Physics potential of ESS (cid:23) SB in the presence of a light sterile neutrino

: ESS (cid:23) SB is a proposed neutrino super-beam project at the ESS facility. We study the performance of this setup in the presence of a light eV-scale sterile neutrino, considering 540 km baseline with 2 years (8 years) of (cid:23) ((cid:22) (cid:23) ) run-plan. This baseline o(cid:11)ers the possibility to work around the second oscillation maximum, providing high sensitivity towards CP-violation (CPV). We explore in detail its capability in resolving CPV generated by the standard CP phase (cid:14) 13 , the new CP phase (cid:14) 14 , and the octant of (cid:18) 23 . We (cid:12)nd that the sensitivity to CPV induced by (cid:14) 13 deteriorates noticeably when going from 3 (cid:23) to 4 (cid:23) case. The two phases (cid:14) 13 and (cid:14) 14 can be reconstructed with a 1 (cid:27) uncertainty of (cid:24) 15 0 and (cid:24) 35 0 respectively. Concerning the octant of (cid:18) 23 , we (cid:12)nd poor sensitivity in both 3 (cid:23) and 4 (cid:23) schemes. Our results show that a setup like ESS (cid:23) SB working around the second oscillation maximum with a baseline of 540 km, performs quite well to explore CPV in 3 (cid:23) scheme, but it is not optimal for studying CP properties in 3+1 scheme. (4.5 (cid:27) We (cid:12)nd very similar result for the case of IH (not shown). The right panel of (cid:12)gure 2 displays the discovery potential of CPV induced by (cid:14) 14 for the NH case. The magenta band is obtained by varying the true values of the CP phase (cid:14) 13 in the range [ (cid:0) (cid:25); (cid:25) ] while marginalizing over their test values in the same range in the (cid:12)t. We observe that ESS (cid:23) SB has a limited sensitivity to the CP phase (cid:14) 14 , which is always below the 2 (cid:27) level.

New SBL experiments are under construction, with the aim of testing this intriguing hypothesis (see the review in [26]). The new SBL experiments are sensitive to the characteristic L/E dependency due to the oscillations intervening at the new mass-squared splitting. This will allow them to measure with precision the value ∆m 2 new ∼ 1 eV 2 and the new mixing angles of the sterile sector. However, as already stressed in the literature, the SBL experiments will be unable to furnish any information about the CP-violation (CPV) structure of the sterile sector. Even the simplest extended framework involving only one neutrino state, the so-called 3+1 scheme, entails two additional CP phases with respect JHEP12(2019)174 to the standard framework. Therefore, after a hypothetical discovery made at the SBL experiment, we will face the problem of finding a way to determine these new CP phases.
In order to measure any CP phase one must be sensitive to the quantum interference of two different oscillation frequencies. In the 3+1 scenario, in SBL experiments, only the new frequency is observable, while both the standard (solar and atmospheric) frequencies have no effect at all. For this reason the SBL setups have no sensitivity to CPV (both in 3-flavor and 3+1 schemes). As first shown in [27], things are qualitatively different in LBL setups, since in these experiments the interference between two different frequencies becomes observable. In fact, the LBL experiments are able to detect both the effects of the standard CP phase and those of the new ones. For this reason, the LBL experiments are complementary to the SBL ones in nailing down the properties of sterile neutrinos.
The new-generation of LBL experiments [28][29][30][31][32][33][34][35][36][37] are designed to have a central role in the search of CPV phenomena. In this paper, we focus on the proposed super beam experiment to be performed at the European Spallation Source (ESSνSB). This facility will have a very powerful neutrino beam with an average power of 5 MW, and the flux is expected to peak around 0.25 GeV. We assume that these neutrinos will travel a distance of 540 km providing the opportunity to work around the second oscillation maximum.
Our present study is complementary to other recent investigations performed about DUNE [38][39][40][41][42][43][44], T2HK [44][45][46], and T2HKK [44,47]. Other studies on the impact of light sterile neutrinos in LBL setups can be found in [48][49][50][51][52][53][54][55][56]. We underline that while our study deals with charged current interactions, one can obtain valuable information on active-sterile oscillations parameters also from the analysis of neutral current interactions (see [12][13][14][15] for constraints from existing data and [43,57] for sensitivity studies of future experiments.) The paper has the following structure. In section 2, we detail the theoretical framework and also describe the properties of the 4-flavor ν µ → ν e transition probability. In section 3, the ESSνSB setup is described in detail. In section 4 we present the details of our numerical study. In section 5 we briefly explain the (lack of) sensitivity to the neutrino mass hierarchy and to the octant of θ 23 making use of the bievents plots. In section 6 we describe the sensitivity to CPV and the ability to reconstruct the CP phases. Finally, we trace the conclusions in section 7.
2 Transition probability in the 4-flavor scheme

