Hot Topics from the BABAR Experiment

With a sample of about 384 million BBbar pairs recorded with the BABAR detector, we search for the flavor-changing charged current transition B+ -> \tau\nu and perform an amplitude analysis of the effective flavor-changing neutral current transition B+ -> \phi(1020)K*(892)+. We also extend our search for other K* final states in the decay B0 -> phi(1020)K*0 with a large K*0 -> K+pi- invariant mass. Two samples of events with one reconstructed hadronic B decay or one reconstructed semileptonic B decay are selected, and in the recoil a search for B+ -> \tau\nu is performed. We find a 2.6 sigma (3.2 sigma not including expected background uncertainty) excess in data which can be converted to a preliminary branching fraction central value of BR(B+ -> \tau\nu ) = (1.20 +0.40-0.38 +0.29-0.30 +-0.22) 10^-4. With the decay B+- -> \phi(1020)K*(892)+-, twelve parameters are measured, where our measurements of f_L=0.49+-0.05+-0.03, f_perp=0.21+-0.05+-0.02, and the strong phases point to the presence of a substantial helicity-plus amplitude from a presently unknown source.Comment: 14 pages, 33 postscript figures, proceedings of the 5th Flavor Physics And CP Violation Conference (FPCP 2007) C07/05/1

The Matrix Element Method: Past, Present, and Future

The increasing use of multivariate methods, and in particular the Matrix Element Method (MEM), represents a revolution in experimental particle physics. With continued exponential growth in computing capabilities, the use of sophisticated multivariate methods-- already common-- will soon become ubiquitous and ultimately almost compulsory. While the existence of sophisticated algorithms for disentangling signal and background might naively suggest a diminished role for theorists, the use of the MEM, with its inherent connection to the calculation of differential cross sections will benefit from collaboration between theorists and experimentalists. In this white paper, we will briefly describe the MEM and some of its recent uses, note some current issues and potential resolutions, and speculate about exciting future opportunities.Comment: 3 pages, no figures. Snowmass white paper. Minor revisions. References adde

Geolocating the Higgs Boson Candidate at the LHC

The latest results from the ATLAS and CMS experiments at the CERN Large Hadron Collider (LHC) unequivocally confirm the existence of a resonance, $X$, with mass near 125 GeV which could be the Higgs boson of the Standard Model. Measuring the properties (quantum numbers and couplings) of this resonance is of paramount importance. Initial analyses by the LHC collaborations disfavor specific alternative benchmark hypotheses, e.g. pure pseudoscalars or gravitons. However, this is just the first step in a long-term program of detailed measurements. We consider the most general set of operators in the decay channels $X \to ZZ$, $WW$, $Z\gamma$, $\gamma\gamma$ and derive the constraint implied by the measured rate. This allows us to provide a useful parametrization of the orthogonal independent Higgs coupling degrees of freedom as coordinates on a suitably defined sphere.Comment: 5 pages, 4 figures. Corresponds with version published in Physical Review Letters as "Spherical Parametrization of the Higgs Boson Candidate". Changes in conventions (minus signs, etc.) from previous arXiv version. Supplemental information is presented separately-- this information is part of the main document in the previous arXiv versio

Nonstandard Higgs Couplings from Angular Distributions in h→Zℓ+ℓ−h\to Z \ell^+\ell^-

We compute the fully differential rate for the Higgs-boson decay $h\to Z\ell^+\ell^-$, with $Z\to\ell^{'+}\ell^{'-}$. For these processes we assume the most general matrix elements within an effective Lagrangian framework. The electroweak chiral Lagrangian we employ assumes minimal particle content and Standard Model gauge symmetries, but is otherwise completely general. We discuss how information on new physics in the decay form factors may be obtained that is inaccessible in the dilepton-mass spectrum integrated over angular variables. The form factors are related to the coefficients of the effective Lagrangian, which are used to estimate the potential size of new-physics effects.Comment: 16 pages, 3 figures. Text unchanged, references adde

Polarization in B->VV Decays

Factorizable amplitudes in B decays to light vector meson pairs give a longitudinal polarization satisfying 1- f_L =O(1/m_b^2). This remains formally true when non-factorizable graphs are included in QCD factorization, and is numerically realized in B->Rho Rho. In \Delta S=1 decays a QCD penguin annihilation graph can effectively contribute at leading power to the transverse and longitudinal amplitudes. The observed longitudinal polarization, f_L (B->phi K^*) \approx 50%, can therefore be accounted for in the SM. The ratio of perpendicular to parallel transverse rates provides a sensitive test for new right-handed currents. The transverse b->sg dipole operator amplitudes are highly suppressed. CP violation measurements can therefore discriminate between new contributions to the dipole and four quark operators. SU(3)_F violation in QCD penguin amplitudes can easily be O}(1), in general, due to annihilation. Implications for B->Rho K^* polarization and New Physics searches are pointed out.Comment: 17 pages, 6 figures. added comment on cancelation of linear divergence, comment on new physics, 1 ref., an acknowledgement, corrected typo