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Measurement of the B0s Oscillation Frequency:
Matter-Antimatter Transformations at 3 THz
Prof. Joseph Kroll
University of Pennsylvania
UCSD16 May 2006
16 May 2006 Joseph Kroll - UCSD Seminar 2
Presenting results on ms and |Vtd/Vts|
Data are from the CDF Collaboration at Fermilab
CDF = 60 Institutions, > 700 Physicists
All results are preliminary unless indicated otherwise
16 May 2006 Joseph Kroll - UCSD Seminar 3
Tevatron Performance
Typical L = 1032 cm-2 s-1
∫Ldt = 1.5 fb-1
This analysis uses full data set: 1 fb-1
16 May 2006 Joseph Kroll - UCSD Seminar 4
Neutral Meson Flavor Oscillations (Mixing)
Due to phase space suppression:K0
L very long-lived: 5.2£ 10-8 s(K0
S: 0.0090£ 10-8 s)
1954: over 50 years ago
16 May 2006 Joseph Kroll - UCSD Seminar 5
Long-Lived Neutral Kaon
Led to discovery of CP Violation in 1964 (Nobel Prize in 1980)BF(K0
L ! +-) = 0.2%
Discovered in 1956 Phys. Rev. 103, 1901 (1956)
16 May 2006 Joseph Kroll - UCSD Seminar 7
Neutral B Meson Flavor Oscillations
= 1/ = 1.6 psec
Units: We use ~=1 and quote m in ps-1
To convert to eV multiply by 6.582£ 10-4
16 May 2006 Joseph Kroll - UCSD Seminar 9
Basic Measurement Principle
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, at the true value of ms
Amplitude “A” is 0, otherwise
“mixed”: particle decays as antiparticle
16 May 2006 Joseph Kroll - UCSD Seminar 10
Status of Published Results on ms
Results from LEP, SLD, CDF I ms > 14.4 ps-1 95% CL
see http://www.slac.stanford.edu/xorg/hfag/osc/PDG_2006/index.html
Amplitude method:H-G. Moser, A. Roussarie,NIM A384 p. 491 (1997)
16 May 2006 Joseph Kroll - UCSD Seminar 11
Recent Result from DØ Collaboration
17 < ms < 21 ps-1 @ 90% CL
1st reported direct experimental upper bound
Probability“Signal” israndom fluctuationis 5%
V. M. Abazov et al. hep-ex/0603029submitted to Phys. Rev. Lett.
16 May 2006 Joseph Kroll - UCSD Seminar 12
Recent Result from the CDF Collaboration
Probability“Signal” israndom fluctuationis 0.5%
16 May 2006 Joseph Kroll - UCSD Seminar 13
The Flavor Parameters (CKM Matrix)
mass eigenstates ≠ weak eigen.
weak mass
related by Cabibbo-Kobayashi-Maskawa Matrix
V is unitary: VyV = 1 Measurements + Unitarity assuming 3 generations
PDG: S. Eidelman et al. Phys. Lett. B 592, 1 (2004) Ranges are 90% CL
These fundamental parameters must be measured
16 May 2006 Joseph Kroll - UCSD Seminar 14
Wolfenstein Parametrization Illustrates Hierarchy
Original reference: L. Wolfenstein, PRL, 51, p. 1945 (1983)See also: J. Charles et al., Eur. Phys. J. C41, p. 1 (2005); ibid, hep-ph/0406184
from hep-ph/0406184
Expand matrix in small parameter: = Vus = sinCabibbo» 0.2
3 £ 3 complex unitary matrix: 3 real & 1 imag. parameters ≡ 3 angles, 1 phase
16 May 2006 Joseph Kroll - UCSD Seminar 15
Neutral B Meson Flavor Oscillations
Flavor oscillations occur through2nd order weak interactions
e.g.
