Transcript Slide 1
The Observation of B
0 s
– B
0 s
Oscillations
The CDF Collaboration Joseph Kroll University of Pennsylvania 1 st St. Ocean City, NJ, 7 Feb. 2003, H 2 O 35 0 F DPF/JPS Waikiki, HI 2 Nov 2006
Northern New Jersey, Saturday, 28 Oct. 2006
2 Nov 2006
photos: Alex Riviera – see www.localswell.com
J. Kroll (Penn) 2
Today’s Results Made Possible by Excellent Tevatron Performance Tevatron has delivered 2 fb -1 CDF has collected 1.6 fb -1 this analysis 1.0 fb -1 Today’s results Reported in 2 papers by A. Abulencia et al. (CDF collaboration):
PRL,
97
, 021802 (2006) hep-ex/0609040, accepted by PRL 2 Nov 2006 3
Two-State Quantum Mechanical System Common decay modes
!
2-state QM system Eigenstates of 2-state system (neglecting CP violation) “Light” (CP-even) mass & width “Heavy” (CP-odd) Start (t=0) with particle
2 Nov 2006 J. Kroll (Penn)
Antiparticle exists at time t!
4
Importance of Neutral B Meson Oscillations Cabibbo-Kobayashi-Maskawa
Matrix
fundamental parameters that must be measured weak mass Oscillation frequencies (
m d ,
m s ) determine poorly known V td , V ts |V td /V ts | measures one side of Unitary Triangle see Z. Ligeti Plenary New particles in loops alter expectations
test Standard EWK Model 2 Nov 2006 SM prediction:
m s
»
18ps -1 5
All factors well known except from Lattice QCD calculations (Okamoto, hep-lat/0510113) Limits precision on V td , V ts to ~ 10% Theoretical uncertainties reduced in ratio: Plenary talk J. Shigemitsu ~ 4% PDG 2006 2 Nov 2006 J. Kroll (Penn) 6
Some History Important prehistory: 1983: long B hadron lifetime 1986: 1 st evidence of B mixing from UA1 2006 APS Panofsky Prize
C. Albajar
et al.,
PLB,
186
, 247 (1987)
1987: Definitive observation of B 0 mixing by ARGUS - indicates UA1 must be B s , heavy top (>50 GeV) - 1989 confirmed by CLEO
H. Albrecht
et al.,
PLB,
192
, 245 (1987)
1990’s: LEP, SLC, Tevatron - time-integrated meas. establishes B s - measure time-dependent B 0 mixes oscillations - lower limits on B s oscillation frequency 2000: B factories improve precision of B 0 oscillation frequency 2006: Tevatron discovers B s oscillations - two-sided 90% CL limit by DØ
V. M. Abazov
et al.,
PRL,
97
, 021802 (2006)
This talk - 1 st measurement of oscillation frequency by CDF - definitive observation of oscillation signal by CDF
A. Abulencia
et al.,
PRL,
97
, 021802 (2006) & hep-ex/0609040, acc. by PRL 2 Nov 2006 J. Kroll (Penn) 7
How Do We Measure Oscillation Frequency?
