1. g a b Part 1: Matter-Antimatter Asymmetry
New Results from the BaBar Experiment
Part 1: Matter-Antimatter Asymmetry
Part 2: CP Violation and the SM
Part 3: Beyond the Standard Model
K. Honscheid
Dept. of Physics
Ohio State University
K. Honscheid, WSU Apr. 15, 2005

2. Matter, Energy and the Big Bang
Einstein showed us that matter and energy are equivalent
When matter and antimatter meet, they annihilate into energy
Energy can also materialize as particle-antiparticle pair
armed with this understand of antimatter we can revisit the issue of antimatter in the universe.
Predict: nMatter/nPhoton~ 0
Exp: nb/ng~ (6.1 +/- 0.3) x (WMAP)
K. Honscheid, WSU Apr. 15, 2005

3. Transition to broken electroweak symmetry provides these conditions
So how can this happen?
In 1967, A. Sakharov showed that the generation of the net baryon number in the universe requires:
Baryon number violation (Proton Decay)
Thermal non-equilibrium
C and CP violation (Asymmetry between particle and anti-particle)
explain baryon number
explain baryogenesis
B violation to create net B number
CP symmetry, which relates matter to antimatter,
is necessary or the baryon violating processes would
be cancelled out by anti-baryon violating processes
Thermal non-equilibrium because in hot early universe,
particle abundances are in equilibrium determined by temperature
and mass, and since by CPT theorem particles and antiparticles
have same mass then in thermal equilbirum have same
abundance.
Transition to broken electroweak symmetry provides these conditions
K. Honscheid, WSU Apr. 15, 2005

4. Experimental Possibilities:
Get equal amounts of matter and anti-matter
Wait…
See what’s left (in anything)
K. Honscheid, WSU Apr. 15, 2005

5. PEP-II Asymmetric B Factory
collide 9 GeV e- on 3.1 GeV e+
approved in fall 93 as presidential initiative,
completed in 99, reached design lumi in 2000
While I will report mostly on BaBar results there is a competing experiment in Japan. The Belle detector and the KEK B factory are also working extremely well and there is a great scientific competition going on between the two collaborations.
Stanford Linear Accelerator Center,
Stanford, California
K. Honscheid, WSU Apr. 15, 2005

6. The BaBar Experiment
my goal is to present our results in a way that simplifies understanding – but simple should not be construed as easy. All these measurements are extremely difficult an require the talents of all these people.
K. Honscheid, WSU Apr. 15, 2005

7. Preparing the Matter – Antimatter Sample
B mesons contain a b quark and a light anti-quark.
mB = 5.28 GeV (~5x mProton)
BB Threshold
The Upsilon(4S) - a copious, clean source of B meson pairs
1 of every 4 hadronic events is a BB pair
No other particles produced in Y(4S) decay
Equal amounts of matter and anti-matter
motivation for asymmetric B factory
Collect a few 108 B0 B0 pairs
K. Honscheid, WSU Apr. 15, 2005

8. Analysis techniques
Threshold kinematics: we know the initial energy of the system
Event topology
Signal
Signal
(spherical)
explain that the initial state is known
Delta E
the beam energy is better known (2-3 MeV) than the reconstructed energy (20 MeV) -> mes
Background
Background
(jet-structure)
K. Honscheid, WSU Apr. 15, 2005

9. Searching for the Asymmetry
227 x 106 B0 Mesons
Count B0K+ Decays
227 x 106 B0 Mesons
Count B0K-+ Decays
Is N(B0K+ ) equal to N(B0K-+ )?
Introduce B->Kpi and explain importance of PID. Mention Cerenkov effect and particle’s velocity
K. Honscheid, WSU Apr. 15, 2005

10. How to Tell a Pion from a Kaon
Angle of Cherenkov light is related to particle velocity
Transmitted by internal reflection
Detected by~10,000 PMTs
Particle
Quartz bar
Cherenkov light
Active Detector Surface
speed trap for particles
K. Honscheid, WSU Apr. 15, 2005

