LHCb physics prospects for CP violation measurements
with 0.2 and 1 fb−1
Anton Poluektov
The University of Warwick, UK,
Budker Institute of Nuclear Physics, Novosibirsk, Russia
15-20 July 2010
On behalf of the LHCb collaboration
Anton Poluektov
LHCb prospects for CPV
Rencontres de Blois, 15-20 July 2010
1/16
CP violation in the Standard Model
W
CKM
matrix (Wolfenstein
parametrization):

 
gVij
qj
Vus
Vcs
Vts
Unitarity: Vij∗ Vjk = δik

Vub
1 − λ2 /2
λ
Aλ3 (ρ − i η)
2
2

Vcb  = 
−λ
1 − λ /2
Aλ
Vtb
Aλ3 (1 − ρ − i η)
−Aλ2
1
b − d triangle (i = b, k = d )
Vu
dV ∗
ub
∼ λ2
∗
∗
∗ V
Vub
ud + Vcb Vcd + Vtb Vtd = 0
Vt
α(φ2 )
γ(φ3 )
sV ∗
tb ∼
∗ V + V∗ V + V∗V = 0
Vub
us
tb ts
cb cs
2
∗
λ
Vts V tb ∼
βs
λ2
β(φ1 )
∗
Vcd Vcb
∼ λ2
Anton Poluektov
b − s triangle (i = b, k = s)
LHCb prospects for CPV
Vcs V ∗ ∼ 2
cb
λ
∗
Vus Vub
∼ λ4
Vud
 Vcd
Vtd
qi
β = 21.7◦ ± 0.9◦
α = 89◦ ± 4◦
◦
γ = 70◦ +14
−21◦
βs = 0.01811 ± 0.00085 rad
Rencontres de Blois, 15-20 July 2010
2/16
CP violation in heavy flavors
The way to search for New Physics, complementary to direct high-energy
searches.
CP violation in B system (B + , B 0 )
Search for NP by comparing CPV parameters in loop- and
tree-dominated decays.
CP violation in Bs system
CPV phase φs : small in SM, large NP contribution possible.
CP violation in charm
Mixing observed (in the combination, but no observation in the single
experiment so far), no CPV visible (neither direct nor in mixing).
Anton Poluektov
LHCb prospects for CPV
Rencontres de Blois, 15-20 July 2010
3/16
Flavor physics at the LHC
bb cross-section: 0.5 mb (14 TeV)
Flavor ratio: B + : B 0 : Bs : Λb : Bc = 40% : 40% : 10% : 10% : 0.1%.
Altas, CMS
Central detectors, |η| < 2.5
High pt trigger threshold
LHCb
Optimized B meson acceptance
Forward spectrometer,
2 < η < 5 (15 − 300 mrad)
Softer low pt triggers
Efficient for hadronic B decays
Design luminosity
2 × 1032 cm−2 s−1 ,
2 fb−1 per nominal year.
Anton Poluektov
LHCb prospects for CPV
Rencontres de Blois, 15-20 July 2010
4/16
Flavor physics at the LHC: LHCb experiment
bb cross-section: 0.5 mb (14 TeV)
Flavor ratio: B + : B 0 : Bs : Λb : Bc = 40% : 40% : 10% : 10% : 0.1%.
√
s = 7 TeV, bb cross-section
reduced by ∼ 50% compared to
14 TeV. Can partially
compensate by lower
background, lower thresholds.
Integrated luminosity
milestones:
0.2 fb−1 by the end of 2010
1 fb−1 in 2011.
> 200 nb−1 collected,
∼ 10 nb−1 analysed (first results
next week at ICHEP!).
Anton Poluektov
LHCb prospects for CPV
Rencontres de Blois, 15-20 July 2010
5/16
LHCb detector: features
Needed for efficient B physics:
Good PID (π/K /p/µ separation):
B decay products separation
Flavor tagging (p < 100 GeV)
Anton Poluektov
LHCb prospects for CPV
Good vertexing (σt ≃ 40 fs):
Decay time measurement,
esp. for fast Bs oscillations
Background suppression
(vertex separation)
Rencontres de Blois, 15-20 July 2010
6/16
CPV in mixing of Bs : φs phase
b
B0s
t, c, u
W
s
W
t, c, u
∗
b Vcb
s
0
Bs
B0s
c
c
J/ψ
s
φ
W + Vcs
b
s
Interference between decays Bs → J/ψ(µµ)φ(KK ) with and without
mixing. φs (SM) = −2βs = −0.036 ± 0.002.
Measured from the time-dependent asymmetry
f sin φs sin ∆ms t
ACP (t) = − cosh ∆Γs ηt/2−η
f cos φs sinh ∆Γs t/2
P→VV decay. Angular analysis
to separate CP-odd and
CP-even states.
Flavor tagging needed for
time-dependent asymmetry.
First 13 nb−1 : do not expect
signal, observe components:
J/ψ → µµ, φ → KK .
