1. ACTIVITIES @ VALENCIA b mass effects at the Z 0 peak from 3 and 4 jet events P. Bambade, M.J. Costa, J. Fuster and P. Tortosa b mass effects have been observed at DELPHI at the Z 0 energy by measuring the ratio of the norma- lised n-jet rate for b over light quark hadronic Z 0 decays: n = 3 and 4 jets Jet clustering algorithms: 3 jets NLO massive calculations G. Rodrigo et al. Phys. Rev. Lett. 79 (1997) 193 M. Bilenky et al., Phys. Rev. D60 (1999) 114006 4 jets LO calculations A. Ballestrero et al., CERN-2000-09 3 jets NLO calculations It is the most precise measurement of m b (M Z ) e+e+ e-e- q q Herwig Pythia DELPHI Preliminary Predictions from generators are confronted with data First study of R 4 bl. NLO not yet available!!! R 4 bl Hadron level LO – m b (M Z ) LO – M b LO corrected for hadronisation DELPHI Preliminary Hadron level R 4 bl ycyc ycyc Cambridge Durham Cambridge Parton level DELPHI Preliminary M.J. Costa, A.Oyanguren, P. Tortosa I MPROVED |V cb | M EASUREMENT FROM S PECTRAL M OMENTS FROM S PECTRAL M OMENTS M. Battaglia, M. Calvi, P. Gambino, A. Oyanguren, P. Roudeau, L. Salmi, J. Salt, A. Stocchi, N.Uraltsev V cb b c q2q2 V cb (now)=0.0419(1±0.016| meas ± 0.015| fit ± 0.010| pert ) before the use of moments V cb had ± 0.05| theo uncertainty ! In the near future, analyses with larger statistics will give a better measurement of Spectral Moments and will improve the V cb value. DELPHI has measured |V cb | by using the information given by Spectral Moments ( hep-ph/0210319 ). The lepton and hadron moments (M i (E l ) and M i (M x )) in inclusive b semileptonic de- cays give constraints on theoretical parameters which allow to determine V cb : V cb is one fundamental parameter of the SM. It governs the transitions between b and c quarks and has to be determined ex- perimentally. At the moment, the dominant uncertainties on V cb are from theoretical origin so new methods and analyses beco- me necessary to improve this measurement. V cb gives the scale of the unitarity triangle Compton Imaging for Medical Applications Compton Imaging In conventional single photon imaging systems mechanical collimators are used to determine the direction of the incoming photons, coupling detector sensitivity and spatial resolution. Replacing the septa by silicon detectors overcomes the sensitivity-resolution tradeoff. This method, known as electronic collimation, can improve detector sensitivity by orders of magnitude, while remaining independent from spatial resolution. Contrary to conventional Anger cameras, spatial resolution improves with increasing gamma-ray energies. Photons coming from the object to be imaged compton-scatter in the silicon detector and are absorbed in the scintillator. Determining the impact points and the energy deposited in the first detector, it is possible to locate the source and reconstruct the image. Spatial resolution depends mainly on the uncertainty in the scattering angle, which is driven by the uncertainty in the energy measured by the silicon sensors. Therefore, a good energy resolution for these detectors (~1keV) is essential. G. Llosá, J. Bernabeu, J. Fuster, C. García, C. Lacasta, F.J. Sánchez Experimental data have been taken with a Compton Camera prototype at the University of Michigan. Images have been reconstructed employing the List Mode Likelihood method. These results were obtained with 300  m thick silicon pad detectors (8x32 pads, 1.4x1.4 mm pitch). New 1mm thick detectors and improved versions of electronics are currently being tested for a new prototype. Very High Resolution small animal PET Detects the two photons from positron annihilation. Its resolution approaches the physical limit, the range of positrons in the tissue, about 350  m. First Results Applications Ring Geometry Compton Camera Simulations predict that this arrangement with 16 mm of silicon detectors would improve by more than 300 times the efficiency of conventional gamma cameras with the same resolution. Reconstructed 131 I point source on top of a uniform disc. Compton Prostate Probe. The combination of an intrarectal silicon probe, placed close to the prostate, and an external scintillator would improve resolution by a factor 4 and sensitivity by an order of magnitude.