11. background subtracted
Searching for the Asymmetry
227 x 106 B0 Mesons
Count B0K+ Decays
227 x 106 B0 Mesons
Count B0K-+ Decays
Is N(B0K+ ) equal to N(B0K-+ )?
B0K+
BABAR
B0K+
background subtracted
BABAR
K. Honscheid, WSU Apr. 15, 2005

12. Direct CP Violation in B Decays
Using
We obtain
First confirmed observation of direct CP violation in B decays
K. Honscheid, WSU Apr. 15, 2005

13. Part 2: CP Violation in the Standard Model
CP Operator:
coupling q’ q’
CP( ) = g g* q J q J
Mirror
To incorporate CP violation
g ≠ g*
(coupling has to be complex)
Quantum-mechanically, the CP operator converts particles to anti-particles and also the coupling constants become the complex conjugates.
no complex phases in strong and em interactions. what about the weak interaction?
K. Honscheid, WSU Apr. 15, 2005

14. The Kobayashi-Maskawa Matrix
The weak interaction can change the favor of quarks and lepton
Quarks couple across generation boundaries
Mass eigenstates are not the weak eigenstates
The CKM Matrix rotates the quarks from one basis to the other
Vcb
Vub u d t c b s l l3 l2
l=cos(qc)=0.22 d’
Vud
Vus
Vub d s’ =
Vcd
Vcs
Vcb s b’
Vtd
Vtb b
K. Honscheid, WSU Apr. 15, 2005

15. The Unitarity Triangle Visualizing CKM information from Bd decays
The CKM matrix Vij is unitary with 4 independent fundamental parameters
Unitarity constraint from 1st and 3rd columns: i V*i3Vi1=0
Testing the Standard Model
Measure angles, sides in as many ways possible
SM predicts all angles are large u
Vud Vus Vub
Vcd Vcs Vcb
Vtd Vts Vtb c t
CKM phases
(in Wolfenstein convention)
unitarity
4 parameters (3 real, 1 complex phase)
many representations. Wolfenstein – matches hierarchy shown on previous slide
In this representation the Vtd and Vub – the small elements in the corner carry a complex phase. UT
will be our guide for the remainder of the talk.
K. Honscheid, WSU Apr. 15, 2005

16. Understanding CP Violation in B  Kp
Tree decay g
A1 = a1 eif1 eid1
A1 = a1 e if1
B K-p+ +
A2 = a2 eif2 eid2
Penguin decay
A1 = a1 e-if1 eid1
A1 = a1 e -if1
B K+p- +
A2 = a2 e-if2 eid2
include the strong phase (doesn’t change sign)
more than one amplitude with different weak phase; (A = A1+A2)
Now let’s revisit our B->Kpi decays and see if they fit into this model.
A B meson decays by emitting a virtual W boson and converting into a u (or c) quark. This plus the remnant from the B make up the pi in the final state and the W hadronizes into the K. Here is Vub and with it the complex phase that
changes sign in a CP operation. We call this a tree diagram.
Define asymmetry
since the amplitudes are squared the asymmetry is 0.
Now this is a quark level description. The quarks hadronize via the strong interaction and there can be a strong
phase. This does not change sign under CP.
Still, no asymmetry.
What we need is a second amplitude like this diagram (penguin – more about this later). You see we reach the
same final state. Two amplitudes interfere and it is in this interference where we get a difference between the B0 and the
B0bar decay. With a little bit of math in can be shown that
weak phase difference
strong phase difference
great – bad (that’s also what made the interpretation of the Kaon results to difficult)
need a way to eliminate or at least reduce strong uncertainties. Very difficult if we use two different decay diagrams.
Fortunately, nature helps. because
G(B) – G(B)
G(B) + G(B)
|A|2 – |A|2
|A|2 + |A|2
= 0
~ 2 sin(f1 - f2) sin(d1 - d2)
Asymmetry = =
K. Honscheid, WSU Apr. 15, 2005

