The BaBar Detector

Cherenkov Detector 144 quartz bars K, π, p separation Electromagnetic Calorimeter 6580 CsI crystals e+ ID, π 0 and γ reco Drift Chamber 40 layers tracking + dE/dx Instrumented Flux Return 12-18 layers of RPC/LST μ ID Silicon Vertex Tracker 5 layers (double-sided Si sensors) vertexing + tracking (+ dE/dx) e + [3.1 GeV] e - [9 GeV] 1.5T Magnet The BaBar Detector


The BaBar Detector. Electromagnetic Calorimeter 6580 CsI crystals e+ ID, π 0 and γ reco. Instrumented Flux Return 12-18 layers of RPC/LST μ ID. e + [3.1 GeV]. Cherenkov Detector 144 quartz bars K, π , p separation. Drift Chamber 40 layers tracking + dE/dx. - PowerPoint PPT Presentation

Transcript of The BaBar Detector

Page 1: The BaBar Detector

Cherenkov Detector 144 quartz bars K, π, p separation

Electromagnetic Calorimeter6580 CsI crystals

e+ ID, π0 and γ reco

Drift Chamber40 layers

tracking + dE/dx

Instrumented Flux Return 12-18 layers of RPC/LST

μ ID

Silicon Vertex Tracker5 layers (double-sided Si sensors)vertexing + tracking (+ dE/dx)

e+ [3.1 GeV]

e- [9 GeV]

1.5T Magnet

The BaBar Detector

Page 2: The BaBar Detector

Status of the Collaboration (Oct 2007)

74 Institutions in 10 countries

Although fewer babarians than last year, with more than 200 students and postdocs the collaboration continues to be on a very strong


Faculty PhD Staff Postdoc Grad Non-PhD Totals

Canada 10 2 7 19

France 14 12 3 12 4 45

Germany 7 4 1 15 27

Italy 27 28 15 14 84

Netherlands 1 1 2

Norway 2 1 3

Russia 2 6 2 1 11

Spain 3 2 3 8

United Kingdom 18 1 12 12 1 44

United States 72 47 40 64 19 242

Totals 153 101 75 131 25 485

Page 3: The BaBar Detector

z(vtx Breco) ~ 80mt(ps)+5-5 0

Silicon Vertex Tracker (SVT)

sin2 from B0(cc)K0

System management: Italy and US Software coordinator: Italian Operation managers: shared equally

between Italy (+Spain) and US


double-sided silicon sensors 5 layers 150.000 readout channels provides vertexing, tracking

and dE/dx

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Drift Chamber (DCH)

Thin Al forwardendplate

Beryllium inner wall

• 40-layer small-cell chamber– 7104 drift cell formed from hexagonal wire


– 80&120m Al wires and 20m Tungsten sense wires

• Layer organized into superlayers– wire directions in axial-u-v pattern

• 80:20 helium:isobutane gas mixture– low-mass gas and small Lorentz angle

Average distance resolution in the cell is 120m

dE/dx resolution is 7.5-8.0%


Page 5: The BaBar Detector

Detector of Internally Reflected Cherenkov light (DIRC)

>4 separationat 3 GeV/c

Cher. angle vs. momentum for pions and kaons



Page 6: The BaBar Detector

Electromagnetic Calorimeter (EMC)

• Tallium-doped CsI crystals

• Barrel: 5760 crystalsForward endcap: 820 crystals

• 16÷17 radiation lengths

• 16o<<142o polar angle coverage(90% in CM frame)

M(0) = 6÷7 MeV

Energy and angular resolutions: 0 reconstruction

Page 7: The BaBar Detector

Instrumented Flux Return (IFR)• Absorber-detector alternating layers

for and KL detection:

– Bwd endcap: original RPC (18 layers);

– Fwd endcap: new RPC (16 layers) in streamer or avalanche mode;

– Barrel: old degraded RPC replaced by LST in summer 2004/2006 (12 layers)

• Italy + US teams – Detectors and read-out built in Italy

(both RPC and LST)

– System Managers: 1 Italy + 1 US for each subsystem;

– Operation Managers: 2/3 Italy + 1/3 US

-ID performance

Page 8: The BaBar Detector

t =0We need to know the flavour of the B at a reference


B 0


The two mesons oscillate coherently : at any given

time, if one is a B0 the other is necessarily a B0

In this example, the tag-side meson decays first.

It decays semi-leptonically and the charge of the

lepton gives the flavour of the tag-side meson :

l = B 0 l = B 0. Kaon tags also used.

tagB 0l (e-, -) =0.56

z = t c rec


t picoseconds later, the B 0 (or

perhaps it is now a B 0) decays.

B 0


d0B b


At t=0 we know this

meson is B0

How time-dependent decay rates are measured

Page 9: The BaBar Detector

Threshold kinematics: we know the initial energy of the Y(4S) system,

therefore we know the energy and magnitude of momentum of each B

2*2*BbeamES pEm **

beamB EEE

Background Background



Event topology

Signal Signal

Several analyses use an unbinned maximum likelihood fit to extract parameters of interest

Key analysis techniques

Page 10: The BaBar Detector

Measurement of CKM angle Measure 180 – – = through time dep.

