1. Measurement of the phase of Bs mixing with Bs ϕϕ
M. Needham
ICHEP Valencia 2nd July 2014
On behalf of the LHCb Collaboration

2. Outline Introduction +dataset Time dependent analysis in Bs ϕϕ
Triple product measurement in Bs ϕϕ
Summary
LHCB-PAPER
Studies exploit full
LHCb Run 1 dataset of
3fb-1

3. Introduction B _ B -D f  D Observable phase s = -2s = M - 2 D
In the Standard Model expected s small for in Bs ϕϕ
Larger values possible in models of New Physics such as Supersymmetry and Little Higgs
Direct CP violation also possible
Direct CP

4. Introduction: Bs ϕϕ Gluonic penguin decay. BR ~2 × 10-5
SM cancellation between decay +
mixing phases ϕs is 0.01 with
0.02 uncertainty (arXiv: )
Room for New Physics even if ϕs constrained by measurements in other modes
LHCb: ideal place to measure due large dataset + hadronic trigger
Build on previous time dependent
measurement using 880 events corresponding
to 1fb-1 of data collected in 2011
[PRL 110 (2013) ].
Yielded 68% CL of [-2.46,-0.76] rad
p-value
of SM 16 %

5. Time dependent angular analysis
P + S – wave amplitudes/ strong phase
P wave three polarization amplitudes
CP even (A0, A||) CP odd (Aperp)
S-wave CP odd and even components
CP violating phase ϕs
Direct CP violation parameter |λ|

6. Time dependent angular analysis
Angular acceptance from
simulation
Time acceptance
from data

7. Dataset
2011
2012
Full Run 1 dataset + new multi-variate selection yields 3950 signal candidates
Around 4.5x number from previous analysis

8. Analysis Ingredients Time resolution model from
Physics parameters in Γs, ΔΓs, Δms
from other LHCb analyses
Time resolution model from
simulation. Calibrated on data
σt ~ 43 fs
Unbinned maximum
likelihood fit to mass,
time and angles
Opposite + same side tagging
calibrated using B+  J/ψK+
and semi-leptonic B decays.
See talk of M. Dorigo
Time acceptance due to cuts
in the trigger determined
from Bs Dsπ data
Angular acceptance for signal
from simulation

9. Fit Projections
CP Even
CP Odd
S-wave

10. ϕs results
Results consistent with no CP violation and the Standard Model expectation
Main systematic uncertainties from angular and decay time acceptance.
Uncertainties due to included in Γs, ΔΓs, Δms, tagging included in the statistical uncertainty

11. Triple Product Asymmetries
Datta + London: arXiv:hep-ph/
Gronau + Rosner: arXiv:hep-ph/ v2
CP-odd/CP-even interference terms Im(A0*A) + Im(A//* A) are proportional to Triple products + are odd under time reversal
Sign according to cosθ1 cosθ2 V U
Non-zero TPs: T violation + hence CP violation
Extraction of TP asymmetries simple counting exercise:
Zero in the Standard Model, non zero if weak phases of polarization
amplitudes different

12. Triple Product results
Triple products consistent with zero. Consistent with previous
LHCb/CDF results, improve precision by factor of two
Main systematics from mass model, angular and time acceptance

13. Summary
Full LHCb Run 1 dataset + latest flavour tagging used to make precision measurement of CP violation in Bs ϕϕ decay
Updated values for triple products also given
Results consistent with Standard Model prediction of small CP violation
Expect factor of two improvement in precision with Run 2 data
Key channel for LHCb upgrade where precision will reach ~ 0.03 level
providing high precision probe of Standard Model (theory uncertainty 0.02)

14. Backup

15. The LHCb Detector Muon System RICH Detectors Vertex Locator VELO
pp collision Point
~ 1 cm B
Calorimeters
Tracking System