| 1. |
- Abelev, Betty, et al.
(författare)
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Long-range angular correlations on the near and away side in p-Pb collisions at root S-NN=5.02 TeV
- 2013
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 719:1-3, s. 29-41
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Tidskriftsartikel (refereegranskat)abstract
- Angular correlations between charged trigger and associated particles are measured by the ALICE detector in p-Pb collisions at a nucleon-nucleon centre-of-mass energy of 5.02 TeV for transverse momentum ranges within 0.5 < P-T,P-assoc < P-T,P-trig < 4 GeV/c. The correlations are measured over two units of pseudorapidity and full azimuthal angle in different intervals of event multiplicity, and expressed as associated yield per trigger particle. Two long-range ridge-like structures, one on the near side and one on the away side, are observed when the per-trigger yield obtained in low-multiplicity events is subtracted from the one in high-multiplicity events. The excess on the near-side is qualitatively similar to that recently reported by the CMS Collaboration, while the excess on the away-side is reported for the first time. The two-ridge structure projected onto azimuthal angle is quantified with the second and third Fourier coefficients as well as by near-side and away-side yields and widths. The yields on the near side and on the away side are equal within the uncertainties for all studied event multiplicity and p(T) bins, and the widths show no significant evolution with event multiplicity or p(T). These findings suggest that the near-side ridge is accompanied by an essentially identical away-side ridge. (c) 2013 CERN. Published by Elsevier B.V. All rights reserved.
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| 2. |
- Abelev, Betty, et al.
(författare)
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Measurement of prompt J/psi and beauty hadron production cross sections at mid-rapidity in pp collisions at root s=7 TeV
- 2012
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; :11
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Tidskriftsartikel (refereegranskat)abstract
- The ALICE experiment at the LHC has studied J/psi production at mid-rapidity in pp collisions at root s = 7 TeV through its electron pair decay on a data sample corresponding to an integrated luminosity L-int = 5.6 nb(-1). The fraction of J/psi from the decay of long-lived beauty hadrons was determined for J/psi candidates with transverse momentum p(t) > 1,3 GeV/c and rapidity vertical bar y vertical bar < 0.9. The cross section for prompt J/psi mesons, i.e. directly produced J/psi and prompt decays of heavier charmonium states such as the psi(2S) and chi(c) resonances, is sigma(prompt J/psi) (p(t) > 1.3 GeV/c, vertical bar y vertical bar < 0.9) = 8.3 +/- 0.8(stat.) +/- 1.1 (syst.)(-1.4)(+1.5) (syst. pol.) mu b. The cross section for the production of b-hadrons decaying to J/psi with p(t) > 1.3 GeV/c and vertical bar y vertical bar < 0.9 is a sigma(J/psi <- hB) (p(t) > 1.3 GeV/c, vertical bar y vertical bar < 0.9) = 1.46 +/- 0.38 (stat.)(-0.32)(+0.26) (syst.) mu b. The results are compared to QCD model predictions. The shape of the p(t) and y distributions of b-quarks predicted by perturbative QCD model calculations are used to extrapolate the measured cross section to derive the b (b) over bar pair total cross section and d sigma/dy at mid-rapidity.
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| 3. |
- Abelev, Betty, et al.
(författare)
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Underlying Event measurements in pp collisions at root s=0.9 and 7 TeV with the ALICE experiment at the LHC
- 2012
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; :7
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Tidskriftsartikel (refereegranskat)abstract
- We present measurements of Underlying Event observables in pp collisions at root s = 0 : 9 and 7 TeV. The analysis is performed as a function of the highest charged-particle transverse momentum p(T),L-T in the event. Different regions are defined with respect to the azimuthal direction of the leading (highest transverse momentum) track: Toward, Transverse and Away. The Toward and Away regions collect the fragmentation products of the hardest partonic interaction. The Transverse region is expected to be most sensitive to the Underlying Event activity. The study is performed with charged particles above three different p(T) thresholds: 0.15, 0.5 and 1.0 GeV/c. In the Transverse region we observe an increase in the multiplicity of a factor 2-3 between the lower and higher collision energies, depending on the track p(T) threshold considered. Data are compared to PYTHIA 6.4, PYTHIA 8.1 and PHOJET. On average, all models considered underestimate the multiplicity and summed p(T) in the Transverse region by about 10-30%.
