Measurement of charged-particle multiplicities in gluon and quark jets in pp虅 collisions at 鈭歴 = 1:8 TeV
Physical Review Letters 94:17 (2005)
Abstract:
We report the first largely model independent measurement of charged particle multiplicities in quark and gluon jets, NMeasurements of bottom-antibottom azimuthal production correlations in proton-antiproton collisions at s=1.8TeV
Physical Review D Particles Fields Gravitation and Cosmology 71:9 (2005) 1-39
Abstract:
We have measured the azimuthal angular correlation of bb虅 production, using 86.5pb-1 of data collected by Collider Detector at Fermilab (CDF) in pp虅 collisions at s=1.8TeV during 1994-1995. In high-energy pp虅 collisions, such as at the Tevatron, bb虅 production can be schematically categorized into three mechanisms. The leading-order (LO) process is "flavor creation," where both b and b虅 quarks substantially participate in the hard scattering and result in a distinct back-to-back signal in final state. The "flavor excitation" and the "gluon splitting" processes, which appear at next-leading-order (NLO), are known to make a comparable contribution to total bb虅 cross section, while providing very different opening angle distributions from the LO process. An azimuthal opening angle between bottom and antibottom, 螖, has been used for the correlation measurement to probe the interaction creating bb虅 pairs. The 螖 distribution has been obtained from two different methods. One method measures the 螖 between bottom hadrons using events with two reconstructed secondary vertex tags. The other method uses bb虅鈫�(J/ 蠄X)(X鈥�) events, where the charged lepton () is an electron (e) or a muon (渭), to measure 螖 between bottom quarks. The bb虅 purity is determined as a function of 螖 by fitting the decay length of the J/蠄 and the impact parameter of the. Both methods quantify the contribution from higher-order production mechanisms by the fraction of the bb虅 pairs produced in the same azimuthal hemisphere, ftoward. The measured ftoward values are consistent with both parton shower Monte Carlo and NLO QCD predictions. 漏 2005 The American Physical Society.High precision survey and alignment of large linear accelerators
XXII International Linear Accelerator Conference (LINAC 2004) Joint Accelerator Conferences Website (JACoW) (2005) 690-692
Abstract:
Future linear accelerators require new survey techniques to achieve the necessary alignment precision. For TESLA, the demanded accuracy for the alignment of the components is 0.5mm horizontal and 0.2mm vertical, both on each 600m section. Other proposed linear colliders require similar accuracies. These demands can not be fulfilled with common, open-air geodetic methods, mainly because of refraction in the tunnel. Therefore the RTRS (Rapid Tunnel Reference Surveyor), a 25m long measurement train performing overlapping multipoint alignment on a regular tunnel reference network is being developed. Two refraction-free realizations of this concept are being developed at the moment: GeLiS measures the horizontal co-ordinates using multipoint alignment with stretched wires as strightness reference. In areas of the tunnel where the accelerator is following the earth curvature GeLiS measures the vertical co-ordinate using a new hydrostatic levelling system (HLS). LiCAS is based on laser straightness monitors (LSM) combined with frequency scanning interferometry (FSI) in an evacuated system. LiCAS measures both coordinates with respect to its LSM-beam and thus is suitable for geometrically straight tunnel sections. Both measurement systems will be placed on a train, which could do the reference survey autonomous or semiautonomous.Measurement of the tt虅 production cross section in pp虅 collisions at 鈭歴=1:96 TeV using kinematic fitting of b-tagged lepton+jet events
Physical Review D Particles Fields Gravitation and Cosmology 71:7 (2005) 1-11
Abstract:
We report a measurement of the tt虅 production cross section using the CDF II detector at the Fermilab Tevatron. The data consist of events with an energetic electron or muon, missing transverse energy, and three or more hadronic jets, at least one of which is identified as a b-quark jet by reconstructing a secondary vertex. The background fraction is determined from a fit of the transverse energy of the leading jet. Using 162 卤 10 pb -1 of data, the total cross section is found to be 6.0 卤 1.6(stat.) 卤 1.2(syst.) pb, which is consistent with the standard model prediction. 漏 2005 The American Physical Society.Search for excited and exotic electrons in the egamma decay channel in pp collisions at sqrt[s] = 1.96 TeV.
Phys Rev Lett 94:10 (2005) 101802