1 october 25 th, 2002gerhard raven, nnv 2002 cp violation: observing matter-antimatter asymmetries...

October 25th, 2002 Gerhard Raven, NNV 2002 1

CP Violation: CP Violation: Observing Matter-Antimatter Observing Matter-Antimatter

AsymmetriesAsymmetries

NNV meetingOctober 25th 2002

Gerhard Raven Vrije Universiteit Amsterdam

& NIKHEF

1964 1999


Searches for Anti-Matter in the UniverseSearches for Anti-Matter in the Universe

• Universe around us is matter dominated – Absence of anti-nuclei amongst cosmic rays in our galaxy– Absence of intense ray emission due to annihilation of

distant galaxies in collision with antimatter

Anti-Matter Spectrometer


Matters dominates the visible universeMatters dominates the visible universe

• Where has the anti-matter gone?• In 1966, Andrei Sakharov showed

that the generation of a net baryon number requires:1. Baryon number violating

processes (e.g. proton decay)2. Non-equilibrium state during the

expansion3. Violation of C and CP symmetry

• Standard Model CP-violation is very unlikely to be sufficient to explain matter asymmetry in the universe– It means there is something

beyond the SM in CP violation somewhere, so a good place for further investigation

-4 -6N(anti-Baryon) 10 -10

N(Baryon)

All searches for primordial antimatter have only yielded limits:


Three Important Symmetries Three Important Symmetries

• Parity, P– Parity reflects a system through the origin. Converts

right-handed coordinate systems to left-handed ones.– Vectors change sign but axial vectors remain unchanged

• x x , L L

• Charge Conjugation, C– Charge conjugation turns a particle into its anti-particle

• e e K K

• Time Reversal, T– Changes, for example, the direction of motion of particles

• t t

• CPT Theorem– One of the most important and generally valid theorems in local

quantum field theory.– All interactions are invariant under combined C, P and T– Implies particle and anti-particle have equal masses and lifetimes


Weak Force breaks C, breaks P, Weak Force breaks C, breaks P, but it conserves CP (really?)but it conserves CP (really?)

• 1957, -decay of 60Co:Weak Interaction breaks both

C and P symmetry maximally!

• Despite the maximal violation of C and P symmetry, the combined operation, CP, seemed exactly conserved

• But, in 1964, Christensen, Cronin, Fitch and Turlay observed CP violation in decays of Neutral Kaons!

W+

e+R

L

W

eR

L

W

eL

R

W+

e+L

R

P

C


The neutral Kaon system and CP violationThe neutral Kaon system and CP violation

• Kaons are mesons (qq bound states) with Strangeness = ±1. The neutral kaons are:

and can be produced by the strong interaction (which conserves Strangeness) via, e.g.:

• But K 0 and K 0 are not the mass eigenstates. It was long thought that those were given by the following states of definite CP (because of their decay properties):

• A state produced as K 0 or K 0 can be seen as a superposition of KS and KL

0 0

0 0

1, 1,

21

, 1,2

S

L

K K K CP

K K K CP

0

0

( ), 1

( ), 1

K ds S

K ds S

0 p K 0 0 1 1S

0 0

0 0

,CP K K

CP K K


Two very different kaonsTwo very different kaons

• While the K 0 and K 0 are charge conjugate states, the KS and KL are not, and they have different decay modes and lifetimes

• KS and KL decay to 2 or 3 pions, one can show that the 2 final state has CP 1, and the 3 state has CP 1

• Because the mass of 3 pions is very close to the mass of the kaon, the 2 and 3 final states have very different phase space factors leading to very different lifetimes of the KS and KL

• Wonderful for experiments! Easy to separate KS from KL

10

8

2 0.9 10 s

3 5.2 10 s

S

L

K

K

CP 1

CP 1


Discovery of CP violation in KDiscovery of CP violation in K00 decay decay

• In 1964, Cronin, Fitch et al. observed the long lived KL (which was presumed to be CP-odd) decaying into , which is a CP -even final state!– This decay occurs only ~0.2% of the time

• The long lived particle is therefore not a CP eigenstate, implying Weak Interaction violates CP

• We now refer to the two different neutral kaons KL and KS as :

1 2

2 1

32 10

S

L

K K K

K K K

K1 and K2 are the CP even and odd eigenstates,

not KS and KL


Tagged K0 and K0 production:

pp K+K0- K+(+ -) -

K-K0+ K-(+ -) +

How to tell matter from anti-matterHow to tell matter from anti-matter

A(KS)

(t)

A(KL)

K0(t=0)

Opposite signs for KL-KS interference term between K0 and K0

•If CP were conserved, KL wouldn’t

decay to , and there would be no interference…

-A(KS)

(t)

A(KL)

K0(t=0)

CP

D.Banner et al., PRD 1973

CPLEAR, PLB 1999

K0

K0

(K0-K0)/(K0+K0)

decaytime / KS


Kobayashi and Maskawa and CP ViolationKobayashi and Maskawa and CP Violation

• Proposed an bold explanation of CP violation in K decay based on the minimal Standard Model and dynamics within :– CP violation appears only in the charged current weak interaction of

quarks– There is a single source of CP Violation

Complex Quantum Mechanical Phase in the coupling matrix

– Need at least three Generations of Quarks to allow this

• at that time only u,d,s known!

