babar: risultati recenti e prospettive fernando ferroni universita’ di roma “la sapienza”...
TRANSCRIPT
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BaBar: Risultati recenti e prospettive
Fernando FerroniUniversita’ di Roma “La Sapienza” & I.N.F.N. Roma1
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BABARBABAR Collaboration Collaboration
China [1/5]Inst. of High Energy Physics, Beijing
Germany [3/23]Ruhr U BochumTU DresdenU Rostock
France [5/51]LAPP, AnnecyLAL OrsayLPNHE des Universités Paris 6/7Ecole PolytechniqueCEA, DAPNIA, CE-Saclay
United Kingdom [10/71]U of BirminghamU of BristolBrunel UniversityU of EdinburghU of LiverpoolImperial CollegeQueen Mary & Westfield CollegeRoyal Holloway, University of LondonU of ManchesterRutherford Appleton Laboratory
Italy [12/89]INFN BariINFN FerraraINFN Frascati INFN GenovaINFN MilanoINFN Napoli
Canada [4/15]U of British ColumbiaMcGill UU de MontréalU of Victoria
INFN PadovaINFN PaviaINFN PisaINFN Roma INFN TorinoINFN Trieste
Norway [1/2]U of Bergen
Russia [1/7]Budker Inst., Novosibirsk
USA [36/253]Caltech, PasadenaUC, IrvineUC, Los AngelesUC, San DiegoUC, Santa BarbaraUC, Santa CruzU of CincinnatiU of ColoradoColorado StateElon CollegeFlorida A&MU of IowaIowa State ULBNLLLNLU of LouisvilleU of MarylandU of MassachusetsMITU of MississippiMount Holyoke CollegeNorthern Kentucky UU of Notre DameORNL/Y-12U of OregonU of PennsylvaniaPrairie View A&MPrincetonSLACU of South CarolinaStanford UU of TennesseeU of Texas at DallasVanderbiltU of WisconsinYale U
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PEPII
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BaBar
SVT: z resolution ~70 micronsTracking: (pT)/pT = 0.13% pT 0.45%
DIRC: K- separation > 3.4 for P<3.5GeVEMC: E/E = 1.33%E-1/4 2.1%
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PEPII & BaBar
Physics Motivation: CP in B
Results:
Mixing & Lifetimes
sin 2b
Rare decays
Perspectives
Outline
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Origin of masses
Remote energy scale (Gravity)
CP Violation and our universe
Particle physics in new millennium
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Needed for matter-antimatter asymmetry
Standard Model CP-Violation (CKM)
thought to be insufficient to explain
universe asymmetry
37 years of intense experimental and
theoretical effort of background
Why CP violation ?
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CP Violation in SM
SM with three generation accommodatesCP violation through phase in CKM matrix
SM predicts a variety of CP violatingasymmetries in the B-system, some ofwhich can be cleanly interpreted interms of CKM matrix elements
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The Triangle
Bd D*
CP
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The Unitarity Triangle
The sides are determined by measurements ofthe magnitudes of CKM elements
CP asymmetries to fCP measures angles oftriangle, in some cases with little or no theoretical ambiguities
Goal of the B-physics program is tooverconstrain triangle, critically test CKMstructure of SM
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CP measurement
Reconstruct a CP eigenstate
Flavour tag with other B
Measure z ---> t = tCP - ttag
Fit time evolution
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B decay topology
c/2
c
250
=0.56
Y(4S)
Measurementof z
Reconstruction of the CP eigenstate
Tag of the other B
B0
B0
Lifetime,Mixing,
CP
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Smearing of an asimmetry
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PEPII-BaBar Operations
Design: 3.0 nb-1/s 135 pb-1/d ~0.80 fb-1/w ~ 3.3 fb-1/m
Achieved : 3.28 184 1.03 3.8
Data from 1999-2000 run• 20.7 fb-1 on-resonanceN((4S)) = 22.74 ±0.36 million• 2.6 fb-1 off-resonance
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PEPII-BaBar Operations
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Interaction region
Permanent magnets inside the support tube
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J/ Ks Event at BaBar
B0J/ Ks
J/->
Ks ->
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DIRC: Detection of Internally Reflected Cherenkov light
144 quartz bars (1.7 cm thick)10752 PMT in 6 m3 of purified water
Total space: 8 cm (0.14 X0)
e-
e+
New design for a Cherenkov detector
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K/ separation
Pion-Kaon separation at high momenta
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Mixing and sin2
Common wrong tag fractions and resolution functionparameters can be determined by a large Bflav sample
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Bflav sample
B0 D(*) -, D(*) -, D(*) -a1+, J/K*0
B D(*)0, J/K-, SK-
E=E*B - s /2 ~15 MeVmES= (s/4 - p*B
2) ~3MeV
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B reconstruction
*beam
* EEE B −=
Y(4S) -> BB
mES
signalmES sideband
energy difference
E sideband
2*2beamES
*BpEm −=
energy substituted (constrained) mass
one more pion...
