Transcript Searches for FCNC Decays Bs(d) → μ+μ-

B Physics at the Hadron Colliders:
Bs Meson and New B Hadrons
Introduction to B Physics
Tevatron, CDF and DØ
b Baryon
Selected Bs Results
Conclusion
Matthew Herndon, March 2007
University of Wisconsin
APS April Meeting
BEACH 04
J. Piedra
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If not the Standard Model, What?
Standard Model predictions validated to high precision, however
Standard Model fails to answer many fundamental questions
Gravity not a part of the SM
What is the very high energy behaviour?
At the beginning of the universe?
Grand unification of forces?
Dark Matter?
Astronomical observations of indicate that
there is more matter than we see
Baryogenesis and
Where is the Antimatter?
Why is the observed universe mostly matter?
Look for new physics that could explain these mysteries
Look at weak processes which have often been the most unusual
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A Little History
Everything started with kaons
Flavor physics is the study of bound states of
quarks.
Kaon: Discovered using a cloud chamber in 1947
by Rochester and Butler.
Could decay to pions and had a very long lifetime:
10-10 sec
Bound state of up or down quarks with a
new particle: the strange quark!
Needed the weak force to understand it’s interactions.
K0
Neutron kaons were some of the most interesting kaons
Rich ground for studying new physics
d
What was that new physics? New particles, Rare decays, CP
s
violation, lifetime/decay width differences, oscillations
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B Hadrons
New physics and the b Hadrons
Very interesting place to look for new physics(in our time)
Higgs physics couples to mass so b hadrons are interesting
Same program. New Hadrons, Rare decays, CP violation, , oscillations
State of our knowledge on Heavy b Hadrons last year
Hints for Bs seen: by UA1 experiment in 1987.
Bs and Lb Seen: by the LEP experiments and Tevatron Run 1
s
b
Some decays seen
However
Bs oscillation not directly seen
 not measured
b
CP violation not directly seen
u
d
Most interesting rare decays not seen
No excited Bs or heavy b baryons observed
A fresh area to look for new physics!
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The Tevatron
-
1.96TeV pp collider
Excellent performance and improving
each year
Record peak luminosity in 2007:
2.8x1032sec-1cm-2
TRIGGERS ARE CRITICAL
CDF/DØ Integrated Luminosity
~2fb-1 with good run requirements
through end now
All critical systems operating
including silicon
Have doubled the data twice in the last
few years
B physics benefits from more data
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CDF and DØ Detectors
CDF Tracker
Silicon |η|<2, 90cm long, rL00 =1.3 - 1.6cm
96 layer drift chamber 44 to 132cm
EXCELLENT TRACKING: MASS RESOLUTION
Triggered Muon coverage: |η|<1.0
EXCELLENT TRACKING:
TIME RESOLUTION
DØ Tracker
Silicon and Scintillating Fiber
Tracking to |η|<2
EXCELLENT TRACKING: EFFICIENCY
New L0 on beam pipe!
Triggered Muon coverage: |η|<2.0
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The Results!
Combining together excellent detectors and accelerator performance
Ready to pursue a full program of B hadron physics
Today…
New Heavy b Baryons
Bs → μμ
 Bs and CP violation
Direct CP violation
Bs Oscillations
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New B Hadrons
Lb only established b baryon LEP/Tevatron
Tevatron: large cross section
and samples of Lb baryons
First possible heavy b baryon:
= 3/2+(b*)
b: b{qq}, q = u,d; JP = SQ + sqq
= 1/2+ (b)
Predictions from HQET,
Lattice QCD, potential
models, sum rules…
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b Reconstruction
Strategy:
Establish a large sample of
decays with an optimized
selection and search for:
b+  Lb+
Lb: NLb = 3184
Estimate backgrounds:
Random Hadronization tracks
Other B hadrons
Combinatoric
Extract signal in combined fit of Q
distribution
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b Observation
Observe b signal for all
four expected b states
> 5s significance level
b-
59  15  7
 b+
32  13  4
b-*
69  18  11
b+*
77  17  8
Mass differences
m(b) - m(Lb)
194.1  1.2  0.1MeV/c2
m(b*) - m(b)
21.2  1.9  4 MeV/c2
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Bs(d) → μ+μ- Method
Rare decay that can be enhanced in
Higgs, SUSY and other models
Relative normalization search
Measure the rate of Bs(d) → μ+μ- decays
relative to B J/K+
Apply same sample selection criteria
9.8 X 107 B+ events
Systematic uncertainties will cancel out in
the ratios of the normalization
Example: muon trigger efficiency same for
J/ or Bs s for a given pT
400pb-1
(N cand  N bg )  B  B  f u
BF(Bs    ) 

