Rare, radiative and electroweak penguin decays of heavy flavour - - PowerPoint PPT Presentation
Rare, radiative and electroweak penguin decays of heavy flavour hadrons at LHCb Carla Marin Benito on behalf of the LHCb collaboration Rencontres de Moriond Electroweak La Thuile, Italy, 17-23 March 2019 Rare decays of b hadrons
Carla Marin Benito
Rencontres de Moriond Electroweak
La Thuile, Italy, 17-23 March 2019
Flavour-changing neutral-currents (FCNC) forbidden at tree-level in SM:
✁
W − W − γ u, c, t b s
✁
u, c, t u, c, t γ H− b s
Sensitive to new particles at higher scales than direct searches. Model-independent description: Operator Product Expansion. Heff ∝
i
+ C NP
i
◮ Wilson Coefficients (Ci) are extracted from global fits to the data. ◮ Any deviation from SM calculations would point to New Physics effects. Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 1 / 15
Several deviations in differential branching ratios (BR) and angular
JHEP 06 (2014) 133
]
4
c /
2
[GeV
2
q
5 10 15 20
]
2
/GeV
4
c ×
[10
2
q /d B d
1 2 3 4 5 LCSR Lattice Data
LHCb
−
µ
+
µ
+
K →
+
B ]
4
c /
2
[GeV
2
q
5 10 15 20
]
2
/GeV
4
c ×
[10
2
q /d B d
1 2 3 4 5 LCSR Lattice Data −
µ
+
µ K → B LHCb ]
4
c /
2
[GeV
2
q
5 10 15 20
]
2
/GeV
4
c ×
[10
2
q /d B d
5 10 15 20 LCSR Lattice Data
LHCb
−
µ
+
µ
*+
K →
+
B
JHEP 09 (2015) 179, JHEP 06 (2015) 115, PhysRevD.93.074501, JHEP 02 (2016) 104
BR theory predictions affected by large uncertainties
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 2 / 15
Global fits point to additional contributions to C9 or C9 and C10 From Eur.Phys.J.C(2017)77:377 See also
Nucl Phys B 909 (2016) 737-777, JHEP 06 (2016) 092,
JHEP 1801 (2018) 093, etc.
And talks this afternoon and tomorrow! Several NP model proposed to accommodate the data: Leptoquarks [eg. Phys.Rev.D94,115005], Z’ [eg. Phys.Rev.D93,074003], etc. → Crucial to improve these measurements and add new modes! → Clean tests provided by Lepton Flavour Universality measurements, see talk by T. Humair with new results!
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 3 / 15
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 4 / 15
arXiv:1812.06004
Highly-suppressed decay with BR ∝ |Vub|2
◮ Run 1 + 2016 data (4.7 fb−1) ◮ Mmin
µ+µ− < 980 MeV
/c2
◮ Exploit corrected mass variable:
Mcorr =
µµµ + pT′2 + pT′
◮ Veto charmonium resonances ◮ Normalize to B+ → J/ψK +
]
2
c [MeV/
corr
M
4000 5000 6000 7000
)
2
c Candidates / (50 MeV/
20 40 60 80 100 120 140 160
2011-16 LHCb
Total Fit Data Combinatorial Misidentified Partially reconstructed Prediction from PAN (2018) 81:347
Only one theoretical estimate (vector-meson dominance): B(B+ → µ+µ−µ+νµ) ∼ 1.3 × 10−7 [PAN (2018) 81:347]
No signal observed, best world limit set
B(B+ → µ+µ−µ+νµ) < 1.6 × 10−8 at 95% CL.
