Recent Results from BaBarAdrian BevanOn the behalf of the BaBar collaborationHELLENIC SOCIETY FOR THE STUDY OF HIGH ENERGY PHYSICS All results are preliminary unless otherwise stated

Athens, '03

Talk Outline Theoretical Motivation

The PEP-II accelerator & BaBar Detector

Experimental issues Vertex reconstruction Flavour tagging Particle Identification background suppression techniques

Results sin2, sin2, direct CP Violation searches, rare decays

Summary and Outlook

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Physics Background CP Violation CP Violation is one of Sakharovs conditions for obtaining a matter antimatter asymmetry in the universe.

The observed CP Violation explained by the Standard Model of Particle Physics is 9 orders of magnitude too small to explain our universe

There must be some kind of new physics to discover in the flavour sector

Standard Model mechanism for CP Violation in weak interactions is given by a single complex phase in the CKM matrix.CP Violating phase presentlarge uncertainty in magnitude and phaserelated to a phase in the unitarity triangleA. D. Sakharov (1967) JTEP Letters 5, 24

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Experimental constraints before the B-factory era

(CP Violation measurements prior to 1999) Observed effects have been entirely in the kaon system

This defined our knowledge of CP Violation in the SM 1964, Christensen et al. discovered CP Violation in K2 decay

Following 37 years: measured several CP Violation effects in

Semi-leptonic kaon decay, ~10-3 Non-leptonic kaon decay, +-, 00: CP Violation in mixing: ~10-3 CP Violation in decay: / ~10-3 (KTeV/NA48) Observed a CP Violating asymmetry in KL+-e+e- (13% effect)(observed a T odd asymmetry in this decay as well)

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CP-LEAR measured T violation obtained an upper limit on CPT Violation from

There are still important measurements to do with kaons

over-constraining the CKM matrix is the aim

With the advent of the B factories, we were able to test this description for the first time!

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Unitarity of the CKM matrix gives 6 triangles in the complex plane; 9 relations in all few triangles have all sides with the same order in kaon system is not one of these interesting one for the Bd/u system is The Unitarity Triangle:mixingThe CKM Matrix in terms of Bd/u decay

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For neutral K, B, D mesons strong eigenstates are not CP eigenstates

mass eigenstates are an admixture of different strong eigenstates

particle antiparticle (mixing), f = 2Neutral Meson Phenomenology(mixing is very suppressed in the case of D mesons)if q/p1 have CP Violationin mixing; e.g. K=2.3x10-3CP evenCP odd

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Direct CP Violation (f = 1)need interference between diagrams with different strong (i) and weak phases (i):

Direct CPV only seen in ; ' ~ few 10-6

theory predicts large asymmetries in B+/0 (few to ~80%)

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Observing CP violation at the U(4S)Three observable interference effects:CP violation in mixing (|q/p| 1)(direct) CP violation in decay (|A/A| 1)CP violation in interference of mixing and decay (Iml 0)

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Searching for Direct CP Violation & probing New Physics with Bu/dLarge ACP requires amplitudes of similar orderbu: suppressed tree: i.e. charmless decayslarge predicted ACPbs,d: penguins: radiative decays good for constraining BSMsmall predicted ACP

Understand penguins

Access to , and

Sensitive to New Physics effects via loops minimal SUGRA: BXs, K+, K0+ R-parity Violating SUSY: KS SUSY searches K*

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Experimental Issuesinteresting modes have small branching fractionslarge light quark continuum background qqquarks below threshold are u,d,s & cother B background

Need good K/ separation

Need to boost to do time dependent CP measurements

require good vertex resolution for CP measurements

need to tag the flavour of the B (as a particle/anti particle)

understand charge biasdetector: trigger, tracking; reconstructionevent selection, particle ID, analysisphysics: differences in (anti)particle interaction in matter (e.g. K)

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On the whole - very similar designs with many common features for both Belle and BaBar:

e+e- colliders

run on the U(4S) resonance produce ~100% BB pairs

run 40 MeV below resonance for qq background studies

To measure CP violation in the B system, need to measure vertex difference of the evolving BB system (Dt) silicon device

need asymmetric beam energiesThe Accelerator & Experiment(PDG 2002)

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E(e-) = 9.0 GeVE(e+) = 3.1 GeV 0.56Design AchievedLuminosity (cm-2 s-1) 3 x 1033 5 x 1033

Int. Lum / day (pb-1) 135 341

Int. Lum / month (fb-1) 3.3 7.2The PEP-II e+e- collider

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SVT: 5 layers double-sided Si. Crucial for measuring t.

