# Presentation: 625250

## Electroweak Penguin B Decays:b→s,d  and b→s,d ll

**Electroweak Penguin ****B Decays:*****b******→******s,d *********** and *****b******→******s,d ll***

**Jeffrey Berryhill**
**University of California, Santa Barbara**
**For the BaBar Collaboration**

**LNS Journal Club Seminar**
**April 1, 2005**** **

**Penguins being inspected carefully for new physics.**

## b→ s,d Penguin Operators

**general Hamiltonian**
**of b****→s transitions**

**C7  “photon penguin” **
**C8  “gluon penguin”**
**C9  “Z penguin”**
**C10 “W box”**
**C7’, C9’, C10’  = opposite helicity projection of C7, C9, C10**
**Plus:**
**CS, CP = scalar and pseudoscalar**** FCNCs (e.g. Higgs penguin)**
**In SM, “t-penguins” dominate b****→****s; u- and c-penguins non-negligible for b****→****d**
**b****→****s, b****→****d, s****→****d, etc. ****could all have different C****i**** from new physics**

## Inclusive b→s  Rate

**Inclusive b****→****s ******** Rate**

**“****Total Branching Fraction” ****→**** PBF at E******** (min) = 1.6 GeV**
** ****Requires (model-dependent) extrapolation of spectral shape**
**Excellent agreement with Standard Model predictions at 10% level**
**Constrains   |C7|****2**** + |C7’|****2**

**BaBar sum of exclusive**
**BaBar Inclusive, E******** > 1.9 GeV**

**Theory uncertainty could improve to ~5% (NNLO)??**

**Belle Inclusive, E******** > 1.8 GeV**

**CLEO Inclusive, E******** > 2.0 GeV**

** ****Experimental uncertainty:  **
**systematics limited from large background subtraction**
**Could improve to 5% with 500-1000 fb****-1**

## b→ s Asymmetries

**Direct CP asymmetry generally constrained to < 5%**
**Isospin asymmetry precision ~5%**
**All measurements statistics limited for forseeable future**

**First ever **
**CP asymmetry **
**measurement of**
**b****→****(s+d) ******
**First ever **
**isospin breaking **
**measurement**
**of b****→****s ******

**Optimal b****→****s******** asymmetries truncate photon spectrum. (For ACP, E******** > 2.1 GeV) **
**Does this spoil SM comparison?**

## b  d  Branching Fractions

***b***** ******** *****d***** ******** Branching Fractions**

- central value

- 90% C.L. upper limit

**Combined significance **
**Belle+BaBar = 2.6 ******

**5******** observation expected for 1 ab****-1****/experiment**

## B→  CKM Impact

**Taken at face value, an intriguingly low |Vtd/Vts|**
**is inferred.**

**For ****************, ********R is negligible and form factor ratio**
**                           ********2**** ~ 1.2 ****± 0.1**

**What, if anything, can be done **
**to improve the estimate of the**
**form factor ratio (B****→********/B****→********)?**

**Belle+BaBar ********0******** **

**Until Bs mixing is observed, **
**this will be the most **
**experimentally precise**** **
**estimator of Vtd/Vts**

## The Physics of  b  s l l

**	****	****	**
**3 separate penguin diagrams, 3 body decay has non-trivial kinematic distributions**
**C****7    ****photon penguin****	****	****from *****b → s *********
**C****9    ****(mostly)****  ****Z penguin**
**C****10  ****(mostly)**** ****W box****	****	****unique to *****b→ s ll***

**15% uncertainty in inclusive rate**

**BF(*****b******→******s***********) = 4.2 ****± 0.7 10****-6**

**Also sensitive to **
**Ci’, CS, CP**

## Dilepton Mass Distribution

**J/******** K****(*)**

******(2S)K(*)**

**Pole at q****2**** ****≈ 0**** for K*ee **
**(nearly on-shell B****→****K*******
**Huge long-distance **
**contribution from**
**B ****→****charmonium decays**
**What q****2**** range is **
**insensitive to long **
**distance contributions,**
**LD-SD interference??**
** **

