lhcb eduardo rodrigues university of glasgow supa lectures, glasgow, january 2011 part iv cp...

LHCb

Eduardo RodriguesUniversity of Glasgow

SUPA Lectures, Glasgow, January 2011

CP VIOLATION

Part IV

CP violation and B Physics

Part IV

CP Violation and B Physics

Chris Parkes

Chris Parkes 2

Outline

PHENOMENOLOGY AND EXPERIMENTS

III. CP violation and Kaon physics

IV. CP violation and B physicsB factories, old and future experiments

Mixing in neutral B mesons

Benchmark B decays

Rare B decays

V. CP Violation and D physics

VI. Concluding remarksPresent status and future ahead

Chris Parkes 3

Overview of B (and D) physics CPV experiments

B factories (2000 2010): electron-positron at γ(4S) resonance BaBar (SLAC, USA), Belle (KEK, Japan)

Discovered CP Violation in B system, angle β Tested CKM mechanism D mixing established

BelleII for high luminosity Super KEK-B starts 2015 TeVatron run II (2001 2011):

Proton- anti-proton CDF, D0

Discovered Bs Mixing LHC (2009 )

LHCb (also ATLAS and CMS to some extent) Discovered Bsμμ

CP Violation in Bs system D mixing at 5σ

Chris Parkes 4

Of the 6 orthogonality relations the CKM matrix satisfies

the “bd” term is central in many B-meson decays:

CP violation studies with B mesons?

tbtstd

cbcscd

ubusud

CKM

VVV

VVV

VVV

Vikjkj

ijVV *

b t d,s

s,d t bW W

b

s,d

d,s

t tb

W

WcdcbVV *

udubVV *tdtbVV *

“The” unitarity triangle (“bd”)

0*** bdtdtbcdcbudub VVVVVV

butransitions

bctransitions

B0

mixing

Of the 6 orthogonality relations the CKM matrix satisfies

the “bd” term is central in many B-meson decays:

0*** bdtdtbcdcbudub VVVVVV

butransitions

bctransitions

B0

mixing

B factories,

old and future experiments

Chris Parkes 6

Ingredients of B physics experimentOscillations time dependent

measure time from distance (d=γct) travelled in experiment

hence B needs to be produced boosted

Symmetric e+e- won’t work ! p-p ok, partons different energies

B decays (lifetime=1.5ps) – observe decay products

Bs oscillations very fast

excellent Vertex Detector

Final state decay products (mostly) : pion, kaon; electron, muon,

Need excellent particle ID

B-hadrons are heavy and long-lived !

Chris Parkes 7

Idea of an asymmetric "B factory"

Oddone & Dorfan in PEP-II Tunnel, 2003

• ϒ(4s) since heavy enough to decay into BB

• Produce the (4S) with a strong boost in lab frame – different energies e-, e+

• BB in coherent state – oscillate together (EPR Paradox)

• Find if B or B at decay time from final state

• Deduce the t from the distance between the two B vertices along the boost axis

Chris Parkes 8

B factories PEP-II (BaBar) and KEKB (Belle)

• Asymmetric beams boosted B’s

• Time difference between B decays z

Chris Parkes 9

High rate– statistics limited channel

Why study CP violation at a hadron collider?

Clean environment– no additional tracks

Initial state– B0B0 or B+B-

B mesons ~ 20% stot

– simpler triggering Rich programme but messy environment

e+ e-

(BaBar)

pp(D0)

Production of all typesBs and b-hadrons

_

Chris Parkes 10

~ 6.23 Km long √s = 1.96 TeV

Started operation in 1987

Run I : collected about 100 pb-1 until 1996

Run II: between 2001 and 2011

(after long shutdown until 2000)

CDF and D0 @ TeVatron, Fermilab

Chris Parkes 11

LHC @ CERN and LHCb

9 km diameter

GenevaJura

CERN

Chris Parkes 12

LHCb environment

LHC environment pp collisions at ECM = 8 / 14 TeV

tbunch = 25/50 ns 40/20 MHz bunch crossing rate

<L> = 4.1032 cm-2 s-1 @ LHCb interaction region

Forward peaked, correlated production

~ 1 cm

Bp-p collision

Measure distance production

(primary vertex p-p) till decay

(B decay vertex) to get timeLHCb VErtex LOcator (VELO)

Silicon detector discs along beam direction

pp

Chris Parkes 13

The LHCb experiment @ the LHC – characteristics

Forward spectrometer

Acceptance: 1.9 < h < 4.9

Nr of B’s / year: 1012

Detector: excellent tracking excellent PID

Reconstruction: - muons: easy - hadronic tracks: fine - electrons: OK - p0’s: possible but difficult - neutrinos: no

p p

Tracking:Silicon & Straw tubesMagnetic field

Calorimeters:Electromagnetic &Hadronic calorimeters- Critical (with muons) for triggering

