Página 10 dos resultados de 19478 itens digitais encontrados em 0.030 segundos

The WITCH experiment: Acquiring the first recoil ion spectrum

Kozlov, V. Yu.; Beck, M.; Coeck, S.; Delahaye, P.; Friedag, P.; Herbane, M.; Herlert, A.; Kraev, I. S.; Tandecki, M.; Van Gorp, S.; Wauters, F.; Weinheimer, Ch.; Wenander, F.; Zakoucky, D.; Severijns, N.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 22/07/2008
Relevância na Pesquisa
45.89%
The standard model of the electroweak interaction describes beta-decay in the well-known V-A form. Nevertheless, the most general Hamiltonian of a beta-decay includes also other possible interaction types, e.g. scalar (S) and tensor (T) contributions, which are not fully ruled out yet experimentally. The WITCH experiment aims to study a possible admixture of these exotic interaction types in nuclear beta-decay by a precise measurement of the shape of the recoil ion energy spectrum. The experimental set-up couples a double Penning trap system and a retardation spectrometer. The set-up is installed in ISOLDE/CERN and was recently shown to be fully operational. The current status of the experiment is presented together with the data acquired during the 2006 campaign, showing the first recoil ion energy spectrum obtained. The data taking procedure and corresponding data acquisition system are described in more detail. Several further technical improvements are briefly reviewed.; Comment: 11 pages, 6 figures, conference proceedings EMIS 2007 (http://emis2007.ganil.fr), published also in NIM B: doi:10.1016/j.nimb.2008.05.150

Highlights from the NA60 experiment

Ferretti, A.; Arnaldi, R.; Averbeck, R.; Banicz, K.; Castor, J.; Chaurand, B.; Cicalò, C.; Colla, A.; Cortese, P.; Damjanovic, S.; David, A.; De Falco, A.; Devaux, A.; Drees, A.; Ducroux, L.; En'yo, H.; Floris, M.; Förster, A.; Force, P.; Guettet, N.; G
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 23/05/2007
Relevância na Pesquisa
45.89%
The NA60 experiment is a fixed-target experiment at the CERN SPS. It has measured the dimuon yield in Indium--Indium collisions with an In beam of 158 AGeV/c and in p-A collisions with a proton beam of 400 and 158 AGeV/c. The results allow to address three important physics topics, namely the study of the rho spectral function in nuclear collisions, the clarification of the origin of the dimuon excess measured by NA50 in the intermediate mass range, and the J/psi suppression pattern in a collision system different from Pb-Pb. An overview of these results will be given in this paper.; Comment: 4 pages, 6 figures, proceeding for the Rencontres de Moriond - QCD and Hadronic interactions - La Thuile (Italy), March 17-24 2007

First results on double beta decay modes of Cd, Te and Zn isotopes with the COBRA experiment

The COBRA collaboration; Bloxham, T.; Boston, A.; Dawson, J.; Dobos, D.; Fox, S. P.; Freer, M.; Fulton, B. R.; Gößling, C.; Harrison, P. F.; Junker, M.; Kiel, H.; McGrath, J.; Morgan, B.; Münstermann, D.; Nolan, P.; Oehl, S.; Ramachers, Y.; Reeve, C.;
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 18/07/2007
Relevância na Pesquisa
45.89%
Four 1cm^3 CdZnTe semiconductor detectors were operated in the Gran Sasso National Laboratory to explore the feasibility of such devices for double beta decay searches as proposed for the COBRA experiment. The research involved background studies accompanied by measurements of energy resolution performed at the surface. Energy resolutions sufficient to reduce the contribution of two-neutrino double beta decay events to a negligible level for a large scale experiment have already been achieved and further improvements are expected. Using activity measurements of contaminants in all construction materials a background model was developed with the help of Monte Carlo simulations and major background sources were identified. A total exposure of 4.34 kg.days of underground data has been accumulated allowing a search for neutrinoless double beta decay modes of seven isotopes found in CdZnTe. Half-life limits (90% C.L.) are presented for decays to ground and excited states. Four improved lower limits have been obtained, including zero neutrino double electron capture transitions of Zn64 and Te120 to the ground state, which are 1.19*10^{17} years and 2.68*10^{15} years respectively.; Comment: 8 pages, 7 figures

