Eli Ben-Haïm LPNHE - IN2P3 - Sorbonne University (Paris)

On behalf of the BABAR collaboration

The BABAR detector

e- (9 GeV)

e+ (3GeV)

Magnet 1.5T

Electromagnetic calorimeter

Detector of Cherenkov light

Drift Chamber

Silicon Vertex Tracker

Instrumented flux return

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PEP-II: asymmetric beams at Υ(4S) threshold

BABAR is well suited for the measurements presented here: clean environment, hermetic detector, excellent PID, good π0 reconstruction

Eli Ben-Haim Moriond EW, March 22nd 2019

The BABAR dataset

3 Eli Ben-Haim Moriond EW, March 22nd 2019

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

Vus in tau decays

Branching fractions of τ− → K− nπ0 ντ (n = 0,1,2,3) and τ− → π− nπ0 ντ (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

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Main ways to determine |Vus|

5 Eli Ben-Haim Moriond EW, March 22nd 2019

τ−→K−nπ0ντ

Kaon decays   (Kℓ3) K → πℓυ   (Kℓ2) K → ℓυ / K → ℓυ

  CKM unitarity τ lepton decays

  “Inclusive” τ → s (sum of exclusives) ⭐ This talk τ → Kυτ / τ → πυτ

  The results from τ decays are systematically lower à Inclusive τ → s is 3.1σ lower than the derivation based on CKM unitarity

|Vus| from “inclusive” τ → s

  Significant part of the experimental uncertainties originates from τ− → K− nπ0 ντ

  Large theoretical uncertainty

6 Eli Ben-Haim Moriond EW, March 22nd 2019

R(...) ⌘ BF (...)

BF (⌧ ! e⌫⌧⌫e)

[JHEP 01 (2003), 060 ; PRL 94 (2005), 011803]

R(⌧ ! Xs⌫)

|Vus|2=

R(⌧ ! Xd⌫)

|Vud|2� �R⌧,SU3

Break-down of sources of relative uncertainties on |Vus|(τ → s) [%]

τ−→K−nπ0ντ

[Plot from Alberto Lusiani]

Analysis method Basics

  Signal modes (1-prong): τ−→K− nπ0 ντ (n=0,1,2,3)

τ−→π− nπ0 ντ (n=3,4) 7 Eli Ben-Haim Moriond EW, March 22nd 2019

τ−→K−nπ0ντ

  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 π0 → γγ require no additional γ

  Apply reconstruction- and PID- eff. corrections based on MC and control samples

  Correct for fake γ from neutrons in the EM calorimeter

  Control modes w/ similar topology, σ(BF) ~ 1%: τ−→π− nπ0 ντ (n=0,1,2)

τ−→µ− νµ ντ

e+/µ+

Analysis method Event selection

8 Eli Ben-Haim Moriond EW, March 22nd 2019

τ−→K−nπ0ντ

  Requirements to suppress different types of background events:   [qq] 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 K0S → 2π0 and η → 3π0 are subtracted as backgrounds

Mode # selected events

Purity (%) ε(%)

τ– → K− ντ 80715 77 0.99 τ– → K− π0 ντ 146948 65 2.16 τ– → K− 2π0 ντ 17930 38 1.34 τ– → K− 3π0 ντ 1863 21 0.13 τ– → π− 3π0 ντ 58598 83 0.49 τ– → π− 4π0 ντ 1706 57 0.12

Background and cross-feed   Plots: p of the single

signal-hemisphere track for the 6 signal modes

  MC distributions weighted according to the measured BFs

  Generally: small S/B ratio.

