# Presentation: 856902

## FCNC B decays

- _Fit_
- Unbinned maximum likelihood fit is performed in *m**ES** *and* *Δ*E *(*m**ES**, *Δ*E* and *m**K**π*) to extract signal yields of *B→Kl**+**l**- *(*B→K*****l**+**l**-*)
- Other signal parameters fixed to values from simulation or charmonium control samples
- Peaking background: same shape as signal with yields fixed
- Combinatorial background:  empirical shape fitted to data with a floating normalization
- _Results_
_***B→Kl***__***+***__***l***__***-***_
**Significance ~8****σ**
_***B→K***__*******__***l***__***+***__***l***__***-***_
- Assume *BF*(*B→K*****e**+**e**-*)/ *BF*(*B→K*****μ**+**μ**-*) = 1.33 to account for contribution from photon penguin pole near *m**ll* = 0 [Ali *et al. *PRD **66 **034002 (2002)]
**Significance ~3.3****σ**** **(including systematics)

- _Introduction_
- The branching fraction for *B→Kl**+**l**-** *(*B→K*****l**+**l**-*)* *is predicted to be around 0.5×10-6 (1.5×10-6) with an accuracy of 35%
- 8 decay modes studied: *B**+**→K**+**l**+**l**-*, *B**0**→K  l**+**l**-**, B**+**→K***+**l**+**l**-** *and *B**0**→K   l**+**l**- ** *(*l*=*e *or *μ*)* *
- A data sample of 122.9×106 *BB *decays is used
**Run 3 (2002-2003) data included**
- _Event selection_
*B*-candidates are formed by combining an oppositely charged lepton pair with a *K**±** *or *K , *and for the *B→K*****l**+**l**- *modes, a π± to form a *K*** *candidate
- Photons from Bremsstrahlung are recovered for electron tracks
- The *K**+** *are identified using the DIRC and *dE/dx *
- _B-reconstruction_
- The* B-*candidates are peaked strongly in two kinematic variables:
-    where *E**b** *is the beam energy in the centre of mass frame and, *m**i *and **p***i* are the masses and three-momenta of the *B*-candidate’s daughters
- _Background_
- Non-peaking background arises from random combinations of* *particles from *BB* and *qq* events
- Peaking background in *m*ES and Δ*E* arises from:
*B**→J/**ψ**(**ψ**(2s))K**(*)*
*B→K*****γ** *followed by photon conversion
- Hadronic *B*-decays in which a π+π- pair is identified* *as a* **μ**+**μ**-** *pair* ** *
- After cuts peaking background less than ≤ **0.7 events** in each mode

- The inclusive branching fractions for *B**→X**s**l**+**l**-**,* where *l *is either an *e *or *μ, *are predicted to be (4.2±0.7) ×10-6 for *m**ll**>*0.2 GeV/*c**2 *[Ali, hep-ph/0210183]
- Sample of 88.9 ×106 *BB* events used
- Reconstruct ~50% of all final states by selecting oppositely charged electron or muon pairs combined with a *K**± *or *K  ,** *and up to 2 pions, one of which may be a π0
- Event selection is optimized in 3 regions of *m(X**s**) *to enhance background rejection at higher *m(X**s**) *
- Similar peaking backgrounds to *B→K**(*)**l**+**l**-*
- Unbinned extended maximum likelihood fit is performed to extract signal yields, and shape and yield of combinatorial background
- The distribution of* m(X**s**) *for* e *and* **μ *shows states beyond the* K*****(892) *contribute to the total yield
**Signal yield 41.4±10.3±1.5, with a statistical significance of 4.6****σ**
- Dominant systematic uncertainties from the measured exclusive *BF*s and the Fermi motion model used for the  *b-*quark in the meson
- With improved measurements of exclusive mode *BFs* and the Fermi motion the systematic uncertainty will **decrease** **significantly**

- Jim Libby (SLAC)

- Measurements of Rare Flavour Changing Neutral Current *B-*decays

_**FCNC **__***B***__** decays**_

_***B***__***→K***__***(*)***__***l***__***+***__***l***__***-***_

_***B→X***__***s***__***l***__***+***__*** l***__***-***_

- Flavour changing neutral current (FCNC) decays appear only at the 1-loop level in the Standard Model
- Examples are the Penguin and *W-*box *b**→sl**+**l**- *decays (right)* *and pure Penguin *b→s**γ** *decay* *(below)* *

- Excellent place to search for new physics because it appears at the same order as the Standard Model
- Some SUSY examples are shown in the figure below
- Theoretical predictions are more precise for inclusive modes than exclusive, due to hadronic uncertainties in the latter, however they are more challenging experimentally
- Measurement of the *b→s**γ** * photon energy spectrum leads to a more accurate simulation of the *b**→ul**ν* lepton momentum spectrum, which is a major uncertainty in the determination of *V**ub*

- Preliminary results from *B**A**B**AR* are presented on *B→K**(*)**l**+**l**-**, B→ X**s** l**+**l**-** *and* B**→K (1430)**γ*

_***B→K***__***2***__*** (1430)***__***γ***_

- Branching fractions for the processes *B**+**→K***+*(1430) *γ** *and* B**0**→K***0*(1430) *γ** *have been measured
- Sub-modes *K***0**→ K**+**π**-* and *K***+**→ K**+**π**0*, *K**0**π**+*
- The spin-2 state is isolated from spin-1 background by fitting to the cosine of the helicity angle (cosθH) as well as Δ*E *and *m*ES

**Signal projections in *****m******K******π***** and |cos****θ****H****|- *****B******0******→K*******0*****(1430) *****γ***

- Simulation after cuts

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