The physics of b s l+ l-:2004 and beyond
Jeffrey Berryhill
University of California, Santa Barbara
January 19, 2004
Super B Factory Workshop
University of Hawaii
Electroweak Penguin Decays and New PhysicsB decays in the SM via electroweak loop diagrams
Many observables accurately predicted with sensitivity to new physics at the electroweak scale (SUSY, e.g.):CP asymmetries, rates, angular distributions
More complex interaction than b to s rates and distributions depend on the magnitude and relative phase of three separate diagrams
b s l+ l- and Effective Field TheoryMatrix elements computed from effective Hamiltonian for b to s transitions
Products of field operators
Wilson coefficients encoding short-distance physics
3 of the 10 b to s operator products give b to s l+l -:
C7: photon penguin (|C7| measured from b to s )
C9,C10 : Z penguin and W box
C9,C10 dominant at high s, C7 dominant at low s, sign of C7 matters
Generally decreases with s
LO: more missing states, lower lepton momenta C7*C9 dominant
HI: fewer missing states, higher lepton momenta C10 dominant
Dilepton Mass Spectrum d/ds
NNLO error = 19%NNLO error = 12%
HI: check for right sign and magnitude
LO: extract s0
Angular Asymmetry vs. Dilepton Mass
Forward-backward asymmetry of lepton pair in the B rest frame
S0 NNLO error = 5%
S0 = 0.162+/-0.008 ~ C7/C9
NNLO error = 5%
CP Asymmetries Like b to s, in the SM ACP in b to s l+ l- is small, < 1%
In B to K* l+l-, can construct 8 different angular and CP asymmetries,all of which are << 1% in the SM (Kruger et al., hep-ph/9907386)
In units of 10-4!
CP asymmetry in AFB(s) for s> m((2S))2 gives access to Im(C10)(Buchalla,Hiller,Isidori, hep-ph/0006136)
Isospin Asymmetry vs. Dilepton Mass
Asymmetry arising from non-factorizable diagrams
Sensitive to b to s 4-quark operators
Feldmann and Matias hep-ph/0212058
C5,C6 dominant
C3,C4 dominant
Independent test of sign of C7!
SUSY Higgs Physics at a B-Factory
In SUSY with large tan, Higgs penguins introduce new scalarand pseudoscalar operators to the b to s Heff, with new Wilsoncoefficients Cs, Cp
b to s e+ e- is unaffectedb to s + - is enhanced (by larger Yukawa coupling)
Ratio of exclusive rates is very precisely predicted in SM:
RK = BF(B to K +-)/BF(B to K e+ e-) = 1 +/- 0.0001 !(Hiller and Kruger, hep-ph/0310219)
RK is a powerful probe of SUSY Higgs with large tan
Complementary observable to the decay rate for Bs to + -
K l+ l-
Includes K and Ks final states
2-D ML fit to (mES , E) data
Background shape and normalization float in the fit
Dilepton mass consistent with signal
BF = (6.5+1.4-1.3+/-0.4)x10-7
Smallest B BF Ever Measured!
K*l+l- Includes K* final states:
K*0 to K+ pi-K*+ to Ks pi+
3-D fit to (mES, E, mK) data
Dilepton mass consistent with signal(all the way down to q2 = 0)
BB background is larger thanin Kll.
BF = 8.8+3.3-2.9+/-1.0 X 10-7
s l+l-
Sum of exclusive final states:1 K or Ks + <= 2 pions (pi0, pi+, pi0pi+, pi+pi-)
M(Xs) < 1.8 GeVP(e) > 0.5 GeV, P(mu) > 1.0 GeV
1-D fit to mES data
>= 3 pion states added negligible significance
K, K* and higher mass states contribute to observed signal
Model-dependence of efficiencyIs the dominant systematic
BF = 6.3+/-1.6+/-1.8 X 10-6
b sl+l- January 2004
Branching fractions in good agreement with SM predictions
Experimental precision of overall rates already comparable totheoretical precision!
“Model Independent” Analysis of Heff
C7 < 0 C7 > 0
C10
C9
Attempt to extract Wilson coefficients C9, C10 directly from total b to s l+ l- BF (|C7| fixed from b to s
Adding more observables will further constrain C9 and C10
Can real and imaginary parts of all coefficients be extracted via a combined fit to all observables (a la b to c l )?