CP violation in buud decays Updated measurement with B

5.4 evidence of CPV in B0+-

Updated measurement of B BFs

Updated measurement with B Solution of isospin analysis consistent with

SM: =[73,117] @68% CL. uncertainty dominated by penguin pollution

Measurement of B()0 through Dalitz plot analysis Data prefers ~90o, no constraints at 95%CL

First ACP(t) measurement of Ba1(1260) Constraint on requires BFs of SU(3)-related

decays and is not available yet.

PRL99, 021603 (2007)PRD76, 091102 (2007)

PRD76, 052007 (2007)

WA B, , combination

PRL98, 181803 (2007)

PRD76, 012004 (2007)

Constraint on with B using isospinanalysis or isospin+SU(3) (shaded, see ref.)

BB 10 383 6

α = [80,107]o U [156,171]o @ 95% Prob.

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Measurement of CKM angle: β

J/Ks,(2)Ks,χc1KS, ηCKS (ηCP=-1)

J/KL (ηCP=+1)


PRD 76, 111102 (2007)

• Improved measurement of CP asymmetries in B0(cc)K(*)0

Average on all channels, theory error <1%

PRL 99, 171803 (2007)

• CP violation in B0D(*)+D(*)- Vector-vector final state angular analysis needed since CP content depends on angular momentum

the CP-even fraction is dominant

Evidence of CP violation at 3.7 CLResult consistent with B0(cc) K(*)0

BB 10 383 6

BB 10 386 6

Page 12: The BaBar Detector

sin 2eff with bs qq penguins

Belle : ~540M BB

BaBar: ~350M BBBaBar still exploits its luminosity significantly better than Belle

SM contribution Possible NP in loops


PRL 98, 031802 (2007)

Page 13: The BaBar Detector

First measurements of B0D0K*0, D0Ks: Update of B-D0K- with D0CP eigenstates Measurement of sin(2+) with time dep. Dalitz plot analysis of


= arg[-VudVub*/VcdVcb*]

It is measured in the interference between B-D0K- and B-D0K-

Many D0 modes are measured to increasethe statistics Update of B-D(*)0K(*)-, D0Ks and KsKK

Measurement of CKM angle

o2223 )5576(

Updated world average

Moriond 08

(stat) (syst)(Dalitz Model)

Submitted to PRDarXiv:0804.2089

To be submitted to PRD-RC



To be submitted to PRD-RC


o)205383(2 arXiv:0712.3469, accepted by PRD

new measurements:= (81 ± 15)o

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1st moment (mean)

2ndmoment (width)

Measurement of |Vcb

|• Semileptonic Cabibbo favoured B→Xcℓ decays

allow to extract the magnitude of the CKM parameters V

cb: Experimental clean but good

understanding of QCD corrections is crucial

• Exclusive decays: B→D*ℓ, clean but need Form Factor normalization at zero recoil, F(1): (from Lattice QCD).

– Exploiting the full kinematics of the B→D*ℓ both the form factors ratios (R1, R2) and the F(1)*|Vub| parameter have been extracted

• Inclusive B→XℓMeasurements: Operator Product Expansion allows to extract V

cb exploiting

the fit to moments of many experimental quantities:– Moments of the hadronic mass distribution, and

moments of the lepton momentum distribution as function of the minimum lepton momentum

PRD77:032002, 2008F(1)|V









decay width d~|Vqb|2mb



|·103=41.88±0.81 (2% error)m

b=4.552±0.055 (1.2% error)

arXiv 0707.2670 (EPS07)Global fit using M

Xc and P


moments from BaBar

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Measurement of |Vub

|• b→uℓ decays allow to extract |V


– |Vub


| provides benchmark for testing New Physics in other processes

• Exclusive measurements:– B→ℓ using different technique: -reconstruction (high

efficiency but low S/N), tagged samples (low efficiency but good S/N). Need Form-Factors (lattice-QCD)

• Inclusive B→Xuℓmeasurements: large background

from b→cℓ Need to cut on q2, Mx, P

lep distribution (or

their combinations) to reduce thisbackground– need to understand QCD (theory), and b-quark motion inside

the B-meson: shape function (from spectra in b→s)


Cut: |Vub



>2.0 GeV 4.440.25exp0.47

theo PRD73:012006,2006


, q2 3.950.26exp0.63

theo PRL95:111801,2005


<1.55 GeV 4.270.20exp0.30

theo arXiv:0708.3702

P+ =E


X| 3.880.25


theo arXiv:0708.3702

mX, q2 4.570.29


theo arXiv:0708.3702

-reco: PRL98:091801(2007)tagged: PRL97:211801(2006)

Around 10% uncertainty from single anlysis

b→uℓ b→cℓ


|·103=4.1 0.3exp -0.4 FF(theo)


