Charmless b-hadron decays - Agenda (Indico) · 2017-03-10 · Charmless Decays Can proceed via tree...
Transcript of Charmless b-hadron decays - Agenda (Indico) · 2017-03-10 · Charmless Decays Can proceed via tree...
Charmless b-hadron decays
Giulio Dujany
on behalf of the LHCb collaboration
XXXIe Rencontres de
Physique de la Vallee d’Aoste
Overview
1 Introduction
2 Baryonic B decaysObservation of the B0
s → pΛK− decay [LHCb-CONF-2016-016]Observation of the B0
(s)→ pph+h′− decays
3 CP violation in b decaysTime dependent CP violation in the B0 → π+π− and B0
s → K+K−
decays [LHCb-CONF-2016-018]Evidence for CP violation inΛ0
b → pπ−π+π− [Nat. Phys. (2017)]
4 Rare B decaysSearch for the B0
s → η′φ decay [arXiv:1612.08110, Submitted to JHEP]Observation of the B0→ K+K− decay [Phys. Rev. Lett. 118 (2017)081801]
5 Conclusions
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 2 / 37
Charmless Decays
Can proceed viatree b→ u
penguin b→ s, b→ dTree, suppressed by Vub, canhave similar magnitude topenguinsSensitivity to weak phases fromtree-penguin interferenceNew physics can appear in loopsProvide inputs and tests forQCD models
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 3 / 37
Baryonic B decays
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 4 / 37
MotivationsMany baryonic B decays still to be studied / observedMulti-body final state tend to have larger BF that 2-body ones
B(B0 → Λ−c pπ+π−) ∼ 10−3 � B(B0 → Λ−
c pπ0) ∼ 10−4
� B(B0 → Λ−c p) ∼ 10−5
B(B0 → ppK0) ∼ 10−6 � B(B0 → pp) ∼ 10−8
Threshold enhancement in baryon-antibaryon systems observed inmany decay modes (see eg. [Eur. Phys. J. C74 (2014) 3026])
Threshold enhancement observed forthe first time by Belle in B± → ppK±
[Phys. Rev. Lett. 88 (2002) 181803]0
20
40
60
80
100
120
2 2.5 3 3.5 4 4.5Mpp
_ (GeV/c2)
dN /
dMpp_
(Eve
nts
/ (G
eV/c
2 ))
Even
ts /
(5 M
eV/c
2 )
0
5
10
3 3.05 3.1 3.15
FIG. 2. The fitted yield divided by the bin size forB+ → ppK+ as a function of pp mass. The charm veto isapplied. The distribution from non-resonant B+ → ppK+
MC simulation is superimposed. The inset shows the pp massdistribution for the J/ψK+ signal region.
the ECL shower width distribution is consistent with MCexpectations for the proton and anti-proton candidates.In addition, we check the branching fraction as the cutson the proton and anti-proton probabilities and likeli-hood ratio are varied. We do not observe any systematictrends beyond statistics.
To verify the analysis procedure and branching frac-tion determination, we remove the J/ψ veto and ex-amine the decay chain B+ → J/ψK+, J/ψ → pp. Aclear signal of 26.4 ± 5.2 events is then observed in the∆E spectrum. We also observe 25.9 ± 5.1 events inthe Mbc distribution. The pp invariant mass spectrumfor J/ψK+ signal candidates is shown as an inset inFig. 2. We use the ∆E yield and the MC detectionefficiency of 0.30 to determine the branching fractionB(B+ → J/ψK+) = (13.1 ± 2.6) × 10−4. This is ingood agreement with the PDG world average, B(B+ →J/ψK+) = (10.0±1.0)×10−4 [12], which was obtained byexperiments that reconstruct the J/ψ in dilepton modes.
We also examined two related decay modes B0 →ppKS and B+ → ppπ+ that may help clarify the inter-pretation of the signal. Measurement of B0 → ppKS willhelp to determine the role of the spectator quark in b → sdecays with baryons, while observation of B+ → ppπ+
will constrain the ratio of the b → u tree and b → spenguin diagrams in decays with baryons.
