Short-baseline Experiments Research Articles

Chasing the light sterile neutrino: status of the STEREO experiment

This article describes the status of the STEREO experiment. STEREO is a short-baseline reactor antineutrino experiment, whose primary goal is to study oscillations involving extra sterile neutrino states with Δm2 ∼ 0.1 − 1 eV, an hypothesis suggested by existing anomalies. Such hypothesis is tested by comparing antineutrino spectra in 6 identical cells located at a increasing distance from the reactor core of the ILL facility. Calibration sources have been used to characterise the detector response, perform energy reconstruction, and study the detection efficiency. Results of these studies, along with preliminary antineutrino and background rates, are reported here. STEREO has started operating in November 2016 and will collect data for 8 reactor cycles. Preliminary results based on 1.5 reactor cycles and ongoing analysis, which are mentioned here, will be released in early 2018.

Probing non-unitary CP violation effects in neutrino oscillation experiments

In the present work, we have considered minimal unitarity violation scheme to obtain the general expression for $$\nu _{\mu }\rightarrow \nu _{\tau }$$ oscillation probability in vacuum and matter. For this channel, we have investigated the sensitivities of short baseline experiments to non-unitary parameters $$|\rho _{\mu \tau }|$$ and $$\omega _{\mu \tau }$$ for normal as well as inverted hierarchical neutrino masses and $$\theta _{23}$$ being above or below maximality. We find that for normal hierarchy, the $$3\sigma$$ sensitivity of $$|\rho _{\mu \tau }|$$ is maximum for non-unitary phase $$\omega _{\mu \tau }=0$$ whereas it is minimum for $$\omega _{\mu \tau }=\pm \pi$$ . For inverted hierarchy, the sensitivity is minimum at $$\omega _{\mu \tau }=0$$ and maximum for $$\omega _{\mu \tau }=\pm \pi$$ . We observe that the sensitivity to measure non-unitarity remains unaffected for unitary CP phase $$\delta =0$$ or $$\delta =\pi /2$$ . We have, also, explored wide spectrum of L/E ratio to investigate the possibilities to observe CP-violation due to unitary ( $$\delta$$ ) and non-unitary ( $$\omega _{\mu \tau }$$ ) phases. We find that the both phases can be disentangled, in principle, from each other for $$L/E<200$$ km/GeV.

Revised neutrino-gallium cross section and prospects of BEST in resolving the gallium anomaly

O(1) eV sterile neutrino can be responsible for a number of anomalous results of neutrino oscillation experiments. This hypothesis may be tested at short base-line neutrino oscillation experiments, several of which are either ongoing or under construction. Here we concentrate on the so-called Gallium anomaly, found by SAGE and GALLEX experiments, and its foreseeable future tests with BEST experiment at Baksan Neutrino Observatory. We start with a revision of the neutrino-gallium cross section, that is performed by utilizing the recent measurements of the nuclear final state spectra. We accordingly correct the parameters of Gallium anomaly and refine the BEST prospects in testing it and searching for sterile neutrinos. We further evolve the previously proposed idea to investigate the anomaly with Zn-65 artificial neutrino source as a next option available at BEST, and estimate its sensitivity to the sterile neutrino model parameters following the Bayesian approach. We show that after the two stages of operation BEST will make 5$\sigma$-discovery of the sterile neutrinos, if they are behind the Gallium anomaly.

Measuring the sterile neutrino CP phase at DUNE and T2HK

The CP phases associated with the sterile neutrino cannot be measured in the dedicated short-baseline experiments being built to test the sterile neutrino hypothesis. On the other hand, these phases can be measured in long-baseline experiments, even though the main goal of these experiments is not to test or measure sterile neutrino parameters. In particular, the sterile neutrino phase delta _{24} affects the charged-current electron appearance data in long-baseline experiment. In this paper we show how well the sterile neutrino phase delta _{24} can be measured by the next-generation long-baseline experiments DUNE, T2HK (and T2HKK). We also show the expected precision with which this sterile phase can be measured by combining the DUNE data with data from T2HK or T2HKK. The T2HK experiment is seen to be able to measure the sterile phase delta _{24} to a reasonable precision. We also present the sensitivity of these experiments to the sterile mixing angles, both by themselves, as well as when DUNE is combined with T2HK or T2HKK.

