# Haut PDF Muon energy reconstruction in ANTARES and its application to the diffuse neutrino flux

### Muon energy reconstruction in ANTARES and its application to the diffuse neutrino flux

(3) IFIC (CSIC-Univ. de Valencia), apdo. 22085, E-46071 Valencia, Spain Abstract The European collaboration ANTARES aims to operate a large neutrino telescope in the Mediterranean Sea, 2400 m deep, 40 km from Toulon (France). Muon neutrinos are detected through the muon produced in charged current in- teractions in the medium surrounding the detector. The Cherenkov light emitted by the muon is registered by a 3D photomultiplier array. Muon energy can be inferred using 3 different methods based on the knowledge of the features of muon energy losses. They result in an energy resolution of a factor ∼ 2 above 1 TeV. The ANTARES sensitivity to diffuse neutrino flux models is obtained from an energy cut, rejecting most of the atmospheric neutrino background which has a softer spectrum. Fake upgoing events from downgoing atmospheric muons are rejected using dedicated variables. After 1 year of data taking, the ANTARES sensitivity is E 2
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### An algorithm for the reconstruction of high-energy neutrino-induced particle showers and its application to the ANTARES neutrino telescope

Though not yet sufficiently sensitive, the presented first shower analysis using the initial 6 years of data taken with the ANTARES neutrino telescope demonstrates the potential of ANTARES to independently confirm and com- plement the measurement of a high-energy astrophysical neutrino flux, as performed by IceCube. In order to meet this important goal, several improve- ments of the analysis have been identified and are under way. Building on the gained experience, a second shower reconstruction strategy is developed. It improves on the angular resolution and increases the shower event selection efficiency, while continuing to provide the necessary strong suppression of the atmospheric muon background. Using the track reconstruction already em- ployed in our previous searches for a diffuse flux with muon neutrinos [15, 16], an analysis combining both track-like and shower-like events is in progress. With the addition of the remaining ANTARES data until the scheduled end of its operation time in 2017, this combined search is expected to reach a sensitivity at the level of the flux discovered by IceCube [4].
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### A Fast Algorithm for Muon Track Reconstruction and its Application to the ANTARES Neutrino Telescope

1. Introduction The main goal of neutrino telescope experiments such as AMANDA [1], IceCube [2], NT-200 in lake Baikal [3] and ANTARES [4] is the observation of high energy neutrinos from non-terrestrial sources. These instruments detect Cherenkov light from the passage of relativistic charged particles produced in neutrino interactions in the detector or its surrounding material. By measuring the photon arrival times at known positions, the particle trajectory can be re- constructed. The flight direction of these particles is nearly colinear with the incident neutrino direction for neutrinos above 10 TeV. The best angular resolution can be reached for ν µ , ¯ν µ charged current interactions where the measured particle is a muon that can travel several kilometres in water at TeV energies. Events induced by neutrinos from astrophysical sources must be distinguished from background which originates in the Earth’s atmosphere. Whereas atmospheric neutrinos are considered a non-reducible background (at least without the use of their energy), atmo- spheric muons can in principle be excluded by simple geometrical considerations. To exclude the contribution from downward-going atmospheric muons, it is sufficient to identify upward-going events, which can only be produced by neutrinos. This distinction requires a reliable determination of the elevation angle, because downward-going at- mospheric muons outnumber upward-going atmospheric neutrinos by 5 to 6 orders of magnitude for typical neutrino telescope installation depths.
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### Measurement of the atmospheric $\nu_e$ and $\nu_\mu$ energy spectra with the ANTARES neutrino telescope

If arriving in the detector an atmospheric muon, or a muon produced in a neutrino CC interac- tion with vertex far from the instrumented volume, induces a long sequence of hits characteristic of a long track. The track reconstruction algorithm used in off-line ANTARES analyses is called AAFit [23] and it is based on a likelihood fit that exploits a detailed parametrisation of the prob- ability density function for the time of the hits. The algorithm provides the track direction with its estimated angular uncertainty and a proxy for the muon energy loss, which can be used to estimate the parent neutrino energy. The reconstruction quality is determined by a parameter, referred to as Λ, which is based on the maximum value of the likelihood fit and the number of degrees of freedom of the fit. The AAFit method is described in [23] and in this analysis it is mainly used to remove the largest fraction of atmospheric muons in the data sample. These events are downward going and can be significantly suppressed by a combination of cuts based on the reconstructed track direction and the Λ quality parameter, as described in [24].
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### An algorithm for the reconstruction of neutrino-induced showers in the ANTARES neutrino telescope

