Eli Ben-Ham LPNHE - IN2P3 - Sorbonne University (Paris) On behalf of - PowerPoint PPT Presentation

Eli Ben-Haïm LPNHE - IN2P3 - Sorbonne University (Paris) On behalf of the BABAR collaboration

The BABAR detector Silicon Vertex Tracker Magnet 1.5T PEP-II: asymmetric e + (3GeV) beams at Υ (4S) threshold Drift Chamber (9 GeV) - e Detector of Instrumented Cherenkov light flux return Electromagnetic calorimeter BABAR is well suited for the measurements presented here: clean environment, hermetic detector, excellent PID, good π 0 reconstruction Eli Ben-Haim Moriond EW, March 22nd 2019 2

The BABAR dataset BABAR in operation: 1999 –2008 The analyses presented use the full BaBar dataset: ~430 fb -1 at the Υ (4S) ~50 fb -1 40 MeV below (off peak) ( à ∼ 435M τ + τ − pairs) Eli Ben-Haim Moriond EW, March 22nd 2019 3

V us in tau decays Branching fractions of τ − → K − n π 0 ν τ (n = 0,1,2,3) and τ − → π − n π 0 ν τ (n = 3, 4) Partially documented in Tau 2018 proceedings (https://scipost.org/SciPostPhysProc.1.001) First presented in ICHEP 2018 Expected to be published in 2019 Eli Ben-Haim Moriond EW, March 22nd 2019 4

τ − → K − n π 0 ν τ Main ways to determine |V us | Kaon decays (K ℓ 3 ) K → πℓυ (K ℓ 2 ) K → ℓυ / K → ℓυ CKM unitarity τ lepton decays “Inclusive” τ → s (sum of exclusives) ⭐ This talk τ → K υ τ / τ → πυ τ The results from τ decays are systematically lower à Inclusive τ → s is 3.1 σ lower than the derivation based on CKM unitarity Eli Ben-Haim Moriond EW, March 22nd 2019 5

τ − → K − n π 0 ν τ |V us | from “inclusive” τ → s BF ( ... ) R ( τ → X s ν ) = R ( τ → X d ν ) R ( ... ) ≡ − δ R τ ,SU 3 BF ( τ → e ν τ ν e ) | V us | 2 | V ud | 2 [JHEP 01 (2003), 060 ; PRL 94 (2005), 011803] Significant part of the experimental uncertainties originates from τ − → K − n π 0 ν τ Large theoretical uncertainty Break-down of sources of relative uncertainties on |V us |( τ → s) [%] [Plot from Alberto Lusiani] Eli Ben-Haim Moriond EW, March 22nd 2019 6

Analysis method τ − → K − n π 0 ν τ Basics Divide event into two hemispheres along thrust axis Require one track in each (oppositely charged) and no additional tracks e ± or µ ± (tag side) π ± or K ± (signal side) Reconstruct 0 to 4 π 0 → γγ require no additional γ Apply reconstruction- and PID- eff. corrections based on MC and control samples e + / µ + Correct for fake γ from neutrons in the EM calorimeter Control modes w/ similar topology, σ (BF) ~ 1%: Signal modes (1-prong): τ − →π − n π 0 ν τ (n=0,1,2) τ − → K − n π 0 ν τ (n=0,1,2,3) τ − →µ − ν µ ν τ τ − →π − n π 0 ν τ (n=3,4) Eli Ben-Haim Moriond EW, March 22nd 2019 7

Analysis method τ − → K − n π 0 ν τ Event selection Requirements to suppress different types of background events: [q q ] low multiplicity and large thrust [Bhabha and dimuon events] large missing mass [Two photon events] cut on transverse momentum/missing energy Signal final states with K 0 S → 2 π 0 and η → 3 π 0 are subtracted as backgrounds Mode # selected Purity (%) ε (%) events τ – → K − ν τ 80715 77 0.99 τ – → K − π 0 ν τ 146948 65 2.16 τ – → K − 2 π 0 ν τ 17930 38 1.34 τ – → K − 3 π 0 ν τ 1863 21 0.13 τ – → π − 3 π 0 ν τ 58598 83 0.49 τ – → π − 4 π 0 ν τ 1706 57 0.12 Eli Ben-Haim Moriond EW, March 22nd 2019 8

