Rare and Semileptonic Decays of B and K
Rare and Semileptonic Decays of B and K Mesons Jeffrey D. Richman University of California, Santa Barbara BABAR Collaboration Particles and Nuclei International Conference Santa Fe, Oct. 27, 2005
Outline l Goals and challenges l KL p 0 nn l l The “kaon revolution”: KL p+e- n, |Vus|, and the recalibration of kaon branching fractions Electroweak penguin/box diagram processes: B K*g, B rg, B Xs g and B K l+l-, B K* l+l- l Semileptonic B decays and the measurement of |Vcb |, |Vub |, mb, mc l [Leptonic B decays: Bs m+m-, B+ t + nt] l Perspective and conclusions Far too many topics to cover. . . my apologies! Parallel session talks contain many more details (Bizjak, Godang, Koeneke, Mohapatra, …)
Rare and Semileptonic Decays: Goals Rare decay: loop/box process test SM at 1 -loop level new (heavy) particles can be produced in virtual intermediate states; can compete with SM amps search for effects of new physics Semileptonic decay: tree diagram measure |Vij| determine quark masses, QCD parameters
Common theme: understanding dynamics • Amplitude factorizes single hadronic current • Form factors/QCD parameters can sometimes be extracted from data or be calculated • Precise rate predictions possible for some processes • Methods: HQET, heavy-quark expansions, lattice QCD, … Understanding dynamics is an important goal in itself!
CKM matrix: b and s decays are both suppressed! (Wolfenstein parametrization) 5 highlighted Vij: discuss in this talk! unitarity: 6 triangles, all with same area
BABAR
KL p 0 nn • KL decay directly measures h (height of unitarity triangle)! • SM prediction: • Use K+ p 0 e+ n measurement to compute hadronic current. Buras, Schwab, & Uhlig, hep-ph/0405132; very small theory errors achievable. E 949, PRL 93, 031801 (2004)
Preliminary results on KL p 0 nn from KEK E 391 a 1. Measure g position and energy in Cs. I 2. Reconstruct decay vertex assuming Mgg=M(p 0). • Prelim. result uses 1. 14 x 109 KL decays; e=0. 73 x 10 -2 • So far, only very small fraction of data used. • No events observed in signal box • E 391 a goal 3. Signature: z(vertex) and pt Major backgrounds • Proposal in preparation for follow-on experiment at J -PARC
K pen , |Vus|, and the “kaon revolution” Review of Particle Properties, 2002 experiment: BR, t. K short distance radiative corr. Sirlin, Nucl. Phys. B 196, 83 (1982) long distance rad. corrections KLen: 1 form factor I-spin corr. for K+ decay K+en: 1/2 theory: q 2=0 exp’t: shape Cirigliano et al. , Eur. Phys. J C 35, 53 (2004) Andre, hep-ph/0406006 Leutwyler & Roos, Z. Phys. 25, 91 (1984) +other work in progress
Recalibration of KL branching fractions KTe. V measured 6 largest KL modes [PRL 93, 181802 -1 (2004)] • Account for 99. 93% of decays; 5 ratios of branching fractions • 105 -106 events/mode; careful treatment of radiation from electrons. • Measurement of KL semilep form factors (1. 7%-4. 2% shifts) [hepex/0406003, 0406006] fit to all new meas. E. Blucher, Lepton-Photon 2005
Extraction of |Vus| E. Blucher, Lepton-Photon 2005 Average of recent results: • KLOE, KTe. V, NA 48, ISTRA+ • correlations taken into account Competing method: G(K+ m+ n) [KLOE, hep-ex/0509045] + lattice [MILC, PRD 70, 114501 (2004); Marciano, PRL 93, 231803 (2004)]
Radiative penguin decays of B mesons Now it’s a physics program! Observation of B K* g CLEO II (1993): Loops in B decays! PRL 71, 674 (1993) cited >500 times!