Conversion probability
For the ESSνSB baseline (540 km), matter effects are very small. This allows us to limit the discussion to the case of propagation in vacuum. As first shown in [27], the ν µ → ν e the conversion probability is the sum of three contributions (2.4) The first term is positive definite and depends on the atmospheric mass-squared splitting. It provides the leading contribution to the transition probability. The expression of this term is given by where ∆ ≡ ∆m 2 31 L/4E is the (atmospheric) oscillating factor, L and E being the neutrino baseline and energy, respectively. The other two terms in eq. It should be noticed that at the first (second) oscillation maximum one has ∆ ∼ π/2 (∆ ∼ 3π/2). For this reason, in ESSνSB, which works at the second oscillation maximum, one expects an enhanced sensitivity to the CP phase δ 13 . Indeed, in spite of the lower statistics, we will see how ESSνSB can attain a sensitivity similar to that obtained in the higher statistics experiment T2HK, which works at the first oscillation maximum. The third term in eq. (2.4) appears as a new genuine 4-flavor effect, and is connected to the interference of sterile and atmospheric frequencies. It can be written in the form [27] P INT II 4s 14 s 24 s 13 s 23 sin ∆ sin(∆ + δ 13 − δ 14 ) . (2.7) From eqs. (2.5)-(2.7), we can observe that the transition probability depends upon three small mixing angles: the standard angle θ 13 and two new angles θ 14 and θ 24 . We notice that the estimates of such three mixing angles (calculated in the 3-flavor framework [58][59][60] for θ 13 , and in the 4-flavor scheme [61][62][63][64] for θ 14 and θ 24 ) are similar and one has s 13 ∼ s 14 ∼ s 24 ∼ 0.15 (see table 1). Therefore, one can consider these three angles as small parameters having the same order . We note also that the ratio of the solar over the -3 -

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atmospheric mass-squared splittings, α ≡ ∆m 2 21 /∆m 2 31 ± 0.03 can be treated as of order 2 . From eqs. (2.5)-(2.7), we deduce that the first (leading) contribution is of the second order, while the two interference terms are of the third one. However, differently from the standard interference term in eq. (2.6), the new sterile induced interference term in eq. (2.7) is not proportional to ∆, so it is not enhanced at the second oscillation maximum. Because of this feature, as it will be confirmed by our numerical simulations, the performance of ESSνSB in the 3+1 scheme is not as good as that of those experiments which work at the first oscillation maximum, such as T2HK and DUNE.

Experimental specifications
In this section, we briefly discuss the specifications of the experimental setup ESSνSB. ESSνSB is a proposed superbeam on-axis experiment where a very high intense proton beam of energy 2 GeV with an average beam power of 5 MW will be delivered by the European Spallation Source (ESS) linac facility running at 14 Hz. The number of protons on target (POT) per year (208 days) will be 2.7×10 23 [65][66][67][68]. It is worth to mention here that the future linac upgrade can push the proton energy up to 3.6 GeV. This highly ambitious and exciting facility is expected to start taking neutrino data around 2030. We have obtained the fluxes from [69] and these on-axis (anti)neutrino fluxes arising from the 2 GeV protons on target peaks around 0.25 GeV. In this case a 500 kt fiducial mass Water Cherenkov detector similar to the properties of the MEMPHYS detector [70,71] has been proposed to explore the neutrino properties in this low energy regimes. It has been shown in [65] that if the detector is placed in any of the existing mines located in between 300-600 km from the ESS site at Lund, it will make possible to achieve 5σ confidence level discovery of leptonic CP-violation up to the 50% coverage of the whole range of CP phases. A detailed study on the CP-violation discovery capability of this facility with different baseline and different combinations of neutrino and antineutrino run time has also been explored in [72]. In this work, we consider a baseline of 540 km from Lund to Garpenberg mine located in Sweden and also we have matched the event numbers of table 3 and all other results given in [65]. At this baseline, it fully covers the second oscillation maximum and it provides the opportunity to explore the CP-asymmetry which (in the 3-flavor scheme) is three times larger than the CP-asymmetry at the first oscillation maximum. Although the main drawbacks for going to the second oscillation maximum come from the significant decrease of statistics and cross-sections compared to the first oscillation maximum, the high intense beam of this excellent facility takes care of those difficulties and make the statistics competitive to provide exciting results. All our simulations presented here for this setup have been done assuming 2 yrs of ν and 8 yrs ofν running with a most optimistic consideration of uncorrelated 5% signal normalization and 10% background normalization error for both neutrino and antineutrino appearance and disappearance channels respectively. For more details of the accelerator facility, beamline design, and detector facility of this setup please see [65].

