the physics of flavor: half a billion b quarks for babar

The Physics of Flavor:The Physics of Flavor:Half a Billion b QuarksHalf a Billion b Quarks

for BaBarfor BaBar

Jeffrey BerryhillUniversity of California, Santa Barbara

For the BaBar Collaboration

Texas A&M Physics ColloquiumNovember 22, 2004

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Quarks, Flavor Violation, Quarks, Flavor Violation, and CP Violationand CP Violation

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aTm 22 Nov 04 Jeffrey Berryhill (UCSB) 3

Quarks and the problem of Quarks and the problem of mass mass

Up type (q=+2/3)

Mass

(GeV/c2)

Up u 10-3

Charm c 1

Top t 175

Down type

(q=-1/3)

Mass

(GeV/c2)

Down d 5 10-3

Strange s 10-1

Bottom b 5

Standard Model “explanation” of quark mass:Six quark species with unpredicted masses Spanning almost six orders of magnitude

The origin of different fermion generations, masses, flavor violation, and CP violation are all arbitrary parameters of electroweak symmetry breaking. A comparative physics of the quark flavors directly probes this little-known sector.


Quarks and their Strong Quarks and their Strong InteractionsInteractions

Quarks cannot be detected in isolation, only as bound statesA quark/anti-quark pair forms a bound state (mesons)

Flavor u,d s c b t

spin 0

mesons

+ (ud)

0 (uu-dd)

K+ (us)

KS0 (ds+sd)

D+ (cd)

D0 (cu)

B0 (db)

B+ (ub)

none

spin 1

mesons

+ (ud)

(uu-dd)

(uu+dd)

K*+ (us)

K*0 (ds)

(ss)

D*+ (cd)

D*0 (cu)

J/(cc)

(bb) none

b quarks are the heaviest flavor with measureable bound states→

B mesons are a natural starting point for studying the other flavors


The (Cabibbo-Kobayashi-Maskawa) CKM matrix: complex amplitude of each possible transition

Conservation of probability → CKM matrix is unitary

3X3 unitary matrix has (effectively) four degrees of freedom: 3 angles + 1 complex phase

Photon, gluon or Z boson: quark flavor conserving interactions

W boson: changes any down type flavor to any up type flavor

Quarks and Flavor ViolationQuarks and Flavor Violation

ijV

ud us ub

cd cs cb

td ts tb

V V V

V V V V

V V V

d

qI = s

b

u

qJ = c

t


Pairs of down (or pairs of up) type quarks can spontaneously swap flavor for anti-flavor via two flavor-violating exchanges “Meson Mixing” aka “Flavor oscillation”

Quarks and Flavor Violation: Quarks and Flavor Violation: MixingMixing

0B 0B

Prob(B0 → B0) ≈ exp( - t)/2 * ( 1 – cos(m t) )

Similar to neutrino oscillation, except decay term added Mixing time ~few ps

Sensitive to Vtd, top quark!


Quarks andQuarks and CP ViolationCP Violation

For a particle(s) f with momentum p and helicity

C : Charge conjugation operator C f(p, ) = f(p, )P : Parity reversal operator P f(p, ) = f(-p, -) CP f(p, ) = f(-p, -)CP eigenstate: particle = anti-particle (Ex: qq mesons)

CP conservation → left-handed particles have the same physics as right-handed anti-particles

Obviously violated for our (baryon-asymmetric) local universe!

In the Standard Model CP violation originates from complex phase in CKM matrix → in general, Vij ≠

Vij*


Three Paths to CP ViolationThree Paths to CP Violation

1. CP violation in meson mixing

Mixing rate of meson to final state f not the same asMixing rate of anti-meson to same final anti-state

In the Standard Model, very small ~10-

3

CP violation in K0 decays first observed through this path forty years ago!

0B 0B 0B0B

f f

≠2 2

CP violation → an observable O of particles (f1,f2,…) such that O(f1,f2,…) ≠ O(CP(f1,f2,…)) = O(f1, f2, …)



2. CP violation in meson decay → “Direct CP violation”

0B 0B

f f

≠2 2

Decay rate of meson to final state f not the same asDecay rate of anti-meson to same final anti-state

Recently observed in B0 →K+ - at the 10% level!