, (14) with P shower = P (N, d, t res |shower) and P muon = P (N, d, t res |muon). These PDFs are based on the same Monte Carlo simulations mentioned in section 2 with an energy spectrum proportional to E −2 for the cosmic neutrinos that induce the showers. The likelihood function shown in equa- tion (14) was developed to achieve an optimal separation of the shower and muon distributions. This likelihood parameter can be combined with the zenith angle, reconstructed by the established muon-track ﬁtting algo- rithm [2]: On events that have been reconstructed as down-going a harder likelihood ratio cut can be applied. The distribution for this quantity plot- ted before and after the combined cut is shown in ﬁgure 8. This method further reduces the number of atmospheric muons by more than one order of magnitude. Even so, the majority of the remaining events consists still of misreconstructed atmospheric muons.
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### New constraints on all flavor Galactic diffuse neutrino emission with the ANTARES telescope

Abstract The flux of very high-energy neutrinos produced in our Galaxy by the interaction of accelerated cosmic rays with the interstellar medium is not yet determined. The characterization of this flux will shed light on Galactic accelerator features, gas distribution morphology and Galactic cosmic ray transport. The central Galactic plane can be the site of an enhanced neutrino production, thus leading to anisotropies in the extraterrestrial neutrino signal as measured by the IceCube Collaboration. The ANTARES neutrino telescope, located in the Mediterranean Sea, offers a favourable view on this part of the sky, thereby allowing for a contribution to the determination of this flux. The expected diffuse Galactic neutrino emission can be obtained linking a model of generation and propagation of cosmic rays with the morphology of the gas distribution in the Milky Way. In this paper, the so-called “Gamma model” introduced recently to explain the high-energy gamma ray diffuse Galactic emission, is assumed as reference. The neutrino flux predicted by the “Gamma model” depends of the assumed primary cosmic ray spectrum cut-off. Considering a radially-dependent diffusion coefficient, this proposed scenario is able to account for the local cosmic ray measurements, as well as for the Galactic gamma ray observations. Nine years of ANTARES data are used in this work to search for a possible Galactic contribution according to this scenario. All flavour neutrino interactions are considered. No excess of events is observed and an upper limit is set on the neutrino flux of 1.1 (1.2) times the prediction of the “Gamma model” assuming the primary cosmic ray spectrum cut-off at 5 (50) PeV. This limit excludes the diffuse Galactic neutrino emission as the major cause of the “spectral anomaly” between the two hemispheres measured by IceCube.
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### All-flavor Search for a Diffuse Flux of Cosmic Neutrinos with Nine Years of ANTARES Data

with single power law energy spectrum. Two possible spectral indexes are considered for the optimization of the event selection: Γ = 2.0 and Γ = 2.5. The most abundant background comes from penetrating atmospheric muons reaching the apparatus. The MUPAGE simulation code [20, 21] is used to produce samples of atmospheric muon bundles deep underwater. The Earth can be used as a shield to reduce the influence of these muons, by discarding events that are reconstructed as downward-going. Nonetheless, a certain amount of atmospheric muon events could still be mis-reconstructed as upward-going. A selection based on the event reconstruction quality parameters (see below) allows for a significant reduction of their amount.
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### First Search for Point Sources of High Energy Cosmic Neutrinos with the ANTARES Neutrino Telescope

ν , where E ν is the neutrino energy. The median of this angular error is 0.5 ± 0.1 degrees. For the subset of data in which the full 12-line detector was operational, the resolution is estimated to be 0.4 ± 0.1 degrees. The systematic uncertainty on this quantity has been estimated by varying the time resolution of the OMs ∆ t in the simulation. The allowed range of ∆ t is determined by requiring that the Λ distribution in the resulting simulation be compatible with the observed atmospheric neutrino events. The best agreement between data and simulation is obtained for ∆ t = 2.5 ns. Hence, this value is used for all simulations in this analysis, in particular for extracting the central value of the allowed range of angular resolutions. A time resolution of 3.4 ns is found to be incompatible with the neutrino flux model at the 2σ level, where the uncertainty is taken from Barr et al. (2006). This places an upper bound on the time resolution, which translates into a 1 σ systematic uncertainty on angular resolution of 0.1 degrees. This uncertainty incorporates, to first order, all effects which have a net result of degrading the time resolution, such as possible mis-alignments and inaccuracies in the simulation of light propagation in the water or the transit time distribution of the PMT. A similar analysis with analogous results has been performed using downgoing muon data instead of upgoing neutrino candidates.
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### First Search for Dark Matter Annihilation in the Sun Using the ANTARES Neutrino Telescope

