Measurement of CP violation and CKM matrix in LHCb

EPS – HEP 09 Krakow 16-22 July 2009
Measurement of CP violation
and CKM matrix in LHCb
Marta Calvi
University of Milano Bicocca and INFN

CP violation and CKM matrix
• Current laboratory measurements of CPV CPV are in in agreement with
SM predictions, encoded in the CKM matrix, but
observation of universe requires much more.
• Unitarity relations represented by triangles.
“db”
Still space for finding effects due to NP in less constrained
elements like γ and βs angles.
HEP 2009 - M.Calvi
UT constraints from tree
measurements only
“sb”
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The B B0 sB0 mixing in B 0J/ J/ψφ ψφ
s s
• A CP violating phase arises from interference between B Bs decay
to J/ J/ψφ ψφ ψφ ψφ directly or via mixing
• In the SM:
Bs J/ J/ψφ ψφ ψφ is dominated dominated by a single weak weak phase, well predicted:
HEP 2009 - M.Calvi
Φ J/
SM
J/ψφ ψφ ψφ
SM = -2βs
+ δP Penguin contribution
s +
estimated ~ ~10 10-4-10 -2βs = (-0.037 ( 0.037±0.002) 0.002) rad from UT fits
B s
B s
f =J/ψφ ψφ
10 -3
3

B0 sB0 with New Physics
s
• New particles could contribute to the B Bs-Bs box diagram modifying
the SM prediction, adding a new phase :
• This new phase will also modify other measurements:
where:
HEP 2009 - M.Calvi
is calculated in the SM:
4