Details of the numerical analysis
This section details the numerical analysis adopted to produce the sensitivity results presented in the following sections. To compute the sensitivity measurements along with the -5 -

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bi-events plots we have used the GLoBES software [73,74] and its new tool [75] which can include the sterile neutrinos. In this paper, we have adopted the same strategy for the simulation described in section 4 of ref. [76]. The true values of the oscillation parameters together with their marginalization ranges considered in our simulations are presented in table 1. Our benchmark choices for the three-flavor neutrino oscillation parameters closely resemble those obtained in the latest global fits [58][59][60], although we have made the true choice of the atmospheric mixing angle to be maximal (45 • ), 2 and in the fit, it has been marginalized over its allowed range as mentioned in the third column of table 1. Concerning the active-sterile mixing angles we have taken the benchmark values very close to those obtained in the global fit analyses [61][62][63][64] performed within the 3+1 scheme. 3 In all our simulations, we have assumed normal hierarchy 4 (NH) as the true choice and we have kept it fixed also in the fit. In fact, we are assuming that the correct hierarchy will be already known by the time ESSνSB will start to take data. The two mixing angles θ 12 and θ 13 have been kept fixed in the data as well as in the fit taking into account the stringent constraints provided by the solar and the reactor data. We have also kept the two mass-squared differences ∆m 2 21 and ∆m 2 31 fixed at their true choices and they have not been marginalized in the fit. δ 13 (true) has been taken from its allowed range of [−π, π], while in the fit we have marginalized over its full range depending on the analysis requirement. In our simulations, we consider the constant line-averaged Earth matter density of 2.8 g/cm 3 following the Preliminary Reference Earth Model (PREM) [77]. The new mass-squared splitting ∆m 2 41 arising in the 3+1 scheme is taken as 1 eV 2 following the present preference of the short-baseline data. 5 This large value of ∆m 2 41 induces fast oscillations which get averaged out due to the finite energy resolution of the detector. As a result the sign of ∆m 2 41 is irrelevant in this setup. Now, the new mixing angles θ 14 and θ 24 emerging out of the 3+1 framework, have been taken fixed at their true values in the data as well as in the fit. 6 The true value of the new CP phase δ 14 is taken in its allowed range [−π, π] and its test value has been marginalized over the allowed range if required. The mixing angle θ 34 has been considered to be zero both in the data and in theory. This choice makes the presence of its associated phase δ 34 irrelevant in the simulation. 7 2 Recent 3ν global fits [58][59][60] sligthy prefer non-maximal θ23 with two nearly degenerate solutions: one is < 45 • , in the lower octant (LO), and the other is > 45 • , in the higher octant (HO). However, maximal mixing is still allowed at 2σ confidence level. 3 We stress that assuming smaller values for θ14 and θ24 the impact of active-sterile oscillations would decrease. As a consequence the sensitivity to CPV induced by δ14 would be reduced. On the other hand, the deterioration of the sensitivity to the CPV induced by the standard CP phase δ13 would be less. 4 We have checked that the results with the true choice of inverted hierarchy are similar to the results presented in this work. 5 We stress that our sensitivity results would remain unaltered provided ∆m 2 41 0.1 eV 2 . 6 We point out that our choice to fix the fit values of θ14 and θ24 is well justified if one assumes (as we do) that one has precise information on these two parameters coming form SBL experiments. In such a case, the marginalization of θ14 and θ24 in the fit would provide minor modifications to our results. 7 According to our parametrization followed in eq. (2.1), the νµ → νe oscillation probability in vacuum is independent of θ34 (and δ34). However it has a higher order ( 4 ) impact in presence of matter effect, which in case of ESSνSB baseline is very small. Hence θ34 (and δ34) can safely be ignored in the simulation. A detailed discussion including some analytical understanding regarding this issue is given in the appendix of ref. [27]. In our analysis, we do not consider any near detector of ESSνSB which may help to reduce the systematic uncertainties and might give some information on the two mixing angles θ 14 and θ 24 . However, it would give no information regarding the active and sterile CP phases which is our main issue of interest in the present work. It is worth to underline here that in all our simulations we have performed a spectral analysis making use of the binned events spectra. In the statistical analysis we not only marginalize over the oscillation parameters but also over the nuisance parameters adopting the well-known "pull" method [78,79] to calculate the Poissonian ∆χ 2 . We display our results in terms of the squared-root of ∆χ 2 which represents nσ (n ≡ ∆χ 2 ) confidence level statistical significance for one degrees of freedom (d.o.f).

