decays at BaBar and Belle Alessandro Pilloni Sapienza Universit di - PowerPoint PPT Presentation

Recent results on violation of discrete symmetries in charm decays at BaBar and Belle Alessandro Pilloni “Sapienza” Università di Roma – INFN sez. Roma 1 on behalf of the BaBar Collaboration CHARM 2015 Detroit – May 21 st , 2015

Outline • CPV in charm decays • Recent BaBar results • CPV in 𝐸 + → 𝐿 + 𝐿 − 𝜌 + PRD 87, 052010 (2013) 𝑀 = 476 fb −1 • CPV in 𝐸 + → 𝐿 𝑇 + → 𝐿 𝑇 + → 𝐿 𝑇 0 𝐿 + , 𝐸 𝑡 0 𝐿 + , 𝐸 𝑡 0 𝜌 + PRD 87, 052012 (2013) 𝑀 = 469 fb −1 • Recent Belle results • Time-dependent analysis of 𝐸 0 → 𝐿 𝑇 0 𝜌 + 𝜌 − PRD 89, 091103 (2014) 𝑀 = 921 fb −1 • Conclusions (the use of charge conjugate reactions is implied thourough) 2 A. Pilloni – Recent results on CPV in charm decays at BaBar and Belle

CPV in charm sector In the SM, CPV in processes involving charm hadrons is expected to be small, at the level of 10 −3 or less GIM and CKM suppression 𝐵 𝐷𝑄 ∝ log 𝑛 𝑐 × 𝜇 5 = 𝑃(10 −3 ) 𝑛 𝑑 No top enhancement! Any CPV signal is likely due to New Physics, although sizeable long-distance effects might affect some SM predictions 3 A. Pilloni – Recent results on CPV in charm decays at BaBar and Belle

The BaBar experiment The Babar detector was located at the interaction point of PEP II at SLAC Asymmetric 𝑓 + 𝑓 − collider, mostly at 𝑡 ∼ 10.58 GeV Cherenkov detector (DIRC): 144 fused silica bars; 11000 PMT Drift Chamber: 40 layers Silicon Vertex Tracker (SVT): 5 double layers ∫ 𝑀 𝑒𝑢 ∼ 517 fb −1 close to the Υ 4𝑇 , Υ(2𝑇) , Υ(3𝑇) peaks, 670 × 10 6 𝑑 𝑑 pairs 4 A. Pilloni – Recent results on CPV in charm decays at BaBar and Belle

Dalitz plot analysis of 𝐸 + → 𝐿 + 𝐿 − 𝜌 + Singly Cabibbo-suppressed decays, uniquely sensitive to new physics Probe gluonic penguin and chromomagnetic dipole operators 3-body decay allows the search for CP asymmetries in the Dalitz plot 5 A. Pilloni – Recent results on CPV in charm decays at BaBar and Belle

Event selection and signal reconstruction Two tracks consistent with 𝐿 hypothesis • 𝑞 𝑈 𝜌 > 300 MeV/c , good track quality • • 𝑞 𝐸 ∈ [2.4, 5.0] GeV/c , reject 𝐶 background Background from misidentified 𝐸 ∗+ → 𝐸 0 𝜌 + • removed 𝐷𝑁 help in Joint PDF for flight distance and 𝑞 𝐸 • discriminating signal from background 228k 𝐸 + signal yield, 92% purity Search for CPV with: 𝐵 𝐷𝑄 integrated over the Dalitz plot 1. 𝐵 𝐷𝑄 in 4 Dalitz plot regions 2. Comparison of binned 𝐸 ± Dalitz plot 3. BaBar coll. 4. Comparison of Legendre polynomial moment distributions for 𝐿 + 𝐿 − and 𝐿 − 𝜌 + systems PRD 87, 052010 (2013) 𝑀 = 476 fb −1 5. Comparison of parametrized fits to Dalitz plot (model-dependent) 6 A. Pilloni – Recent results on CPV in charm decays at BaBar and Belle

𝐵 𝐷𝑄 in the Dalitz plot regions (C) (D) Asymmetry integrated over the Dalitz plot (B) (A) 𝑩 𝑫𝑸 = 𝟏. 𝟒𝟖 ± 𝟏. 𝟒𝟏 ± 𝟏. 𝟐𝟔 % 7 A. Pilloni – Recent results on CPV in charm decays at BaBar and Belle

Model-independent searches for CPV 𝑆 = 𝑂(𝐸 + )/𝜗 + 𝑜 𝐸 + −𝑆𝑜 𝐸 − Normalized residual analysis Δ = 𝑂(𝐸 − )/𝜗 − 𝜏 2 𝐸 + +𝑆 2 𝜏 2 𝐸 − , = 1.020 ± 0.006 • consistent with no CPV at 72% level 8 A. Pilloni – Recent results on CPV in charm decays at BaBar and Belle