Differential
decay rate:
B 0J/ J/ψ(µµ)φ(ΚΚ)
ψ(µµ)φ(ΚΚ)
s
PVV VV decay : mixture of CP CP-even even
(ℓ=0,2) and CP odd (ℓ=1) final states.
An angular analysis allows to separate
statistically the decay amplitudes.
3 angles Ω=( Ω=( θ,φ,ψ θ,φ,ψ
) ) to describe the final decay products directions.
A0 (0) CP even
A || (0) CP even
A⊥ (0) CP odd
HEP 2009 - M.Calvi
Bs
Bs
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Time dependent decay amplitudes amplitudes
Depend on 8 physics parameters:
Φ, Γ s, ∆Γ s, ∆m s, R ┴, R ||, δ ┴, δ ||
From Tevatrons results:
∆ms well measured, hints
of deviation from SM in Φ
HEP 2009 - M.Calvi
High sensitivity
to small Φ values
when B/B initial
state is determined
by Flavour tagging
(∆ms terms)
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LHCb @ LHC
High bb production in pp collisions at √s= s=14TeV 14TeV
σ inel = 80 mb
σ bb = 500 µb b N ∼10 10 12 bb events in L int = 2 fb fb-1 1
(1 nominal year 10 107 s at 2x10 32 cm -2s-1 )
~40% in the forward region
LHCb single arm forward detector
HEP 2009 - M.Calvi
TED data June 2009
(secondary particles
bb angular
correlation in pp
collisions at
√s=14 TeV
Detector ready
and operational
downstream LHC beam stopper)
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B 0J/ J/ψ(µµ)φ( ψ(µµ)φ(KK KK) ) reconstruction
reconstruction
s
Full MC simulation
all trigger levels
included:
Signal yield (2 fb -1 ) 117 k
B(long-lived) /S 0.5
B(prompt J/ψ) ψ) /S 1.6
• High efficiency for di di-muon muon trigger εtot~70% tot~70%
• Baseline event selection is lifetime lifetime-unbiased: unbiased:
Full MC: inclusive J/ψ(µµ)
small proper time and angular acceptance corrections needed.
High background from prompt J/ J/ψ: ψ: ψ: harmless in βs fit,
can allow the determination of proper time resolution.
Alternative analysis under study: higher statistic sensitivity.
• Large use of control channels:
Measure resolution and acceptance for
proper time and angular distributions.
Flavour tagging
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Channel Yield
(2 fb -1 )
B/S
total
BdJ/ψ ψ ψ K* 490 k 6.7
BuJ/ψ ψ K+ 940 k 1.9
B sD sπ ~70k 0.4
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B0J/ψ(µµ) ψ(µµ) ψ(µµ)K*(Kπ) ψ(µµ) oscillations
for opposite side taggers
Flavour Tagging
Tagger Tag eff. mistag ε(1 ε(1−2ω ε(1 2ω 2ω) 2ω 2
From combination of several methods (electron, muon, kaon,
inclusive vertex, same side kaon)
B
Qvtx –
µ −, e− K –
Opposite side 45% 36.5% 3.3%
+ same side 56% 33.3% 6.2%
Calibration and validations on control channels
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PV
K +
Bs
BsD s (KK KKπ) ) π π oscillations
for same side tagger
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ψ
B 0J/ J/ψφ ψφ : fits results
s
• Sensitivity studies with 2fb 2fb-1 (one nominal year) : σ(2β σ(2βs) σ(2β ) ~0.03
Good convergence for all physics parameters, all “detector parameters” can also be fitted.
• Systematics
Systematics: : Angular distortions
distortions (± 5%) 77%
%
Proper time resolution ( (40 40 ± 4 fs fs) ) 5%
Mistag rate (0.34 ( 0.34 ± 0.01) 77%
%
∆β s/β s
Ignoring a possible 55-10
10% % S-wave wave contamination will introduce a ~15 15% % bias on βs. .
Included in the fit will reduce the resolution ~20 20% but allows cos2 cos2βs measurement
HEP 2009 - M.Calvi
θ φ
τ
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Sensitivity versus integrated Luminosity
First important results can come already from 2010 running.
Reduced
LHC collision
energy √s=14TeV
If true βs value is the current Tevatron measurement (NP ( NP-like) like)
we should measure it from BsJ/ J/ψ(µµ)φ ψ(µµ)φ ψ(µµ)φ ψ(µµ)φ with 200 pb
pb -1
With 10 fb -1 > 33σ
evidence of non non-zero zero βs even if only SM.
Other channels also under study: BsJ/ J/ψ( ψ( ψ(ee ψ( ee)φ )φ )φ, )φ )φ )φ,
BsJ/ J/ψη ψη ψη, ψη , , B +
sD s Ds
− …
1 !
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sin(2 sin(2β) ) with B0J/ J/ψ(µµ) ψ(µµ)KS(ππ ππ)
Will be the first time dependent CP
asymmetry measurement at LHCb: LHCb
with 200 pb -1 expect expect σ(sin2 (sin2β β β )~0.06
Channel Signal yield
(2 fb -1 )
σ(sin2 (sin2β β β )~0.020 in 2 fb fb-1 B/S
B dJ/ψ K S 94 k 0.6
With additional luminosity will give insight into possible NP contributions
to bccs ccs. . Will also constrain constrain direct direct CP asymmetry.
NP from b→sss sss penguin decays
Good perspective at LHCb for Bs→φφ φφ φφ. φφ
Channel Yield (2 fb -1 ) B/S (90% CL)
Bs → φ φ φ 3100 < 0.8
Bd → φ φ KS 920 < 1.1
HEP 2009 - M.Calvi
Time dependent analysis of angular
distribution of flavour tagged events:
σ stat ( φ Bs → φφ NP ) = 0.11 in 2 fb –1
φφ
φφ
From B d →φK S expect σ(sin2β eff) ≈0.23
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+
B
b
u
u
s
c
u
+
K
0
D
γ measurements
● Many approaches to γ angle measurements. Most powerful through
‘B ‘BDK’ DK’ strategies (charged and neutral B modes). D final state is
common to D D0 and D D0 .
+
B
b
u
● Opportunity for LHCb to make a contribution already with 200 pb -1
expect ~10k events BD( D(hh hh)K )K .
● Dalitz plot analysis giving currently the single best γ results: LHCb will
reconstruct in BD( D(KSππ ππ ππ ππ ππ)K ππ ππ ππ)K
~6.800 events /2 fb -1 with B/S

• LHCb
Conclusions
LHCb detector is on place and operational, ready for data taking
at LHC start start-up. up.
• 2β
2β
2β s value could bring good news for NP: first LHCb results could
come already from 2010 running. Expected sensitivity ~0.03/ 2 fb fb-1 • Extensive
Extensive LHCb program includes studies on many hadronic
channels for measurements on all CKM matrix parameters,
as well as searches for rare decays.
• First year data will also provide a lot of inclusive measurements
and studies on control channels.
• In the coming years LHCb results will finally provide a strong
improvement to flavour physics, in particular to the knowledge
of the B Bs sector.
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HEP 2009 - M.Calvi
BACKUP
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Angular acceptance checks with B0J/ J/ψK* K*
• Measurement of polarization amplitudes and phases in the B0J/ J/ψK* *
decay from fit to time dependent angular distributions
distributions.
• Comparison with existing results from from B Factories and Tevatron will
validate the use of simulated acceptance functions and allow estimation
of systematic uncertainties to 2β 2β 2βs
related to angular acceptance.
• Strong constrain already for a ± 5% modified
angular acceptance .
HEP 2009 - M.Calvi
θ
±5% modification
of acceptance
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