measurement of the b 0 s oscillation frequency: matter-antimatter transformations at 3 thz prof....

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


Tevatron Performance

Typical L = 1032 cm-2 s-1

∫Ldt = 1.5 fb-1

This analysis uses full data set: 1 fb-1


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


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)


Neutral Meson Mixing (Continued)


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


Until Two Months Ago…

at least 3.5 cycles per lifetime


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


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)


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.


Recent Result from the CDF Collaboration

Probability“Signal” israndom fluctuationis 0.5%


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


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


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


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


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)


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


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


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


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)


Measurement … In a Perfect World

what about detector effects?

“Rig

ht

Sig

n”

“Wro

ng

Sig

n”


Realistic Effects

flavor tagging power,background

displacementresolution

momentumresolution

mis-tag rate 40% L) ~ 50 m p)/p = 5%


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


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


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


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


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)


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


Silicon Vertex Tracker (SVT)

d0

Luciano Ristori, INFN-Pisa


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


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


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


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


The Same Signal at CDF Today

48,000

s

Purity: 75% from direct semileptonic B0s decay


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


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


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


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


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


Semileptonics: Correction for Missing Momentum

Reconstructed quantity Correction Factor (MC) Decay Time


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


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


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


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


Increase Tagging Power with “Binning”

Example: lepton tags

pt

rel


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


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)


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


Kaons Produced in Vicinity of B’s

Larger fraction of Kaons near B0s compared to B0, B+, as expected

Ph. D. Thesis, Denys Usynin


Compare PerformanceData and Simulation

Check prediction for kaon tag on B+, B0

Good agreement between data & MCSystematic based on comparisons

K

K


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)


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


Amplitude Scan: Hadronic Decays


Amplitude Scan: Semileptonic Decays


Combined Amplitude Scan


Results: Amplitude Scan

A/A = 3.5 Sensitivity25.3 ps-1


Measured Value of ms

- log(Likelihood) Hypothesis of A=1 compared to A= 0


Significance: Probability of Fluctuation

Probability ofrandom fluctuationdetermined from data

Probability = 0.5%(2.8)

Below threshold toclaim “observation”Continue improvinganalysis to increasepotential significance


Determination of |Vtd/Vts|

Previous best result: D. Mohapatra et al.(Belle Collaboration)hep-ex/0506079

CDF


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)


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


Additional Slides for Reference


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


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


Amplitude Scan: Hadronic Period 1

Bs ! Ds / Ds



Bs ! Ds / Ds


Semileptonic Scan: Period 1


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


The Beauty Unitary Triangle

of Chau & Keungparametrization is


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


http://www.slac.stanford.edu/xorg/ckmfitter/ckm_intro.htmlJ. Charles et al., Eur. Phys. J. C41, p. 1 (2005); ibid, hep-ph/0406184

measurement of the b 0 s oscillation frequency: matter-antimatter transformations at 3 thz prof....

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