SUSY-related Lepton and Hadron Flavor Results from Belle Yutaro Sato

Transcription

1 SUSY-related Lepton and Hadron Flavor Results from Belle Yutaro Sato For the Belle Collaboration (Nagoya Univ., KMI) 27 th Aug. 2015, Lake Tahoe, USA

2 New physics search at Belle 2 New particles (e.g. SUSY particles) could enter in the tree, loop, and box diagrams. Observables (such as branching fraction or asymmetry) are modified. Tree Loop Box Topics covered in this talk : 1. B D ( ) τν with hadronic tag (arxiv: , submitted to PRD) 2. B πτν with hadronic tag 3. B s φγ, γγ (PRD 91, (R)(2015)) 4. A CP (B X s+d γ) (PRL 114, (2015))

3 Belle Experiment Integrate luminosity [fb -1 ] 3 KEKB accelerator and Belle detector at Tsukuba, Japan. Asymmetric e + e energy to boost B mesons Data taking for Good particle ID capability (p, π ±, K ±, γ, e, μ, K L 0 ) Good momentum resolution σ P t P t = 0.19P t 0.30 β % KEKB accelerator e e + SC solenoid (1.5T) CsI(Tl) 16X 0 TOF counter L int. > 1 ab 1 L peak = cm 2 s 1 Time [year] Aerogel Cherenkov cnt. (n=1.015~1.030) e + (3.5 GeV) ~3 km circumference e (8 GeV) Central Drift Chamber small cell +He/C 2 H 6 Si vtx. det. (3/4 lyr. DSSD) m / K L detection 14/15 lyr. RPC+Fe

4 Hadronic tagging with Neural Network 4 B e e + B Signal side Signal decay Tag side B tag is completely reconstructed from hadronic decay (B D ( ) X, J/ψX, ). Event selection by using NeuroBayes (neural network) exclusive decays are used. Especially, useful for final states with neutrinos. (e.g.) B D ( ) τν, πτν, NIMA 654, 432 (2011)

5 Sensitive to charged Higgs. Observables R D = B D ( ) τν with Hadronic Tag B (B Dτν) B (B Dlν) (l = e, μ) Several systematic uncertainties mostly cancel out in the ratio. V cb, (part of) form factors, experimental efficiencies. All measurements indicate R D higher than SM. Selection B tag is reconstructed by hadronic tagging based on Neural network. Leptonic τ decays are used. Same final state as B D ( ) lν 4 D ( ) l final states (D + l, D 0 l, D + l, D 0 l) No further tracks or π 0 q 2 > 4 GeV GeV 2 2 < M miss < 8.0 GeV 2 b W + /H + Virtual boson mass-squared q 2 = (p B p D ( )) 2 Missing mass-squared 2 M miss = (p Beam p Btag p D ( ) p l ) 2 5 ν τ c

6 2 Split sample at M miss Fit Strategy = 0.85 GeV 2 /c 4 B D ( ) τν with hadronic tag 6 D ( ) lν enhanced D ( ) τν enhanced D 0 l samples (@MC) D 0 l samples (@MC) D ( ) τν-signal Sig. (Dτν) 2 Fit in M miss to determine D ( ) lν Fit in Neural Network output to separate sig. from bkg. (mainly D lν) Bkg. (D lν)

7 Fit Strategy 4 D ( ) l channels are simultaneously fitted. B D ( ) τν with hadronic tag 7 D ( ) lν enhanced D ( ) τν enhanced D 0 l samples (@MC) D 0 l samples (@MC) Total 12 free parameters Small backgrounds are fixed, 4 parameters for B D lν relying MC expectation. 2 parameters for R D ( ) Events with falsely reconstructed D ( ) assuming isospin symmetry is determined by sideband of Δm (m D ). 2 parameters for cross-feed from D l to Dl 4 parameters for B D lν

8 Fit for D l Samples B D ( ) τν with hadronic tag 8 D lν-enhanced region 2 (M miss < 0.85 GeV 2 /c 4 ) D τν-enhanced region 2 (M miss > 0.85 GeV 2 /c 4 ) B D lν (normalization) B D τν (signal) D + l D 0 l

9 Fit for Dl Samples B D ( ) τν with hadronic tag 9 Dlν-enhanced region 2 (M miss < 0.85 GeV 2 /c 4 ) Dτν-enhanced region 2 (M miss > 0.85 GeV 2 /c 4 ) B D lν (normalization, CF) B D lν (normalization) B D τν (signal, CF) B D τν (signal) D + l D 0 l

10 Result R D = stat. ± syst. R D = stat. ± syst. Results B D ( ) τν with hadronic tag Analysis is repeated for type-ii 2HDM with tanβ/m H+ = 0.5 GeV Belle result is consistent with SM and BaBar result within 2σ.

