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

K* l+l- should have comparable sensitivity to AFB as s l+ l- Precision in s0 ~ 5%.

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