Se Search arch for for th the e Lep Lepton ton Fl Flavor - PowerPoint PPT Presentation

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Charged Lepton Flavor Violation • CLFV highly suppressed in SM, allowed in many BSM models + clear exp. signature = “NP” Theoretical constraints on the limit (indirect): BF ( Υ 3𝑇 → 𝑓 ± 𝜈 ∓ ) < 2.0 × 10 −8 (2000) [1] • No experimental measurement of the decay 𝜱 𝟒𝑻 → 𝒇 ± 𝝂 ∓ yet! • Some 𝒇 ± 𝝊 ∓ 𝒃𝒐𝒆 𝝂 ± 𝝊 ∓ Limits Measurements Results CL (%) Collaboration BF (Υ(3𝑇) → 𝑓 ± 𝜐 ∓ ) < 5.0 × 10 -6 90 BaBar Collaboration (2010) [2] BF (Υ(3𝑇) → 𝜈 ± 𝜐 ∓ ) < 4.1 × 10 -6 90 BaBar Collaboration (2010) [2] BF (Υ(3𝑇) → 𝜈 ± 𝜐 ∓ ) < 20.3 × 10 -6 95 CLEO Collaboration (2008) [3] Indirect Search Provides limit assuming Unitarity Some of the direct experimental bounds from vector particles decay Measurements Results CL (%) Collaboration BF (Φ → 𝑓 ± 𝜈 ∓ ) < 2.0 × 10 -6 90 SND Collaboration (2010) [4] BF (𝐾/Ψ → 𝑓 ± 𝜈 ∓ ) < 1.6 × 10 -7 90 BES III Collaboration (2013) [5] BF (𝑎 0 → 𝑓 ± 𝜈 ∓ ) < 7.5 × 10 -7 95 ATLAS Collaboration (2014) [6] Direct Search Nafis isa Tasneem eem 2

The BaBar Detector at PEP-II Nafis isa Tasneem eem 3

Data Sample, Signal and Backgrounds Sources of Main Backgrounds 𝑓 + 𝑓 − → 𝜐 𝜐 Data Υ(3𝑇 ) , Luminosity Upsilon Numbers 𝑡 = 10.355 (fb -1 ) e ν𝜉 (4.06 ± 0.04) × 10 6 0.93 ± 0.01 𝜈ν𝜉 (3%) Pre-blinded Sample (117.7 ± 1.2) × 10 6 27.0 2 ± 0.16 Unblinded Sample (121.7 ± 1.2) × 10 6 27.96 ±0.16 Removed with kinematics cuts Total MC Signal (for Background) Generators 𝑓 + 𝑓 − → 𝜈𝜈 Decayed in flight, 𝑓 + 𝑓 − → 𝜈 + 𝜈 − KK2F Material interaction, e 𝑓 + 𝑓 − → 𝑓 + 𝑓 − Mis-ID etc. BHWIDE 𝜈 𝑓 + 𝑓 − → 𝜐 + 𝜐 − KK2F 𝑓 + 𝑓 − → 𝑣𝑒𝑡 𝑓 + 𝑓 − → e e EvtGen 𝑓 + 𝑓 − → 𝑑 𝑓 𝑑 EvtGen 𝜈 Generic Υ(3𝑇 ) MC EvtGen Mis-ID MC signal: 𝒇 + 𝒇 − → 𝜱 𝟒𝑻 → 𝒇 ± 𝝂 ∓ : 103000 events Removed with PID Nafis isa Tasneem eem 4

