Heavy-ion physics with the ALICE experiment at the CERN Large Hadron Collider Schukraft, J.
Philosophical transactions - Royal Society. Mathematical, Physical and engineering sciences/Philosophical transactions - Royal Society. Mathematical, physical and engineering sciences,
02/2012, Letnik:
370, Številka:
1961
Journal Article
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After close to 20 years of preparation, the dedicated heavy-ion experiment A Large Ion Collider Experiment (ALICE) took first data at the CERN Large Hadron Collider (LHC) accelerator with proton ...collisions at the end of 2009 and with lead nuclei at the end of 2010. After a short introduction into the physics of ultra-relativistic heavy-ion collisions, this article recalls the main design choices made for the detector and summarizes the initial operation and performance of ALICE. Physics results from this first year of operation concentrate on characterizing the global properties of typical, average collisions, both in proton-proton (pp) and nucleus-nucleus reactions, in the new energy regime of the LHC. The pp results differ, to a varying degree, from most quantum chromodynamics-inspired phenomenological models and provide the input needed to fine tune their parameters. First results from Pb-Pb are broadly consistent with expectations based on lower energy data, indicating that high-density matter created at the LHC, while much hotter and larger, still behaves like a very strongly interacting, almost perfect liquid.
The 5thinternational Conference on Hard and Electromagnetic Probes in High-Energy Nuclear Collisions was held in May 2012 in Cagliari, Italy. This contribution summarises some of the experimental ...highlights presented at the meeting, concentrating on new results from LHC and RHIC on parton energy loss (‘jet-quenching’) and heavy quark meson production (‘quarkonia suppression’).
Early November 2010, the LHC collided for the first time heavy ions, Pb on Pb, at a centre-of-mass energy of 2.76 TeV/nucleon. This date marked both the end of almost 20 years of preparing for ...nuclear collisions at the LHC, as well as the start of a new era in ultra-relativistic heavy ion physics at energies exceeding previous machines by more than an order of magnitude. This contribution summarizes some of the early results from all three experiments participating in the LHC heavy ion program (ALICE, ATLAS, and CMS), which show that the high density matter created at the LHC, while much hotter and larger, still behaves like the very strongly interacting, almost perfect liquid discovered at RHIC. Some surprising and even puzzling results are seen in particle ratios, jet-quenching, and Quarkonia suppression observables. The overall experimental conditions at the LHC, together with its set of powerful and state-of-the-art detectors, should allow for precision measurements of quark-gluon-plasma parameters like viscosity and opacity.
BackgroundEvaluation of various sonographic techniques in diagnosis and follow-up of salivary gland involvement in Sjögren's Syndrome is part of on-going investigations. Virtual Touch Tissue ...Quantification (VTTQ) sonography, as modern sonographic method, enables the objective measurement of parotid and submandibular gland stiffness in SS, as recent reports could demonstrate. Consequently the consideration emerges, if VTTQ is suitable to monitor the response to local or systemic treatment.ObjectivesIs Virtual Touch Tissue Quantification sonography suitable to monitor the response to a liposomal local therapy in Sjögren's Syndrome?Methods50 patients with pSS, diagnosed according to the AECG criteria, were included (group 1). As comparison group 50 patients were chosen with condition following radiotherapy of the head and neck region (including the salivary glands, group 2). Clinical data were collected and sonographic examination including VTTQ was performed. Subjective symptoms were evaluated via visual analogue scales (VAS). After a two-months period of liposomal local therapy sonographic examination including VTTQ was repeated and subjective symptoms were re-evaluated. In group 1, right side parotid and submandibular glands were examined; in group 2, the – in regard to the irradiated side – ipsi- and contralateral parotid and submandibular glands were examined.ResultsBefore local treatment, the mean VTTQ value of parotid glands in group 1 was 2.99m/s2 (SD 0.93); in group 2, the mean VTTQ value of the ipsilateral parotid glands was 2.35m/s2 (SD 0.7) and of the contralateral parotid glands was 2.14m/s2 (SD 0.55). Mean VTTQ value of the submandibular glands in group 1 was 2.15m/s2 (SD 0.57); in group 2, the mean VTTQ value of the ipsilateral submandibular glands was 2.27m/s2 (SD 0.69) and of the contralateral submandibular glands was 2.17m/s2 (SD 0.57).After two-months treatment with locally applied liposomes a significant decline of VTTQ values could be observed both in parotid glands in group 1 (2.33m/s2, SD 0.70, p<0.001) and in ipsilateral (2.20m/s2, SD 0.56, p=0.01) and contralateral (2.07m/s2, SD 0.50, p=0.047) parotid glands in group 2. Submandibular glands did not show any significant change in both groups.A significant reduction of the subjective sensation of xerostomia could be observed (p=0.0001).ConclusionsWith the application of Virtual Touch Tissue Quantification sonography a decline in parotid gland stiffness could be observed both in Sjögren's Syndrome and condition following radio therapy accompanied by a significant improvement of the subjective sensation of xerostomia. The seromucous submandibular glands did not show any changes compared to the serous parotid glands.Disclosure of InterestNone declared
We present the combined results on electron-pair production in 158 GeV/n Pb-Au (\(\sqrt{s}\) = 17.2 GeV) collisions taken at the CERN SPS in 1995 and 1996, and give a detailed account of the data ...analysis. The enhancement over the reference of neutral meson decays amounts to a factor of 2.31 \(\pm0.19 (stat.)\pm0.55 (syst.)\pm0.69 (decays)\) for semi-central collisions (28\(\%\)\(\sigma/\sigma_{geo}\)) when yields are integrated over m > 200 MeV/c2 in invariant mass. The measured yield, its stronger-than-linear scaling with \(N_{\rm ch}\), and the dominance of low pair pt strongly suggest an interpretation as thermal radiation from pion annihilation in the hadronic fireball. The shape of the excess centring at \(m\approx\) 500 MeV/c2, however, cannot be described without strong medium modifications of the \(\rho\) meson. The results are put into perspective by comparison to predictions from Brown-Rho scaling governed by chiral symmetry restoration, and from the spectral-function many-body treatment in which the approach to the phase boundary is less explicit.
After close to 20 years of preparation, the dedicated heavy ion experiment ALICE took first data with proton collisions at the LHC starting in November 2009 and first Pb–Pb data in November 2010. ...This article summarizes initial operation and performance of ALICE as well as first results from both pp and Pb–Pb collisions.
We report a measurement of low-mass electron pairs observed in 158 GeV/nucleon Pb-Au collisions. The pair yield integrated over the range of invariant masses 0.2 ≤
m≤ 2.0 GeV/c
2 is enhanced by a ...factor of 3.5 ± 0.4 (stat) ± 0.9 (syst) over the expectation from neutral meson decays. As observed previously in S-Au collisions, the enhancement is most pronounced in the invariant-mass region 300-700 MeV/c
2. For Pb-Au we find evidence for a strong increase of the enhancement with centrality. In addition, we show that the enhancement covers a wide range in transverse momentum, but is largest at the lowest observed
p
⊥.
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