Experiment BEST-2 with 58Co neutrino source

T.V. Ibragimova; V.A. Matveev; V.N. Gavrin; V.V. Gorbachev

REVIEW 4 major objections 6 minor 62 references

Experiment BEST-2 with 58Co neutrino source

T0 review · 4 major / 6 minor · reviewed 2026-08-10 · deepseek-v4-flash

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Pith's one-line read BEST-2, a proposed 400-kCi 58Co source inside a three-zone gallium target, claims to determine sterile-neutrino oscillation parameters (Δm², sin²2θ) to tens of percent at 3σ and to observe, for the first time, an oscillation pattern in…

desk verdict A credible design study for a three-zone gallium experiment with a 58Co source; the headline 3σ parameter-determination claim overreaches, but the proposal is sound enough to referee. read the letter →

arxiv 2501.08127 v1 pith:6OIYJ6DE submitted 2025-01-14 hep-ex

V.N. Gavrin , V.V. Gorbachev , T.V. Ibragimova , V.A. Matveev This is my paper · ORCID

classification hep-ex

keywords galliumanomalysterileneutrinoscobalt-58sourceneutrinooscillationsthree-zonetargetshort-baselineenergydependenceexperiment

verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

The paper proposes a new gallium-source experiment, BEST-2, to test the gallium anomaly — the persistent deficit of neutrino captures seen in calibration runs with intense artificial sources. The experiment places a 400-kCi 58Co neutrino source at the center of a gallium target split into three concentric zones and measures the capture rate in each zone separately. The central claim is that if short-baseline oscillations into sterile neutrinos exist with parameters in the sensitivity region (Δm² roughly 0.5–5.5 eV²), the experiment will determine both Δm² and sin²2θ with errors of several tens of percent at 3σ. Because 58Co emits nearly monoenergetic 1497 keV neutrinos, the three zone rates can reveal a distance-dependent oscillation pattern — a 'few-many-few' sequence — that no oscillation experiment has observed before. The same data also test whether the gallium anomaly depends on neutrino energy, since the cobalt neutrino energy is about twice that of previous chromium and argon sources.

What carries the argument

The load-bearing object is the three-zone gallium target with a common center: an inner sphere (average thickness ~52 cm) and two cylindrical shells (each ~27 cm thick), containing about 7.7, 14.7, and 26.8 tonnes of gallium. The 58Co source sits at the common center; its nearly monoenergetic 1497 keV neutrinos have a capture cross section of $253\times 10^{-46}$ cm² on $^{71}$Ga, about 4.4 times larger than for $^{51}$Cr. For each zone the paper computes the distance distribution of captures by Monte Carlo, then forms expected rates under oscillations with survival probability $P_{ee}$ and works with ratios $R_i/R_j$; the sensitivity regions are defined by $D(l,k) = \max_{i<j}|R_i/R_j - 1|$ compared with a fixed 7% statistical error for the outer zones. The 400-kCi source is produced by $(n,p)$ reactions on nickel in a fast-neutron reactor, giving about 891 events in the inner zone over ten 16-day exposures.

What would settle it

Run BEST-2 as proposed and compare the three zone rates after the ten exposures: if every pairwise ratio deviation is below 1σ (D(l,k) < 7%), the predicted few-many-few oscillation pattern is absent; alternatively, a total capture rate that differs from the previous gallium-experiment average by more than 2σ would disprove sterile oscillations as the main cause of the gallium anomaly.

Watch

Extended reading notes

Core claim

The paper's core discovery claim is that dividing the gallium target into three independent concentric zones around a 58Co source turns the gallium anomaly from a single deficit number into a distance-resolved measurement. For monochromatic neutrinos, the survival probability $P_{ee} = 1 - \sin^2 2\theta\,\sin^2(1.27\,\Delta m^2 L/E)$ oscillates with distance $L$, and the ratios of capture rates in the three zones are sensitive to $\Delta m^2$ in a continuous band from about 0.5 to 5.5 eV². The authors show by Monte Carlo zone-geometry and a $\Delta\chi^2$ analysis that if the true $(\Delta m^2,\sin^2 2\theta)$ lies in this band, the allowed region is compact and both parameters are determined to tens of percent at 3σ; outside the band, allowed $\Delta m^2$ values fragment into many disconnected ranges. They also claim this will be the first experiment to observe an actual oscillation curve of rate versus distance for fixed-energy neutrinos, and that a total rate differing by more than 2σ from previous gallium experiments would indicate an energy dependence incompatible with sterile oscillations as the main explanation.