Mass ordering and θ 23 octant sensitivity in the 4-flavor scheme
It is well known that in the 3-flavor scheme ESSνSB has scarce sensitivity to both these two properties. Concerning the MH hierarchy, the lack of sensitivity is due to the fact that matter effects are very small in ESSνSB. The low sensitivity to the octant of θ 23 is imputable to the fact that ESSνSB works at the second oscillation maximum, which is more narrow than the first one. These features, together with the lower statistics, render ESSνSB much less sensitive than other experiments (T2HK for example) to the octant of θ 23 .
Here we confirm similar findings also in the 4-flavor scheme. This conclusion can be easily understood through a discussion at the level of the neutrino and antineutrino appearance events. The left panel of figure 1 reports the bievent plots, where the x-axis represents the number of ν e events and the y-axis represents theν e events. The two ellipses represent the JHEP12(2019)174 3-flavor model and can be obtained by varying the CP phase δ 13 in the range [−π, π]. The solid (dashed) ellipse corresponds to the NH (IH). The centroids of the two ellipses basically coincide, hence it is clear that the setup cannot discriminate the MH. This is qualitatively different with respect to what occurs in other LBL experiments (T2HK [46] and especially DUNE [41]), where the two ellipses get separated due to the presence of the matter effects. In the 3+1 scheme, two CP phases are present and their variation in the range [−π, π] gives even more freedom. The bievent plots obtained varying both the CP phases δ 13 and δ 14 are represented by colored elongated blobs in the left panel figure 1. The two blobs corresponding to the two hierarchies are completely overlapped. This implies that, similarly to the 3-flavor scheme, one does not expect any sensitivity to the MH in the 3+1 scheme as well.
The right panel of figure 1 reports the ellipses (blobs) obtained in the 3-flavor (4flavor) cases for two values of θ 23 chosen in the two opposite octants. We have taken sin 2 θ 23 = 0.42 (0.58) as benchmark values. We observe that in both schemes there is a partial overlapping between the regions representing the two octants. The degree of overlapping increases when going from 3-flavor to the 3+1 scheme. Therefore, we expect a poor sensitivity to the octant of θ 23 both in 3ν and 4ν schemes. Differently from T2HK, the spectral information is not of great help due to the low statistics. This is confirmed by the numerical simulations (not shown) performed by including the full energy spectrum in the fit.

CP-violation searches in the 4-flavor framework
In this section, we analyze the capability of ESSνSB of pinning down the extended CPV sector entailed by the 3+1 scheme. First we assess the sensitivity to the CPV induced by the CP phase δ 13 and δ 14 . Second we discuss the capability of reconstructing the true values of the two phases δ 13 and δ 14 .