Same diagrams and formula for ms for Bs except replace “d” with “s”
All factors known well except “bag factor” £ “decay constant”
md = 0.505 § 0.005 ps-1 (1%) (PDG 2005) from Lattice QCD calculations – see Okamoto, hep-lat/0510113
From measurement of md derive |V*tbVtd|2
16 May 2006 Joseph Kroll - UCSD Seminar 16
B Meson Flavor Oscillations (cont)
If we measure ms then we would know the ratio ms/md
Many theoretical quantities cancel in this ratio, we are left with
Ratio measures |Vtd/Vts|This is why ms ishigh priority in Run II
Using measured md & B masses, expected |Vts/Vtd|
Predict ms » 18 ps-1
We know what to expect
M. Okamoto Lattice 2005hep-lat/0510113PoS LAT2005 (2005) 013
16 May 2006 Joseph Kroll - UCSD Seminar 17
Why is this Interesting? Probe of New Physics
Supersymmetric particles 4th Generation
Additional virtual particlesincrease ms
Measured value can be usedto restrict parameters in models
e.g., Harnik et al. Phys. Rev. D 69 094024 (2004) e.g., W. Huo Eur. Phys. J. C 24 275 (2002)
16 May 2006 Joseph Kroll - UCSD Seminar 18
Experimental Steps for Measuring Bs Mixing
1. Extract B0s signal – decay mode must identify b-flavor at decay (TTT)
Examples:
2. Measure decay time (t) in B rest frame (L = distance travelled) (L00)
3. Determine b-flavor at production “flavor tagging” (TOF)
“unmixed” means production and decay flavor are the same
“mixed” means flavor at production opposite flavor at decay
Flavor tag quantified by dilution D = 1 – 2w, w = mistag probability
16 May 2006 Joseph Kroll - UCSD Seminar 19
Measuring Bs Mixing (cont.)
4. Measure asymmetry
these formulas assume perfect resolution for t
Asymmetry is conceptual: actually perform likelihood fit to expected“unmixed” and “mixed” distributions
16 May 2006 Joseph Kroll - UCSD Seminar 20
1st Evidence: Time Integrated Mixing:
is the time integrated mixing probability
In principle, a measurement of determines m - 1st Bd mixing measurements were measurements - d = 0.187 § 0.003 (PDG 2005) - this does not work for Bs: s = 0.5 (the limit as x!1)
Inclusive measurements at hadron colliders, LEP, SLC yield
1987
16 May 2006 Joseph Kroll - UCSD Seminar 21
Discovery of Neutral B Flavor Oscillations
Implications: mtop>50 GeV/c2
Top quark is heavier than expectedEllis, Hagelin, Rudaz, Phys. Lett. B 192, 201 (1987)
UA1 1987: Evidence for B0 & B0s mixing
Followed up by observationof B0 mixing by ARGUS:H. Albrecht et al., (25 June 87) Phys. Lett. B 192, 245 (1987)
16 May 2006 Joseph Kroll - UCSD Seminar 22
Measurement … In a Perfect World
what about detector effects?
“Rig
ht
Sig
n”
“Wro
ng
Sig
n”
16 May 2006 Joseph Kroll - UCSD Seminar 23
Realistic Effects
flavor tagging power,background
displacementresolution
momentumresolution
mis-tag rate 40% L) ~ 50 m p)/p = 5%
16 May 2006 Joseph Kroll - UCSD Seminar 25
B Physics at Hadron Machines
Strong interaction produces bb pairs
Example of lowest order (LO) s2
Example of next leading order (NLO) s3
NLO contribution comparable to LO contributionsee P. Nason, S. Dawson, R. K. EllisNucl. Phys. B273, p. 49 (1988)
called “flavor creation”
“gluon splitting”
“flavor excitation”
b pairs produced close in y
16 May 2006 Joseph Kroll - UCSD Seminar 26
B Physics at Hadron Machines (cont.)