BBAABBARARBBAABBARAR

0

0

BB K

K

BlueRed

mBCandidate mass


If B0 and B0 decay to the same final state fCP, there is interference between amplitude of direct decay and amplitude of mixing followed by decay

In the presence of CP violating phases in these amplitudes, can induce large time-dependent asymmetry with frequency equal to mixing frequency:


cos( ) sin( )CP CP CPf f fA C mt S mt

0 implies Direct ViolationCPf

C CP

3.Time dependent asymmetry of meson/anti-meson decay rate to a common final state

≠0B0B

2fCP

0B

0B2

fCP


CKM UnitarityCKM Unitarity

,

0,1

2

3 0,0

1

ud ub

cd cb

V V

V V

td tb

cd cb

V V

V V

Inner product of first and third columns of CKM matrix is zero:

Rescale, rotate and reparameterize to describe a Unitarity Triangle in the complex plane

Measure sides (decay rates) and angles (CP violation)to test unitarity


b Quarks andb Quarks and CKM UnitarityCKM Unitarity

,

0,1

2

3 0,0

1

ud ub

cd cb

V V

V V

td tb

cd cb

V V

V V

B decay rates, CP asymmetries measure the entire triangle! Triangle sides: B+→ l-decay rate measures b→u transition (|Vub|) Bmixing rate measures |Vtd|

Angles: B0 → + - time dependent CP asymmetry measures sin 2 B0→ J/ KS

0 time dependent CP asymmetry measures sin 2B+→ D(*)K+ decay rates measure

Need large sampleof B0, B+ mesons produced undercontrolled conditions

B Factory ExperimentsB Factory ExperimentsTM


Asymmetric B FactoriesAsymmetric B Factories

Y(4S) meson: bb bound state with mass 10.58 GeV/c2

Just above 2 x mass of B meson → decays exclusively to B0 B0 (50%) and B+ B- (50%)

B factory: intense e+ and e- colliding beams with ECM tuned to the Y(4S) mass Use e beams with asymmetric energy → time dilation due to relativistic speeds keeps B’s alive long enough to measure them (decay length ~0.25mm)

S:B = 1:4

e+3.1 GeV

e-9 GeV

Y(4S)

Y(4S)B0

B0


PEP-II at the Stanford Linear PEP-II at the Stanford Linear Accelerator CenterAccelerator Center

BaBar detectorBaBar detector

LinacLinac

PEP-II Storage RingsPEP-II Storage Rings

SF Bay ViewSF Bay View


PEP-II performancePEP-II performance

PEP-II top luminosity: 9.2 x 1033cm-2s-1 (more than 3x design goal 3.0 x 1033)

1 day record : 681 pb-1

About 1 Amp of current per beam, injected continuously

Run1-4 data: 1999-2004 On peak 205 fb-1

(e+e- →Y(4S)) = 1.1 nb →227M Y(4S) events produced

Run1

Run2

Run3

Run4

454 million b quarks produced!Also ~108 each of u, d, s, c, and

Jeffrey Berryhill (UCSB)

INFN, Perugia & UnivINFN, Roma & Univ "La Sapienza"INFN, Torino & UnivINFN, Trieste & Univ

The Netherlands [1/5]NIKHEF, Amsterdam

Norway [1/3]U of Bergen

Russia [1/11]Budker Institute, Novosibirsk

Spain [2/2]IFAE-BarcelonaIFIC-Valencia

United Kingdom [10/66]U of BirminghamU of BristolBrunel UU of EdinburghU of LiverpoolImperial CollegeQueen Mary , U of LondonU of London, Royal Holloway U of ManchesterRutherford Appleton Laboratory

USA[38/300]

California Institute of Technology

UC, IrvineUC, Los AngelesUC, RiversideUC, San DiegoUC, Santa BarbaraUC, Santa CruzU of CincinnatiU of ColoradoColorado StateFlorida A&MHarvardU of IowaIowa State ULBNLLLNLU of LouisvilleU of MarylandU of Massachusetts, AmherstMITU of MississippiMount Holyoke CollegeSUNY, AlbanyU of Notre DameOhio State UU of OregonU of PennsylvaniaPrairie View A&M UPrinceton USLAC

U of South CarolinaStanford UU of TennesseeU of Texas at AustinU of Texas at DallasVanderbiltU of WisconsinYale

Canada [4/20]U of British ColumbiaMcGill UU de MontréalU of Victoria

China [1/5]Inst. of High Energy Physics,

Beijing

France [5/51]LAPP, AnnecyLAL Orsay

May 3, 2004

The BABAR Collaboration

11 Countries 80 Institutions593 Physicists

LPNHE des Universités Paris VI et VIIEcole Polytechnique, Laboratoire Leprince-RinguetCEA, DAPNIA, CE-Saclay

Germany [5/31]Ruhr U BochumU DortmundTechnische U DresdenU HeidelbergU Rostock

Italy [12/101]INFN, BariINFN, FerraraLab. Nazionali di Frascati dell' INFNINFN, Genova & UnivINFN, Milano & UnivINFN, Napoli & UnivINFN, Padova & UnivINFN, Pisa & Univ &

ScuolaNormaleSuperiore


The BaBar detectorThe BaBar detector

Cherenkov Detector (DIRC)