Electromagnetic emission from hot medium measured by the PHENIX experiment at RHIC

Sakaguchi, Takao; Collaboration, for the PHENIX
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.89%
Electromagnetic radiation has been of interest in heavy ion collisions because they shed light on early stages of the collisions where hadronic probes do not provide direct information since hadronization and hadronic interactions occur later. The latest results on photon measurement from the PHENIX experiment at RHIC reflect thermodynamic properties of the matter produced in the heavy ion collisions. An unexpectedly large positive elliptic flow measured for direct photons can not be explained by any of the current models.; Comment: Talk contributed to Rutherford Centennial Conference, Aug 8-12, 2011, held in Manchester, UK

Determination of neutrino incoming direction in the CHOOZ experiment and Supernova explosion location by scintillator detectors

Apollonio, M.; Baldini, A.; Bemporad, C.; Caffau, E.; Cei, F.; Declais, Y.; de Kerret, H.; Dieterle, B.; Etenko, A.; Foresti, L.; George, J.; Giannini, G.; Grassi, M.; Kozlov, Y.; Kropp, W.; Kryn, D.; Laiman, M.; Lane, C. E.; Lefievre, B.; Machulin, I.; M
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/06/1999
Relevância na Pesquisa
45.89%
The CHOOZ experiment measured the antineutrino flux at a distance of about 1 Km from two nuclear reactors in order to detect possible neutrino oscillations with squared mass differences as low as 10**-3 eV**2 for full mixing. We show that the data analysis of the electron antineutrino events, collected by our liquid scintillation detector, locates the antineutrino source within a cone of half-aperture of about 18 degrees at the 68% C.L.. We discuss the implications of this experimental result for tracking down a supernova explosion.; Comment: Submitted to Physical Review D

Double Spin Asymmetries of Inclusive Hadron Electroproductions from a Transversely Polarized $^3\rm{He}$ Target

The Jefferson Lab Hall A Collaboration; Zhao, Y. X.; Allada, K.; Aniol, K.; Annand, J. R. M.; Averett, T.; Benmokhtar, F.; Bertozzi, W.; Bradshaw, P. C.; Bosted, P.; Camsonne, A.; Canan, M.; Cates, G. D.; Chen, C.; Chen, J. -P.; Chen, W.; Chirapatpimol, K
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.89%
We report the measurement of beam-target double-spin asymmetries ($A_\text{LT}$) in the inclusive production of identified hadrons, $\vec{e}~$+$~^3\text{He}^{\uparrow}\rightarrow h+X$, using a longitudinally polarized 5.9 GeV electron beam and a transversely polarized $^3\rm{He}$ target. Hadrons ($\pi^{\pm}$, $K^{\pm}$ and proton) were detected at 16$^{\circ}$ with an average momentum $<$$P_h$$>$=2.35 GeV/c and a transverse momentum ($p_{T}$) coverage from 0.60 to 0.68 GeV/c. Asymmetries from the $^3\text{He}$ target were observed to be non-zero for $\pi^{\pm}$ production when the target was polarized transversely in the horizontal plane. The $\pi^{+}$ and $\pi^{-}$ asymmetries have opposite signs, analogous to the behavior of $A_\text{LT}$ in semi-inclusive deep-inelastic scattering.; Comment: Published in PRC (92.015207), nuclear experiment, high-energy experiment

Experimental Parameters for a Reactor Antineutrino Experiment at Very Short Baselines

