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Mvillanueva Tau-Workshop-2018.Pdf Prospects for � lepton physics at Belle II Michel Hernández Villanueva Outline: Department of Physics Cinvestav, Mexico • Achievements of B-factories in � lepton physics. On behalf of the Belle II collaboration • The Belle II experiment. 15th International Workshop on • First results with early data. Tau Lepton Physics • Prospects of � lepton Amsterdam, Netherlands, Sep 24, 2018 physics Rap God – Eminem B Factories • B-Factory: Production of b pairs. • � factory too! �(e+e- —> �(4s)) = 1.05 nb �(e+e- —> � �) = 0.92 nb Michel H. Villanueva 2 � lepton physics results at B factories Lint (fb-1) Lifetime and CPT test CP-Violation LFV limits Mass and CPT test CP-Violation LFV limits Limits in Mass and CPT test τ → μγ SCC searches Belle Limits in τ → ℓℓℓ BaBar Electric Limits in dipole limit τ → μγ τ → ℓℓℓ Michel H. Villanueva 3 Next gen: Belle II collaboration • 800+ members, 108 institutions, 25 countries • Located in KEK at Tsukuba, Japan Mt. Tsukuba Linac Michel H. Villanueva 4 Next gen: SuperKEKB • Super B-Factory (And � factory too!) �(e+e- —> �(4s)) = 1.05 nb �(e+e- —> � �) = 0.92 nb • Integrated luminosity expected: 50 ab-1 (x50 than previous B factories) 4.6x1010 � pairs @KEK Tsukuba, Japan Michel H. Villanueva 5 Next gen: SuperKEKB “Nano-beams”: vertical beam size is 50nm at the IP. KEKB • Challenges at L=8x1035 1/cm2/s: - Higher background (Radiative Bhabha, Touschek, beam- SuperKEKB gas scattering, etc.). - Higher trigger rates (High performance DAQ, computing). Michel H. Villanueva 6 Belle II Detector Michel H. Villanueva 7 SuperKEKB luminosityBelle II Schedule projection Data taking in phase II was performed with all Goal of Be!e II/SuperKEKB subsystems, except vertex detectors. ) -1 3 months (ab They are being installed and they will be ready for phase III. Integrated luminosity 9 months/year 20 days/month ) -1 s -2 (cm Peak luminosity Calendar Year Phase II Phase III (Partial Belle II) (Full Belle II) Michel H. Villanueva 8 First collisions on Phase II Most of the Belle II detector subsystems are working well. We have signals involving photons and charged tracks. + − Ks → π π π0 → γγ Michel H. Villanueva 9 �→3�� in Belle II early data Candidates: 3 - 1 prong decay + − e e → (τ → 3 tracks)(τtag → track) hadrons We are assuming pion hypothesis in signal side. ⌫⌧ • Thrust axis: nˆ thrust such that Vthrust is maximum. ⌧ 1800 Signal Belle II Simulation 1600 ⌧ nˆthrust Events 1400 ττ Tag 1200 uu+dd+ss cc 1000 eeγ 800 other ` ⌫¯` 600 ⌫⌧ 400 cm 200 i p~i nˆthrust Vthrust = | · cm | 0 p~i 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 P i | | thrust value P Michel H. Villanueva 10 �→3�� in Belle II early data 1000 Belle II 2018 (Preliminary) Data After selection cuts, we Events MC total (stat ⊕ sys) have an agreement 800 -1 Ldt = 291 pb ± between distributions in ∫ τsig → 3π ν data an MC. 600 τsig → other qq Performance of the 400 other subsystems is good. 200 0 1.5 1 0.5 M ± [GeV] Data / MC 3π 0 0.5 1 1.5 2 2.5 3 3.5 M 3π± [GeV] M3� distribution @ 291 pb-1 Michel H. Villanueva 11 �→3�� in Belle II early data Michel H. Villanueva 12 Measurement of � mass • Measured in the decay mode Mmin distribution @ 291 pb-1: � → 3��, 600 using a pseudomass technique Belle II 2018 (Preliminary) Data Events MC total (stat ⊕ sys) developed by the ARGUS 500 -1 Ldt = 291 pb ∫ τ → 3π±ν collaboration: sig 400 τsig → other qq 300 • M = M2 + 2(E − E )(E − P ) other min 3π beam 3π 3π 3π 200 100 • The distribution of the pseudomass 0 is fitted to a empirical edge function. 1.5 1 0.5 M [GeV] Data / MC min • A first measurement of m� at Belle II 0 0.5 1 1.5 2 2.5 3 3.5 M [GeV] is performed using the data collected min during the Phase II. Michel H. Villanueva 13 Measurement of � mass ) 70 Our result, obtained from Belle II early 2 Belle II 60 data 2018 (Preliminary) 50 2 Data m� = (1776.4 ± 4.8 (stat)) MeV/c 40 -1 L dt = 291 pb ∫ Is consistent with previous Events / ( 5.0 MeV/c 30 experimental results. 