Semileptonic B physics at CLEO Ron Poling University

Semileptonic B physics at CLEO Ron Poling University of Minnesota CLEO-c Collaboration CLEO Collaboration Ron Poling WIN 03 October 7, 2003

CESR and CLEO: 23 years of B Physics Three generations of detectors, ~170 Ph. D. ’s, ~360 papers Ron Poling WIN 03 October 7, 2003 2

The Global Program of CKM Tests • Goal: redundant determinations of sides and angles of the Unitarity Triangle(s) • CLEO’s Role: Vcb or Vub – Measure UT sides through |Vcb| and |Vub| in semileptonic B decays. – Detailed studies to guide interpretation and help clear the “fog” of nonperturbative effects. • Challenging experimentally and theoretically. Ron Poling WIN 03 October 7, 2003 3

B Semileptonic Branching Fraction • CLEO II: 10 fb-1 at (4 S) – Mature, well-understood detector, data, Monte Carlo, generators, etc. CLEO - Preliminary • Lepton-Tagged Analysis – ptag>1. 4 Ge. V/c plus accompanying electron with pe>0. 6 Ge. V/c. – Charge, angular correlations to separate primary (B Xe ) from secondary (B D Ye ). • Refined electron ID, background and efficiency determinations. – Maximize understanding and minimize momentum dependence. Preliminary: B(B Xe )=(10. 88 0. 08 0. 33)% Ron Poling WIN 03 October 7, 2003 4

BSL – Still small-ish, but consistent • Good agreement among different techniques, experiments. • Measurements at (4 S) have come up and LEP Z 0 average has come down. – Most recent LEP fit result is (10. 59 0. 22)% Ron Poling WIN 03 October 7, 2003 5

The Reality of Semileptonic B Decays • We idealize them as… Vcb or Vub • View of b decay obscured by… – Hadronic effects describable by both perturbative and nonperturbative QCD. – Uncertainty about our assumption of quark-hadron duality. • The real picture is… • Available tools include Heavy Quark Effective Theory and Lattice QCD. Must be validated by experiment. Ron Poling WIN 03 October 7, 2003 6

HQET+OPE • Expresses observables of inclusive b decay as expansions in inverse powers of MB (Voloshin +Shifman, …). • One parameter at order QCD/MB: – ~ MB – mb is the energy of light-quark and gluon degrees of freedom in the B meson. • Two parameters at order 2 QCD/M 2 B : – 1 – negative of the average b-quark momentum squared. – 2 – energy of the hyperfine interaction of the b spin with the light degrees of freedom (from B*-B splitting: 2 = (0. 128 0. 010) Ge. V). • Six more parameters at order 3 QCD/M 3 B (Gremm and Kapustin): – 1, 2, T 1, T 2, T 3, T 4 (not all independent). • Meaning of parameters depends on choices: order of perturbative ( 0( s/ )2 ) and nonperturbative (1/M 3 B) expansions and mass scheme. Consistency required. |Vcb| is what counts! Ron Poling WIN 03 October 7, 2003 7

Data from different processes will tell us if this approach provides a coherent picture of inclusive B decays. MOMENTS, INC. – CLEO Branch • B Xs Photon-Energy Moments • B Xl Lepton-Energy Moments • B Xl Hadronic Recoil Mass Moments First and second moments, different lepton-energy ranges… Lots of complementary information. Ron Poling WIN 03 October 7, 2003 8

Measuring B Xs Photon-energy spectrum at (4 S) Continuum must be suppressed. • Use all available tools! – Traditional shape variables. – Pseudo-reconstruction: demand consistency with B K(n) – Use neural net to compute signal probability and measure spectrum of “weights. ” – Subtract continuum with below (4 S) data. – Subtract backgrounds with Monte Carlo, informed by data wherever possible. Ron Poling WIN 03 October 7, 2003 9

Measuring B Xs • CLEO II – 10 fb-1 • PRL 87, 251807 (2001) • Hard measurement, simple interpretation: – Almost two-body, with broadening by Fermi motion, gluon bremsstrahlung, boost of B’s at (4 S) – <E > gives nearly direct access to. Next, measure the moments of the E spectrum by fitting to model of Ali-Greub or HQT calculation of Kagan-Neubert: Ron Poling WIN 03 October 7, 2003 10

Hadronic Mass Moments in B Xcl • Select events with leptons with – 1. 5 < pl < 2. 5 Ge. V/c • “ reconstruction” to measure p. • Calculate approximate hadronic recoil mass using l (take advantage of p. B small): PRL 88, 251808 (2001) • Construct continuum-subtracted spectrum and fit to mixture: – B Dl (CLEO FF’s) • – B D*l (CLEO FF’s) – High-mass, nonresonant by models (ISGW 2, Goity/Roberts) Use fit components to compute moments: = 0. 251 0. 023 0. 062 Ge. V 2 = 0. 639 0. 056 0. 178 Ge. V 2 Ron Poling WIN 03 October 7, 2003 11

Interpreting the Moments • First moments E and MX 2 - MD 2 fitted to extract and 1. • Combined solution is = 0. 35 0. 070 0. 10 Ge. V 1 = -0. 236 0. 071 0. 078 Ge. V 2 • Precise meaning of parameters is scheme- and order-dependent; these are to order 1/MB 3, order 0 s 2 in MS scheme. Ron Poling WIN 03 October 7, 2003 12

