Rare decays and New Physics studies

1
Rare decays and New Physics studies

• Owen Long
• University of California, Riverside
• Physics in Collision 2006
• July 8, 2006
• Búzios, Brazil

2
A new era of flavor physics
CKM parameters r and h circa 1998
How things look today, thanks to the B factories,
Tevatron experiments, and theoretical
developments.
Remarkable consistency with the CKM model!
3
Wheres the New Physics?

• Not in tree level decays!
• Data consistent with CKM unitarity.
• CP violating observables consistent with CKM
  picture (mostly).
• Looking for something subtle
• Measurement precision limited by strong
  interaction (non-perturbative).
• Uncertainties are multiplicative.
• To find something small, competing SM process
  must be small.

Rare decays!
4
Loop-mediated processes

• Poor physicists window to the TeV scale.
• Can we tell if this is there?
• Can we say with confidence that its not there?

SM
NP?
Diagrams from G.Kane et al., PRD 71, 035015 (2004)
5
How to get around hadronic uncertainties
Topics covered in this presentation

• Make them cancel
• CP asymmetries
• penguin dominated charmless hadronic decays (fK,
  hK,)
• Avoid hadrons!
• Leptonic, semileptonic, and radiative decays
• B?mm, B?tn, b?sg, B?(r,?)g, b?sll
• Do both
• ACP in b?sg (super clean)
• AFB in B?Kll (pretty clean)

6
CP asymmetries in b?s penguin decays
7
CP asymmetries in penguin decays

• CPA theoretically clean if one amplitude
  dominates
• Same reason as J/? Ks.
• Sub-dominant b?u amplitudes have different weak
  phase
• Small direct CPV and correction to effective
  mixing phase
• NP amplitudes larger than SM b?u contribution may
  be present!
• Look for large correction to Sf and/or Cf from NP

NP?
Leading SM
Mixing-induced CPV
Direct CPV
8
The b? s penguin and SM pollution
Dominant
Color-suppressed tree not present for fKs.
Suppressed
CKM smaller by 0.02
Competing u-penguin CKM suppressed. Some modes
also have a b?u tree contribution. Impressive
amount of theoretical work in the past 4 years.
.
9
Model predictions for SM pollution

• Many approaches (models) for dealing with
  unavoidable hadronic amplitudes.
• SU(3) flavor symmetry
• Use data to constrain amplitude ratios.
• Factorization
• Popular theoretical framework for computing
  hadronic matrix elements for 2-body decays.

SM deviation of S from sin2b.
2-body modes M.Beneke, PLB 620, 143
(2005) 3-body modes Cheng, Chua, Soni, PRD 72,
094003 (2005)
Blue bars theory error from 1s variations on
input parameters (CKM, form factors, ) Gold bars
(under blue) complete scan of allowed input
values. Require BFs within 3s. Blue column
current experimental error on sin2b from
charmonium K0.
10
The golden mode fK0
Nsig7813

• Golden for two reasons
• Pure b?sss transition
• Experimentally clean
• Only the KL direction is detected, not its
  energy. Use B mass constraint in reconstruction.

Nsig11412
Nsig9818
Babar PRD 71, 091102 (2005) Belle hep-ex/0507037
11
fK0 CP asymmetries
Babar PRD 71, 091102 (2005) Belle hep-ex/0507037
Belle 386M BB
Belle 386M BB
Best flavor tags
Best flavor tags
Babar 227M BB
Babar S 0.50 0.25 0.06 C 0.00 0.23
0.05 Belle S 0.44 0.27 0.05 C -0.14
0.17 0.07
Expect S0.70, C0 in Standard Model
12
h K0
Belle 386M BB Nsig83035

• Branching fraction is unusually large (which is
  good!)
• Eta is not a pure ss state (some uu) but model
  estimates give small SM pollution in CP asymmetry
  (also good!).
• Also reconstructed in both KS and KL channels.

Babar 232M BB Nsig80440
Babar PRL 94, 191802 (2005) and hep-ex/0507087.
Belle hep-ex/0507037
13
h K0
Belle 386M BB
Babar 232M BB
Weakest flavor tags
Best flavor tags
Babar S 0.36 0.13 0.03 C -0.16 0.09
0.02 Belle S 0.62 0.12 0.04 C 0.04 0.08
0.06
Precision same as 2001 observation of CP
violation in J/yKS! Average S is about 2s below
SM expectation.
Results using KS and KL
Babar PRL 94, 191802 (2005) and hep-ex/0507087.
Belle hep-ex/0507037
14
Experimental status

• Measurements in many channels now.
• Most measurements are low. Factorization
  predictions of SM effects go the other way.
• Naïve penguin average is gt2 sigma below (cc)K.
• All of these measurements are statistics limited.
• B factories will accumulate x2 to x3 times more
  data.
• Super B factory???

