Sensitivity study of at the Belle II experiment Outline Michel - PowerPoint PPT Presentation


 Sensitivity study of 𝜐→𝜃𝜌𝜉 at the Belle II experiment Outline Michel Hernández Villanueva, • B-factories and 𝜐 Cinvestav Group 
 physics. Mexico City • Second class currents • 𝜐→𝜃𝜌𝜉 decay 28 Sep 2017 • Outlook.

B Factories • B-Factory 
 BR ( Υ (4 S ) → B ¯ B ) > 96% 10.58 GeV • 𝝊 factory too! 
 𝝉 (e + e - —> 𝜱 (4s)) = 1.05 nb 
 𝝉 (e + e - —> 𝝊 𝝊 ) = 0.92 nb Michel H. Villanueva 2 2

Integrated Luminosity of B factories 6.54x10 8 𝝊 ’s 3.98x10 8 𝝊 ’s High-luminosity experiments. Michel H. Villanueva 3 3

SuperKEKB • Super B-Factory 
 (And 𝝊 factory too!) • Integrated luminosity expected: 50 ab -1 
 (4.6x10 10 𝝊 pairs) • Full physics program starts: 
 late 2018 @KEK 
 Tsukuba, Japan Michel H. Villanueva 4

Belle II Detector Michel H. Villanueva 5

Belle II MC samples MC Sample: 
 ~ 2 ab -1 
 (1 ab -1 for training, 
 1 ab -1 for analysis). Michel H. Villanueva 6


 Mexican Contribution • 504 cores 
 ~1.4% CPU usage 
 3.7 KHS06 
 of the grid 70 TB storage 7

The 𝜐→𝜃𝜌𝜉 decay • In this work, we are studying the feasibility to measure the decay 
 𝜐→𝜃𝜌𝜉 , 
 in order to get information related at: • Second class currents. • Scalar and tensorial Disadvantage: We cannot detect 𝜉 currents. Michel H. Villanueva 8

The 𝜐→𝜃𝜌𝜉 decay Mechanisms in the SM: isospin violation 1 • + The corresponding suppression of the SM contribution can make new • physics visible. Charged Higgs Leptoquark 
 exchange exchange 1 R. Escribano, S. Gonzalez, P. Roig; Phys.Rev. D94 (2016) no.3, 034008 Michel H. Villanueva 9

Some recent theoretical predictions BR V (x10 5 ) BR S (x10 5 ) BR V+S (x10 5 ) Ref Model [8] 0.36 1.0 1.36 MDM, 1 resonance [9] [0.2, 0.6] [0.2, 2.3] [0.4, 2.9] MDM, 1 and 2 resonances [10] 0.44 0.04 0.48 Nambu-Jona-Lasinio Analiticity, Unitarity [11] 0.13 0.20 0.33 [12] 0.26 1.41 1.67 3 coupled channels Largest difference comes 
 [8] S. Nussinov + A. Soffer, PRD78, (2008) from scalar form factor. [9] N. Paver + Riazuddin, PRD82, (2010) [10] M. Volkov D. Kostunin, PRD82, (2012) [11] S. Descotes-Genon+B. Moussallam, EJPC74, (2014) [12] R. Escribano, S. Gonzalez, P. Roig; Phys.Rev. D94 (2016) no.3, 034008 • BR( 𝜐→𝜃𝜌𝜉 ) ~ 10 -5 Accesible at Belle II luminosity. Michel H. Villanueva 10

The 𝜐→𝜃𝜌𝜉 decay NP contributions (scalar and tensorial currents) can be studied in the • framework of an effective field theory 1 Constraints on scalar and tensor • couplings can be obtained from CLEO experimental upper limits on branching Belle fractions. SM CLEO BaBar BaBar Belle SM 1 E. A. Garcés, MHV, G. López Castro, P. Roig; arXiv:1708.07802 Michel H. Villanueva 11

Previous Results 470 fb -1 670 fb -1 • This decay mode should have already been discovered if there were no strong background. • Control of the background is essential. Michel H. Villanueva 12