Control Data Sample Luminosity (fb -1 ) Data Purpose 𝐸𝑏𝑢𝑏 Υ(4𝑇 ) 𝑃𝑜 𝑆𝑓𝑡𝑝𝑜𝑏𝑜𝑑𝑓 , 𝑡 = 10.58 78.31 ± 0.35 Estimate Continuum Background Preselected as 𝑓 ± 𝜈 ∓ events Systematics 𝐸𝑏𝑢𝑏 Υ(4𝑇 ) 𝑃𝑜 𝑆𝑓𝑡𝑝𝑜𝑏𝑜𝑑𝑓 , 𝑡 = 10.58 78.31 ± 0.35 Systematics Preselected as 𝜈 ± 𝜈 ∓ events 𝐸𝑏𝑢𝑏 Υ(4𝑇 )Off Resonance 7.752 ± 0.04 BG Control Sample 𝐸𝑏𝑢𝑏 Υ(3𝑇 )On Resonance , 𝑡 = 10.355 27.96 ± 0.16 Systematics Preselected as 𝜈 ± 𝜈 ∓ events 𝐸𝑏𝑢𝑏 Υ(3𝑇 )Off Resonance 2.62 ± 0.02 BG Control Sample Nafis isa Tasneem eem 5

Analysis Methodology : A Background filter to select 𝑓 ± 𝜈 ∓ events Pre-Selec Selection tion: • User r defin fined ed Sele lection tion: Applied on the pre=selected events • PID Selecti ection: n: Multivariate Technique applied, 16 different PID selector used in optimization ( 𝐶 ) 𝑇 • Pre-Selection: User defined Selection: Distance of closest approach of any track vertex w.r.t. the beam spot in 2 tracks (1 electron and 1 muon in the final state), one in each Drift Chamber hemisphere, • in x - y plane < 1 cm and in z < 4 cm. 24 ∘ < 𝜄 𝑀𝑏𝑐 < 130 ° EMC acceptance for both tracks. Number of hits in the Drift Chamber > 0. Transverse Momentum p T > 100 MeV. Exactly 2 oppositely charged tracks ; Lepton momenta must satisfy the following condition Polar angle of the two tracks: 2.8 < ( 𝜄 1 + 𝜄 2 ) < 3.5 2 2 𝑞 𝜈 𝑞 𝑓 𝑡 𝐹 𝐶𝑓𝑏𝑛 − 1 + 𝐹 𝐶𝑓𝑏𝑛 − 1 < 0.01 where 𝐹 𝐶𝑓𝑏𝑛 = 2 Sum of momentum of the two tracks |P 1 | +|P 2 | > 9 GeV. 𝐷𝑁 > 179 ° Angle between the two lepton tracks must satisfy 𝜄 12 One and only one electron of two tracks defined by E/P > 0.8 to ensure they are emerged as back to back. Acolinearity angle associated with the two tracks < 0.1 radians in CM. Energy deposit by Muon track on the Electromagnetic Calorimeter should be greater than 50 MeV. Nafis isa Tasneem eem 6

Data/MC Comparison BaBar Preliminary Distribution of 𝑓 ± 𝜈 ∓ mass before applying any user defined selection criteria, only preselection criteria has applied for 3% pre-unblinded sample. Nafis isa Tasneem eem 7

Selection Criteria in (N-1) plots (N-1) plots  all cuts applied except that on the variable plotted BaBar Preliminary BaBar Preliminary 2 2 𝑞 𝜈 𝑞 𝑓 𝐹 𝐶𝑓𝑏𝑛 − 1 + 𝐹 𝐶𝑓𝑏𝑛 − 1 < 0.01 𝑡 where 𝐹 𝐶𝑓𝑏𝑛 = 2 BaBar Preliminary BaBar Preliminary The angle between the two 𝐷𝑁 > lepton tracks must satisfy 𝜄 12 179 ° to emerged as back to back. Energy deposit by Muon track on EMC should be greater than 50 MeV. Nafis isa Tasnee eem 8

All Selection Criteria Applied BaBar Preliminary Mass distribution of 𝑓 ± 𝜈 ∓ after all selection criteria are applied Nafis isa Tasneem eem 9

