Evidence for B s Mixing and measurement of m s at CDF

XXXIII International Conference On High Energy Physics, 28 July 2006 - MoscowXXXIII International Conference On High Energy Physics, 28 July 2006 - Moscow

Evidence for BEvidence for Bss Mixing and Mixing and

measurement of measurement of mmss at CDF at CDFS. Giagu and CDF Collaboration

University of Rome “La Sapienza”

INFN Sezione di Roma 1

S.Giagu - ICHEP 2006, MoscowS.Giagu - ICHEP 2006, Moscow

22

OutlineOutline

• Introduction

• Search for Bs-Bs oscillations in CDF

• Impact on the overall UT fit

• Work in progress and Outlook

CDF Collaboration, “Measurement of the Bs-Bs Oscillation Frequency”hep-ex/0606027 – accepted by Physical Review Letters


33

B Meson Flavor OscillationsB Meson Flavor Oscillations

s, s,

s, s,In the SM generated via F=2 2nd order weak interactions, dominated by the exchange of a top quark

2*22

222

||6

)(tbtqBBB

tWFq VVBfm

xSmGm

qqq

Form factors and B-parameters from Lattice calculations are

known at ~15% level

Mixing involves CKM elements,measuring Δmq constraints

the unitarity triangle New exotic particles may

run in the loop mixing sensitive to NP

Neutral B mesons can spontaneously transform in the corresponding antiparticle

44

many theoretical uncertainties cancel in the ratio

• • |Vts|/|Vtd| can be determined at ~4%

mmss and the side of UT and the side of UTmd f2

BBB [(1-)2+2] circle centered in ()=(1,0)

f2BBB known at 15% from LQCD

2

2

22

2

2

2

td

ts

Bd

Bs

td

ts

BdBd

BsBs

Bd

Bs

d

s

V

V

m

m

V

V

Bf

Bf

m

m

m

m

047.0035.0210.1

(hep-lat/0510113)

Experimental challenge:|Vts| >> |Vtd| ms >> md needs to resolve > 2.3 THz oscillations

Status of ms measurements: LEP/SLD/CDF-I: ms > 14.4 ps-1 @ 95% CL HFAG Average for PDG 2006

D0 Run-II: ms [17,21] ps-1 @ 90% CL Phys. Rev. Lett. 97, 021802 (2006)

55

1. Collect as many Bs as possible• Tevatron, Trigger (SVT)

2. Extract Signal • Bs flavor at decay inferred from decay products

3. Measure proper decay time of the Bs meson• L00, per event primary vertex, candidate specific decay time resolution

4. Determine Bs flavor at production (flavor tagging) • PID (TOF, dE/dx) • Flavor tag quantified by Dilution: D=1-2w, w = mistag probability

5. Measure asymmetry between unmixed and mixed events• In practice: perform likelihood fit to expected unmixed and mixed distributions

Road map to Road map to mmss measurement measurementvertexing (same) side

“opposite” side

e,Jet

14

4

3

2

BS

SeSD tsm

A

22

2

2

1

tmDPP

PPtA

nomixmix

mixnomix

cos)(5

66

Event Selection: Fully Hadronic BEvent Selection: Fully Hadronic Bss

used in this analysis

Decay mode Events

BsDs () 1600

Bs Ds (K* K) 800

Bs Ds (3) 600

Bs Ds3 ( ) 400

Bs Ds3 (K*K) 200

Total 3600

Cleanest decay mode:BsDs[] [KK]

• Bs momentum completely reconstructed• Excellent decay time resolution, good S/N• Small BR low statistic• Good sensitivity at high values of ms

77

• Minv(l+Ds) helps reject BG• BG Sources:

• Ds + fake lepton from PV• Bs,dDsDX (DslX)• cc

Event Selection: Semileptonic BEvent Selection: Semileptonic Bss

• Missing momentum ()• Poorer decay time resolution• Large BR high statistic• Good sensitivity at low values of ms

48000 l+Ds candidates, 75% are from Bs decay

Ds Mass

l+Ds Mass

,, 0* KKDs

88

Proper decay time reconstructionProper decay time reconstruction

Bp

BmL

Lct

Txy

)(

Detector length scale and proper treatment of

detector/selection biases controlled by performing lifetime measurements

Decay CDF [ps]

(stat. only)

PDG 06 [ps]

B0 D-+ 1.508 0.017 1.530 0.009

B- D0- 1.638 0.017 1.638 0.011

Bs Ds() 1.538 0.040 1.466 0.059

RUN 304720 EVENT 109026PV

D decay B

decayLxy

99

• Finite resolution dilutes the amplitude of mixing asymmetry:

• Sensitivity maximized by making full use of all available information:– layer-00, candidate specific primary vertex and decay time resolution

• Resolution measured in data in large samples of prompt D meson decays• D+ combined with prompt tracks to mimic B0-like topologies

Decay time resolutionDecay time resolution

oscillation period @ ms=18 ps-1

2

2

)( t

t

m

eD

4 sampling per cycle

Hadronic decays gives CDF sensitivity at much larger values of ms than previous experiments

M(lDs) > 3.3 GeV/c

first bin of ct

1010

Flavor Tagging PerformancesFlavor Tagging PerformancesTwo types of flavor tags used in CDF

– OST: produce bb pairs: find 2nd b, determine flavor, infer flavor of 1st b• calibrated on large samples of B0 ad B+ decays

– SST: use charge correlation between the b flavor and the leading product of b hadronization

• performances (D) evaluated in MC, after extensive comparison data VS MC

Same-side kaon tag increases effective statistics ~4

εD2 Hadronic (%) εD2 Semileptonic (%)

Muon 0.48 0.06 (stat) 0.62 0.03 (stat)

