Eli Ben-Ham LPNHE - IN2P3 - Sorbonne University (Paris) On behalf of - - PowerPoint PPT Presentation
Eli Ben-Ham 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 (4S) threshold Drift Chamber (9 GeV) - e
Eli Ben-Haïm LPNHE - IN2P3 - Sorbonne University (Paris) On behalf of the BABAR collaboration
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
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
(https://scipost.org/SciPostPhysProc.1.001) First presented in ICHEP 2018 Expected to be published in 2019
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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
Significant part of the
experimental uncertainties
τ− → K− nπ0 ντ
Large theoretical
uncertainty
6 Eli Ben-Haim Moriond EW, March 22nd 2019
R(...) ≡ BF(...) BF(τ → eντνe)
[JHEP 01 (2003), 060 ; PRL 94 (2005), 011803]
R(τ → Xsν) |Vus|2 = R(τ → Xdν) |Vud|2 − δRτ,SU3
Break-down of sources of relative uncertainties on |Vus|(τ → s) [%] τ−→K−nπ0ντ
[Plot from Alberto Lusiani]
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-
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+
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 K0
S → 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
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
p [GeV/c] 0.5 1 1.5 2 2.5 3 3.5 Events / 0.1 [GeV/c] 0.5 1 1.5 2 2.5 3 3.5 4 4.5
3
10 × p [GeV/c] 0.5 1 1.5 2 2.5 3 3.5 Events / 0.1 [GeV/c] 0.5 1 1.5 2 2.5 3 3.5 4 4.5
3
10 × p [GeV/c] 0.5 1 1.5 2 2.5 3 3.5 Events / 0.1 [GeV/c] 100 200 300 400 500 600 700 800 900 p [GeV/c] 0.5 1 1.5 2 2.5 3 3.5 Events / 0.1 [GeV/c] 100 200 300 400 500 600 700 800 900 p [GeV/c] 0.5 1 1.5 2 2.5 3 3.5 Events / 0.1 [GeV/c] 1 2 3 4 5 6 7
3
10 × p [GeV/c] 0.5 1 1.5 2 2.5 3 3.5 Events / 0.1 [GeV/c] 1 2 3 4 5 6 7
3
10 × p [GeV/c] 0.5 1 1.5 2 2.5 3 3.5 Events / 0.1 [GeV/c] 20 40 60 80 100 p [GeV/c] 0.5 1 1.5 2 2.5 3 3.5 Events / 0.1 [GeV/c] 20 40 60 80 100
Data
τ
ν
→
τ
ν K
→
τ
ν η
→
τ
ν
µ
ν
→
τ
ν
→
τ
ν π
→
τ
ν π K
→
τ
ν π η
→
τ
ν
e
ν
→
τ
ν π
→
τ
ν π π
→
τ
ν K
→
τ
ν π η
→
+
µ →
+
e
τ
ν π π
→
τ
ν π π π
→
τ
ν π K
→
τ
ν π π η
→
q q →
+
e
τ
ν π π π
→
τ
ν π π π π
→
τ
ν K K
→
Rest →
p [GeV/c] 0.5 1 1.5 2 2.5 3 3.5 Events / 0.1 [GeV/c] 0.5 1 1.5 2 2.5 3 3.5
3
10 × p [GeV/c] 0.5 1 1.5 2 2.5 3 3.5 Events / 0.1 [GeV/c] 0.5 1 1.5 2 2.5 3 3.5
3
10 × p [GeV/c] 0.5 1 1.5 2 2.5 3 3.5 Events / 0.1 [GeV/c] 20 40 60 80 100 p [GeV/c] 0.5 1 1.5 2 2.5 3 3.5 Events / 0.1 [GeV/c] 20 40 60 80 100
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
10 Eli Ben-Haim Moriond EW, March 22nd 2019
τ−→K−nπ0ντ
0.6 0.7 0.8
) [%]
τ
ν
→
B(
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
) [%]
τ
ν π
→
B(
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 5 10
]
10 × )) [ (ex. K
τ
ν π 2
→
B(
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
)) [%] (ex. K
τ
ν π 3
→
B(
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
]
10 × )) [ η , (ex. K
τ
ν π 3
→
B(
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 , (ex. K
τ
ν π 4
→
B(
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)
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]
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 2018
f
, N
l3
K 0.0008 ± 0.2231 = 2+1+1, PDG 2018
f
, N
l2
K 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
PHIPSI 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
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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−
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
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D0→K−π+e+e−
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]
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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
Distributions similar to those from LHCb in D0→K−π+µ+µ−
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.
Improvement of the |Vus| determination through hadronic τ decays
The results presented here are expected to be published soon The decay D0→K−π+e+e− has been observed for the first time
A search for LNV/LFV in D0→h−h’−ℓ+ℓ+ and D0→h−h’+ℓ−ℓ+
Eli Ben-Haim Moriond EW, March 22nd 2019 18