Extracting |Vcb| from (B Xcl ) • Ingredients: Ø (B Xcl ) = (10. 8 0. 3)% (CLEO) Ø B and B (PDG), f+ / f 00 (CLEO) SL = (0. 44 0. 02) 10 -10 Me. V 0 • Result: |Vcb| = 0. 041 0. 0005 0. 0007 0. 0009 Overall precision: ~3% + quark-hadron duality. Ron Poling WIN 03 October 7, 2003 13

|Vcb| from B D*l d /dw PRL 88, 251808 (2001) 0. 0388 0. 0011 |Vcb|=(42. 6± 1. 2± 2. 3) 10 -3 Ron Poling WIN 03 October 7, 2003 14

New and Improved Measurement of the Hadronic Mass Moments in B Xcl hep-ex/0307081 - Contributed to Lepton-Photon 2003 • Compute recoiling hadronic mass from charged lepton and neutrino kinematics - neutrino “detection. ” • Near hermeticity of CLEO II Neutrino=“What’s missing” Fit 3 -dimensional differential decay rate, extract hadronic mass squared as a function of lepton-energy cut (pl > 1 Ge. V/c). Ron Poling WIN 03 October 7, 2003 15

Fit Projections • Selection criteria: – Cuts to enhance reconstruction – Continuum suppression – Efficiency ~2% for B Xcl • Sample to fit: 122 K events • Components of fit: HQET+measured FFs – B Dl – B D*l – B D**l – – ISGW 2 B (Xc)NRl Goity/Roberts B Xul ISGW 2+NR Secondaries CLEO MC Fake Leptons, Continuum fixed with data Ron Poling WIN 03 October 7, 2003 16

Results PRELIMINARY Fits Mode-by-Mode BRs + Generator-Level Info (Fraction above pl cut, moment value for that cut. ) Moment Value for B Xcl PRELIMINARY DELPHI: energy and hadronic mass moments for full lepton-energy spectrum. hep-ph/0210319 • Consistent with previous CLEO measurements, Ba. Bar summer ’ 03 • Interpretation continues Ron Poling WIN 03 October 7, 2003 17

B Xcl Energy Moments PRD 67, 072001 (2003) e Pending…El moments down to 0. 6 Ge. V Ron Poling WIN 03 October 7, 2003 18

Improved Inclusive Measurement of |Vub| • End-point technique: – Isolate B Xul by looking above (and just below) the B Xcl kinematic limit. – Used for b u discovery (CLEO, ARGUS) and CLEO 93: |Vub|/|Vcb|= 0. 08 0. 02 Significant model dependence. • Can now do better: – Better knowledge of B Xcl. – B Xs helps determine fraction of spectrum in end point. B Xs spectrum shape function fu Ron Poling WIN 03 October 7, 2003 19

Measuring B Xul PRL 88, 231803 (2002) Ø 2. 0 < pl <2. 6 Ge. V/c Ø Suppress continuum with neural net (energy flow w. r. t. lepton). Less q 2 - and M(Xu)-dependent. Ø Estimate B Xcl by fitting inclusive spectrum. Components reflect state-of-the-art on form factors, b. r. ’s, etc. Ø Trade-off: B Xcl uncertainty vs. spectral-fraction uncertainty. Ron Poling WIN 03 October 7, 2003 ON b cl OFF b ul excess 20

Extracting |Vub| • Hoang, Ligeti, Manohar; Uraltsev: • Determine from B Xs shapefunction fits (Kagan-Neubert). In preparation: Paper with details of fits for shape-function parameters and fu values for phase-space regions other than just end point. Ron Poling WIN 03 October 7, 2003 21

Branching Fractions and q 2 Dependence of B l and B ( )l and Extraction of |Vub| hep-ex/0304019 to be published in PRD • Exclusive reconstruction of B ( / / / )l through neutrino “detection. ” • Near hermeticity of CLEO II Neutrino=“What’s missing” Signal defined by… Ron Poling WIN 03 October 7, 2003 22

• CLEO II 10 fb-1 • Event selection to enhance reconstruction, suppress continuum B l (pl > 1. 0 Ge. V/c) • Fit Mml and E in three bins in q 2 to find branching fractions B l (pl > 1. 5 Ge. V/c) Ron Poling WIN 03 October 7, 2003 23

B l • Extracting |Vub| – Fit d /dq 2 – Discriminates among FFs • B l – FF dependence is small – Disfavors ISGW 2 B l • B l – Larger FF dependence greater model uncertainty in |Vub| Ron Poling WIN 03 October 7, 2003 24

RESULTS Ron Poling WIN 03 October 7, 2003 25

Comparisons and CKM Impact 90% c. l. contours |Vub|/10 -3 Ron Poling WIN 03 October 7, 2003 26

Perspectives and Prospects • CLEO is still contributing on |Vub| and |Vcb|. – Sample smaller than B factories, but well understood with mature tools. – We’re all limited by theoretical uncertainties. • Continuing and forthcoming CLEO CKM-related measurements: – Completion of moment measurements, coordinated fits of all available inputs. – Inclusive b ul for all CLEO II and CLEO III via multidimensional fit and bigger phase-space acceptance. • CESR-c/CLEO-c will have significant impact on CKM. See the upcoming of Karl Ecklund. Ron Poling WIN 03 October 7, 2003 27