Recent results from LHCb
Anton Poluektov
The University of Warwick, UK,
Budker Institute of Nuclear Physics, Novosibirsk, Russia
6 June 2011
On behalf of the LHCb collaboration
Anton Poluektov
Recent results from LHCb
PPP9, 3-6 June 2010
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LHCb physics programme
Detector performance optimised for searches of CP violation and rare
decays in B-mesons. The physics programme includes
Rare B decays
Bs0 → µµ
B 0 → K ∗ `+ `−
Radiative B decays
CP violation in B system (B + , B 0 , Bs )
Tree-level processes (B → DX )
Loop-mediated processes (charmless B decays)
CP violation in Bs mixing: φs phase
Quarkonium studies.
Charm studies
Production and spectroscopy
CP violation in charm
Soft QCD physics
Electroweak physics
Anton Poluektov
Recent results from LHCb
PPP9, 3-6 June 2010
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Flavor physics at the LHC
bb cross-section: 280 µb (7 TeV)
[LHCb, Phys. Lett. B 694 209-216 (2010)]
b b̄ pairs are produced mostly in forward and backward directions.
Flavor ratio: 40% B + : 40% B 0 : 10% Bs0 : 10% Λ0b : 0.1% Bc .
Requirements
Ability to recontruct (and trigger on)
low pt tracks
Efficient trigger for leptonic and
purely hadronic B decays
Good vertexing for time-dependent
measurements (esp. for fast Bs0
oscillations)
Good PID (π/K /p/µ/e separation)
for final state selection and flavor
tagging.
Anton Poluektov
Recent results from LHCb
PPP9, 3-6 June 2010
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LHCb detector
A. A. Alves Jr. (LHCb collaboration), 2008 JINST 3 S08005
One-arm forward spectrometer, 2 < η < 5 (15 − 300 mrad)
Trigger: L0 (hardware): 1 MHz, HLT (software): 3–4 kHz
Design luminosity 2 × 1032 cm−2 s−1
Anton Poluektov
Recent results from LHCb
PPP9, 3-6 June 2010
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LHCb detector
Analysis techniques
Background suppression
based on event topology
(impact parameters,
vertex displacement for B
and charm)
Anton Poluektov
Time-dependent
measurements: measure
lifetime based on vertex
displacement (σt ' 40 fs)
Recent results from LHCb
Flavor tagging: use decay
products of the
opposite-side B (OS) and
π, K associated with
same-side B (SS)
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Status of LHCb experiment
2010: 37 pb−1
2011: 210 pb−1 and counting
Luminosity levelled at 3 × 1032
50% higher than design value.
Expect 200-300 pb−1 for summer conferences, 1 fb−1 by the end of 2011.
R
Analyses reported here are based on Ldt ∼ 37 pb−1 taken in 2010.
All results are preliminary unless journal reference given.