Observation of the b dg decays B r (w) g Belle, 386 M BB BABAR, 211 M BB hep-ex/0506079 PRL 94, 011801 (2005) Mode BABAR (10 -6) (2. 1 s signif. ) Belle (10 -6) (5. 5 s signif. ) 8. 2 evts 20. 8 evts 5. 9 evts Belle Ali, Lunghi, Parkhomenko, PLB 595, 323 (2004) Belle good agreement w/global CKM fit
Inclusive B Xs g Decay • Canonical process for testing the SM at 1 loop level • Provides powerful constraints on new physics models • Major effort by theory community to compute QCD and EW corrections; NLL calculation complete; NNLL calculation forseen Hurth, Lunghi, Porod, Nucl. Phys. B 704, 56 (2005); see also Neubert, Eur. Phys. J C 40, 165 (2005); Buras et al. , Nucl. Phys. B 631, 219 (2002) Belle, PRL 93, 061803 (2004) fully incl. HFAG July 2005 BABAR sum of 38 excl. modes PRD 72, 052004 (2005)
Moments of B Xs g Photon Energy Spectrum (see talk by Karsten Koeneke, Section VI. 4) Used in determination of mb, |Vcb |, and | Vub | 2 nd Moment (Ge. V 2) 1 st Moment (Ge. V) Minimum Eγ (Ge. V) hep-ex/0507001 D. Benson, I. I. Bigi and N. Ultrasev Nucl. Phys. B 710, 371 -401 (2005) Minimum Eγ (Ge. V)
Electroweak penguins B Kl+l- and B K*l+l- • With l+l- pair, can produce both pseudoscalar and vector mesons • New physics can affect both rate and kinematic distributions. BABAR hep-ex/0507005 (229 M BB) Belle prelim. hep-ex/0410006, 0508009
B Kl+l- and B K*l+l- : branching fractions Theory errors mainly due to form factors. (rarest observed B decay) pole at low q 2
B K*l+l-: Lepton F-B Asymmetry Lepton angular distribution in l+ l- rest frame Belle: lepton A(FB) [raw] hep-ex/0508009 386 M BB SM NP scenarios constraints on Wilson coeffs describing short-distance physics
Precision measurement of |Vcb| and the atomic physics of B mesons • inclusive semileptonic rate Observables • inclusive lepton-energy spectrum (moments) • inclusive recoil hadron mass spectrum (moments) Heavy-quark expansion theory params: |Vcb|, mb, mc, mp , m. G , r. D , r. LS chromomagnetic expec. value kinetic expec. value Darwin term spin-orbit kinetic scheme BABAR, PRL 93, 011803 (2004) Benson, Bigi, Mannel & Uraltsev, hep-ph/0410080 Gambino & Uraltsev, Eur. Phys. J. C 34, 181 (2004)
|Vcb| and inclusive parameters from B Xcln and B Xs g Buchmuller and Flacher; hep-ph/0507253 • Fit to moments of inclusive distributions in B Xc l n and B Xs g • Experiments: BABAR, Belle, CDF, CLEO, DELPHI all moments kinetic mass scheme <2% errors D*ln zero rec.
Measuring |Vub | is hard, but the error is shrinking Large b c background; suppression cuts introduce dependence on theory predictions for kinematic distributions. Lepton spectrum endpoint analysis BABAR hep-ex/0509040 continuum data (off res) b c subtraction b u Fully reconstructed B recoil analysis p e- Belle Xu Breco D* n e+ Brecoil l hep-ex/0505088
|Vub | inclusive measurements Eℓ endpoint • Key CKM constraint • Use mb and QCD parameters extracted from inclusive B Xc l n and B Xs g spectra. • Many methods with uncertainties around 10%. • Uncertainty from mb has been reduced to 4. 5%. • With more data, the |Vub| uncertainties could be pushed down to 5%-6. 5%. Eℓ vs. q 2 m. X vs. q 2 expt mb, theory
Measuring |Vub| using B p l n and lattice QCD B 0 p+ l- n form-factor predictions Fermilab/MILC HPQCD f+(q 2) is relevant form factor for B p l n (l=e, m) At fixed q 2, lepton momentum spectrum is exactly known in this mode, since only one form factor. HPQCD: hep-lat/0408019 restricted q 2 range Fermilab/MILC: hep-lat/0409116
B p l n: branching fraction and q 2 distribution Becher and Hill, hep-ph/0509090 Relatively flat distribution in spite of rapidly changing form factor. Consequence of p 3 factor in decay rate. HFAG averages
Search for Bs m+m- and B 0 l+l- Highly suppressed in the SM • • Bd suppressed by |Vtd/Vts|2 • No SM signals expected at Tevatron or at B factories, but can have large enhancements from new physics. SM predict. CDF Strong correlation with neutralino-proton cross section in m. SUGRA! Beck, Kim, Ko hep-ph/0406033 D 0 BABAR Belle - -
Perspective/Conclusions K Physics • Early results from 1 st dedicated KL p 0 nn experiment • KL branching fractions re-measured: 5% to 8% shifts • |Vus| shift: +3% • Unitarity of 1 st row of CKM matrix looks better; work in progress on |Vud| B Physics • B rg observed; provides interesting constraint on |Vtd|/|Vts| • Many b sg and b sl+l- modes observed; studies of kinematic distributions are especially interesting • |Vcb| measured to 2% via inclusive method; mb well determined • |Vub| precision now below 10%. • Keep pushing inclusive vs. exclusive crosscheck! • Leptonic B decays providing interesting sensitivity to new physics • B factories will push to 1 ab-1. Many more results to come!