Heeger, K. M.; Littlejohn, B. R.; Mumm, H. P.; Tobin, M. N.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 10/12/2012
Relevância na Pesquisa
45.89%
Reactor antineutrinos are used to study neutrino oscillation, search for signatures of non-standard neutrino interactions, and to monitor reactor operation for safeguard applications. The flux and energy spectrum of reactor antineutrinos can be predicted from the decays of the nuclear fission products. A comparison of recent reactor calculations with past measurements at baselines of 10-100m suggests a 5.7% deficit. Precision measurements of reactor antineutrinos at very short baselines O(1-10 m) can be used to probe this anomaly and search for possible oscillations into sterile neutrino species. This paper studies the experimental requirements for a new reactor antineutrino measurement at very short baselines and calculates the sensitivity of various scenarios. We conclude that an experiment at a typical research reactor provides 5{\sigma} discovery potential for the favored oscillation parameter space with 3 years of data collection.; Comment: 22 pages, 18 figures, 4 tables

The Qweak Experiment -- A search for new physics at the TeV Scale by measurement of the proton's weak charge

Ramsay, W. D.; Collaboration, for the Qweak
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 27/02/2007
Relevância na Pesquisa
45.89%
From a distance, the proton's weak charge is seen through the distorting effects of clouds of virtual particles. The effective weak charge can be calculated by starting with the measured weak coupling at the Z-pole and "running" the coupling to lower energy or, equivalently, longer distances. Because the "electroweak radiative corrections" or "loop diagrams" which give rise to the running depend not only on known particles, but on particles which have not yet been discovered, a difference between the calculated and measured weak charges may signal new physics. A measurement of Qweak to 4% will be sensitive to new physics at the few TeV scale. The Qweak experiment is based on the fact that the parity-violating longitudinal analyzing power, Az, in electron-proton scattering at low momentum transfer and small scattering angle, is proportional to the proton's weak charge. The experiment plans to measure the predicted Az of -0.3 ppm with a combined statistical and systematic uncertainty of 2.2%, corresponding to a total uncertainty of 4% of Qweak. This requires a statistical precision of 5 x 10^-9, which can be achieved in 2200 hours with an 85% polarized, 180 microamp electron beam incident on a 0.35 m liquid hydrogen target. A synchronous data acquisition system will integrate the detector current signals over each spin state and extract the helicity correlated...

Recent results on event-by-event fluctuations from the RHIC Beam Energy Scan program in the STAR experiment

Sahoo, Nihar Ranjan
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 06/07/2014
Relevância na Pesquisa
45.89%
Event-by-event fluctuations of global observables in relativistic heavy-ion collisions are studied as probes for the QCD phase transition and as tools to search for critical phenomena near the phase boundary. Dynamical fluctuations in mean transverse momentum, identified particle ratios and conserved quantities (such as net-charge, net-baryon) are expected to provide signatures of a de-confined state of matter. Non-monotonic behavior in the higher-moments of conserved quantities as a function of beam energy and collision centrality are proposed as signatures of the QCD critical point. To study the QCD phase transition and locate the critical point, the STAR experiment at RHIC has collected a large amount of data for Au+Au collisions from $\sqrt{s_{NN}} = 7.7-200$~GeV in the RHIC Beam Energy Scan (BES) program. We present the recent beam energy scan results on dynamical fluctuations of particle ratios and two-particle transverse momentum correlations at mid-rapidity. Higher-moments of the net-charge and net-proton multiplicity distributions as a function of beam energy will be presented. We give a summary of what has been learnt so far and future prospectives for the BES-II program.; Comment: 9 figures, 8 pages; Invited talk presented at the 30th Winter Workshop on Nuclear Dynamics (WWND 2014)...