17. B0 B0 Mixing and CP Violation
f = b
A neutral B Meson
CPV through interference between mixing and decay amplitudes
Interference between ‘B  B  fCP’ and ‘B  fCP’
The SM allows B0 B0 oscillations
N(B0)-N(B0)
N(B0)+N(B0)
the neutral B meson has a personality disorder. While it was created as B0 it doesn’t stay one. Like the other neutral mesons the SM allows B0 oscillations via this box diagram
beautiful measurement of the oscillation as function of time. The mixing frequency has been measured to great accuracy and is about 0.5 ps-1
If we now select decays of a B0 to a CP eigenstate a state that can also be reached from a B0bar we can use the interference between the direct decay and the mixed decay to measure the CP phases
Only one decay diagram – hadronic uncertainties cancel.
the complex CKM phase is beta – with 2 Vtd couplings we will get 2beta in the asymmetry. If the B decay has no
weak phase by itself we will measure sin(2beta)
Mixing frequency Dmd  0.5 ps-1
B0 fraction ~ sin(Dmd Dt)
K. Honscheid, WSU Apr. 15, 2005

18. Time-Dependent CP Asymmetriesb c c
CP Eigenstate: hCP = -1 W+ B0 s d d
Amplitude of CP asymmetry
Quark subprocess B0
mixing K0
mixing
psi Ks
time dependence – mixing part
cpv amplitude
but integrates to 0
need to measure time dependence – the lifetime of the B is only 1.5 ps – by the way.
K. Honscheid, WSU Apr. 15, 2005

19. Time-dependent analysis requires B0 flavor tagging
We need to know the flavour of the B at a reference t=0.
Dz = Dt gbc
At t=0 we know this meson is B0
B 0
rec
B 0
(4S)
bg =0.56
l - (e-, m -)
B 0
tag
The two mesons oscillate coherently : at any given time, if one is a B0 the other is necessarily a B0
In this example, the tag-side meson decays first.
It decays semi-leptonically and the charge of the lepton gives the flavour of the tag-side meson :
l - = B l + = B 0.
Kaon tags also used.
Dt picoseconds later, the B 0 (or perhaps its now a B 0) decays.
There is an additional slight complication as our B0B0bar pair is in a coherent state
Tagging
explain lepton tag. We also use a kaon tag from a subsequent D decay. Combined the tagging efficiency is roughly 30%
K. Honscheid, WSU Apr. 15, 2005

20. Step by Step Approach to CP Violation
B tagged
1. Start with a few x 108 B0 B0 pairs (more is better)
2. Reconstruct one B0 in a CP eigenstate decay mode
3. Tag the other B to make the matter/antimatter distinction
4. Determine the time between the two B0 decays, Dt
5. Plot Dt distribution separately for B and B tagged events
6. Extract ACP and sin2b
Dt (ps)
sin 2b
sinDmDt
okay, let’s do it
detector resolution
amplitude modified by misttags.
ACP(Dt)
Dt (ps)
K. Honscheid, WSU Apr. 15, 2005

21. Results: sin 2b and the observation of CP
227 million BB pairs
J/yKs and other b  cc s final states
CP = -1
B  J/ Ks0, Ks0  p+p-, p0p0
B  (2S) Ks0
B  c1 Ks0
B  J/ K*0, K*0  Ks0
B  c Ks0
7730 events
(1-2w) sin(2b)
w = mis-tag fraction
With this device and the rest of the BaBar detector we then collected almost 230 million BB events and analyzed the data
looking for psiKs final states plus, of course, a tag for the other B in the event.
We ended up with 7730 events and shown here is the decay time difference for B0 tags and B0bar tags
clear difference. no asymmetry in the background.
The second plot shows the raw asymmetry and the fit result is
CP = +1
B  J/ KL0
BaBar result: sin2b =   0.023
K. Honscheid, WSU Apr. 15, 2005