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Bflav sample
6368 evtsPurity ~ 84%
7645 evtsPurity ~ 86%
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Run I Data Set
23M BB pairs recorded
3 fb-1 of continuum
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CP sample (Ks modes)
J/ Ks (+-)259 (purity 98%)
J/ Ks (00)50 (84%)
(2s)Ks (+-)55 (97%)
J/ l l
(2S) l l J/
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Final CP sample of K0s modes
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CP sample (KL modes)
Reconstructed with EMC
Reconstructed with IFR
92 signalPurity =40%
108 signalPurity =51%
Neutral clusters not consistent with noise, or 0 are considered as KL candidates
B mass constraint is imposed
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Tagging
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Vertexing
Use per event error and parametrize the resolution function with scaling factors
tz/< c>
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Lifetimes
B0 = 1.546 0.032 0.022 psB+ = 1.673 0.032 0.022 psB+/ B0 = 1.082 0.026 0.011
PDG
1.55±0.03 1.65±0.03 1.06±0.03
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Mixing adronico/leptonico
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Mixing : compilation
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Fitting procedure
Mixing and sin2b measurements are done with the same strategy: do a global fit to all the events that can carry information
Mixing : tagged flavour eigenstates
sin2 : tagged flavour and CP eigenstates
Extract as many parameters as possible from data
parameter #params Sensitive evts
sin2 1 CPmd 1 flavour
w&w 8 flavourtresolution 9 flavourandCP
Background 6 sidebands
Backgroundw 8 sidebands
Backgroundt 3 sidebands
Biggest correlation with sin2 7.6%
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Log Likelihood vs sin 2
KL
KS
Total
sin 2 = 0.34 0.20(stat) 0.05(sys)
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Systematics
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Asymmetries
J/KL
J/KS
sin20.25 0.22 (stat)
sin20.87 0.51 (stat)
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Asymmetries
Total CP tagged sample : 529 events
164 of background mainly in J/KL
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sin2 by decay mode
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sin2 by tagging category (Ks only)
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Compilation of all known results
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Comparison to predictions of non-CP
K
|Vub/Vcb|, Md,Ms
sin 2
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New fuel for sin2B DD)
The Standard Model predicts time-dependent CP-violating asymmetries in the decays B0 DD proportional to sin2
D ReconstructionD D0, D0
D0 K, K0, K, KS
D K, KS, KK
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New fuel for sin2
Beware of this one(non flying birds !)
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B DD, Signal
Nsignal = 31.8 EventsNBkg = 6.2 Events
Estimated from sideband in E and MES
Br(B0DD) = (8.0 ± 1.6 (stat) ± 1.2 (syst)) 10-4
(But angular analysis to do CP)
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Charmless two-body B decays
Direct CP search
Time-dependent CP asymmetry sin(2), 0 sin(2)
Theoretical model validation
b
d d
u
d,s
b
d
d,suud
Vub
Vud,s
Vtd,sVtb
+, K+
-
+, K+
-t
W
W
B0
Cabibbo-suppressed tree
diagrams
penguin diagrams
B0
u
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Charmless decays
(h+h-
)(h+)(h+)
K0 as KS to +-
K+K-
K*+ K+0,KS +
Fully reconstructed decaysEfficiency (with daughter BF)
00,h+0,h+0,h+h: 10-45% ,3-20%
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Composite particles
KS mass
4.3 MeV
mass
8.5 MeV
< E > ~ 3 GeV
mass
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Background suppression
Jet-like topology
cos S
signal
background
cos(S) cosine of angle between sphericity axes of B and rest of the
event
Background dominatedby continuum qqbarproduction (u,d,s,c)
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Background suppression
Fisher discriminant
signal
hh E sideband (dots) continuum hh MC(his)
(dots) B- D0 (his)hh MC
background
Linear combination of event-shape variables (cones)
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Likelihood analysis
Use an extended global likelihood fit to extract different signal yields (NS) in each topology
mES, E, Fisher(cosTh), ( mass), C
Independent control sample to study Probability Density Function for both BKG and SIG
Gaussian 2.6 MeV
B- Do-
ARGUS function
h+h- E sideband
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More PDFs
E with pion hypothesis
signal MC
-0.15 0.15 GeV
Background udsc
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More PDFs (Cherenkov)
C – C
Control sample: D*+ D0
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Results
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Systematics
Variation in %
Vary PDF parameters alternative PDF
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Results
Likelihood visualization onto mES
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Predicting or disproving models
B.Beneke et al.
inputSM
CLEO/Belle/BaBar (my) average: 0.26 +/- 0.06
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Radiative decays (B K0
CKM matrix elements Vtd, Vts
No considerable CP asymmetry expected in Standard Model (< 1%)
Sensitive to New Physics (SUSY,W H
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B0 K0, Signal and Backgrounds
B0 K0
ee qq
ee qq X0
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B K0, Signal Estimation
Yield: Nsignal = 139.2 ± 13.1 eventsBr(B0 K039± 0.41 (stat) ± 0.27(syst)) 10-5
MES Distribution-200 MeV < E < 100 MeV
ACP = -0.035 0.094 (stat) 0.022 (syst)
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The near future
Expect to have 40fb-1 more by the end of the run II
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The near future: recoil physics
In 20 fb-1 (present stat ~ 5 times more by end of 2002):
• 12 K fully reconstructed hadronic B mesons• 40 K semi-exclusive B (maybe one/two missing particles)• 20 K semi-leptonic B (one missing)
Will be able to reconstruct single B in modes with BF ~10-4 - 10-5
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The immediate future
The usual painful start-up
however better than last year
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while the competitor…..
Belle is doing very well
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The near future for sin2
BaBar will collect ~0.5 ab-1
We will know sin2 at the ~0.02 level by 2005
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The far future
It could be a new machine at slightly higher energy [Y(5S)] and asymmetry and considerably higher luminosity (10 36 cm -2 s -1)
You’re all invited !