Load-bearing premise

The determination claim collapses if the true oscillation parameters lie outside the claimed sensitivity region or if the real outer-zone counting-rate uncertainties exceed the fixed 7% used to draw the sensitivity boundaries, because the paper asserts without a quantitative check that this simplification has virtually no effect.

Editorial extensions

If this is right

If the oscillation hypothesis is right and the parameters lie in the sensitivity band, BEST-2 determines $\Delta m^2$ and $\sin^2 2\theta$ with few-tens-of-percent errors at 3σ, including the usually hard-to-measure $\Delta m^2$.
If the three-zone rates show the predicted few-many-few pattern, it would be the first direct observation of a neutrino oscillation periodicity in distance for fixed-energy neutrinos.
If the measured total capture rate differs by more than 2σ from previous gallium source experiments, the gallium anomaly depends on neutrino energy and sterile oscillations cannot be its main cause.
If the zone rates agree within errors, the experiment either rules out oscillations with $\Delta m^2$ below about 5.5 eV² at the tested amplitudes or pushes $\Delta m^2$ above 5.5 eV².
The source production scheme requires only about 70 days of irradiation in a fast-neutron reactor using 15 kg of natural nickel (or about 10 kg enriched), making the experiment feasible with existing reactor fluxes.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

My inference: since the paper's own Fig. 10 shows PROSPECT and T2K data already exclude a large part of the claimed sensitivity region, the most probable experimental outcome may be a null or inconclusive zone-ratio pattern; the durable value of BEST-2 could then lie in sharpening the gallium-anomaly deficit and testing its energy dependence rather than in determining oscillation parameters.
My inference: the fixed 7% outer-zone error should be replaced by a full Monte Carlo of the actual systematic budget — source activity calibration, extraction efficiencies per zone, 60Co contamination, and counter background — because the sensitivity-region boundaries in Fig. 10 are drawn from that single number.
My inference: the same three-zone distance-resolved design could be repeated with a second monoenergetic source of different energy (the paper discusses 65Zn) to disentangle energy dependence from distance dependence in the gallium anomaly without changing the target geometry.

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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Desk Editor's Note

read the letter

Plainly: this is a serious design study, not a measurement, and its headline sensitivity claim is overstated in a way that doesn't sink the proposal. The genuinely new piece is the combination of a 58Co source with a three-zone gallium target. That buys two things: a test of the gallium anomaly's energy dependence (1.5 MeV vs ~0.75 MeV) and a distance-dependent ratio pattern that could in principle pin down Δm², which BEST couldn't. The paper handles the standard pieces well: Monte Carlo capture-length distributions, a realistic 10-exposure schedule, Poisson error estimates with a solar-neutrino background term, and source production numbers that at least pass the sanity check. The radiation-safety and heat-release estimates are a plus.

The soft spots are where the stress-test puts them. The 'several tens of percent at 3σ' determination claim is built from a detection threshold—D(l,k) > 3σ with a fixed 7% per-zone error—and then one illustrative χ² contour. That threshold is not equivalent to a compact, unique 3σ allowed region, especially with three pairwise ratios and a max taken over them (trials factor). The paper states the simplification 'virtually' doesn't affect the boundaries but doesn't show it. It also doesn't fold source activity, cross-section, or extraction-efficiency systematics into the contours, and it ignores the fact that oscillation suppression changes the per-zone errors. The blind zones near Δm²=6 and 8 eV² and the unbounded regions in Fig. 12 are consistent with this. So I'd treat the sensitivity map as indicative, not as a certified parameter-estimation reach.