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| 4. |
- Abbondanno, U, et al.
(författare)
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New experimental validation of the pulse height weighting technique for capture cross-section measurements
- 2004
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 521:2-3, s. 454-467
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Tidskriftsartikel (refereegranskat)abstract
- The accuracy of the pulse height weighting technique for the determination of neutron capture cross-sections is investigated. The technique is applied to measurements performed with C6D6 liquid scintillation detectors of two different types using capture samples of various dimensions. The data for well-known (n, gamma) resonances are analyzed using weighting functions obtained from Monte Carlo simulations of the experimental set-up. Several causes of systematic deviation are identified and their effect is quantified. In all the cases measured the reaction yield agrees with the standard value within 2%.
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| 5. |
- Blanco, A, et al.
(författare)
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Progress in timing Resistive Plate Chambers
- 2004
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 535:1-2, s. 272-276
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Tidskriftsartikel (refereegranskat)abstract
- Timing RPCs are Resistive Plate Chambers made with glass and metal electrodes separated by precision spacers. Typical gas gaps are a few hundred micrometers wide. Such counters were introduced in 1999 and have since reached timing accuracies below 50 ps sigma with efficiencies above 99% for MIPs. Applications in high-energy physics have already taken place with several more under study. Some recent developments include the extension of the counting rate capability by over one order of magnitude, to 25 kHz/cm(2), with time resolutions below 100 ps sigma. A prototype RPC-based Positron Emission Tomograph yielded a reconstructed point-source resolution of 0.6 mm FWHM and a modified timing RPC design, featuring 50 mum pitch anode strips, allowed to reach extremely good position resolution for hard X-rays in digital readout mode. An analytically solvable model has allowed us to clarify the basic factors influencing the time resolution.
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| 6. |
- Francke, T, et al.
(författare)
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High rate (up to 10(5) Hz/cm(2)), high position resolution (30 mu m) photosensitive RPCs
- 2004
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 533:1-2, s. 163-168
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Tidskriftsartikel (refereegranskat)abstract
- In many applications there is a need for high position resolution VUV and UV imagers. For these applications we have developed and successfully tested 1D and 2D VUV imaging detectors based on microgap RPCs. Two versions of these detectors were extensively tested: one filled with photosensitive vapours and the other one with the GaAs cathode coated by a 400 nm thick CsI layer. The main feature of these detectors is the high position resolution-30 mum in digital form. Additionally, it is spark-protected and can operate at high counting rates (up to 10(5) Hz/cm(2)). In this study the results in application for these detectors for spectroscopy are presented.
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| 7. |
- Francke, T, et al.
(författare)
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Photosensitive gaseous detectors and their applications
- 2004
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 525:1-2, s. 1-5
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Tidskriftsartikel (refereegranskat)abstract
- This paper reviews a large and important class of position sensitive detectors called photosensitive gaseous detectors (PGDs). Their main application rests in the imaging of UV photons. There are however, successful efforts to extend their sensitivity to visible light. With some modifications, PGDs can also be used in the imaging of X-rays and particles.
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| 8. |
- Garibaldi, F., et al.
(författare)
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A PET scanner employing CsI films as photocathode
- 2004
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 525:1-2, s. 263-267
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Tidskriftsartikel (refereegranskat)abstract
- Medical imaging is a fundamental tool in the diagnosis, treatments, and monitoring of disease processes as cancer. Detectors of large area and high Field Of View are necessary to scan the whole body in a reasonable time. Relatively large area photodetectors are necessary even for imaging of small mice and rats with high sensitivities and spatial resolutions, generally obtained by using pinhole or multipinhole collimators. Standard PET scanners, with scintillators coupled to photomultipliers, have generally a limited detector area due to the high costs of both scintillators and photomultipliers. In this respect, the replacement of photomultipliers with gaseous photodetectors represents a possible solution of the problem and brings the additional advantage to provide devices with sensitive areas free from dead regions. In this paper we report on a PET scanner equipped with a multiwire proportional chamber with a CsI thin film as photoconverter. A similar approach has already been successfully pursued in nuclear and particle physics experiments. A prototype of such a PET detector has been designed and built, and will be tested soon. Possible solutions for increasing the photoelectron number, and thus the detector performance, are presented.