For B0 → ppKS, after the application of the charm
and Λc vetoes, no significant signal is observed in ei-ther the ∆E or Mbc distribution. A fit to the ∆E dis-tribution gives 6.4+4.4
−3.7 events. Applying the Feldman-Cousins procedure [13], we obtain an upper limit ofless than 16 events at the 90% confidence level (C.L.).After reducing the detection efficiency by the system-atic error, we obtain an upper limit at 90% C.L. ofB(B0 → ppK0) < 7.2 × 10−6.
In the B+ → ppπ+ mode, after the application ofthe charm veto we perform a fit to the ∆E distributionthat allows for B+ → ppπ+ signal and a reflection frommisidentified B+ → ppK+ decays. This fit gives a signalyield of 16.2+8.6
−8.0 events and a significance of 2.1σ. Theexcess in the ∆E fit corresponds to a branching fractionB(B+ → ppπ+) = (1.9+1.0
−0.9±0.3)×10−6 or an upper limitof B(B+ → ppπ+) < 3.7 × 10−6 at 90% C.L. after takinginto account the systematic error.
We have observed a significant signal (5.6σ) for thedecay B+ → ppK+. This is the first b → s decay modewith baryons in the final state. In the future, this modecan be used to search for direct CP violation [2]. Wefind that its pp mass spectrum is inconsistent with phasespace and is peaked toward low mass. This feature is sug-gestive of quasi two-body decay. It is also possible thatthe decay is a genuine three-body process and that thisfeature of the M(pp) spectrum is a baryon form factoreffect [14,15].
We wish to thank the KEKB accelerator group for theexcellent operation of the KEKB accelerator. We ac-knowledge support from the Ministry of Education, Cul-ture, Sports, Science, and Technology of Japan and theJapan Society for the Promotion of Science; the Aus-tralian Research Council and the Australian Departmentof Industry, Science and Resources; the National Sci-ence Foundation of China under contract No. 10175071;the Department of Science and Technology of India; theBK21 program of the Ministry of Education of Koreaand the CHEP SRC program of the Korea Science andEngineering Foundation; the Polish State Committee forScientific Research under contract No. 2P03B 17017; theMinistry of Science and Technology of the Russian Fed-eration; the Ministry of Education, Science and Sportof Slovenia; the National Science Council and the Min-istry of Education of Taiwan; and the U.S. Departmentof Energy.
[1] Hereafter, the inclusion of the charge conjugate mode isimplied.
[2] G. Eilam, M. Gronau, and J. Rosner, Phys. Rev. D 39,819 (1989).
[3] X. Fu et al. (CLEO Collaboration), Phys. Rev. Lett. 79,
5
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 5 / 37
Short historyB factories
2002: First observation of a baryonic B decay [Phys. Rev. Lett. 88 (2002)181803]Observation and study of many B0 and B+ baryonic decays, both withcharm in the final state and charmlessObserved threshold enhancement in baryon-antibaryon invariant massof several decays
LHCb2013: First observation of 2-body charmless baryonic modeB+ → pΛ(1520) and first evidence of CP violation in a baryonic B decayseen in B+ → ppK+ [Phys. Rev. Lett. 113, 141801 (2014)]2013: First evidence of the very suppressed B0 → pp [J. High Energy Phys.10 (2013) 005]2014: First observation of a baryonic B+
c decay (B+c → J/ψppπ+) [Phys.
