Neutrino Reconstruction Research Articles

Vectorised Neutrino Reconstruction by Computing Graphs

Many particle physics analyses are adopting the concept of vectorised computing, often making them increasingly performant and resource-efficient. While a variety of computing steps can be vectorised directly, some calculations are challenging to implement. One of these is the analytical neutrino reconstruction which involves fitting that naturally varies between events. We show a vectorised implementation of the analytical neutrino reconstruction using a graph computing model. It uses established deep learning software libraries and is natively portable to local and external hardware accelerators such as GPUs. Using the example of ttH events with a semi-leptonic final state, we present performance studies for our implementation.

Complex analysis of Askaryan radiation: A fully analytic model in the time domain

The detection of ultra-high-energy (UHE, $\ensuremath{\ge}10\text{ }\text{ }\mathrm{PeV}$) neutrinos via detectors designed to utilize the Askaryan effect has been a long-time goal of the astroparticle physics community. The Askaryan effect describes radio-frequency radiation from high-energy cascades. When a UHE neutrino initiates a cascade, cascade properties are imprinted on the radiation. Thus, observed radiation properties must be used to reconstruct the UHE neutrino event. Analytic Askaryan models have three advantages when used for UHE neutrino reconstruction. First, cascade properties may be derived from the match between analytic function and observed data. Second, analytic models minimize computational intensity in simulation packages. Third, analytic models can be embedded in firmware to enhance the real-time sensitivity of detectors. We present a fully analytic Askaryan model in the time domain for UHE neutrino-induced cascades in dense media that builds upon prior models in the genre. We then show that our model matches semianalytic parametrizations used in Monte Carlo simulations for the design of IceCube-Gen2. We find correlation coefficients greater than 0.95 and fractional power differences $<5%$ between the fully analytic and semianalytic approaches.

Polarized vector boson scattering in the fully leptonic WZ and ZZ channels at the LHC

Isolating the scattering of longitudinal weak bosons at the LHC is an important tool to probe the ElectroWeak Symmetry Breaking mechanism. Separating polarizations of W and Z bosons is complicated, because of non resonant contributions and interference effects. Additional care is necessary when considering Z bosons, due to the γ/Z mixing in the coupling to charged leptons. We propose a method to define polarized signals in ZZ and W+Z scattering at the LHC, which relies on the separation of weak boson polarizations at the amplitude level in Monte Carlo simulations. After validation in the absence of lepton cuts, we investigate how polarized distributions are affected by a realistic set of kinematic cuts (and neutrino reconstruction, when needed). The total and differential polarized cross sections computed at the amplitude level are well defined, and their sum reproduces the full results, up to non negligible but computable interference effects which should be included in experimental analyses. We show that polarized cross sections computed using the reweighting method are inaccurate, particularly at large energies. We also present two procedures which address the model independent extraction of polarized components from LHC data, using Standard Model angular distribution templates.

Prospect for measuring theCPphase in thehττcoupling at the LHC

The search for a new source of CP violation is one of the most important endeavors in particle physics. A particularly interesting way to perform this search is to probe the CP phase in the $h\tau\tau$ coupling, as the phase is currently completely unconstrained by all existing data. Recently, a novel variable $\Theta$ was proposed for measuring the CP phase in the $h\tau\tau$ coupling through the $\tau^\pm \to \pi^\pm \pi^0 \nu$ decay mode. We examine two crucial questions that the real LHC detectors must face, namely, the issue of neutrino reconstruction and the effects of finite detector resolution. For the former, we find strong evidence that the collinear approximation is the best for the $\Theta$ variable. For the latter, we find that the angular resolution is actually not an issue even though the reconstruction of $\Theta$ requires resolving the highly collimated $\pi^\pm$'s and $\pi^0$'s from the $\tau$ decays. Instead, we find that it is the missing transverse energy resolution that significantly limits the LHC reach for measuring the CP phase via $\Theta$. With the current missing energy resolution, we find that with $\sim 1000\,\textrm{fb}^{-1}$ the CP phase hypotheses $\Delta = 0^\circ$ (the standard model value) and $\Delta = 90^\circ$ can be distinguished, at most, at the 95\% confidence level.