**Dilepton q****2**

## Inclusive b→sll Rate

**Agreement with Standard Model predictions at 10% level**
**Total rate constrains  |C9|****2**** + |C10|****2**

**Other observables:**
**Partial rate vs. q****2**
**AFB**
**ACP**
**ACP in AFB**

**Sums over exclusive final states K(Ks) + n********ll**
**Cuts on M(Xs) to suppress B backgrounds**
**M(Xs) < 2 GeV.  Does this spoil the inclusive**
**predictions??**

**70****±****14 events in 140 fb****-1**
**(Belle)**

## B → K(*)ll Total Rates

**difference = 2.6******

**difference = 1.9******

**BaBar and Belle branching fractions ****agree with SM predictions**
**Experimental uncertainty already better than theory**
**Difference between BaBar and Belle becoming significant?**

**Smallest B branching fractions ever measured**

**45****±12 K*ll events in 208 fb****-1**
**above photon pole (BaBar)**
**79±11 K*ll events in 253 fb****-1**
**Above photon pole (Belle)**

## K(*)/K(*)ee Ratio

**Sensitive to “****neutral Higgs penguin****”**
**for SUSY with large tan ******
**scalar penguins ****CS, CP**
**Ratio  ****R(K) = BF(B****→**** K********)/BF(B****→****Kee)**
**isolates Yukawa enhancement in muon mode**
**In SM, equal to unity with very high precision**
**Also contributes to R(K*) **
**(=1 above the photon pole) **
**(My BaBar + Belle) average **
**RK < 1.85   90%CL**
**Complementary to Tevatron B****s****→******** limit,**
**but B****s**** ****→ ******** will be the bellwether for forseeable future**

**K(*)********/K(*)ee Ratio**

**B****s**** ****→******** excluded**

**R****K**** excluded **

**Hiller & Kruger hep-ph/0310219**

## Forward-Backward Asymmetry

**Dilepton q****2**

**       ****dA****FB****/dq****2**

**Standard Model**

**C****i**** modified by SUSY**

**Angular asymmetry of lepton**** (anti-lepton)**
**angle with B (anti-B) momentum in dilepton**
**rest frame **
**Varies with dilepton q****2**
**Theoretically clean(??)**** probe of relative **
**size and phase of C****7****/C****9****/C****10**
**What is form factor uncertainty of A****FB****??**** **
**Can be ****dramatically modified by **
**new physics**** **
**Zero of A****FB**** provides simple, precise (15%)**
**relation between C****7 ****and C****9  ****(for LHCb/SuperB)**

## K(*)ll Partial Rates & “raw AFB” (Belle, 253 fb-1)

**Raw AFB appears to have SM sign for C10*Re(C9) at high q****2**
**Need quantitative, efficiency corrected measurement**

## B  K*l+l-AFBat Future Experiments

-  *s* = (*m*/*m*B)2

*A*FB(*s*)

- 	LHCb: 4400 K*0  events/year, S/B > 0.4
*	**A*FB(*s*) reconstructed using toy MC (two years data, background subtracted)Zero point located to ±0.04
- 	ATLAS: 2000 events, S/B = 7 (30 fb-1)

***^***

***^***

***^***

**What range of q****2**** has comparable **
**theory error?**

## There is more than one angle

**Dist. of all three angles (*********l)*********) is useful **

**There is more than one angle**

**Kruger&Matias (hep-ph/0502060) predicted features of**
**this distribution integrated over low q****2**** region < 6 GeV****2**

**SM**

**SM**

** ****C7’ from NP**

** ****C7’ from NP**

**Competitive alternative to B****→****K********* TDCPV?**

## b→ dll decays

**SM rate for B ****→ ********ll (few 10****-8****) may eventually be observable at B factories**

## Summary

**b ****→ ****s ******** penguin decays:****  **
**    ****precision constraints on C7, C7’**
**    ****rates are systematics limited**
**    ****asymmetries are statistics limited and theoretically precise**
**b****→ ****d ******** penguin decays:**
**    ****nearing observation of exclusive decays**
**    ****improved theory precision would have a big impact on CKM constraints **
**b****→ ****s ll penguin decays:**
**    ****total rates: exp. error comparable to theory error**
**    ****rich set of new constraints on penguin operators emerging from**
**          ****partial rates **
**          ****angular asymmetries (lepton angle and possibly K* polarization?)**
**          ****e/******** rate asymmetries**
**b****→**** d ll penguin decays:****  **
**    ****B ****→******** ll may eventually be observable by B factories**