Prospects for improved understanding of isotopic reactor antineutrino fluxes

Predictions of antineutrino fluxes produced by fission isotopes in a nuclear reactor have recently received increased scrutiny due to observed differences in predicted and measured inverse beta decay (IBD) yields, referred to as the 'reactor antineutrino flux anomaly.' In this paper, global fits are applied to existing IBD yield measurements to produce constraints on antineutrino production by individual plutonium and uranium fission isotopes. We find that fits including measurements from highly 235U-enriched cores and fits including Daya Bay's new fuel evolution result produce discrepant best-fit IBD yields for 235U and 239Pu. This discrepancy can be alleviated in a global analysis of all datasets through simultaneous fitting of 239Pu, 235U, and 238U yields. The measured IBD yield of U238 in this analysis is (7.02 +/- 1.65) x 10^-43 cm2/fission, nearly two standard deviations below existing predictions. Future hypothetical IBD yield measurements by short-baseline reactor experiments are examined to determine their possible impact on global understanding of isotopic IBD yields. It is found that future improved short-baseline IBD yield measurements at both high-enriched and low-enriched cores can significantly improve constraints for 235U, 238U, and 239Pu, providing comparable or superior precision to existing conversion- and summation-based antineutrino flux predictions. Systematic and experimental requirements for these future measurements are also investigated.

What measurements of neutrino neutral current events can reveal

We show that neutral current (NC) measurements at neutrino detectors can play a valuable role in the search for new physics. Such measurements have certain intrinsic features and advantages that can fruitfully be combined with the usual well-studied charged lepton detection channels in order to probe the presence of new interactions or new light states. In addition to the fact that NC events are immune to uncertainties in standard model neutrino mixing and mass parameters, they can have small matter effects and superior rates since all three flavours participate. We also show, as a general feature, that NC measurements provide access to different combinations of CP phases and mixing parameters compared to CC measurements at both long and short baseline experiments. Using the Deep Underground Neutrino Experiment (DUNE) as an illustrative setting, we demonstrate the capability of NC measurements to break degeneracies arising in CC measurements, allowing us, in principle, to distinguish between new physics that violates three flavour unitarity and that which does not. Finally, we show that NC measurements can enable us to restrict new physics parameters that are not easily constrained by CC measurements.

Reactor fuel fraction information on the antineutrino anomaly

We analyzed the evolution data of the Daya Bay reactor neutrino experiment in terms of short-baseline active-sterile neutrino oscillations taking into account the theoretical uncertainties of the reactor antineutrino fluxes. We found that oscillations are disfavored at 2.6σ with respect to a suppression of the 235U reactor antineutrino flux and at 2.5σ with respect to variations of the 235U and 239Pu fluxes. On the other hand, the analysis of the rates of the short-baseline reactor neutrino experiments favor active-sterile neutrino oscillations and disfavor the suppression of the 235U flux at 3.1σ and variations of the 235U and 239Pu fluxes at 2.8σ. We also found that both the Daya Bay evolution data and the global rate data are well-fitted with composite hypotheses including variations of the 235U or 239Pu fluxes in addition to active-sterile neutrino oscillations. A combined analysis of the Daya Bay evolution data and the global rate data shows a slight preference for oscillations with respect to variations of the 235U and 239Pu fluxes. However, the best fits of the combined data are given by the composite models, with a preference for the model with an enhancement of the 239Pu flux and relatively large oscillations.

Theoretical challenges in neutrino scattering studies

New and more precise measurements of neutrino cross sections in the few GeV energy region have renewed interest in a better understanding of electroweak interactions on nucleons and nuclei. This interest comes from neutrino oscillation experiments and their need to reduce systematic errors. Neutrino fluxes used in contemporary long and short baseline experiments (K2K, T2K, MINOS, NOvA, MiniBooNE, MINERvA, …) are peaked in the 1–5 GeV energy domain. In this context, I will present some details about the theoretical development in the description of (anti)neutrino-induced quasielastic scattering and the role of multi-nucleon mechanisms.

Neutrinos from a pion beam line: nuPIL

We describe a novel configuration for a neutrino beam line that can simultaneously support both long and short baseline experiments. The neutrino beams originate from pions that are first focused by a magnetic horn, as in a conventional neutrino beam. However, in the case of nuPIL, the horn is followed by a magnetic lattice that is used to select the pion charge and then transports the pions in a production straight. This produces extremely pure neutrino and anti-neutrino beams, while minimizing the amount of beam power that is transported underground for the long-baseline physics program. This configuration greatly simplifies the civil construction leading to a large cost reduction. The principles of the design of nuPIL are presented, together with tracking results and the resulting neutrino flux. The potential of the facility for CP-violation searches, in the framework of the DUNE experiment, is discussed and compared to that of an optimized beam from LBNF.

