www.postersession.comXXIX International Conference on Neutrino Physics and Astrophysics, June 22 to July 2, 2020. XXIX International Conference on Neutrino Physics and Astrophysics, June 22 to July 2, 2020. Exposure-background duality in the searches of neutrinoless double beta decay M. K. SinghInstitute of Physics, Academia Sinica, Taipei, Taiwan Institute of Physics, Academia Sinica, Taipei, Taiwan Based on: M. K. Singh, H. T. Wong et al., Phys. Rev. D 101, 013006 (2020). Background can be predicted. Poisson statistics handles: (i) Low background; (ii) Rare processes. Model - Inverse correlation between G0ν and |M0ν|2. Decay rates (1 event/ton-yr with full efficiency) are similar at given <mββ> and constant gA. No favored 0νββ isotope. ∑ (ton-year) . ɛ𝐑𝐨𝐈 𝑵𝐨𝐛𝐬 𝟎ν α 𝟏 <𝒎𝜷𝜷> 𝟐 Realistic interpretation lies within a factor of [0.5, 2.0]. RoI = w1/2 (FWHM): Not the optimal choice when B0 →0. Alternative choice: RoI ≡w3σ (Qββ ± 3σ), thus εRoI ≅100%. Better sensitivity by a factor of εRoI (w1/2 = 0.76). Covered 𝑻𝟏/𝟐 𝟎𝝂is 32% longer, or Σ is 24% less. Background Index (BI) defined as: BI= 𝐁𝟎(𝐑𝐨𝐈) ∑ Universally applicable. BI < 0.21 counts/w1/2-ton-yr cover <𝒎𝜷𝜷𝟗𝟓% 𝐈𝐇> BI < 0.033 counts/w1/2-ton-yr cover <𝒎𝜷𝜷− 𝐈𝐇> Standard-Model-allowed irreducible background 𝒁 𝑵𝑨𝜷𝜷→ 𝒁+𝟐 𝑵−𝟐𝑨𝜷𝜷+ 𝟐 𝒆+ 𝟐 𝝂[Goeppert-Mayer, 1935] Worse resolution (Δ) Larger RoI Larger 2νββ Background Resolutions under BImin conditions Δ ≤ (0.3-0.9)% cover <𝒎𝜷𝜷− 𝐈𝐇> Δ ≤ (0.1-0.3)% cover <𝒎𝜷𝜷− 𝐍𝐇> ♣MJD Best Resolution Δ(76Ge) = 0.12% BI < 6×10−10 counts/(w1/2-ton-yr) Covering <𝒎𝛃𝛃−𝐍𝐇> will require large and costly exposure. Reduction of BI will be playing increasingly significant. Same exposure can probe longer 𝑻𝟏/𝟐 𝟎ν and smaller <mββ> with decreasing background. ▲Half-life in Mass Mechanism : 𝟏 𝑻𝟏/𝟐 𝟎𝝂 = 𝑮𝟎𝝂𝒈𝑨 𝟒𝑴𝟎𝝂𝟐<𝒎𝜷𝜷> 𝒎𝒆 𝟐 ▲Effective Mass: <mββ> = |U𝒆𝟏 𝟐|m1 + |U𝒆𝟐 𝟐|m2eiα + |U𝒆𝟑 𝟐|m3eiβ| ▲Experimentally measurable Half-life: ▲Combined Half-life: 𝑻𝟏/𝟐 𝟎𝝂= 𝒍𝒏𝟐. 𝑵𝑨𝜷𝜷. 𝒕𝐃𝐀𝐐. ɛ𝑹𝒐𝑰 𝑵𝒐𝒃𝒔 𝟎𝝂 = 𝒍𝒏𝟐. 