  Much cross feed; better accounted for thanks to the simultaneous fit

  Differences between Data-MC within systematic uncertainties

9 Eli Ben-Haim Moriond EW, March 22nd 2019

τ−→K−nπ0ντ

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Data τν -π → -ττν

0K -π → -τ τν η - K→ -τ

τν µ

ν -µ → -τ

τν - K→ -τ τν 0π -π → -τ

τν 0π

0K -π → -τ τν 0

π η - K→ -ττν eν - e→ -τ

τν 0π - K→ -τ τν 0

π 0π -π → -τ

τν 0

K - K→ -τ τν 0π η -π → -τ -µ +µ → -e+e

τν 0π 0

π - K→ -τ τν 0π

0π 0

π -π → -ττν 0

π 0

K - K→ -τ τν 0π 0

π η -π → -τ q q → -e+e

τν 0π 0

π 0π - K→ -τ τν 0

π 0π

0π 0

π -π → -ττν 0 K

0K -π → -τ Rest→ -τ

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K− ντ K− π0 ντ

K− 2π0 ντ K− 3π0 ντ

π− 3π0 ντ π− 4π0 ντ

BABAR Preliminary

BABAR Preliminary

BABAR Preliminary

BABAR Preliminary

BABAR Preliminary

BABAR Preliminary

Results: branching fractions comparison to world average and previous results

10 Eli Ben-Haim Moriond EW, March 22nd 2019

τ−→K−nπ0ντ

0.6 0.7 0.8) [%]τν

- K→ -τB(

CLEO 1994 0.090± 0.070 ±0.660

DELPHI 1994 0.180±0.850

ALEPH 1999 0.014± 0.025 ±0.696

OPAL 2001 0.029± 0.027 ±0.658

BaBar 2010 0.010± 0.006 ±0.692

HFLAV Spring 2017 0.010±0.696

BaBar ICHEP 2018 0.021± 0.003 ±0.717

A.L. elab.CKM 2018

0.4 0.5 0.6) [%]τν 0π - K→ -τB(

CLEO 1994 0.070± 0.100 ±0.510

ALEPH 1999 0.024± 0.026 ±0.444

OPAL 2004 0.023± 0.059 ±0.471

BaBar 2007 0.018± 0.003 ±0.416

HFLAV Spring 2017 0.015±0.433

BaBar ICHEP 2018 0.015± 0.002 ±0.505

A.L. elab.CKM 2018

0 5 10]-410×)) [0 (ex. Kτν 0π 2- K→ -τB(

CLEO 1994 3.000± 10.000 ±9.000

ALEPH 1999 1.500± 2.000 ±5.600

HFLAV Spring 2017 2.204±6.398

BaBar ICHEP 2018 0.338± 0.117 ±6.151

A.L. elab.CKM 2018

0.9 1 1.1 1.2)) [%]0 (ex. Kτν 0π 3-π → -τB(

ALEPH 05C 0.058± 0.069 ±0.977

HFLAV Spring 2017 0.075±1.029

BaBar ICHEP 2018 0.038± 0.006 ±1.168

A.L. elab.CKM 2018

2 4 6]-410×)) [η,0 (ex. Kτν 0π 3- K→ -τB(

ALEPH 1999 1.100± 2.100 ±3.700

HFLAV Spring 2017 2.161±4.284

BaBar ICHEP 2018 0.238± 0.164 ±1.246

A.L. elab.CKM 2018

K− ντ K− π0 ντ

K− 2π0 ντ K− 3π0 ντ

π− 3π0 ντ

0.1 0.15)) [%]η,0 (ex. Kτν 0π 4- h→ -τB(

ALEPH 2005 0.035± 0.037 ±0.112

HFLAV Spring 2017 0.039±0.110

BaBar ICHEP 2018 0.007± 0.004 ±0.090

A.L. elab.CKM 2018

π− 4π0 ντ

  The new BABAR results improve the knowledge of these BFs except for BF(τ−→K− ντ) (for which the 2010 result has better accuracy)

Plots from Alberto Lusiani

(CKM 2018)

Impact on Vus (I)

11 Eli Ben-Haim Moriond EW, March 22nd 2019

τ−→K−nπ0ντ

Break-down of sources of relative uncertainties on |Vus|(τ → s) [%] including new measurements

Substantial improvement from the present analysis

[Plot from Alberto Lusiani]

Impact on Vus (II)

12 Eli Ben-Haim Moriond EW, March 22nd 2019

τ−→K−nπ0ντ

Break-down of sources of

uncertainties on |Vus|(τ → s)