Measure asymmetry A as a function of proper decay time t “unmixed”: particle decays as particle “mixed”: particle decays as antiparticle For a fixed value of
m s , data should yield Amplitude “A” is 1 @ true value of
m s Amplitude “A” is 0 otherwise Amplitude method:
H-G. Moser, A. Roussarie, NIM
A384
p. 491 (1997)
Units: [
m] =
~
ps -1
, ~
=1 then
m in ps -1 . Multiply by 6.582
£
10 -4 to convert to eV 2 Nov 2006 J. Kroll (Penn) 8
Start 2006: Published Results on
m s source: http://www.slac.stanford.edu/xorg/hfag/osc/PDG_2006/index.html
Results from LEP, SLD, CDF I >3.4 cycles per lifetime
m s > 14.4 ps -1 95% CL 1 0
2 Nov 2006
Amplitude @
m s = 15 ps -1 Average 0.48
§
0.43
J. Kroll (Penn)
15 Frequency
m s (ps -1 )
9
April 2006: Result from the CDF Collaboration
A. Abulencia
et al
., Phys. Rev. Lett., 97 , 062003 (2006)
Probability that random fluctuations mimic this signal is 0.2% (3
) Assuming signal hypothesis: measure
m s likelihood ratio Since then goal has been to observe signal with > 5
significance
2 Nov 2006 J. Kroll (Penn) 10
Ingredients in Measuring Oscillations opposite-side K – jet charge 2 nd B tags production flavor Dilution D = 1 – 2w w = mistag probability
= efficiency
D 2 = effective tagging power
2 Nov 2006 J. Kroll (Penn)
Decay mode tags b flavor at decay Proper decay time from displacement (L) and momentum (p)
11
Key Experimental Issues Uncertainty on Amplitude Signal size Signal to Background Production flavor Tag performance Proper time Resolution
2 Nov 2006
CDF’s strengths efficient tracking, displaced track trigger excellent mass resolution Particle ID: TOF, dE/dx lepton id, Kaon id with TOF Silicon on beampipe (Layer 00)
J. Kroll (Penn)
Fully reconstructed signal crucial
12
Improvements that led to Observation
• • • •
Same data set (1 fb -1 ) Proper decay time resolution unchanged Signal selection
– – –
Neural network selection for hadronic modes add partially reconstructed hadronic decays use particle id (TOF, dE/dx) (separate kaons from pions)
•
looser kinematic criteria possible due to lower background
–
additional trigger selection criteria allowed Production Flavor tag
–
opposite-side tags combined using neural network
•
also added opposite-side kaon tag
–
neural network combines kinematics and PID in same-side K tag
2 Nov 2006 J. Kroll (Penn) 13
Example: Fully Reconstructed Signal Cleanest decay sequence Add partially reconstructed decays: Also use 6 body modes: Hadronic signal increased from 3600 to 8700
2 Nov 2006 J. Kroll (Penn) 14
Semileptonic Signals Semileptonic signal increased from 37000 to 61500
2 Nov 2006 J. Kroll (Penn) 15
Decay Time Resolution: Hadronic Decays Maximize sensitivity: use candidate specific decay time resolution <
t > = 86
£
¼ period for
m s = 18 ps -1 10 -15 s Superior decay time resolution gives CDF sensitivity at much larger values of
m s than previous experiments Oscillation period for
m s = 18 ps -1
2 Nov 2006 J. Kroll (Penn) 16
Semileptonics: Correction for Missing Momentum Reconstructed quantity Correction Factor (MC) Decay Time T = 2
/
m s Reconstructed momentum fraction
2 Nov 2006 J. Kroll (Penn)
proper decay time (ps)
17
2 Nov 2006
Same Side Flavor Tags Charge of K tags flavor of B s at production Need particle id TOF Critical (dE/dx too) Our most powerful flavor tag:
D 2 = 4-5% (Opposite-side tags:
D 2 = 1.8%)
J. Kroll (Penn) 18
Results: Amplitude Scan A/
A = 6.1
Sensitivity 31.3 ps -1 Hadronic & semileptonic decays combined 2 Nov 2006 J. Kroll (Penn) 19
Measured Value of
m s
- log(Likelihood)
Hypothesis of A=1 compared to A=0 2 Nov 2006 J. Kroll (Penn) 20
2 Nov 2006 Significance: Probability of Fluctuation -17.26
J. Kroll (Penn) Probability of random fluctuation determined from data 28 of 350 million random trials have L < -17.26
Probability = 8
£
10
-
8 (5.4
) Have exceeded standard threshold to claim observation 21
Asymmetry (Oscillations) in Time Domain 2 Nov 2006 Period 0.35 ps Aside: for B 0 Period = 12.6 ps J. Kroll (Penn) 22
Summary of CDF Results on B 0 s Mixing A. Abulencia et al., hep-ex/0609040, accepted by Phys. Rev. Lett.
Observation of B s Oscillations and precise measurement of
m s Precision: 0.7% Probability random fluctuation mimics signal: 8
£
10 -8 ( 2.83 THz, 0.012 eV) Most precise measurement of |V td /V ts | 2 Nov 2006 20 year quest has come to a conclusion J. Kroll (Penn) 23