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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.

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The BaBar Detector

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  1. The BaBar Detector Electromagnetic Calorimeter 6580 CsI crystals e+ ID, π0 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 e- [9 GeV] Silicon Vertex Tracker 5 layers (double-sided Si sensors) vertexing + tracking (+ dE/dx) 1.5T Magnet

  2. 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 foundation.

  3. Silicon Vertex Tracker (SVT) • double-sided silicon sensors • 5 layers • 150.000 readout channels • provides vertexing, tracking and dE/dx sin2b from B0(cc)K0 Responsabilities • System management: Italy and US • Software coordinator: Italian • Operation managers: shared equally between Italy (+Spain) and US 0 -5 +5 Dt(ps) sz(vtx Breco) ~ 80mm

  4. Drift Chamber (DCH) • 40-layer small-cell chamber • 7104 drift cell formed from hexagonal wire pattern • 80&120m Al wires and 20m 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 Canada-France-Italy-US Beryllium inner wall Average distance resolution in the cell is 120m dE/dx resolution is 7.5-8.0% Thin Al forward endplate

  5. Detector of Internally Reflected Cherenkov light (DIRC) SIGNAL FORMATION LAYOUT PERFORMANCE >4sseparation at 3 GeV/c Cher. angle vs. momentum for pions and kaons

  6. Electromagnetic Calorimeter (EMC) • Tallium-doped CsI crystals • Barrel: 5760 crystalsForward endcap: 820 crystals • 16÷17 radiation lengths • 16o<q<142o polar angle coverage(90% in CM frame) p0 reconstruction Energy and angular resolutions: s M(p0) = 6÷7 MeV

  7. 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) -ID performance • 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

  8. t =0 Dz = Dt gbc bg =0.56 l - (e-, m -) The two mesons oscillate coherently : at any given time, if one is a B0 the other is necessarily a B0 Dt picoseconds later, the B 0 (or perhaps it is now a B 0) decays. 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 0l+ = B 0. Kaon tags also used. (4S) How time-dependent decay rates are measured We need to know the flavour of the B at a reference t=0. At t=0 we know this meson is B0 B 0 rec B 0 B 0 tag

  9. Key analysis techniques Threshold kinematics: we know the initial energy of the Y(4S) system, therefore we know the energy and magnitude of momentum of each B • Event topology Signal Signal (spherical) Background Background (jet-structure) Several analyses use an unbinned maximum likelihood fit to extract parameters of interest

  10. Measurement of CKM angle a Constraint on a with Bpp using isospin analysis or isospin+SU(3) (shaded, see ref.) • Measure 180 – b – g = a through time dep. CP violation in buud decays • Updated measurement with Bpp • 5.4s evidence of CPV in B0p+p- • Updated measurement of Bpp BFs • Updated measurement with Brr • Solution of isospin analysis consistent with SM: a=[73,117] @68% CL. uncertainty dominated by penguin pollution • Measurement of B(rp)0 through Dalitz plot analysis • Data prefers a~90o, no constraints at 95%CL • First ACP(t) measurement of Ba1(1260)p • Constraint on a requires BFs of SU(3)-related decays and is not available yet. PRL99, 021603 (2007) PRD76, 091102 (2007) PRD76, 052007 (2007) PRD76, 012004 (2007) WA Bpp, rp, rr combination PRL98, 181803 (2007) α = [80,107]o U [156,171]o @ 95% Prob.

  11. Measurement of CKM angle: β • Improved measurement of CP asymmetries • in B0(cc)K(*)0 PRL 99, 171803 (2007) Average on all channels, theory error <1% J/Ks,(2)Ks,χc1KS, ηCKS (ηCP=-1) J/KL (ηCP=+1) • CP violation in B0D(*)+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 3.7s CL Result consistent with B0(cc) K(*)0 PRD 76, 111102 (2007)

  12. sin 2beff with bs qq penguins SM contribution Possible NP in loops B0h’Ks PRL 98, 031802 (2007) BaBar: ~350M BB BaBar still exploits its luminosity significantly better than Belle Belle : ~540M BB

  13. Moriond 08 Measurement of CKM angle g Updated world average • g = arg[-VudVub*/VcdVcb*] • It is measured in the interference between B-D0K- and B-D0K- • Many D0 modes are measured to increasethe statistics g = (81 ± 15)o new measurements: • Update of B-D(*)0K(*)-, D0Kspp and KsKK Submitted to PRD arXiv:0804.2089 (syst) (Dalitz Model) (stat) To be submitted to PRD-RC • First measurements of B0D0K*0, D0Ksp+p-: • Update of B-D0K- with D0CP eigenstates • Measurement of sin(2b+g) with time dep. Dalitz plot analysis of B0D-Ksp+: To be submitted to PRD-RC arXiv:0712.3469, accepted by PRD

  14. Plep>0.8GeV 1stmoment (mean)‏ 2ndmoment (width)‏ Measurement of |Vcb| decay width d~|Vqb|2mb5 • Semileptonic Cabibbo favoured B→Xcℓ decays allow to extract the magnitude of the CKM parameters Vcb: 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→Xℓ Measurements: Operator Product Expansion allows to extract Vcb 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, 2008 F(1)|Vcb|·103=34.4±0.3stat1.1syst Br=4.690.04stat0.34syst % |Vcb|·103=37.41.2exp1.4F(1) arXiv 0707.2670 (EPS07)‏ Global fit using MXc and Plep moments from BaBar |Vcb|·103=41.88±0.81 (2% error)‏ mb=4.552±0.055 (1.2% error)‏

