 --> K^+\pi^-) = (12.5^{+3.0}_{-2.6}^{+1.3}_{-1.7}) x 10^{-6}, where the first uncertainty is statistical and the second is systematic. For the decay B^0 --> K^+K^- we find no significant signal and set an upper limit of B(B^0 --> K^+K^-) 6.6 x 10^{-6} at the 90% confidence level