arXiv subjects

S. Marti i Garcia

Publications and source records attributed to S. Marti i Garcia.

6 recordsLinked to original sources

arXiv2008

Alignment of the Pixel and SCT Modules for the 2004 ATLAS Combined Test Beam

A small set of final prototypes of the ATLAS Inner Detector silicon tracker (Pixel and SCT) were used to take data during the 2004 Combined Test Beam. Data were collected from runs with beams of different flavour (electrons, pions, muons and photons) with a momentum range of 2 to 180 GeV/c. Four independent methods were used to align the silicon modules. The corrections obtained were validated using the known momenta of the beam particles and were shown to yield consistent results among the different alignment approaches. From the residual distributions, it is concluded that the precision attained in the alignment of the silicon modules is of the order of 5 micrometers in their most precise coordinate.

physics.ins-det↗

arXiv1997

Experimental determination of the b quark mass in DELPHI

The running mass of the b quark as defined in the MS-bar renormalization scheme, m_b, was measured at the M_Z scale using 2.8 million hadronic Z^0 decays collected by the DELPHI experiment at LEP. The result is m_b(M_Z) = 2.67 +- 0.25 (stat.) +- 0.34 (frag.) +- 0.27(theo.) GeV/c^2 which differs from that obtained at the Upsilon scale, by m_b(M_Υ/2)-m_b(M_Z) = 1.49 +- 0.52 GeV/c^2. This measurement, performed far from the $b\bar{b}$ production threshold, provides the first experimental observation of the running of the quark masses.

hep-ex↗

arXiv1997

Review of the measurements of the strong coupling constant at LEP 2

Since 1995, LEP has steadily increased the center of mass energy of the colliding beams, from the M_Z resonance to 133, 161 and 172 GeV. New measurements of the strong coupling constant, alpha_s, at these energies have been performed by the LEP experiments, L3, ALEPH, OPAL and DELPHI. In this article, the new results are summarized, and combined with the previous LEP measurement of alpha_s(M_Z) in order to obtain an updated LEP average of alpha_s(M_Z) = 0.120 +- 0.005.

hep-ex↗

arXiv1996

Experimental studies of QCD using flavour tagged jets with DELPHI

Identified $b\overline{b}g$ and $q\overline{q}γ$ events from DELPHI are used to measure the ratio of the mean charged particle multiplicity distribution between gluon and quark jets. The dependence of this ratio with the jet energy is established using about three million Z$^0$ decays. Results from all other detectors are discussed and compared. A nice agreement is found among all them. The ratio between the normalized total three-jet cross sections of $b\overline{b}g$ and $q\overline{q}g, q \equiv u,d,s$ events is also determined. The preliminary value obtained indicates that $b$ quarks are experimentaly seen to radiate less than light quarks due to their higher mass. The suggested experimental error is $\sim$300 MeV for the $b$ mass determination at the M$_Z$ scale.

hep-ex↗

arXiv1996

Performance of The ATLAS_A Silcion Detector with Analogue Read Out

The performace of an ATLAS-A silicon micro-strip detector prototype with FELIX 128 analogue read out chip has been studied. The noise level and the signal to noise ratio have been measured as a funtion of both detector bias and temperature. No evidence of micro-discharge was observed for detector bias voltages up to 300 V.

hep-ex↗

arXiv1995

Estudi de la dependència energètica de les diferències entre jets de quarks i gluons utilitzant el detector DELPHI de LEP

Three jet events arising from decays of the $Z^0$ boson, collected by the DELPHI detector at LEP, were used to measure differences in the properties of quark and gluon jet fragmentation. Gluon jets were anti-tagged in $b\bar{b}g$ events, by identifiying $b$ quark jets with high purities. Unbiased quark jets came from events $q\bar{q}γ$ with two jets plus one photon. A comparison of quark and gluon jet properties in different energy ranges was performed for the first time and within the same detector. The average value of the ratio of the mean charged multiplicities of gluon and quark jets was measured to be \[ 1.232 \pm 0.026 (\mbox{esta.}) \pm 0.018 (\mbox{sist.}) \] where the fraction of b-quark initiates jets was 11\% and the Durham jet finding algorithm has been used for the selection of three jet events. In agreement with QCD an increase of this ratio with energy was observed at a $3σ$ level. A further dependence of this ratio related with the angular acceptance of the algorithm used to reconstruct jets was also measured. Gluon jets have a broader energy and particle flow around its jet axis than quark jets of equivalent energy. The string effect has been observed in fully symmetric three-jet events. The ratio $R_γ$ of the charged particles flow in the $q\bar{q}$ inter-jet region of the $q\bar{q}g$ and $q\bar{q}γ$ samples was measured in agreement with the perturbative QCD expectation \[ \frac{(N_{qq})_{q\bar{q}g}}{(N_{qq})_{q\bar{q}γ}} = 0.058 \pm 0.06 (\mbox{stat.+sist.}) \] The dependence of the mean charged multiplicity on the hadronic center-of-mass energy was analysed in photon plus $n$-jet events. A value for

hep-ex↗