Results from the search for eV-sterile neutrinos with IceCube

The IceCube neutrino telescope at the South Pole has measured the atmospheric muon neutrino spectrum as a function of zenith angle and energy. Using IceCubes full detector configuration we have performed searches for eV-scale sterile neutrinos. Such a sterile neutrino, motivated by the anomalies observed in short-baseline experiments, is expected to have a significant effect on survival probability due to matter-induced resonant effects for energies of order 1 TeV. This effect makes this search unique and sensitive to small sterile mixing angle values. This work comprises results obtained using up-going muon neutrinos taken with one year of full detector configuration.

Light Detection System simulations for SBND

The Liquid Argon Time Projection Chamber (LArTPC) detectors are becoming the state of the art for neutrino detection and therefore play a major part in the US-based neutrino programme. LArTPCs detect primarily the ionization charge, but argon is also an excellent scintillator generating on the order of 40 000 photons per MeV of deposited energy. Until recently the scintillation light in liquid argon neutrino detectors has been mostly used as a source of trigger for beam and off-beam events, but it carries information that could be used to enhance the physics capabilities of these detectors. Newly designed short baseline experiments, in particular the Short Baseline Near-Detector - SBND, are putting significantly more focus on exploiting and developing the scintillation light capabilities of LArTPCs. This document will describe the simulation constructed for the SBND experiment to develop new applications of using scintillation light in LArTPCs that would take them beyond the state of the art of current liquid-argon detectors. We will discuss the application of scintillation light to determine timing, position and energy of neutrino events in liquid argon.

Improvements in the simulation code of the SOX experiment

The aim of the SOX experiment is to test the hypothesis of existence of light sterile neutrinos trough a short baseline experiment. Electron antineutrinos will be produced by an high activity source and detected in the Borexino experiment. Both an oscillometry approach and a conventional disappearance analysis will be performed and, if combined, SOX will be able to investigate most of the anomaly region at 95% c.l. This paper focuses on the improvements performed on the simulation code and on the techniques (calibrations) used to validate the results.

XXVII International Conference on Neutrino Physics and Astrophysics (Neutrino2016)