 
 BsBs
NB 
fs


N(B+)=2225
BR(B   J /K  )  BR(J /    )
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Discriminating Variables
4 primary discriminating variables
Mass M
CDF: 2.5σ window: σ = 25MeV/c2
DØ: 2σ window: σ = 90MeV/c2
CDF λ=cτ/cτBs, DØ Lxy/sLxy
α : |φB – φvtx| in 3D
Isolation: pTB/( trk + pTB)
CDF, λ, α and Iso:
used in likelihood ratio
D0 additionally uses B and 
impact parameters and vertex
probability
Unbiased optimization
Based on simulated signal and data
sidebands
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Bs(d) → μ+μ- Search Results
CDF Result: 1(2) Bs(d) candidates observed
consistent with
background expectation
BF(Bs  +- ) < 10.0x10-8 at 95% CL
BF(Bd  +- ) < 3.0x10-8 at 95% CL
Decay
Total Expected
Background
Observed
CDF Bs
1.27 ± 0.36
1
CDF Bd
2.45 ± 0.39
2
D0 Bs
0.8 ± 0.2
1.5 ± 0.3
3
D0 Result: First 2fb-1 analysis!
BF(Bs  +- ) < 9.3x10-8 at 95% CL
Worlds Best Limits!
Combined:
BF(Bs  +- ) < 5.8x10-8 at 95% CL
CDF 1 Bs result:
PRD 57, 3811 1998
3.010-6
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New Physics in  Bs
 Bs Width-lifetime difference between eigenstates
Bs,Short,Light  CP even
Bs,Long,Heavy  CP odd
New physics can contribute in penguin diagrams
CPCons
Bsmeas  Bs
cos(s ), s   SM   NP
 s  2 s
Measurements
Directly measure lifetimes in Bs J/
Separate CP states by angular
distribution and measure lifetimes
Measure lifetime in Bs  K+ KCP even state

Search for Bs → Ds(*)Ds(*)
CP even state
May account for most of the lifetime-width
difference
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Many Orthogonal Methods!
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 Bs Results: Bs J/
DØ Run II Preliminary
DØ Run II Preliminary
Assuming no CP violation
 Bs = 0.12  0.09  0.02 ps-1
Non 0  Bs
D0: PRL 98, 121801 2007
Putting all the measurements together
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 Bs CP Violation Results
Allowing for CP Violation

meas
Bs
 
SMCPCons
Bs
cos(
SM
 )
NP
Combine with searches for CP
violation in semileptonic B decays
 Bs = 0.17  0.09 ps-1
 = NP + SM = -0.70 +0.47-0.39
D0: hep-ex/0702030
Consistent with SM  Bs = 0.10  0.03 SM = -0.03 - +0.005
M. Herndon
U. Nierste hep-ph/0406300
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Bs: Direct CP Violation
Direct CP violation expected to be large in some Bs decays
Some theoretical errors cancel out in B0, Bs CP violation ratios
Challenging because best direct CP violation modes, two body decays, have overlapping
contributions from all the neutral B hadrons
Separate with mass, momentum imbalance, and dE/dx
First Observations
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B0: Direct CP Violation
-0.107  0.018 +0.007-0.004
Hadron colliders competitive with B factories!
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Bs: Direct CP Violation
BR(Bs  K) = (5.0  0.75  1.0) x 10-6
Good agreement with recent prediction
ACP expected to be 0.37 in the SM
Ratio expected to be 1 in the SM
Lipkin, Phys.Lett. B621 (2005) 126
New physics possibilities can be
probed by the ratio
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Bs Mixing: Overview
-
Measurement of the rate of conversion from matter to antimatter: Bs  Bs
Determine b meson flavor at production, how long it lived, and flavor at decay
to see if it changed!
tag
Bs
p(t)=(1 ± D cos mst)
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Bs Mixing
tag
Bs
Tag
D0
OST
Decay
Performance(D2)
2.48  0.21  0.07%
CDF OST
1.8%
CDF SST
3.7%(4.8%)
Candidates
CDF Bs  Ds(2)
5600
CDF Bs  Ds-*+, Bs  Ds- +
3100
CDF Bs  DslX
D0
Bs  DslX
61,500
41,000(+1600)
Large samples, good flavor tagging, great time resolution
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Bs Mixing: DØ Results
Key Features
Result
Sen: 95%CL
16.5ps-1
Sen: sA(@17.5ps-1)
0.7
A/sA
1.6
Prob. Fluctuation
8%
Peak value: ms
19ps-1
Limits: 17-21ps-1 @90CL
One experiment with more sensitivity
than the whole generation of
experiments before!
PRL 97, 021802 2006
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Bs Mixing: Results
Key Features
Result
Sen: 95%CL
31.3ps-1
Sen: sA(
)
@17.5ps-1
A/sA
2.8THz
0.2
6
Prob. Fluctuation
8x10-8
Peak value: ms
17.75ps-1
A >5s Observation!
PRL 97, 242003 2006
Can we see the oscillation?
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Bs Mixing: CKM Triangle
Tevatron
ms = 17.77  0.10 (stat)  0.07 (syst) ps-1
|Vtd| / |Vts| = 0.2060  0.0007 (stat + syst) +0.0081
-0.0060(lat. QCD)
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B Physics Conclusion
Tevatron making large gains in our understanding of B Physics
First new heavy baryon, b, observed
Factor of 30
New stringent limits on rare decays:
BF(Bs 
+-
)<
9.3-10x10-8
improvement
at 95% CL
over run 1
Precise measurement of  Bs
And first look at the
 Bs = 0.12  0.09 ± 0.02 ps-1
CP violating phase
On the hunt for direct CP violation
ACP(Bs  K) = 0.39  0.15  0.08
2.5s
First measurements-0.18
of ms
ms = 17.77  0.10 (stat)  0.07 (syst) ps-1
M. Herndon
One of the primary
goals of the
Tevatron
accomplished!
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