– CP is not an approximate symmetry, large phase differences possible

1972


The weak decay of quarks and leptonsThe weak decay of quarks and leptons

• The weak interaction can change the flavour of quarks and leptons– Leptons only change into the other lepton in the same generation

– But quarks can change into a quark of any charge changing generation

W

e

W

b W

c

b W

u


The weak coupling of quarksThe weak coupling of quarks

• The coupling strength at the vertex is given by gVij

– g is the universal Fermi weak coupling

– Vij depends on which quarks are involved

– For leptons, the coupling is just g• For 3 generations, the Vij can be

written as a 3x3 matrix– This matrix is referred to as the CKM

matrix (Cabibbo, Kobayashi, Maskawa)

• We can view this matrix as rotating the quark states from a basis in which they are mass eigenstates to one in which they are weak eigenstates

b W

cgVcb

b

s

d

VVV

VVV

VVV

b

s

d

tbtstd

cbcscd

ubusud

ud us ub

CKM cd cs cb

td ts tb

V V V

V V V

V V V

V


CP violation and the SM: the CKM matrixCP violation and the SM: the CKM matrix• With 3 families, the CKM matrix is a 33 complex unitary matrix

– 18 parameters, with 9 constraints, 6 of which can be represented as triangles in the complex plane, e.g.

– With 6 quarks, 5 (relative) phases are unphysical and can be ‘rotated away’ be redefining the quark fields

• Requires 18-9-5=4 independent parameters to describe it:– 3 real numbers & 1 complex non-trivial phase

–It is the non-trivial phase which is responsible for all CP violation–All CP violating observables are due to interference

–CP violation is “built” into the Standard Model iff 3 generations

* * * 0ud ub cd cb td tbV V V V V V


Intermezzo: LEP @ CERNIntermezzo: LEP @ CERN

Maybe the most important result from LEP:“There are three generations of light

neutrinos”

L3

Aleph

OpalDelphi

Geneva Airport “Cointrin”MZ


Unitarity of the CKM matrixUnitarity of the CKM matrixThe CKM Matrix: Wolfenstein The CKM Matrix: Wolfenstein ParameterizationParameterization

Complex phase

λ =Vus = sin(Cabibbo) = 0.2205 ±0.0018A =Vcb/ λ2 = 0.83±0.06

=

Measurements are usually summarized by plotting their constraints on the- plane

d•s* = 0 (K system)

s•b* = 0 (B system)

d•b* = 0 (B system)

•All triangles have the same area: A6•Out of 6 triangles, the “db*” one (together with the “tu*” one) is “special”:

•It has all sides O(3)•And thus large angles


From CKM matrix to CP ObservablesFrom CKM matrix to CP Observables

CP D+D– | H | B0 = |A|e+i D+D– | H | B0 = |A|e-i

B0

• The phase shift due to any single side of the triangle is not observable, but relative phase shifts between sides are:

| B0 f |2 – | B0 f |2 = – 4 |A1| |A2| sin(1– 2) sin(1 –2) (i = non-CKM phase of Ai)

CPf B0 f

|A1| e+ie+i

|A2 | e+ie+i

|A1| e-ie+i

|A2| e-ie+i

A2

A1

B0 f

A1

A2B0 f

• Reflecting a quark process involving W bosons in the CP mirror induces a CP-violating phase shift in the transition amplitude: Vcd Vcb*

Vcd* Vcb

| B0 D+D- |2 – | B0 D-D+ |2 = 0


How can we measure the angles?How can we measure the angles?

• What are the theoretical requirements for an observable interference sensitive to unitarity triangle angles?– At least two interfering amplitudes– with different CKM phases (sides of the triangle)– and with different non-CKM phases

• What conditions lead to a large observable asymmetry?– asymmetry = (|A|2 – |A|2) / (|A|2 + |A|2) (triangle area) / (length of sides)

B system should have much larger asymmetries than kaons!

• What kinds of interference can we calculate?– In order to extract unitarity triangle angle(s) (1 – 2) from a measurement,

we must know the value of the non-CKM phase shift ( – ):• asymmetry sin(1 – 2) sin(1 –2)

– When these phase shifts are due to long-distance QCD effects, they are generally not calculable (but it may be possible to measure them).

• This is the reason why the asymmetry measurements in K decays are hard to interpret!

• Need a ‘clean’ non-CKM phase!


Produce an bb bound state, (4S),in e+e- collisions: e+e- (4S) B0B0 and sometimes observe an B0B0 event!