Sensitivity to CP-violation
The sensitivity of CPV produced by a fixed (true) value of a CP phase δ true ij can be defined as the statistical significance at which one can reject the test hypothesis of no CPV, i.e. the two (test) cases δ test ij = 0, π. In the left panel of figure 2, we report the discovery potential of CPV induced by δ 13 . We have assumed that the hierarchy is known a priori and is NH. The dashed black curve correspond to the 3-flavor scheme while the green band to the 3+1 scheme. In the 3+1 scenario, we fix the test and true values of θ 14 = 9 0 and θ 24 = 9 0 . The green band is attained by varying the unknown true value of δ 14 in the range of [−π, π] and marginalizing over its test values. We observe that in the 3+1 scheme there is a deterioration of the sensitivity. Adopting δ 13 = −90 0 as a benchmark value in the 3-flavor (4-flavor) scheme one has 8.2σ (4.5σ) sensitivity. We find very similar result for the case of IH (not shown). The right panel of figure 2 displays the discovery potential of CPV induced by δ 14 for the NH case. The magenta band is obtained by varying the true values of the CP phase δ 13 in the range [−π, π] while marginalizing over their test values in the same range in the fit. We observe that ESSνSB has a limited sensitivity to the CP phase δ 14 , which is always below the 2σ level. In both panels the MH is fixed to be the NH (both true and test value). The black dashed curve corresponds to the 3-flavor case while the colored band correspond to the 3+1 scheme. In this last case, we have fixed the true and test values of θ 14 = θ 24 = 9 0 and varied the unknown value of the true δ 14 in its entire range of [−π, π] while marginalizing over test δ 14 in the same range.
We think that it is useful to make a comparison between the results obtained here for ESSνSB with those found for T2HK in our work [46]. We notice that in the 3-flavor scheme both experiments have a similar sensitivity to CPV induced by δ 13 , having both a maximal sensitivity of about 8σ for the values δ 13 ±90 0 . This is possible because, despite of the lower statical power, ESSνSB benefits of the amplification factor proportional to ∆, which is three times bigger at the second oscillation maximum with respect to the first one. In contrast, in the presence of a sterile neutrino, the performance is much worse in ESSνSB. In fact, one can notice the two following features: i) The deterioration of the sensitivity to the CPV driven by δ 13 when going from the 3-flavor to the 3+1 scheme is much more pronounced in ESSνSB than in T2HK. Taking the values δ 13 = ±90 0 as a benchmark (where the maximal sensitivity is attained) in [46], we found for T2HK only a weak reduction of the sensitivity from 8σ to 7σ (see figure 4 in [46]). In ESSνSB, we now find a severe reduction from 8σ to 4.5σ (see left panel of figure 2); ii) The sensitivity to the CPV induced by the CP phase δ 14 is considerably lower in ESSνSB than in T2HK (2σ vs 5σ for δ 14 = ±90 0 ). The explanation of such a different performance in the 3+1 scheme of the two experiments can be traced to the fact that T2HK (ESSνSB) works around the first (second) oscillation maximum. As already noticed in subection 2.2, the new interference term (which depends on δ 14 ), at the second oscillation maximum is not amplified by the factor ∆ as it happens for the standard interference term (which depends on δ 13 ). In addition, as remarked in [46] in T2HK the spectral information plays a crucial role in guaranteeing a good performance in the 3+1 scheme. Indeed, in [46], we explicitly showed that even if there is a complete degeneracy at the level of the event counting, the energy spectrum provides additional  The two black marks represent the cases of no CPV (δ 13 = 0, π) while the two colored ones correspond to the cases of maximal CPV (δ 13 = −π/2, π/2). The non-zero distance between the black marks and the colored ones implies that events counting can detect the CPV induced by the phase δ 13 . The second panel refers to the 3+1 scheme. In this case a fixed value of δ 13 is represented by an ellipse, where δ 14 varies in the range [−π, π]. The non-zero distance between the black ellipses and the two colored ones implies that events counting is sensitive to CPV induced by the phase δ 13 also in the 3+1 case. However, the distances are reduced with respect to the 3-flavor case. Therefore, the sensitivity decreases. The right panel refers to the 3+1 scheme and illustrates the sensitivity to the CPV induced by δ 14 . In this case we plot four ellipses corresponding to the four values of δ 14 (while δ 13 is varying in the range [−π, π]). Each of the two ellipses (blue and red) corresponding to maximal CPV induced by δ 14 intercepts the two ellipses (solid and dashed black) corresponding to no CPV induced by δ 14 . In the crossing points the events counting is completely insensitive to CPV induced by the new CP phase δ 14 .
information which breaks such a degeneracy and boosts the sensitivity. In ESSνSB, the role of the spectral information is substantially reduced because of the energy range at the second oscillation maximum is very narrow and the low statistics does not allow to exploit the information contained in the spectrum. Hence, we conclude that ESSνSB is not particularly suited for the CPV related searches in the presence of sterile neutrinos. The situation can be further clarified by inspecting the 3-panel bievent plot displayed in figure 3. The left panel refers to the standard 3-flavor framework. In this case the model lies on the (green) ellipse, which is obtained by varying δ 13 in the range [−π, π]. The two black marks represent the cases of no CPV (δ 13 = 0, π) while the two colored ones correspond to the cases of maximal CPV (δ 13 = −π/2, π/2). The non-zero distance between the black marks and the colored ones implies that events counting can detect the CPV induced by the phase δ 13 . The second panel refers to the 3+1 scheme. In this case a fixed value of δ 13 is represented by an ellipse, where δ 14 varies in the range [−π, π]. The non-zero distance between the black ellipses and the two colored ones implies that events counting is sensitive to CPV induced by the phase δ 13 also in the 3+1 case. However, the distances are reduced with respect to the 3-flavor case. Therefore, the sensitivity decreases as found in the numerical simulation as shown in the left panel of figure 2. The right panel of figure 3 refers to the 3+1 scheme and illustrates the sensitivity to the CPV induced by δ 14 .
In this case we plot four ellipses corresponding to the four values of δ 14 (while δ 13 is varying  in the range [−π, π]). Each of the two ellipses (blue and red) corresponding to maximal CPV induced by δ 14 intercepts the two ellipses (solid and dashed black) corresponding to no CPV induced by δ 14 . In the crossing points the events counting is completely insensitive to CPV induced by the new CP phase δ 14 . Therefore there are always (unlucky) combinations of the CP phases for which the event counting cannot determine if there is CPV induced by δ 14 . Notwithstanding in the right panel of figure 2, we observe that there is ∼ 2σ sensitivity for δ 14 = ±90 0 . We have checked that such a residual sensitivity comes from the spectral shape information. As already remarked above, this information in ESSνSB is much weaker compared to T2HK, and as a consequence the sensitivity remains quite low.