𝑵𝑨 𝑴(𝑨𝜷𝜷) . ∑. ɛ𝑹𝒐𝑰 𝑵𝒐𝒃𝒔 𝟎𝝂 𝑴𝟎𝝂𝟐[𝒈𝑨 𝟒. 𝑯𝟎𝝂] = 𝟏 <𝒎𝜷𝜷>𝟐 𝟏 ∑. 𝑵𝒐𝒃𝒔 𝟎𝝂 ɛ𝑹𝒐𝑰; 𝑯𝟎𝝂≣𝒍𝒏𝟐 𝑵𝑨 𝑴𝑨𝜷𝜷.𝒎𝒆𝟐 Formulation Discovery Potential ∑𝐢=𝟎 𝐍𝐨𝐛𝐬 𝟑𝛔−𝟏 𝐏𝐢; 𝐁𝟎≥𝟏−𝟎. 𝟎𝟎𝟏𝟑𝟓 ∑𝐢= 𝐍𝐨𝐛𝐬 𝟑𝛔 ∞ 𝐏𝐢; [𝐁𝟎+ 𝐒𝟎] ≥𝟎. 𝟓 Only integer counts can be observed in an experiment. Theme Theme::T To reach the following target sensitivities: (i) <𝒎𝜷𝜷− 𝐈𝐇> = 1.4×10-3 eV, (ii) <𝒎𝜷𝜷+ 𝐈𝐇> = 5.1×10-2 eV, (iii) <𝒎𝜷𝜷𝟗𝟓% 𝐈𝐇> = 2.0×10-2 eV (iv) <𝒎𝜷𝜷− 𝐍𝐇> = 7.8×10-4 eV, (v) <𝒎𝜷𝜷+ 𝐍𝐇> = 4.3×10-3 eV, (vi) <𝒎𝜷𝜷𝟗𝟓% 𝐍𝐇> = 3.0×10-3 eV. Relating 𝑻𝟏/𝟐 𝟎𝝂with <mββ> - Model for |M0ν| Required Exposure and Background Limiting Irreducible Background Summary Conversion to Realistic Configurations Considered: IA = 100%, εexpt = 100% and “unquenched” free nucleon value of gA =1.27 Conversion: In realistic experiments: Σ’ ≃Σ. 𝟏 IA . 𝟏 ɛexpt .WΣ(gA) and BI’(Σ’) ≃BI· Σ Σ’ § Neutrinoless double beta decay (0νββ) [Furry, 1939] 𝒁 𝑵𝑨𝜷𝜷→ 𝒁+𝟐 𝑵−𝟐𝑨𝜷𝜷+ 𝟐 𝒆 ●Forbidden in Standard Model !!! ●∆L = 2 !!! § Observation of 0νββ implies new physics:● ●Neutrinos Neutrinosare areMajorana Majoranaparticles particles( (νν= =ത ν) )● ●Lepton Leptonnumber numberviolations violations● ●Effective Effectivelight lightMajorana MajoranaNeutrino NeutrinoMass Mass< <mmββββ>>≠≠0 0 § Energetically possible for 35 nuclei ●A few are experimentally relevant § Present work: Required Exposure vs Background Introduction STEP-1 STEP-2 R. G. H. Robertson, Mod. Phys. Lett. A 28, 1350021 (2013). Target exposure: Next-generation 0νββ projects 10 ton-year to cover IH GERDA: Background level = 𝟏. 𝟎−𝟎.𝟒 +𝟎.𝟔counts/keV-ton-yr or BI ∼3 counts/w1/2-ton-yr. Choice: BI ≡ BI0 = 1 count/w1/2-ton-yr requires 110 ton-yr cover <mββ>− 𝐈𝐇 11 Mton-yr cover <mββ>− 𝐍𝐇 Suppression in BI: [1 to 10−3] counts/(w1/2-ton-yr) contributes reduction in exposure BImin equivalently Σmin condition: Single observed event can establish signal at 𝐏𝟓𝟎 𝟑𝛔 Preferred hardware specification space Σ=10 ton-yr Next generation: BImin<5.1×10−5 counts/w1/2-ton-yr <mββ> > (5.8×10−3)eV <mββ>+ 𝐍𝐇= 4.3×10−3eV Be