Anton Poluektov
LHCb prospects for CPV
Rencontres de Blois, 15-20 July 2010
7/16
CP violation in mixing of Bs : φs phase
-1
∆Γ (ps )
CDF Run II Preliminary
0.6
95% CL
68% CL
0.4
SM prediction
-1
L = 5.2 fb
0.2
0.0
-0.2
-0.4
-0.6
-1
Expect ∼ 30000 Bs → J/ψφ decays
with 1 fb−1 .
B/S ∼ 2 (mostly prompt component, easy to separate by proper
time).
Anton Poluektov
LHCb prospects for CPV
0
βs (rad)
1
CDF 5.2 fb−1 : now consistent
with SM (0.8σ).
Expect sensitivity competitive
to Tevatron with 0.2 fb−1
σ(φs ) ∼ 0.07 with 1 fb−1
If NP ∼ CDF measurement,
5σ discovery with 1 fb−1 .
Rencontres de Blois, 15-20 July 2010
8/16
Flavor-specific CP-asymmetry
Charge asymmetry in semileptonic b decays: aslq =
Γ(B 0q →µ+ X )−Γ(Bq0 →µ− X )
Γ(B 0q →µ+ X )+Γ(Bq0 →µ− X )
D0 [arXiv:1005.2757]: Using like-sign dimuon asymmetry and inclusive
charge asymmetry, Absl = aslb + asls = (−0.96 ± 0.25 ± 0.15)%
−4
Absl (SM) = −2.3+0.5
−0.6 × 10 .
Need good control of systematic factors:
Background asymmetry
Detector asymmetry δc (flip B-field)
Production asymmetry δp
(difficult at pp-machine!)
Time-dependent
charged
asymmetry:
aslq
aslq
δpq
cos ∆mq t
q
δcq
Asl (t) = 2 − 2 − ( 2 + 2 ) cosh ∆Γq t/2 .
Take time-independent component:
→ get rid of δp
0 → D (KK π)µν
d
s
Using Bs,d
s,d
Measure difference ∆As,d
sl = Asl − Asl :
−3 with 1 fb−1
σ(∆A
)
≃
10
fs
→ cancel δc
Anton Poluektov
LHCb prospects for CPV
Rencontres de Blois, 15-20 July 2010
9/16
CP violation in B decays with trees
∗
b Vub
u
c
W+
B+
D0
s
Vus
K+
W+
Vcs
s
K+
B+
u
b
u
∗
Vcb
c
D0
u
Provides SM reference for loop-induced decays.
Angle γ appears in the interference of amplitudes with Vub and another
CKM element.
Interference between decays with D 0 and D 0 (B ± , B 0 self-tagged).
Need D 0 and D 0 to decay into the same final state:
D 0 → KK , K π, KS ππ, ...
Interference between decays with and without mixing (for B 0 , Bs
time-dependent). Can use charged D.
Many decay modes involved with comparable sensitivity.
Anton Poluektov
LHCb prospects for CPV
Rencontres de Blois, 15-20 July 2010
10/16
B ± → DK ± time-integrated measurements
CPV magnitude determined by rB =
difference δB
D → ππ, KK , K π
Observables - charge asymmetries
and allowed-suppressed ratios:
AADS ≡
RADS =
B(B − →D(K + π − )K − )−B(B + →D(K − π + )K + )
B(B − →D(K + π − )K − )+B(B + →D(K − π + )K + )
|A(B + →D 0 K + )|
,
|A(B + →D 0 K + )|
D → KS ππ, KS KK
Observable - D decay Dalitz plot
density (different for B + and B − ):
|A± | = 2
Br (B ± →[K ∓ π ± ]D K ± )
Br (B ± →[K ± π ∓ ]D K ± )
strong phase
+ re
i δB ±i γ
2
Input from charm studies (D amplitude ratios, strong phase differences —
CLEO).
Practically no theoretical uncertainty.
Measured parameters: rB , δB , γ.
γ sensitivity depends on rB , δB values.
Anton Poluektov
LHCb prospects for CPV
Rencontres de Blois, 15-20 July 2010
11/16
22
20
18
LHCb
Preliminary
16
s = 7 TeV Data
NSignal
m0
σGauss
=
=
=
22.9 ± 5.3
5260.5 ± 3 MeV
± 2.5 MeV
12
14
Events / ( 10 )
Events / ( 22 )
Today (13 nb−1 ): B → Dπ
signal is seen.
Events / ( 10 )
CPV in trees: LHCb sensitivity
12
10
8
6
22
20
18
16
14
12
10
8
6
4
2
0
18
LHCb
Preliminary
NSignal
m0
σGauss
s = 7 TeV Data
1800
16
LHCb
Preliminary
14
s = 7 TeV Data
1850
=
=
=
1900
NSignal
m0
σGauss
41
± 7.6
1863.7 ± 1.9 MeV
8.96
± 1.5 MeV
1950
mK-π+ (MeV/c2)
=
=
=
± 8.5
35.3
1866.7 ± 3.9 MeV
± 4.3 MeV
12.6
12
10
4
8
2
0
6
5000
5500
4
mDπ (MeV/c2)
2
0
1800
1850
1900
1950
mK-π+π+ (MeV/c2)
2010 (0.2 fb−1 ): Precision comparable to B factories (σγ ∼ 12 − 15◦ )
2011 (1 fb−1 ):
B → D(hh)K : Nsignal ∼ 3000 events
B → Dsup (K π)K : Nsignal ∼ 400 events
D → D(Ks ππ)K : Nsignal ∼ 1500 events.