15
Experimental status

• No signs of direct CP violation, which would
  indicate either
• Unusually large SM corrections
• New physics
• More statistics desirable!

16
Leptonic B decays
17
Bs?m m-

• Strong constraints on NP models with extended
  Higgs sector.
• BF can be greatly enhanced (100 x SM) for large
  tanb!

Standard Model
New Physics?
Theoretical prediction
18
Bs?mm- experimental status

• Hadron colliders (Tevatron, LHC)
• Bs production threshold above Upsilon(4S). Not
  produced at current B factories.
• bb production cross section huge! (x20000
  larger than sbb in ee- at Upsilon(4S) for
  Tevatron).
• Non-bb production x1000 larger (QCD background).
• Muons easy to trigger on.

19
Bs?mm- CDF analysis
3 discriminating variables combined in likelihood
ratio.
primary vertex
20
Bs?mm- CDF analysis
3 discriminating variables combined in likelihood
ratio.
Decay length
l
primary vertex
21
Bs?mm- CDF analysis
3 discriminating variables combined in likelihood
ratio.
Da
Pointing consistency
primary vertex
22
Bs?mm- CDF analysis
3 discriminating variables combined in likelihood
ratio.
Isolation
primary vertex
23
Bs?mm- CDF analysis
3 discriminating variables combined in likelihood
ratio.
24
Bs?mm- CDF analysis
Normalized using
CDFII preliminary, 780 pb-1
Beats B factory by x3
Bs?mm limit only a factor of 30 above SM
prediction.
25
Example of Bs?mm- constraints on NP
S. Baek et al., JHEP 0502067(2005) mSUGRA
analysis
Neutralino-proton scattering cross section (pb).
26
B- ? t- n
Least helicity suppressed
B decay constant (lattice QCD)
Left side of Unitarity Triangle
Standard Model prediction
Error on fB from lattice calculation 10 Error
on Vub from SL decays 7.5
New Physics Charged Higgs contribution
27
B- ? t- n experimental approach
Recent Belle analysis, 447M BB (hep-ex/0604018)

• Very challenging due to the presence of at least
  two neutrinos.
• Fully reconstruct the other B in the event (the
  tag B). Efficiency (0.14)
• Reconstruct observable tau daughters in a few
  exclusive modes (81 of total, Efficiency 33).
• Require nothing else in the event
• No extra tracks
• Calorimeter energy should be close to zero.

Tag B meson
28
B- ? t- n experimental results
Recent Belle analysis, 447M BB (hep-ex/0604018)
Number of events in signal region
Blue histogram is background MC
Expected BG 32.8 4.6 Events observed 54
Unbinned likelihood fit of EECL
Signal yield
Significance of signal 4.2s
Signal distribution
Measured branching fraction
Signal region
Standard Model calculation
Remaining (extra) energy in electromagnetic
calorimeter
29
B- ? t- n impact on New Physics
2 Higgs doublet model W.S.Hou, PRD 48, 2342
(1993).
Branching fraction enhanced by rH.
Model prediction
Constraint on rH from Belle measurement
30
Radiative and semileptonic rare B decays
31
b ? s g and b ? s ll-
Short-distance physics
Operator product expansion
g penguin
Effective Wilson coefficients
Semileptonic vector
Semileptonic axial-vector
Hadronic matrix element calculations
Standard Model predictions observables give
measurements or constraints on the effective
Wilson coefficients.
32
b?sg decay rate
The most effective NP killer Gino Isidori,
hep-ph/0401079

• Semi-inclusive approach
• Sum of many Xs states (e.g. Kp, Kpp, KKKp, )
• Uncertainties from missing final states
• Fully inclusive approach
• Only reconstruct photon
• Suppress huge continuum (qq) background with
  lepton tag (S.L. decay of other B).
• Subtract remaining continuum using off-resonance
  data.
• Methods have similar precision
• Limited by systematic uncertainties.

33
b?sg decay rate
Heavy Flavor Averaging Group (HFAG) world average
(Eg gt 1.6 GeV) (See hep-ex/0603003 and references
therein)
experimental stat. and syst.
Small b?dg subtraction
Eg shape function
Next-to-leading-order theoretical prediction (Eg
gt 1.6 GeV) (Buras, Czarnecki, Misiak, Urban, NPB
631, 219 (2002))

• Remarkably good agreement.
• Large improvements (experiment and theory)
  unlikely.
• Fixes magnitude of C7 (g penguin Wilson
  Coefficient) to the Standard Model value. Sign
  of C7 not determined

34
b?sg CP asymmetry

• New Physics can still hide in b?sg without
  affecting the overall rate significantly.
• Standard Model ACP prediction is theoretically
  clean
• Large ACP is smoking gun for New Physics and can
  tell us what kind of New Physics.
• Minimal Flavor Violation (MFV) ACP lt 2
• Models with squark mixing ACP of order 10

