Search for New Physics Search for New Physics with B-Mesons with - - PowerPoint PPT Presentation

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Stefan Spanier

Search for New Physics with B-Mesons Search for New Physics with B-Mesons Stefan Spanier University of Tennessee

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Stefan Spanier

Dark Energy: ~70% Dark Matter: ~25%

• Energy budget of Universe

Antimatter: 0%

~25% ~70%

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Stefan Spanier

• Understanding the Small = Understanding the Big ?

      

In Big-Bang Cosmology Universe initially contained equal amounts

• f matter, anti-matter and photons

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

Today’s (visible) Universe has a lot of cosmic micro- wave photons and a tiny bit of matter: One baryon per 109 microwave photons. Only one anti-particle per 109 particles.

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

T< 3K

matter anti-matter photons

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Stefan Spanier

• Baryogenesis

q q q q q _ q _ q _ q _ q _ q

B symmetric B anti-symmetric

q q,l _

Rate r

q,l q _

Rate r _ Condition I Condition II : r  r CP Violation

_

Condition III freeze out

q q q q _

Non-equilibrium

_ Standard Model provides the ingredients !

Toy Model of Baryogenesis

3 fundamental conditions to construct a baryon asymmerty

• A. Sakharov

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

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Stefan Spanier

• Standard Model - CP Symmetry

C : 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 implies CP violation.  CP violation can be ingredient to explain 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

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Stefan Spanier

CP violation in the Standard Model is 10 orders of magnitude too small ! It may have happened here ! But …

1015 K Electroweak Era (100 GeV) 1013 K Quark-Hadron transition (1 GeV) 109 K Nucleosynthesis light elements created 20 K Galaxies form 3 K Today 1028 K Grand Unification Transition 10-10 s 10-6 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

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Stefan Spanier

u c t d s b d 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 !

u d u

p : _

_ _ _

C p = p

_ _ _ _ _ _ _ _ _ _

Charge + 2/3

• 1/3
• 1

Charge + 1/3

• 2/3

+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

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Stefan Spanier

• CP Violation in the Standard Model

W b c,u () (0,0) (1,0)

  

b u

arg( )

d t

arg( )

CP magnitude ~ triangle area)

u c t d s b

 

~1

• parametrize transitions with

3 strengths and one complex phase 

the phase is accessible with B mesons !

/

 

DK, K… J/ K0 , K0, D*D* …

, 

Branching Fractions < 10-4

b _ d

CKM matrix

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Stefan Spanier

• CP Violation Phenomenology

To observe CP-violation (phase) a particle decay needs to depend

• n at least two complex amplitudes A1 and A2

decay rate  amplitude2

• Only one amplitude:

|A1 | 2 = |a1ei1|2 = |a1|2  rate not sensitive to phase

• Two amplitudes:

|A1 + A2|2 = |a1 ei1 + a2 ei2|2 = a1

2 + a2 2 + 2 a1 a2 cos(1 – 2)

 rate depends on phase

Quantum Mechanics 101

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Stefan Spanier

• Relevant Amplitudes in B-Meson Decays

Tree amplitude Penguin Amplitude

weak coupling

~Vcb Vcs

*

~Vtb Vts

*

W e.g. B0  J/ K0

S

e.g. B0   K0

S

W b c

c s

d d J/ K0

S

_

_ _ _

gluon b

t

d

_



K0

S

B0 B0

s

s _ s d

_

_ d d s s Ks η’ B

g g ~

b s

+

(δ 23

d

RR)

b ~

R

s ~

R

• Penguins allow for Physics Beyond

the Standard Model !

• Different Penguins in different ways

e.g. additional Phase from Supersymmetry ?

b d

b d

new coupling

Study Penguins !!!

s d s

s

s s d

s

_ _

_



K0

S

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Stefan 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(

, j i j i j i j ia

a 2

• R

R        



• CP violation 

Rate(B0  f )  Rate(B0  f ) _ _

hadronic

time

i

 : weak phases

i

 : strong phases

i i

i i i

e e a

 



i

A

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Stefan Spanier

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

B B K K  

   

 

BABAR



Asymmetry NK-+  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 B0K+- (B0K-+)

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• B0 B0 Oscillation Measurement

Amix(t) = unmix – mix unmix + mix

Bd Bd

_

W b d b d

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+)

= m d = 0.493  0.012stat  0.009sys ps-1

D

• c

W+ e e+

D-

 D cos (md t)  (t)

W - e e-

c

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Stefan 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 B0 e+e- Y(4S) B0 _ _ J/ K0

S /  K0 S

time

sin2 = 0 : no CP violation sin2  0.7 : expected in Standard Model for J/ K0

S and  K0 S

with 4% theoretical uncertainty in SM, only.