~17% of B0 and B0 mesons mix before they decay: m ~ 0.5/ps, B ~ 1.5 ps

BB00BB00 mixing: ARGUS, 1987 mixing: ARGUS, 1987

0*122

*2

02

10*

111*1

01

,

,

DDDB

DDDB

first hint of a really large mtop!

|B0 (t) cos(m t/2) |B0 + i e+2imixing sin(m t/2) |B0

|B0 (t) cos(m t/2) |B0 + i e-2imixing sin(m t/2) |B0


CPCP violation in the inference between mixing and violation in the inference between mixing and decaydecay

Neutral B meson mixing provides an error-free

source of non-CKM phase shift, by 90o ( i ):

B0(t) fCP

B0

cos(mt/2)

i sin(mt/2) e +2imixing

B0A e+idecay

A e-idecay

CP

B0(t) fCP

B0cos(mt/2)

i sin(mt/2) e-2imixing

B0

A e-idecay

A e+idecay

0 0

0 0

( ( ) ) ( ( ) )( )

( (

sin(2 -2 )s

) )

in(

( ( ) )

) mixing decay

CP

CP CPphys physf

CP CPp

d

hys phys

B t f B t fA t

B t f B

m

f

t

t

Sin(2mix-2decay)

= 0.75

This leads to a time-dependent CP asymmetry

with a very clean interpretation directly in terms of CKM phases!


Golden Decay Mode: BGolden Decay Mode: B00 J/J/KK00SS

• 2mixing - 2decay =arg{ }

• Theoretically clean way to measure • Clean experimental signature• Branching fraction: O(10-4)

• “Large” compared to other CP modes!

Time-dependent CP asymmetry

sin 2( ) sin( ) CP CPA t m t CP = +1

B0 J/ K0L

CP = -1 B0 J/ K0

S

B0 (2s) K0S

B0 c1 K0

S

“Golden Modes”

J/J/

KK00SS

BB00


The The Quest Quest for for CP ViolationCP Violation in the in the B SystemB System

The The Quest Quest for for CP ViolationCP Violation in the in the B SystemB System

ATLAS

BTEBTEVV

CLEO 3BBAABBARAR

BELLE

2007?

199919992000

2007

2002

Mission StatementMission StatementMission StatementMission StatementObtain precision measurements

in the domain of the charged weak interactions

for testing the CKM sector of the Standard Model, andprobing the origin of the

CP violation phenomenon

2002


B meson productionB meson production

BaBar & Belle

D0/CDF HERA-B LHCb

PEP-II/KEKB Tevatron

HERA LHC

mode e+e- pp pA pp

Start datataking 1999 2002 200? 2007

s (GeV) 10.4 = M(4S)

2000 42 14000

bb/qq 1/4 1/1000 1/1000000

1/160

Nqq/s (Hz) 20 20k 10M 13M

Nbb/s (Hz) 5 20 20 100000

<B flight distance> (m) 260 450 9000 10000

Branching ratios CP-channels: 10-4 and smaller:Must produce MANY B mesons

•e+e- B factories: •clean events•easy trigger (>99% for all B)•only B+ and Bd produced

•Hadron colliders: •huge b production rate•low sbb/sinel -> triggering!•large B flight distance

• excellent proper time resolution•both Bd and Bs


B Meson Production: the “easy” way…B Meson Production: the “easy” way…

• Electron-Positron collider: e+e- (4s) B0B0

– Only 4s resonance can produce B meson pair – Low B0 production cross-section: ~1 nb– Clean environment, coherent B0B0 production

B-Factoryapproach

B0B0 threshold

BB

thre

shold

28.0hadr

bb

CESRCLEO


(4S): Coherent B(4S): Coherent B00BB00 production production

• B0B0 system evolves coherentlyuntil one of them decays (EPR!)– CP/Mixing oscillation clock only starts

ticking at the time of the first decay, relevant time parameter t:

– B mesons have opposite flavour at time t=0– Half of the time CP B decays first (t<0)

• Integrated CP asymmetry is 0:

• Coherent production requires time dependent analysis

At tcp=0

B0

B0

At t=0

B0

B0

t = tCP - tOtherB

Coherent

Incoherent

-

+ +

-t(ps)

t(ps)


A Symmetric Collider won’t work…A Symmetric Collider won’t work…

• CP asymmetry is a time-dependent process– ACP t between two B decays, t ~ ps

– In reality one measures decay distance between two B decays

• In symmetric energy e+e- collider, where (4S) produced at rest, daughter B’s travel ~ 20m– Too small a distance to discern with today’s detector

technology

l 40 m

Btag BCP

5.3 GeV 5.3 GeV

e+


Solution: Boost the CMS!Solution: Boost the CMS!

+e-e

Coherent BB pair

z

Δ zΔ tβγ c

B

Btag

z

Start the Clock

| | 260Bz c m

This can be measured using a silicon vertex detector!