τ − → K − n π 0 ν τ Background and cross-feed 3 3 3 3 10 10 10 10 × × × × Events / 0.1 [GeV/c] Events / 0.1 [GeV/c] Events / 0.1 [GeV/c] Events / 0.1 [GeV/c] 7 7 Plots: p of the single 4.5 4.5 BABAR K − ν τ BABAR K − π 0 ν τ 6 6 4 4 Preliminary Preliminary 3.5 3.5 signal-hemisphere track 5 5 3 3 4 4 2.5 2.5 for the 6 signal modes 2 2 3 3 1.5 1.5 2 2 1 1 MC distributions 1 1 0.5 0.5 0 0 0 0 weighted according to 0 0 0.5 0.5 1 1 1.5 1.5 2 2 2.5 2.5 3 3 3.5 3.5 0 0 0.5 0.5 1 1 1.5 1.5 2 2 2.5 2.5 3 3 3.5 3.5 p [GeV/c] p [GeV/c] p [GeV/c] p [GeV/c] the measured BFs Events / 0.1 [GeV/c] Events / 0.1 [GeV/c] Events / 0.1 [GeV/c] Events / 0.1 [GeV/c] BABAR K − 3 π 0 ν τ BABAR 900 900 K − 2 π 0 ν τ 100 100 Preliminary 800 800 Preliminary 700 700 Generally: small S/B 80 80 600 600 500 500 60 60 ratio. 400 400 40 40 300 300 200 200 Much cross feed; better 20 20 100 100 0 0 0 0 0 0 0.5 0.5 1 1 1.5 1.5 2 2 2.5 2.5 3 3 3.5 3.5 0 0 0.5 0.5 1 1 1.5 1.5 2 2 2.5 2.5 3 3 3.5 3.5 accounted for thanks to p [GeV/c] p [GeV/c] p [GeV/c] p [GeV/c] 3 3 10 10 × × the simultaneous fit Events / 0.1 [GeV/c] Events / 0.1 [GeV/c] Events / 0.1 [GeV/c] Events / 0.1 [GeV/c] 3.5 3.5 π − 3 π 0 ν τ π − 4 π 0 ν τ 100 100 3 3 Differences between 2.5 2.5 80 80 BABAR BABAR 2 2 60 60 Data-MC within Preliminary Preliminary 1.5 1.5 40 40 1 1 systematic uncertainties 20 20 0.5 0.5 0 0 0 0 0 0 0.5 0.5 1 1 1.5 1.5 2 2 2.5 2.5 3 3 3.5 3.5 0 0 0.5 0.5 1 1 1.5 1.5 2 2 2.5 2.5 3 3 3.5 3.5 p [GeV/c] p [GeV/c] p [GeV/c] p [GeV/c] - 0 - - - K - - Data τ → π ν τ → η ν - - K τ → µ ν ν τ → π ν τ τ τ µ τ - 0 - 0 0 - K - - 0 - K - τ → ν τ → π π ν τ → η π ν - e - - K τ → ν ν τ → π π ν τ τ τ e τ τ - 0 0 0 0 0 + - - - - + - - K - e e - τ → π ν τ → π π π ν τ → π η π ν → µ µ - K K τ → ν τ τ τ τ - 0 0 0 0 0 0 0 0 - K - - - 0 - - - + τ → π π ν τ → π π π π ν τ → π η π π ν e e q q - K K → τ → π ν τ τ τ τ - 0 0 0 0 Eli Ben-Haim Moriond EW, March 22nd 2019 0 0 0 0 9 - K - - 0 τ → π π π ν τ → π π π π π ν - Rest - - K K τ → τ → π ν τ τ τ