PrefaceThe XXVII International Conference on Neutrino Physics and Astrophysics (Neutrino 2016) was organised jointly by Imperial College London and the Institute of Physics. The conference took place at the Royal Geographical Society, South Kensington between the 4th and the 9th of July 2016. A little over 700 delegates attended the conference, a record, confirming the rising trend in attendance at the conference that is indicative of the growing international interest in the field. The 82 invited plenary presentations covered all aspects of neutrino physics, as well as the most important recent developments in astroparticle physics, astronomy and cosmology. Of the 82 plenary speakers, 20% were female, 54% hailed from European institutes, 30% were from the Americas and 15% were from Asia. One speaker was from Africa. Approximately 450 poster abstracts were received of which it was possible to accommodate 400 in four congested but vibrant poster sessions.The conference was opened by Professors T. Kajita and A. McDonald who had been awarded the Nobel Prize for Physics in 2015 in recognition of their pioneering work in the discovery of neutrino oscillations. New results were presented from all the world’s major neutrino experiments. T2K showed new data on the long-baseline oscillation of muon anti-neutrinos. Together with new data from NOvA and reactor experiments a “preference” for the violation of the matter-antimatter symmetry was reported. Observations of extra-galactic neutrinos (ICECUBE) were presented. Together with the ground-breaking evidence for gravitational waves, reviewed at the meeting, these measurements pave the way for multi-messenger astronomy.Clear evidence for an additional contribution to the neutrino spectrum at ~5 MeV was reported by all reactor neutrino experiments. Progress in the study of anomalies that may hint at the existence of sterile neutrinos was reviewed and the status of experiments that aim to determine the absolute mass scale of neutrinos was discussed. New measurements of neutrino-nucleus cross sections, including electron-neutrino-nucleus cross sections were reported. These measurements, together with advances in the theoretical description of neutrino interactions pave the way for the improved understanding necessary for present and future long- and short-baseline experiments to fulfil their potential.Major new initiatives, DUNE and SBN in the US and Hyper-K in Japan, were discussed. These experiments seek to deliver unparalleled sensitivity to the violation of the matter-antimatter symmetry in neutrino oscillations. Current neutrinoless-double-beta-decay experiments that seek to determine the Majorana or Dirac nature of the neutrino were reviewed. New results were presented by GERDA phase II, KamLAND-Zen, the MAJORANA demonstrator and NEMO-3, and the status of ongoing or upcoming experiments, EXO-200, CUORE, SuperNEMO were reported. The prospects for an exciting future effort were also discussed.The presentation of neutrino experiments was complemented by discussion related phenomenological aspects; from neutrino oscillations to lepton-number and flavour violation, from neutrinos in astrophysics and cosmology to the connection with dark matter. Progress in theoretical neutrino physics was reported, with emphasis on the origin of neutrino masses, mixing and CP-invariance violation in extensions of the Standard Model and their phenomenological consequences, such as the generation of a matter-antimatter asymmetry in the early Universe via the leptogenesis mechanism.In parallel to the scientific programme, a number of outreach events were organised to showcase our science, to highlight the opportunities for impact that arise from our research and to reach out to school students and the public. The well-known science communicator Professor Brian Cox gave a public lecture on Wednesday the 6th July 2016. Tickets were free and allocated using a ballot system; the lecture was oversubscribed by roughly a factor of three. On the 5th and 6th of July, groups of students from junior high schools in outer London attended a day of neutrino-themed activities in Imperial’s purpose-built Wohl Reach-Out Laboratory. The activities included a planetarium session on supernova neutrinos and the chance for the students to build their own cosmic-ray detectors to detect neutrino-induced muons. Students from across the UK were invited to enter a competition to create a design to be painted on the magnetic shielding walls of the MICE experimental hall at the Rutherford Appleton Laboratory (RAL). The two winners received their prizes from B. Cox and A. McDonald at the start of the public lecture.All the slides presented at the conference, together with videos of the presentations and the contributions submitted to the proceedings can be found at:http://neutrino2016.iopconfs.org/programmeNeutrino 2016 was an exciting event in which past achievements were celebrated and ground-breaking new results were discussed. We look forward with excitement and anticipation to Neutrino 2018 that will take place in the beautiful city of Heidelberg.Ken Long, Imperial College London and STFCSilvia Pascoli, Institute for Particle Physics Phenomenology, Durham University, Durham

Formal Uncertainty and Dispersion of Single and Double Difference Models for GNSS-Based Attitude Determination.

With multi-antenna synchronized global navigation satellite system (GNSS) receivers, the single difference (SD) between two antennas is able to eliminate both satellite and receiver clock error, thus it becomes necessary to reconsider the equivalency problem between the SD and double difference (DD) models. In this paper, we quantitatively compared the formal uncertainties and dispersions between multiple SD models and the DD model, and also carried out static and kinematic short baseline experiments. The theoretical and experimental results show that under a non-common clock scheme the SD and DD model are equivalent. Under a common clock scheme, if we estimate stochastic uncalibrated phase delay (UPD) parameters every epoch, this SD model is still equivalent to the DD model, but if we estimate only one UPD parameter for all epochs or take it as a known constant, the SD (here called SD2) and DD models are no longer equivalent. For the vertical component of baseline solutions, the formal uncertainties of the SD2 model are two times smaller than those of the DD model, and the dispersions of the SD2 model are even more than twice smaller than those of the DD model. In addition, to obtain baseline solutions, the SD2 model requires a minimum of three satellites, while the DD model requires a minimum of four satellites, which makes the SD2 more advantageous in attitude determination under sheltered environments.

Latest results from Double Chooz

Double Chooz is a short-baseline neutrino disappearance experiment. It detects νe produced in the power plant of Chooz, France, where is located. The main goal of the experiment is the measurement of θ13 mixing angle and in 2011 for the first time the experiment observed an indication for a non zero value of such an oscillation parameter. The mixing angle was successively measured using only the far detector finding the best fit value of sin2(2θ13) = 0.090−0.029+0.032. The near detector is under construction and will start data taking by the middle of 2014 allowing the reduction of the systematic errors. In this paper I make a review of the Double Chooz experiment, focusing in particular on the latest results of the measurement of the mixing angle θ13 relying on the neutron absorption on Gadolinium. I also present results proving the capability of Double Chooz to identify the ortho-positronium. This has been done in an event-by-event basis for the first time in a large liquid scintillator experiments, and can be an additional handle for the electron/positron discrimination in future detectors based on such technology.