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| 9. |
- Iacobaeus, Christian, et al.
(författare)
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A novel portal imaging device for advanced radiation therapy
- 2001
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Ingår i: Nuclear Science, IEEE Transactions on. - Nuclear Science, IEEE Transactions on : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9499 .- 1558-1578. ; 48:4, Part 2, s. 1496-1502
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Tidskriftsartikel (refereegranskat)
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| 10. |
- Iacobaeus, C., et al.
(författare)
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Advances in capillary-based gaseous UV imaging detectors
- 2004
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 525:02-jan, s. 42-48
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Tidskriftsartikel (refereegranskat)abstract
- We studied gain and position resolution of gaseous UV-photon detectors combining single- and cascaded-glass capillary-plate multipliers and CsI photocathodes. Two modes of operation were investigated: a conventional one, where the main amplification occurs within capillary holes and a parallel-plate amplification mode, where the main amplification occurs between the capillary plate and the readout anode. Results of these studies demonstrate that in the parallel-plate amplification mode one can reach both high gains (> 10(5)) and good position resolutions (similar to 100 mum) even with a single-element multiplier. This offers a compact amplification structure, which can be used in many applications.
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| 11. |
- Iacobaeus, C., et al.
(författare)
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Study of capillary-based gaseous detectors
- 2004
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Ingår i: IEEE Transactions on Nuclear Science. - 0018-9499 .- 1558-1578. ; 51:3, s. 952-959
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Tidskriftsartikel (refereegranskat)abstract
- We have studied gain versus voltage characteristics and position resolutions of multistep capillary plates (two or three capillary plates operating in a cascade), as well as capillary plates operating in a mode when the main amplification occurs between plates or between the capillary plate and the readout plate (parallel plate amplification mode). Results of these studies demonstrated that in the parallel-plate amplification mode one can reach both high gains (>10(5)) and good position resolutions (similar to100 mum) even with a single step arrangement. It offers a compact amplification structure, which can be used in many applications. For example, in preliminary tests we succeeded to combine it with a photocathode and use it as a position sensitive gaseous photomultiplier. CsI coated capillary plates could also be used as a high position resolution and high rate X-ray converter.
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| 12. |
- Kim, J. G., et al.
(författare)
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Electron avalanches in liquid argon mixtures
- 2004
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 534:3, s. 376-396
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Tidskriftsartikel (refereegranskat)abstract
- We have observed stable avalanche gain in liquid argon when mixed with small amounts of xenon (xe) in the high electric field (> 7 MV/cm) near the point of a chemically etched needle in a point-plane geometry. We identify two gain mechanisms, one pressure dependent, and the other independent of the applied pressure. We conclude that the pressure dependent signals are from avalanche gain in gas bubbles at the tip of the needle, while the pressure-independent pulses are from avalanche gain in liquid. We measure the decay time spectra of photons from both types of avalanches. The decay times from the pressure-dependent pulses decrease (increase) with the applied pressure (high voltage), while the decay times from the pressure-independent pulses are approximately independent of pressure or high voltage. For our operating conditions, the collected charge distribution from avalanches is similar for 60 or 122 keV photon sources. With krypton additives, instead of Xe, we measure behavior consistent with only the pressure-dependent pulses. Neon and TMS were also investigated as additives, and designs for practical detectors were tested.
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| 13. |
- Lorusso, G, et al.