Radio frequency birefringence in south polar ice and implications for neutrino reconstruction

Using a bistatic radar echo sounding (RES) system developed for calibration of the RICE particle astrophysics experiment at the South Pole, we have studied radio frequency (RF) reflections off the bedrock. The total propagation time of ∼ns-duration, vertically ( z ˆ ) broadcast radio signals, as a function of polarization orientation in the horizontal plane, provides a direct probe of the geometry-dependence of the ice permittivity to a depth of 2.8 km. We observe clear birefringent asymmetries along z ˆ in the lowest half of the ice sheet, at a fractional level ∼0.3%. This result is in contrast to expectations based on measurements at Dome Fuji, for which birefringence was observed in the upper 1.5 km of the ice sheet. This effect, combined with the increased radio frequency attenuation expected near the bedrock, renders the lower half thickness of South Polar ice less favorable than the upper half of the ice sheet in terms of its ultra-high energy neutrino detection potential.

The physics impact of proton track identification in future megaton-scale water Cherenkov detectors

In this paper, we investigate the impact in future megaton-scale water Cherenkov detectors of identifying proton Cherenkov rings. We estimate the expected event rates for detected neutral current and charged current quasi-elastic neutrino interactions from atmospheric neutrinos in a megaton-scale Super-Kamiokande-like detector with both 40% and 20% photo-cathode coverage. With this sample we examine the prospects for measuring the neutrino oscillation pattern, and searching for sterile neutrinos. We also determine the size of selected charged current quasi-elastic samples in a 300-kton fiducial volume Super-Kamiokande-like detector from examples of both conventional super-beams and beta-beams proposed in the literature. With these samples, it is shown that full kinematic neutrino reconstruction using the outgoing proton can improve the reconstructed energy resolution, and give good neutrino versus anti-neutrino tagging capabilities, adding important capabilities to water Cherenkov detectors in future projects. We determine the beam parameters necessary to make use of this technique and present distributions of neutrino and anti-neutrino selection efficiencies.

Study ofD0→π−e+νe,D+→π0e+νe,D0→K−e+νe, andD+→K¯0e+νein tagged decays of theψ(3770)resonance

Using psi(3770) --> DDbar events collected with the CLEO-c detector at the Cornell e+ e- storage ring, tagged by fully reconstructing one D meson in a hadronic decay mode, we measure absolute branching fractions and differential decay rates for D0 --> pi- e+ nu(e), D+ --> pi0 e+ nu(e), D0 --> K- e+ nu(e), and D+ --> anti-K0 e+ nu(e). The measured decay rates are used to study semileptonic form factors governing these transitions and to test unquenched Lattice QCD (LQCD) calculations. We average our results with previously published CLEO-c measurements of the same quantities using a neutrino reconstruction technique. Combining LQCD calculations of form factor absolute normalizations f+(0) and measurements of f(pi)+(0)*|Vcd| and f(K)+(0)*|Vcs|, we find |Vcd| = 0.223(8)(3)(23) and |Vcs| = 1.019(10)(7)(106), where the uncertainties are statistical, experimental systematic, and from LQCD, respectively.

Study of the DecaysD0→π−e+νe,D0→K−e+νe,D+→π0e+νe, andD+→K¯0e+νe

Using 1.8 million DDbar pairs and a neutrino reconstruction technique, we have studied the decays D^0 -> K^- e^+ nu_e, D^0 -> pi^- e^+ nu_e, D^+ -> Kbar^0 e^+ nu_e, and D^+ -> pi^0 e^+ nu_e. We find B(D^0 -> pi^- e^+ nu_e) = 0.299(11)(9)%, B(D^+ -> pi^0 e^+ nu_e) = 0.373(22)(13)%, B(D^0 -> K^- e^+ nu_e) = 3.56(3)(9)%, and B(D^+ -> Kbar^0 e^+ nu_e) = 8.53(13)(23)%. In addition, form factors are studied through fits to the partial branching fractions obtained in five q^2 ranges. By combining our results with recent unquenched lattice calculations, we obtain |Vcd| = 0.217(9)(4)(23) and |Vcs| = 1.015(10)(11)(106).