The more practical issue is Fig. 10: PROSPECT and T2K already exclude much of the claimed region. The paper acknowledges this but still frames the experiment as able to 'determine' parameters in that region. If the real world sits in the excluded part, BEST-2 becomes a confirmation/null experiment, not a measurement—still valuable, but not what the abstract promises. The source activity of 400 kCi is plausible but depends on unverified reactor irradiation assumptions.

All of this is fixable in a revision. The authors are transparent about what is assumed, and the physics is standard. This deserves serious refereeing, and I'd want the referee to ask for a coverage calculation and a systematic error budget before publication. For anyone working on the gallium anomaly, it's worth reading now.

Referee Report

4 major / 6 minor

Summary. The paper proposes a new gallium-source experiment, BEST-2, using a 400 kCi 58Co neutrino source placed at the center of a three-zone gallium target. The stated goals are to test the gallium anomaly, to determine the sterile-neutrino oscillation parameters (Δm², sin²2θ) if they lie in the claimed sensitivity region (approximately Δm² from 0.5 to 5.5 eV²), and to search for an energy dependence of the gallium anomaly by comparing with previous 51Cr and 37Ar source experiments. The expected event rates are obtained from the standard survival probability, Monte Carlo path-length distributions for the three target zones, an assumed exposure schedule (m = 10 irradiations of t1 = 16 days), and published cross sections. Sensitivity regions in Section 12 are built from the maximum pairwise deviation of zone capture-rate ratios relative to a fixed 7% statistical error, with illustrative χ² allowed regions in Figs. 11 and 12. The paper also contains estimates of source production in fast-neutron reactors, heat release, and radiation safety.

Significance. If the sensitivity claim is validated, BEST-2 would be a valuable and distinctive experiment: it would use a monochromatic source at higher energy than previous gallium sources, and the three-zone layout could in principle reveal a distance-dependent oscillation pattern rather than only an overall rate deficit. The paper is useful as a design study: it gives concrete target geometry, exposure scheduling, source-production requirements, and a transparent discussion of blind zones and of the restrictive impact of PROSPECT data. The main quantitative claim, however, is not yet established at the level asserted in the abstract and conclusion, because the sensitivity criterion of Section 12 is not equivalent to the parameter-estimation criterion of Section 13, and because the fixed 7% error assumption is not derived from the per-zone errors in Table 1 or from a full error budget. The experiment's practical discovery potential is also substantially reduced by the PROSPECT exclusions shown in Fig. 10, a point the paper acknowledges but does not quantify.

major comments (4)

[Section 12 and Section 13] The central claim that oscillation parameters will be determined with errors of several tens of percent at 3σ is not supported by the sensitivity criterion used in Section 12. The sensitivity regions are defined by D(l,k) = max_{i<j}|R_i/R_j − 1| compared with a fixed σ = 7%, while the parameter-determination claim is illustrated in Figs. 11 and 12 with the χ² contours of Section 13. These are different statistics: D > 3σ for a grid point does not imply that the 3σ allowed region is a single compact set containing the true point. Indeed, Fig. 12 shows an unbounded allowed region immediately outside the claimed sensitivity boundary, and the text itself identifies blind zones near Δm² = 6 and 8 eV². The authors should provide a coverage-style simulation: for a grid of true (Δm², sin²2θ) inside the claimed region, generate measured rates with realistic per-zone statistical errors, compute the Section 13 χ² contours, and demonstrate that the 3σ region is compact, contains the true values, and yields parameter uncertainties of several tens of percent. Without such a check, the quoted precision is an extrapolation from a detection threshold to a parameter-estimation statement.
[Section 12, Table 1] The fixed 7% statistical error is asserted rather than derived. Table 1 gives per-zone relative statistical errors of 3.8%, 5.6%, and 5.8% for α = 1, and the maximum over three pairwise ratios introduces a trials factor that is not discussed. In addition, oscillation-induced suppression changes the number of events in each zone and therefore changes the per-zone statistical errors themselves, an effect the fixed-σ approximation ignores. The text states that the simplification has "virtually no effect" on the sensitivity boundaries, but no quantitative comparison is shown. The authors should propagate the actual statistical errors, the trials factor, and the principal systematic uncertainties (source activity, extraction efficiency, 71Ge counting efficiency, 60Co contamination, cross-section uncertainty) into the sensitivity contours and show how the claimed 3σ boundary changes. This is load-bearing because the sensitivity region is the basis for the paper's main conclusion.
[Section 13, Figs. 11 and 12] The χ² function in Section 13 includes a covariance matrix V with "statistical and systematic, including uncorrelated, experimental errors," but the numerical content of V is never specified, and the example contours in Figs. 11 and 12 do not state which systematic terms were included. Since the paper's headline claim is a quantitative 3σ parameter-determination precision, the error model used to produce these figures must be documented: the values of all uncorrelated systematic uncertainties, how they enter V, and how they affect the size and shape of the allowed regions. As written, the examples do not demonstrate that the claimed precision survives a realistic error budget.
[Section 12, Fig. 10] The paper acknowledges that PROSPECT data "almost completely exclude" the region to which BEST-2 is sensitive, yet the abstract and introduction present the experiment as able to determine sterile oscillation parameters in a wide range. Because the central claim is explicitly conditional on the true parameters lying inside the sensitivity region, the practical import depends on how much of that region remains allowed after existing constraints. The authors should quantify the overlap between the claimed sensitivity region and the currently allowed parameter space (including the T2K-allowed region and the IceCube region) and state clearly what BEST-2 can uniquely test. If the overlap is small, the primary framing should be revised to emphasize the energy-dependence test of the gallium anomaly and the confirmation of the anomaly itself, rather than broad sterile-parameter determination.

