In this paper we present the specific hardware and firmware requirements and modifications to ope... more In this paper we present the specific hardware and firmware requirements and modifications to operate the Liquid Argon Calorimeter (LiArg) ROD motherboard in the Hadronic Tile Calorimeter (TileCal) environment. Although the use of the board is similar for both calorimeters there ...
In order to study further the long-range correlations ("ridge") observed recently in p+Pb collisi... more In order to study further the long-range correlations ("ridge") observed recently in p+Pb collisions at √ s NN = 5.02 TeV, the second-order azimuthal anisotropy parameter of charged particles, v 2 , has been measured with the cumulant method using the ATLAS detector at the LHC. In a data sample corresponding to an integrated luminosity of approximately 1 µb −1 , the parameter v 2 has been obtained using two-and four-particle cumulants over the pseudorapidity range |η| < 2.5. The results are presented as a function of transverse momentum and the event activity, defined in terms of the transverse energy summed over 3.1 < η < 4.9 in the direction of the Pb beam. They show features characteristic of collective anisotropic flow, similar to that observed in Pb+Pb collisions. A comparison is made to results obtained using two-particle correlation methods, and to predictions from hydrodynamic models of p+Pb collisions. Despite the small transverse spatial extent of the p+Pb collision system, the large magnitude of v 2 and its similarity to hydrodynamic predictions provide additional evidence for the importance of final-state effects in p+Pb reactions.
We have used a low repetition rate (1 kHz), femtosecond laser amplifier in combination with a spa... more We have used a low repetition rate (1 kHz), femtosecond laser amplifier in combination with a spatial light modulator (SLM) to write optical waveguides with controllable cross-section inside a phosphate glass sample. The SLM is used to induce a controllable amount of astigmatism in the beam wavefront while the beam ellipticity is controlled through the propagation distance from the SLM to the focusing optics of the writing setup. The beam astigmatism leads to the formation of two separate diskshaped foci lying in orthogonal planes. Additionally, the ellipticity has the effect of enabling control over the relative peak irradiances of the two foci, making it possible to bring the peak irradiance of one of them below the material transformation threshold. This allows producing a single waveguide with controllable cross-section. Numerical simulations of the irradiance distribution at the focal region under different beam shaping conditions are compared to in situ obtained experimental plasma emission images and structures produced inside the glass, leading to a very satisfactory agreement. Finally, guiding structures with controllable crosssection are successfully produced in the phosphate glass using this approach.
A study of the surface modification induced by single femtosecond laser pulses in phosphate glass... more A study of the surface modification induced by single femtosecond laser pulses in phosphate glass has revealed surface swelling at fluences just below the ablation threshold. This behavior is different from that observed in other dielectric materials. Optical micrographs obtained with monochromatic light show a pattern of Newton rings within the swollen region whose number scales inversely with the illumination wavelength, acting as a micro Fabry-Perot etalon. The swollen surface layer has lower refractive index than the bulk glass and can reach a maximum thickness of 820 nm. We relate these findings to results obtained during subsurface waveguide writing inside phosphate glass, which also show a refractive index decrease at energies near threshold for waveguide fabrication. We have identified low density free-electron plasma to be the trigger of the refractive index change.
The effect of the heavy b-quark mass on the two, three and four-jet rates is studied using LEP da... more The effect of the heavy b-quark mass on the two, three and four-jet rates is studied using LEP data collected by the DELPHI experiment at the Z peak in 1994 and 1995. The rates of b-quark jets and light quark jets (= uds) in events with n = 2, 3, and 4 jets, together with the ratio of two and four-jet rates of b-quarks with respect to light-quarks, R b n , have been measured with a double-tag technique using the CAMBRIDGE jetclustering algorithm. A comparison between experimental results and theory (matrix element or Monte Carlo event generators such as PYTHIA, HERWIG and ARIADNE) is done after the hadronisation phase. Using the four-jet observable R b 4 , a measurement of the b-quark mass using massive leading-order calculations gives: m b (M Z) = 3.76 ± 0.32 (stat) ± 0.17 (syst) ± 0.22 (had) ± 0.90 (theo) GeV/c 2. This result is compatible with previous three-jet determinations at the M Z energy scale and with low energy mass measurements evolved to the M Z scale using QCD renormalisation group equations.
A combination of low numerical aperture focusing optics, in order to minimize spherical aberratio... more A combination of low numerical aperture focusing optics, in order to minimize spherical aberration, and beam shaping with a slit has been used to produce waveguides in fused silica by femtosecond laser writing. Waveguides with circular cross section and low losses are produced over a large depth window (>7mm) without changing any experimental parameter. Diffraction induces beam divergence along the axis perpendicular to the slit, leading to a shift of the focal plane. The focal intensity distribution can be predicted by a hybrid model combining Gaussian beam propagation with imaging of the slit into the material.