20 10 2 mτ = (1776.4 ± 4.8) MeV/c Belle (2007) 0 BaBar (2009) 2 BES III (2007) Pull 0 −2 1.7 1.72 1.74 1.76 1.78 1.8 1.82 1.84 ARGUS (1992) 2 Mmin (GeV/c ) Belle II (2018) PDG average 1770 1775 1780 1785 2 mτ (MeV/c ) Michel H. Villanueva 14 Prospects of � lepton physics • The enormous amount of e+e- collisions that are expected from the Belle II experiment features an unique environment for the study of � physics with high precision. • Further details can be looked at “The Belle II Physics Book”, which is now available at: arXiv:1808.10567 Michel H. Villanueva 15 where they are extrapolatedCLEO, from BaBar, Belle Belle results andBaBar, assuming LHCb the and results, integrated Belle respectively, luminosity experiments.Fig. while of Purple 177: red 50 boxes, ab circles blue express inverted the triangles, Belle green II triangles future and prospects, yellow boxes show following basic selection criteria: observables and introduce background reduction(BGx0) techniques. beam As background in a order result, to we study introduced its impact the on thein distributions this of more various physics contaminated environment. was performed using MCparticles samples, from in order tomore serious determine concern the compared to feasibilityBeam the of background Belle studies. experiment due to the small number of daughter 10 Table 135. Bhabha (for background (BG) is from from an extended unbinned maximum-likelihoodin fit Figs. to 178(a) the and (b) for signal events in the signaluncertainties. region. After fixing thesein quantities, the we signal open region the are blind blinded and when evaluate determining the the number selection of criteria and the systematic We first studied generic SM-decaying ◦ ◦ The upper limit obtained from this analysis yields The observed − 7 • For charged particles: • • For photon clusters: ) at 90% C.L. Track fit p-value E | ∆ γ t Current 90% C.L. upper limits for the branching fraction of cluster > 90% C.L. upper limits for LFV τ decays BR the of for Upperlimits 10 0 Assuming BellefulldatasetII (50ab 10 10 10 10 10 Michel H.Villanueva e . -10 100(forward endcap) ⌧ -9 -8 -7 -6 -5 γ | ) events. The cuts imposed to reduce the background are summarised in LFV decay. A preliminary M < - l e γ - γ µ 50 ns. µ γ γ - 0 e- π – 0 µ -π ∆ e η - lP > µ η E - e η' 0 - ' 0 µ η - 0 distributions at Belle (4 ⌧ . e K ⌧ S0 01; - µ K lS ! - S ! e f At Belle II, the beam background in 0 - 0 µ- f0 e `⌫ ρ - 0 µ µ ρ 0 ` - γ e K* ⌫ , - µ K* lV 0 ⌧ and - . e K* 0 090(barrel) - +extra µ K* e- φ µ- φ ⌧ - ⌧ e- ω 506/688 ⌧ µ ω ! of magnitude. of Improvementof 2orders + e- e+ e- ! ⌧ - e+ e- µ- − - e e µ+ µ lll γ - + - γ µ µ- µ µ- , respectively. The signal yield is evaluated + pairs generated with (BGx1) and without γ -1 16 e µ e , - + - events and radiative di-muon (for e 0 µ µ ): study in the presence of beam background - + - . e- π π- 160(backwards endcap) GeV; + . µ π π- 9 e- + K - π - See Ami’s talk on Tuesday Tuesday talkon Ami’s See Br + ⇥ µ π K - + - e- K+ π- 10 ( µ K π - + - � ⌧ e- K+ K- lhh M 8 µ K K decays. LFV ! - 0 0 ⌧ e K K S0 S0 ⌧ - µ µ K K LFV decays obtained in the CLEO, S S γ - - + + µ e π- + π- – ⌧ π µ π γ - ∆ - + − e K π- + - ⌧ ( π µ K E - + - e K e K pairs [1511]) are shown LFV searches becomes a - + - γ K µ K distribution. The main - )) = 4 π Λ Λ - π- Λ h K Λ NewPhysics.of is aclearsignature LFV Observation of - K Λ . ⌧ 5 Belle II LHCb Belle BaBar CLEO − ⇥ LFV analyses 1 . 10 − 8 µ (1 γ . ) or 2 ⇥ CP violation in �→Ks �(≥0�0)� • The decay of the � lepton to final states containing a Ks meson will have a nonzero decay-rate asymmetry due to CP violation in the kaon sector. Γ(τ+ → π+K0ν¯ ) − Γ(τ− → π−K0ν¯ ) A = S τ S τ τ + + 0 − − 0 Γ(τ → π KSν¯τ) + Γ(τ → π KSν¯τ) • The SM prediction1,2 is SM −3 Aτ = (3.6 ± 0.1) × 10 • BaBar measured: 2.8 � away BaBar ± ± −3 Aτ = (−3.6 2.3 1.1) × 10 from SM An improved measurement of A is a priority at Belle II. J.P. Lees et.al (BaBar) � Phys.Rev D85 (2012) 031102 1 I. I. Bigi and A. I. Sanda, Phys. Lett. B 625, 47 (2005). 2 Y. Grossman and Y. Nir, JHEP 2012.4 (2012). Michel H. Villanueva 17 CP violation in �→Ks �� • CPV that could arise from a charged scalar boson exchange. It can be detected as a difference in the decay angular distributions • • With 50 ab-1 data at Belle II, we expect 70 times improvement, i.e., |���| < (0.5 - 3.8) × 10−4, at 90% C.L. assuming the central value ��� = 0. M. Bischofberger et. al (Belle) Michel H. Villanueva 18 PRL 107 (2011) 131801 Michel Parameters ⌫⌧ When spin of � lepton is not determined, �, �, � and � are the experimentally accessible ⌫¯ parameters used in describing the phase ` space distribution of � leptonic decays.
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