22. b g a The Unitarity Triangle (0,0) (0,1) (r,h) Vub Vud Vcd Vcb *
Vtd Vtb g a b
Successfully reached the main goal of the B factory program
now let’s go for more
[23.3 ± 1.5]o
K. Honscheid, WSU Apr. 15, 2005

23. yKs is not the only CP Eigenstate
Access to a from the interference of a b→u decay (g) with B0B0 mixing (b)
B0B0 mixing
Tree decay g
a = p - b - g
harder because of the lower BR
sin2a
ACP(t)=sin(2a)sin(DmdDt).
K. Honscheid, WSU Apr. 15, 2005

24. Time-dependent ACP of B0→p+p-
Blue : Fit projection
Red : qq background + B0→Kp cross-feed
found about 500 events
BR result in fact obtained from 97MBB
K. Honscheid, WSU Apr. 15, 2005

25. Houston, we have a problemq pp Kp
B0  p+p-
B0  K+p-
B0p+p-
157  19
(4.7  0.6  0.2) x 10-6
B0K+p-
589  30
(17.90.9 0.7) x 10-6
Penguin/Tree ~ 30%
K. Honscheid, WSU Apr. 15, 2005

26. The route to sin(2a): Penguin Pollution
Access to a from the interference of a b→u decay (g) with B0B0 mixing (b)
B0B0 mixing
Tree decay
Penguin decay  g
Inc. penguin contribution
now the formalism gets slightly more complicated
the “C” term direct CP violation due to the interference of the T and P decays but our sin(2a) term gets also modified
and the question is how can we obtain a from aeff?
How can we obtain α from αeff ?
Time-dep. asymmetry :
NB : T = "tree" amplitude P = "penguin" amplitude
K. Honscheid, WSU Apr. 15, 2005

27. How to estimate |a-aeff| : Isospin analysis
Use SU(2) to relate decay rates of different hh final states (h  {p,r})
Need to measure several related B.F.s
2|-eff|
not enough data but maybe we can limit a-aeff
if A00 is very small…
look for this decay
Difficult to reconstruct.
Limiting factor in analysis
Gronau, London : PRL65, 3381 (1990)
K. Honscheid, WSU Apr. 15, 2005

28. Now we need B0→p0p0 |a-aeff |< 35°
61±17 events in signal peak (227MBB)
Signal significance = 5.0s
Detection efficiency 25%
3 B.F.s
B0p+p-
B+  p+p0
B0  p0p0
2 asymmetries
Cp+p-
Cp0p0
Using isospin
relations and
Large penguin pollution ( P/T )
Isospin analysis not currently viable in the B→pp system
|a-aeff |< 35°
B±→r±p0
we indeed found 60 decays with manageable background
not good enough
Time-integrated result gives :
K. Honscheid, WSU Apr. 15, 2005

29. B → rr: Sometimes you have to be lucky
P → VV decay three possible ang mom states:
S wave (L=0, CP even)
P wave (L=1, CP odd)
D wave (L=2, CP even)
r helicity angle
We are lucky:
~100% longitudinally polarized!
Transverse component taken as zero in analysis
PRL 93 (2004)
K. Honscheid, WSU Apr. 15, 2005

30. Time dependent analysis of B→r+r-
Maximum likelihood fit in 8-D variable space
very clean tags
32133 events in fit sample
fine but what about rho0rho0?
K. Honscheid, WSU Apr. 15, 2005

31. Searching for B→r0r0 B (B→r+r-) = 33 x 10-6
Similar analysis used to search for r0r0
Dominant systematic stems from the potential interference from B→a1±p± (~22%)
c.f. B→p+p-
B.F.= 4.7 x 10-6
and B→p0p0
B.F.= 1.2 x 10-6
B (B→r+r-) = 33 x 10-6
K. Honscheid, WSU Apr. 15, 2005

32. Isospin analysis using B→rr
The small rate of means
|a-aeff | is small[er]
P/T is small in the B→rr system
(…Relative to B→pp system)
No isospin violation (~1%)
No EW Penguins (~2%)
|a-aeff |< 11°
K. Honscheid, WSU Apr. 15, 2005