T.Hurth, E.Lungh, W.Porod NP B704, 56 (2005)
Standard Model
35
b?sg CP asymmetry

• New Physics can still hide in b?sg without
  affecting the overall rate significantly
• Standard Model ACP prediction is theoretically
  clean

T.Hurth, E.Lungh, W.Porod NP B704, 56 (2005)
Standard Model
Babar
PRL 93, 021804 (2004)
Belle
PRL 93, 031803 (2004)
Cleo
PRL 86, 5661 (2001)
World Ave.
HFAG hep-ex/0603003
36
b?dg

• Amplitude CKM suppressed by Vtd/Vts 0.2
  w.r.t. b?sg
• Smaller SM amplitude ? higher NP sensitivity.
• BF suppressed by 0.04 w.r.t. b?sg.
  Experimentally very tough!
• Two SM amplitudes with CP-violating relative
  phase.
• Significant direct CPV expected within SM (10).
• Constrains Vtd/Vts within SM
• similar to role of Dmd/Dms in CKM analysis.
• some hadronic uncertainties cancel in ratio of
  exclusive modes.

37
b?dg
Belle result using 386M BB
PRL 96, 221601 (2006)
Combined result using isospin relation. 5.1 s
significance.
38
b?dg

• Results slightly controversial. Babar update
  coming soon.
• No hints of new physics.
• Constraint on Vtd/Vts supports CKM unitarity.

Plot by Jeff Berryhill, Babar rad. Penguin group
39
b ? s l l-

• Governed by three short-distance operators
• Relative contributions depend on q2 (square of
  di-lepton invariant mass).
• Differential measurements vs q2 measure A-V
  interference ? constrain Wilson coefficients (Ci).

g penguin
Semileptonic axial-vector
Semileptonic vector
40
Inclusive b ? s l l-

• Some NP models have SM value of C7 but the
  opposite sign (C7 ? -C7).
• One way for NP to wiggle out of C7 set from
  b?sg.
• Inclusive b?sll rate calculations to lt20
  accuracy away from charmonium resonances.

Example of New Physics with C7 ? -C7
T. Goto et al., PRD 55, 4273 (1997)
Destructive interference becomes
constructive! Factor of 2 rate enhancement.
Standard Model
41
Inclusive b ? s l l-

• Experiments measure the sum of many exclusive
  modes
• One Ks or K plus 0 or more pions. Assume KL
  modes KS modes.
• Avoid charmonium resonances.
• Extrapolate measurement to fully inclusive BF.
• Measure BF vs q2 and compare to theory
• Theoretical uncertainties vary with q2.

Babar PRL 93, 081802 (2004) Belle PRD 72,
092005 (2005) Theory P. Gambino et al., PRL 94,
061803 (2005)
Clean window 1 lt q2 lt 6 GeV2
Wrong-sign C7 strongly disfavored. No NP here
42
B?K ll- forward-backward asymmetry

• Vector (C7,C9) and axialvector (C10)
  contributions interfere.
• Forward-backward asymmetric in di-lepton CMF.
• Relative strength of V and A couplings varies
  with square of di-lepton invariant mass (q2).

• Features of the AFB(q2) curve can test the signs
  and magnitudes of C9 and C10.

43
B?K ll- forward-backward asymmetry
Example New Physics analysis of A.Ali, E.Lunghi,
C.Greub, and G.Hiller PRD 66, 034002 (2002).
B?K()ll exclusive and b?sll inclusive rate
measurements constrain New Physics contributions
to C9 and C10.
SM
Standard model at (0,0)
Anything in yellow ring is allowed by
B?(Xs,K())ll rate measurements.
44
B?K ll- forward-backward asymmetry
Example New Physics analysis of A.Ali, E.Lunghi,
C.Greub, and G.Hiller PRD 66, 034002 (2002).
B?K()ll exclusive and b?sll inclusive rate
measurements constrain New Physics contributions
to C9 and C10.
1
2
SM
3
2
SM
1
3
Large deviations in AFB possible!
45
B ? K l l-

• Both B factories have established signals in Kll
  channels.
• Use Kll channel for null test (AFB0 in SM).
• Statistics are low (50 to 100 signal events).
• Non-negligible background (signal fraction 50)
• Not enough for precision scan of AFB vs q2, but
  can make interesting rough measurements already