0.22 0.225|us|V

= 2+1+1, PDG 2018f, Nl3K 0.0008±0.2231

= 2+1+1, PDG 2018f, Nl2K 0.0007±0.2253

CKM unitarity, PDG 2018 0.0009±0.2256

s incl., HFLAV Spring 2017→ τ 0.0021±0.2186

s incl., A.L. PHIPSI 2019→ τ 0.0019±0.2195

A. LusianiPHIPSI 2019

  Slight increase of the central value and reduced uncertainty Vus from τ → s “inclusive” branching fractions is still ~3σ away from the value derived from CKM unitarity

Eli Ben-Haim Moriond EW, March 22nd 2019

Lepton universality test in D decays

First observation of the decay D0 → K− π+ e+ e−

PRL 122, 081802 (2019)

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Introduction and motivations

  Several measurements in B-meson decays indicate possible deviations from lepton universality à Do electrons and muons couple with equal strength in D-meson decays?

  LHCb measured BF(D0→K−π+µ+µ−) [PLB 757 (2016) 558] ; while the e+e− mode was not yet observed

  D0→K−π+e+e− are FCNC processes ⇒ small in the SM (forbidden at tree level)

14 Eli Ben-Haim Moriond EW, March 22nd 2019

D0→K−π+e+e−

  Short-distance contributions (when no resonances are present): loop/box diagrams (BF ~ O(10-9))

  Long-distance contributions such as D0→K−π+ρ0(e+e−) may reach BF ~ O(10-6)

  Certain beyond-standard-model scenarios enhance the BF

e+

e−

Analysis strategy

  Reconstruct D0→K−π+e+e− and D0→K−π+π+π− from D*+→D0 π+ produced in cc continuum

  Maximum-Likelihood Fit to m(D0) and Δm = m(D*+) − m(D0)   Apply candidate-by-candidate reconstruction efficiencies and normalize to

D0→K−π+π+π− to determine D0→K−π+e+e− branching fraction:

  Reconstruction and event selection:   Slow π (from D*) with charge opposite to that of the K (from D0)   D0 momentum in the center-of-mass frame > 2.4 GeV/c

(rejects D0 from B-meson decays and most of the continuum background)   Particle ID requirements for all particles

15 Eli Ben-Haim Moriond EW, March 22nd 2019

D0→K−π+e+e−

Results in the m(e+e-) ~ m(ρ) region 0.675 < m(e+e−) < 0.875 GeV/c2

Agrees with the SM prediction [JHEP 04 (2013) 135] and with the LHCb measurement in the same mass range: BF(D0→K−π+µ+µ−) = (4.17 ± 0.12 ± 0.40) × 10−6 [PLB 757 (2016) 558]

16 Eli Ben-Haim Moriond EW, March 22nd 2019

D0→K−π+e+e−

BF(D0→K−π+e+e−) = (4.0 ± 0.5 [stat.] ± 0.2 [syst.] ± 0.1 [norm.]) × 10−6

No evidence for deviation from equal lepton

coupling strengths

68 ± 9 signal candidates

Significance: 9.7 σ

sPlot

sPlot

Distributions similar to those from LHCb in D0→K−π+µ+µ−

Results in other m(e+e-) ranges

17 Eli Ben-Haim Moriond EW, March 22nd 2019

D0→K−π+e+e−

ϕ region: 3.8+2.7

−1.9 signal events (1.8σ) BF(D0→K−π+e+e−) < 0.5 ×10−6

at 90% C.L.

Continuum ranges (all white regions): Residual resonant contributions subtracted

(probe NP in short distance contributions, SM: O(10-9) ) 19±7 signal events (2.6σ)

BF(D0→K−π+e+e−) < 3.1 ×10−6 at 90% C.L.

Conclusions

  Improvement of the |Vus| determination through hadronic τ decays à still ~3σ away from the value derived from CKM unitarity

  The results presented here are expected to be published soon

  The decay D0→K−π+e+e− has been observed for the first time à Comparing to BF(D0→K−π+µ+µ−) from LHCb, no evidence of deviation from equal lepton coupling strength

  A search for LNV/LFV in D0→h−h’−ℓ+ℓ+ and D0→h−h’+ℓ−ℓ+

(h(’) = K, π ; ℓ = e, µ) is being finalized

Eli Ben-Haim Moriond EW, March 22nd 2019 18

BABAR continues to produce exciting physics results, adding more information and using more sophisticated analysis techniques to probe new physics effects