Electron 0.09 0.03 (stat) 0.10 0.01 (stat)

JQ/SecVtx 0.30 0.04 (stat) 0.27 0.02 (stat)

JQ/Displ’d trk 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 0.96 (syst) 4.00 1.12 (syst)

1111

ct [cm]K-factorisolation

St

D

pT [GeV/c]

LikelihoodLikelihood

Amplitude method(*): scan ms space: fix ms fit for A:A consistent with 1 mixing detected at the given ms

=

k k k k k k=sig,bg

sig

for each event:

pdg

Procedure checked on B0 by fitting for md

Courtesy of J.Kroll

(*) H-G.Moser, A.Roussarie,NIM A384 (1997)

Data fitted with an unbinned likelihood function to the expected unmixed and mixed distributions

1212

ResultsResultsLikelihood ratio:

A=1 VS A=0 hypothesis

P-value = 0.2% (>3)

.)(.).(208.0

.)(07.0.31.17

008.0006.0

001.0002.0

133.018.0

theosyststatV

V

pssyststatm

ts

td

s

small systematic uncertaintydominated by knowledge of the absolute scale of the decay-time measurement

A/A (17.3 ps-1) = 3.7

hep-ex/0606027 – accepted by PR

L

Inputs from PDG 06 and ξ=1.210 (hep-lat/0510113)+0.047

-0.035

1313Impact on the overall UT FitImpact on the overall UT Fit

sB

SMsB

sss

i

BSMB

fullB eCAA

2

025.0397.0

034.0197.0

UTfit Coll.: hep-ph/0605213

and Vincenzo’s talk

Similar results from CKMfitter group: http://ckmfitter.in2p3.fr and Stephane T’Jampens talk

SM fit SM+NP fit

CBs = 0.97 ± 0.27

025.0316.0

055.0203.0

angles onlyno angles

CDFmeasurement

CKM fit (no Δms)(21.5 ± 2.6) ps-1

http://ckmfitter.in2p3.fr/

1414

CDF Run II Preliminary L=1 fb-1

Work in progressWork in progress• Collecting new integrated luminosity• Squeezing maximum information from the data we already have:

1. Systematic use of Neural Networks in signal extraction:

• use decays modes previously discarded cause high BG

• more signal in already used modes

2. Use partially reconstructed BsDs*/K and Ds:• large BR• good momentum resolution

3. Improve Flavor taggers:• OST: +15% D2

• NN to combine OS taggers• OSKT

• SSKT: ~+10% D2

• better use of combined PID and kinematics

BsDs+-+ (Ds +--)

NBs = 220

BsDs+ (Ds-)

1515

Summary and OutlookSummary and Outlook• CDF finds evidence for flavor oscillations in the Bs sector• Probability of a random fluctuation 0.2%• Measurement of the mixing frequency with <2% precision • Most precise measurement of |Vtd/Vts|

.)(.).(208.0

.)(07.0.31.17

008.0006.0

001.0002.0

133.018.0

theosyststatV

V

pssyststatm

ts

td

s

An important and precise experimental input for the overall test of the SM and the end of a very long effort to measure ms

… but not the end of the CDF B-physics programme


1616

Random SlidesRandom Slides


1717

Data SampleData SampleBs candidates collected by SVT trigger

• TTT: two displaced tracks• L+SVT: lepton + displaced track(s)

Typical inst. Luminosity 1032 cm-2 s-1

~1.4 fb-1 collected by CDF~1 fb-1 (good runs) used in this analysis

PV

d0 = impact parameter

Decay Vertex

used in this analysis


1818Other results on Other results on mmss

LEP, SLD, CDF-I

1st direct single experiment upper boundms [17,21] ps-1 @ 90% CL

Null hypothesis probability: 5%

D0 Coll.: Phys. Rev. Lett. 97, 021802 (2006)

Recent from D0 collaboration

ms > 14.4 ps-1@ 95% CL

HFAG Average for PDG 2006


1919

Example of Specific Trigger for B PhysicsExample of Specific Trigger for B Physics

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.

PV

d0 = impact parameter

Decay Vertex


2020Semileptonics: Semileptonics: Correction for Missing MomentumCorrection for Missing Momentum

Reconstructed quantity Correction Factor (MC) Decay Time

oscillation period @ ms=18 ps-1


2121

PIDPID

K

Separartion Power Combined PID: TOF + dE/dx


2222

Systematic UncertaintiesSystematic 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


2323

Incertezze sistematiche su Incertezze sistematiche su mmss

• systematic uncertainties from fit model evaluated on toy Monte Carlo

• have negligible impact

• only relevant systematic: knowledge of lifetime scale

Syst. Unc

All other syst. < 0.01ps-1

SVX Alignment 0.04 ps-1

Track Fit Bias 0.05 ps-1

PV bias from tagging

0.02 ps-1

Total 0.07 ps-1

All relevant systematic uncertainties are common between hadronic and semileptonic samples


2424

Amplitude Scan: Hadronic decaysAmplitude Scan: Hadronic decays

data period 1 data period 2

data periodo 3


2525

Amplitude Scan: Semileptonic decaysAmplitude Scan: Semileptonic decays

data period 1 data period 2

data period 3


2626

• Exploit peculiarity of each tagger to minimize mistag probability • example: soft muon tag

from c decay

Parameterization of the tagging decisionParameterization of the tagging decision

pt

rel

jet axisfrom b decay


2727

SSKT CalibrationSSKT Calibration• Dilution measured in high statistic samples of light B meson decays and

compared with the results of simulation

Dominant source of systematic uncertainty: Data/MC agreement ~O(14%)


2828

Negative log likelihood ratioNegative log likelihood ratio

Evidence for B s Mixing and measurement of m s at CDF

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