Anton Poluektov
Recent results from LHCb
PPP9, 3-6 June 2010
6/25
Rare decays: Bs → µ+ µ−
Motivation
µ+
b̄
µ+
b̄
¯t̃
ū, c̄, t̄
s̄
γ, Z
Bs0
Bs0
W
χ̃±
u, c, t
µ−
s
FCNC, helicity suppression
SM expectation: (3.2±0.2)×10−9
H 0 , A0
s
µ−
Sensitive to NP contributions
6β
MSSM: Br (Bs → µ+ µ− ) ' tan
M4
A
E. Gamiz et al., Phys. Rev. D 80 014503 (2009)
Measurement technique
Looking at 2D distribution of
µ+ µ− invariant mass
Geometrical likelihood (0 < GL < 1)
based on kinematic and topological variables
Use B → hh0 and B → J/ψX for calibration
Anton Poluektov
Recent results from LHCb
PPP9, 3-6 June 2010
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Rare decays: Bs → µ+ µ−
Results and prospects
GL
Phys. Lett. B 699, 330-340 (2011)
1
0.9
0.8
Bd0 search window
0.7
LHCb
R
Ldt = 37 fb−1
0.6
0.5
Bs0 search window
0.4
0.3
0.2
0.1
0
4500
5000
5500
6000
6500
mµµ (MeV/c2)
Br (Bs0 → µ+ µ− ) < 5.6 × 10−8 (95% CL)
Br (Bd0 → µ+ µ− ) < 1.5 × 10−8 (95% CL)
Plot by W. Hopkins (FPCP2011)
Expect Br < 6 × 10−9 with 1 fb−1 (2011)
Anton Poluektov
Recent results from LHCb
PPP9, 3-6 June 2010
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Rare decays: B 0 → K ∗ µ+ µ−
Motivation
µ−
γ, Z 0
SM:
b̄
ū, c̄, t̄
s̄
W
B0
d
µ−
µ−
µ+
H0
νµ
µ+
W
b̄
K∗
d
W
ū, c̄, t̄
B0
d
NP:
s̄
K∗
b̄
s̄
g̃
B0
d
µ+
d˜¯
d
K∗
d
−6
FCNC, Br = (1.05+0.16
−0.13 ) × 10
Description in terms of Wilson coefficients: C7 , C9 , C10
Measurement technique and current constraints
Measurement of angular distributions as functions of q 2 = mµ2 + µ− .
∂2Γ
∂θ∂q 2
=
3
4 FL
sin2 θ + 38 (1 − FL )(1 + cos2 θ) + AFB cos θ
Longitudinal polarisation fraction FL , forward-backward asymmetry AFB .
CDF
Babar
Belle
Belle favours C7 = −C7SM scenario (2.7σ from SM)
Anton Poluektov
Recent results from LHCb
PPP9, 3-6 June 2010
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Rare decays: B 0 → K ∗ µ+ µ−
Results and prospects
B 0 → K ∗ µ+ µ− and its control sample B + → K + µ+ µ− are clearly seen:
Expected 1 fb−1 sensitivity in 1 < q 2 < 6 GeV2 :
σ(AFB ) = 0.07
B 0 → K ∗ µ+ µ−
B + → K + µ+ µ−
Anton Poluektov
If C7 = −C7SM , can exclude SM solution at 4σ.
Recent results from LHCb
PPP9, 3-6 June 2010
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CP violation: charmless B decays
B 0 → K π and Bs0 → K π asymmetries
LHCb-CONF-2011-011
ACP (B 0 → K + π − ) = −0.074 ± 0.033 ± 0.008
ACP (Bs0 → π + K − ) = 0.15 ± 0.19 ± 0.02
B 0 → K +π−
B 0 → K −π+
Corrected for detection asymmetry
(from D ∗ → Dπ)
and production asymmetry
(from B + → J/ψK + : AP = −0.024 ± 0.013)
HFAG: ACP (B 0 → K + π − ) = −0.098+0.012
−0.011
CDF: ACP (Bs0 → π + K − ) = 0.39 ± 0.15 ± 0.08
Bs → π + K −
Anton Poluektov
Bs → π − K +
Recent results from LHCb
PPP9, 3-6 June 2010
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CP violation: B → DX
Motivation
Measure CKM angle γ in the interference of b → c ūs and b → uc̄s
amplitudes:
∗ V V
γ = arg Vub∗ Vuscs
cb
∗
Vus
s
ū
b
B−
Vcb
ū
b
K−
B−
c
ū
Vub
D0
∗
Vcs
ū
u
c̄
D0
s
ū
K−
Only tree-level processes, very low theoretical uncertainty
Approaches to γ measurement
Need to combine various modes:
Counting measurements with B → D(hh)K (ADS, GLW)
Dalitz plot analysis with B → D(KS0 h+ h− )K
Dalitz plot analysis of B 0 → D(hh)K π
Time-dependent analysis of Bs0 → Ds K
All offer comparable sensitivity (∼ 10◦ with 1 fb−1 ).