Improved Search for $\bar \nu_\mu \rightarrow \bar \nu_e$ Oscillations in the MiniBooNE Experiment

The MiniBooNE Collaboration; Aguilar-Arevalo, A. A.; Brown, B. C.; Bugel, L.; Cheng, G.; Church, E. D.; Conrad, J. M.; Dharmapalan, R.; Djurcic, Z.; Finley, D. A.; Ford, R.; Garcia, F. G.; Garvey, G. T.; Grange, J.; Huelsnitz, W.; Ignarra, C.; Imlay, R.;
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.89%
The MiniBooNE experiment at Fermilab reports results from an analysis of $\bar \nu_e$ appearance data from $11.27 \times 10^{20}$ protons on target in antineutrino mode, an increase of approximately a factor of two over the previously reported results. An event excess of $78.4 \pm 28.5$ events ($2.8 \sigma$) is observed in the energy range $200

A Circulating Hydrogen Ultra-High Purification System for the MuCap Experiment

Ganzha, V. A.; Kravtsov, P. A.; Maev, O. E.; Schapkin, G. N.; Semenchuk, G. G.; Trofimov, V.; Vasilyev, A. A.; Vznuzdaev, M. E.; Clayton, S. M.; Kammel, P.; Kiburg, B.; Hildebrandt, M.; Petitjean, C.; Banks, T. I.; Lauss, B.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 10/05/2007
Relevância na Pesquisa
45.89%
The MuCap experiment is a high-precision measurement of the rate for the basic electroweak process of muon capture, mu- + p -> n + nu . The experimental approach is based on an active target consisting of a time projection chamber (TPC) operating with pure hydrogen gas. The hydrogen has to be kept extremely pure and at a stable pressure. A Circulating Hydrogen Ultrahigh Purification System was designed at the Petersburg Nuclear Physics Institute (PNPI) to continuously clean the hydrogen from impurities. The system is based on an adsorption cryopump to stimulate the hydrogen flow and on a cold adsorbent for the hydrogen cleaning. It was installed at the Paul Scherrer Institute (PSI) in 2004 and performed reliably during three experiment runs. During several months long operating periods the system maintained the hydrogen purity in the detector on the level of 20 ppb for moisture, which is the main contaminant, and of better than 7 ppb and 5 ppb for nitrogen and oxygen, respectively. The pressure inside the TPC was stabilized to within 0.024% of 10 bar at a hydrogen flow rate of 3 standard liters per minute.; Comment: submitted to Nucl. Instr. Methods Phys. Res. A

The Igex 76ge Neutrinoless Double-Beta Decay Experiment: Prospects for Next Generation Experiments

Aalseth, C. E.; Avignone III, F. T.; Brodzinski, R. L.; Cebrian, S.; Garcia, E.; Gonzalez, D.; Hensley, W. K.; Irastorza, I. G.; Kirpichnikov, I. V.; Klimenko, A. A.; Miley, H. S.; Morales, A.; Morales, J.; de Solorzano, A. Ortiz; Osetrov, S. B.; Pogosov,
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 12/02/2002
Relevância na Pesquisa
45.89%
The International Germanium Experiment (IGEX) has analyzed 117 mole yr of 76Ge data from its isotopically enriched (86% 76Ge) germanium detectors. Applying pulse-shape discrimination (PSD) to the more recent data, the lower bound on the half-life for neutrinoless double-beta decay of 76Ge is: $T_{1/2}(0\nu)> 1.57 \times 10^{25}$ yr (90% C.L.). This corresponds to an upper bound in the Majorana neutrino mass parameter,$$, between 0.33 eV and 1.35 eV, depending on the choice of theoretical nuclear matrix elements used in the analysis.

Detail study of the medium created in Au+Au collisions with high $p_T$ probes by the PHENIX experiment at RHIC