Rev. Lett. 113, 152003 (2014)]
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 6 / 37
Observation of theB0
s → pΛK− decay
[LHCb-CONF-2016-016]
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 7 / 37
Analysis strategy [LHCb-CONF-2016-016]
Goal: Observe first B0s baryonic decay
I Look for three-body decay as larger BF expected than 2-body
Signal: B0s → pΛK−
Normalisation mode: B0 → pΛπ−
Bsgn
Bnorm=
fd
fs
Nsgn
Nnorm
εnorm
εsgn
Dataset: LHCb Run I dataset(3 fb−1), divided per year andreconstruction categorySelection: neural networkagainst combinatorialbackground, particleidentification criteria on chargedhadrons
[JINST 10 (2015) P02007]
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 8 / 37
Fit [LHCb-CONF-2016-016]
Perform a simultaneous fit to signal (B0s → pΛK−) and normalisation
mode (B0 → pΛπ−) for all categoriesI Share shape parametersI Constrain cross-feed background from different final states
Backgrounds considered: combinatorial, B0s → pΣK−, B0 → pΣπ−
m(pΛπ) [MeV/c2]
LHCbPreliminary
4900 5000 5100 5200 5300 5400 5500 5600
Can
didates/(15
MeV/c
2)
0
20
40
60
80
100
120
140
160
180
m(pΛK) [MeV/c2]
LHCbPreliminary
4900 5000 5100 5200 5300 5400 5500 5600
Can
didates/(15
MeV/c
2)
0
10
20
30
40
50
60
70
80
Observe B0s → pΛK− with statistical significance> 15σ
(260± 21 signal candidates from the fit to all the categories)
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 9 / 37
Results [LHCb-CONF-2016-016]
First observation of a baryonic B0s decay!
Branching fraction measured to be
B(B0s + B0
s → pΛK−) = [ 5.48+0.82−0.80(stat)±0.60(syst)
±0.51(Bnorm) ±0.32(fs/fd)]× 10−6
Observed threshold enhancement in pp mass spectra (backgorundsubtracted)
m(pΛ) [ GeV/c2]2.5 3 3.5 4 4.5 5S
um
ofsW
eigh
ts/(20MeV/c
2)
LHCbPreliminary
0
10
20
30
40
50
B0→ pΛπ−
m(pΛ) [ GeV/c2]2.5 3 3.5 4 4.5S
um
ofsW
eigh
ts/(20MeV/c
2)
LHCbPreliminary
0
5
10
15
20
25
30
B0s → pΛK−
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 10 / 37
Observation of theB0(s)→ pph+h′− decays
[LHCb-PAPER-2017-005, In preparation]
New
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 11 / 37
Analysis strategy [LHCb-PAPER-2017-005, In preparation]
Goal: Observe and measure BF of charmless B0(s)→ pph+h′− modes
I Only known B(B0→ ppK∗0) = (1.24+0.28−0.25)× 10−6 (BaBar and Belle)
Signal: B0(s)→ pph+h′− (h(′) = K or π)
I Excluding the charmonium region: m(pp) < 2.85 GeVI Veto D0 andΛc
Normalisation mode: B0→ (J/ψ→ pp)(K∗0→ K+π−), same selectionas signal except charm vetoesDataset: LHCb Run I dataset (3 fb−1)Selection: BDT against combinatorial background, particleidentification on hadrons (each candidate only in one final statesample)Simultaneous fit to invariant mass of 3 final states3-D fit in m(ppK±π∓), m(pp) and m(K±π∓) for normalisation mode
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 12 / 37
Simultaneous signal fits [LHCb-PAPER-2017-005, In preparation]
]2 [MeV/cKK)pm(p5200 5300 5400 5500
)2C
andi
date
s / (
8 M
eV/c
0
20
40
60
80
100
120
140
160
180DataTotal fit
KKp p→ 0B
KKp p→ s0B
πKp p→ 0BComb. bkgd.
LHCbPreliminary
]2 [MeV/c)πKpm(p5200 5300 5400 5500
)2C
andi
date
s / (
5 M
eV/c
0
100
200
300
400
500
600
700 DataTotal fit
πKp p→ 0B
πKp p→ s0B
ππp p→ 0BComb. bkgd.
LHCbPreliminary
nppK+K−
B = 68± 17 nppK+K−
Bs= 635± 32
nppK±π∓
B = 4155± 83 nppK±π∓
Bs= 246± 39
nppπ+π−
B = 902± 35 nppπ+π−
Bs= 39± 16
First strong evidence First observations
]2 [MeV/c)ππpm(p5200 5300 5400 5500
)2C
andi
date
s / (
10
MeV
/c
0
50
100
150
200
250
300DataTotal fit
ππp p→ 0B
ππp p→ s0B
πKp p→ 0BComb. bkgd.