minor comments (6)

[Section 1] The sentence "The article was accepted in the JETP" is extraneous in the manuscript text and should be removed or moved to a footnote.
[Section 3, Eq. (1)] Equation (1) and its surrounding text appear with garbled or overlapping characters in the manuscript; the survival probability should be typeset cleanly and all symbols (E, L, Δm², θ) defined in the text.
[Section 5] The cross-section uncertainty "(1.0 +0.17 -0.07)" is unclear; it should be stated explicitly as a fractional uncertainty on σ = 253×10⁻⁴⁶ cm², with the reference to Bahcall's evaluation.
[Section 10] The phrase "For nickel enriched in isotope 68" should read "enriched in ⁵⁸Ni," and the abundance and mass numbers in that paragraph should be checked for consistency.
[Section 12, Fig. 10] The exclusion and allowed contours from PROSPECT, KATRIN, T2K, and IceCube are shown or mentioned without specifying the confidence level and oscillation channel used for each; the figure caption and text should provide this information.
[Table 2] The entries n_i in Table 2 are expected mean counts, but the table and text do not state this explicitly or give uncertainties; clarify that these are expectation values for the stated exposure schedule.

Circularity Check

0 steps flagged · score 0.0 of 10

No circularity: the sensitivity projections rest on standard external inputs and are not equivalent to the claims they support.

full rationale

BEST-2 is a design/sensitivity study. The oscillation signal is computed from the standard vacuum survival probability (Eq. 1) with published cross sections and source decay data; the expected event numbers follow from source activity, target geometry, exposure schedule, and measured 71Ge efficiencies taken from previous gallium experiments. The Section 12 sensitivity region is constructed by comparing expected pairwise counting-rate ratios against a fixed 7% statistical error, which is a projection rather than a fitted parameter renamed as a prediction. The 3σ parameter-determination claim is conditional on the true parameters lying in that region and is illustrated with independent χ² contours in Figs. 11 and 12. Even if the D-threshold criterion may not be logically equivalent to a full χ² allowed-region analysis, that is a statistical-validity concern, not circularity. Self-citations to BEST and SAGE supply prior data, efficiencies, and anomaly normalization, but the central calculation does not reduce to those citations: geometry, masses, activity, and exposure times enter independently, and no equation is defined in terms of the result it is used to predict.