Sakaguchi, Takao; collaboration, for the PHENIX
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 11/04/2014
Relevância na Pesquisa
45.89%
Recent results on high $p_T$ identified hadrons in Au+Au collisions from the PHENIX experiment are presented. The $R_{\rm AA}$ for $\pi^0$ and $\eta$ are found to be very consistent. The second and fourth order collective flow of $\pi^0$s have been measured and found that $v_4/v_2^2$ is consistent with the one observed in lower $p_T$ region. Assuming the suppression of the $\pi^0$ yield at highest $p_T$ arises from energy loss of partons, we found that the energy loss is $L^3$ dependent, where $L$ is the path length of the partons in the medium. The $\delta p_T/p_T$'s of high $p_T$ hadrons are computed from 39GeV Au+Au over to 2.76TeV Pb+Pb, and found that they vary by a factor of six. We have seen a smooth trend in $\delta p_T/p_T$ from RHIC energy to LHC energy when plotting against charged multiplicity of the systems.; Comment: 4 pages, 5 figures, proceedings for the 6th International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions (Hard Probes 2013), Nov 4-8, 2013 in Stellenbosch, South Africa

The Pb Radius Experiment (PREX)

Mammei, Juliette; Collaboration, for the PREX
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 14/09/2012
Relevância na Pesquisa
45.89%
We report the first measurement of the parity-violating asymmetry APV in the elastic scattering of polarized electrons from 208Pb from the Lead Radius Experiment PREX which ran in Hall A at the Thomas Jefferson National Accelerator Facility (JLab). APV is sensitive to the radius of the neutron distribution Rn. The Z boson that mediates the weak neutral interaction couples mainly to neutrons and provides a clean, model-independent measurement of the RMS radius Rn of the neutron distribution in the nucleus and is a fundamental test of nuclear structure theory. The result, APV = 0.656 +/- 0.060(stat) +/- 0.014(syst) ppm, corresponds to a difference between the radii of the neutron and proton distributions Rn - Rp = 0.33 +16 -18 fm and provides the first electroweak observation of the neutron skin which is expected in a heavy, neutron-rich nucleus.; Comment: Proceedings of CIPANP 2012

Measurement of identified charged hadron spectra with the ALICE experiment at the LHC

Collaboration, L. Milano for the ALICE
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 16/08/2013
Relevância na Pesquisa
45.89%
The ALICE experiment features multiple particle identification systems. The measurement of the identified charged hadron $p_{t}$ spectra in proton-proton collisions at $\sqrt{s}=900$ GeV will be discussed. In the central rapidity region ($|\eta|<0.9$) particle identification and tracking are performed using the Inner Tracking System (ITS), which is the closest detector to the beam axis, the Time Projection Chamber (TPC) and a dedicated time-of-flight system (TOF). Particles are mainly identified using the energy loss signal in the ITS and TPC. In addition, the information from TOF is used to identify hadrons at higher momenta. Finally, the kink topology of the weak decay of charged kaons provides an alternative method to extract the transverse momentum spectra of charged kaons. This combination allows to track and identify charged hadrons in the transverse momentum ($p_{t}$) range from 100 MeV/c up to 2.5 GeV/$c$. Mesons containing strange quarks (\kos, $\phi$) and both singly and doubly strange baryons (\lam, \lambar, and \xip + \xim) are identified by their decay topology inside the TPC detector. Results obtained with the various identification tools above described and a comparison with theoretical models and previously published data will be presented.; Comment: 11 pages...

Light neutral mesons production in p-A collisions at $\sqrt{s} = 27.5$ GeV with the NA60 Experiment

Uras, Antonio
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 31/12/2011
Relevância na Pesquisa
45.89%
The NA60 experiment has studied low-mass muon pair production in proton-nucleus (p-A) collisions with a system of Be, Cu, In, W, Pb and U targets using a 400 GeV/$c$ proton beam at the CERN SPS. Thanks to the collected data sample of 180\,000 low mass muon pairs, the most precise measurement currently available was performed for the electromagnetic transition form factors of the $\eta$ and $\omega$ mesons. The $\rho$ line shape was quantitatively investigated, and its effective temperature measured for the first time in elementary collisions. The transverse momentum spectra for the $\omega$ and $\phi$ mesons have been studied in the full $\pt$ range accessible, up to 2 GeV/$c$. The cross section ratios $\sigma_\rho/\sigma_\omega$ and $\sigma_\phi/\sigma_\omega$ have been considered in full $\pt$ as a function of the size of the production target. The nuclear dependence of the production cross sections of the $\eta$, $\omega$ and $\phi$ mesons has finally been studied in terms of the power law $\sigma_\mathrm{pA} \propto \mathrm{A}^\alpha$, where the $\alpha$ parameter has been found to increase as a function of $\pt$.; Comment: On behalf of the NA60 Collaboration. arXiv admin note: substantial text overlap with arXiv:1108.0970