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 5 / 15
b → Λµ+µ−
JHEP 09 (2018) 146
It is a b→ sℓ+ℓ− transition complementary to B0 → K ∗0µ+µ− Richer angular distribution due to baryon spin and polarisation Analysis performed with data recorded during 2011 – 2016 (5 fb−1) Focus on low recoil region, 15 < q2 < 20 GeV2/c4 Analysis exploits method of moments [JHEP 11 (2017) 138]: d5Γ dΩ = 3 32π2
34
Kifi(Ω)
◮ fi angular functions ◮ Ki coefficients [Phys. Lett. B724 (2013) 27] Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 6 / 15
b → Λµ+µ−
JHEP 09 (2018) 146
Full set of angular observables measured for the first time: All parameters compatible with SM predictions K11,...,34 compatible with no initial Λ0
b polarization
i
K
5 10
Value
0.4 − 0.2 − 0.2 0.4
LHCb
SM prediction
Asymmetries measured from combination of observables
Aℓ
FB = 3 2K3 = −0.39 ± 0.04 ± 0.01
Ah
FB = K4 + 1 2K5 = −0.30 ± 0.05 ± 0.02
Ahℓ
FB = 3 4K6 = +0.25 ± 0.04 ± 0.01
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 7 / 15
b → Λγ
LHCb-PAPER-2019-010
Λ0
b → Λγ is a FCNC b→ sγ transition:
Heff ∝ V ∗
tsVtb(C7O7 + C ′ 7O′ 7)
BR in SM: 10−7 − 10−5, large uncertainties from form factors Best limit so far by CDF: B(Λ0
b → Λγ) < 1.9 × 10−3 at 90% CL.
→ large room for improvement Λ0
b → Λγ offers access to the photon polarization [J.Phys.G24 (1998) 979]
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 8 / 15
b → Λγ
LHCb-PAPER-2019-010
Search performed using 2016 data (1.7 fb−1) Very challenging mode:
◮ long Λ lifetime ◮ no direction from γ cluster
→ cannot reconstruct Λ0
b
decay vertex!
p π− Λ0
b
Λ γ
PV
Dedicated online and offline reconstruction:
◮ Λ0
b momentum as direct sum of Λ and γ momenta
◮ large combinatorial background expected
→ large signal to background separation is crucial
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 9 / 15
b → Λγ
LHCb-PAPER-2019-010
High performance BDT using XGBoost algorithm Output requirement optimised using Punzi figure of merit: FoM = ǫS σ/2 + √NB , σ = 5 Working point: 99.8% background rejection with 1/3 signal efficiency Exploit neutral PID tools to reject background from π0
[LHCb-PUB-2015-016]
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 10 / 15
b → Λγ
LHCb-PAPER-2019-010
Use well-know B0 → K ∗0γ as normalization mode: N(Λ0
b → Λγ)
N(B0 → K ∗0γ) = fΛ0
b
fB0 × B(Λ0
b → Λγ)
B(B0 → K ∗0γ)× B(Λ→ pπ−) B(K ∗0 → K +π−)× ǫ(Λ0
b → Λγ)
ǫ(B0 → K ∗0γ)
fΛ0
b
fB0 from recent LHCb measurement at 13 TeV [arXiv:1902.06794]
Input branching fractions from PDG Efficiencies from simulation and calibration samples
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 11 / 15
b → Λγ
LHCb-PAPER-2019-010
From simultaneous unbinned maximum likelihood fit:
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 12 / 15
b → Λγ
LHCb-PAPER-2019-010
From simultaneous unbinned maximum likelihood fit: Signal excess with 5.6 σ significance → first observation of Λ0
b → Λγ
Branching fraction measurement within range of SM predictions
B(Λ0
b → Λγ) = (7.1 ± 1.5 ± 0.6 ± 0.7) × 10−6
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 12 / 15
b → Λγ
LHCb-PAPER-2019-010
Analysis statistically limited. Main systematics: Source Uncertainty (%) Data/simulation agreement 7.7 Λ0
