Semileptonic B physics at CLEO Ron Poling University of Minnesota CLEO Collaboration CLEO-c Collaboration

Ron Poling WIN03 October 7, CESR and CLEO: 23 years of B Physics Three generations of detectors, ~170 Ph.D.’s, ~360 papers

Ron Poling WIN03 October 7, The Global Program of CKM Tests Goal: redundant determinations of sides and angles of the Unitarity Triangle(s) CLEO’s Role: –Measure UT sides through |V cb | and |V ub | in semileptonic B decays. –Detailed studies to guide interpretation and help clear the “fog” of nonperturbative effects. Challenging experimentally and theoretically. V cb or V ub

Ron Poling WIN03 October 7, B Semileptonic Branching Fraction CLEO II: 10 fb -1 at  (4S) –Mature, well-understood detector, data, Monte Carlo, generators, etc. Lepton-Tagged Analysis –p tag >1.4 GeV/c plus accompanying electron with p e >0.6 GeV/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. CLEO - Preliminary Preliminary: B (B  Xe )=(10.88  0.08  0.33)%

Ron Poling WIN03 October 7, B SL – Still small-ish, but consistent Good agreement among different techniques, experiments. Measurements at  (4S) have come up and LEP Z 0 average has come down. –Most recent LEP fit result is (10.59  0.22)%

Ron Poling WIN03 October 7, The Reality of Semileptonic B Decays We idealize them as… The real picture is… View of b decay obscured by… –Hadronic effects describable by both perturbative and nonperturbative QCD. –Uncertainty about our assumption of quark-hadron duality. Available tools include Heavy Quark Effective Theory and Lattice QCD. Must be validated by experiment. V cb or V ub

Ron Poling WIN03 October 7, HQET+OPE Expresses observables of inclusive b decay as expansions in inverse powers of M B (Voloshin +Shifman, …). One parameter at order  QCD /M B : –  ~ M B – m b 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) GeV). 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. |V cb | is what counts!

Ron Poling WIN03 October 7, M OMENTS, I NC. – CLEO Branch B  X s  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. Data from different processes will tell us if this approach provides a coherent picture of inclusive B decays.

Ron Poling WIN03 October 7, Measuring B  X s  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-  (4S) data. –Subtract backgrounds with Monte Carlo, informed by data wherever possible. Photon-energy spectrum at  (4S)  Continuum must be suppressed.

Ron Poling WIN03 October 7, Measuring B  X s  CLEO II – 10 fb -1 PRL 87, (2001) Hard measurement, simple interpretation: –Almost two-body, with broadening by Fermi motion, gluon bremsstrahlung, boost of B’s at  (4S) – 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 WIN03 October 7, Hadronic Mass Moments in B  X c l Select events with leptons with –1.5 < p l < 2.5 GeV/c “ reconstruction” to measure p. Calculate approximate hadronic recoil mass using l (take advantage of p B small): Construct continuum-subtracted spectrum and fit to mixture: –B  Dl (CLEO FF’s) –B  D * l (CLEO FF’s) –High-mass, nonresonant by models (ISGW2, Goity/Roberts) Use fit components to compute moments: =   GeV 2 =   GeV 2 PRL 88, (2001)

Ron Poling WIN03 October 7, Interpreting the Moments First moments  E   and  M X 2 - M D 2  fitted to extract  and 1. Combined solution is  = 0.35   0.10 GeV  1 =   GeV 2 Precise meaning of parameters is scheme- and order- dependent; these are to order 1/M B 3, order  0  s 2 in MS scheme.

Ron Poling WIN03 October 7, Extracting |V cb | from  (B  X c l ) Ingredients:  (B  X c l ) = (10.8  0.3)% (CLEO)   B 0 and  B  (PDG), f +  / f 00 (CLEO)  SL = (0.44  0.02)  MeV Result: |V cb | =    Overall precision: ~3% + quark-hadron duality.

Ron Poling WIN03 October 7, |V cb | from B  D * l d  /dw  |V cb |=(42.6±1.2±2.3)  PRL 88, (2001)

Ron Poling WIN03 October 7, New and Improved Measurement of the Hadronic Mass Moments in B  X c l hep-ex/ 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 (p l > 1 GeV/c).

Ron Poling WIN03 October 7, Fit Projections Selection criteria: –Cuts to enhance reconstruction –Continuum suppression –Efficiency ~2% for B  X c l Sample to fit: 122K events Components of fit: –B  Dl –B  D*l –B  D**l ISGW2 –B  (X c ) NR l Goity/Roberts –B  X u l ISGW2+NR –Secondaries CLEO MC –Fake Leptons, Continuum fixed with data  HQET+measured FFs

Ron Poling WIN03 October 7, Fits  Mode-by-Mode BRs + Generator-Level Info (Fraction above p l cut, moment value for that cut.)  Moment Value for B  X c l Results Consistent with previous CLEO measurements, BaBar summer ’03 Interpretation continues PRELIMINARY DELPHI: energy and hadronic mass moments for full lepton-energy spectrum. hep-ph/ PRELIMINARY

Ron Poling WIN03 October 7, B  X c l Energy Moments PRD 67, (2003) Pending…E l moments down to 0.6 GeV e 

Ron Poling WIN03 October 7, Improved Inclusive Measurement of |V ub | End-point technique: –Isolate B  X u l by looking above (and just below) the B  X c l kinematic limit. –Used for b  u discovery (CLEO, ARGUS) and CLEO 93: |V ub |/|V cb |= 0.08  0.02 Significant model dependence. Can now do better: –Better knowledge of B  X c l. –B  X s  helps determine fraction of spectrum in end point. B  X s  spectrum  shape function  f u

Ron Poling WIN03 October 7, Measuring B  X u l  2.0 < p l <2.6 GeV/c  Suppress continuum with neural net (energy flow w.r.t. lepton). Less q 2 - and M(X u )-dependent.  Estimate B  X c l by fitting inclusive spectrum. Components reflect state-of-the- art on form factors, b.r.’s, etc.  Trade-off: B  X c l uncertainty vs. spectral-fraction uncertainty. b  ul excess ON OFF b  cl PRL 88, (2002)

Ron Poling WIN03 October 7, Hoang, Ligeti, Manohar; Uraltsev: Determine from B  X s  shape- function fits (Kagan-Neubert). Extracting |V ub | In preparation: Paper with details of fits for shape-function parameters and f u values for phase-space regions other than just end point.

Ron Poling WIN03 October 7, Branching Fractions and q 2 Dependence of B  l and B  (  )l and Extraction of |V ub | Exclusive reconstruction of B  (  /  /  /  )l through neutrino “detection.” Near hermeticity of CLEO II  Neutrino=“What’s missing” hep-ex/ to be published in PRD Signal defined by…

Ron Poling WIN03 October 7, B  l (p l > 1.0 GeV/c) B  l (p l > 1.5 GeV/c) CLEO II 10 fb -1 Event selection to enhance reconstruction, suppress continuum Fit M ml and  E in three bins in q 2 to find branching fractions

Ron Poling WIN03 October 7, Extracting |V ub | –Fit d  /dq 2 –Discriminates among FFs B  l –FF dependence is small –Disfavors ISGW2 B  l –Larger FF dependence  greater model uncertainty in |V ub | B  l B  l

Ron Poling WIN03 October 7, RESULTS

Ron Poling WIN03 October 7, Comparisons and CKM Impact |V ub |/ % c. l. contours

Ron Poling WIN03 October 7, CLEO is still contributing on |V ub | and |V cb |. –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. Perspectives and Prospects