144 quartz barsK, separation

Electromagnetic Calorimeter6580 CsI crystals

e+ ID, and reco

Drift Chamber40 layers

Tracking + dE/dx

Instrumented Flux Return19 layers of RPCs and KL ID

Silicon Vertex Tracker

5 layers of double sided silicon strips

e+ [3.1 GeV]

e- [9 GeV]


Our Friendly CompetitorsOur Friendly Competitors

Measuring the Measuring the Standard Model Standard Model

CP Violating PhaseCP Violating PhaseTM


BB00 → J/→ J/ K KSS00 and sin 2 and sin 2

Decay dominated by a single “tree-level”Feynman diagram: b → ccs

J/ identified cleanly by decay to a lepton pair; KS identified cleanly by decay to pion pair.Both particles are CP eigenstates → both B0 and B0 decay to them

Time-dependent CP violation has amplitude sin 2 and frequency m

Works for several other b →ccs decays as well; results can be combined


Time-Dependent CP Violation: Experimental Time-Dependent CP Violation: Experimental techniquetechnique

Fully reconstruct decay to CP eigenstate f

Determine time between decays from vertices Determine flavor and vertex

position of other B decay

Asymmetric energiesproduce boosted Υ(4S), decaying into coherent BB pair

l-

K-

e- e+

B0

B0

Δz=(βγc)Δt

J/ψ

KS

µ+

µ- π+

π-

Compute CP violating asymmetry A(t) = N(f ; t) – N(f ; t) N(f ; t) + N(f ; t)

(t) ≈ 1 ps


sin 2 fit results

sin2β = 0.722 0.040 (stat) 0.023 (sys)

J/ψ KL (CP even) mode(cc) KS (CP odd) modes

Raw asymmetry A(t) ≈ ( 1 – 2w ) sin 2 sin mt

Signal yield, background yield, sin 2, flavor tagging, t resolution function all from simultaneous maximum likelihood fit to signal+control samples


Consistency checksConsistency checks

Χ2=11.7/6 d.o.f.

Prob (χ2)=7%

Χ2=1.9/5 d.o.f.

Prob (χ2)=86%

J/ψKS(π+π-) Lepton tags

ηF=-1 modes Cleanestcharmonium sample

Purest flavor tagging mode


CKM Unitarity Triangle: Experimental CKM Unitarity Triangle: Experimental Constraints Constraints

Constraints fromConstraints from

Decay ratesDecay rates and and Mixing RatesMixing Rates


CKM Unitarity Triangle: Experimental CKM Unitarity Triangle: Experimental ConstraintsConstraints



CP violation inCP violation inKaon decayKaon decay


CKM Unitarity Triangle: Experimental CKM Unitarity Triangle: Experimental ConstraintsConstraints



CP violation inCP violation inKaon decayKaon decay

CP violation inCP violation inbb→→ ccs ccs

Remarkablevalidation ofthe CKM mechanismfor both flavorviolation andCP violation!

CP Violation Redux:CP Violation Redux:Trees vs. PenguinsTrees vs. Penguins

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A Third Path to Flavor ViolationA Third Path to Flavor Violation

1. Tree diagram decay: down → up

2. Box diagram: neutral meson mixing

3. Penguin diagram: down-type changesto down-type via emission & reabsorptionof W; top-quark couplings Vtd, Vts dominate

SM penguins are suppressed; new physics can compete directly!


identified cleanly by decay to a kaon pair; KS identified cleanly by decay to pion pair.Both particles are CP eigenstates

Decay rate 100X smaller than J/ KS

→ small signal, large background

BB00 → → K KSS00 and sin 2 and sin 2

Decay dominated by a single “gluonic penguin”Feynman diagram: b → sss

0Bb s

s

sd

dg

, ,u c t

0SK

W

, , ( )CPKK

114 ± 12 B0 → KS events out of ½ billionb quarks produced!

Time-dependent CP violating asymmetry A can be measured in the same way as J/ KS

Same combination of CKM complex phases as J/ KS → same relation between A and sin 2


BB00 → → K K00 and sin 2 and sin 2Fit ResultFit Result

B0KSB0KS 0 0.29 0.31SK

S

0tagB

0tagB0 1

SK

B0KLB0KL 0 1.05 0.51

LKS

0tagB

0tagB0 1

LK

sin 2= S( K0) = +0.50 ± 0.25 ±0.07vs. S( K0) = +0.72 ± 0.04 ±0.02

Consistent with tree decays, about 1 low


Trees(green) vs. Penguins(yellow): Trees(green) vs. Penguins(yellow): BaBar DataBaBar Data

Averaging overmany penguindecays:

BaBar discrepancy with tree decays

= -2.7


Trees(green) vs. Penguins(yellow): Trees(green) vs. Penguins(yellow): World AverageWorld Average


World discrepancy with tree decays

= -3.5


Trees(green) vs. Penguins(yellow): Trees(green) vs. Penguins(yellow): World AverageWorld Average

Red boxes:estimate from theory of errorsdue to neglectingother decay amplitudes


World discrepancy with tree decays

= -3.5


New Physics ScenariosNew Physics Scenarios

•New physics at the electroweak scale generically introduces new large flavor-violating or CP-violating couplings to quarks

→Existing flavor physics measurements severely limit types of new physics!