Model-independent searches for CPV Method introduced by Babar coll. PRD 76, 011102 (2007) Legendre polynomial moment analysis: Two body mass distributions 𝑛(𝐿 + 𝐿 − ) and 𝑛(𝐿 − 𝜌 + ) weighted by (2𝑚 + 1)/4𝜌 𝑄 𝑚 (cos 𝜄 𝐼 ) 𝑚 𝐸 + −𝑆𝑋 𝑚 𝐸 − 𝑚 = 𝑋 𝑚 the weighted 𝑗th mass bin, and 0 ≤ 𝑚 ≤ 7 𝑌 𝑗 𝑗 𝑗 𝑚 2 𝐸 − , with 𝑋 𝑗 𝑚 2 𝐸 + +𝑆 2 𝜏 𝑗 𝜏 𝑗 consistent with no CPV at 11% and 13% level 9 A. Pilloni – Recent results on CPV in charm decays at BaBar and Belle

Model-dependent search for CPV Fit to Dalitz plot using isobar model Firstly to combined 𝐸 ± datasets (no CPV) Resonances modeled with RBW 𝑔 0 (980) with an effective BW 10 A. Pilloni – Recent results on CPV in charm decays at BaBar and Belle

Model-dependent search for CPV Allow CPV in resonances with at least 1% fit fraction 𝑁 𝑠 2 − 𝑁 𝑠 2 𝑠 𝐷𝑄 = 𝑁 𝑠 2 + 𝑁 𝑠 2 , Δ𝜚 𝐷𝑄 = 𝜚 𝑠 − 𝜚 𝑠 𝑦 𝑠 = 𝑁 𝑠 cos 𝜚 𝑠 , 𝑧 𝑠 = 𝑁 𝑠 sin 𝜚 𝑠 11 A. Pilloni – Recent results on CPV in charm decays at BaBar and Belle

+ → 𝐿 + → 𝐿 0 𝐿 + , 𝐸 𝑇 0 𝜌 + Search for CPV in 𝐸 (𝑡) 𝑇 𝑇 BaBar coll. PRD 87, 052012 In the SM 𝐵 𝐷𝑄 expected to be dominated 𝑀 = 469 fb −1 by CPV in 𝐿 0 − 𝐿 0 mixing 𝐿 + and 𝜌 + PID, p T > 400 MeV/c • Multivariate analysis to • 𝑞 𝐸 ∈ [2.6, 5.0] GeV/c , 𝑞 𝐸 𝑡 ∈ [2.0, 5.0] GeV/c further improve S/B 0 flight length > 3 × significance • 𝐿 𝑇 + → 𝐿 𝑇 𝐸 + → 𝐿 𝑇 + → 𝐿 𝑇 0 𝐿 + 0 𝐿 + 0 𝜌 + 𝐸 𝑡 𝐸 𝑇 159k events 288k events 14k events 12 A. Pilloni – Recent results on CPV in charm decays at BaBar and Belle

Analysis of detector-induced asymmetries A large sample of 𝜌 and 𝐿 tracks from 𝐶 𝐶 events to estimate detector-induced asymmetries Correction factors have been measured and applied to the signal 𝐿 𝜌 ratio error 13 A. Pilloni – Recent results on CPV in charm decays at BaBar and Belle

𝐵 𝐷𝑄 results and systematic errors 𝐸 + → 𝐿 𝑇 + → 𝐿 𝑇 + → 𝐿 𝑇 0 𝐿 + 0 𝐿 + 0 𝜌 + 𝐸 𝑡 𝐸 𝑇 𝐵 𝐷𝑄 = 0.13 ± 0.36 % 𝐵 𝐷𝑄 = −0.05 ± 0.23 % 𝐵 𝐷𝑄 = 0.6 ± 2.0 % 14 A. Pilloni – Recent results on CPV in charm decays at BaBar and Belle

Final 𝐵 𝐷𝑄 results 𝐿 0 produced, − sign 𝐿 0 produced, + sign • Results are compatible with SM expectations • CPV dominated by Kaon mixing • No evidence of CPV in the Δ𝐷 transitions 15 A. Pilloni – Recent results on CPV in charm decays at BaBar and Belle

The Belle experiment The Belle detector was located at the interaction point at KEKB in Japan ∫ 𝑀 𝑒𝑢 ∼ 977 fb −1 close to the Υ(1𝑇 − 5𝑇) peaks, 1.3 × 10 9 𝑑 𝑑 pairs 16 A. Pilloni – Recent results on CPV in charm decays at BaBar and Belle

