2
2
2
ˆ
ˆ
td
ts
BB
BB
B
B
d
s
V
V
fB
fB
M
M
Δm
Δm
dd
ss
d
s
Search for Bs oscillations at D
tbtstd
cbcscd
ubusud
VVV
VVV
VVV
1)1(
21
)(21
23
22
32
AλiηρAλ
Aλλλ
iηρAλλλ
Constraining the CKM matrix
8.0 ,22.0 ALarge uncertainty
Precise measurement of Vtd • properly constrain the CKM matrix• yield info on strength of CP-violation
Vtd can be measured via• rare kaon decay • mixing in the B system
) ( 2
QCDVm tdd F but large QCD effects dominate the extraction of Vtd
Neutral B meson transition from particle to anti-particle state, and vice-versa Weak eigenstates mass eigenstatesCaused by higher order flavor changing weak interactions: mq= m(Bo
heavy) - m(Bolight)
mq |VtbVtq|2
Mixing parameters xq= mq/q and yq= q/ q where q=d,s
First oscillations observed at ARGUS (’87) in the Bd system
signaled a large top quark mass (later verified by CDF and DØ)
What is mixing ?
consider ratio from Lattice QCD
1005.0507.0 psmd
md has been precisely measured: the world average is
a direct measurement of ms + md(current value) + Vts(relatively well known) Vtd
Central Scintillator
Forward Mini-drift chamb’s
Forward Scint
Shielding
Tracking: Solenoid,Silicon,Fiber Tracker,Preshowers
New Electronics,Trigger,DAQ
Calorimeter
Central PDTs
Large production cross-sectionAll B species, including Bs, Bc, b
Rich B Physics program at DØ benefits from :• Large muon acceptance: || < 2• Forward tracking coverage: || < 1.7 (tracking), || < 3 (silicon)• Robust muon trigger
A typical oscillation analysis involves:
– Selection of final states suitable for the study
• Tagging the meson flavor at decay time (final state)
• Tagging the meson flavor at production time (initial state)
– Proper time reconstruction for each meson candidate
Essential ingredients of a mixing analysis
Bs mixing studies at DØ: XDlB SS
The Tevatron B-factory and the new DØ
Bs oscillates at least 30 times faster than B0 ! a Bs mixing measurement is extremely challenging.
We think we understand the mixing of B’s… A deviation from this simple diagram is a deviation from the Standard Model (New Physics)
KTheoretical uncertainties reduced in ratio (10% 4%)
SM or NP ?
TeV 1.96at 150)( bbbpp 0at 7)( Znbbbee
)4(at 1)( SYnbbbee
jet charge
Decay modetags b flavorat decay
2nd B tags production flavor
Dilution D = 1 – 2ww = mistag probability = efficiencyD2 = effective tagging power
Proper decay time from displacement (L)and momentum (p)
2/)(2
2
2),( tmt e
BS
SNDmS
Average statistical significance
# of reconstructed events
Flavor taggingsignal purity
proper time resolution
Measure asymmetry A as a function of proper decay time t
“unmixed”: particle decays as particle
For a fixed value of ms, data should yieldAmplitude “A” is 1 @ true value of ms
Amplitude “A” is 0 otherwise
“mixed”: particle decays as antiparticle
Units: [m] = h ps-1, h =1 then m in ps-1. Multiply by 6.582 x 10-4 to convert to eV
Amplitude method:H-G. Moser, A. Roussarie,NIM A384 p. 491 (1997)
ms < 21 ps-1 @ 90% CL assuming Gaussian errorsFirst direct two-sided bound on ms
PRL 97, 021802 (2006)
Amplitude Scan
Log-likelihood Scan
New Result: Combination of additional Ds decay modes
Future Prospects:
Add Same Side Tagging, hadronic modes
Add more data (4-8 fb-1 in next 3 years) with improved
detector – additional layer of silicon between beampipe
and Silicon Tracker (Layer0) – better impact parameter
resolution
Future Prospects:
Add Same Side Tagging, hadronic modes
Add more data (4-8 fb-1 in next 3 years) with improved
detector – additional layer of silicon between beampipe
and Silicon Tracker (Layer0) – better impact parameter
resolution
µ, e