(författare)
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Time-energy relation of the n_TOF neutron beam : energy standards revisited
- 2004
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 532:3, s. 622-630
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Tidskriftsartikel (refereegranskat)abstract
- The accurate determination of neutron cross-sections as a function of the neutron energy at a time-of-flight facility requires a precise knowledge of the time-energy relation for the neutron beam. For the n-TOF neutron beam at CERN, produced by spallation of high-energy protons on a Pb target, the time-energy relation is connected to the production mechanism and to the subsequent moderation process. A calibration of the neutron energy scale is proposed based on detailed Monte Carlo simulations of the facility. This time-energy relation has been experimentally validated by means of dedicated measurements of standard energy resonances, from 1 eV to approximately 1 MeV. On the basis of the present measurements, it is proposed to correct the energy of the 1.3 eV resonance of 193 Ir, which is commonly considered as an energy standard.
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| 14. |
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| 15. |
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| 16. |
- Pancin, J, et al.
(författare)
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Measurement of the n(-)TOF beam profile with a micromegas detector
- 2004
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 524:1-3, s. 102-114
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Tidskriftsartikel (refereegranskat)abstract
- A Micromegas detector was used in the neutron Time-Of-Flight (n-TOF) facility at CERN to evaluate the spatial distribution of the neutron beam as a function of its kinetic energy. This was achieved over a large range of neutron energies by using two complementary processes: at low energy by capture of a neutron via the Li-6(n, alpha)t reaction, and at high energy by elastic scattering of neutrons on gas nuclei (argon + isobutane or helium + isobutane). Data are compared to Monte Carlo simulations and an analytic function fitting the beam profile has been calculated with a sufficient precision to use in neutron capture experiments at the n-TOF facility.
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| 17. |
- Periale, L., et al.
(författare)
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The development of gaseous detectors with solid photocathodes for low-temperature applications
- 2004
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 535:02-jan, s. 517-522
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Tidskriftsartikel (refereegranskat)abstract
- There are several applications and studies in fundamental research, which require the detection of VUV light at cryogenic temperatures. For these applications, we have developed and successfully tested special designs of gaseous detectors with solid photocathodes able to operate at low temperatures: sealed gaseous detectors with MgF2 windows and windowless detectors. We have experimentally demonstrated that both primary and secondary (due to the avalanche multiplication inside liquids) scintillation light can be recorded by photosensitive gaseous detectors. The results of this work may allow one to significantly improve the operation of some noble liquid TPCs.
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| 18. |
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| 19. |
- Thunberg, S., et al.
(författare)
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Dose reduction in mammography with photon counting imaging
- 2004
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. ; , s. 457-465
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Konferensbidrag (refereegranskat)abstract
- The purpose of this study was to investigate if the glandular dose to the breast in mammography can significantly be reduced without compromising image quality, when using photon counting technology, in a multi-slit scanning photon counting detector, compared to a conventional film mammography system and commercial available digital mammography systems with TFT-array detectors. A CDMAM phantom study, with two different thicknesses of additional PMMA absorber, 4 cm and 7 cm respectively, has shown that multi-slit scanning photon counting detector technology can reduce the dose, without reducing the image quality. This comparison was made to two commercial available digital mammography systems Senographe 2000D (from GEMS) and Selenia (from Lorad). The results show that dose can be reduced with 63% to 77%, depending on object thickness, when using XCT for mammography. This dose reduction has also been verified clinically through a small pilot study with patients and specimen, where the comparison was made between XCT and film.
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| 20. |
- Östling, J., et al.
(författare)
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A radiation-tolerant electronic readout system for portal imaging
- 2004
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 525, s. 308-312
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Tidskriftsartikel (refereegranskat)abstract
- A new electronic portal imaging device, EPID, is under development at the Karolinska Institutet and the Royal Institute of Technology. Due to considerable demands on radiation tolerance in the radiotherapy environment, a dedicated electronic readout system has been designed. The most interesting aspect of the readout system is that it allows to read out similar to 1000 pixels in parallel, with all electronics placed outside the radiation beam-making the detector more radiation resistant. In this work we are presenting the function of a small prototype (6 x 100 pixels) of the electronic readout board that has been tested. Tests were made with continuous X-rays (10-60 keV) and with alpha particles. The results show that, without using an optimised gas mixture and with an early prototype only, the electronic readout system still works very well.
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| 21. |
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