(golden modes)

flavor tag

Quantum entangled

mixing

 contains CP phase)

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Stefan 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 B0 e+e- Y(4S) B0 _ _

 K0

S

time

flavor tag

Quantum entangled

mixing



+ direct CP violation

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Stefan 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 b e- e+ 



d d



Y(4s) L = 1

d ~ 30 m

mass(B) = 5.28 GeV/c2

uu,dd,ss ~ 2.1 nb cc ~ 1.3 nb bb ~ 1.05 nb

hadrons

e+ e-

[CLEO]

(energy)

Off On ) MeV ( M E

) S 4 ( CM 



PEP-II BABAR

_ _

• B Meson Production

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Stefan Spanier

• Asymmetry Measurement with BaBar



B Decay Time (ps)

perfect time resolution resolution function

LEP/CDF B Factories

perfect time resolution 

B Decay Time Difference (ps)

e- : 9 GeV e+ 3 GeV

B

J/

e e

KS

 

B

, e, K

z Lorentz Boost =0.56 z> = <t>c ~ 250 m

L





Flavor tag Partial reconstruction Full reconstruction .. instead of ~ 30 m in CM

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Stefan Spanier

1650 mA e- 2500 mA e+ 4 ns bunch spacing ~ 8 BB pairs / s BaBar integral luminosity fb-1

Run1 Run2

Y(4s) - 40 MeV

Run3 Run4 Run5

330 M BB pairs

2000 2006

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Stefan Spanier

• BaBar Collaboration
• 10 countries
• 63 institutions
• ~550 physicists

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Stefan Spanier

• BaBar Detector

e- e+

1.5T Solenoid Instrumented Flux Return

19 layers of RPCs

Limited Streamer tubes in upper/lower barrel sextant Silicon Vertex Tracker

5 layers of double sided Si strips

Electromagnetic Calorimeter

6580 CsI(Tl) crystals

Drift Chamber

40 axial stereo layers

DIRC

144 synthetic fused silica bars 11000 PMTs

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Stefan Spanier

• The Cherenkov Detector

B

, e, K (~80%)

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

Cherenkov angle [rad] track momentum [GeV/c]

in quartz

cosC () = 

 n()



 v/c

identify particle also by measuring the number of photons N

for certain d

Number of photons track momentum [GeV/c] N  L sin2C L = pathlength in medium

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Stefan Spanier

• The DIRC

water n3

water

4.9 m 1.17 m 35 mm x 17 mm

Pinhole focus

C

4 synthetic fused silica bars glued together

air n2

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

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Stefan Spanier

• DIRC Parts
• 12 DIRC sectors
• each has one aluminum box with

12 quartz bars kept in nitrogen atmosphere

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Stefan 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

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Stefan Spanier

In a typical multihadron event 11 randomly distributed photons and ~240 signal photons (8 tracks)

ttravel z

• Reconstruction

predict photon arrival time from geometry (t) = 1.7 ns time resolution ± 8 ns window

3D

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Stefan Spanier

Energy-substituted mass Energy difference Event shape

Main background from continuum events: Some standard discrimination variables:

2 * 2 * B beam ES

p E m  

* * beam B

E E E   

events B B

events q q e e 

 

 

c s d u q q q e e , , , ,  

 

* = e+e CM frame

• Event Variables

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Stefan Spanier

• The Golden Standard Model Mode

mES [GeV/c2 ]

signal region

J/ K0

S + similar

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Stefan 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

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Stefan Spanier

L

B K  

S

B K K K   

   

 

full background continuum bkg

Golden Modes CP = +1 CP = -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

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Stefan Spanier

B0KS B0KL

tag

B

tag

B

tag

B

tag

B

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

• B0   K0 combined likelihood fit

after signal prob. cut

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KS00 K0

K+K-K0

’K0

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

• Measurements of CP in Penguins

Standard Model

sin2 Direct CP Violation

CP in Interference between Mixing & Decay

?

SLIDE 32

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

SLIDE 33

• 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

ub us cb cs tb ts

V V V V V V

* * *

 

Bs Bd

ub ud cb cd tb td

V V V V V V

* * *

 

s d

~ 0.004 (SM) u,c,t

cb csV

V * 

cb csV

V * 

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

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Strategy

We 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=0,1,2 P=(-1)L → CP=±1

Transversity Basis {cos,,cos}

SLIDE 35

B Reconstruction – Vertex Detector

Secondary Vertex Impact Parameter

- + K+ K - - p p Bs B B in jet  J

SLIDE 36

The CMS Detector

TRACKER MUON ENDCAPS

Cathode Strip Chambers (CSC)  position Resistive Plate Chambers (RPC)  time Resistive Plate Chambers (RPC)  timing Drift Tubes (DT)  position 66M Silicon Pixels, 3layers (barrel), 2 forward disks Silicon Strips: 10 barrel layers, 3+9 disks ECAL Scintillating PbWO4 Crystals HCAL Plastic scintillator&Brass

SOLENO ID B = 3.8 T MUON BARREL =1.2 2.4

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CKM Fitter

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Standard Model Physics – Rare Decays

Bs

0μ+μ- and B0μ+μ-

strongly suppressed in the SM

• forbidden at tree level
• Cabibbo suppressed
• helicity suppressed
• require an internal quark annihilation

Decay BF SM Bs

0 → μ+μ−

(3.7 ± 0.2) × 10−9 B0 → μ+μ− (1.1 ± 0.1) × 10−10

Buras arXiv:1009.1303.

b ) (d s u c t , ,  b ) (d s

















W+ W- W+ Z0

t t

0 ~ l ~ d ~ 0 ~ h0,H0 H+ New Physics sensitivity comparable to e, B   Non-Observation binds parameter space  Complementary to direct searches at LHC

SLIDE 40

Result

B

S

B

Combined 2011/2012 data 4.3

9 . 1 9 .

10 . 3 ) (

    

    

S

B BF

9

10 1 . 1 ) (

  

     B BF

at 95% C.L.

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Stefan 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