Anton Poluektov
Recent results from LHCb
PPP9, 3-6 June 2010
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CP violation: B → DX
First studies with B → DX modes:
B → Dπ, B → DK , Bs → Ds π
Measurement of fragmentation fractions fs /fd
Provides normalisation for Bs0 branching ratios
Vital for measurement of e. g. Bs0 → µ+ µ−
B 0 → D −π+
Combination of
B 0 → D −K +
Br (Bs0 →Ds− π + )
Br (B 0 →D − π + )
and
LHCb-CONF-2011-013
Bs0 → Ds− π +
Br (Bs0 →Ds− π + )
:
Br (B 0 →D − K + )
fs /fd = 0.245 ± 0.017 ± 0.018(syst) ± 0.018(theory)
Anton Poluektov
Recent results from LHCb
PPP9, 3-6 June 2010
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CP violation: B → DX
First studies with B → DX modes:
First observation of B → DK ππ
LHCb-CONF-2011-024
Cabibbo-suppressed modes, can be used for γ
First observation of
Bs → DK ∗
LHCb-CONF-2011-008
Control sample for
B 0 → DK ∗ and Bs → Dφ
B 0 → D +K −π+π−
Br (B 0 →D + K − π + π − )
Br (B 0 →D + π−π + π − )
Br (B − →D 0 K − π + π − )
Br (B − →D 0 K − π + π − )
Anton Poluektov
B − → D 0K −π+π−
= (5.2±0.9±0.5)×10−2
=
(9.6±1.5±0.8)×10−2
Recent results from LHCb
Br (B 0s →D 0 K ∗0 )
Br (B 0 →D 0 ρ0 )
=
1.39 ± 0.31 ± 0.17 ± 0.18
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CP violation: B → DX
First studies with B → DX modes:
Measurement of ∆ms
Bs0 → Ds− (φπ − )π +
Bs0 → Ds− (K ∗ K − )π +
LHCb-CONF-2011-005
∆ms scan
Bs0 → Ds− (K + K − π − )π +
Bs0 → Ds− π + π + π −
∆ms = (17.63 ± 0.11 ± 0.04) ps−1 .
4.6σ statistical significance.
Anton Poluektov
Recent results from LHCb
Time-dep. asymmetry
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Bs0 → K + K − effective lifetime
Motivation
Penguin-dominated decay.
Lifetime difference can be affected by NP: ∆Γs = ∆ΓSM
cos ϕNP
s
SM
∆Γs /Γs = 0.133 ± 0.032
Can obtain lifetime difference from the comparison of
−1
−1
τflavor
= (ΓL + ΓH )/2 and τKK
' ΓL
Results
Two approaches:
LHCb-CONF-2011-018
Absolute lifetime measurement (correct for proper time acceptance and
biases)
Measurement relative to B 0 → K − π +
τBs0 →KK = 1.440 ± 0.096 ± 0.010 ps
CDF:
τBs0 →KK = 1.53 ± 0.18 ± 0.02 ps
PDG:
τflavor = 1.472+0.024
−0.026 ps
Anton Poluektov
Recent results from LHCb
PPP9, 3-6 June 2010
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CP violation: Bs → J/ψφ
Motivation
Measure CP violation in the interference of decays with and w/o mixing
ϕD
b̄
t̄
b̄
s̄
c̄
W
Bs0
J/ψφ
ϕM
B 0s
ϕM :
−ϕD
Bs0
W
+N P ?
s
B 0s
W
t
CP violating phase ϕs = ϕM − 2ϕD ;
ϕD :
s̄
s
b
ϕSM
s
J/ψ
c
Bs0
φ
' −2βs = 0.0363 ± 0.0017
Measurement technique
Time-dependent flavor-tagged decay
rate
Angular analysis to distinguish
between CP-even and CP-odd
components
7D fit! (m, t, tag, mistag rate, 3 angles)
Anton Poluektov
Recent results from LHCb
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CP violation: Bs → J/ψφ
Results
LHCb-CONF-2011-006
836 ± 60 Bs → J/ψφ events
φs ∈ [−2.7, −0.5] rad at 68% CL.