4s

()(4S) = 0.56

Brec


PEP-II: PEP-II: Asymmetric B Factory @ SLAC B Factory @ SLAC

= 0.56, s = M(4S)

HER LER

Energy (GeV) 9.0 3.1

Number of bunches 1658 1658

Beam Current (A) 1.0 2.1

Peak L ( 1033 cm-2s-1 or nb-

1/s)4.6

Collisions every 4.2 ns..fortunately most collisions

don’t result in an interaction

Linac

LER

LER

HER


BaBar and Belle: available dataBaBar and Belle: available data

•Both experiments started data taking in 1999 only 2 weeks apart•After 3 years, both experiments ~90M BB each

•out to 360M qq events on tape•size of BaBar database: ~650TB•>1000M fully simulated MC events (Geant4)•LEP: ~3M qq events per experiment…

•CP samples are O(1000) (or much less!) events


The Roadmap to sin2The Roadmap to sin2

+e-e

Brec

z Btag

z

Exclusive

B Meson

Selection

and Vertex

Reconstruction

Exclusive

B Meson

Selection

and Vertex

Reconstruction-π

0sK +π

+μ

-μ

Tag Vertex Reconstruction

Tag Vertex Reconstruction

FlavourTaggingFlavourTagging

e+K-

Measurements• B±/B0 Lifetimes

• B0 B0-Mixing

• CP-Asymmetries• sin(2)

Ingredienta) Reconstruction of B mesons in

flavour eigenstatesb) Tag B vertex reconstruction

c) Flavour Tagging (+ a + b)

d) Reconstruction of B mesons in CP eigenstates (+ a + b + c)

Hig

her p

recisio

n

Incre

asin

g c o

mple

xity


(2S) Ks

+- +-

Example of a Fully Reconstructed Example of a Fully Reconstructed EventEvent

B0 D*+ -fast

D0+

soft

K-+

‘’fish eye’’ view

fast

soft

B0(t)

At t=0 (i.e. when the D* decay happened), the ‘CP’ B was/would have been a B0

EPR

!Kb

c s

In general, use charges of identified•leptons,•kaons,•soft pions

from the “the rest of the event” to tag B flavour


B meson selection at B meson selection at (4S)(4S)

mES

E

sidebands

signal region

E [

MeV

]

mES [GeV/c2]

Two main kinematic variables for exclusively reconstructed B candidates:i) E = EB

cms - s/2•There are exactely 2 B mesons produced, nothing else•A signal B candidate must carry (in the CMS) half the CMS energy

ii) MES = s/4-pB2

•Invariant mass, substituting the measured B energy with the better-known s/2.

2 2 2 2beamE E E

10 40 MeVE

22.6 MeV/ cESm

2

2 2 2 2

ESm pbeam beamB

pm

J/Ks (-)


The The CPCP Sample Sample

Mode Ntag Purity (%)

J/Ks (-) 974 96.5

J/Ks () 170 88.5

(2s)Ks 150 96.9

cKs 80 94.5

cKs 132 63.4

(cc)Ks 1506 92.2

J/KL 988 55.2

J/K*0(Ks 0) 147 81.2

All CP 2641 78.2

B0 J/ K0S

(2s) K0S

c1 K0

S

c K0

S

J/ K*(K0S0)


| |/

41 sin(2 )sin(

d

f

Bd

B

te

CP,f (Δt) m t

| |/

41 sin(2 )sin(

d

f

Bd

B

te

CP,f (Δt) m t

1 (1 2 )sin(

42 )sin

d

d

B

B|Δt|/τ

CP, f def (Δt) η Δm Δtwβ

τ

R1 (1 2 )sin(4

2 )sind

d

B

B|Δt|/τ

CP, f def (Δt) η Δm Δtwβ

τ

R

t Spectrum of t Spectrum of CPCP events events

00tag BB 00

tag BB

perfect flavour tagging & time

resolution

Mistag fractions wAnd Resolution function R

CP PDF

00tag BB 00

tag BB

realistic mis-tagging & finite time

resolution

1 (1 2 )cos( )4

dB

Bd|Δt|/τ

mixing, dwef (Δt) Δm Δt

τ

R1 (1 2 )cos( )

4dB

Bd|Δt|/τ

mixing, dwef (Δt) Δm Δt

τ

R

Mixing PDFmeasured from fully reco’d flavour sample, B0 -> D(*)+ -, … (~10x more events)


•All analysis were done “blind” to eliminate possible experimenters’ bias

–In general, measurements of a quantity “X” are done with likelihood fits – blinding done by replacing “X” with “X+R” in likelihood fits

–R is draw from a Gaussian with a width a several times the expected error

–Random number sequence is “seeded” with a “blinding string”

–The reported statistical error is unaffected

–It allows all systematic studies to be done while still blind

–Example: the BaBar sin(2) result for ICHEP02 was “unblinded” 2 weeks before paper was submitted to hepex/PRL!

Blind AnalysisBlind Analysis


“ “Golden” and J/Golden” and J/KKLL

sin2 = 0.741 0.067 (stat) 0.033 (syst)sin2 = 0.741 0.067 (stat) 0.033 (syst)

sin2 = 0.755 0.074 sin2 = 0.723 0.158

hep-ex/0207042, Accepted by PRL

BaBar


Compilation of sin2Compilation of sin2 Measurements Measurements

World average~13 significant

CP is broken in B decays

sin2 = 0.73 0.06

CP asymmetry in B J/ KS,L

is large


Interpretation of the ResultInterpretation of the Result

One solution for is consistent with measurements

of sides of the unitarity triangle

Method as in Höcker et al,hepex/0104062 (see also many other recent global CKM analyses)

Error on sin2 is still dominated by statistics and will decrease ~1/for the forseeable future…

Ldt

The KM mechanism has successfully

survived its first precision test!