b fit model
3.0 B0 → K ∗0γ backgrounds 2.7 Size of simulated samples 1.7 Efficiency ratio 0.7 Sum in quadrature 8.9 fΛ0
b/fB0
8.7 Input branching fractions 3.0 Sum in quadrature 9.2 from external measurements.
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 13 / 15
Rare FCNC b-hadron decays provide high sensitivity to NP effects
Experimental status
Tensions wrt SM in both differential BR and angular observables Updates and new analyses ongoing to confirm them Lepton Flavour Universality observables provide complementary tests (see talk by T. Humair tomorrow)
Latest results from LHCb
Best world limit on B+ → µ+µ−µ+νµ Full angular analysis of Λ0
b → Λµ+µ−: compatible with SM
First observation of Λ0
b → Λγ: first step towards photon polarisation
measurement Many more results with Run 2 data are underway
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 14 / 15
Rare FCNC b-hadron decays provide high sensitivity to NP effects
Experimental status
Tensions wrt SM in both differential BR and angular observables Updates and new analyses ongoing to confirm them Lepton Flavour Universality observables provide complementary tests (see talk by T. Humair tomorrow)
Latest results from LHCb
Best world limit on B+ → µ+µ−µ+νµ Full angular analysis of Λ0
b → Λµ+µ−: compatible with SM
First observation of Λ0
b → Λγ: first step towards photon polarisation
measurement Many more results with Run 2 data are underway
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 14 / 15
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 15 / 15
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 16 / 15
JINST3 (2008) S08005
Excellent µ identification Good momentum resolution Neutral particle identification Photon eneregy measurement
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 17 / 15
JHEP 10 (2015) 034 Trend not observed so far in b→ dℓ+ℓ− but precision is lower:
JHEP 10 (2015) 034
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 18 / 15
Deviations in optimised angular observable P′
5 in B0 → K ∗0µ+µ−:
P′
5 = S5
√
FL(1−FL)
[JHEP 05 (2013) 137]
]
4
c /
2
[GeV
2
q
5 10 15
5
' P
1 − 0.5 − 0.5 1 (1S) ψ / J (2S) ψ
LHCb data Belle data ATLAS data CMS data SM from DHMV SM from ASZB
JHEP 02 (2016) 104, Phys.Rev.Lett.118(2017)11,111801, JHEP 10 (2018) 047, Phys.Lett.B781(2018)517-541 Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 19 / 15
P′
5 =
S5
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 20 / 15
b → Λµ+µ−
JHEP 09 (2018) 146
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 21 / 15
b → Λµ+µ−
JHEP 09 (2018) 146
]
2
c ) [MeV/
−
µ
+
µ
−
π p ( m
5400 5500 5600 5700 5800
)
2
c Candidates / (20 MeV/
20 40 60
LHCb
−
π p long 2011 + 2012
]
2
c ) [MeV/
−
µ
+
µ
−
π p ( m
5400 5500 5600 5700 5800
)
2
c Candidates / (20 MeV/
20 40 60 80 100
LHCb
−
π p downstream 2011 + 2012
]
2
c ) [MeV/
−
µ
+
µ
−
π p ( m
5400 5500 5600 5700 5800
)
2
c Candidates / (20 MeV/
20 40 60
LHCb
−
π p long 2015 + 2016
]
2
c ) [MeV/
−
µ
+
µ
−
π p ( m
5400 5500 5600 5700 5800
)
2
c Candidates / (20 MeV/
20 40 60 80 100
LHCb
−
π p downstream 2015 + 2016
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 22 / 15
b → Λµ+µ−
JHEP 09 (2018) 146
Exploit method of moments to cope with small statistics and large number
d5Γ dΩ = 3 32π2
34
Kifi(Ω) Project individual angular observables through weighting functions gi(Ω) Ki = d5Γ dΩ gi(Ω)dΩ Per-candidate weights to compensate non-uniform efficiencies and background contamination Ki =
wngi(Ωn)/
wn
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 23 / 15
b → Λµ+µ−
JHEP 09 (2018) 146
From JHEP 11 (2017) 138 and Phys.Rev.D91 (2015) 114012
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 24 / 15
b → Λγ significance
From profile likelihood:
5 10 15 20
6 −
10 ×
) γ Λ →
b
Λ ( B
5 10 15 20 25 30
Projection of Profile of NLL
LHCb Preliminary
Cross-checked with pseudoexperiments
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 25 / 15
b → Λγ
The Λ0
b → Λγ decay gives access to the photon polarisation in b→ sγ:
Heff ∝ V ∗
tsVtb(C7O7 + C ′ 7O′ 7)
αSM
γ
= P(γL) − P(γR) P(γL) + P(γR) = C ′
7
C7 = 1 + O ms mb
right-handed polarisation can be enhanced in SM extensions
[Atwood et al., Phys.Rev.Lett.79:185-188,1997]
dΓ dcosθp ∝ 1 − αγαp,1/2cosθp with αp,1/2 = 0.642 ± 0.07
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 26 / 15
b → Λγ
So far, photon polarisation only studied in b-mesons. Baryons offer complementary measurements!
