Stefan Spanier University of Tennessee

1Stefan Spanier

Search for New Physicswith B-Mesons

Search for New Physicswith B-Mesons

Stefan SpanierUniversity of Tennessee

2Stefan Spanier

DarkEnergy:~70% Dark

Matter:~25%

• Energy budget of Universe

Antimatter: 0% ~25%

~70%

3Stefan Spanier

• Understanding the Small = Understanding the Big ?

In Big-Bang Cosmology Universeinitially contained equal amounts of matter, anti-matter and photons

Most particles & anti-particlesannihilated each other while the Universe was still very dense to form photons.

Today’s (visible) Universehas a lot of cosmic micro-wave photons and a tinybit of matter: One baryon per109 microwave photons.Only one anti-particle per109 particles.

Sometime a process distinguishing particles from anti-particles was at work…

T< 3K

matteranti-matterphotons

4Stefan Spanier

• Baryogenesis

qq

q

q

q_

q_

q_

q_q_

q

B symmetric

B anti-symmetric

q q,l_Rate r

q,lq_

Rate r_

Condition I Condition II : r r CP Violation_

Condition III

freeze out

qq

q

q_

Non-equilibrium

_

Standard Model provides the ingredients !

Toy Model of Baryogenesis

3 fundamental conditions to construct a baryon asymmertyA. Sakharov

Disclaimer: There are many realizations, but all need CP violation.

5Stefan Spanier

• Standard Model - CP SymmetryC : charge conjugation (particle – antiparticle)P : parity P x = -x , P( x v ) = ( x v )

For decay of particle X into final state f:

CP ( X f ) = X f

• A difference between decay rates of a particle and its Anti-particle impliesCP violation.

CP violation can be ingredient toexplain ratio of matter to anti-matter.

- C and P maximally violated in the Standard Model

- 1964 CP violation observed in neutral kaon decays !

_ _x

-x

6Stefan Spanier

CP violation in the Standard Model is10 orders of magnitude too small !

It may havehappenedhere ! But …

1015 K Electroweak Era (100 GeV)1013 K Quark-Hadron transition

(1 GeV)

109 K Nucleosynthesislight elements created

20 K Galaxies form

3 K Today

1028 K Grand Unification Transition

10-10 s10-6 s

1 min

1 Byr

14 Byr

10-35 s

Something else has happened !B-factory can reach > 1016 K …~

SM Higgs is heavy (125 GeV [LHC]) no departure from thermal equilibrium

7Stefan Spanier

u c t d s bd s b u c t

e- e e e+

• Standard Model of Particle Physics

C: Charge conjugation symmetry

In today’s accelerators (cosmic rays) particles and anti-particles are created and annihilate in pairs !

ud

u

p :_

__

_

C p = p_

_ _ _

_ _ _

_ _ _

Charge+ 2/3- 1/3

-1

0

Charge+ 1/3- 2/3

0

+1

Quarks

Leptons

mass

B=1/3

L=1

particles anti-particles

B=-1/3

anti-proton

L=-1

C

Standard Model

Baryon number

Lepton number

8Stefan Spanier

• CP Violation in the Standard ModelWb c,u

()

(0,0) (1,0)

b uarg( )

d targ( )

CP magnitude ~ triangle area)

u c t

ds b

~1

- parametrize transitions with 3 strengths and one complex phase

the phase is accessiblewith B mesons !

/

DK, K… J/ K0 , K0, D*D* …

,

Branching Fractions < 10-4

b_

d

CKM matrix

9Stefan Spanier

• CP Violation Phenomenology To observe CP-violation (phase) a particle decay needs to dependon at least two complex amplitudes A1 and A2

decay rate amplitude2

• Only one amplitude: |A1 |

2 = |a1ei1|2 = |a1|2

rate not sensitive to phase

• Two amplitudes: |A1 + A2|

2 = |a1 ei1 + a2 ei2|2

= a12 + a2

2 + 2 a1 a2 cos(1 – 2)

rate depends on phase

Quantum Mechanics 101

10Stefan Spanier

• Relevant Amplitudes in B-Meson DecaysTree amplitude Penguin Amplitude

weak coupling ~Vcb Vcs * ~Vtb Vts

*

W

e.g. B0 J/ K0S e.g. B0 K0

S

W

b cc

s

d d

J/

K0S

_ _

_

_

gluon

b t

d

_

K0S

B0B0

ss

_

sd

_

_

d d

s

s Ks

η’

B0 g

g~b s

+(δ 23

dRR)b

~R

s~R

• Penguins allow for Physics Beyond the Standard Model !

• Different Penguins in different wayse.g. additional Phase from

Supersymmetry ?

b

d

b

dnew couplingStudy Penguins !!!

s

ds

ss

sd

s

_

__

K0S

11Stefan Spanier

• Direct CP Violation

Short range, long range (rescattering) hadronic interactions need

to be understood ! New Physics can change the expected rates.