Babar
K ll-
229 M BB Nsignal 56
Belle
386 M BB Nsignal 114
Babar PRD 73, 092001 (2006) Belle
hep-ex/0603018 (sub. to PRL)
mes (GeV/c2)
46
B?K ll- AFB(q2) experimental results
Both experiments favor positive integrated
asymmetry
AFB(Kll)
(3.4s)
Belle
Belle
(SM sign for A7)
Babar
Crosscheck on Kll where no AFB expected
consistent with SM (zero).
AFB(Kll)
Belle
Babar
Babar
Babar PRD 73, 092001 (2006) Belle
hep-ex/0603018 (sub. to PRL)
47
B?K ll- AFB(q2) experimental results
Belle
(SM sign for A7)
Belle
Belle Fit for leading terms (Ai/A7) of effective
Wilson coefficients (Ci/C7). Wrong-sign A9A10
combination excluded at 98.2 C.L.!
Babar
Babar PRD 73, 092001 (2006) Belle
hep-ex/0603018 (sub. to PRL)
48
Summary

• Precision studies of loop-mediated B decays probe
  New Physics at high mass scales.
• The B factories and the Tevatron experiments have
  made impressive progress which has been matched
  by our theoretical colleagues
• No serious challenges to the Standard Model yet.
• B factories will accumulate x2 to x3 more data
• Leaves many clean probes of New Physics limited
  by statistics.
• LHC experiments will continue with some but not
  all measurements / searches
• A Super B factory would be highly desirable for
  exploring the flavor sector of any New Physics
  discovered at the LHC.

49
Backup
50
Babar K()ll analysis
Babar PRD 73, 092001 (2006)
control sample
Expect zero for Kll (control sample)
(For q2 gt 1.0 GeV2/c4)
51
Super B factories the physics case
SuperKEKB
5ab-1
50ab-1
LHCb 2fb-1
CPV (b g s)
FCNC
w/ n
CKM
From H. Yamamoto at DIF2006. See also
http//belle.kek.jp/superb and hep-ex/0406071
52
Super B factories

• The full discovery potential of rare decays will
  not be realized by the current B factories.
• Each experiment will collect only x2 to x3 more
  data.
• Measurements of theoretically clean observables
  all statistics limited.
• Very serious efforts underway to investigate
  feasibility of Super B factories
• ee- Upsilon(4S) machines with luminosities x25
  to x100 higher!

53
Super B factories two concepts

• Super KEK-B
• Higher current (1.3/1.8A) ? (4.1/9.1A).
• Moderate by decrease (6.2mm) ? (3.0mm).
• Target luminosity (4 to 8 x1035 1/cm2s) (5 to 10
  x109 BB/year)
• LOI 2004 (http//belle.kek.jp/superb)
• New idea storage ring similar to an ILC damping
  ring. IP similar to ILC final focus.
• Very low emittance.
• No current increase (1.4/2.5A).
• Aggressive by decrease (10mm)?(0.08mm).
• Target luminosity (10 x1035 1/cm2s) (12 x109
  BB/year)
• Potentially lower machine backgrounds w.r.t.
  Super KEK-B (limited detector RD required).
• Nice synergy with ILC RD.
• 3rd workshop recently held at SLAC, June 2006.
• (http//www-conf.slac.stanford.edu/superb/Default.
  htm)

54
Example of Bs?mm- constraints on NP
R. Dermisek et al., JHEP 0509029 (2005) Minimal
SO10 with soft SUSY breaking.
55
Constraints on NP in B mixing
What can we say about New Physics in a model
independent way?
Example analysis of UTfit collaboration
Analysis input
Standard constraints in Unitarity Triangle
analysis.
Rare decays not used as inputs.
UTfit collaboration http//utfit.roma1.infn.it,
hep-ph/0605213
56
Constraints on NP in B mixing
What can we say about New Physics in a model
independent way?
Example analysis of UTfit collaboration
Allow arbitrary New Physics in B mixing amplitudes
Analysis input
NP
SM
,
Expect
If theres no New Physics.
UTfit collaboration http//utfit.roma1.infn.it,
hep-ph/0605213
57
Constraints on NP in B mixing
Example analysis of UTfit collaboration
NP
SM
,
Expect
If theres no New Physics.

• Could be telling us that NP has Minimal Flavor
  Violation (MFV)
• Only source of flavor and CP violation is SM
  Yukawa couplings.
• Phase of DB2 amplitudes and Dmd/Dms unaffected
  by NP.

UTfit collaboration http//utfit.roma1.infn.it,
hep-ph/0605213
58
NP in b?s transitions

• In light of previous slide, still room for NP in
  b?s sector.
• Example SUSY with non-zero off-diagonal sfermion
  mass terms using mass-insertion approximation.

Constraints from rare decays
B? Xs g
B? Kll
Both constraints
L. Silvestrini hep-ph/0510077
59
NP in b?s transitions

• In light of previous slide, still room for NP in
  b?s sector.
• Example SUSY with non-zero off-diagonal sfermion
  mass terms using mass-insertion approximation.

Sizable deviations still allowed