The global χ2 track fitter in ATLAS Cornelissen, T G; Elsing, M; Gavrilenko, I ...
Journal of physics. Conference series,
07/2008, Letnik:
119, Številka:
3
Journal Article
Recenzirano
Odprti dostop
While many high energy experiments use track fitting software that is based solely on the Kalman Filter technique, the ATLAS offline reconstruction also has several global track fitters available. ...One of these is the GlobalChi2Fitter, which is based on the scattering angle formulation of the track fit. One of the advantages of this method over the Kalman fit is that it can provide the scattering angles and related quantities (e.g. the residual derivatives) to the alignment algorithms. The algorithm has been implemented in the new common tracking framework in ATLAS, the philosophy of which is to improve the modularity and flexibility of the tracking software. This flexibility has proven crucial for the understanding of the data from the testbeam and cosmic runs. An overview of recent results will be presented, in particular the results from the combined tracking with the inner detector and the muon spectrometer using the cosmics data.
A search for excited lepton production in e(+)e(-) collisions was performed using the data collected by the DELPHI detector at LEP at centre-of-mass energies ranging from 189 GeV to 209 GeV, ...corresponding to an integrated luminosity of approximately 600 pb(-1). No evidence for excited lepton production was found. In searches for pair-produced excited leptons, lower mass limits were established in the range 94-103 GeV/c(2), depending on the channel and model assumptions. In searches for singly-produced excited leptons, upper limits on the parameter f/Lambda were established as a function of the mass.
High track densities and event rates in the LHC tracking detectors put stringent demands on the track reconstruction software in terms of performance, speed and maintainability over the experiment's ...lifetime. The ATLAS experiment is therefore commissioning a new software for the track and event reconstruction in the Inner Detector, which will allow to use common code for the off-line and high-level trigger reconstruction, as well as for different detector set-ups. This is achieved by breaking the algorithmic structure down to small, independent modules which communicate by common interfaces and use a new, global event data model. The Inner Detector has just completed the new track reconstruction within this framework and has successfully applied it to all kinds of simulated LHC events as well as test tracks from the real detectors. The preparation for the first real LHC data is now continuing at a fast pace, for example by integrating the algorithms to calibrate and align the detector further into the new Inner Detector software, and by implementing new tracking techniques from the literature.
The production of single charged and neutral intermediate vector bosons in e(+)e(-) collisions has been studied in the data collected by the DELPHI experiment at LEP at centre-of-mass energies ...between 183 and 209 GeV, corresponding to an integrated luminosity of about 640 pb(-1). The measured cross-sections for the reactions, determined in limited kinematic regions, are in agreement with the Standard Model predictions.
Di-jet production in γγ collisions at LEP2 Adam, W.; Amapane, N.; Anjos, N. ...
The European physical journal. C, Particles and fields,
2008/12, Letnik:
58, Številka:
4
Journal Article
Recenzirano
Odprti dostop
The production of two high-
p
T
jets in the interactions of quasi-real photons in
e
+
e
−
collisions at
from 189 GeV to 209 GeV is studied with data corresponding to an integrated
e
+
e
−
luminosity ...of 550 pb
−1
. The jets reconstructed by the
k
⊥
-cluster algorithm are defined within the pseudo-rapidity range −1<
η
<1 and with jet transverse momentum,
p
T
, above 3 GeV/c. The differential di-jet cross-section is measured as a function of the mean transverse momentum
of the jets and is compared to perturbative QCD calculations.
A determination of the single W spin density matrix (SDM) elements in the reaction e(+)e(-) -> W+W--> l nu q (q) over bar (l=e/mu) is reported at centre-of-mass energies between 189 and 209GeV. ...The data sample used corresponds to an integrated luminosity of 520pb(-1) taken by DELPHI between 1998 and 2000. The single W SDM elements, rho(W +/-)(tau tau') (tau,tau'=+/- 1 or 0), are determined as a function of the W- production angle with respect to the e(-) beam direction and are obtained from measurements of the W decay products by the application of suitable projection operators, Lambda(tau tau'), which assume the V-A coupling of the W-boson to fermions. The measured SDM elements are used to obtain the fraction of longitudinally polarised Ws, with the result: sigma(L)/sigma(tot) = 24.9 +/- 4.5 (stat) +/- 2.2 (syst)% at a mean energy of 198 GeV. The SDM elements are also used to determine the triple gauge couplings Delta g(1)(Z), Delta kappa(gamma), lambda(gamma) and g(4)(Z), (kappa) over tilde (Z) and (lambda) over tilde (Z). For the CP-violating couplings the results of single parameter fits are: g(4)(Z) = -0.39(-0.20)(+0.19) (kappa) over tilde (Z) = -0.09(-0.05)(+0.08) (lambda) over tilde (Z) = -0.08 +/- 0.07. The errors are a combination of statistical and systematic errors. All results are consistent with the Standard Model.
Measurements of Z gamma* production are presented using data collected by the DELPHI detector at centre-of-mass energies ranging from 183 to 209 GeV, corresponding to an integrated luminosity of ...about 667 pb(-1). The measurements cover a wide range of the possible final state four-fermion configurations: hadronic and leptonic (e(+) e(-) q (q) over bar, mu(+) mu(-) q (q) over bar ,q (q) over barv (v) over bar), fully leptonic (l(+) l(-) l' (+) l'(-)) and fully hadronic. nal states (q (q) over barq (q) over bar, with a low mass q (q$) over bar pair). Measurements of the Z gamma* cross-section for the various. nal states have been compared with the Standard Model expectations and found to be consistent within the errors. In addition, a total cross-section measurement of the l(+) l(-) l'(+)l'(-) cross-section is reported, and found to be in agreement with the prediction of the Standard Model.
Hadronic events from the data collected with the DELPHI detector at LEP within the energy range from 89 GeV to 209 GeV are selected, their jet rates are determined and compared to predictions of four ...different event generators. One of them is the recently developed APACIC++ generator which performs a massive matrix element calculation matched to a parton shower followed by string fragmentation. The four-jet rate is used to measure alpha_s in the next-to-leading-order approximation yielding alpha_s(M_Z^2) = 0.1175 +/- 0.0030. The running of alpha_s determined by using four-jet events has been tested. The logarithmic energy slope is measured to be d\alpha_s^{-1} / d\log E_{cm} = 1.14 +/- 0.36. Since the analysis is based on four-jet final states it represents an alternative approach to previous DELPHI alpha_s measurements using event shape distributions.
A search for the pair production of fourth generation b'-quarks was performed using data taken by the DELPHI detector at LEP-II. The analysed data were collected at centre-of-mass energies ranging ...from 196 to 209 GeV, corresponding to an integrated luminosity of 420 pb(-1). No evidence for a signal was found. Upper limits on BR(b'-> bZ) and BR(b'-> bZ) were obtained for b' masses ranging from 96 to 103 GeV/c(2) stop. These limits, together with the theoretical branching ratios predicted by a sequential four generations model, were used to constrain the value of R-CKM=vertical bar V-cb(') /V-tb'V-tb vertical bar there V-cb', V-tb' and V-tb are elements of the extended CKM matrix.
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