−0.4 −0.2 0.0 0.2 0.4 0.6 0.8 1.0
Re(CNP
7 ) −0.6 −0.4 −0.2 0.0 0.2 0.4 0.6
Re(C′,NP
7
)
flavio v0.14.1
αγ A∆Γ(Bs → φγ) BR(B → Xsγ) SK∗γ Angular B0 → K∗0ee All radiative except αγ All radiative All combined
From Flavio
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 27 / 15
Some models predict LFV to explain LFU violation LFV effectively forbidden in the SM → null test Large heavy-hadron samples allow to put stringent limits LHCb results with Run 1 data: in short, all compatible with SM so far Decay Branching ratio limit Reference τ − → pµ+µ+ 4.4 × 10−7
PHYSICS LETTERS B 724 (2013)
τ + → pµ+µ− 4.4 × 10−7
PHYSICS LETTERS B 724 (2013)
B0
s → e+µ−
1.1 × 10−8
PHYS.REV.LETT. 111 (2013) 141801
B0 → e+µ− 2.8 × 10−9
PHYS.REV.LETT. 111 (2013) 141801
τ → µµµ 4.7 × 10−8
JHEP 02 (2015) 121
D0 → e+µ− 1.3 × 10−8
Searches for b → Xℓ+ℓ−′ LFV decays ongoing
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 28 / 15
New results using 3 fb−1 (2011-2012) and improved selection: Enhanced in NP models up to O(10−11) Search in bins of output classifier to enhance sensitivity Results compatible with background only hypothesis
)
±
µ
±
e → B BF(
0.5 1 1.5
9 −
10 ×
s
CL
0.2 0.4 0.6 0.8 1 LHCb
)
±
µ
±
e →
s
B BF(
2 4 6 8
9 −
10 ×
s
CL
0.2 0.4 0.6 0.8 1 LHCb
Most stringent limits on these decays: B(B0
s → e+µ−) < 5.4 × 10−9 at 90% C.L.
B(B0 → e+µ−) < 1.0 × 10−9 at 90% C.L.
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 29 / 15
Angular and CP asymmetries in D0 → hhµ+µ− [Phys.Rev.Lett.121(2018)091801]:
D0 → π+π−µ+µ−
AFB = (3.3 ± 3.7 ± 0.6)% A2φ = (−0.6 ± 3.7 ± 0.6)% ACP = (4.9 ± 3.8 ± 0.7)%
D0 → K +K −µ+µ−
AFB = (0 ± 11 ± 2)% A2φ = (9 ± 11 ± 1)% ACP = (0 ± 11 ± 2)%
◮ differential asymmetries also measured
Search for the rare Λ+
c → pµ+µ− [PHYS. REV. D 97, 091101 (2018)]:
◮ No signal outside the φ and ω regions
B(Λ+
c → pµ+µ−) < 7.7 × 10−8 at 90% C.L.
Update of D0 → µ+µ− search ongoing
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 30 / 15
Search for K 0
S → µ+µ− with 3 fb−1 [EUR. PHYS. J. C, 77 10 (2017) 678]:
Compatible with background only: B(K 0
S → µ+µ−) < 0.8 × 10−9 at
90% C.L.
9
10 × )
+
µ →
S
B(K
1 2 3
CL
0.8 0.85 0.9 0.95 1
LHCb
Evidence for Σ→ pµ+µ− with 3 fb−1 [PHYS.REV.LETT.120, 221803 (2018)]: Excess with 4.1σ significance: B(Σ→ pµ+µ−) = (2.21.8
−1.3) × 10−8
HyperCP excess [PRL(94)021801] not confirmed
]
2
c [MeV/
−µ
+µ p
m
1200 1300 1400
)
2
c Candidates / ( 5 MeV/
1 2 3 4 5 6 7 8
LHCb
−
µ
+
µ p →
+
Σ
Data Full model
−
µ
+
µ p →
+
Σ Background
Exploring also other modes: K 0
S → ℓ+ℓ−ℓ+ℓ−, K 0 S → π0µ+µ−, Λ decays... Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 31 / 15
LHCb major upgrade for Run 3, could go to 300 fb−1 in HL-LHC!
b→ sγ
σstat(A∆, αγ, AIm,2
T
) < 1%
explore also b→ dγ
B0
s → µ+µ−
σ(B) ∼ 1.8%(stat), ∼ 4%(syst) σ( B(B0
s→µ+µ−)
B(B0→µ+µ−)) ∼ 10% stat. limited
σ(τ eff
µ+µ−) ∼ 2% and CP(t) analyses!
b→ sℓ+ℓ−
Carla Marin (carla.marin@cern.ch) Rare, radiative and EW decays at LHCb Moriond EW 2019 32 / 15