View
56
Download
2
Category
Preview:
DESCRIPTION
Measurement(s) of ϕ s at LHCb. Yasmine Amhis On behalf of the LHCb Collaboration. From Y. Nir Lecture @ CERN April 2012. The B 0 s neutral system. Time Evolution. Diagonalizing this Hamiltonian leads to two mass eigenstates with masses M H(L) and decay width Γ H(L). - PowerPoint PPT Presentation
Citation preview
Measurement(s) of ϕs at LHCb
Yasmine AmhisOn behalf of the LHCb Collaboration
Yasmine Amhis - HQL 20122From Y. Nir
Lecture @ CERN April 2012
Yasmine Amhis - HQL 2012
The B0s neutral system
3
Time E
volu
tion
Diagonalizing this Hamiltonian leads to two masseigenstates with masses MH(L) and decay width ΓH(L)
Yasmine Amhis - HQL 20124
ϕs in a box
• Measure relative phase difference : ϕs= ϕM − 2ϕD between two “legs”.
• In SM + Ignoring penguins : ϕD ~ 0
ϕsSM ~ ϕM
is predominantly determined by arg(Vts )
is predicted to be small ≈ − 0.04 [Charles et al. Phys. Rev. D84 (2011) 033005]
New Physics (NP) can add large phases:
ϕs = ϕs
SM + ϕsNP
Bs decay to a flavour eigenstate
Yasmine Amhis - HQL 20125
ϕs
Ambiguity Measurement
Dramatis personae du jour
6
ϕsAmbiguity Measurement
Dramatis personae du jour
Yasmine Amhis - HQL 20127
Flavour Tagging
Currently use Opposite Side Tagger, fully optimized and calibrated on data
Effective tagging efficiency(2.29 ±0.07 ±0.26)%
arXiv:1204.5675
Time dependent CP asymmetry needs to identify the initial flavour of reconstructed Bs
0 mesons (initial state a b or b quark).
Yasmine Amhis - HQL 20128
Decay time resolution
oWe measure from data using prompt J/ψ which decay at t = 0 ps.o Width is found to be about 40 - 45 fs. o Use per-event estimate of the decaytime resolution.
Yasmine Amhis - HQL 20129
The Golden Channel
Yasmine Amhis - HQL 201210
Theoretically :o b→ccs tree dominance leads to precise prediction of ϕs
in SM.o P → VV, admixture of CP-odd and CP-even states, measure also ΔΓs.
Experimentally : o Relatively large branching ratio.o Easy to trigger on muons from J/ψ → μ+μ-.
The Observableso 3 “P-wave” amplitudes of KK system.o 1 “S”-wave amplitude.o10 terms with all the interferences. o ϕs
, ΔΓs, , Γs …
Yasmine Amhis - HQL 201211
There is a two-fold ambiguity in the solutions :
o ϕs and π - ϕs
and ΔΓs changes sign
Yasmine Amhis - HQL 201212
o Full 2011 data set of 1 fb−1 is used. o Simple cut selections based on kinematics. o Most background removed by decay time cut t > 0.3 ps. o Very clean signal∼ 21200 signal candidates.
LHCb-CONF 2012-004
Yasmine Amhis - HQL 201213
Fit
pro
ject
ion
s
CP-even
CP-odd
CP Content clearly seperated
Yasmine Amhis - HQL 201214
Systematic uncertainties
Yasmine Amhis - HQL 201215
Resu
lts
ΔΓs is the first observed non-zero value. All the measurements are compatible with SM.
Yasmine Amhis - HQL 201216
Us and the rest of the world
Yasmine Amhis - HQL 201217
Resolving the ambituity
18
Yasmine Amhis - HQL 2012
Resolving the ambiguous solution The sign of ΔΓs
Y. Xie et al., JHEP 09 (2009) 074]
K+K− P-wave :Phase of Breit-Wigner amplitudeincreases rapidly across φ(1020)mass region
K+K− S-wave:Phase of Flatté amplitude for f0(980)relatively flat (similar for non-resonance)
Phase difference between S- and P-wave amplitudesDecreases rapidly across φ(1020) mass region
Resolution method: choose the solution with decreasing trend of
δs −δP vs mKK in the φ(1020) mass region
Resolving the ambiguous solution The sign of ΔΓs
19
Submitted PRL arXiv:1202.4717v2 o Use a sample of 0.37 fb -1 o Split data into 4 bins of mKK
o In each bin measure :• Fraction of S-wave• Measure relative strong
phase difference : δS – δperp
δS –
δp
erp ΔΓs < 0
ΔΓs > 0
Solution I is selected by the data
Yasmine Amhis - HQL 201220
Yasmine Amhis - HQL 201221
Previous analysis was Bs J/ψf0(980) PL B707 (2012) 497
All m(ππ) range found to be CP-odd :
97.7% @ 95% C.L [arXiv:1204.5643]
Now use wider m(ππ) range hence : Bs J/ψ ππ
Yasmine Amhis - HQL 201222
o Selection using a Boosted Decision Tree.o Maximum likelihood fit to time and mass.o Approx. 7400 signal events in 1fb-1
Simpler decay rate expression since there is no angular structure
Yasmine Amhis - HQL 201223
Result
ϕs = -0.02 ± 0.17(stat.) ± 0.02(syst.) rad.
arXiv1204.5675 Submitted to PLB
o Uses Γs and ΔΓs from the Bs J/ψΦ analysis (+ correlation) PRL 108 (2012) 101803o Uses Δms from Bs→ Ds (3)π PL B709 (2012) 177
Yasmine Amhis - HQL 201224
Conclusion
24
Γs = 0.6580 ± 0.0054(stat.) ± 0.0066(syst.) ps-1;
ΔΓs = 0.116 ± 0.018(stat.) ± 0.006(syst.) ps-1;
ϕs = -0.001 ± 0.101(stat.) ± 0.027(syst.) rad.
ϕs = -0.002 ± 0.083(stat.) ± 0.027(syst.) rad.
o LHCb has presented new preliminary results using the full 2011 data (1 fb-1)
o From an analysis of the J/ψϕ channel we find:
o From an analysis of the J/ψππ channel we find:
ϕs = -0.02 ± 0.17(stat.) ± 0.02(syst.) rad.
o Combining both results we find:
o We resolve the 2-fold ambiguity and find: ΔΓs > 0 .
Yasmine Amhis - HQL 201225
Yasmine Amhis - HQL 201226
Systematics
Yasmine Amhis - HQL 201227
Yasmine Amhis - HQL 201228
Yasmine Amhis - HQL 201229
Conclusion
Yasmine Amhis - HQL 201230
Recommended