Search for sterile neutrinos in muon neutrino disappearance mode at FNAL

The NESSiE Collaboration has been setup to undertake a conclusive experiment to clarify the muon-neutrino disappearance measurements at short baselines in order to put severe constraints to models with more than the three-standard neutrinos. To this aim the current FNAL-Booster neutrino beam for a Short-Baseline experiment was carefully evaluated by considering the use of magnetic spectrometers at two sites, near and far ones. The detector locations were studied, together with the achievable performances of two OPERA-like spectrometers. The study was constrained by the availability of existing hardware and a time-schedule compatible with the undergoing project of multi-site Liquid–Argon detectors at FNAL. The settled physics case and the kind of proposed experiment on the Booster neutrino beam would definitively clarify the existing tension between the nu _{mu } disappearance and the nu _{e} appearance/disappearance at the eV mass scale. In the context of neutrino oscillations the measurement of nu _{mu } disappearance is a robust and fast approach to either reject or discover new neutrino states at the eV mass scale. We discuss an experimental program able to extend by more than one order of magnitude (for neutrino disappearance) and by almost one order of magnitude (for antineutrino disappearance) the present range of sensitivity for the mixing angle between standard and sterile neutrinos. These extensions are larger than those achieved in any other proposal presented so far.

Capabilities of long-baseline experiments in the presence of a sterile neutrino

Assuming that there is a sterile neutrino, we ask what then is the ability of long-baseline experiments to i) establish that neutrino oscillation violates CP, ii) determine the three-neutrino mass ordering, and iii) determine which CP-violating phase or phases are the cause of any CP violation that may be observed. We find that the ability to establish CP violation and to determine the mass ordering could be very substantial. However, the effects of the sterile neutrino could be quite large, and it might prove very difficult to determine which phase is responsible for an observed CP violation. We explain why a sterile neutrino changes the long-baseline sensitivities to CP violation and to the mass ordering in the ways that it does. We note that long-baseline experiments can probe the presence of sterile neutrinos in a way that is different from, and complementary to, the probes of short-baseline experiments. We explore the question of how large sterile-active mixing angles need to be before long-baseline experiments can detect their effects, or how small they need to be before the interpretation of these experiments can safely disregard the possible existence of sterile neutrinos.

Non-standard interactions and the CP phase measurements in neutrino oscillations at low energies

We study the effects of non-standard interactions (NSI) and the genuine CP phase $\delta_D$ in neutrino oscillations at low, $E_\nu \lesssim 1\,\mbox{GeV}$, and very low, $E_\nu \lesssim 0.1\,\mbox{GeV}$, energies. For experimental setup with baseline and neutrino energy tuned to the first 1-3 oscillation maximum, we develop a simple analytic formalism to show the effects of NSI. The vacuum mimicking and its violation as well as the use of the separation basis play a central role in our formalism. The NSI corrections that affect the CP phase measurement mainly come from the violation of vacuum mimicking as well as from the corrections to the 1-3 mixing angle and mass-squared difference. We find that the total NSI correction to the $\nu_\mu - \nu_e$ probability $P_{\mu e}$ can reach $20\% - 30\%$ ($1 \sigma$) at T2(H)K. Correspondingly, the correction to the CP phase can be as large as $50^\circ$ and hence significantly deteriorates the CP sensitivity at T2(H)K. The proposed TNT2K experiment, a combination of T2(H)K and the short baseline experiment $\mu$Kam that uses the Super-K/Hyper-K detector at Kamioka to measure the oscillation of the antineutrinos from muon decay at rest ($\mu$DAR), can substantially reduce the degeneracy between NSI and the genuine CP phase $\delta_D$ to provide high CP sensitivity. The NSI correction to $P_{\mu e}$ is only $2\%$ ($1 \sigma$) for $\mu$DAR neutrinos.