Assumptions & free parameters 4 free parameters · 6 assumptions · 0 invented entities

The central claim rests on standard neutrino oscillation physics and on prior measured cross sections and BEST anomaly rates. The main free choices are the source activity, the assumed oscillation amplitude, the fixed 7% error model, and the exposure schedule. No new particles or forces are introduced by this paper; the sterile neutrino is inherited from prior literature. The source production assumptions (reactor flux, (n,p) cross section) are unverified inputs.

free parameters (4)

Source activity A = 400 kCi = 400 kCi
Chosen so that the inner zone collects about 700 events, matching BEST statistics; all sensitivity estimates scale with this value (Section 9).
Oscillation amplitude sin²2θ = 0.30 for sensitivity figures = 0.30
Representative amplitude taken from the BEST result; used in Figs. 5-6 to show capture-rate ratios. The paper notes sin²2θ ~ 0.4 ± 0.2 at 95% CL from BEST.
Fixed statistical error σ = 7% for sensitivity boundaries = 7%
Used to define the D(l,k) = 1σ, 2σ, 3σ regions in Section 12; paper asserts it approximates the outer-zone statistical error and that the simplification has negligible effect, but no derivation is provided.
Exposure schedule t1 = 16 days, t2 = 1 day, m = 10 exposures = t1=16 d, t2=1 d, m=10
Chosen to maximize total events; the expected N = 891 in the inner zone depends on these values (Section 8).

assumptions (6)

standard math Two-neutrino survival probability P_ee = 1 - sin²2θ sin²(1.27 Δm² L/E) describes electron neutrino disappearance
Eq. (1) is used for all expected-rate calculations; assumes vacuum oscillations, no matter effects, standard for short-baseline analyses.
domain assumption The gallium anomaly deficit, R = 0.80 ± 0.05, from previous source experiments is a genuine effect
Used to scale the required source activity (Section 9) and to categorize potential outcomes (Section 14).
domain assumption Oscillation parameters around sin²2θ ≈ 0.3 from BEST are representative
Used as a benchmark in Figs. 5-6 and the sensitivity region construction; the paper notes sin²2θ ≈ 0.4 ± 0.2.
ad hoc to paper The fixed 7% statistical error in outer-zone rates is a faithful approximation of the real error
Introduced in Section 12 to define sensitivity boundaries; the paper asserts negligible effect without a quantitative check.
domain assumption The 58Co source can be produced at 400 kCi in about 70 days using the stated fast-reactor flux and (n,p) cross section
Section 10; based on handbook cross section (0.1439 b) and reactor flux (2×10^15 cm^-2 s^-1), not yet demonstrated.
standard math Poisson statistics with a counter-background factor α ≈ 1 describe the measurement errors
Section 11; used to compute statistical errors δ in Table 1 and to estimate sensitivity.

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Cite this review

Pith. "Pith review of Experiment BEST-2 with 58Co neutrino source." pith.science (2026). https://pith.science/paper/6OIYJ6DE

@misc{pith2026250108127,
  author       = {Pith},
  title        = {Pith review of: Experiment BEST-2 with 58Co neutrino source},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/6OIYJ6DE}},
  note         = {Machine review of arXiv:2501.08127}
}

read the original abstract

The article describes a new experiment with an artificial neutrino source 58Co on a gallium target GGNT (SAGE). The goal of the experiment is to study the gallium anomaly. The experiment makes it possible to find the parameters of oscillation transitions of electron neutrinos to sterile states in a wide range of parameters. Including the parameter {\Delta}m2, the experimental determination of which usually causes significant difficulties. An important feature of the experiment is the possibility of identifying the dependence of the gallium anomaly on the neutrino energy.

Figures

Figures reproduced from arXiv: 2501.08127 by the authors.

**Figure 1.** Dependences of expected counting rates in two zones of the gallium target in the BEST experiment and their ratio on the parameter Δm 2 for a fixed value of the parameter sin2 2θ = 0.30 3. The purpose of the experiment BEST-2 BEST-2 experiment with the neutrino source 58Co is designed for a detailed study of the gallium anomaly. The experiment will obtain data on the dependence of the gallium anomaly on the neutrino … view at source ↗

**Figure 2.** Fig.2 [PITH_FULL_IMAGE:figures/full_fig_p005_2.png] view at source ↗

**Figure 3.** Schematic diagram of the gallium target in the [PITH_FULL_IMAGE:figures/full_fig_p006_3.png] view at source ↗