DCH: 40 layers in 10 super- layers, axial and stereo.

DIRC: Array of precisely machined quartz bars. Excellent Kaon identification.

EMC: Crystal calorimeter (CsI(Tl)) Very good energy resolution. Electron ID, 0 and reco.

IFR: Layers of RPCs within iron. Muon and neutral hadron (KL)The BABAR experiment

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Detection of Internally Reflected Cherenkov Light (DIRC)Measure angle of Cherenkov lightTransmitted by internal reflectionDetected by~10,000 PMTsexcellent K/ separationParticle Identification (PID)

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Measuring CP Violation from time dependence1. Start with data sample of BB pairs

2. Reconstruct one B in a CP eigenstate decay mode

3. Tag the other B to make the matter/antimatter distinction 4. Determine the time between the two B decay vertices, t

5. Plot t distribution and do CP fit for S and C.

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Event Selection TechniquesUse beam energy to constrain mass & energy difference

MES ~ 3 MeVE ~ 15-80 MeV; larger with neutralsqq background

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Event Selection Techniques B events are spherical u,d,s,c is jets

shape variablesu,d,s,cB event Maximum Likelihood fits or cut based analysis off-resonance & E sidebands are used to parameterise light quark background flavour-tagging (e, , K, slow from other B)

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B Flavour TaggingTagging algorithm with physics-based neural networksInputs include leptons, kaons, slow- (from D*), and high-momentum tracksOutputs combined and categorized by mistag probability (w)

5 mutually exclusive categories:Lepton isolated high-momentum leptons

Kaon I high quality kaons or correlated K+ and slow--

Kaon II lower quality kaons, or slow-

Inclusive unidentified leptons, poor-quality kaons, high-momentum tracks

Untagged no flavor information is usedQ = (1-2w)2 = (28.1 0.7)%

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Tagging: example of Charmless B DecaysTagging efficiency is very different for signal and background

Strong bkg suppression in categories with the lowest mistag prob (Lepton/Kaon)

plots shown are for h+h-, a rare decay with significant backgrounds.81/fb B h+h- sample split by tagging category150100

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Vertex Reconstruction Resolution function parameters obtained from data for both signal and backgroundSignal from sample of fully reconstructed B decays to flavor eigenstates: D*(, , a1)Background from data sideband samplewithout the boost would have z~20m

e.g. CLEO

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Dominant amplitudes for b ccs decay:

Both amplitudes have the same weak phase:

For B0 -> J/Y Ks we obtain:Golden Mode for CP Violation in B decay(theoretically clean)Measuring

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sin 2bmostly CP even

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Latest result on 88M BB events

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B0 Ksc.f. world average: sin2 = 0.73 0.06>2 difference.Belle measures -0.730.640.18~60 events

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Also have results fromD*D*, Ks, J/0but interpretation of the measurement of S and C in terms of the weak phase is plagued by uncertainty

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Measuring aInteresting modes to measure aneed to perform an Isospin analysis of branching ratios of B0 and B0 to 2p final states to determine shift in a due to the presence of penguin diagramsdoing a quasi 2 body analysis will eventually have to analysethe whole Dalitz plot.In analogy to these modes one needs to analyse the time dependence of this decay and extract a from an isospin analysis of each of the three partial waves (L=0,1,2) in the final state (full angular analysis is required)

The shift in a from penguin diagrams is expected to less than that in pp

Work is now in preparation for analysis of modes the time evolution of p+p- gives the shifted value of aneed a neutral B meson decay with several contributing processes that interfere in order to be able to measure the phase

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CP Violation in B0 p+p-

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The Isospin Analysis:Measure f (f) for B(B) fromAlready haveNeed to measureGrossman Quinn bound

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Fit projection in sample of pp-selected events

The first side of the Isospin triangle: B+p+p-PRL 2002 89 281802 fit , K simultaneously