LHCbPreliminary
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 13 / 37
Substructures in m(h+h′−) [LHCb-PAPER-2017-005, In preparation]
B0s → ppK+K−
]2 [MeV/cm(KK)1000 2000 3000
)2 W
eigh
ted
cand
idat
es/(
40 M
eV/c
0
0.01
0.02
0.03
0.04
0.05LHCbPreliminary
B0→ ppK±π∓
]2 [MeV/c)πm(K1000 2000 3000
)2 W
eigh
ted
cand
idat
es/(
80 M
eV/c
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09 LHCbPreliminary
Efficiency-corrected andbackground-subtractedVector mesons visible(φ(1020), K∗(892)0, ρ0(770))
B0→ ppπ+π−
]2 [MeV/c)ππm(1000 2000 3000
)2 W
eigh
ted
cand
idat
es/(
80 M
eV/c
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08LHCbPreliminary
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 14 / 37
Threshold enhancement in m(pp) [LHCb-PAPER-2017-005]
B0s → ppK+K−
]2 [MeV/c)pm(p2000 2500 3000
)2 W
eigh
ted
cand
idat
es/(
50 M
eV/c
0
0.02
0.04
0.06
0.08
0.1
0.12 LHCbPreliminary
B0→ ppK±π∓
]2 [MeV/c)pm(p2000 2500 3000
)2 W
eigh
ted
cand
idat
es/(
50 M
eV/c
0
0.02
0.04
0.06
0.08
0.1
0.12 LHCbPreliminary
Efficiency-corrected andbackground-subtractedClear threshold enhancement
B0→ ppπ+π−
]2 [MeV/c)pm(p2000 2500 3000
)2 W
eigh
ted
cand
idat
es/(
50 M
eV/c
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14LHCbPreliminary
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 15 / 37
Results [LHCb-PAPER-2017-005, In preparation]
3 first observations and a strong evidence
Decay channel Significance [σ] Branching fraction / 10−6
B0→ ppK+K− 4.1 0.126±0.031±0.013±0.006B0→ ppK±π∓ > 25 6.6 ±0.3 ±0.3 ±0.3B0→ ppπ+π− > 25 3.0 ±0.2 ±0.2 ±0.1B0
s → ppK+K− > 25 4.6 ±0.3 ±0.3 ±0.2 ±0.3B0
s → ppK±π∓ 6.5 1.45 ±0.24 ±0.12 ±0.07 ±0.08B0
s → ppπ+π− 2.6 0.46 ±0.19 ±0.05 ±0.02 ±0.03
val± stat± syst± σ(B)± σ(fs/fd)
Upper limit set on B(B0s → ppπ+π−)
B(B0s → ppπ+π−) < 7.3× 10−7 at 90% CL
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 16 / 37
CP violation in b decays
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 17 / 37
Time dependent CPviolation in the
B0 → π+π− andB0
s → K+K− decays
[LHCb-CONF-2016-018]
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 18 / 37
Motivations [LHCb-CONF-2016-018]
Time dependent asymmetries linked to CPV parameters Cf , Sf and A∆Γf
A(t) =Γ
B0(s)→f
(t) − ΓB0(s)→f(t)
ΓB
0(s)→f
(t) + ΓB0(s)→f(t)
=−Cf cos(∆md,st) + Sf sin(∆md,st)
cosh(∆Γd,s
2 t)+ A∆Γ
f sinh(∆Γd,s
2 t)
|Cf |2 + |Sf |
2 + |A∆Γf |2 = 1
Rich set of physics processes contributes to B0→ π+π− andB0
s → K+K− decays (Tree and penguin contributions, neutral B mixing,possible new physics in loops)Time dependent CPV sensitive to CKM phases
I angles γ and βs measured in [Phys. Lett. B 741 (2015) 1]
Cπ+π− and Sπ+π− well constrained by B-factories and LHCbCK+K− and SK+K− measured only by LHCb using 1 fb−1 (2011) and nomeasurement for A∆Γ
K+K− [JHEP 10 (2013) 183]
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 19 / 37
Analysis strategy [LHCb-CONF-2016-018]