Vertexing:High precision silicon detectors (10μm position resolution) very close to collision point

B flight path of the order 5-10mm

RICH performance:Cherenkov radiation.Measures velocity, combine with momentum to get massParticle identification in p range 1-100 GeVp, K ID efficiency > 90%, misID<~10%

Mission statement

- Search for new physics probing the flavour structure of the SM- Study CP violation and rare decays with beauty & charm hadrons

Mission statement

- Search for new physics probing the flavour structure of the SM- Study CP violation and rare decays with beauty & charm hadrons

Mixing in neutral B mesons

Chris Parkes 15

Neutral B-mesons “identity card”: 2 types of neutral B mesons

24;72.0

8.17

5.0103.3

1.0,105

1

113

3

s

ss

d

dd

s

d

s

ss

d

dd

mx

mx

psm

psGeVm

yy

Neutral B system in nature

Oscillations parameter

Small lifetime differences

Large mass differences(~100 times larger in Bd

case compared to K system)

B0 = db

Bs = sb

B0 = db

Bs = sb

B=+1B=-1

Reminder of Natural Units, =c=1

Energy GeV Momentum GeV/c (abbreviated to GeV) Mass GeV/c2

Length (GeV/c)-1 c=0.197GeVfm=1 [1fm=1E-15m]– Natural unit of length 1GeV-1=0.197fm

Time (GeV/ )-1 =6.6E-25GeVs– Natural unit of time 1GeV-1=6.6E-25s

Cross-section (GeV/c)-2 1barn=10-28m2

– Natural unit of xsec =1GeV-2=0.389mb Charge - ‘Heavyside-Lorenz units’ ε0=1 Use dimensionless ‘fine structure constant’

137

1

44

2

0

2

e

c

e

Can quote mass

in seconds-1

Chris Parkes 17

b

du, c, t W-

W+_

d

b_u, c, t

b

d u, c, tW- W+

_

d

b_

u, c, t___

B0B0-

(and similarly for Bs)

Neutral B-mesons mixing

Feynman (box) diagrams for neutral B-meson mixing:

Dominated by top quark contribution :

Chris Parkes 18


b

du, c, t W-

W+_

d

b_u, c, t

b

d u, c, tW- W+

_

d

b_

u, c, t___

B0B0-

12

*12

M

M

p

q

*

*

tdtb

tdtb

VV

VV

p

qFor B0

For B0s *

*

tstb

tstb

VV

VV

p

q




Sensitivity to a CKM triangle side and

angle b

Sensitivity to side and equivalent angle bs

Chris Parkes 19


b

du, c, t W-

W+_

d

b_u, c, t

b

d u, c, tW- W+

_

d

b_

u, c, t___

B0B0-




Chris Parkes 20

ARGUS, 1987

Observed a fully reconstructed, mixed, event, with no possible background.

Measured the like-sign lepton fraction, and found that ~17% of B0 mesons mix before they decay tB~1.5 ps, Dm~0.5/ps

Phys. Lett. B 192, 245 (1987)

2

12

1

0.00002 psGeV

0.5ps

tB

mm

c

Discovery of B0 mixing

First hint of a really large top mass !

Chris Parkes 21

Belle: K. Abe et al., PRD 71, 072003 (2005) Babar: B. Aubert et al., PRD 73, 012004 (2006)

Belle: B0 lifetime BaBar: md

Some state-of-the-art B0 mixing measurements

B0 oscillates once every 8 decay times ! (2 /p Dm )t

Chris Parkes 22

Measuring Bs mixing – tagging & decay time

opposite-side K

jet charge

Decay modetags b flavorat decay

2nd B tags production flavor Proper decay timefrom displacement (L)and momentum (p)

Need to determine:– Flavour at production tagging– Flavour at decay, from final state– B decay length

Chris Parkes 23

Bs Mixing Measurement

CDF discovery 2006, LHCb measurement 2011

Oscillations occur at 3 trillion Hz !

Observed amplitude is not 1 as smeared

- Mistag (B or B) of events

- Resolution on time

Line is fitted oscillations

Points are data

Low background

Most precise measurement of |Vtd/Vts|

Δms= 17.768 ± 0.023 (stat) ± 0.006 (syst) ps−1

Chris Parkes 24

Key Points – B experiments & mixing

• Dedicated Experiments

• Asymmetric e+e- collider B Factories (Babar, Belle, Belle II)

• pp collider (LHCb)

• B needs to be boosted

• Excellent Vertexing and Particle ID

• Neutral systems: B0 and Bs

• Very different oscillation rates

• Very fast Bs oscillations (3 trillion Hz!)