Backup slides
Huge program on B decays to charmless hadronic final states. . . see H. Jawahery talk for hadronic b s decays (10 -6)
Observation of the b dg decays B r (w) g BABAR Belle Note: naïve expectation is G(B+ r+g)=2 G(B 0 r 0 g)=2 G(B 0 wg) BABAR/Belle discrepancy on B 0 r 0 g; to be resolved with more data.
BABAR
B Xs g New Physics Sensitivity • Constraints on Two Higgs doublet models (Type II) • m. H = charged Higgs mass • tanb = ratio of vacuum expectation values of the two doublets • Hou [PRD 48, 2342 (1993)], Gambino & Misiak [Nucl. Phys B 611, 338 (2001)], Neubert [Eur. Phys. J C 40, 165 (2005)]. future projections current BABAR data 90% C. L. allowed regions (above lines) combined 2 ab-1 1 ab-1 0. 5 ab-1
Search for leptonic B- decays • helicity suppressed • CKM suppressed (Vub) • annihilation diagram • tree-level sensitivity to HNon-relativistic mesons (2 heavy quarks): Predicted leptonic branching fractions: (|Vub| = 0. 0039, f. B = 200 Me. V) meson B (en) B (mn) B (tn) p+ K+ B+
Search for B- t- n BABAR, hep-ex 0507069 t reconstruction: a major challenge • fully reconstruct other B in event • require lepton (or pion) and no additional observed energy (2 -3 n) e- Eextra Belle, hep-ex/0507034 e+ te- n nt e SM B(B+ t n) nt Backgrnd Expected signal x 10 BABAR (232 M BB) Belle (275 M BB)
Search for Bs m+m- and B 0 l+l. Highly suppressed in the SM • • Bd suppressed by |Vtd/Vts|2 • No SM signals expected at Tevatron or at B factories, but can have large enhancements from new physics. SM predict. CDF D 0 BABAR - 90% C. L. Belle -
Bs m+m- and SUSY Dermisek, Raby, Roszkowski, Ruiz de Austri, hep-ph/0507233 Baek, Kim, Ko, hep-ph/0406033 Dark matter cross section s(cp) vs. B(Bs m+m-).
Experiment vs. Lattice: D K l n form factor
Measuring |Vub| using B p l n BABAR PRD 72, 051102 (2005) Projection to 1 ab-1 (data taken to be on BK fit curve from present measurement). In the high q 2 region alone, we will measure the branching fraction with an uncertainty of (6 -7)% , or (3 -3. 5)% uncertainty on |Vub |. Lattice theorists expect to reach 6%, so exclusive/inclusive will be similar.
Precision measurement of |Vcb|: fits to moments of lepton spectrum and hadron recoil spectrum BABAR PRL 93: 011803 (2004) m. X moments ● = used, ○ = unused in the nominal fit BABAR c 2/ndf = 20/15 Eℓ moments Red line: OPE fit Yellow band: theory errors
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