Measurement of theB0→π−l+νForm-Factor Shape and Branching Fraction, and Determination of|Vub|with a Loose Neutrino Reconstruction Technique

We report the results of a study of the exclusive charmless semileptonic decay, B0-->pi(-l)(+nu), undertaken with approximately 227 x 10(6) BB pairs collected at the Upsilon(4S) resonance with the BABAR detector. The analysis uses events in which the signal B decays are reconstructed with an innovative loose neutrino reconstruction technique. We obtain partial branching fractions in 12 bins of q2, the momentum transfer squared, from which we extract the f + (q2) form-factor shape and the total branching fraction B(B0-->pi(-l)(+nu))=(1.46+/-0.07stat+/-0.08syst) x 10(-4). Based on a recent unquenched lattice QCD calculation of the form factor in the range q2>16 GeV2, we find the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element /Vub/ to be (4.1+/-0.2stat +/- 0.2syst(+0.6)-0.4_{FF}) x 10(-3), where the last uncertainty is due to the normalization of the form factor.

Neutrino reconstruction with topological information

In general a decay with a missing (not detected) particle cannot be fully reconstructed apart from a few exceptions. For example, if the momentum of the decaying particle is known or if the missing energy in an event is measured precisely, then the missing particle 4-momentum can be determined. Here a new method is proposed that utilizes additional information about the topology of a decay: the direction from the primary to the secondary vertex combined with momentum conservation allows the determination of the missing particle momentum up to a twofold ambiguity. The semileptonic decay of the B s 0 mesons is considered as an example to illustrate this method and to compare its performance against conventional approaches.

Measurement of /V(ub)/ using inclusive B-->X(u)lnu decays with a novel X(u)-reconstruction method.

We report the measurement of an inclusive partial branching fraction for charmless semileptonic B decay and the extraction of /V(ub)/. Candidates for B-->X(u)lnu are identified with a novel X(u) reconstruction method based on neutrino reconstruction via missing 4-momentum and a technique called "simulated annealing." Based on 86.9 fb(-1) of data taken with the Belle detector, we obtain DeltaB(B-->X(u)lnu;M(X)<1.7 GeV/c2,q2>8.0 GeV2/c2)=[7.37+/-0.89(stat)+/-1.12(syst)+/-0.55(b-->c)+/-0.24(b-->u)]x10(-4) and determine |V(ub)|=[4.66+/-0.28(stat)+/-0.35(syst)+/-0.17(b-->c)+/-0.08(b-->u)+/-0.58(theory)]x10(-3).

Hadronic spectral moments in semileptonicBdecays with a lepton energy cut

We compute the first two moments $〈{(s}_{H}\ensuremath{-}{m}_{D}^{2}{)}^{1,2}〉$ of the final hadronic invariant mass in the inclusive decay $\stackrel{\ensuremath{\rightarrow}}{B}{X}_{c}\mathcal{l}\overline{\ensuremath{\nu}},$ in the presence of a cut ${E}_{\mathcal{l}}^{\mathrm{min}}$ on the charged lepton energy. These moments may be measured directly by experiments at the $\ensuremath{\Upsilon}(4S)$ using the neutrino reconstruction technique, which requires such a cut. Measurement of these moments will place constraints on the nonperturbative parameters $\overline{\ensuremath{\Lambda}}$ and ${\ensuremath{\lambda}}_{1},$ which are relevant for extracting the quark masses ${m}_{b}$ and ${m}_{c},$ as well as the CKM angle ${V}_{\mathrm{cb}}.$ We include terms of order ${\ensuremath{\alpha}}_{s}^{2}{\ensuremath{\beta}}_{0}$ and ${1/m}_{b}^{3}$ in the operator product expansion, and use the latter to estimate the theoretical uncertainty in the extraction of $\overline{\ensuremath{\Lambda}}$ and ${\ensuremath{\lambda}}_{1}.$