Thrust axis cm · ˆ • Thrust axis: such that 
 ˆ P i | ~ n thrust | n thrust p i V thrust = P i | ~ p i cm | V thrust is maximum. ˆ n thrust The thrust axis define a plane which splits the signal side space in two. tag side Michel H. Villanueva 13

2 ways to reconstruct 𝜃 cm · ˆ • Thrust axis: such that 
 ˆ P i | ~ n thrust | n thrust p i V thrust = p i cm | P i | ~ V thrust is maximum. 3-prong 1-prong BR( 𝜃 —> 𝜌𝜌𝜌 0 ) = 22.92% BR( 𝜃 —> 𝛿𝛿 ) = 39.41% γ γ π π γ γ π π 0 ν τ Signal side π η η ν τ τ e + e + e − τ e − τ τ Tag side ` ` ¯ ¯ ν ` ν ` ν τ ν τ Michel H. Villanueva 14

𝜐→𝜃𝜌𝜉 signal events Selection criteria :tag + 1 or 3 charged + 2 or 3 𝛿 . • Signal events generated: 4M . 
 • (2M for training and 2M for sensitivity study). E ff : 13.56% E ff : 3.70% 3 × 10 Events / ( 0.002 ) 200 180 160 π 0 → γγ 140 120 100 80 60 η → γγ 40 20 0 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 2 Invariant Mass γ γ [GeV/c ] η → π + π − π 0 Mis-reconstructed 𝜌 0 𝛿 from other sources 3-prong 1-prong BR( 𝜃 —> 𝛿𝛿 ) = 39.41% BR( 𝜃 —> 𝜌𝜌𝜌 0 ) = 22.92% Michel H. Villanueva 15

𝜐→𝜃𝜌𝜉 bkg events E ff : 0.34% 1-prong 1 ab -1 MC Background sources: 
 • - 𝝊𝝊 pair 
 - bb pair 
 𝜌 0 veto 
 tau pair - qq pair applied. E ff : 0.002% 1 ab -1 MC E ff : 0.006% bb pair qq pair 1 ab -1 MC Michel H. Villanueva 16

BDT variables (1-prong) TMVA used for this test. 3 10 × 0.12 No. de Background Eficiencia • cos( 𝜄 miss ) • ∠ ( 𝜃 , 𝜌 ) 1200 0.1 ✏ • PID e ( 𝜌 ) 1000 √ • ∠ (p miss , V thrust ) a/ 2 + B Optimal 
 0.08 cut 800 • PID µ ( 𝜌 ) • M miss 0.06 600 • PID K ( 𝜌 ) • P t ( 𝜌 ) 0.04 400 • E( 𝛿 ) • 𝜃 ( 𝜃 ) 0.02 Optimization 200 Punzi proposed by 0 Punzi, G. 
 • ∠ ( 𝛿 , 𝛿 ) 𝜃 − 0.1 − 0.05 0 0.05 0.1 0.15 0.2 0.25 0.3 Corte en BDT at arXiv preprint physics/0308063 Correlation Matrix (signal) Correlation Matrix (background) TMVA overtraining check for classifier: BDT Linear correlation coefficients in % Linear correlation coefficients in % 100 100 dx (p ,V ) (p ,V ) -19 33 -18 100 Signal (test sample) Signal (training sample) -1 25 -2 -32 37 4 -6 -1 100 4 4 1 -2 miss thrust miss thrust 80 80 / cos( θ ) cos( θ ) 6 -55 -6 -3 8 100 -18 Background (test sample) Background (training sample) -3 -54 -1 14 2 100 1 -4 -2 (1/N) dN miss miss 5 60 60 #PID ( ) #PID ( ) Kolmogorov-Smirnov test: signal (background) probability = 0.81 (0.063) π -2 -9 -2 2 9 2 -2 100 -1 π 4 1 3 3 -7 100 -2 e e 40 40 #PID ( ) #PID ( π ) -3 8 18 6 100 -6 π -6 6 6 -3 100 -4 -24 -4 -2 2 -2 12 -7 -2 µ µ 4 20 20 #PID ( ) #PID ( π ) -20 -5 -5 100 π 3 -10 -6 100 -3 8 -1 7 -12 -4 14 4 -4 -2 1 K K U/O-flow (S,B): (0.0, 0.0)% / (0.0, 0.0)% E( ) + E( ) E( ) + E( ) γ γ 0 γ γ 5 -8 -5 -50 -9 100 -6 6 -3 33 0 4 -24 1 -54 -8 100 -5 6 2 -1 37 1 2 1 2 3 ∠ ( η , π ) -15 -60 41 100 -8 -12 18 9 -32 ∠ ( η , π ) -3 -6 15 26 100 -9 -2 12 -4 -19 20 20 − − M M -7 -37 100 41 -54 -5 8 2 -2 -3 -19 10 100 26 -50 -4 6 3 -6 miss − 40 miss − 40 η η 2 19 100 -20 -3 -54 10 100 10 15 -5 -10 3 -55 1 -2 -1 4 η η − 60 − 60 Pt 100 -37 -60 -9 25 Pt 100 -19 -6 -8 3 -6 12 -24 7 -24 1 -1 1 1 4 π π − 80 − 80 ∠ ( γ , γ ) ∠ ( γ , γ ) 1 100 19 -15 -3 100 10 -3 -3 5 6 12 -7 4 -1 -4 -2 -1 1 -2 4 η η − 100 − 100 η E( η E ∠ Pt M #PID #PID #PID cos( ∠ ∠ P M # # # c ∠ ( ∠ (p ( ∠ ( P P P o ( γ , ( γ γ t ( γ I s p η ) + E( , η ) I D D I D ( γ η , γ η ) miss π θ ) miss , π + θ π ) ( ( ( ,V π ) E ( ( ( π π ) π π π ) π , V 1 ) µ e ) ) miss 1 ( ) µ e ) ) miss γ K miss γ K miss η ) η ) thrust ) thrust ) 2 2 0 0.6 0.4 0.2 0 0.2 0.4 − − − Michel H. Villanueva 17 BDT response

