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
S.Giagu - ICHEP 2006, MoscowS.Giagu - ICHEP 2006, Moscow
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
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• 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
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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
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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
S.Giagu - ICHEP 2006, MoscowS.Giagu - ICHEP 2006, Moscow
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Random SlidesRandom Slides
S.Giagu - ICHEP 2006, MoscowS.Giagu - ICHEP 2006, Moscow
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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
S.Giagu - ICHEP 2006, MoscowS.Giagu - ICHEP 2006, Moscow
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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
S.Giagu - ICHEP 2006, MoscowS.Giagu - ICHEP 2006, Moscow
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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
S.Giagu - ICHEP 2006, MoscowS.Giagu - ICHEP 2006, Moscow
2020Semileptonics: Semileptonics: Correction for Missing MomentumCorrection for Missing Momentum
Reconstructed quantity Correction Factor (MC) Decay Time
oscillation period @ ms=18 ps-1
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PIDPID
K
Separartion Power Combined PID: TOF + dE/dx
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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
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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
S.Giagu - ICHEP 2006, MoscowS.Giagu - ICHEP 2006, Moscow
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Amplitude Scan: Hadronic decaysAmplitude Scan: Hadronic decays
data period 1 data period 2
data periodo 3
S.Giagu - ICHEP 2006, MoscowS.Giagu - ICHEP 2006, Moscow
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Amplitude Scan: Semileptonic decaysAmplitude Scan: Semileptonic decays
data period 1 data period 2
data period 3
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• 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
S.Giagu - ICHEP 2006, MoscowS.Giagu - ICHEP 2006, Moscow
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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%)
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Negative log likelihood ratioNegative log likelihood ratio