• Mixing through box diagrams with top quark

• Flavour tagging at production

• Flavour tagging at decay

Benchmark B decays: α, β,ϒ

Chris Parkes 26

The CKM matrix in terms of the Wolfenstein parameters

B0 and Bs mixing phases sensitivity

CKM angle measurements with B decays

1ˆˆ12

1

21

423

22

52

32

iAAiA

AiA

iA

VCKM

iub eV

itd eV si

ts eV

cdcbVV *

udubVV *tdtbVV *

“The” unitarity triangle (“bd”)

a

g b

The standard techniques for the angles

b : B0 mixing (phase β) (+ single b c decay)a : B0 mixing (phase β) + single b u decay (phase γ)g : b u (phase γ) (interference with b c)

Chris Parkes 27

Measurement of sin(2b) – B0 J/Y Ks decay

Measurement type : time-dependent CP asymmetries of B decay to CP-eigenstate final state

The “golden mode” B0 J/Y Ks :

Theoretically clean way of measuring the b angle

Clean experimental signature (J/Yμ+μ-; Ks+-)

Large (for a B meson) branching ratio ~ 10-4

ff

ffCP tA

)(

The B-factories were built for the

measurement of b !c.f. CPLEAR K0 to π+π-

+

e-iφ

Amplitude 1 Amplitude 2

Process via interference with/without mixing

Chris Parkes 28

Angles – measured from interference

Both give same rate - Interference necessary but not sufficient

Two routes A1,A2 to same final state

- hence interference sensitive to phase

Chris Parkes 29

Angles – measured from interference

Additional phase κ that doesn’t flip under CP, allows ϕ to be measured

Oscillation & Decay

30

t=0 t

B0

B0

B0

B0

B0

B0

Amplitude

Amplitude

Rate

Rate

Measuring a CKM angle

31

But in B system and put

Gives: This extra i is the phase difference (here k=900) we need

1. Origin of extra phase k

2. Origin of weak phase ϕ

If and hence Lets assume we can write

Making these substitutionsThe two phase differences give terms

The rate difference is time dependent

( hence assumed i.e. no direct CP Violation)

Measuring a CKM angle

32

simplifying

Time dependent oscillations with amplitude of asymmetry given by phase ϕ

As x~1, only part of an oscillation seen

Chris Parkes 33

Aside on getting CKM phase or phase *

Feynman rules:

Vud if incoming d-quark or outgoing anti-d quark

Vud* if incoming u-quark or outgoing anti-u quark

Quantities to find:

Chris Parkes 34

Which CKM angle is measured ?

Chris Parkes 35

Showing that φ=2β from CKM elements

Chris Parkes 36

Chris Parkes 37

ff

ffCP tA

)(

β accurately

measured

β=21.5±0.80

(HFAG summer 2012)

Chris Parkes 38

Measurement of sin(2a) – B0 pp decay ?

Tree diagrams only:

Routes to final state

with and without mixing.

Interference of these gives angle.

mixing decay

Chris Parkes 39

Measurement of sin(2a) – B0 pp decay ?

But there is another route to this same final state with non-negligible

amplitudeHence not a clean measurement of α

Solutions: use channels with small penguin

contributiuons, or correct for penguin effect

Chris Parkes 40

Measurement of sin(2a) – B0 pp (and other hh) decays

No identification

Purity = 9.5%

With pion identification

Purity = 85%, Eff. =90%

LHCb:

particle identification is crucial !

From all channels α moderately well measured

α=85.4±4.00 (CKM fitter Aug. 2013)

Chris Parkes 41

B D0 K : - theoretically very clean way of measuring g

- sensitivity to g from interference between the 2 diagrams

- only requirement: D0 and D0 decay to common final state

- final state contains D - final state contains D-bar

Measurement of g – popular (family of) methods

u

bB 0D

u

c

Ku

s

u

b

B

Ku

s

0Dc

u

*uscbVV *

csubVV

Currently least well measured angle but LHCb changing this

Note – charged B here, so no mixing

Weak phase

But also relative strong phase (δ) between

the amplitudes of the two diagrams

- nuisance parameter

Chris Parkes 42

1ˆˆ12

1

21

423

22

52

32

iAAiA

AiA

iA

VCKM

In both cases only complex phase is in Vub element, so this measures γ

Measuring gamma

1. Why is this γ ?

2. How to get round strong phase

Interference of amplitudes sensitive to

Chris Parkes 43

1ˆˆ12

1

21

423

22

52

32

iAAiA

AiA

iA

VCKM

In both cases only complex phase is in Vub element, so this measures γ

Measuring gamma

1. Why is this γ ?

2. How to get round strong phase

Interference of amplitudes sensitive to

or

Hence using all four processes can get γ

Combining all channels

γ poorly measured yet

γ=68.0±8.30 (CKM fitter Aug. 2013)

Hot Topic -

Semi-leptonic B Asymmetry

CP Violation in mixing

Chris Parkes 45

Like sign dimuon asymmetryD0 Collab.

