A GPU based multidimensional amplitude analysis to search for tetraquark candidates

The demand for computational resources is steadily increasing in experimental high energy physics as the current collider experiments continue to accumulate huge amounts of data and physicists indulge in more complex and ambitious analysis strategies. This is especially true in the fields of hadron spectroscopy and flavour physics where the analyses often depend on complex multidimensional unbinned maximum-likelihood fits, with several dozens of free parameters, with an aim to study the internal structure of hadrons. Graphics processing units (GPUs) represent one of the most sophisticated and versatile parallel computing architectures that are becoming popular toolkits for high energy physicists to meet their computational demands. GooFit is an upcoming open-source tool interfacing ROOT/RooFit to the CUDA platform on NVIDIA GPUs that acts as a bridge between the MINUIT minimization algorithm and a parallel processor, allowing probability density functions to be estimated on multiple cores simultaneously. In this article, a full-fledged amplitude analysis framework developed using GooFit is tested for its speed and reliability. The four-dimensional fitter framework, one of the firsts of its kind to be built on GooFit, is geared towards the search for exotic tetraquark states in the $B^0 \rightarrow J/\psi K \pi$ decays and can also be seamlessly adapted for other similar analyses. The GooFit fitter, running on GPUs, shows a remarkable improvement in the computing speed compared to a ROOT/RooFit implementation of the same analysis running on multi-core CPU clusters. Furthermore, it shows sensitivity to components with small contributions to the overall fit. It has the potential to be a powerful tool for sensitive and computationally intensive physics analyses.Comment: Replaced with the published version. Added the journal reference and the DO

Amplitude analysis of Ds+→π+π−π+D_s^{+} \rightarrow \pi^{+} \pi^{-} \pi^{+}

Utilizing the data set corresponding to an integrated luminosity of $3.19$ fb$^{-1}$ collected by the BESIII detector at a center-of-mass energy of 4.178 GeV, we perform an amplitude analysis of the $D_s^+\to\pi^+\pi^-\pi^+$ decay. The sample contains 13,797 candidates with a signal purity of $\sim$80%. The amplitude and phase of the contributing $\pi\pi$ ${\cal S}$ wave are measured based on a quasi-model-independent approach, along with the amplitudes and phases of the ${\cal P}$ and ${\cal D}$ waves parametrized by Breit-Wigner models. The fit fractions of different intermediate decay channels are also reported.Comment: 14 pages, 6 figure

Measurement of the neutral D meson mixing parameters in a time-dependent amplitude analysis of the D^0→π^+π^−π^0 decay

We perform the first measurement on the D^0−D^0 mixing parameters using a time-dependent amplitude analysis of the decay D^0→π^+π^−π^0. The data were recorded with the BABAR detector at center-of-mass energies at and near the Υ(4S) resonance, and correspond to an integrated luminosity of approximately 468.1  fb^(−1). The neutral D meson candidates are selected from D^∗(2010)^+→D^0π^+_s decays where the flavor at the production is identified by the charge of the low-momentum pion, π^+_s. The measured mixing parameters are x=(1.5±1.2±0.6)% and y=(0.2±0.9±0.5)%, where the quoted uncertainties are statistical and systematic, respectively

Fast algorithm for real-time rings reconstruction

The GAP project is dedicated to study the application of GPU in several contexts in which real-time response is important to take decisions. The definition of real-time depends on the application under study, ranging from answer time of μs up to several hours in case of very computing intensive task. During this conference we presented our work in low level triggers [1] [2] and high level triggers [3] in high energy physics experiments, and specific application for nuclear magnetic resonance (NMR) [4] [5] and cone-beam CT [6]. Apart from the study of dedicated solution to decrease the latency due to data transport and preparation, the computing algorithms play an essential role in any GPU application. In this contribution, we show an original algorithm developed for triggers application, to accelerate the ring reconstruction in RICH detector when it is not possible to have seeds for reconstruction from external trackers

{Measurement of the mixing parameters of neutral charm mesons and search for indirect \textit{\textbf{CP}} violation with \boldmathD0→KS0π+π−D^0\to K^0_S\pi^+\pi^- decays at LHCb

Mixing is the time-dependent phenomenon of a neutral meson (in this case charm meson $D^0$) changing into its anti-particle ($\bar{D}^0$) and vice versa. This occurs because the mass eigenstates, denoted $D_1$ and $D_2$ are linear combinations of the flavour eigenstates $D^0$ and $\bar{D}^0$. Mixing is governed by two parameters $x$ and $y$ defined as: $x\equiv(m_1-m_2)/\Gamma$ and $y\equiv(\Gamma_1-\Gamma_2)/(2\Gamma)$ where $\Gamma$ is the average decay width. CP-violation can occur in mixing or in the interference between mixing and decay. The CP-violation parameters $|q/p|$ and $\phi$ describe the superposition of the flavour eigenstates and the mass eigenstates: $\vert{D_{1,2}}=p\vert{D^0}\pm q\vert{\bar{D}^0}$. The self-conjugate decay $D^0\to K^0_S\pi^+\pi^-$ offers direct access to the mixing and CP-violation parameters through a time and phase-space dependent fit to the Dalitz variables and decay-time of this decay. This thesis reports a measurement of the mixing and \CP-violation parameters using data collected at the LHCb experiment in the Run 2 data-taking period in 2016-2018, corresponding to an integrated luminosity of 6~fb$^{-1}$. This analysis uses $D^0$ mesons originating from semi-leptonic $B$ meson decays. The $D^0\to K^0_S\pi^+\pi^-$ decay is modelled by expressing the three-body decay as the superposition of successive two-body decays through intermediate resonances. The blinded mixing parameters are found to be: \begin{equation*} \begin{split} x &= (x.xx \pm 0.86_{\text{stat}} \pm 0.39_{\text{syst}} \pm 0.24_{\text{model}})\times 10^{-3} \\ y &= (y.yy \pm 0.76_{\text{stat}} \pm 0.59_{\text{syst}} \pm 0.26_{\text{model}})\times 10^{-3} \end{split} \end{equation*} where the uncertainties are statistical, systematic and from the choice of amplitude model. The \CP-violation parameters are expressed in terms of $\Delta x$ and $\Delta y$ which are defined as the difference in mixing parameters measured for $D^0$ and $\bar{D}^0$: \begin{equation*} \begin{split} \Delta x &= (0.00 \pm 0.59) \times 10^{-3} \\ \Delta y &= (0.00 \pm 0.51) \times 10^{-3} \\ \end{split} \end{equation*} the uncertainties are currently statistical only and the results are blind

Amplitude analysis of the D+ → π−π+π+ decay and measurement of the π−π+ S-wave amplitude

An amplitude analysis of the D+ → π −π +π + decay is performed with a sample corresponding to 1.5 fb−1 of integrated luminosity of pp collisions at a centre-of-mass energy √ s = 8 TeV collected by the LHCb detector in 2012. The sample contains approximately six hundred thousand candidates with a signal purity of 95%. The resonant structure is studied through a fit to the Dalitz plot where the π −π + S-wave amplitude is extracted as a function of π −π + mass, and spin-1 and spin-2 resonances are included coherently through an isobar model. The S-wave component is found to be dominant, followed by the ρ(770)0π + and f2(1270)π + components. A small contribution from the ω(782) → π −π + decay is seen for the first time in the D+ → π −π +π + decay