Figures from the paper (9 more)

**Figure 4.** Figure 4: Distributions of neutrino capture probabilities by gallium depending on the distance [PITH_FULL_IMAGE:figures/full_fig_p006_4.png]

**Figure 5.** Figure 5: Neutrino capture rates in three zones of [PITH_FULL_IMAGE:figures/full_fig_p007_5.png]

**Figure 6.** Figure 6: Pairwise ratios of neutrino capture rates in three zones of the [PITH_FULL_IMAGE:figures/full_fig_p007_6.png]

**Figure 7.** Figure 7: shows the number of events in the target spherical zone of the target when irradiated with a 58Co source with an activity of 0.40 MCi, depending on the duration of one exposure t1, which is the same for all irradiations [PITH_FULL_IMAGE:figures/full_fig_p008_7.png]

**Figure 8.** Figure 8: shows the dependence of the amount of registered atoms of 71Ge N from the number of exposures m (formula (2)). With the initial neutrino capture rate p = 36 days-1, it is possible in m = 10 irradiations to achieve the required number of events in the first (spherical) …

**Figure 9.** Figure 9: shows curve of reach the activity for 15 kg of natural nickel under conditions where the resulting 58Co does not burn out, i.e. does not interact with neutrons in the reactor [PITH_FULL_IMAGE:figures/full_fig_p010_9.png]

**Figure 10.** Figure 10: shows the sensitivity regions of the BEST-2 experiment with a 58Co source with an activity of 400 kCi for a 3-zone gallium target for determining the parameter Δm 2 . The regions of sensitivity to the determination of oscillation parameters were determined by the rati…

**Figure 11.** Figure 11: Fig.11. An example of the regions of a [PITH_FULL_IMAGE:figures/full_fig_p015_11.png]

**Figure 12.** Figure 12: An example of the regions of allowed oscillation parameters that are not within the sensitivity region of the experiment: (Δm 2 , sin2 2θ) = (6.0 eV2 , 0.3) at the measured count rates (R1, R2, R3) = (0.84, 0.82, 0.85) 13. Sensitivity regions for determining oscillati…

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Reference graph

Works this paper leans on

62 extracted references · 54 canonical work pages

[1]

Introduction In recent years, attempts have been made to explain the unusual results of a number of neutrino experiments – LSND [1], MiniBooNE [2 -4], short -baseline reactor experiments [5 -7], gallium experiments with artifi cial neutrino sources [8 -11] – by the fe atures of individual experiments, in which the systematics has not been sufficiently stu...

work page
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new physics

Gallium anomaly The efficiency of the solar neutrino experiments SAGE and GALLEX [8 -11] was tested in calibration experiments with intense artificial sources of 51Cr and 37Ar. The rates of registration of monochromatic neutrinos from sources obtained in four experiments turned out to be lower than expected by 2.6σ [12]: predicted m easured v vR = = 0.87 ...

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[3]

few -many-few

The purpose of the experiment BEST-2 BEST-2 experiment with the neutrino source 58Co is designed for a deta iled study of the gallium anomaly. The experiment will obtain data on the dependence of the gallium anomaly on the neutrino energy E and on the distance between the points of neutrino birth and capture L. The leading hypothesis explaining the galliu...

work page
[4]

All procedures of the BEST -2 experiment repeat the procedures of the BEST experiment

Features of the new experiment The new experiment is a natural continuation of the BEST experiment [25], which confirmed the gallium anomaly. All procedures of the BEST -2 experiment repeat the procedures of the BEST experiment. A compact neutrino source will be placed in the center of a gallium target divided into zones, in which the neutrino capture rat...

work page
[5]

due to the introduction of the third target zone, the sensitivity to the distances L between the points of emission and capture neutrino has been increased, and also

work page
[6]

This difference will make it possible to determine the oscillation parameter Δm2 in a wide range of values

a neutrino source with higher energy than in the BEST experiment was used . This difference will make it possible to determine the oscillation parameter Δm2 in a wide range of values. The second oscillation parameter, sin22θ, determines the suppression of the capture rate in the target as a whole, and is currently know n with satisfactory accuracy [25] (s...