Data, BG Selection Summary & Signal Efficiency in (N-1) Cuts BG Events 𝑪𝑯 𝑭𝒘𝒇𝒐𝒖𝒕 Can andidate (N-1) Selection Signal Efficiency  eµ 𝜱 𝟒𝑻 MC 𝜱 𝟓𝑻 𝑷𝒐 𝜱 𝟒𝑻 𝑷𝒐 (27.02 fb −1 ) Pre-selection 82612 7134301 152445188 0.2355 ± 0.0013 14.7 ± 2.3 PID selection 0 18 0.2684 ± 0.0012 82.7 ± 6.03 263.4 ± 9.7 Lepton Momentum 302 0.2402 ± 0.0013 0.44 ± 0.44 37.7 ± 3.7 Back to back 39 0.2495 ± 0.0013 13.9 ± 2.2 EMC acceptance 0 17 0.2452 ± 0.0013 17.6 ± 2.5 EMC Energy 0 19 0.2342 ± 0.0013 STAT 12.2 ± 2.1 STAT All Cuts 0 15 • BG events are the equivalent events on 27.0 fb -1 • Uncertainties are statistical Note: For the 3% Pre-blinded sample (0.93 fb -1 ): N Data =1, agrees with BG estimate: 0.43 ± 0.07 events Nafis isa Tasneem eem 10

Systematic Uncertainty and Background BaBar Preliminary Systematic Uncertainty on Efficiency: • Tracking, PID, kinematics, trigger determined using controlled sample of tau’s in the “ Side Bands ” where “lepton momentum” and “back to back” cuts are reversed : 1.2% • Systematic uncertainty on “ lepton momentum ” cut: 2.9% • Systematic uncertainty on “ back to back ” cut: 1.1% Systematic Uncertainty on 𝑂 𝑍 (3s ) : [8] Total Uncertainty on 𝑂 𝑍 (3s ) at Run 7 Dataset: 1% • Source of BG No. of events after all selection criteria Mass distributions for  (3S)On data Υ (4S)On Data: 12.2 ± 2.3 Continuum and MC control samples (  -pair) Υ (3S) MC: 0 ± 0.9 Peaking Nafis isa Tasneem eem 11

Summary on Efficiency, Background and Candidate Values Sources Uncertainties  SIG (SYST) • In the “Lepton. Momentum” cut 0.029 • In the “Back to back” cut 0.011 • In all other cuts on the Side bands 0.012  SIG (SYST  STAT) 0.2342 ± 0.0077 SYST ± 0.0013 STAT 0.2342 ± 0.0078 (4.06 ± 0.04)  10 6 N  (0.93 fb -1 ) (117.7 ± 1.2)  10 6 N  (27.02 fb -1 ) 0.42 ± 0.7 Background (0.93 fb -1 ) 12.2 ± 2.3 Background (27.0 fb -1 ) Candidate seen (0.93 fb -1 ) 1 Candidate seen (27.0 fb -1 ) 15 Nafis isa Tasneem eem 12

Results: Branching Fraction and Upper limit 𝐂𝐆 = 𝑶 𝐄𝐛𝐮𝐛 − 𝑶 𝑪𝑯 = (𝟐. 𝟏 ± 𝟐. 𝟓 𝑻𝑼𝑩𝑼 (𝑶 𝑬𝑩𝑼𝑩 ) ± 𝟏. 𝟗 𝑻𝒁𝑻𝑼 ) × 𝟐𝟏 −𝟖 𝜻 𝒕𝒋𝒉 × 𝑶 𝚽 Measurements Upper Limit with Confidence Level of 90% Observed Upper limit Expected Upper limit Υ(3𝑇) → 𝑓 ± 𝜈 ∓ Barlow Method [9] CLs Method [10] Barlow Method CLs Method < 3.6 × 10 -7 < 3.6 × 10 -7 < 2.3 × 10 -7 < 2.8 × 10 -7 Unblinded Data Sample (27.0 fb -1 ) Nafis isa Tasneem eem 13

Conclusion • On behalf of the BaBar Collaboration we presented the preliminary result on experimental upper limits of a data sample (27.02 fb -1 ) 𝑪𝑮( 𝜱(𝟒𝑻) → 𝒇 ± 𝝂 ∓ ) < 3.6 × 10 -7 with Confidence Level of 90% • This is the first reported experimental upper limits on 𝛷(3𝑇) → 𝑓 ± 𝜈 ∓ Nafis isa Tasneem eem 14