Rate difference:

)sin()sin(,

jijiji

jiaa2- RR

•CP violation Rate(B0 f ) Rate(B0 f )_ _

hadronictime

i : weak phases i : strong phases

ii iii eea iA

12Stefan Spanier

From 454 million neutral B decays reconstruct 1606 signals.Challenge: distinguish K+- from +- and K+K- which are also present.

0

0

BB K

K

BABAR

AsymmetryNK-+

NK+-

NK+-NK-+

-+

= -0.133 0.030stat 0.009syst

_

Significant asymmetry (13%) is 100,000 stronger than the one measured in neutral kaon decays.

4.2

Bang on Standard Model expectation

[ Phys.Rev.Lett. 93 (2004) 131801]

• Direct CP Violation in B0K+- (B0K-+)

13Stefan Spanier

• B0 B0 Oscillation Measurement

Amix(t) =unmix – mix unmix + mix

Bd0Bd

0_

Wb d

bd t-W

- -

t

B0, B0 can oscillate (mix) into each other one more amplitude_

Box amplitude:~ Vtb Vtd

*

Characteristic decay products tag the B0 flavor:

_

6.3 ps 12.6 ps

N(e+e-) – N(e-e-/e+e+)N(e+e-) + N(e-e-/e+e+)

=

md = 0.493 0.012stat 0.009sys ps-1

D

-cW+

e

e+

D-

D cos (md t) (t)

W -e

e-

c

14Stefan Spanier

• CP Violation in Interference between Mixing and Decay Observe as an asymmetry between transitions of particle % anti-particle.The cleanest way is via a decay of B0 into a CP eigenstate:

B0

B0e+e-Y(4S)

B0_

_J/ K0

S / K0S

time

sin2 = 0 : no CP violationsin2 0.7 : expected in Standard Model for J/ K0

S and K0S

with 4% theoretical uncertainty in SM, only.

(golden modes)

flavor tag

Quantumentangled

mixing

contains CP phase)

15Stefan Spanier

• CP Violation in Interference between Mixing and Decay Observe as an asymmetry between transitions of particle % anti-particle.The cleanest way is via a decay of B0 into a CP eigenstate:

B0

B0e+e-Y(4S)

B0_

_ K0S

time

flavor tag

Quantumentangled

mixing

+ direct CP violation

16Stefan Spanier

Use Electron-Positron collider– Y(4S) resonance decays nearly 100% into B-meson pairs (B+B-,B0B0)– Accelerator can be tuned in; production just above threshold – Clean environment– Coherent B0B0 production b

be-e+

d

d

Y(4s)

L = 1

d ~ 30 m

mass(B) = 5.28 GeV/c2

uu,dd,ss ~ 2.1 nbcc ~ 1.3 nbbb ~ 1.05 nb

hadronse+

e-

[CLEO]

(energy)

OffOn

)MeV(ME )S4(CM

PEP-IIBABAR

_

_

-

• B Meson Production

17Stefan Spanier

• Asymmetry Measurement with BaBar

B Decay Time (ps)

perfect time resolution

resolution function

LEP/CDF

B Factoriesperfect time resolution

B Decay Time Difference (ps)

e- : 9 GeV

e+ 3 GeV

BJ/

ee

KS

B

, e, K

z

Lorentz Boost =0.56z> = <t>c ~ 250 m

L

Flavor tagPartial reconstruction

Full reconstruction

.. instead of ~ 30 m in CM

18Stefan Spanier

1650 mA e-

2500 mA e+

4 ns bunch spacing~ 8 BB pairs / s

BaBa

r in

tegr

al lu

min

osit

y fb

-1

Run1

Run2

Y(4s) - 40 MeV

Run3

Run4

Run5330 M BB pairs

2000 2006

19Stefan Spanier

• BaBar Collaboration

• 10 countries• 63 institutions • ~550 physicists

20Stefan Spanier

• BaBar Detector

e-

e+

1.5T Solenoid

Instrumented Flux Return19 layers of RPCsLimited Streamer tubes in upper/lower barrel sextant

Silicon Vertex Tracker5 layers of double sided Si strips

Electromagnetic Calorimeter6580 CsI(Tl) crystals

Drift Chamber40 axial stereo layers

DIRC144 synthetic fused silica bars11000 PMTs

21Stefan Spanier

• The Cherenkov Detector B

, e, K

(~80%)

identify particle by measuring C , with momentum p is known from tracking:

Cher

enko

v an

gle

[rad

]

track momentum [GeV/c]

in quartz

cosC () = n() v/c

identify particle alsoby measuring thenumber of photons N

for certain d

Num

ber

of p

hoto

ns

track momentum [GeV/c]

N L sin2CL = pathlength in medium

22Stefan Spanier

• The DIRC

water n3

water

4.9 m 1.17 m

35 mm x 17 mm

Pinhole focus

C

4 synthetic fused silica barsglued together

air n2

Typical DIRC photon: 400 nm, ~ 200 bounces, ~ 5 m path in quartz.