Results: branching fractions τ − → K − n π 0 ν τ comparison to world average and previous results K − ν τ K − π 0 ν τ π − 3 π 0 ν τ Plots from CLEO 1994 CLEO 1994 Alberto Lusiani 0.510 0.100 0.070 0.660 ± 0.070 ± 0.090 ± ± DELPHI 1994 ALEPH 1999 (CKM 2018) 0.444 0.026 0.024 0.850 0.180 ± ± ± OPAL 2004 ALEPH 1999 0.471 ± 0.059 ± 0.023 0.696 ± 0.025 ± 0.014 BaBar 2007 ALEPH 05C OPAL 2001 0.416 ± 0.003 ± 0.018 0.977 ± 0.069 ± 0.058 0.658 ± 0.027 ± 0.029 HFLAV Spring 2017 HFLAV Spring 2017 BaBar 2010 0.433 0.015 1.029 0.075 0.692 0.006 0.010 ± ± ± ± BaBar ICHEP 2018 BaBar ICHEP 2018 HFLAV Spring 2017 0.505 0.002 0.015 1.168 0.006 0.038 ± ± ± ± 0.696 ± 0.010 BaBar ICHEP 2018 0.4 0.5 0.6 0.9 1 1.1 1.2 A.L. elab. A.L. elab. 0.717 0.003 0.021 - ± ± - - 0 B( K 0 ) [%] - 0 τ → π ν B( τ → π 3 π ν (ex. K )) [%] τ τ CKM 2018 CKM 2018 0.6 0.7 0.8 A.L. elab. - - B( τ → K ν ) [%] τ CKM 2018 K − 2 π 0 ν τ K − 3 π 0 ν τ π − 4 π 0 ν τ CLEO 1994 9.000 10.000 3.000 ± ± ALEPH 1999 ALEPH 1999 ALEPH 2005 5.600 2.000 1.500 3.700 2.100 1.100 0.112 0.037 0.035 ± ± ± ± ± ± HFLAV Spring 2017 HFLAV Spring 2017 HFLAV Spring 2017 6.398 ± 2.204 4.284 ± 2.161 0.110 ± 0.039 BaBar ICHEP 2018 BaBar ICHEP 2018 BaBar ICHEP 2018 6.151 0.117 0.338 1.246 0.164 0.238 0.090 0.004 0.007 ± ± ± ± ± ± 0 5 10 2 4 6 0.1 0.15 A.L. elab. A.L. elab. A.L. elab. - 0 - 0 - 0 - -4 - -4 - 0 0 0 B( τ → K 2 π ν (ex. K )) [ × 10 ] B( τ → K 3 π ν (ex. K , η )) [ × 10 ] B( τ → h 4 π ν (ex. K , η )) [%] τ τ τ CKM 2018 CKM 2018 CKM 2018 The new BABAR results improve the knowledge of these BFs except for BF( τ − → K − ν τ ) (for which the 2010 result has better accuracy) Eli Ben-Haim Moriond EW, March 22nd 2019 10

τ − → K − n π 0 ν τ Impact on V us (I) Break-down of sources of relative uncertainties on |V us |( τ → s) [%] including new measurements [Plot from Alberto Lusiani] Substantial improvement from the present analysis Eli Ben-Haim Moriond EW, March 22nd 2019 11

τ − → K − n π 0 ν τ Impact on V us (II) K , N = 2+1+1, PDG 2018 l3 f 0.2231 0.0008 ± K , N = 2+1+1, PDG 2018 l2 f 0.2253 0.0007 ± CKM unitarity, PDG 2018 0.2256 0.0009 Break-down of ± s incl., HFLAV Spring 2017 τ → sources of 0.2186 0.0021 ± uncertainties on s incl., A.L. PHIPSI 2019 τ → 0.2195 0.0019 ± |Vus|( τ → s) 0.22 0.225 A. Lusiani |V | us PHIPSI 2019 Slight increase of the central value and reduced uncertainty V us from τ → s “inclusive” branching fractions is still ~3 σ away from the value derived from CKM unitarity Eli Ben-Haim Moriond EW, March 22nd 2019 12