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The BABAR Experiment and B Factory Operations TThhee BBAABBAARR EExxppeerriimmeenntt:: SSttaattuuss aanndd PPllaannss Steven Robertson Institute of Particle Physics Canadian Association of Physicists Congress 2008 Québec City, Québec June 10, 2008 OOuuttlliinnee ● Flavour physics overview ● The BABAR experiment and B factory operations ● Run 7 and ongoing analysis activities ● Some recent Canadian highlights Sep 3, 2008 The BABAR Experiment Steven Robertson, Institute of Particle Physics 2 WWhhyy FFllaavvoouurr?? Flavour sector contains 20 (22) of 25 (27) parameters of the SM, which are intrinsically connected to EW physics and symmetry breaking ● Tantalizing structure (similarly for lepton sector) which is not predicted by the SM: Vud Vus Vub ● All known CP violation phenomenology arises V = Vcd Vcs Vcb from a single complex phase in VCKM Vtd Vts Vtb ● B sector provides access to a substantial fraction of the CKM matrix either at tree level d or via one-loop processes * π V ud u ● Indirect probes of New Physics from b Vcb c “redundant” determinations of CKM + 0 parameters or from rare decay searches Β D u u Sep 3, 2008 The BABAR Experiment Steven Robertson, Institute of Particle Physics 3 EEffffeeccttiivvee tthheeoorryy aapppprrooaacchh ● Loop-level flavour processes (FCNCs) can act as probes of mass scales far beyond the CM energies of accelerator-based experiments In explicit models: Effective flavour- New Physics scale ● Λ ~ mass of virtual particles violating couplings (e.g. Fermi theory.: mW) ● C ~ (loop coupling) x (flavour coupling) Increasing luminosity (e.g. SM/MFV: αw x CKM) Precision flavour measurements provide bounds on ratio C / Λ i.e. they constrain coupling strengths at any given mass scale Sep 3, 2008 The BABAR Experiment Steven Robertson, Institute of Particle Physics 4 UUnniittaarriittyy TTrriiaannggllee ccoonnssttrraaiinnttss ● Unitarity of CKM matrix implies relationships between CKM elements which can be tested experimentally ● Bd meson Unitarity Triangle (UT): B0 → π+π− 0 + − b → ulν B → ρ ρ B0B0 mixing * b V u α td V V * d tb V u * γ VcdVcb β B0 → D*π B → ψKS b → clν + 0 + B → φK B → D CP K S ● “Tree-level” determination of UT parameters permits the SM mechanism for CP violation to be tested Sep 3, 2008 The BABAR Experiment Steven Robertson, Institute of Particle Physics 5 TTrreeeess vvss ppeenngguuiinnss Unitarity of CKM matrix implies relationships between CKM elements which can be tested experimentally b→ccs J/ψ ● Bd meson Unitarity Triangle (UT): B0 B0 → π+π− K0 0 + − B → ρ ρ + b → ulν B0B0 mixing b→sss W u,c,t * V b s b ϕ u α td V s V * 0 g d tb B u V d s * d 0 γ VcdVcb β K New Physics g~ B0 → D*π B → ψKS b s ~ ~ ϕ b → clν b s + 0 + B → φK 0 s/d B → D CP K S B g s/d d d K0 ● “Redundant” determinations of UT parameters in modes which proceed via different mechanisms (i.e. tree vs loop) can yield information about possible New Physics contributions Sep 3, 2008 The BABAR Experiment Steven Robertson, Institute of Particle Physics 6 TTrreeeess vvss ppeenngguuiinnss ● Determination of sin2β from ● Determination of sin2β from b→ccs modes consistent with penguin-dominated modes not overall CKM fit (both including as clearly consistent with SM and excluding kaon constraints): expectation: Sep 3, 2008 The BABAR Experiment Steven Robertson, Institute of Particle Physics 7 RRaarree ddeeccaayyss Searches for “rare” decay processes can provide additional NP sensitivity since the NP contribution may be comparable or larger than the (suppressed) SM rate ● Leptonic B, Ds or D decays: ● Flavor-changing neutral currents (FCNCs) qi q j q qi j 2 (mq )23(13) ● Lepton flavour violation (e.g. in τ decays): Sep 3, 2008 The BABAR Experiment Steven Robertson, Institute of Particle Physics 8 TThhee BBAABBAARR eexxppeerriimmeenntt ● Currently ~350 physicists from eleven nations Sep 3, 2008 The BABAR Experiment Steven Robertson, Institute of Particle Physics 9 ϒϒ((44SS)) The ϒ(4S) is a bb resonance which d l o lies just above the mass h s e threshold for production of BB r h t meson pairs. B B ● Cross section of ~1.1nb ~1.1 million BB pairs per fb-1 B0B0 pair is produced in The two B mesons evolve a coherent L=1 state in phase until one decays (EPR situation) PEP-II BABAR Off On ⇒ Enables studies of time-dependence of decays of “flavour-tagged” neutral B mesons ECM -M Υ(4S) (MeV) Sep 3, 2008 The BABAR Experiment Steven Robertson, Institute of Particle Physics 10 PPEEPP--IIII AAssyymmmmeettrriicc BB FFaaccttoorryy First collisions: 1998 Final collisions: April 2008 Collide 9.0 GeV electrons with 3.1 GeV positrons for ϒ(4S) CM Energy = 10.58 GeV Design luminosity 3.0 x 1033 cm-2 s-1 Record luminosity 12.07 x 1033 cm-2 s-1 Number of bunches: 1720 Beam current: (HER) 1.875 A (LER) 2.9 A Sep 3, 2008 The BABAR Experiment Steven Robertson, Institute