CeSOX sensitivity studies

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Ma#hieu VIVIER, Guillaume MENTION

CEA-‐Saclay, DSM/IRFU/SPP

CeSOX kick-‐oﬀ meeCng

Paris, February 5

th

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L/E spectrum modeling and χ

2

§  _{Model computes L/E expected anti-ν}_e_{spectrum. It includes:}

o  Production of anti-ν_e: 144Pr beta spectrum (see M. Durero talk about modeling of 144Pr beta spectrum)+ source finite size effects

o  Detection of anti-ν_e: up to date IBD cross-section, number of proton targets, detection efficiency

o  Energy and position reconstruction resolutions o  Systematics uncertainties:

•  _{Fully correlated normalization uncertainty related to source activity uncertainty} o  (3+1) sterile neutrino model

§  χ2_analysis:

where i runs over (L/E) bins

X

i

✓

N

obs_i

(1 + ↵)N

exp_i

(✓,

m

2

)

stat i

◆2

+

✓

↵

◆2

P

⌫¯e!¯⌫e

= 1

sin

2

_{(2✓) sin}

2

✓

1.27 m

2

_L

E

◆

IBD

(E

e

) =  p

e

E

e

(1 +

rec

+

rad

+

WM

)

•  _{κ = 9.596 × 10}-44_cm2_MeV-1

•  _{Recoil & WM corrections from Fayans (1985)} •  Radiative corrections from Vogel (1984)

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Model ingredients: L & E distributions

E

L

An%-‐nu path length distribu%on

AntiNu source energy spectrum, Pr144_OptWM

True neutrino energy E [MeV]

Counts per 1.00 keV bins

0 0.5 1 1.5 2 2.5 3 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 144_{Pr
an%-‐nu
spectrum}

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Model ingredients: L/E resolution functions

L_rec/E_rec [m MeV−1]

arbitrary units

Normalized L/E resolution function − 1.8 MeV < E 3 MeV, 3 m < L < 13 m

0 2 4 6 8 10 12 14 0 1 2 3 4 5 6 7 Solid lines: − Eres = 5%/sqrt(E) − Vres = 15 cm Dot−dashed lines: − Eres = 5%/sqrt(E) − Vres = 50 cm Dashed lines: − Eres = 15%/sqrt(E) − Vres = 15 cm

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Model ingredients: L/E resolution

§  _{Width of L/E resolution as a function of L/E:}

L/E [m MeV−1] L/E [m MeV − 1 ] 1.8 MeV < E < 3 MeV − 3 m < L < 13 m 1 2 3 4 5 6 7 8 9 10 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 E = 5% − L = 15 cm E = 5% − L = 50 cm E = 15% − L = 15 cm

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Number of expected IBD candidates

Distance/

Activity 75 kCi 100 kCi 140 kCi

6 m 14230 18970 26580 8.25 m 7060 9410 13180 12 m 3230 4310 6030 CeSOX – R < 4.25 m CeSOX nominal Distance/

Activity 75 kCi 100 kCi 140 kCi

6 m 35220 47040 65650

8.25 m 16040 21370 29940

12 m 7140 9520 13320

CeSOX – R < 5.5 m

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L/E spectrum expected in Borexino

Counts per 0.10 m MeV

− 1 bin 0 50 100 150 200 250 300 350 No oscillations sin2(2 new) = 0.29, m 2 new = 0.25 eV 2 sin2(2 new) = 0.10, m 2 new = 3 eV 2 sin2(2 new) = 0.29, m 2 new = 10 eV 2 L/E (m MeV−1)

(Osc/no osc) ratio

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 0.7 0.75 0.8 0.85 0.9 0.95 1

§  _{Statistical error bars only}

§  _{Average L/E is around 3.2 m MeV}-1_:

corresponds to resolution of 0.1 m MeV-1

§  _{Exponential damping of oscillations} because of detector resolution §  _{Small Δm}2_{(≤ 0.5 eV}2_{) hardly visible}

because of detector size, unless mixing is large

§  _{Good for intermediate Δm}2_{(0.5 – 5 eV}2₎

§  _{High Δm}2_{oscillations averaged because}

binning size > oscillation length + exponential damping: hardly visible unless large mixing angle

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CeSOX χ

2 _sensitivity

§  _{Take 0.2 m MeV}-1_{bins (twice L/E resolution)}

§  _{Compute sensitivity to « no oscillation » hypothesis, according to χ}2_{formula shown}

previously §  Δχ2_{= χ}2_-χ2

min follows χ2 distribution with 2 dof

§  _{In next slides, chose 95% CL, Δχ}2_{= 6}

§  _{Reminder: χ}2_{contours are statistically averaged contours}_{. If we perform N realizations, allowing for}

statistical fluctuations, the average of obtained contours must give the contour displayed on sensitivity plots.

sin2(2_new)

m new

2

(eV

2)

CeSOX nominal − 100 kCi, 8.25 m from center, 1.5 years, 95% CL

10−2 10−1 100 10−2 10−1 100 101 102 rate + shape shape only Reactor anomaly, PRD 83 073006 (2011), 95% CL Reactor anomaly, PRD 83 073006 (2011), 90% CL sin2(2_new) mnew 2 (eV 2 )

CeSOX upgraded − 100 kCi, 8.25 m from center, 1.5 years, 95% CL

10−2 10−1 100 10−2 10−1 100 101 102 rate + shape shape only Reactor anomaly, PRD 83 073006 (2011), 95% CL Reactor anomaly, PRD 83 073006 (2011), 90% CL

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CeSOX contours features

sin2(2 _new) m new 2 (eV 2 )

CeSOX nominal − 100 kCi, 8.25 m from center, 1.5 years, 95% CL

10−2 10−1 100 10−2 10−1 100 101 102 rate + shape shape only Reactor anomaly, PRD 83 073006 (2011), 95% CL Reactor anomaly, PRD 83 073006 (2011), 90% CL

Losc much bigger than detector size

P ≈ 1 – α sin2(2θ) Δm2

L_osc comparable to detector size, but still less than 1 oscillation period is contained in

the detector.