22% (1.2σ) from SM
Expect ×30 more data in 2011
⇒ σφs ∼ 0.13 rad
Further improvement by including SS tagging
Anton Poluektov
Recent results from LHCb
PPP9, 3-6 June 2010
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CP violation: Bs → J/ψf0
Observation of Bs → J/ψf0 (980) decay
Phys. Lett. B 698, 115–122 (2011)
Can be used in the same way as Bs → J/ψφ, but no angular analysis is
needed (pure CP-odd)
111±14 Bs0 → J/ψf0 events
12.8σ significance
Anton Poluektov
Br (Bs0 →J/ψf0 ,f0 →π + π − )
Br (Bs0 →J/ψφ,φ→K + K − )
Recent results from LHCb
+0.027
= 0.252+0.046
−0.032 −0.033
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Observation of Bs0 → K ∗0 K ∗0
Motivation
Pure b → s penguin
SM prediction (QCD factorisation):
+0.16
−6
Br = (7.9+4.3
−3.9 ) × 10 , fL = 0.72−0.21
M. Beneke, J. Rohrer and D.S. Yang, Nucl. Phys. B774, 64. (2007)
Potentially interesting for time-dependent CPV measurement
Results
LHCb-CONF-2011-019
34.5 ± 7.4 events,
7σ significance
Br (Bs0 → K ∗0 K ∗0 ) =
(1.95 ± 0.47 ± 0.51 ± 0.29(fs /fd )) × 10−5
Anton Poluektov
Recent results from LHCb
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Quarkonium studies
X (3872) mass measurement
LHCb-CONF-2011-021
MX (3872) = 3871.96 ± 0.46 ± 0.10 MeV/c 2
Statistically limited, expect much better precision in 2011.
First observation of double J/ψ production in pp collisions
Sensitive to charm tetraquark, χb → J/ψJ/ψ
LHCb-CONF-2011-009
σJ/ψJ/ψ = 5.6 ± 1.1 ± 1.2 nb
(2 < y < 4.5, pT < 10 GeV/c)
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Recent results from LHCb
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Conclusion
Excellent LHCb performance demonstrated in 2010 data.
All essential analysis techniques are shown to work:
Flavor tagging
Time-dependent measurements
Angular analyses
Momentum calibration for precision mass measurements
Competitive or world-best measurements are performed with only
37 fb−1
Bs → µµ upper limit
First observations in hadronic B decays
Quarkonium studies
Get ready for exciting 2011 data: we have already ×6 more data on
tape.
Anton Poluektov
Recent results from LHCb
PPP9, 3-6 June 2010
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Semileptonic B decays
∗+ −
Observation of B 0s → Ds2
µ ν̄X
Phys. Lett. B 698 14-20 (2011)
∗
(2573)+ peaks in D 0 K + spectrum
Observe Ds1 (2536)+ and Ds2
∗+
Br (B 0s →Ds2
X µ− ν̄)
= (3.3±1.0±0.4)%
Br (B 0s →X µ− ν̄)
0
+
−
Br (B s →Ds1 X µ ν̄)
= (5.4 ± 1.2 ± 0.5)%
Br (B 0s →X µ− ν̄)
Anton Poluektov
Recent results from LHCb
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Quarkonium studies
J/ψ production
Eur. Phys. J. C 71, 1645 (2011)
Prompt J/ψ production cross-section in pT < 14 GeV/c, 2 < y < 4.5:
σ(pp → J/ψX ) = 10.52 ± 0.04 ± 1.40+1.64
−2.20 µb
Reasonable agreement with models
Anton Poluektov
Recent results from LHCb
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Quarkonium studies
Υ(1S) production
LHCb-CONF-2011-016
σ(pp → Υ(1S)X ) = 108.3 ± 0.7+30.9
−25.8 nb in pT < 15 GeV/c, 2 < y < 4.5.
Reasonable agreement with models
Anton Poluektov
Recent results from LHCb
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