In this paper we present the specific hardware and firmware requirements and modifications to ope... more In this paper we present the specific hardware and firmware requirements and modifications to operate the Liquid Argon Calorimeter (LiArg) ROD motherboard in the Hadronic Tile Calorimeter (TileCal) environment. Although the use of the board is similar for both calorimeters there ...
In order to study further the long-range correlations ("ridge") observed recently in p+Pb collisi... more In order to study further the long-range correlations ("ridge") observed recently in p+Pb collisions at √ s NN = 5.02 TeV, the second-order azimuthal anisotropy parameter of charged particles, v 2 , has been measured with the cumulant method using the ATLAS detector at the LHC. In a data sample corresponding to an integrated luminosity of approximately 1 µb −1 , the parameter v 2 has been obtained using two-and four-particle cumulants over the pseudorapidity range |η| < 2.5. The results are presented as a function of transverse momentum and the event activity, defined in terms of the transverse energy summed over 3.1 < η < 4.9 in the direction of the Pb beam. They show features characteristic of collective anisotropic flow, similar to that observed in Pb+Pb collisions. A comparison is made to results obtained using two-particle correlation methods, and to predictions from hydrodynamic models of p+Pb collisions. Despite the small transverse spatial extent of the p+Pb collision system, the large magnitude of v 2 and its similarity to hydrodynamic predictions provide additional evidence for the importance of final-state effects in p+Pb reactions.
We have used a low repetition rate (1 kHz), femtosecond laser amplifier in combination with a spa... more We have used a low repetition rate (1 kHz), femtosecond laser amplifier in combination with a spatial light modulator (SLM) to write optical waveguides with controllable cross-section inside a phosphate glass sample. The SLM is used to induce a controllable amount of astigmatism in the beam wavefront while the beam ellipticity is controlled through the propagation distance from the SLM to the focusing optics of the writing setup. The beam astigmatism leads to the formation of two separate diskshaped foci lying in orthogonal planes. Additionally, the ellipticity has the effect of enabling control over the relative peak irradiances of the two foci, making it possible to bring the peak irradiance of one of them below the material transformation threshold. This allows producing a single waveguide with controllable cross-section. Numerical simulations of the irradiance distribution at the focal region under different beam shaping conditions are compared to in situ obtained experimental plasma emission images and structures produced inside the glass, leading to a very satisfactory agreement. Finally, guiding structures with controllable crosssection are successfully produced in the phosphate glass using this approach.
A study of the surface modification induced by single femtosecond laser pulses in phosphate glass... more A study of the surface modification induced by single femtosecond laser pulses in phosphate glass has revealed surface swelling at fluences just below the ablation threshold. This behavior is different from that observed in other dielectric materials. Optical micrographs obtained with monochromatic light show a pattern of Newton rings within the swollen region whose number scales inversely with the illumination wavelength, acting as a micro Fabry-Perot etalon. The swollen surface layer has lower refractive index than the bulk glass and can reach a maximum thickness of 820 nm. We relate these findings to results obtained during subsurface waveguide writing inside phosphate glass, which also show a refractive index decrease at energies near threshold for waveguide fabrication. We have identified low density free-electron plasma to be the trigger of the refractive index change.
The effect of the heavy b-quark mass on the two, three and four-jet rates is studied using LEP da... more The effect of the heavy b-quark mass on the two, three and four-jet rates is studied using LEP data collected by the DELPHI experiment at the Z peak in 1994 and 1995. The rates of b-quark jets and light quark jets (= uds) in events with n = 2, 3, and 4 jets, together with the ratio of two and four-jet rates of b-quarks with respect to light-quarks, R b n , have been measured with a double-tag technique using the CAMBRIDGE jetclustering algorithm. A comparison between experimental results and theory (matrix element or Monte Carlo event generators such as PYTHIA, HERWIG and ARIADNE) is done after the hadronisation phase. Using the four-jet observable R b 4 , a measurement of the b-quark mass using massive leading-order calculations gives: m b (M Z) = 3.76 ± 0.32 (stat) ± 0.17 (syst) ± 0.22 (had) ± 0.90 (theo) GeV/c 2. This result is compatible with previous three-jet determinations at the M Z energy scale and with low energy mass measurements evolved to the M Z scale using QCD renormalisation group equations.
A combination of low numerical aperture focusing optics, in order to minimize spherical aberratio... more A combination of low numerical aperture focusing optics, in order to minimize spherical aberration, and beam shaping with a slit has been used to produce waveguides in fused silica by femtosecond laser writing. Waveguides with circular cross section and low losses are produced over a large depth window (>7mm) without changing any experimental parameter. Diffraction induces beam divergence along the axis perpendicular to the slit, leading to a shift of the focal plane. The focal intensity distribution can be predicted by a hybrid model combining Gaussian beam propagation with imaging of the slit into the material.
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Papers by A. Ferrer