B0/B0s

B0/B0s

t=0 t

B0/B0s

B0/B0s

B0/B0s

B0/B0s

d d

bBo

c

μ-

ν

W-

D+

example decay:

• Produce BB pair (or Bs)

• If one oscillates before decaying

get two like sign leptons (++ or --)

• If no CP Violation in mixing get

N++ =N--

Chris Parkes 46

New Physics ? Situation unclear –improved measurements needed(excellent PhD project…)

Like sign dimuon asymmetry: current results

D0 – B and Bs decays inclusively

Tevatron: proton anti-proton – equal matter anti-matter

LHC proton proton – production asymmetry, makes analysis more tricky

but statistics higher

LHCb – Bs only:

first result compatible SM and D0 !

Asy

mm

etry

B0 s

Asymmetry B0

World average 2.9σ away from SM !

Direct CP Violation in B0/Bs

including discovery of

CP Violation in Bs system

Chris Parkes 48

Time-integrated measurement: Direct CP Violation

Direct CP Violation: two-body B0 & Bs decays

Chris Parkes 49



Chris Parkes 50



Use f

Chris Parkes 51

However several different two-body B decays

Separate with Particle ID and mass for B0/Bs


(also Λb, 3-body backgrounds)

Bhh, (h=K,π)

10.5σ

Asymmetry

Chris Parkes

52

PRL110, 221601 2013

B B

BsBs6.5σ

Asymmetry FIRST CP


Dalitz Plots – three body decays

Bhhh

Chris Parkes 54

Dalitz Plot – Visualize three body decays

Dalitz Plot: Scatter plot in mab2, mac

2

If no intermediate structure then uniformly populated

(inside kinematic bounds)

If intermediate resonances, r,

then plot will have internal structure

Shorter-lived resonances – larger widths

Richard Dalitz

• Energy Conservation sets boundaries of plot

• Q = TA+TB+TC,

• Q energy released in decay of P,

• Ti K.E. of product i

m2bc

Chris Parkes 55

CP Violation in B+hhh

• Make Dalitz plot for B+,B-

• Any difference is CP violation

Dalitz PlotACP in Dalitz plot bins

• Local regions of large CP violation(empty bands in plot are regions that have been cut-out as used as cross-checks)

ρ0(770), f0(980)

K*(890), K*(1430)

χc0

• Resonances seen in plot

Rare B decays

Chris Parkes 57

Rare Decay Loops

Chris Parkes 58

Rare B decays – All active research topics at LHCb

DECAY TYPE B.R. (approx.)

B0 K*0 g Bs f g

B0 w gRadiative penguin

4.0 x 10-5

2.1 x 10-5

4.6 x 10-7

B0 K*0 m+ m- Electroweak penguin 1.2 x 10-6

Bs f f

B0 f KS

Gluonic penguin1.3 x 10-6

1.4 x 10-6

Bs m+ m - Rare box diagram 3.5 x 10-9

Radiative penguin

Chris Parkes 59

The B(s) m+m- decay (1/2)

• Really really rare! But well predicted in SM

SM box SM Penguin

• Sensitive to New Physicsin SUSY models

• Unique Experimental signature• Easy to identify / trigger – good for ATLAS/CMS as well

60

25 year long search

Phys.Rev.Lett. 108 (2012) 231801

SM theory

Powerful constraint on SUSY

Chris Parkes 61

Key Points – B section

• CKM Angles

• Measured from interference of two routes to same final state

• sin(2b) – B0 J/Y Ks

• sin(2a) – B0 p+p- decay, and the problem of ‘’penguin pollution’’

• angle ϒ - B- D0 K-, and strong phases

• Semileptonic B asymmetry, D0 experiment discrepancy with SM

• Discovery of (Direct) CP Violation in Bs system, LHCb

• BsK- π+

• Dalitz Plots and use as tools for CP violation, LHCb

• B+hhh

• Rare B Decays

• Discovery of LHCb

lhcb eduardo rodrigues university of glasgow supa lectures, glasgow, january 2011 part iv cp...

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