several GeV) coming from the Sun could not be explained by other known astrophysical processes. In this paper an indirect search for dark matter by looking for high-energy neutrinos coming from the Sun, using the 2007-2008 data recorded by the ANTARES neutrino tele- scope, is reported. The layout of the paper is as follows. In Section 2 , the main features of the ANTARES neutrino telescope and the reconstruction algorithm used in this work are described. In Section 3 , the Monte Carlo simulation of the WIMP signal, the background expected from atmospheric muons and neutrinos, and the grid scan performed to explore the parameter space of the CMSSM and MSSM-7 models are reported. In Section 4 , the method used to optimise the selection of the neutrino events is described. Finally, the results obtained are discussed in Section 5 , where limits on the neutrino flux are derived from the absence of a signal coming from the Sun’s direction. The corresponding limits on the spin-dependent and the spin-independent WIMP-proton cross-sections are obtained and compared to the predictions of the CMSSM and MSSM-7 theoretical models.
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### Prompt atmospheric neutrino flux in perturbative QCD and its theoretical uncertainties

gives a ∼ 5 − 10% increase at E ν ∼ 10 5 − 10 8 GeV. With the nCTEQ15 PDF set, we can see the effect of the updated PDF is about 3 − 44% at the same energy range by comparing the charm induced fluxes with nCTEQ15-proton PDFs and the BERSS results. We also found that the result with nCTEQ15-nitrogen is less than for proton targets by ∼ 20 − 35% due to the nuclear effect. The combined effect of these factors listed above result in the muon neutrino fluxes that are 40 − 60% lower than the BERSS results. In Fig. 2, for completeness, we presented the tau
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### First combined search for neutrino point-sources in the Southern Hemisphere with the ANTARES and IceCube neutrino telescopes

the background of atmospheric muons and neutrinos only (Aartsen et al. 2013c,b). The specific origin of these events is currently unknown. Some authors propose that at least part of the flux may have a galactic origin (Ahlers et al. 2015; Anchordoqui et al. 2014a,b; Bai et al. 2014; Fox et al. 2013; Padovani & Resconi 2014; Razzaque 2013), whereas others have focused on the extragalactic component (Cholis & Hooper 2013; Kalashev et al. 2013; Roulet et al. 2013; Stecker 2013). Meanwhile the ANTARES experiment has proven the feasibility of the Cherenkov telescope technique in sea water (Adri´ an-Mart´ınez et al. 2012a, 2013b). While its instrumented volume is significantly smaller than that of IceCube, its geographical location provides a view of the Southern sky with significantly reduced background for neutrino energies below 100 TeV, and hence better sensitivity to many predicted Galactic sources of neutrinos in this part of the sky. The complementarity of the detectors with respect to Southern sky sources, due to their different geographical location, size and atmospheric muon background, allows for a gain in sensitivity by combining the analyses of data from both experiments in a joint search for point-like sources. The level of improvement depends on the details of the assumed astrophysical flux, in particular on its energy spectrum and the existence of a possible high-energy cut-off. The energy spectra are not yet known and predictions vary widely depending on the source model.
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### All-sky search for high-energy neutrinos from gravitational wave event GW170104 with the Antares neutrino telescope