BDT against combinatorial background, particle identificationselection to reduce contamination from other B→ hh′ modes to∼ 10% of the signal.CPV coefficients determined from unbinned maximum likelihood fitto
I Mass, decay time, per-event mistag probability, per-event decay timeerror
I Simultaneous fit to π+π−, K+K− and K+π− mass spectra
Production asymmetry determined from B0 → K+π− andB0
s → K−π+
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 20 / 37
Analysis strategy [LHCb-CONF-2016-018]
Mistag probability and decay time resolution dilute amplitude of timedependent asymmetries
Use opposite side taggers calibrated using B0 → K+π−
Determine per-event decay time resolution from decay time errorcomputed in reconstruction calibrated with B0 → K+π− andB0
s → D+s π
+
PV
pp
X
X
X
SVSS pion SS proton SS kaon
K+
OS vertex charge OS charm
SV
b → c b → X l–
c → s
OS kaon
OS muon OS electron
TV
same sideopposite side
b
bq
q
quX–
l–
K–
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 21 / 37
Results [LHCb-CONF-2016-018]
Resultsofthesimultaneousfit
19
p+p- spectrum(LHCb Preliminary)
LHCb
-CON
F-20
16-018
statisticalerroronly
Resultofthesimultaneousfit
21
K+K- spectrum(LHCb Preliminary)
LHCb
-CON
F-20
16-018
statisticalerroronly
Cπ+π− = −0.24±0.07±0.01
Sπ+π− = −0.68±0.06±0.01
CK+K− = 0.24±0.06±0.02
SK+K− = 0.22±0.06±0.02
A∆ΓK+K− = −0.75±0.07±0.11
val± stat± syst
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 22 / 37
Results [LHCb-CONF-2016-018]
Results in agreement with [JHEP 10 (2013) 183] and approximatelytwice more preciseNaive CPV significance (neglect correlations and sum in quadrature)
I (CK+K− , SK+K− ,A∆ΓK+K−) is 4.7σ from (0,0, 1)
I (CK+K− , SK+K−) is 4.6σ from (0,0)I CK+K− and SK+K− are 3.6σ and 3.3σ from 0 respectively
First evidence of CPV in B0s → K+K− decay
Best measurement of Sπ+π− from a single experimentUpdate also with same sign taggers will follow soon
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 23 / 37
Evidence for CP violationinΛ0
b→ pπ−π+π−
[Nat. Phys. (2017)]
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 24 / 37
Motivations [Nat. Phys. (2017)]
CPV predicted by SM in baryons but not observed yetInΛ0
b → pπ−π+π− tree and penguin diagrams have similar amplitudeLocal CPV in multibody decays can be larger that global CPVPossible to use T-odd observables (triple products)
CT = ~pp ·(~pπ−
fast×~pπ+
)∝ sinΦ
AT =N(CT > 0) − N(CT < 0)
N(CT > 0) + N(CT < 0)
AT =N(−CT > 0) − N(−CT < 0)
N(−CT > 0) + N(−CT < 0)
CP-violating observable
aT−oddCP =
12(AT −AT
)P-violating observable
aT−oddP =
12(AT +AT
)
0
�⇡+
⇡�slow ⇡�
fast
p
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 25 / 37
Analysis strategy [Nat. Phys. (2017)]
Search for CPV inΛ0b → pπ−h+h′− (h(′) = K or π) using triple
productsUseΛ0
b → (Λ+c → pK−π+)π− where no CPV is expected as control
modeSimultaneous fit to m(pπ−h+h′−)
N(Λ0b → pπ−π+π−) = 6646± 105 (stat)
]2c) [GeV/−π+π−πp(m5.2 5.4 5.6 5.8 6
)2 cE
vent
s/(9
MeV
/
0
500
1000
1500
Full fit−π+π−πp →0
bΛPart-rec. bkg.Comb. bkg.