work page
[7]

It is assumed that the 58Co source will be produced by irradiating nickel in a fast neutron reactor using the reaction CopnNi 58 27 58 28 ),( , i.e

Source for a new experiment BEST-2 experiment, which was originally proposed with a 65Zn source [29 ,30], will use a 58Co monochromatic neutrino source. It is assumed that the 58Co source will be produced by irradiating nickel in a fast neutron reactor using the reaction CopnNi 58 27 58 28 ),( , i.e. the main mass of the active part of the source will con...

work page
[8]

This can be achieved by increasing the number of gallium target zones, which will be at different distances from the source

Dividing the Ga target into zones In the new experiment, to determine the oscillation parameter Δm2, it is necessary to measure the capture rates at different neutrino path lengths, so it is important to increase the spatial resolution of the detector. This can be achieved by increasing the number of gallium target zones, which will be at different distan...

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[9]

Note that here transitions into any states can be investigated, including antineutrinos, since only electron neutrinos are registered on the gallium target

Effect of oscillation parameters on counting rates In this experiment, the hypothesis of electron neutrino oscillations into sterile states with large values of the parameter Δm2 (~1 eV2) will be investigated. Note that here transitions into any states can be investigated, inc...
[10]

Exposure time BEST-2 experiment will collect events according to the scheme of other gallium experiments. The measurement cycle consists of several procedures: 1) irradiation of the gallium target with neutrinos from the source; 2) extraction of 71Ge atoms produced in neutrino...
[11]

In the BEST experiment, the statistics of events in one zone w as approximately 700 events

Source activity To estimate the sensitivity of the experiment with the 58Co source, the statistics of the BEST experiment [25] were used . In the BEST experiment, the statistics of events in one zone w as approximately 700 events. Therefore, in the new experiment, the activity...
[12]

at higher neutrino energy, the capture cross section in the new experiment is 4.4 times higher
[13]

Therefore, the duration of exposures increases (t1 = 16 days versus 9 days in the BEST)

a longer lifetime of the source in the new experiment (T 1/2 = 71 days versus 27 .7 days in the BEST), due to which later irradiations make a higher contribution. Therefore, the duration of exposures increases (t1 = 16 days versus 9 days in the BEST)
[14]

Taking into account the wide s pectrum of neutrons in fast neutron reactors, the cross section of such a reaction will probably be less: σ = 0.1439 b [34]

Source production A source of 58Co can be produced in a fast neutron reactor by the reaction CopnNi 58 27 58 28 ),( (4) For neutrons with an energy of 14 -15 MeV, the cross section of reaction (4) can be estimated using the scheme proposed in [33], and it is equal to σ = 0.34 ...
[15]

We will assume that the number of extracted 71Ge atoms has a Poisson distribution, in which the statistical err or is equal to the square root of the number of events N=

Statistical errors of measurements Let us estimate the statistical errors of gallium measurements with a source. We will assume that the number of extracted 71Ge atoms has a Poisson distribution, in which the statistical err or is equal to the square root of the number of even...
[16]

Sensitivity to the oscillation parameters determination Figure 10 shows the sensitivity regions of the BEST-2 experiment with a 58Co source with an activity of 400 kCi for a 3-zone gallium target for determining the parameter Δm2. The regions of sensitivity to the determinatio...
[17]

In the region of the studied parameters, we find the most probable (BF, best fit ) the value of ( Δm2, 16 sin22θ)bf, at which the function χ2 = χ2min takes a minimum value

Sensitivity regions for determining oscillation parameters The regions of a llowed values of the oscillation parameters are determined by the function )()()2sin,( 1222 calcmeas T calcmeas RRVRRm  −−= − [24], where m easR  and calcR  are the vectors of the ratios of th...
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To do this, we will set two parameters – 1) the total count ing rate for all target zones R0 and 2) the maximum difference between the count ing rates in different target zones ΔR

Potential results of the BEST-2 experiment Let us consider what physical results can be obtained in the BEST-2 experiment. To do this, we will set two parameters – 1) the total count ing rate for all target zones R0 and 2) the maximum difference between the count ing rates in ...
[19]