Detector contains more than 1 oscillation period, best performances are here.

Sensitivity to oscillations is degraded because of exponential damping + size of

oscillations < binning size. Compensated

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Different confidence levels

§  _{With different confidence level @ 90, 95 and 99 %:}

Rate + shape Shape only

sin2(2 )

m

2 [eV 2]

CeSOX nominal − 100 kCi, 8.25 m from center, 1.5 years

10−2 10−1 100 10−2 10−1 100 101 102 90% C.L 95% C.L 99% C.L sin2(2 ) m 2 [eV 2 ]

CeSOX nominal − 100 kCi, 8.25 m from center, 1.5 years

10−2 10−1 100 10−2 10−1 100 101 102 90% C.L 95% C.L 99% C.L

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Impact of source-detector distance

CeSOX − 1.5 years, 95% CL 10−2 10−1 100 10−2 10−1 100 101 102 D = 6 m D = 8.25 m D = 12 m CeSOX − 1.5 years, 95% CL 10−2 10−1 100 10−2 10−1 100 101 102 D = 6 m D = 8.25 m D = 12 m Shape only Rate + shape

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§  Take a spherical source and increase radius:

§  _{Source extension doesn’t make any differences…}

Impact of source extension

CeSOX − 1.5 years, 95% CL 10−2 10−1 100 10−2 10−1 100 101 102 Point−like source R source = 7.5 cm R_source = 50 cm CeSOX − 1.5 years, 95% CL 10−2 10−1 100 10−2 10−1 100 101 102 Point−like source R source = 7.5 cm R_source = 50 cm

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Impact of energy resolution

CeSOX − 1.5 years, 95% CL 10−2 10−1 100 10−2 10−1 100 101 102 E = 2.5% E = 5% E = 10% CeSOX − 1.5 years, 95% CL 10−2 10−1 100 10−2 10−1 100 101 102 E = 2.5% E = 5% E = 10%

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Impact of position resolution

CeSOX − 1.5 years, 95% CL 10−2 10−1 100 10−2 10−1 100 101 102 _R = 5 cm R = 15cm R = 50 cm CeSOX − 1.5 years, 95% CL 10−2 10−1 100 10−2 10−1 100 101 102 _R = 5 cm R = 15cm R = 50 cm

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Impact of source activity

CeSOX − 1.5 years, 95% CL 10−2 10−1 100 10−2 10−1 100 101 102 A = 75 kCi A = 100 kCi A = 140 kCi CeSOX − 1.5 years, 95% CL 10−2 10−1 100 10−2 10−1 100 101 102 A = 75 kCi A = 100 kCi A = 140 kCi

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CeSOX vs CeLAND

sin2(2 new) m new 2 (eV 2)

CeSOX vs CeLAND − 1.5 years, 95% CL

10−2 10−1 100 10−2 10−1 100 101 102

CeSOX − 100 KCi, 8.25 m from center, R < 4.25 m CeLAND − 65 kCi, 9.6 m from center, R < 6.5 m Reactor anomaly, PRD 83 073006 (2011), 95% CL Reactor anomaly, PRD 83 073006 (2011), 90% CL sin2(2 new) m new 2 (eV 2)

CeSOX upgraded vs CeLAND − 1.5 years, 95% CL

10−2 10−1 100 10−2 10−1 100 101 102

CeSOX − 100 KCi, 8.25 m from center, R < 5.5 m CeLAND − 65 kCi, 9.6 m from center, R < 6.5 m Reactor anomaly, PRD 83 073006 (2011), 95% CL Reactor anomaly, PRD 83 073006 (2011), 90% CL

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Conclusions

§  _{Competitive limits with CeSOX nominal scenario. Most of the anomaly parameter space is}

covered at 95% C.L.

§  _{Very good limits with upgraded Borexino detector: better than KamLAND taking into}

account the transport constraints (higher activity is achievable if deploying at Borexino).

§  _{Contours more sensitive to energy resolution than vertex resolution.}

§  Source extension does not impact the sensitivity

§  Other systematic uncertainty studies ongoing…

o  Effect of fiducial volume uncertainty (what is the fiducial volume uncertainty in Borexino?)

o  Effect of a « radius scale » uncertainty? (Is there any systematic bias associated to the vertex reconstruction in Borexino?) – KamLAND collaboration claimed one in their volume calibration paper (Berger et al. (2009)).

o  Effect of an energy scale uncertainty? (What is the energy scale uncertainty in Borexino?)

o  Any backgrounds systematics that we should include in the sensitivity study? Strongly depends on source impurities content…

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