b quarks then fragment to B hadrons
B factories running on Y(4S) only produce lightest B mesons
Hadron colliders (and e+e- colliders running above Y(4S)) produce other B’s
fragmentation is hard: B hadron gets large fraction of b quark E
Many unique B measurements at hadron colliders
e.g., ms, Bs rare decays, observation Bc, b lifetime
16 May 2006 Joseph Kroll - UCSD Seminar 27
B Production at Tevatron
The inclusive b cross-section is enormous: on the order of 100b
For L = 1031 cm-2s-1 (1032) £ L = 1kHz (10kHz)
Much of this not useful (trigger, acceptance, analysis selection criteria)The useful cross-section is order 10b
This is still well above production cross-section at B Factories, Z pole
The CDF Collaboration, D. Acosta et al., Phys. Rev. D65, 052005 (2002)
B factory rate: L = 1034 cm-2s-1 £ L = 10 Hz
£ L » 100 Hz
16 May 2006 Joseph Kroll - UCSD Seminar 28
Trigger Strategy for B Physics
Exploit the characteristics of B production and decay
1. B mass relatively large decay products have relatively high pT
require pT > 1.5 – 2.0 GeV/c or larger
2. B decay produces high pT leptons (electron and muon)
B! X, e X & B! J/ X, J/!+-
3. B’s have long decay distance trigger on displaced tracks
B0s
D-s +
-
K-
K+
d0
4. Combine lepton & displaced track
b large, butinelastic » 103 larger
16 May 2006 Joseph Kroll - UCSD Seminar 29
Silicon trackingDrift chamber
Lumi monitor
Hadronic Calorimetry
Muon systems
Iron shielding
Solenoid and TOF
ElectromagneticCalorimetry
CDF II
Front-end elec. & DAQ: 7.6 MHz clock (132 ns)
16 May 2006 Joseph Kroll - UCSD Seminar 30
Key Features of CDF for B Physics
• “Deadtime-less” trigger system– 3 level system with great flexibility
– First two levels have pipelines to reduce deadtime
– Silicon Vertex Tracker: trigger on displaced tracks at 2nd level
• Charged particle reconstruction – Drift Chamber and Silicon– excellent momentum resolution: R = 1.4m, B = 1.4T
– lots of redundancy for pattern recognition in busy environment
– excellent impact parameter resolution
• Particle identification– specific ionization in central drift chamber (dE/dx)
– Time of Flight measurement at R = 1.4 m
– electron & muon identification
16 May 2006 Joseph Kroll - UCSD Seminar 31
Silicon Vertex Tracker (SVT)
d0
Luciano Ristori, INFN-Pisa
16 May 2006 Joseph Kroll - UCSD Seminar 32
Example of Specific Trigger for B Physics
Hadronic Path – designed for B0s! D-
s+Level 1 - 2 XFT tracks with pT > 1.5 GeV - opposite charge - < 135o
- |pT1| + |pT2| > 5.5 GeV
Level 2 - confirm L1 requirements - both XFT tracks - SVT 2<15 - 120 m< |d0| <1mm - 2o < < 90o
- Decay length Lxy > 200m
Level 3 - confirm L2 with COT & SVX “offline” quality track reco.
At Level 3 usingtrigger criteria
16 May 2006 Joseph Kroll - UCSD Seminar 33
Semileptonic
B0s Decay Modes
•Fully reconstructed better decay time resolution•Lower statistics•Signal 3,700
•Not fully reconstructed poorer decay time resolution•Higher statistics•Signal 36,000
Hadronic
}•{
• }{
Majority of signal collected with displaced track trigger
16 May 2006 Joseph Kroll - UCSD Seminar 34
Example: Fully Reconstructed Signal
Cleanest decay sequence
Four charged particles infinal state: K+ K- + -
Also use 6 body modes:
Used for ms analysis
Signal: 1600This mode only
16 May 2006 Joseph Kroll - UCSD Seminar 35
1992: First Direct Evidence of Bs
Signal
Well knownbackground
poorly knownbackground(small)
Signal: 16.0 § 4.3 () 17.0 § 4.5 (K*0K)
D. Buskulic et al. (Aleph) Phys. Lett. B 294, 145 (1992)
also:P. Abreu et al. (Delphi) Phys. Lett. B 289, 199 (1992)P. D. Acton et al. (Opal) Phys. Lett. B 295, 357 (1992)
Sample: 450K hadronic Z
16 May 2006 Joseph Kroll - UCSD Seminar 36
The Same Signal at CDF Today
48,000
s
Purity: 75% from direct semileptonic B0s decay
16 May 2006 Joseph Kroll - UCSD Seminar 37
Lifetime Measurement
production vertex25m £ 25 m
Decay position
Decay time inB rest frame
B0s) = 1.538 § 0.040 ps
(statistical error only)PDG 2006: 1.466 § 0.059 ps
16 May 2006 Joseph Kroll - UCSD Seminar 38
Aside: Recent b Lifetime from CDF
Uses fully reconstructed b ! J/ instead of semileptonic: c+ l-l
Analysis led by UCSD post-docs M. Neubauer, E. Lipedes
Signal542 § 38
16 May 2006 Joseph Kroll - UCSD Seminar 39
Unexpected result: Lifetime much larger than previously measured
Precision of this measurementcomparable to World average
Problem with semileptonics? - sample composition - boost correction
Measured lifetimes with control modes(B0, B+) agree well with other exps.