2.2 Search above the Antares horizon A search for coincident neutrino candidates de- tected above the Antares horizon was carried out by selecting downgoing events with β smaller than 1 ◦ . The cuts are optimized on a com- bination of Λ and the number of hits used in the reconstruction, where a hit corresponds to a PMT signal above a given threshold. The number of hits can be considered as a proxy of the muon/neutrino energy. Indeed, downgo- ing atmospheric muons are less likely to produce a number of hits as large as that produced by very high-energy cosmic neutrinos. Anew, the selection criteria were optimized such that one event occurring within the signal time window of 1000 s and located inside the GW error box located above the Antares horizon would lead to a detection with a significance level of 3σ. The final set of cuts is chosen as the one maximizing the fraction of surviving signal events. The fi- nal sample is mostly composed of atmospheric muons with a total of 8.2 × 10 −2 background events expected above the Antares horizon within ±500 s. The median neutrino energy that would be detected by Antares for a E −2 signal spectrum is about a factor of 10 higher for this analysis compared to the search below the hori- zon described in Section 2.1 .
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### Measurement of Atmospheric Neutrino Oscillations with the ANTARES Neutrino Telescope

Downgoing atmospheric muons were simulated with the program MUPAGE [12, 13] which provides parametrised muon bundles at the detector. Upgoing neutrinos were simulated according to the parametrisation of the atmospheric ν µ flux from [14] in the energy range from 10 GeV to 10 PeV. The Cherenkov light, produced inside or in the vicinity of the detector instrumented volume, was propagated taking into account light absorption and scattering in sea water [15]. The angular acceptance, quantum efficiency and other characteristics of the PMTs were taken from [6] and the overall geometry corresponded to the layout of the ANTARES detector [2]. The optical noise was simulated from counting rates observed in the data. At the same time, the definition of active and inactive channels has been applied from data runs as well. The generated statistics corresponds to an equivalent observation time of 100 years for atmospheric neutrinos and ten months for atmospheric muons.
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### Searches for Point-like and extended neutrino sources close to the Galactic Centre using the ANTARES neutrino Telescope

equatorial coordinates RA=−46.8 ◦ and Dec=−64.9 ◦ and corresponds to a 2.2σ background fluctuation. In addition, upper limits on the flux normalization of an E −2 muon neutrino energy spectrum have been set for 50 pre-selected astrophys- ical objects. Finally, motivated by an accumulation of 7 events relatively close to the Galactic Centre in the recently reported neutrino sample of the IceCube telescope, a search for point sources in a broad region around this accumulation has been carried out. No indication of a neutrino signal has been found in the
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### Model-independent search for neutrino sources with the ANTARES neutrino telescope

Abstract A novel method to analyse the spatial distribution of neutrino candi- dates recorded with the ANTARES neutrino telescope is introduced, searching for an excess of neutrinos in a region of arbitrary size and shape from any direction in the sky. Techniques originating from the domains of machine learning, pattern recognition and image process- ing are used to purify the sample of neutrino candidates and for the analysis of the obtained skymap. In contrast to a dedicated search for a specific neutrino emission model, this approach is sensitive to a wide range of possible morphologies of potential sources of high-energy neu- trino emission. The application of these methods to ANTARES data yields a large-scale excess with a post-trial significance of 2.5σ. Applied to public data from IceCube in its IC40 configuration, an excess con- sistent with the results from ANTARES is observed with a post-trial significance of 2.1σ.
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### Monte Carlo simulations for the ANTARES underwater neutrino telescope

The bulk of primary cosmic rays arriving at the top of the atmosphere has been represented with five groups of nuclei: protons, He, the C, N and O group, the Mg and Si group and Fe, produced according to a power law E −2 over an energy range between 1 and 10 5 TeV/nucleon and zenith angles from 0 ◦ to 85 ◦ . A total number of showers larger than 10 10 has been simulated. All muons from showers reaching the sea level with energies larger than about 500 GeV are transported to the detector using the program MUSIC [54], a 3-dimensional muon propagator accounting for the main processes of muon energy loss. The properties of each muon hitting the can surface are registered for future processing. Each event has a weight accounting for the spectrum used in the generation. This allows the application of a reweight- ing procedure at the analysis stage to account for chemical composition of the primary cosmic rays. Different hypotheses for the primary cosmic ray composition have been considered [52].
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### First all-flavor neutrino pointlike source search with the ANTARES neutrino telescope

from the vertical axis of the detector (R sh < 300 m) and on the vertical distance above the centre of the detector (|Z sh | < 250 m ) are applied. RDF. A different shower reconstruction algorithm was originally developed for diffuse flux anal- yses [18]. Among all available quality parameters provided by this reconstruction chain, a subset of five parameters that showed a high potential to separate atmospheric muon tracks from shower events was chosen as input in a Random Decision Forest (RDF ) classification. The distribution of the RDF parameter for cosmic neutrinos and atmospheric muons and neutrinos after applying the cuts prior to the RDF cut is shown in Figure 12-left. Only shower events with RDF > 0.3 are used in this analysis.
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### Measurement of the atmospheric muon flux with a 4 GeV threshold in the ANTARES neutrino telescope