Projected Statistical Uncertainty: K l+ l-
2 ab-1
1034
10 ab-1
1035
50 ab-1
1036
K l+ l-
All s
5.4% 2.4% 1.1%
K l+ l-
Low s
6.9% 3.1% 1.4%
K l+ l-
High s
11.5% 5.1% 2.3%
Based on HFAG average stat. errors, relative efficiency vs. s of BaBar RED = detector systematics limited for absolute rate
Projected Statistical Uncertainty: K* l+ l-
2 ab-1
1034
10 ab-1
1035
50 ab-1
1036
K* l+ l-
All s
7.0% 3.1% 1.4%
K* l+ l-
Low s
9.9% 4.4% 2.0%
K* l+ l-
High s
13.8% 6.2% 2.8%
Based on HFAG average stat. errors, relative efficiency vs. s of BaBarRED = detector systematics limited for absolute rate
Projected Statistical Uncertainty: s l+ l-
2 ab-1
1034
10 ab-1
1035
50 ab-1
1036
s l+ l-
All s
4.5% 2.0% 0.9%
s l+ l-
Low s
7.5% 3.4% 1.5%
s l+ l-
High s
11.4% 5.1% 2.3%
Based on HFAG average stat. errors, relative efficiency vs. s of BaBarRED = detector systematics limited for absolute rateBLUE = probably theory systematics limited for absolute rate
Physics prospects beyond 1034
•The BAD NEWS: Absolute rates and even partial absolute rates will be systematics limited in the B-factory (1034) era
•The GOOD NEWS: Relative rates and asymmetries will be statistics limited for both 1035 and 1036
Model Independent Analysis beyond 1034
Fit directly for C9 and C10 using the AFB spectrum (Nakao study for SuperBelle)
C7 is fixed from future precise b to s BF
Detector design considerations
•Need efficient lepton ID down to the lowest lab momentum possible (1 GeV cut on muons cuts into efficiency at low s)
•Lepton fake rate not the highest priority (peaking backgrounds are low)
•Better vertex separation will improve background rejectionWorse separation will not seriously degrade sensitivity
The Competition 1-2 years of design luminosity with hadrons= 50 ab-1 with electrons!!
1/sqrt(4400)=1.5%= SuperB precision
Physics prospects beyond 1034 With Competition
•The BAD NEWS: One or more successful hadron experiments can do better with most measurementsthan e+e- experiments, even with 50 ab-1.
•Possible Exceptions: •RK : precise Kee is difficult with hadron experiments.
•sll observables : probably done better at e+e-(though not uniquely), but do they tell us something exclusive modes will not?
Conclusions•The b s l+ l- system has a rich set of observables sensitive to new physics at the electroweak scale
•In the SuperB era, absolute rate measurements will be systematics limited, but many relative rates and asymmetrieswith high sensitivity to new physics will be statistics limited:
Forward-backward asymmetry vs. dilepton massCP and isospin asymmetries
•Most of these measurements can be done (in theory, done better) by hadron experiments
•Ratio of rates RK = BF( K )/BF( Kee ) is a measurement unique to a SuperB Factory with access to Higgsphysics in SUSY models with large tan
Combinatorial Background:Reduction and Estimation
Background from random track combinations in BB or continuum events
Continuum events reduced with Fisher discriminant:Fox-Wolfram momentsB angle with CM z axisB angle with thrust axisKl mass
BB events reduced with likelihood function: missing energyB vertex probabilitiesB angle with CM z axis
Separate background from signal with multivariate discriminants
Signal efficiency verified with J/K(*) events
Background reduction verified with:sideband events K(*)e events
cut cut
Peaking Background:Reduction and Estimation
Backgrounds with the same shape in (mES, E) as signal
Veto most of it , estimate the rest from MC and control samplesB Decays to
J/ K(*), ’ K(*)
B Decays to h+h- K(*)
500 fb-1 MC
Veto events in the (mll , E) plane
Residual bkgrd. from fitto charmonium MC J/ veto ’ veto
h+h- K(*) events in dataconvolved with ratesfor h to fake e,
D toK(*)events vetoed for K(*) modes
0.01 events 0.33 events