33. a g b The Unitarity Triangle (0,0) (0,1) (r,h) Vub Vud Vcd Vcb *
Vtd Vtb g b
[103 ± 11]o a
being able to measure 2 angles is already a surprise but let’s go for 3
[23.3 ± 1.5]o
K. Honscheid, WSU Apr. 15, 2005

34. The 3rd Angle: g Basic Idea Color suppressed
no help due to mixing unless we have Bs mesons
D0-kk or pp, Kspi0
acp depends strongly on ratio which is not well known.
K. Honscheid, WSU Apr. 15, 2005

35. First Look at the Data
Only a loose bound on rB with current statistics: (rB)2 = 0.19±0.23
BABAR-CONF-04/039
just a first look
Several other methods are being investigated
More data would help a lot…
K. Honscheid, WSU Apr. 15, 2005

36. Combined Experimental Constraint on g
BABAR & Belle combined
more data and this might actually work
K. Honscheid, WSU Apr. 15, 2005

37. g a b The Unitarity Triangle [103 ± 11]o (0,0) Vub Vud Vcd Vcb *
Vtd Vtb a b
so here we are. 5 years into the B factory program and we not only have established CPV in the B system but
we have also measured the three angles of the UT (okay 2 ½)
I leave it as an exercise for you to add up the three angles and compare the result to 180.
[ ]o
[23.3 ± 1.5]o
K. Honscheid, WSU Apr. 15, 2005

38. Putting it all together
The complex phase in the CKM matrix correctly describes CPV in the B meson system.
Based on SM CPV the baryon to photon ratio in the universe should be nb/ng~ 10-20
Experimentally we find nb/ng~ (6.1±0.3) x (WMAP) h
this is a confusing plot because it combines 30 years worth of information.
Consistent
But not enough r
K. Honscheid, WSU Apr. 15, 2005

39. Part 3: Consistency Checks
Part 3: Beyond the Standard Model
Part 3: Consistency Checks
FCNC transitions bsg and bdg are sensitive probes of new physics
Precise Standard Model predictions.
Experimental challenges for bdg (Brg Bwg)
Continuum background
Background from bsg (BK*g) (50-100x bigger)
Ali et al hep-ph/
this could give Vtd – one of the UT sides. Maybe this is too long or too short?
K. Honscheid, WSU Apr. 15, 2005

40. Combined B0r0g,B0wg,B-r-g results
No signals observed
No signals but the limits on Vtd become meaningful
@90% CL
K. Honscheid, WSU Apr. 15, 2005

41. CKM constraints from Br(w)g
BABAR BF ratio upper limit < → |Vtd/Vts| < (90% CL)
Ali et al. hep-ph/
(z2,DR) = (0.85,0.10)
no theory error
(z2,DR) = (0.75,0.00)
with theory error
Penguins are starting to provide meaningful CKM constraint
rg 95% CL BABAR allowed region (inside the blue arc)
K. Honscheid, WSU Apr. 15, 2005

42. New CP Violating Phases in Penguin Decays?
+ mixing lCP = -e-2b t s d
W -
Vtb
Vts*
+ mixing lCP = -e-2b
we could also look for new phases due to new heavy particles in penguin loops
+ mixing lCP = -e-2b
K. Honscheid, WSU Apr. 15, 2005

43. Update on BfKo Belle 114 ± 12 events 98 ± 18 events preliminary
hep-ex/
preliminary
114 ± 12 events SM
Belle
[BELLE-CONF-0435]
98 ± 18 events
we could also look for new phases due to new heavy particles in penguin loops
K. Honscheid, WSU Apr. 15, 2005