What Next?What Next?

These 2 measurements both depend on the Bd mixing diagram…

Which could be ‘polluted’ by physics beyond the SM!

b

d

ss

sd

Same decay as J/ KS: should measure same sin(2) only if no ‘new’ contribution to this process

KS

B0

To hunt for and disentangle contributionsfrom ‘new physics’ beyond the SM, need to

• Measure all angles ‘cleanly’(no theoretical uncertainties!)• 1 down, 2 to go…

• In redundant ways (they may not be!)• Consider many Bs modes

• Improve the measurements of the ‘sides’


The TEVATRON: BThe TEVATRON: Bss mixing! mixing!

x s

DD -- ZEROZERO

CDFCDF

TEVATRONTEVATRON

•Run II has started (finally)•Main Injector added•Much improved CDF and D0 detectors•B physics reach:

•Bs Ds (Bs mixing)•Bs J/ (angle )•Bs DsK (angle )

ms = xs/ ~ 27

Current limit (LEP, SLD): ms > 14.4/ps (95%CL)

hint at 17.5/ps?


The Next GenerationThe Next Generation

Precision tests of the consistency of the KM picture requires

•MANY more B decays,•Access to Bs decays

A dedicated B-physics experiment at the LHC:

LHCb


A Dedicated B detector: LHCbA Dedicated B detector: LHCb

@LHC, B mesons are mainly produced forward

A detector designed for•Measurements of and •Exploration of the Bs sector•Very rare B decays

See parallel session talks:•Bart Hommels •Hella Snoek•Marko Zupan


LHCb contribution after LHCb contribution after 11 year of running: year of running:

From Bfactories


Summary and OutlookSummary and Outlook

• CP is not a symmetry of nature!• CP violation is a pure QM effect due to interference• We can make an absolute (not just relative!) statement of

what is matter, and what is anti-matter

• After almost 40 years, CP violation has been observed in a system other than kaons: B decays• CP violation is not something specific to kaons!• CP is very much broken in B decays• And we can finally make a quantitative interpretation• The KM ‘ansatz’ has survived its first real test…

• In the coming years, additional measurements in B-decays, at PEP-II, KEK-B, the Tevatron, and ultimately at the LHC will tell us whether there is more to CP than “just KM” • Exciting times ahead!


CP Violation Saves The World!

People around the world are grateful to particle physicists today as a doomed visit from the Planet-X delegation was called off at the last minute after it was found they were made of anti-matter. “I never thought this CP stuff was useful”, one physicst was overheard saying, ”but they claimed that sin(2) = - 0.78, and we are sure we agreed on all the sign conventions so there was only one option left…”

??

X or X?


BACKUP SLIDESBACKUP SLIDES


0 0B

Sources of interferencesπρ

0B πρ0πππ

πρB0

πρB0

)t(B0 0πππ

0B

0ππππρ )t(B0 0B

)δα2(sin strong

α2

strongδ

Higher resonances,

with different strong phases, might spoil the measurement

Measurement of sin2Measurement of sin2 with B-> with B->

mES

E

0B

61692 yield

510)3.05.01.3( BF

BABAR (20.7 fb-1) prelim

Exploit interferences in the 3 final stateo Fit to the time-dependent Dalitz ploto In principle, extract without ambiguity

Need at least 1,500 events with B/S<2o needed, but color-suppressed


Prospects for Measuring Prospects for Measuring

• decays to extract– CPV in mixing/decay– clean theoretically,

• pure tree amplitudes – no penguin pollution

– …but time-dependent CP asymmetries at the few % level

• decays to extract – interference

D π sin(2 ) 0 (DCS)*B D π 0 *B D π

Original construction by Gronau & Wiler:

2

0B D K 0B D K

0 0 0 where , CPD K D D f


mmdd Measurement in Comparison Measurement in Comparison

• Precision md measurement (3%) with Bflav sample is still statistically limited

• Systematic error under control (2%)– Dominated by uncertainty on B

– Followed by resolution fcn and tagging-vertexing correlations.