Combined σγ ∼ 6 − 8◦
Anton Poluektov
LHCb prospects for CPV
Rencontres de Blois, 15-20 July 2010
12/16
CP violation in charmless B decays
W
s, d
π, K +
W+
B0
b
u
∗
Vub
u
d, s
b
B
u
π, K +
u
π−
0
π−
d
d
Charmless two-body decays can probe γ.
Observables: time-dependent asymmetries
ACP
f (t) =
mix sin ∆mt
Adir
f cos ∆mt+Af
cosh ∆Γt/2−A∆
f sinh ∆Γt/2
Need flavor tagging and B decay time measurements.
and Adir
Measurable Amix
f
f
contain information about γ.
Can be extracted by
measurements with B 0 and Bs
decays to f = ππ, KK , K π,
using U-spin symmetry
(d − s SU(3) subgroup).
Anton Poluektov
LHCb prospects for CPV
Rencontres de Blois, 15-20 July 2010
13/16
CPV in charmless B decays
Measurements with B 0 performed by B
factories. 1.9σ disagreement between
Belle and BaBar measurements.
LHCb competitive with B factories for
Aππ measurement with 1 fb−1 ,
can measure AKK from Bs .
Adir
ππ
Amix
ππ
Adir
KK
Amix
KK
Anton Poluektov
Current value
0.38 ± 0.06
−0.65 ± 0.07
-
0.2 fb−1
0.13
0.13
0.15
0.11
LHCb prospects for CPV
1 fb−1
0.06
0.06
0.07
0.05
Rencontres de Blois, 15-20 July 2010
14/16
D mixing: D1,2 = pD 0 ± qD 0
2
Arg(q/p) [deg.]
y (%)
CPV in charm
HFAG-charm
FPCP 2010
CPV allowed
1.5
1
x = (M2 − M1 )/Γ,
y = (Γ2 − Γ1 )/2Γ.
80
1σ
2σ
3σ
4σ
5σ
HFAG-charm
FPCP 2010
60
40
20
0
0.5
−20
0
1σ
2σ
3σ
4σ
5σ
−0.5
q/p 6= 1 ⇒ CPV in mixing.
−1
−1
−40
−0.5
0
0.5
1
1.5
−60
−80
2
0.2
0.4
x (%)
0.6
0.8
1
1.2
1.4
1.6
1.8
|q/p|
1000
LHCb
Preliminary
Nsignal = 6304 ± 107
Mass µ = 1862.26 ± 0.14 MeV/c2
s = 7 TeV Data
Mass σ = 8.71 ± 0.14 MeV/c2
800
600
400
Entries / (6 MeV/c2)
Entries / (3 MeV/c2)
Example of a first-year measurement for LHCb: CPV in D → hh.
Observables:
Can reach σ(yCP ), σ(AΓ ) ∼ 0.1%
yCP = τ (K π)/τ (KK ) − 1,
0
0
(×3
better than current limit)
(D →KK )−τ (D →KK )
AΓ = ττ (D
0 →KK )+τ (D 0 →KK )
with only 0.1 fb−1 .
Flavor-tagged signals D ∗± → D 0 π ± , D 0 → KK , K π already seen:
80
70
Nsignal = 179 ± 19
LHCb
Preliminary
Mass µ = 1862.39 ± 0.66 MeV/c2
Mass σ = 6.59 ± 0.71 MeV/c2
s = 7 TeV Data
60
50
40
30
20
200
10
0
Anton Poluektov
1800
1850
1900
mKπ (MeV/c2)
LHCb prospects for CPV
0
1800
1850
1900
mKK (MeV/c2)
Rencontres de Blois, 15-20 July 2010
15/16
Conclusion
Many possibilities to search for CPV at LHCb with first data:
Bs → J/ψφ — competitive with CDF/D0 with 0.2 fb−1 .
Flavor-specific charge asymmetry: measurement complementary to D0:
σ(∆Afs ) ≃ 10−3 with 1 fb−1 .
γ measurements with B → DK (different D decay modes),
time-dependent Bs → Ds K (not covered here) — precision comparable
to B factories with 0.2 fb−1 (σγ ∼ 15◦ ), σγ ∼ 6 − 8◦ with 1 fb−1 .
CPV in charmless decays: B → ππ, K π, KK — comparable to B
factories with 1 fb−1 for B 0 (solve Belle-BaBar disagreement), best
constraint for Bs .
CPV in charm mixing (e.g. yCP from D → hh) — ∼ 3 times
improvement possible with 0.1 fb −1 .
Excellent detector performance confirmed, analyses using first
O(10 nb−1 ) to be reported at ICHEP.
Anton Poluektov
LHCb prospects for CPV
Rencontres de Blois, 15-20 July 2010
16/16