Pavel Krokovny
Heidelberg University
on behalf of LHCb collaboration
• Introduction• LHCb experiment• Physics results
S measurements prospects
• Conclusion
Search for New Physics in CP violating measurements at LHCb
Why CP violation?
• CP violating parameters are well predicted by the Standard Model
• Good sensitivity to New Physics• Huge statistics allows to perform a precise
measurements
LHCb features
• Large bb cross section & acceptance: huge statistics• Efficient trigger: reducing very high background• Excellent vertexing: resolving fast Bs oscillation• Good tracking & PID: signal reconstruction & background
suppression
S measurement in BS mixing
• Bs->J/ is dominated by tree
diagram. (penguin contribution
is in order of 10-3-10-4)
• Interference between direct &
mixing decays gives a CP
violating phase S=M-2D.
• S in SM is small and well
predicted: S=0.03630.017
• Good sensitivity for New
Physics: S=SSM+S
NP
Angular analysis
Flavor tagging• Need to determine BS flavor at production time.
• Two methods: Same Side (Kaon flavor) and Opposite Side (other B flavor)
• Two key parameters: efficiency () and dilution factor D=(1-2)
• Effective tagging power proportional to D2
• OST is calibrated on data using self-tagged B decays: B+D*+, J/K+
• SST calibration: using double tag method
Flavor tagging performance
• Flavor tagger was tuned using 48K B0->D*-+ events
• Then we check performance on 6K B0->D-+ events
• eff(SS+OS) = 4.31.0 %
compatible with MC expectation
• md = 0.4990.0320.003 ps-1
world average: 0.5070.005 ps-1
Mixing in B0D-+
LHCb-Conf 2011-010
BSJ/ signal
LHCb-Conf 2011-006
75728 eventsBs mass
Lifetime
S result
• Feldman-Cousins method used to get CL contours in S- plane
• Statistical errors only (systematic effects found to small in comparison with statistical uncertainty)
LHCb-Conf 2011-006
S prospects
Expectation!
Additional channels for s
• BsJ/ f0
J/ f0 is CP even eigenstate: angular analysis not needed.
Measurement of S to come soon. (error ~1.5 of J/)
First observation!
Phys.Let.B698:115, 2011
measurements
Two set of methods to measure :
• loop diagram: Bhh (possible NP contribution)
• tree diagram: BDK (theoretically clean)
Difference in results will indicate for New Physics.
from Bhh
Large penguins contributions in both decays
Bd/s
/K
/K/K
/K
Bd/s
Method:
Measure time-dependent CP asymmetry for B and BsKK and exploit U-spin flavor symmetry for P/T ratio (R. Fleischer).
Take s, d from J/,J/Ks can resolve
Direct CPV in Bhh
K+- K-+
ACP(BdK)=-0.0880.0110.007 (world average: -0.0980.12)
ACP(BSK)=0.270.080.02 CDF: 0.390.17
K+-K-+
LHCb-Conf-2011-042
37 pb-1
from BDKInterference between tree-level decays; theoretically clean
Parameters: , rB, δ
Three methods for exploiting interference (choice of D0 decay modes):
• Gronau, London, Wyler (GLW): Use CP eigenstates, e.g. D0 h+ h -
• Atwood, Dunietz, Soni (ADS): Use doubly Cabibbo-suppressed decays, e.g. D0 K+π -
• Dalitz plot analysis of 3-body D0 decays, e.g. Ks π+ π-
Vcs* Vub: suppressedFavored: Vcb Vus
*
b
u
s
u u
b
u
cD0
K-
B- B-
u
s
u
c
D0f
Common
final state
K-
iiBKDBA
KDBA eer
0
0
ADS methodD. Atwood, I. Dunietz and A. Soni, PRL 78, 3357 (1997); PRD 63, 036005 (2001)
Enhancement of СР-violation due to use of Cabibbo-suppressed D decays
B–D0K– - color allowed, D0K+π– - doubly Cabibbo-suppressed
B–D0K– - color suppressed, D0K+π– - Cabibbo-allowed
Interfering amplitudes are comparable
coscos2)(
)( 22
fav
supDBDBADS rrrr
KDBBr
KDBBr
R
)()( 00 KDKDrD AA
Measured quantities:
ADSDBADS RrrKDBBrKDBBr
KDBBrKDBBr/sinsin2
)()(
)()(
supsup
supsup
A
ADS analysis at LHCb
4.0 significance
RADS=(1.660.390.24) 10-2
World average: -0.580.21
AADS=-0.390.170.02
World average: 1.60.3 (w/o LHCb)
LHCb-Conf 2011-044
Conclusion
• LHCb shown a good performance in B & charm physics.
• B-factories & Tevatron sensitivity overtaken or matched on many topics using 2010 data only.
• No sign of New Physics yet .• Great potential to search for New Physics in next
years!
Backup
Control Channels
B+ J/ K+
B0 J/ K*0
• Tagging calibration (opposite side)
• Kinematically similar to BsJ/
• Angular acceptance checks: Polarization amplitudes
• Check of tagging performance
J/ amplitudes
LHCb data taking
LHCb collected 37 pb-1 in 2010, and 670 pb-1 in 2011
One day of operation now corresponds to whole 2010 statistics!
B mixing
d b
b d
W
t
t
WBd Bd
Due to the different values of CKM couplings the Bs mixes faster then the Bd
s b
b s
W
t
t
WBs Bs
Bd → Bd
Bd → Bd
Bd mixingBs mixing
Bs → Bs
Bs → Bs
Bs mixing
Both the Bd and Bs mixing have been precisely measured in experiments
5.1 x 1011 Hz 1.8 x 1013 Hz
BS mixing formalism
Additional channels for s
Pure penguin decays
First observation!
LHCb-Conf 2011-019
Br(BsK*K*)=(1.950.470.51 0.29)10-5
Lifetime measurement for BsK+K-
CPV in charm• Indirect CPV: mixing rate of D0D0 and D0D0 differ
• Direct CPV: amplitudes for D0/D0 differ, mixture of mixing and decay diagram.
• The SM predicts very small CPV in charm: O(10-4).
• Can be up to O(10-2) in some NP models.
• Good prospects to search NP in charm!
• Promising modes: CS modes with penguin contribution:
Charge asymmetry in D0h+h-
• Production and soft pion asymmetry cancel in ARAW(f)ARAW(g)
• There is no detection asymmetry in D0h+h-
D0h+h- ACP results
• Fit the mass difference: M(D*)-M(D0)
• Result: ACP(KK)ACP()= (0.280.700.25) %
Belle: (0.860.600.07)%
BaBar: (0.240.62)% naïve difference
CDF: (0.460.33)% w/o systematic
LHCb-Conf 2011-023