• Theoretical hadronic uncertainties limit extraction of |Vtd |

22 2 2 2 2

02( / ) | |

6 d d d

Fd w B t W B td B B

Gm m e S m m m V B f

2 2(210 40MeV)d dB BB f (PDG 2000)


Measurement of sin2Measurement of sin2

3. Reconstruct Inclusively the vertex of the “other” B meson (BTAG)4. Determine the flavour of BTAG to separate B0 and B0

5. compute the proper time difference t 6. Fit the t spectra of B0 and B0 tagged events

(4s)

= 0.56

Tag B

z ~ 110 m Reco Bz ~ 65 m

-z

t z/c

K0

KS0

-

+

1. Fully reconstruct one B meson in CP eigenstate (BREC)2. Reconstruct the decay vertex

+


BB00 B B00 mixing: ARGUS, 1987 mixing: ARGUS, 1987

• Fully reconstructed mixed event and dilepton studies demonstrate mixing

• Integrated luminosity 1983-87:– 103 pb-1

0*122

*2

02

10*

111*1

01

,

,

DDDB

DDDB


Control Sample: Control Sample: Fully-Reconstructed B flavour eventsFully-Reconstructed B flavour events

Cabibbo-favored hadronic decays

“Open Charm” decays

ducb

( )b c c s

0 *0/ ( )B J K K

[GeV/c2]

01

( )B D π /ρ /a

Color suppressed decays into charmonium final states

ES / 2m2 2cm

B = s - p

Select “self-tagging” decays


BBdd ++

BBs s D DssKK

LHCb contributions to CP violationLHCb contributions to CP violation


Sin(2Sin(2) Likelihood Fit) Likelihood Fit

Simultaneous unbinned maximum likelihood fit to t spectra to both flavour and CP samples

35 total free parameters

All t parameters and mistag rates extracted from data Correct estimate of the uncertainty due to statistical error in resolution fcn parameters and mistag rates

Fit Parameterssin2 1Mistag fractions for B0 and B0 tags 8Signal resolution function 8Empirical description of background t 17B lifetime fixed to the PDG value B = 1.548 psMixing Frequency fixed to the PDG value md = 0.472 ps-

1

Global correlation coefficient for sin2b: 14%

tagged flavour sample

tagged CP samples

Driven by


CP violation in mixingCP violation in mixing

Mixing between B0 and B0 can be described can by effective Hamiltonian:

12 describes B0 f B0 via on-shell statesUnlike the kaon system, this is rare: the branching ratios of CP states is very small

M12 describes B0 f B0 via off-shell states

CP violation can occur in the interference between the on-shell and off-shell amplitudes, and leads to However, for B0 mesons, 12 is very small: mixing is dominated by m=2M12

Little CP sensitivity…

0 012 12

* * 0 012 12

Mass Eigenstates 2

L

H

M M B pB qBiH

M M B pB qB

Prob(B0 B0) Prob(B0 B0) |q/p|1


The BaBar DetectorThe BaBar DetectorCerenkov Detector

(DIRC)144 quartz bars

11000 PMs

1.5 T solenoid

Electromagnetic Calorimeter

6580 CsI(Tl) crystals

Drift Chamber40 layers

Instrumented Flux Returniron / RPCs ( / neutral hadrons)

Silicon Vertex Tracker5 double sided layers

e+ (3.1 GeV)

e- (9 GeV)

SVT: 97% efficiency, 15 m z hit resolutionSVT+DCH:(pT)/pT = 0.13 % pT + 0.45 %

DIRC: K- separation: 4.2 @ 3.0 GeV/c 2.5 @ 4.0

GeV/c EMC: E/E = 2.3 %E-1/4 1.9 %


Reconstruct Brec vertex from charged Brec daughters

Determine BTag vertex from charged tracks not

belonging to Brec

Brec vertex and momentum

beam spot and (4S) momentum

High efficiency (97%) Average z resolution is 180 m (<|z|> ~ ct = 260 m) Conversion of z to t takes into account the (small) B

momentum in (4S) frame

t resolution function measured directly from data

Vertex and Vertex and t Reconstructiont Reconstruction

Beam spot

Interaction Point

BREC VertexBREC daughters

BREC direction

BTAG direction

TAG Vertex

TAG tracks, V0s

z

* * * *cos ( )rec rec rec recz c t c t 0* * * *cos ( | |)rec rec rec rec Bz c t c t


Systematic ErrorsSystematic Errors

Signal resolution and vertex reconstruction 0.014 Resolution model, outliers, residual misalignment of the

Silicon Vertex Detector Factor of 3 smaller compared to last publication

Tagging 0.007 possible differences between BCP and Bflavour samples

Backgrounds 0.022 (overall) Signal probability, fraction of B+ background in the signal

region, CP content of background Total 0.05 for J/ KL channel; 0.09 for J/ K*0

Monte Carlo statistics used for validation: 0.014 External parameters (B and m): 0.014 Total: 0.04 for total sample

Error/Sample KS KL K*0 Total

Statistical 0.10 0.19 0.56 0.09

Systematic 0.04 0.06 0.10 0.04


Mixing with Dilepton EventsMixing with Dilepton Events

Very precise mixing measurement– Select events with 2 high

momentum leptons in run 1 • Sample contains ~50% B+

• Fraction of B+ is a free parameter

– Largest syst. are B0 lifetime and resolution function param’zn

md=0.493±0.012±0.009 ps-1

Su

bm

itted

to P

RL:

hep

-ex/0

1 1

2 0

45

20 fb-1


Search for Direct CPSearch for Direct CP

To probe new physics (only use CP=-1 sample that contains no CP

background)|| = 0.92 ± 0.06 (stat) ± 0.02 (syst)