• The great number of possible new couplings can give rise to many different combinations of effects

Ex: Right handed (b →s) squark mixing in gluino penguins could introduce a new phase in b → sss penguins without affecting B mixing nor b → ccs nor b → s


Future and Follow-up MeasurementsFuture and Follow-up Measurements

•Both B factories hope to collect 4-5 X more data over the next 4-5 years•Significance of the penguin problem could double and unambiguouslyfalsify the Standard Model!

•Improved measurements of rates and asymmetries in other penguin decays (b →s , b→ d , b→ s l l, B → K*, ……)

•Fermilab Tevatron can measure Bs , b decays •LHCb, BTeV: scheduled to produce billions of B’s in pp collisions

•Super B Factory: 50X version of B factories


SummarySummary

•The physics of quark flavor, as seen through the b quark, is a rich area of study with wide-ranging implications

•The Standard Model CKM theory of flavor and CP violation holds up well for tree-level processes

•Penguin processes, which are especially sensitive to new physics, could prove to be the lever which cracks the Standard Model wide open

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BackupsBackupsTM


Direct CP Violation: BaBar DataDirect CP Violation: BaBar Data

Direct CP violation consistent with 0 for all modes


Direct CP Violation: World AverageDirect CP Violation: World Average


bb ss Asymmetries: Summary Asymmetries: Summary

sgn0- = -sgn C7

Can we exclude C7 > 0 ?

•BaBar measurements on 82 fb-1

K*, K2* preliminary; Xs published

•CP asymmetries consistent with SM (0.4%) at the ~5% level•K* isospin asymmetry 0- consistent with C7 < 0•Statistics limited up to ~1 ab-1


CKM ConstraintsCKM Constraints


CKM matrix constraintCKM matrix constraint

SU(3) breaking of form factors 2= 0.85 ± 0.10

weak annhilation correction R = 0.1 ± 0.1

Penguins are starting toprovide meaningful CKMconstraint

Reduction of theory errorsnecessary to be competitive with Bd,Bs mixing

Ali et al. hep-ph/0405075

no theory error (2,R) = (0.85,0.10)

theory error (2,R) = (0.75,0.00)

95% C.L. BaBar allowed region (inside the blue arc)


Direct CP Asymmetry: b Direct CP Asymmetry: b →→ssandandBB KK* *

Sum of 12 exclusive,self-tagging B→Xs final states

Xs = K/Ks + 1-3 pionsE > 2.14 GeV

b→s b→s

b →s ACP = (N – N)/(N + N) = 0.025 ± 0.050 ± 0.015

B →K* ACP = -0.013 ± 0.036 ± 0.010 submitted to PRL, hep-ex/0407003

0- = (K*0 ) – (K*- ) = 0.050 ± 0.045 ± 0.028 ± 0.024 (K*0 ) + (K*- )

< 1% in the SM, could receive ~10% contributions from new EW physics Either inclusive or exclusive decays could reveal new physics

B or K charge tags the flavor of the b quark with ~1-2% asymmetry systematic

PRL 93 (2004) 021804, hep-ex/0403035

Asymmetries also measured precisely in exclusive K* decays:

preliminary


Time-Dependent CP Asymmetry inTime-Dependent CP Asymmetry in B B →→K*K*(113 (113 fbfb-1-1))

As in B0→J/ KS, interference between mixed andnon-mixed decay to same final state required for CPV.

In the SM, mixed decay to K* requires wrong photonhelicity, thus CPV is suppressed:

In SM: C = -ACP ≈ -1% S ≈ 2(ms/mb)sin 2 ≈ 4%

Measuring t of K*(→KS0) events requires novel beam-constrained vertexing techinque:

Vertex signal B with intersection of KS trajectory and beam-line

Usable resolution for KS decaying inside the silicon tracker

Validated with B0→J/ KS events


First ever measurement of time-dependent CP asymmetries in radiative penguins!

Likelihood fit of three components(qq, BB, K*)to 5D data (mES,E,Fisher,mK*,t)

K* signal = 105 ± 14 events

S = +0.25 ± 0.63 ± 0.14

C = -0.57 ± 0.32 ± 0.09

submitted to PRL, hep-ex/0405082

Consistent with SM

For C fixed to 0, S = 0.25 ± 0.65 ± 0.14

preliminary

Time-Dependent CP Asymmetry inTime-Dependent CP Asymmetry in B B →→K*K*(113 (113 fbfb-1-1))


preliminary

the physics of flavor: half a billion b quarks for babar

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