+π−π−π+K →0B−π+π−pK →0
bΛ
LHCb
(a)
N(Λ0b → pπ−K+K−) = 1030± 56 (stat)
]2c) [GeV/−K+K−πp(m5.2 5.4 5.6 5.8 6
)2 cE
vent
s/(9
MeV
/
0
200
400
Full fit−K+K−πp →0
bΛPart-rec. bkg.Comb. bkg.
−π+K+K−K →0B+π−π+K−K →0
sB−K−K+pK →0
bΛ−π+π−pK →0
bΛ
LHCb
(b)
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 26 / 37
CPV measurement [Nat. Phys. (2017)]
Global CPV: Results compatible with P andCP conservation conservationLocal CPVΛ0
b → pπ−K+K−: Limited yielddivide only in two bins in m(pK−).Compatible with P and CP conservationLocal CPVΛ0
b → pπ−π+π−: Use twodifferent binning schemes:
I Scheme A: 12 regions dominated by2-body resonances (ρ0(770), ∆++, N∗)
I Scheme B: 10 uniform bins inΦI P symmetry compatible at 2.2σI 3.3σ evidence for CPV found combining
both schemes
Asy
mm
etri
es [
%]
Phase space bin5 10
20 0
20− /ndf=21.1/122χ CP
-oddTa
5 10
20 0
20−
LHCb Scheme A
/ndf=27.9/122χ P-oddTa
Asy
mm
etri
es [
%]
| [rad]Φ|1 2 3
20 0
20− /ndf=30.5/102χ CP
-oddTa
1 2 3
20 0
20−
LHCb Scheme B
/ndf=20.7/102χ P-oddTa
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 27 / 37
Rare B decays
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 28 / 37
Search for the B0s → η′φ
decay
[arXiv:1612.08110, Submitted to JHEP]
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 29 / 37
Motivations [arXiv:1612.08110, Submitted to JHEP]
Proceeds via b→ sss penguin transition likeB0
s → φφ and B0s → η′η′
Predictions cover wide range and have biguncertainties due to limited knowledge onform factors, penguin contributions,ω–φmixing angle and s-quark mass
b s
s s
s
s
W
u, c, tφ, η′
η′, φ
B0s
Theory approach Yield B/10−6 Reference
QCD factorisation 0.05+1.18−0.19 [Nucl.Phys. B 675 (2003) 333-415]
QCD factorisation 2.2+9.4−3.1 [arXiv:hep-ph/0701146]
Perturbative QCD 0.19+0.20−0.13 [Phys.Rev. D 76 (2007) 074018]
Perturbative QCD 20.0+16.3−9.1 [Phys.Rev. D 80 (2009) 114026]
SCET 4.3+5.2−3.6 [Phys.Rev. D 78 (2008) 034011]
SU(3) flav. symm. 5.5± 1.8 [Phys.Rev.D 91 (2014) 014011]
FAT 13.0± 1.6 [arXiv:1608.02819]
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 30 / 37
Analysis strategy [arXiv:1612.08110, Submitted to JHEP]
Signal: B0s → η′φ
Normalisation mode: B+ → η′K+ (B = (70.6± 2.5)× 10−6)Reconstruct η′ candidates as η′ → π+π−γ
Dataset: LHCb Run I dataset (3 fb−1)Blinded until selection strategy finalisedFit: 2D (m(η′K+K−), m(π+π−γ)) and simultaneous for signal andnormalisation modeSensitivity: expected> 5σ (40 events) for B = 4× 10−6
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 31 / 37
Results [arXiv:1612.08110, Submitted to JHEP]
]2 [MeV/cγππm900 950 1000
)2
Candid
ate
s/(8
MeV
/c
0
10
20
30
40
50 LHCb
signal B0s → φφ(π+π−π0) combinatorial comb. with real η′
No indication of the signal (N(B0s → η′φ) = −3.2+5.0
−3.8 )Set upper limit on branching fraction
B(B0s → η′φ) < 0.82(1.01)× 10−6 at 90% (95%) CL
Most central values of theoretical predictions significantly larger