No evidence of direct CP violation due to decay amplitude interference (SCP unchanged in Value)

CP CPf fcos( sin(( )) - )CP df dC mA t St m t

CP

CP

CP

2f

f 2f

1 | λ |

1 | λ |C

CP

CP

CP

ff 2

f

2 Im λ

1 | λ |S

Without SM Prejudice :

If more than one amplitude present then || might be different

from 1


Neutral and Charged B Meson LifetimesNeutral and Charged B Meson Lifetimes

• Simultaneous unbinned maximum likelihood fit to B0/B+ samples• Allt characteristics (both signal

and bkgd) determined from data

• Precision measurements:• 2 % statistical error• 1.5 % systematic error

t (ps)

0 = 1.546 0.032 0.022 ps

= 1.673 0.032 0.022 ps

/0 = 1.082 0.026 0.011

t RF parameterization, t outlier description

Common resolution function for B+ and B0

20 fb-1

PRL 87 (2001)

t distribution well described!

bkgd

signal

+bkgd

outliers


Check “null” control sample: B Flavour Check “null” control sample: B Flavour EventsEvents

•Treat Bflavour sample as CP•No asymmetry seen:“sin2” = 0.00

•Analysis doesn’t create artificial asymmetries

Sample “sin2”

Boflavour 0.00 ± 0.03

B+ -0.02 ± 0.03


Consistency ChecksConsistency Checks

Subsamples

Various Vtx reconstructions


A few words about J/A few words about J/K*K*00(K(KSS00))

J/ K*0(KS0) angular components:

• A|| ,A0 : CP = +1

• A : CP = -1 (define R = |A|2 )

CP asymmetry diluted by D = (1 - 2R)

R = (16.0 ± 3.2 ± 1.4) % (BABAR, to appear in PRL)

Last year, just used R as an additional dilution

Now, perform full angular analysis instead:

O 1D: Treat R as dilution

2D: Use tr

4D: Full angular analysis


• The time and angle dependent decay rate is given by

• The angular terms depend on the transversity angles and amplitudes Ax

• These amplitudes are functions of the strong phases

• D(, Ax) suffers from the sign ambiguity under

• Floating cos(2) does not change the value of sin(2): fit is not very sensitive to cos(2)

• The effect seems large, but it is statistical:

J/J/K*K*00 and cos(2 and cos(2))

φ ,φ

rad

rad

)2(cos2.22sin12cos 2

±0.7 (syst)

±0.7 (syst)


CPCP violating observables for B mesons violating observables for B mesons

• As mentioned, need at least two amplitudes with different phases• In B decays, we can consider

two different types of amplitudes:– Those responsible for decay

– Those responsible for mixing

• This gives rise to three possiblemanifestations of CP violation:– Direct CP violation

• interference between two decay amplitudes– Indirect CP violation

• interference between two mixing amplitudes

– CP violation in the interferencebetween mixed and unmixed decays

d

bW

d

uu

d

B0

B0 B0

b

b d

d

u,c,t

u,c,t

W W


BB00 and B and B00 tagged events and Asymmetry Plot tagged events and Asymmetry Plot

• The curve looks vertically shifted; is this a problem? NO!– The Likelihood is normalized to the sum of all tagged events– The asymmetry is made from the projection of the

Likelihoodfor B0 and B0 tagged

– Since the actual number of the 2 flavours is not identical in data there is a vertical shift

• 471 B0 and 524 B0 tagged golden events• 7530 B0 and 7394 B0 tagged B flavour events

• The weighted average of the fit B0 and B0 tagged events only is right on: 0.747 +/- 0.088– The fit is not sensitive to the individual normalization

• One can make the plot ‘pretty’ by renormalizing the Likelihood curve to the actual numbers


““Renormalized” Renormalized” t spectrum and t spectrum and AsymmetryAsymmetry

Likelihood curve projection

Likelihood curve normalized to the actual # of observed B0 and B0 tags in data


Mistag Rates: The numbersMistag Rates: The numbers

Tagging Category

Efficiency(%)

Mistag Fractionw(%)

B0/B0 diff.w(%)

Q=(1-2w)2

(%)

Lepton 11.1 0.2 8.6 0.9 0.6 1.5 7.6 0.4

Kaon 34.7 0.4 18.1 0.7 -0.9 1.1 14.1 0.6

NT1 7.7 0.2 22.0 1.5 1.4 2.3 2.4 0.3

NT2 14.0 0.3 37.3 1.3 -4.7 1.9 0.9 0.2

All 67.5 0.5 25.1 0.8

(sin2) 1/Q

Mistag fraction as determined from simultaneous fit to Bflav sample


BBdd decays and the Unitarity Triangle decays and the Unitarity Triangle

* * * 0ud ub cd cb td tbV V V V V V

Bd ,, …

Bd J/Ks, D*+D*-,…B D*, DK, K

B , , l, l,…

BdBd, Bd

B D(*)l,D(*),…


Resolution Function ParametersResolution Function Parameters

Score 1.19 0.07

bcore(lepton) 0.01 0.07

bcore(Kaon) -0.24 0.04

bcore(NT1) -0.20 0.08

bcore(NT2) -0.21 0.06

Stail 3.0 (fixed)

btail -2.5 1.7

Soutlier 8 ps (fixed)

ftail 0.05 0.04

foutlier 0.004 0.002

(1 ) ( , )