Mixing and CPV in 𝐸 0 → 𝐿 0 𝜌 + 𝜌 − 𝑇 𝐸 0 ± 𝑟 Mass eigenstates 𝐸 1,2 = 𝑞 𝐸 0 2 2 𝑒Γ 𝐸 0 2 + 𝑟 2 − 𝑟 2 2 𝑓 −Γ𝑢 𝑒𝑢 ∝ 𝐵 𝑔 𝐵 𝑔 cosh Γ𝑧𝑢 + 𝐵 𝑔 𝐵 𝑔 cos Γ𝑦𝑢 𝑞 𝑞 +2𝑆𝑓 𝑟 sinh Γ𝑧𝑢 − 2𝐽𝑛 𝑟 ∗ ∗ 𝑞 𝐵 𝑔 𝐵 𝑔 𝑞 𝐵 𝑔 𝐵 𝑔 sin Γ𝑦𝑢 2 2 𝑒Γ 𝐸 0 2 + 𝑞 2 − 𝑞 2 2 𝑓 −Γ𝑢 𝑒𝑢 ∝ 𝐵 𝑔 𝐵 𝑔 cosh Γ𝑧𝑢 + 𝐵 𝑔 𝐵 𝑔 cos Γ𝑦𝑢 𝑟 𝑟 +2𝑆𝑓 𝑞 sinh Γ𝑧𝑢 − 2𝐽𝑛 𝑞 ∗ ∗ 𝑟 𝐵 𝑔 𝐵 𝑔 𝑟 𝐵 𝑔 𝐵 𝑔 sin Γ𝑦𝑢 Mixing CPV 𝑟 𝑞 ≠ 1 Mixing parameters 𝑦 = Δ𝑛 Γ , 𝑧 = ΔΓ Interference CPV arg 𝑟 2Γ 𝑞 ≠ 0 17 A. Pilloni – Recent results on CPV in charm decays at BaBar and Belle

Mixing and CPV in 𝐸 0 → 𝐿 0 𝜌 + 𝜌 − 𝑇 Total amplitude parametrized as a sum of quasi two-body resonant amplitudes (isobar model) 2 = 𝑛 2 (𝐿 𝑇 𝑏 𝑠 𝑓 𝑗𝜚 𝑠 𝐵 𝑠 (𝑛 − 2 , 𝑛 + 2 ) , 𝑏 𝑠 𝑓 𝑗𝜚 𝑠 𝐵 𝑠 (𝑛 − 2 , 𝑛 + 2 ) , 0 𝜌 ± ) 𝐵 𝑔 = 𝐵 𝑔 = 𝑛 ± 𝑠 𝑠 𝜌 A time-dependent Dalitz plot analysis is needed to extract mixing and CPV parameters 𝜌 0 𝐿 𝑇 𝜌 0 vtx fit 𝐿 𝑇 • Reconstruct 𝐸 ∗+ → 𝐸 0 𝜌 𝑡 + • Flavor tagging by 𝜌 𝑡 charge 𝜌 fit 𝐸 0 vtx • Background suppression 𝜌 𝑡 𝐸 0 • 𝐸 0 proper decay time measurement 𝑚 𝑒𝑓𝑑 𝑞 𝐸0 𝑞 𝐸0 𝑚 𝑒𝑓𝑑 • 𝑢 = 𝑑 𝛾𝛿 ⋅ 𝑞 𝐸0 , 𝛾𝛿 = 𝑓 − 𝐸 ∗ 𝑓 + beamspot 𝑛 𝐸0 18 A. Pilloni – Recent results on CPV in charm decays at BaBar and Belle

Event selection 𝑅 signal 𝑞 𝐸 > 2.5 GeV @ Υ(4𝑇) , region • 𝑞 𝐸 > 3.1 GeV @ Υ(5𝑇) , 𝑁 signal • Removed events with region poorly determined 𝑢 Cuts on 𝑁 𝐸 and • 𝑅 = 𝑁 𝐸 ∗ − 𝑁 𝐸 − 𝑁 𝜌 2D fit to 𝑁 𝐸 and 𝑅 , Yield 1.2M, purity 96% 𝑄𝐸𝐻 < 15 MeV Signal region in 𝑁 𝐸 − 𝑁 𝐸 and 𝑅 ∈ 5.75, 5.95 MeV 𝑀 = 977 fb −1 Belle coll. PRD 89, 091103(R) (2014) 19 A. Pilloni – Recent results on CPV in charm decays at BaBar and Belle

3D analysis of 𝐸 0 → 𝐿 0 𝜌 + 𝜌 − 𝑇 Unbinned ML fit in (𝑛 + , 𝑛 − , 𝑢) • • Fit model with 16 resonances • Background estimated from sidebands: • Combinatorial: 𝑁 sideband RBW Random 𝜌 𝑡 : 𝑅 sideband • • Resolution function: 3 Gaussians 𝟑 (GeV 𝟑 /𝒅 𝟓 ) K matrix 𝒏 + 𝟑 (GeV 𝟑 /𝒅 𝟓 ) 𝒏 − 𝟑 (GeV 𝟑 /𝒅 𝟓 ) 𝒏 𝝆𝝆 LASS 𝟑 (GeV 𝟑 /𝒅 𝟓 ) 𝟑 (GeV 𝟑 /𝒅 𝟓 ) 𝒏 + 𝒏 − 20 A. Pilloni – Recent results on CPV in charm decays at BaBar and Belle