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Measurements of B р Xsl+l- and BрK(*) l+l- at Belle

A. Ishikawa (KEK)

18, Aug, 2004

32

nd

International Conference on High Energy Physics BICC, Beijing, China


Introduction
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bрs l+l
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First observed by Belle in BрKll Proceed through penguin, Z penguin and W box diagrams Sensitive to new physics Sign of Wilson coeffient C7 as well as C9 and C10 can be obtained from q2 distribution and AFB(q 2). BF is low compared with bрs , suppressed by additional em рneed large statistics AFB SM K* l+ l
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C7eff =-C

eff 7 SM

q

2

Ali et al. Phys.Rev. D61 (2000) 074024


Measurement of Bр Xsl+l
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Theoretically clean, ~15% uncertainty on BF. Experimentally challenging
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fully-inclusive di-lepton п impossible with current statistics semi-inclusive Xs reconstruction п possible! One K+ or Ks + 0~4 pions (allow at most one 0 ) 18 decay modes covering 52% of Xs final states. (80% with KL) Electron ID efficiency ~ 95%, fake rate 0.2% @ 1.5GeV Muon ID efficiency ~ 90%, fake rate 1.0% @1.5GeV Mee> 0.2 GeV to suppress Dalitz decays and converted photons Fit to beam constrained mass distribution

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Xs hadron is reconstructed semi-inclusively
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With di-electron or di-muon
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Signal extraction
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- 140/fb data containing 152 million BB is used for this analysis


Measurement of B р Xsl+l- cont'd
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Background suppression is most important in this analysis. Four background sources
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dilepton events from continuum, mostly from charm events. Dominant - backgrounds dilepton events from BB: B р Xl , B р Yl B р J/ Xs events n Veto J/ with dilepton invariant mass B р Xs h+ h- events (h refers kaon or pion ) n Reconstruct Xs h+ h- and multiply momentum and angular dependent lepton ID fake rate.

0.03 events

1.8 events


Dilepton Background suppression
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5 variables into likelihood ratio(LR )
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Event shape, angular distribution of B candidate momentum Missing mass, energy and 2 of vertexing

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LR shape of real data in good agreement that of MC LR >0.9(>0.6 for M<1.1) cut retains 71% signal while removes 90% BG. Reconstruction Efficiencies for electron and muon modes are 2.6% and 2.9% respectively.


Result for Bр Xsl+l
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68Б14 Xsl +l- signal events with 5.8 significance

140/ fb data

32Б10 Xse+e-

36Б9 XsЕ+Е

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68Б14 Xsl+l

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Xse +Е- control sample


Branching Fraction for Bр Xsl+l
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BF is in good agreement with the SM prediction and previous resu lts.

Preliminary


MXs and q2 distributions in Bр Xsl+l
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MXs and q2 distributions are measured. Kll and K* ll are clearly seen. q2 distribution is consistent with the prediction by Ali et al.
Photon pole

K* K

MXs

q

2


Measurement of Bр K(*) l+l
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Large theoretically uncertainty ~30% on BF.
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Mostly from uncertainty in form factor model. Experimental precision is already comparable to theoretical uncertainty. Will be good calibration mode for QCD (form factor) in semi-leptonic B decays clean р more suitable to measure AFB than inclusive decay

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experimentally straightforward
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Reconstruction method is almost same as semi-inclusive analysis. - 253/fb data containing 273 million BB is used for this analysis


Result for Bр K(*) l+l
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253/ fb data

79 Б 10 Kll events and 82 Б 11 K*ll events are observed. BFs are consistent with theoretical prediction.
Preliminary

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Results (x 10-7)

With NNLO calculation
Previous results with NLO calculation(x 10-7)

Since we now use NNLO precision effective Wilson coefficients, which gives larger C 7 than NLO calculation, efficiency of K*ll become smaller ~12%. With NLO efficiency, the BF of K*ll is 14.7 x 10 -7.


A Ratio of Branching fractions
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A ratio of BF of KЕЕ to Kee is sensitive to neutral Higgs emission from internal loop in 2HDM with large tan . If Higgs contribution is large, this ratio is greater than unity.
Y. Wang and D. Atwood Phys. Rev. D68(2003) 094016

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Same ratio for K*ll is sensitive to size of photon pole. In the SM, this ratio is about 0.75.
Preliminary

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Both ratios are consistent with the SM prediction, so far.


q2 distributions for Bр K(*) l+l
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Yellow bands show ranges of theoretical prediction. Both results are consistent with the SM prediction, so far.


First look at A

FB

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Raw AFB in each q 2 region is extracted from Mbc fit. Dotted lines show charmonium veto windows. Kll has no asymmetry, so it is a good control sample. Curves show theoretical distributions including experimental efficiency effect (not fitted lines! ). Both curves are in agreement with data, so far.

J/

'


Summary
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improved measurements of inclusive B р Xs ll and exclusive B р Kll and K*ll. Measured BFs, ratios of BFs and q2 distributions are in good agreement with the SM theoretical prediction.

Preliminary

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First look at AFB