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The Base of the Isospin Triangle: B+p+p0large qq background/K separation

Potential background from r+p-Minimize with tight cut on DE hep-ex/0303028, submitted to PRLSimultaneously fit for pp0/Kp0

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The Missing Sides : B0p0p0Small signal; BR few 10-60 background

Background suppressionEvent shape and flavour tagging to reduce qqCut on M(p+p0) and DE(p+p0p0) to reduce rp0 background, then fix in the fitSignificance including systematic errors = 2.5s

hep-ex/0303028, submitted to PRL

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Bounding penguin pollution:

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K is self tagging CK, SK, SK =0, CK =-1 large expected: ACP() & ACP(K)

signalSXF+BBg

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continuumB-backgroundtotal fit~88106 B pairsDilution from background

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Direct CP Violation Searches Looked for direct CP Violation in many modes

so far no evidence

most precise measurement ~4.6%

charge asymmetry in is 2.5 effect is 2.1 effect

look for updates using more data

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Rare Decays: very rare process

BR ~10-7

penguin + FCNC process

consistent with SM

sensitive to new physics

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radiative penguins new physics probes constrain |Vtd/Vts| (Rt)@90% C.L.78fb-120.7fb-1 Phys Rev Lett 88 101805 (2002)

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Observation of a Narrow Meson Decaying to D+s0 at a Mass of 2.32 GeV/c2hep-ex/03040210D+s

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Other BaBar physics Ive not coveredBaBar has also produced results on B lifetime and mixing; B, m semi-leptonic B decays D mixing fB+B-/fB0B0 to name but a few

in addition to B; have very large and D samples to study

produced in excess of 35 publications

several more preprints have been submitted for publicationhttp://www-public.slac.stanford.edu/babar/BaBarPublications.htm

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Summary Since the start up of BaBar and Belle we have learnt? SM description of CP Violation passed its first real test Observed CP Violation in the B System CP Violation in B system consistent with that in kaons Still not enough CP Violation to explain matter-antimatter asymmetry in the universe

Expect ~500 fb-1 by 2006 (5x current data set)

With this we will: start to test SM by doing alternate measurements of sin2 start to measure with greater precision in several modes continue the search for direct CP Violation work towards over constraining the unitarity triangle can we break it? search for and constrain new physics in the flavour sector

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Constraints on (,)CKM Fitter Group:A. Hcker, H. Lacker, S. Laplace,F. Le Diberder, Eur. Phys. Jour. C21 (2001) 225, [hep-ph/0104062]

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The Plan:o Talk to comprise:1) Theoretical overview:o neutral meson phenomenologyo types of CPV in meson decay [done]o observed CPV phenomenon before the B factory erao The CKM Matrix [done]o The Unitarity Triangle [done]o manifestations measured as time integrated Acp time dependent Acp(t)o new physics probes using rare decays [done][10 min]

2) The Experiment [done]o PEP-IIasymmetric colliding beams Y(4s) resonance runningo BaBarDCH, SVT tracking and vertexing (Delta T, Delta Z)EMC (pi0, photon reconstruction)IFR (muon detection)DIRC, DCH (PID)[5-min]

3a) Data Samples used, the 82/fb ICHEP sample and the 91/fb winter 03 sample3b) Experimental techniquessignal extraction [done]PID [done]Tagging -------- to redoVertexing [done][5min]

4) Results4a) sin2alpha[pp, rp, rr][8min]4b) sin2beta[charmonium, D*D*, phiKs][8min]4c) charmless B decays; b->u, b->s, b->ddirect CP Violation and other CP studies[2min]4d) other interesting results, D* (?), D mixing (?), charged/neutral ratio from Y(4s)B lifetimes and mixing?[0min]5) Summary, Outlook and Conclusions[2min]check the factor of two in the interference term sum.

define charge bias better than just detector, event selection/analysis again this slide is probably getting thrown away I assume that yannis or someone else will talk about the performance of the detector and the storage ringprobably should leave this by spend very little time on it .only comment spent too much time on this slide as I will probably be talking last also emphasize that the delta E resolution is highly mode dependant e.g. 80 MeV for pi0pi0 and ~15 MeV for anything without neutralsspecify the fisher? is there a need to do so?madd in central value of BR(pi0pi0) to this slide