( , )

( , )

tail outlier core t core

tail tail t tail

outlier outlier outlier

R f f G S

f G S

f G


SLAC B Factory PerformanceSLAC B Factory Performance

PEP-II delivered : 77.7 fb-1

BABAR recorded : 73.8 fb-1 (incl. 7.9 fb-1 off peak)

•PEP-II top luminosity: 4.5 x 1033cm-2s-1 (design 3.0 x 1033)

•Average BaBar logging efficiency: > 95%

•Analysis Samples (on peak)

– Run1: 20.7 /fb– Run2a: 9.0 /fb– Run2b: 26.7 /fb– Total: 56.4 /fb

30/fb usedfor mixing

21/fb usedfor lifetime

off-peak

56/fb usedfor CP


sin2sin2, , BB and and mm

• Fixed ,m to PDG 2000:B = 1.548 ps,

m = 0.472 ps-1

• Dependence of sin2 on ,m: sin2 = 0.75 - 0.31(m-0.472 ps-1)

- 0.62(B-1.548 ps)


BB Measurements in BaBar Measurements in BaBar

e-|t|/

Either Brec or Btag can decay first (this analysis)

BaBar/Belle

t resolution

e-t/

true t

B production point known eg. from beam spot

LEP/SLD/CDF/D0…

Need to disentangle resolution function from physics !

measured t

Resolutionfunction Resolution

fcn+

lifetime

Resolution Function + Lifetime =

=


Comparison of Lifetime Ratio MeasurementsComparison of Lifetime Ratio Measurements

(99-01)


Mixing Likelihood FitMixing Likelihood Fit

UnmixMix

f (Δ t) 1 1 2 cos( )4

Bd

d

| Δ t |/τ

Bd

e ΔtΔmw Rτ

Fit Parametersmd 1Mistag fractions for B0 and B0 tags 8Signal resolution function(scale factor,bias,fractions)8+8=16Empirical description of background t 19B lifetime fixed to the PDG value B = 1.548 ps

Unbinned maximum likelihood fit to flavour-tagged neutral B sample

44 total free parameters

All t parameters extracted from data


Mixing Likelihood Fit ResultMixing Likelihood Fit Result

md=0.516±0.016±0.010 ps-1 •PRL

CL=44%

( ) ( )( )

( ) ( )

(1 2 )cos( )

unmixed mixedmix

unmixed mixed

N t N tA t

N t N t

w m t

29.7 fb-1

At t=0 only unmixed events produced (EPR!):

can extract mistag rate from data!

mixA

~1-2w


MiU

xnmix 1 cos( )

4f (Δ t)

Bd

d

| Δ t |/τ

Bd

eΔm Δt

τ

t Distribution of Mixed and Unmixed t Distribution of Mixed and Unmixed EventsEvents

Decay Time Difference (reco-tag) (ps)

UnMixedMixed

0

10

20

30

40

50

60

-8 -6 -4 -2 0 2 4 6 8

perfect flavour tagging & time

resolution

Decay Time Difference (reco-tag) (ps)

UnMixedMixed

0

10

20

30

40

50

60

-8 -6 -4 -2 0 2 4 6 8

realistic mis-tagging & finite time

resolution

Unmix

xMi

f (Δ t) 1 1 2 cos( ) ResolutionFunction4

Bd

d

d

| Δt |/τ

B

e tτ

mw Δ Δ

0 0

0 0

0 0

0 0Mixed:

Unmixed: tagflav

tagflav

tag flav

tagflav

or

or

B B

B B

B B

B B

w: the fraction of wrongly tagged events

md: oscillation frequency

+-


mmdd: Cross Checks and Systematic Errors: Cross Checks and Systematic Errors


• event-by-event (t) from vertex errors• Resolution Function (RF) – 2 models:

– Sum of 3 Gaussians (mixing + CP analyses)

– Lifetime-like bias (lifetime analysis)

t Signal Resolutiont Signal Resolution

(1 ) ( , )

( , )

( , )

tail outlier core t core

tail tail t tail


R f f G S

f G S

f G

(1 ) ( , 0)

( , 0) exp( / )

( , )

tail outlier t core

tail t bias


R f f G S

f G S t S

f G

high flexibility

small correlation with B)

z

Signal MC (B0)

t(meas-true)t

tracks from long-lived D’s in tag vertex asymmetric

RF

~0.6 ps


Sin 2Sin 2 statistical error vs. time statistical error vs. time

ICHEP00

Winter 01

LP01

Winter 02

Still improving fasterthan statistics:

improved resolution,improved efficiency,additional modes,…

1 october 25 th, 2002gerhard raven, nnv 2002 cp violation: observing matter-antimatter asymmetries...

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