mixing measurements s b at the tevatronmoriond.in2p3.fr/qcd/2007/sundaymorning/jesik.pdf · rick...
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Bs mixing measurements
at the Tevatron
Rick Jesik
Imperial College London
Representing theDØ and CDF collaborations
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Bs mixing
m12 stems from the real part of this boxdiagram, dominated by top
12 stems from the imaginary part,dominated by charm
Heavy and light CP eigenstates are expectedto have different widths
New particles in the box can have largeeffects
Important test of CKM formalism
possible new sources of CP violation(needed to explain matter dominance)
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The Fermilab Tevatron
p p
s =1.96 TeV t = 396 ns
CDF
CDF
DØ
DØDØ
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Tevatron Luminosity
Over 2 fb-1 of collisions have been delivered to theexperiments in Run II
Analysis presented today use 1 fb-1
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The CDF Run II Detector
Strong central tracking
Excellent silicon vertexdetector
Good lepton ID
Particle ID (TOF anddE/dx)
Excellent massresolution
Level 1 displacedtrack trigger
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The DØ Run II Detector
Silicon vertex detector
| | < 3.0
Central fiber tracker andpre-shower detectors
| | < 1.6
2 T solenoid magnet
New low pT central muontrigger scintillators
New forward μ system
Excellent muon purity andcoverage: | | < 2.0
Second level displaced tracktrigger, NN B tagging at 3rd
level
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Measuring Bs mixing
reconstruct Bs decays, decay flavor from decay products
measure proper time of the decay (very precisely)
infer Bs production flavor (flavor tagging)
fit unmixed - mixed asymmetry as a function of proper time
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Measured asymmetry
Asymmetry is degraded by
flavor tagging dilution
decay length resolution
momentum resolution
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Bs mixing measurements
At Moriond 2006, D0 presentsthe first two sided limit on dms
Consistent with SM/CKM
CDF soon confirms results
And now has made a precisionmeasurement with the samedata set
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Impact on the Unitarity Triangle
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Impact on the Unitarity Triangle
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Improvements to the CDF analysis
Flavor tagging
added opposite side kaon tag
use Neural Net to combine all opposite side taggers
use NN for same side tag
Increased signal yield
added partially reconstructed decays
use particle ID in the selection
use NN selection for hadronic modes
loosend kinematic selection
Increased the effective statistics by a factor of 2.5!
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Neural Network selection performance
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Bs hadronic decay signals
Use decays with lost or0 in golden mode Ds( ) ( p/p ~ 2%)
Improve selection withPID and NN
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Neural Network SSKT
Neural Network same side kaon tag
particle ID
R
pT
pLrel
pTrel
Also us NN to improveopposite side tags
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Amplitude Scan
A/ A = 6.1 Sensitivity
31.3 ps-1
Hadronic & semileptonic decays combined
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Measurement of ms- log(Likelihood)
Hypothesis of A=1 compared to A=0
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|Vtd| / |Vts|
inputs: m(B0)/m(Bs) = 0.9830 (PDG 2006) = 1.21 +0.047 (M. Okamoto, hep-lat/0510113) md = 0.507 +- 0.005 (PDG 2006)
-0.035
|Vtd| / |Vts| = 0.208 +0.008 (stat + syst)-0.007
d
s
m
m=
2
2
2
td
ts
Bd
Bs
V
V
m
m
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CP violation in B mixing
Search for CPV with part per mil precision by looking forasymmetry in like-sign dimuons and exclusive (untagged)Bs-Dsm events
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Detector Asymmetries
Detector asymmetries on the order of a few % arepresent due to geometry of the muon system
Toroid
Solenoid
Cancel to first
order by
alternating the
muon and
inner tracker
magnet
polarities
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Dimuon sample composition
signal
Backgrounds that
dilute the
asymmetry
Reaction K N Y (Y= , ...)
has no K+N analog
signal backgrounds
with fake
asymmetries
backgrounds
which dilute the
asymmetry
Measured in data using kaons
from semleptonic decays
Cross-check:0076.01281.0)(
024.0001.0136.0)0(
±=
±±=
PDG
D
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Dimuon asymmetry
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Exlcusive
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s and s from Bs J/
Relation of matrix elements to decay and oscillation parameters:
In the Standard Model:
The CP violating phase, is expected to be small
Mass eigenstates are ~ CP eigenstates with definite lifetimes
The J/ final state is a mixture of CP states
L=0, 2; CP even; (A0, A||)
L=1; CP odd; (A )
We allow, however, CP cons. And CPV interference terms
measure two Bs lifetimes, L and H, (or / and ), and by
simultaneously fitting time evolution and angular distribution inuntagged Bs J/ decays
cos2
2
12
12
=
=
HL
LHMMMm
=12
12argM
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Reconstructed Bs J/
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Transversity Analysisz
x
y
J/ Rest Frame
K+
K-
μ+
μ-
x
y
Rest Frame
J/
K+
K-
=transversity
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s Results
D0 Preliminary
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s Results
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Combined results
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Conclusions
We now have measurements of all the Bs mixingparameters from the Tevatron
ms consistent with SM/CKM
precision measurement of Vtd/Vts
s also consistent with SM
CPV phase s still has room for new physics
Expect many more improvements to come
Lots more data (already a factor of two)
More decay modes and new techniques
e.g. flavor tagged J/ + analysis
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Separate amplitude scans
Ds( ) + part.rec.
part.rec. only
Other hadronic
Semileptonic
A/ A = 1.82
A/ A = 3.74 A/ A = 4.45
A/ A = 1.76
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Systematics in measurement of ms
Systematics dominated byct-scale uncertainty