Next step for CDF:use b!c
16 May 2006 Joseph Kroll - UCSD Seminar 40
Decay Time Resolution: Hadronic Decays
<t> = 86 £ 10-15 s¼ period for ms = 18 ps-1
Oscillation period for ms = 18 ps-1
Maximize sensitivity:use candidate specificdecay time resolution
Superior decay timeresolution gives CDFsensitivity at muchlarger values of ms
than previous experiments
16 May 2006 Joseph Kroll - UCSD Seminar 41
Measuring Resolution in Data
Use large prompt D meson sample CDF II, D. Acosta et al., PRL 91, 241804 (2003)
Real prompt D+ from interaction point
pair with random trackfrom interaction point
Compare reconstructed decay point to interaction point
16 May 2006 Joseph Kroll - UCSD Seminar 42
Semileptonics: Correction for Missing Momentum
Reconstructed quantity Correction Factor (MC) Decay Time
16 May 2006 Joseph Kroll - UCSD Seminar 43
B Flavor Tagging
We quantify performance with efficiency and dilution D
= fraction of signal with flavor tag
D = 1-2w, w = probability that tag is incorrect (mistag)
Statistical error A on asymmetry A (N is number of signal)
statistical error scales with D2
16 May 2006 Joseph Kroll - UCSD Seminar 44
Two Types of Flavor Tags
Opposite side
Same side Based on fragmentation tracks or B**
+ Applicable to both B0 and B0s
− other b not always in the acceptance
− Results for B+ and B0 not applicable to B0s
+ better acceptance for frag. tracks than opp. side b
Reminder: for limit on ms must know D
Produce bb pairs: find 2nd b, determine flavor,infer flavor of 1st b
Calibrate on B+, B0 data
Must rely onMC for D
RequiresExtensivecomparisondata and MC
16 May 2006 Joseph Kroll - UCSD Seminar 45
Types of Opposite Side Flavor Tags
Lepton tags
Jet charge tag
Kaon tag
mistags from
jet from b (b) has negative (positive) charge on average
low high D
high low D
Largest D2 @ B factoriesNot used in present analysis
TOF
16 May 2006 Joseph Kroll - UCSD Seminar 46
Calibrate with Large Statistics Samples of B+ & B0
Example: semileptonic signals
Results:D2 = 1.54 § 0.05[ md = 0.509 § 0.010 (stat) § 0.016 (syst)]
Hadronic signals:B+ (D0+) = 26,000B0 (D-+) = 22,000
16 May 2006 Joseph Kroll - UCSD Seminar 47
Increase Tagging Power with “Binning”
Example: lepton tags
pt
rel
16 May 2006 Joseph Kroll - UCSD Seminar 48
Performance of OST’s is Poor – Why?
Part of the problem is acceptance of opposite side b
Generator Level study from K. Lannon, Ph. D. Dissertation, Illinois, 2003
Also opposite-sideB hadron can mix:D = 1 – 2 = 0.76
16 May 2006 Joseph Kroll - UCSD Seminar 49
Same Side Flavor Tags
Based on correlation betweencharge of fragmentation particleand flavor of b in B meson
TOF Critical(dE/dx too)
Decay of P-wave mesonsB** also contributes to B0, B+
(not B0s)
Expected correlationsdifferent for B+, B0, B0
s
Ali & Barriero, Z. Phys. C 30, 365 (1986)Gronau, Nippe, Rosner PRD 47, 1988 (1993)Gronau & Rosner, PRD 49, 254 (1994)
16 May 2006 Joseph Kroll - UCSD Seminar 50
Time of Flight Detector (TOF)
• 216 Scintillator bars, 2.8 m long, 4 £ 4 cm2
• located @ R=140 cm• read out both ends with fine mesh PMT (operates in 1.4 T B field – gain down ~ 400)• measured resolution TOF=100 - 130 ps• (limited by photostatistics)
Kaon ID for B physics
Measured quantities:s = distance travelledt = time of flightp = momentum
Derived quantities:v = s/tm = p/v
16 May 2006 Joseph Kroll - UCSD Seminar 51
Kaons Produced in Vicinity of B’s
Larger fraction of Kaons near B0s compared to B0, B+, as expected
Ph. D. Thesis, Denys Usynin
16 May 2006 Joseph Kroll - UCSD Seminar 52
Compare PerformanceData and Simulation
Check prediction for kaon tag on B+, B0
Good agreement between data & MCSystematic based on comparisons
K
K
16 May 2006 Joseph Kroll - UCSD Seminar 53