If R0 ≈ R and ΔR > 2σ, i.e. the obtained count ing rate approximately coincides with the rate of previous gallium experiments with sources and a significant difference in the count ing rates in different zones of the target is observed, this will mean that the gallium anomaly ...
[20]

If R0 ≈ R and ΔR < 2σ, i.e. the difference in counting rates in different target zones is small, then sterile oscillations remain a possible solution to the gallium anomaly problem, the gallium anomaly will be confirmed at a higher statistical significance level, but the oscil...
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If R0 ≠ R, i.e. the measured count ing rate will differ significantly from the count ing rates in previous gallium experiments, then with any difference in the count ing rates between different target zones the dependence of the gallium anomaly on the neutrino energy will be d...
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The main ones are heat release and radiation activity

Operation of the source The neutrino source 58Co proposed for the BEST-2 experiment will have characteristics that need to be taken into account when working with it. The main ones are heat release and radiation activity. They are significantly higher than the corresponding va...
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new physics

Conclusion The new gallium experiment BEST-2 will investigate the gallium anomaly, which may indicate the manifestation of new physics. The division of the BEST-2 gallium target into 3 independent zones and the use of a monochromatic neutrino source 58Co with an activity of 40...

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[1] [1]

Introduction In recent years, attempts have been made to explain the unusual results of a number of neutrino experiments – LSND [1], MiniBooNE [2 -4], short -baseline reactor experiments [5 -7], gallium experiments with artifi cial neutrino sources [8 -11] – by the fe atures of individual experiments, in which the systematics has not been sufficiently stu...

work page

[2] [2]

new physics

Gallium anomaly The efficiency of the solar neutrino experiments SAGE and GALLEX [8 -11] was tested in calibration experiments with intense artificial sources of 51Cr and 37Ar. The rates of registration of monochromatic neutrinos from sources obtained in four experiments turned out to be lower than expected by 2.6σ [12]: predicted m easured v vR = = 0.87 ...

work page 2019

[3] [3]

few -many-few

The purpose of the experiment BEST-2 BEST-2 experiment with the neutrino source 58Co is designed for a deta iled study of the gallium anomaly. The experiment will obtain data on the dependence of the gallium anomaly on the neutrino energy E and on the distance between the points of neutrino birth and capture L. The leading hypothesis explaining the galliu...

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[4] [4]

All procedures of the BEST -2 experiment repeat the procedures of the BEST experiment

Features of the new experiment The new experiment is a natural continuation of the BEST experiment [25], which confirmed the gallium anomaly. All procedures of the BEST -2 experiment repeat the procedures of the BEST experiment. A compact neutrino source will be placed in the center of a gallium target divided into zones, in which the neutrino capture rat...

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[5] [5]

due to the introduction of the third target zone, the sensitivity to the distances L between the points of emission and capture neutrino has been increased, and also

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[6] [6]

This difference will make it possible to determine the oscillation parameter Δm2 in a wide range of values

a neutrino source with higher energy than in the BEST experiment was used . This difference will make it possible to determine the oscillation parameter Δm2 in a wide range of values. The second oscillation parameter, sin22θ, determines the suppression of the capture rate in the target as a whole, and is currently know n with satisfactory accuracy [25] (s...

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[7] [7]

It is assumed that the 58Co source will be produced by irradiating nickel in a fast neutron reactor using the reaction CopnNi 58 27 58 28 ),( , i.e

Source for a new experiment BEST-2 experiment, which was originally proposed with a 65Zn source [29 ,30], will use a 58Co monochromatic neutrino source. It is assumed that the 58Co source will be produced by irradiating nickel in a fast neutron reactor using the reaction CopnNi 58 27 58 28 ),( , i.e. the main mass of the active part of the source will con...

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[8] [8]

This can be achieved by increasing the number of gallium target zones, which will be at different distances from the source

Dividing the Ga target into zones In the new experiment, to determine the oscillation parameter Δm2, it is necessary to measure the capture rates at different neutrino path lengths, so it is important to increase the spatial resolution of the detector. This can be achieved by increasing the number of gallium target zones, which will be at different distan...

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