5. Summary A simple method for the determination of the atmospheric muon ﬂux and its dependence on depth in the ANTARES neutrino telescope has been presented. The method is based on the mea- surement of photon coincidences between adjacent storeys and has a low energy detection threshold. The atmospheric muon ﬂux has been measured in the depth range from 2030 to 2380 m with a step of 14.5 m using a combined data sample of 5 and 10 line detector conﬁgurations. The data have been corrected for the pres- ence of dead channels and unequal efﬁciencies of the PMTs, which were measured with a novel calibration technique using the natu- ral radioactivity of sea water. A reasonable agreement is found be- tween our data and Monte Carlo simulations.
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### Search for a diffuse flux of high-energy νμ with the ANTARES neutrino telescope

Systematic uncertainties on the expected number of back- ground events in the high energy region (R  1 . 31) include: (i) the contribution of prompt neutrinos, estimated as + − 1 0 . . 7 3 events. In the following, the largest value is conservatively used. (ii) The uncer- tainties from the neutrino ﬂux from charged meson decay as a function of the energy. By changing the atmospheric neutrino spec- tral index by ± 0 . 1, both below and above ∼ 10 TeV (when the conventional neutrino ﬂux has spectral index one power steeper than that of the primary CR below and after the knee, respec- tively), the relative number of events for R  1 . 31 changes at most by ± 1 . 1, keeping in the region R < 1 . 31 the number of MC events equal to the number of data. The migration from the Bartol to the Honda MC [22] produces a smaller effect. The uncertainties on the detector eﬃciency (including the angular acceptance of the optical module [14] , water absorption and scattering length, trigger sim- ulation and the effect of PMT afterpulses) amount to 5% after the normalization to the observed atmospheric ν μ background in the test region.
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### Constraining the contribution of Gamma-Ray Bursts to the high-energy diffuse neutrino flux with 10 yr of ANTARES data

The stochastic nature of GRBs, in addition with the complex dynamical evolution of the jet, makes it hard to reliably determine a bulk Lorentz factor. In the previous ANTARES search, as well as in several IceCube searches, a default value of Γ = 316 was used ( Adrián-Martínez et al. , 2013 ). In Fig. A.11(a) the stacking fluence obtained in this work is compared with the previous ANTARES estimation, both computed with one- zone modelling of NeuCosmA. However, in this work, a novel method for the estimation of Γ is presented, consisting into exploiting the observed correlation among Γ and the burst’s isotropic luminosity, as found by Lü et al. 2012 and reported in Eq. ( 2 ). Nonetheless, such a correlation cannot be used straightforwardly in most of the cases, since it would require the knowledge of the redshift for each GRB of the sample. Unfortunately redshift is unknown in 90 per cent of the cases: in this situation, for each GRB with 𝑧 not measured, up to 1000 values of redshift are randomly extracted from a redshift distribution that follows that of long GRBs detected since 2005 by the Swift satellite (see Fig. 2 ). Then, from such 1000 values of 𝑧, 1000 values of bulk Lorentz factor are calculated through Eq. ( 2 ). By averaging the resulting 1000 values of Γ for an individual GRB, hΓi is obtained. The resulting cumulative neutrino fluence is shown in Fig. A.21(a) , where it is also compared with the expected neutrino fluence estimated by the previous ANTARES analysis ( Adrián-Martínez et al. , 2013 ). The two are observed at a comparable level, even though the latest analysis has more than twice more sources than the previous. This result is in fact a consequence of the neutrino modeling adopted: while past predictions tended to overestimate the expected flux by assuming standard values for model parameters, here an accurate modeling is realized by accounting for variations in these parameters reflecting the properties of observed GRBs. An example is given in Fig. A.21(b) , where the distribution of the hΓi values obtained for each burst is shown and compared with the standard value used in the past. The obtained distribution peaks at a value lower than Γ = 316.
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