Hadronic resonance production with the ALICE experiment in pp and Pb-Pb collisions at LHC energies

Sergey Kiselev for the ALICE collaboration
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 12/11/2013
Relevância na Pesquisa
45.89%
Hadronic resonances $\mathrm{K}^{*}(892)^{0}$, $\phi$(1020) and $\Sigma(1385)^{\pm}$ have been measured by the ALICE experiment in pp collisions at $\sqrt{s}=7$ TeV and in Pb-Pb collisions at $\sqrt{s_{_\mathrm{NN}}}=2.76$ TeV. Transverse momentum spectra, particle ratios, nuclear modification factor and comparison with model predictions are discussed. In addition, ALICE results are compared with data obtained at RHIC energy.; Comment: 3 pages, 3 figures, Proceedings of 16th Lomonosov Conference on Elementary Particle Physics, Moscow, 22/08/2013 - 28/08/2013

Probing the braneworld hypothesis with a neutron-shining-through-a-wall experiment

Sarrazin, Michael; Pignol, Guillaume; Lamblin, Jacob; Petit, Fabrice; Terwagne, Guy; Nesvizhevsky, Valery V.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.89%
The possibility for our visible world to be a 3-brane embedded in a multidimensional bulk is at the heart of many theoretical edifices in high-energy physics. Probing the braneworld hypothesis is thus a major experimental challenge. Following recent theoretical works showing that matter swapping between braneworlds can occur, we propose a neutron-shining-through-a-wall experiment. We first show that an intense neutron source such as a nuclear reactor core can induce a hidden neutron flux in an adjacent hidden braneworld. We then describe how a low-background detector can detect neutrons arising from the hidden world and quantify the expected sensitivity to the swapping probability. As a proof of concept, a constraint is derived from previous experiments.; Comment: 12 pages, 4 figures, final version published in Physical Review D

The CLEAR Experiment

Scholberg, K.; Wongjirad, T.; Hungerford, E.; Empl, A.; Markoff, D.; Mueller, P.; Efremenko, Y.; McKinsey, D.; Nikkel, J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.89%
The Spallation Neutron Source in Oak Ridge, Tennessee, is designed to produce intense pulsed neutrons for various science and engineering applications. Copious neutrinos are a free by-product. When it reaches full power, the SNS will be the world's brightest source of neutrinos in the few tens of MeV range. The proposed CLEAR (Coherent Low Energy A (Nuclear) Recoils) experiment will measure coherent elastic neutral current neutrino-nucleus scattering at the SNS. The physics reach includes tests of the Standard Model.; Comment: To be published in the proceedings of DPF-2009, Detroit, MI, July 2009, eConf C090726

Event-by-event mean p_T fluctuations in pp and Pb-Pb collisions measured by the ALICE experiment at the LHC

Heckel, S. T.; collaboration, for the ALICE
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.89%
Non-statistical event-by-event fluctuations of the mean transverse momentum of charged particles in pp and Pb-Pb collisions are studied using the ALICE experiment at the LHC. Little collision energy dependence is observed in pp. The data indicate a common scaling behaviour with event multiplicity from pp to semi-central Pb-Pb collisions. In central Pb-Pb, the results deviate from this trend, exhibiting a significant reduction of the fluctuation strength. The results are compared with measurements in Au-Au collisions at lower energies and with Monte Carlo simulations.; Comment: 4 pages, 3 figures, proceedings to Quark Matter 2011; only minor changes in the new version (e.g. description of error bars of fig.3 in more detail, ref.5 updated), figures not changed, this is the published version