23Stefan Spanier

• DIRC Parts

- 12 DIRC sectors- each has one aluminum box with

12 quartz bars kept in nitrogen atmosphere

24Stefan Spanier

• DIRC Parts • 6000 liters pure, de-ionized water• 10,752 conventional photo tubes - immersed directly in water, - hexagonal light catchers- max quantum efficiency@410 nm

25Stefan Spanier

In a typical multihadron event11 randomly distributed photonsand ~240 signal photons (8 tracks)

ttravel

z

• Reconstruction predict photon arrival time from geometry

(t) = 1.7 ns time resolution

± 8 ns window

3D

26Stefan Spanier

Energy-substituted mass Energy difference Event shape

Main background from continuum events:Some standard discrimination variables:

2*2*BbeamES pEm **

beamB EEE

eventsBB

eventsqqee

csduqqqee ,,, ,

* = e+e CM frame

• Event Variables

27Stefan Spanier

• The Golden Standard Model Mode

mES [GeV/c2 ]

signal region

J/ K0S + similar

28Stefan Spanier

sin2β = 0.722 0.040 (stat) 0.023 (sys)

J/ψ KL (CP even) mode(cc) KS (CP = -1) modes

Standard Model Value with high precision.

• The Golden Standard Model Mode

29Stefan Spanier

0 0LB K0 0

SB K K K

full backgroundcontinuum bkg

Golden Modes

CP = +1CP = -1

The KL reconstruction is a proof of principle for other charmless modes.Likelihood fit considering signal and background + calibration data …

• B0 K0 - The Penguin Mode

after signal prob. cut after signal prob. cut

30Stefan Spanier

B0KS

B0KL

0tagB

0tagB

0tagB

0tagB

Largest systematic error due to K+K- S-wave: content determined with a moment analysis

• B0 K0 combined likelihood fit

after signal prob. cut

31

KS00

K0

K+K-K0

’K0

sin2

Naïve average of sin2 is 8.3 from 0and discrepancy to SM is 2.8

• Measurements of CP in Penguins

Standard Model

sin2

Dire

ct C

P Vi

olat

ion

CP in Interference between Mixing & Decay

?

Particle Production at LHC

Rate = L cross section, L = Luminosity, = Decay Probability

7 TeV

7 TeV

Soft Scattering Dominates

• Higgs Rate < 0.1 Hz• b-quark production ~108 higher background for any heavy

particle search

• CP violation measured with high precision by the BaBar and Belle in the Bd system in mixing+decay no significant deviation from the Standard Model

• CP violation in mixing O(10-3) in the SM. In Bs system

Search for New Physics in Bs Decays

u,c,t

ubuscbcstbts VVVVVV *** Bs

Bd ubudcbcdtbtd VVVVVV ***

s

d~ 0.004 (SM)

u,c,t

cbcsVV *

cbcsVV *Motivation: indirect access to NP (New Physics) via CP

34

StrategyWe measure CP-violation via the time dependent decay rate for untagged Bs angular analysis is required to split CP-even and CP-odd components of the decay amplitude

0→1 1 so L=0,1,2P=(-1)L → CP=±1 Transversity Basis

{cos,,cos}

B Reconstruction – Vertex Detector

Secondary Vertex

Impact Parameter

-+ K+

K -

-

p pBs

B

B in jet

J

The CMS Detector

TRACKER

MUONENDCAPS

Cathode Strip Chambers (CSC)  positionResistive Plate Chambers (RPC) time

Resistive PlateChambers (RPC) timing

Drift Tubes (DT) position

66M Silicon Pixels, 3layers (barrel), 2 forward disksSilicon Strips: 10 barrel layers, 3+9 disks

ECAL Scintillating PbWO4 Crystals

HCALPlastic scintillator&Brass

SOLENOIDB = 3.8 T

MUON BARREL

=1.2

2.4

CKM Fitter

Standard Model Physics – Rare DecaysBs

0μ+μ- and B0μ+μ-

strongly suppressed in the SM• forbidden at tree level• Cabibbo suppressed• helicity suppressed• require an internal quark annihilation

Decay BF SM

Bs0 → μ+μ− (3.7 ± 0.2) × 10−9

B0 → μ+μ− (1.1 ± 0.1) × 10−10

Buras arXiv:1009.1303. 

b

)(dsuct ,,

b

)(ds

W+

W-W+

Z0t

t0~

l~d~0~

h0,H0H+

New Physics sensitivity comparable to e, B

Non-Observation binds parameter space Complementary to direct searches at LHC

Result

0B

0SB

Combined 2011/2012 data

4.390.1

9.00 100.3)(

SBBF

90 101.1)( BBFat 95% C.L.

43Stefan Spanier

• B mesons are a laboratory to study indirectly new physics.

• CP violation is a necessary ingredient in a baryon-dominated Universe and required in any New Physics.

• BaBar was a very successful e+e- collider experiment

which observed significant CP asymmetries.

• The exploration continues with LHC.

• B mesons continue to be a very good tool to probe

physics beyond the Standard Model.

Conclusions