44. Reaching for more statistics – B 0   K 0 revisited
Analysis does not require that ss decays through f resonance, it works with non-resonant K+K- as well
85% of KK is non-resonant – can select clean and high statistics sample
But not ‘golden’ due to possible additional SM contribution with ss popping
But need to understand CP eigenvalue of K+K-KS:
- f has well defined CP eigenvalue of +1,
- CP of non-resonant KK depends angular momentum L of KK pair
Perform partial wave analysis
Estimate fraction of S wave (CP even) and P wave (CP odd) and calculate average CP eigenvalue from fitted composition
K+K-
Nsig = 452 ± 28 (excl.  res.) OK
Not OK
K. Honscheid, WSU Apr. 15, 2005

45. CP analysis of B  K+K- KS
Result of angular analysis
Result consistent with cross check using iso-spin analysis (Belle)
Result of time dependent CP fit
hfSK+K-KS/(2fCP-even-1)] = ±0.22 ± 0.04 ±0.11
(stat)
(syst)
(fCP-even)
K. Honscheid, WSU Apr. 15, 2005

46. More penguin exercises – B0  KS KS KS
hep-ex/
More penguin exercises – B0  KS KS KS
Use beam line as constraint and accept only KS with sufficient number of SVX hits.
Decay B0  KS KS KS is ‘golden’ penguin – little SM pollution expected
Although 3-body decay, only L=even partial waves allowed:
CP(KSKSKS) = CP(KS) = even
Result consistent with SM
Gershon, Hazumi
hep-ph/ s d K0
hfK0
K. Honscheid, WSU Apr. 15, 2005

47. IP-Constrained Vertexing
Same technique as Ksp0
hep-ex/
beam p0 B0
p +
p -
inflated beam
4mm
200mm KS
Constrain decay products to beam-spot in x-y:
Vertex precision depends on number of hits in SVT
For 4 hits, Dt resolution as good as with charged-tracks (60% events)
Crosscheck with J/yKS:
K. Honscheid, WSU Apr. 15, 2005

48. Combined “sin2b” Results
Dsin2β ~ -2.9 s
Dsin2β ~ -2.9 s +
sin2βPenguin = 0.43 ±0.07
Dsin2β ~ -3.7 s
…but comparison
ignores subleading
diagrams !
K. Honscheid, WSU Apr. 15, 2005

49. Corrections: b→s Decay Amplitude ~ VubVus*
penguin
Decays involving Vub enter with decay phase g
Doubly-CKM suppressed w.r.t dominant diagram
Contributes to all b sss modes
color-allowed tree
color-suppressed tree
Contribute to h’Ks, f0Ks, wKs, but not fKs
[in KKKs (requires ss popup from soft g)]
Contribute to non-resonant KKKs
(requires ss popup from soft g)
K. Honscheid, WSU Apr. 15, 2005

50. Adding Theoretical Uncertainties
size of possible discrepancies Δsin2β have been evaluated for some modes:
estimates of deviations based on QCD-motivated specific models; some have difficulties to reconcile with measured B.R.
Beneke at al, NPB675
Ciuchini at al, hep-ph/
Cheng et al, hep-ph/
Buras et al, NPB697
Charles et al, hep-ph/
model independent upper limits based on SU(3) flavor symmetry and measured b d,sqq B.R.
[Grossman et al, PRD58; Grossman et al, PRD68; Gronau, Rosner, PLB564; Gronau et al, PLB579; Gronau et al, PLB596; Chiang et al, PRD70]
2xΔsin2β
‘naive’ upper limit based on final state quark content,
CKM (λ2) and loop/tree (= ) suppression factors
[Kirkby,Nir, PLB592; Hoecker, hep-ex/ ]
K. Honscheid, WSU Apr. 15, 2005

51. Conclusion
Almost 40 years after the discovery of CP violation in the kaon system we are finally in a position to improve our understanding of CP violation in the Standard Model
Belle and BaBar give consistent results for sin2b. Both work extremely well
The SM prediction of a single phase in the CKM matrix as cause of CP violation appears to be correct.
We now know how to distinguish between matter and anti-matter aliens.
New Physics will be needed to explain the baryon asymmetry in the universe
Will we find hints in CP phases and/or rare decays?
Stay tuned as more data is coming in.
K. Honscheid, WSU Apr. 15, 2005