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 32 / 37
Observation of theB0→ K+K− decay
[Phys. Rev. Lett. 118 (2017) 081801]
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 33 / 37
Motivations [Phys. Rev. Lett. 118 (2017) 081801]
B0 → K+K− and B0s → π+π− proceed via
weak annihilation transitions (all final statequarks different from initial state)Highly suppressed but possibleenhancement from rescattering effectsB0 → K+K− unobserved so far,B0
s → π+π− observed in [JHEP 1210 (2012)037]
Precise BF measurement for the two modesprovides input to improve knowledge ofQCD dynamics in B0
(s) → h+h′−
b
d, s
W
s, d
s, d
u
u
W
b
d, s
s, d
s, d
u
u
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 34 / 37
Analysis strategy [Phys. Rev. Lett. 118 (2017) 081801]
Signal: B0 → K+K− and B0s → π+π−
Normalisation mode: B→ K+π−
Dataset: LHCb Run I dataset (3 fb−1)Blinded until selection strategy finalisedSelection: BDT against combinatorial background, particleidentification criteria on charged hadronsFit: Simultaneous fit to 2-body invariant mass of several mutuallyexclusive subsamples (K+π−, pK−, pπ−, π+π− and K+K−)
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 35 / 37
Results [Phys. Rev. Lett. 118 (2017) 081801]
5.2 5.4 5.6 5.8
)2
cC
an
did
ate
s / (
5 M
eV
/
0
50
100
150
K
+ K→
0B
K+ K→
0sB
π
+ K→
0B
pK→
0bΛ
X
K+ K→0sB
Comb. bkg.
LHCb
]2c [GeV/
K+
Km
5.2 5.4 5.6 5.8
Pu
ll
42024 5 5.2 5.4 5.6 5.8
)2
cC
an
did
ate
s / (
5 M
eV
/
0
100
200
300
400
π
+π →
0sB
π
+π →
0B
π
+ K→
0B
Xπ+
π →0
B
Comb. bkg.
LHCb
]2c [GeV/
π+
πm
5 5.2 5.4 5.6 5.8P
ull
42024
B0 → K+K−
observed at 5.8σ
Measured BF(World’s mostprecise)
B(B0 → K+K−) = [7.80± 1.27(stat)±0.81(syst)±0.21(Bnorm)]× 10−8
B(B0s → π+π−) = [6.91±0.54(stat)±0.63(syst)±0.19(Bnorm)±0.40(fs/fd)]× 10−7
In agreement within uncertainties with pQCD [Phys. Rev. D 85 (2012)094003]
Agreement for B(B0 → K+K−) but significantly largerB(B0
s → π+π−) than QCDF [Phys. Rev. D 80 (2009) 114026]
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 36 / 37
Conclusion
Presented several recent results from the LHCb collaboration:First observation of baryonic Bs decayFirst observation of 3 new B0
(s)→ pph+h′− modes and evidence of afourth one New!First evidence of CPV in B0
s → K+K− (with naive treatment of errors)First evidence of CPV in baryonsWorld’s best limit on B0
s → η′φ
First observation of B0→ K+K− rarest hadronic B decay everobserved!
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 37 / 37
BACKUP
LHCb [Int. J. Mod. Phys. A 30 (2015) 1530022]
Acceptance: 2 < η < 5∼ 1/4 of produced bb pairs.
Decay timeresolution ∼ 45 fs
IP resolution ∼ 20µm
Vertex resolution ∼ 13µmin x y (25 tracks)
∆p/p ∼ 0.5 − 1.0%
ε(µ) ∼ 97%,misID(π→ µ) ∼ 1 − 3%
ε(K) ∼ 95%,misID(π→ K) ∼ 5%
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 39
ReconstructingΛ and K0s [Int. J. Mod. Phys. A 30 (2015) 1530022]
Long
Downstream
Giulio Dujany (Manchester) Charmless b-hadron decays La Thuile 2017 40