BaBar: Risultati recenti e prospettive

Fernando FerroniUniversita’ di Roma “La Sapienza” & I.N.F.N. Roma1

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

PEPII

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%

PEPII & BaBar

Physics Motivation: CP in B

Results:

Mixing & Lifetimes

sin 2b

Rare decays

Perspectives

Outline

Origin of masses

Remote energy scale (Gravity)

CP Violation and our universe

Particle physics in new millennium

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 ?

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

The Triangle

Bd D*

CP

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

CP measurement

Reconstruct a CP eigenstate

Flavour tag with other B

Measure z ---> t = tCP - ttag

Fit time evolution

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

Smearing of an asimmetry

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

PEPII-BaBar Operations

Interaction region

Permanent magnets inside the support tube

J/ Ks Event at BaBar

B0J/ Ks

J/->

Ks ->

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

K/ separation

Pion-Kaon separation at high momenta

Mixing and sin2

Common wrong tag fractions and resolution functionparameters can be determined by a large Bflav sample

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

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...

Bflav sample

6368 evtsPurity ~ 84%

7645 evtsPurity ~ 86%

Run I Data Set

23M BB pairs recorded

3 fb-1 of continuum

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/

Final CP sample of K0s modes

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

Tagging

Vertexing

Use per event error and parametrize the resolution function with scaling factors

tz/< c>

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

Mixing adronico/leptonico

Mixing : compilation

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%

Log Likelihood vs sin 2

KL

KS

Total

sin 2 = 0.34 0.20(stat) 0.05(sys)

Systematics

Asymmetries

J/KL

J/KS

sin20.25 0.22 (stat)

sin20.87 0.51 (stat)

Asymmetries

Total CP tagged sample : 529 events

164 of background mainly in J/KL

sin2 by decay mode

sin2 by tagging category (Ks only)

Compilation of all known results

Comparison to predictions of non-CP

K

|Vub/Vcb|, Md,Ms

sin 2

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

New fuel for sin2

Beware of this one(non flying birds !)

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)

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

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%

Composite particles

KS mass

4.3 MeV

mass

8.5 MeV

< E > ~ 3 GeV

mass

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)

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)

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

More PDFs

E with pion hypothesis

signal MC

-0.15 0.15 GeV

Background udsc

More PDFs (Cherenkov)

C – C

Control sample: D*+ D0

Results

Systematics

Variation in %

Vary PDF parameters alternative PDF

Results

Likelihood visualization onto mES

Predicting or disproving models

B.Beneke et al.

inputSM

CLEO/Belle/BaBar (my) average: 0.26 +/- 0.06

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

B0 K0, Signal and Backgrounds

B0 K0

ee qq

ee qq X0

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)

The near future

Expect to have 40fb-1 more by the end of the run II

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

The immediate future

The usual painful start-up

however better than last year

while the competitor…..

Belle is doing very well

The near future for sin2

BaBar will collect ~0.5 ab-1

We will know sin2 at the ~0.02 level by 2005

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 !