11 Search for B πτν 11 Motivation Deviation from SM in B D ( ) τν decay. B πτν can be also used for SM test. b W + /H + ν τ u Decay amplitude Vector FF Scalar FF B(B πτν)/dq2 B(B πlν)/dq 2 only depends on the ratio of form factors : f0 (q 2 )/f + (q 2 ). Search for first evidence of B πτν

12 Analysis Analysis B tag is reconstructed by hadronic tag based on Neural network. Four one-prong τ decays are used τ eνν, μνν, πν, ρν (τ μνν is only used as veto due to less significance) Signal signature exactly 2 oppositely charged tracks in signal side large missing momentum by (two or three) neutrinos Backgrounds No remaining tracks and K L 0 veto. 2 B πlν is removed by selection on M miss. Backgrounds are suppressed using Boosted Decision Trees. Main backgrounds in signal region : B Dlν, B Dπ with D K L 0 π Signal is extracted from extra energy on ECL (E ECL ) B ν τ π B πτν with hadronic tag ν(s) (e/μ/π/ρ) 12

13 Result Fit is simultaneously performed in all three modes. 4 fit parameters : 1 parameter for Sig. and 3 parameters for b c Bkg. Other background is fixed and systematic uncertainty is estimated. B πτν with hadronic tag 13 Signal yields : 52 ± 24 events B B 0 πτν = (1.52 ± 0.74) 10 4 (stat. only) Close to SM prediction : (9.35 ± 0.38) σ significance including systematic uncertainties. Upper Limits B B 0 πτν < % C.L. B B 0 πτν < % C.L. Dominant syst. sources : Tag side efficiency K L 0 veto efficiency

14 B s φγ, γγ 14 B s φγ First observation by Belle PRL 100, (2008) (23.6 fb -1 ) Update with full Belle data (121.4 fb -1 ) Theoretical prediction is with 30% uncertainty Most precise measurement by LHCb : (35.1 ± 3.5 ± 1.2) 10 6 Nucl. Phys. B867, 1 (2013) Eur. Phys. J.C 55, 577 (2008) PRD 75, (2007) B s γγ Current best upper limits : % C.L. by Belle. Theoretical predictions (2 8) 10 7 PRD 56, 5805 (1997) (1.8 ± 0.4) 10 7 PRD 85, (2012) JHEP 08, 054 (2002) In R-parity violating model, it may be enhanced. Search for first evidence with full Belle data (121.4 fb -1 ) PRL 100, (2008) (23.6 fb -1 )

15 4-dimensional fit 2 2 M bc = E beam p BS ΔE = E BS E beam C NB (Neural network output for continuum suppression) cos θ hel (φ helicity angle) Result of B s φγ Three signal peaks (B s B s, B s B s, B s B s ) B s φγ f s = 17.2 ± 3.0 %, f Bs B s = 87.0 ± 1.7 % f Bs B s = (7.3 ± 1.4)% N sig = Result B B s φγ = (36 ± 5 stat. ± 3 syst. ± 6(f s )) 10 6 (10.7σ significance including systematics) Consistent with theoretical prediction and LHCb result.

16 2-dimensional fit (M bc, ΔE) Result of B s γγ Dominant backgrounds of continuum (ee qq q = u, d, s, c ) are suppressed by neural network output Modified Fox-Wolfram moments and thrust angle are used. B s γγ 16 Best fit line (N sig = ) Fit with the signal yield constrained to U.L. (90% C.L.) Upper Limits B B s γγ < % C.L.

17 A CP (B X s+d γ) 17 A CP = Γ B X s+ d γ Γ(B X s+dγ) Γ B X s+ d γ +Γ(B X s+dγ) Cancellation due to CKM unitarity, Negligible theory error channel A CP (SM) B X s γ [ 0.6%, +2.8%] B X d γ [ 62%, +14%] B X s+d γ 0 Inclusive analysis Only reconstruct photon and charged lepton for tagging. 1.7 < E γ < 2.8 GeV 1.10 < p l < 2.25 PRL 106, (2011) A CP = N+ N N + +N (using tag-lepton)

18 Wrong Tag Fraction and Corrections Measured A meas CP is corrected for various effects. A true 1 CP = 1 2w (Ameas CP A bkg A det ) 1. Wrong tag factor : w = ± B B mixing lepton from D decays K/π miss-identified as lepton 2. Asymmetry from detector : A det = 0.10 ± 0.22 % Lepton ID, tracking 3. Asymmetry from BB bkg : A bkg = 0.14 ± 0.78 % Low E γ region (E γ < 1.7 GeV) in data A CP (B X s+d γ) 18

19 Spectrum after bkg subtraction Result A CP (B X s+d γ) 19 Measure as function of E γ threshold. A CP B X s+d γ = 2.23 ± 4.02 ± 0.78 % with E γ > 2.1 GeV Consistent with SM. Most precise measurement of A CP B X s+d γ. Statistically dominated Leading systematic comes from BB bkg asymmetry

20 Summary 20 Various B decays are sensitive to new physics. New particles such as SUSY particles might enter in the loop diagrams. Charged Higgs might contribute in addition to the W boson. 1. B D ( ) τν with hadronic tag (arxiv: , submitted to PRD) 2. B πτν with hadronic tag 3. B s φγ, γγ (PRD 91, (R)(2015)) 4. A CP (B X s+d γ) (PRL 114, (2015)) There are many SUSY-related results not covered in this talk an a lot of ongoing analysis.

21 Backup 21

22 Neurobayes input 2 M miss B D ( ) τν with Hadronic Tag 22 E ECL q 2, p l CM # of unused π 0 with S γγ < 5 Angle between D ( ) momentum and vertex direction B/D ( ) decay channel identifiers

23 B D ( ) τν with Hadronic Tag 23

24 B D ( ) τν with Hadronic Tag 24

25 B D ( ) τν 25

26 B D ( ) τν 26

27 B πτν with Hadronic Tag 27