Physics reach of DUNE with a light sterile neutrino

We investigate the implications of one light eV scale sterile neutrino on the physics potential of the proposed long-baseline experiment DUNE. If the future short-baseline experiments confirm the existence of sterile neutrinos, then it can affect the mass hierarchy (MH) and CP-violation (CPV) searches at DUNE. The MH sensitivity still remains above 5$\sigma$ if the three new mixing angles ($\theta_{14}, \theta_{24}, \theta_{34}$) are all close to $\theta_{13}$. In contrast, it can decrease to 4$\sigma$ if the least constrained mixing angle $\theta_{34}$ is close to its upper limit $\sim 30^0$. We also assess the sensitivity to the CPV induced both by the standard CP-phase $\delta_{13} \equiv \delta$, and the new CP-phases $\delta_{14}$ and $\delta_{34}$. In the 3+1 scheme, the discovery potential of CPV induced by $\delta_{13}$ gets deteriorated compared to the 3$\nu$ case. In particular, the maximal sensitivity (reached around $\delta_{13}$ $\sim$ $\pm$ $90^0$) decreases from $5\sigma$ to $4\sigma$ if all the three new mixing angles are close to $\theta_{13}$. It can further diminish to almost $3\sigma$ if $\theta_{34}$ is large ($\sim 30^0$). The sensitivity to the CPV due to $\delta_{14}$ can reach 3$\sigma$ for an appreciable fraction of its true values. Interestingly, $\theta_{34}$ and its associated phase $\delta_{34}$ can influence both the $\nu_e$ appearance and $\nu_\mu$ disappearance channels via matter effects, which in DUNE are pronounced. Hence, DUNE can also probe CPV induced by $\delta_{34}$ provided $\theta_{34}$ is large. We also reconstruct the two phases $\delta_{13}$ and $\delta_{14}$. The typical 1$\sigma$ uncertainty on $\delta_{13}$ ($\delta_{14}$) is $\sim20^0$ ($30^0$) if $\theta_{34} =0$. The reconstruction of $\delta_{14}$ (but not that of $\delta_{13}$) degrades if $\theta_{34}$ is large.

A drift line bias estimator: ARMA-based filter or calibration method, and its application in BDS/GPS-based attitude determination

The multi-antenna synchronized receiver (using a common clock) is widely applied in GNSS-based attitude determination (AD) or terrain deformations monitoring, and many other applications, since the high-accuracy single-differenced carrier phase can be used to improve the positioning or AD accuracy. Thus, the line bias (LB) parameter (fractional bias isolating) should be calibrated in the single-differenced phase equations. In the past decades, all researchers estimated the LB as a constant parameter in advance and compensated it in real time. However, the constant LB assumption is inappropriate in practical applications because of the physical length and permittivity changes of the cables, caused by the environmental temperature variation and the instability of receiver-self inner circuit transmitting delay. Considering the LB drift (or colored LB) in practical circumstances, this paper initiates a real-time estimator using auto regressive moving average-based (ARMA) prediction/whitening filter model or Moving average-based (MA) constant calibration model. In the ARMA-based filter model, four cases namely AR(1), ARMA(1, 1), AR(2) and ARMA(2, 1) are applied for the LB prediction. The real-time relative positioning model using the ARMA-based predicting LB is derived and it is theoretically proved that the positioning accuracy is better than the traditional double difference carrier phase (DDCP) model. The drifting LB is defined with a phase temperature changing rate integral function, which is a random walk process if the phase temperature changing rate is white noise, and is validated by the analysis of the AR model coefficient. The auto covariance function shows that the LB is indeed varying in time and estimating it as a constant is not safe, which is also demonstrated by the analysis on LB variation of each visible satellite during a zero and short baseline BDS/GPS experiment. Compared to the DDCP approach, in the zero-baseline experiment, the LB constant calibration (LBCC) and MA approaches improved the positioning accuracy of the vertical component, while slightly degrading the accuracy of the horizontal components. The ARMA(1, 0) model, however, improved the positioning accuracy of all three components, with 40 and 50 % improvement of the vertical component for BDS and GPS, respectively. In the short baseline experiment, compared to the DDCP approach, the LBCC approach yielded bad positioning solutions and degraded the AD accuracy; both MA and ARMA-based filter approaches improved the AD accuracy. Moreover, the ARMA(1, 0) and ARMA(1, 1) models have relatively better performance, improving to 55 % and 48 % the elevation angle in ARMA(1, 1) and MA model for GPS, respectively. Furthermore, the drifting LB variation is found to be continuous and slowly cumulative; the variation magnitudes in the unit of length are almost identical on different frequency carrier phases, so the LB variation does not show obvious correlation between different frequencies. Consequently, the wide-lane LB in the unit of cycle is very stable, while the narrow-lane LB varies largely in time. This reasoning probably also explains the phenomenon that the wide-lane LB originating in the satellites is stable, while the narrow-lane LB varies. The results of ARMA-based filters are better than the MA model, which probably implies that the modeling for drifting LB can further improve the precise point positioning accuracy.