  15. 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→Xuℓ measurements: large background from b→cℓ Need to cut on q2, Mx, Plep distribution (or their combinations) to reduce thisbackground need to understand QCD (theory), and b-quark motion inside the B-meson: shape function (from  spectra in b→s)‏ • B→ℓ Measurement of |Vub| • b→uℓ decays allow to extract |Vub|: • |Vub|/|Vcb| provides benchmark for testing New Physics in other processes +0.6 |Vub|·103=4.1  0.3exp -0.4 FF(theo) -reco: PRL98:091801(2007)‏ tagged: PRL97:211801(2006)‏ b→uℓ b→cℓ Cut: |Vub|·103 Plep>2.0 GeV 4.440.25exp0.47theo PRD73:012006,2006 Elep, q2 3.950.26exp0.63theo PRL95:111801,2005 mX <1.55 GeV 4.270.20exp0.30theo arXiv:0708.3702 P+ =Ex-|PX| 3.880.25exp0.24theo arXiv:0708.3702 mX, q2 4.570.29exp0.30theo arXiv:0708.3702 Around 10% uncertainty from single anlysis

  16. Radiative Decays b→s with 230 million of BB • One loop process: sensitive to New Physics •  spectrum in the recoil of a Breco (almost no background for E>2.2 GeV) • Br=(3.650.850.60)x10-4 • CP asymmetry (<1% in SM, up to 15% in some NP models). Xs from sum of 16 exclusive modes - ACP=(-0.0120.0300.019) • Observation of the b→dtransition with B→ • Br(B→)=(1.10-0.330.370.09)x10-6 • Br(B→)=(0.790.200.220.06)x10-6 • Br(B→)=<0.78x10-6@90%CL with 383million of BB with 347million of BB backgrounds

  17. 383 million BB paper in preparation • 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 BK(*)ℓℓ Forward-backward asymmetry K* longitudinal polarization

  18. Leptonic B Decays ,H Allows extraction of fBVub (fB given Vub)‏ -e,helicity suppressed -Possible enhancement due to New Physics -Bconstraint on the plane tanβ vs Higgs boson mass -Technique: Reconstruct one B meson as either -BDℓX (X = , 0or nothing)‏ -BDxhad the other B is searched for Bℓ, ℓ = , e B e B  B SM predictions O(10-12)‏  4x10-7  1x10-4 < 5.2x10-6 < 5.6x10-6 (1.2±0.4stat±0.4syst)x10-4 combination of semileptonic and hadronic tags at 90 % CL at 90 % CL PRD76,052002(2007)‏ ArXiv: 0801.0697 submitted to PRD PRD77,011107(2008)‏

  19. D mixing and CP violation: Look for signs of new physics (x>>y or CP violation) First evidence of D mixing in D0K+p- Decay modes under analysis: KSpp,KSKK,KK,pp,K3p,Kpp0 Limits on CP violation in KK, pp at O(0.1%) level Dalitz plot Analysis: KSpp, KSKK, ppp0 are also important tools for g analysis Spectroscopy: DsJ* new resonances New charm baryons Measurements of spin Charm Physics PRL 98:211802,2007 D0K+p-: evidence of mixing at 3.9 s . Best fit + No mixing: (0,0) Contours at 1 intervals Fitted signal 4030  88

  20. PRL100:011801,2008  physics B-factories are also taufactories! Kpp • -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 and many other hhhn decays Large improvements compared to PDG in many relevant channels search for /e on 2.07 x 108 e+e-+- events B()<6.8 x 10-8 @90%CL B(e)<1.1 x 10-7 @90%CL search for t into 3 leptons decay on 3.42 x 108 e+e-+- events B(ℓℓℓ)<3.7-8.0 x 10-8 @90%CL

  21. Heavy-Quarkonium Results Important contributions: X(3872) Y(3940)J/ arXiv:0803.2838 arXiv:0711.2047 B+ J/y pp 443/fb 383/fb • new states discovered; new interpretations • improved measurements of resonance parameters 347/fb Combining BABAR and Belle: ~4 mass difference  two X states? B0 DD* PRD 77, 011102 • Interesting possibilities in bottomonium: • search for missing states; • search for NP in Y(nS) decays. Moriond QCD 347/fb observation of enhanced Y(1S) h for Y(4S): unexpected in ordinary quarkonium picture.

  22. Published Results Analyses in Progress 62K+4  K+K-K0SK0L DD* R Units K+K-K0K (2S)‏  K+K-K+K-K+K-   pp J/ s' [GeV] ee Interactions via Initial State Radiation s’ • eeISR eeISRISR X • Xis any allowed final state( JPC = 1)‏ • Radiator function W(s,s) known to <1% • (ee X) measured as a function of mX = s • eeinteractions accessible from threshold up to ~5 GeV • 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))

  23. Final Data Sample Total data collected until September 2007: • 480M BB pairs, • 630M cc events, • 440M t 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

  24. B factories CKM reach today a sin2b ~3.6% 8o ~9% Btn B->rn g 15o

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