Reconstructing the CP phases
So far we have discussed the sensitivity to the CPV induced by the two CP phases δ 13 and δ 14 . Here, we study the ability of the ESSνSB setup to reconstruct the two CP phases. With this aim, we focus on the four benchmark cases shown in figure 4. The first two panels correspond to the CP-conserving cases (0, 0) and (π, π). The lower panels represent two CP-violating scenarios (−π/2, −π/2) and (π/2, π/2). In each panel, we show the regions reconstructed close to the true values of the two CP phases. In this figure we have fixed the NH as the true and test hierarchy. The contours are shown for the two different confidence . 8 We end this section by comparing the performance of the ESSνSB setup with the two other proposed long-baseline facilities: DUNE 9 and T2HK. 10 In figure 5, we show the reconstructed regions for ESSνSB, DUNE, and T2HK for the same benchmark values of the true phases considered in figure 4. To have the visual clearness, we only depict the 3σ (1 d.o.f.) contours. While making this plot, we consider the NH as the true and test hierarchy. The performance of ESSνSB in reconstructing δ 13 is almost similar to that of DUNE and T2HK. In contrast, the reconstruction of δ 14 is slightly better for T2HK and DUNE as compared to ESSνSB.

Conclusions and outlook
We have studied in detail the potential of ESSνSB in the presence of a light eV-scale sterile neutrino with an emphasis on the CPV searches. We have presented our results assuming a baseline of 540 km, which provides a platform to exploit the featutres of the second oscillation maximum. We have found that the sensitivity to CPV driven by the standard CP phase δ 13 substantially deteriorates with respect to the standard 3-flavor case. More specifically, the maximal sensitivity (assumed for δ 13 ∼ ± 90 0 ) drops from 8σ down to 4.5σ if the size of the mixing angles θ 14 and θ 24 is similar to that of θ 13 . The sensitivity to the CPV induced by δ 14 is modest and never exceeds the 2σ level for the baseline choice of 540 km. We have also studied the ability of reconstructing the two phases δ 13 and δ 14 . The 1σ error on δ 13 (δ 14 ) is ∼ 15 0 (35 0 ). As far as the octant of θ 23 is concerned, the benchmark setup under consideration for the ESSνSB experiment provides poor results in the 3-flavor scenario and performs even worse in 3+1 scheme. Needless to mention that ESSνSB benefits a lot from working at the second oscillation maximum and provides excellent sensitivity to CPV in 3ν scheme. However, in the present work we find that this setup with a baseline of 540 km is not optimal for exploring fundamental neutrino properties in 3+1 scenario.