Page 16: The BaBar Detector

with 230 million of BB

Radiative Decays b→s• One loop process: sensitive to New

Physics spectrum in the recoil of a Breco

(almost no background for E>2.2 GeV)

– Br=(3.650.85)x10-4

• CP asymmetry (<1% in SM, up to 15% in some NP models). Xs from sum of 16 exclusive modes

- ACP=(-0.0120.030)

• Observation of the b→dtransition with B→

– Br(B→)=(1.10-0.330.37 0.09)x10-6

– Br(B→)=(0.790.200.22 0.06)x10-6

– Br(B→)=<0.78x10-6@90%CL

with 383million of BBwith 347million of BB




Page 17: The BaBar Detector

• Standard Model

– BF~10-6

• Forward-Backward Asymmetry vs q2

– Kℓℓ is forward-backward symmetric if there are no new scalar operators

– Angular distribution of the lepton in the di-lepton system

– Constraints on the signs of the Wilson coefficients C7,C9,C10

– K* decay angle cos(K) gives longitudinal polarization FL

• Sensitive to C7 sign or new right-handed currents at low q2






lForward-backward asymmetry

383 million BB paper in preparation

K* longitudinal polarization

Page 18: The BaBar Detector

Leptonic B Decays


at 90 % CL (1.2±0.4



combination of semileptonic and hadronic tags

< 5.6x10-6 < 5.2x10-6

1x10-4 4x10-7 O(10-12)

B B Be

Allows extraction of fBVub (fB given Vub)

SM predictions

-Technique: Reconstruct one B meson as either -BDℓX (X = , 0 or nothing) -BDxhadthe other B is searched for Bℓ, ℓ = , e

-e,helicity suppressed-Possible enhancement due to New Physics-Bconstraint on the plane tanβ vs Higgs boson mass



at 90 % CL

ArXiv: 0801.0697

submitted to PRD

Page 19: The BaBar Detector

Charm Physics

• D mixing and CP violation:– Look for signs of new physics (x>>y or CP

violation)First evidence of D mixing in D0K+-

Decay modes under analysis: KS,KSKK,KK,,K3,K0

Limits on CP violation in KK, at O(0.1%) level

• Dalitz plot Analysis:– KS, KSKK, 0 are also important tools for


• Spectroscopy:– DsJ

* new resonances– New charm baryons– Measurements of spin

D0K+-: evidence of mixing at 3.9

. Best fit

+ :(,)No mixing

Contours at 1intervals

PRL 98:211802,2007

Fitted signal4030 88

Page 20: The BaBar Detector

physics B-factories are also tau factories!

-lifetime measurements tests of CPT, lepton universality

-decays with strange quarks very precise measurement of |Vus|, ms

new decay modes via resonance observed

high multiplicity hadronic states rich resonance sub-structures in 3/5 prong

decays limits on decaying into 7/8 pions

direct searches for New Physics lepton flavor violation, lepton number

violation baryon number violation CP violation in lepton sector

B()<6.8 x 10-8 @90%CLB(e)<1.1 x 10-7 @90%CLsearch for into 3 leptons decay on 3.42 x 108 e+e-+- eventsB(ℓℓℓ)<3.7-8.0 x 10-8 @90%CL

search for e on 2.07 x 108 e+e-+- events



Large improvements comparedto PDG in many relevant channels

and many other hhh decays

Page 21: The BaBar Detector

– new states discovered; new interpretations

– improved measurements of resonance parameters

observation of enhanced Y(1S) for Y(4S): unexpected in ordinary

quarkonium picture.

• Interesting possibilities in bottomonium:– search for missing states;

– search for NP in Y(nS) decays.

J Y(3940)J/


B0Combining BABAR and Belle: ~4 mass difference two X states?




Important contributions:

Heavy-Quarkonium ResultsP



, 0













Moriond QCD



Page 22: The BaBar Detector

ee Interactions via Initial State Radiation ee ISR ee ISR ISR X X is any allowed final state ( JPC = 1) Radiator function W(s,s) known to <1% (ee X) measured as a function of mX = s ee interactions accessible from threshold up to ~5 GeV)'().,'()'( 0 sssWs




Measure both exclusive and inclusive cross sections Measure R(s) = had(s)/(s) hadronic contribution to (g-2) and QED(Z0) Form factors, spectroscopy, new states discovery (e.g. Y(4260))

K+K- K0





62K+4 (2S)

s' [GeV]





Published Results Analyses in Progress


Page 23: The BaBar Detector

Final Data Sample Total data collected until

September 2007:– 480M BB pairs,

– 630M cc events,

– 440M

Run 7 (Dec 07- Apr 08), collected:

– 30/fb at Y(3S) and

– 14/fb at Y(2S)

– Scan above the 4S

• Analysis of these data sets has started, results expected for summer'08

– Search for rare decays and detailed bottomonium spectroscopy

Page 24: The BaBar Detector


~3.6% 8o




B B->

B factories CKM reach today