Optimal BDT cut Signal E ff cut = 41.87% 1-prong 20000 Events / ( 0.0025 ) 20000 N sig = 271,258 Events / ( 0.004 ) 18000 = 1.039 0.010 α ± E ff : 13.56% 16000 18000 = 0.540854 0.000051 µ ± 14000 = 0.010962 0.000038 σ ± 16000 12000 n = 2.309 0.039 ± 14000 10000 8000 12000 6000 10000 4000 2000 8000 0 0.4 0.45 0.5 0.55 0.6 0.65 6000 2 Invariant Mass γ γ [GeV/c ] N sig =157,680 
 4000 E ff : 7.88% 2000 0 0.4 0.42 0.44 0.46 0.48 0.5 0.52 0.54 0.56 0.58 0.6 2 Invariant Mass ( ) [GeV/c ] η γ γ Michel H. Villanueva 18

Optimal BDT cut Background E ff cut = 84.51% 1-prong Events / ( 0.0025 ) MC events 0 ( ) ρ → π π ν Events / ( 0.0025 ) MC events MC events 50000 (a ) → π π π ν 1 0 0 0 ( ) π π γ ν ( ρ → π π ) ν ρ → π π ν 7000 b b (a ) (a → π π π ) ν → π π π ν q q 1 1 40000 0 0 π π γ ν π π γ ν N bkg = 2,694,408 b b 6000 b b q q q q 30000 E ff : 0.34% 5000 20000 4000 10000 3000 98,146 events 0 0.4 0.45 0.5 0.55 0.6 0.65 2 Invariant Mass γ γ [GeV/c ] 2000 N bkg =417,217 
 1000 E ff : 5.26x10 -4 𝜈 ± 3 σ 0 0.4 0.45 0.5 0.55 0.6 0.65 2 Invariant Mass [GeV/c ] γ γ Michel H. Villanueva 19

𝜐→𝜃𝜌𝜉 bkg events E ff : 0.028% 3-prong 1 ab -1 MC Background sources: 
 • - 𝝊𝝊 pair 
 3 𝛒𝛒 0 is the mayor issue. - bb pair 
 (This depends of the hadronic input in the generation of MC) - qq pair tau pair E ff : 5.6x10 -6 bb pair E ff : 7.6x10 -6 1 ab -1 MC qq pair 1 ab -1 MC Michel H. Villanueva 20