of Particle Physics 11 TThhee BBAABBAARR ddeetteeccttoorr B factory operations at SLAC since 1999: Magnet flux return EM calorimeter ● Centre of mass energy of 10.58 GeV instrumented with for ϒ(4S) → BB 6580 CsI(Tl) RPCs (→ LSTs) crystals ● Asymmetric beam energies produce 1.5 T boost of βγ=0.56 in lab frame solenoid DIRC – RICH utilizing total internal reflection ) + σ e ( BABAR n (3.1 GeV) o i t K-π separation a r a p e - s e 5-layer silicon π - (9.0 GeV) K vertex detector 40 layer drift chamber (dE/dx) pLAB (GeV/c) σ /p = (0.13 · p /[GeV/c] + 0.45)% pT T T Sep 3, 2008 The BABAR Experiment Steven Robertson, Institute of Particle Physics 12 BBAABBAARR//PPEEPP--IIII OOppeerraattiioonnss ● Final BABAR ϒ(4S) “onpeak” data sample corresponding to an integrated luminosity of 430 fb-1 ~0.5x109 BB pairs ● substantial samples of continuum tau and charm ● also ~45fb-1 of ϒ “narrow resonance” data (surprise!)... ● Sep 3, 2008 The BABAR Experiment Steven Robertson, Institute of Particle Physics 13 IInntteerreessttiinngg ttiimmeess...... Run plan for Run 7 approved until Oct 2008 with luminosity target of ~2x1034 with anticipation of an additional ~50% new data ● substantial upgrades to accelerator during 3-month shutdown in fall 2007 ● BABAR IFR (barrel muon system) upgrade completed prior to 2007 run Dec 21st – Congressional budget cuts (targetted at ILC) result in termination of BABAR run Continues to Oct 2008 effective Jan 1st 2008 ● BABAR successfully argues that physics case for ϒ(3S) & ϒ(2S) justifies a 3-month extension of the run End of ϒ(4S) Run ● PEP-II/BABAR retool Scan accelerator, detector and trigger system within a 3-day period ϒ(3S) Run ϒ(2S) Run over the holiday break Sep 3, 2008 The BABAR Experiment Steven Robertson, Institute of Particle Physics 14 FFiinnaall OOppeerraattiioonnss th ● Monday April 7 2008 (12:43PM) Sep 3, 2008 The BABAR Experiment Steven Robertson, Institute of Particle Physics 15 NNaarrrrooww UUppssiilloonn PPhhyyssiiccss ● New element of BABAR physics 14.5/fb program: Upsilon spectroscopy! @ Y(2S) ● Search for elusive singlet states (ηb and hb) 7.3 0.3(stat) nb ( 7% syst.) ● Hadronic transitions, etc. ~100M ϒ(2S) (~12x CLEO) ● New Physics searches ● Invisible width of ϒ(1S), etc. ● World largest samples by one order of magnitude ● 30.2/fb @ Y(3S) ● 4.2 0.2(stat) nb ( 5% syst.) ~120M ϒ(3S) (x10 Belle, 25x CLEO) Sep 3, 2008 The BABAR Experiment Steven Robertson, Institute of Particle Physics 16 DDiirreecctt HHiiggggss//DDMM sseeaarrcchheess ((??!!)) ● Light (pseudoscalar) Higgs and/or light dark matter candidates can be directly produced in decays of heavy quarkonium states:* ● ϒ → χχ via U (new gauge boson or scalar) + - ● ϒ → A1 γ where A1 → χχ or τ τ Models manage to evade existing Higgs & SUSY LSP limits from e.g. LEP, while predicting quite large branching fractions Can have either completely invisible final states, or (invisible + γ), depending on spin of the mediator ● Require a “tag” to identify that the event has occurred ● Expected sensitivity with BABAR ϒ(3S) data sample Br(ϒ(1S) → invisible) ~few x 10-4 (prelim results “soon”) *B●. McElrath, Light Higgses and Dark matter at Bottom and Charm Factories, arXiv:0712.00116v2 [hep-ph] J. Gunion, D. Hooper and B. McElrath, Light Neutralino Dark Matter in the NMSSM, hep-ph/0509024. Sep 3, 2008 The BABAR Experiment Steven Robertson, Institute of Particle Physics 17 HHiigghh EEnneerrggyy SSccaann ● Last ~two weeks of Run 7 were dedicated to an energy scan of the region above the ϒ(4S) ● 25 MeV steps, 25pb-1 per point (previous scans by CLEO and CUSB in 1984 based on ~100pb-1) ● Motivation: study properties of ϒ(5S) and ϒ(6S) resonances, search for exotic bb states (analogous to “unexpected” Y(4260),Y(4350),Y(4660) charmonium-like states) ● Clear evidence of ϒ(5S) and ϒ(6S) resonances, but not a simple resonance structure ● interference contribution? ● ⇒ Results “soon”... Sep 3, 2008 The BABAR Experiment Steven Robertson, Institute of Particle Physics 18 WWhhaatt nneexxtt?? ● 3-month transition period to prepare detector for “Minimum Maintenance State” (MMS) ● Detector could (with difficulty) be brought back into service from MMS ● Requires continuous monitoring (e..g gases, fluids) but no expert shifters ● “Decommissioning and Disposal” (D&D) to begin in late 2008 or 2009 ● Planning underway – requires agreement between BABAR member countries ● Important to preserve valuable/unique hardware assets ● BABAR collaboration retains ownership of the detector until the end of MMS phase ● The lab will assume ownership at the end of MMS and the responsibility for the D&D Sep 3, 2008 The BABAR Experiment Steven Robertson, Institute of Particle Physics 19 DDeetteeccttoorr rreeuussee ffoorr SSuuppeerrBB ● SuperB project (see talk in Monday morning session) assumes
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