Flavor Tagging Summary
Same-side kaon tag increases effective statistics £ 3 – 4
D2 Hadronic (%) D2 Semileptonic (%)
Muon 0.48 § 0.06 (stat) 0.62§ 0.03 (stat)
Electron 0.09 § 0.03 (stat) 0.10 § 0.01 (stat)
JQ/Vertex 0.30 § 0.04 (stat) 0.27 § 0.02 (stat)
JQ/Prob. 0.46 § 0.05 (stat) 0.34 § 0.02 (stat)
JQ/High pT 0.14 § 0.03 (stat) 0.11 § 0.01 (stat)
Total OST 1.47 § 0.10 (stat) 1.44 § 0.04 (stat)
SSKT 3.42 § 0.98 (syst) 4.00 § 1.02 (syst)
16 May 2006 Joseph Kroll - UCSD Seminar 54
Combining it allunbinned maximum likelihood fit
=
Before fitting for ms: test whole procedure by on B
d mixing
fix ms
integrate over true decay length ct and true k-factorget A(m
s)
k k k k k k=sig,bg
sig
for each event:
pdg
16 May 2006 Joseph Kroll - UCSD Seminar 59
Measured Value of ms
- log(Likelihood) Hypothesis of A=1 compared to A= 0
16 May 2006 Joseph Kroll - UCSD Seminar 60
Significance: Probability of Fluctuation
Probability ofrandom fluctuationdetermined from data
Probability = 0.5%(2.8)
Below threshold toclaim “observation”Continue improvinganalysis to increasepotential significance
16 May 2006 Joseph Kroll - UCSD Seminar 61
Determination of |Vtd/Vts|
Previous best result: D. Mohapatra et al.(Belle Collaboration)hep-ex/0506079
CDF
16 May 2006 Joseph Kroll - UCSD Seminar 62
Summary of CDF Results on B0s Mixing
First direct measurement of ms
Precision: 2.4% Probability of random fluctuation: 0.5%
Most precise measurement of |Vtd/Vts|
All results are preliminary
( 2.76 THz, 0.011 eV)
16 May 2006 Joseph Kroll - UCSD Seminar 63
Perspective and Outlook
• Mixing in Neutral Kaons – led to discovery of CP violation
– necessary condition for matter antimatter asymmetry in Universe.
• Mixing in B0 mesons– led to possibility of observing CP Violation in another system
– validated that SM mechanism for CP Violation is dominant mechanism.
• Discovery of B0 mixing pointed to a much heavier top quark: – Results on B0
s mixing could point to heavier new particles or exclude them
• Establishing B0s mixing sets the stage for the next step:
– measuring CP asymmetries in B0s decays
– could produce unambiguous signals of new physics.
• We are coming to the end of a long story: – a 20 year quest to measure ms
– a tremendous technical achievement
– allows precise measurement of fundamental parameters
16 May 2006 Joseph Kroll - UCSD Seminar 65
Systematic Uncertainties
• related to absolute value of amplitude, relevant only when setting limits – cancel in A/A, folded in in confidence calculation for observation– systematic uncertainties are very small compared to statistical
Hadronic Semileptonic
16 May 2006 Joseph Kroll - UCSD Seminar 66
Systematic Uncertainties on ms
• systematic uncertainties from fit model evaluated on toy Monte Carlo
• have negligible impact
• relevant systematic unc. from lifetime scale
Syst. Unc
SVX Alignment 0.04 ps-1
Track Fit Bias 0.05 ps-1
PV bias from tagging 0.02 ps-1
All Other Sys < 0.01ps-1
Total 0.07 ps-1
All relevant systematic uncertainties are common between hadronic and semileptonic samples
16 May 2006 Joseph Kroll - UCSD Seminar 73
The Unitarity Triangles
V is unitarity
geometric representation: triangle in complex plane
Im
ReVi1V*
k1
Vi2V*k2Vi3V*
k3
There are 6 triangles
Kaon UT
Beauty UT
flat
n.b. these triangles arerescaled by one of the sides
i = 1 is previous page
16 May 2006 Joseph Kroll - UCSD Seminar 74
The Beauty Unitary Triangle
of Chau & Keungparametrization is
16 May 2006 Joseph Kroll - UCSD Seminar 75
http://www.slac.stanford.edu/xorg/ckmfitter/ckm_intro.htmlJ. Charles et al., Eur. Phys. J. C41, p. 1 (2005); ibid, hep-ph/0406184
Results from CKM Fitterwith recent CDF ms result