4,062 research outputs found

    Performance of the CMS electromagnetic calorimeter during the LHC Run II and its role in precision physics measurements

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    Many physics analyses using the Compact Muon Solenoid (CMS) detector at the LHC require accurate, high resolution electron and photon energy measurements. Particularly important are the decays of the Higgs boson resulting in electromagnetic particles in the final state, as well as the searches for very high mass resonances decaying into energetic photons or electrons. Following the excellent performance achieved in Run I at center-of-mass energies of 7 and 8 TeV, the CMS electromagnetic calorimeter (ECAL) is operating at the LHC with proton-proton collisions at 13 TeV center-of-mass energy. The instantaneous luminosity delivered by the LHC during Run II has achieved unprecedented values, using 25 ns bunch spacing. High pileup levels necessitate a retuning of the ECAL readout and trigger thresholds and reconstruction algorithms, to maintain the best possible performance in these more challenging conditions. The energy response of the detector must be precisely calibrated and monitored to achieve and maintain the excellent performance obtained in Run I in terms of energy scale and resolution. A dedicated calibration of each detector channel is performed with physics events exploiting electrons from W and Z boson decays, photons from pi0pi^{0}/etaeta decays, and from the azimuthally symmetric energy distribution of minimum bias events. This contribution describes the calibration strategies and the performance of the CMS ECAL throughout Run II and its role in precision physics measurements with CMS involving electrons and photons

    Latest results on single electroweak boson production from the CMS experiment

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    The production of W and Z bosons is one of the most prominent examples of hard scattering processes at hadron colliders. The measurements of the corresponding inclusive and differential cross sections provide important tests of perturbative quantum chromodynamics and parton dis- tribution functions. Moreover, these processes constitute the main source of background for the searches for dark matter or other exotic final states, making the precise knowledge of W and Z boson kinematic spectra a fundamental tool to search for new physics. This paper reports a sum- mary of the latest measurements of single electroweak boson production carried out by the CMS experiment at the CERN Large Hadron Collider. They are based on data collected at a center-of- mass energy of 8 or 13 TeV. The measurements are performed exploiting the decay of W and Z bosons into electrons or muons, which provide a clean experimental final state with a low level of background. Results are corrected to the stable-particle level through unfolding techniques and compared with theoretical predictions obtained using several generators, allowing to validate different models for the parton shower and hard scattering processes. The main features of the selected analyses are illustrated and their role in the consolidation and development of our current knowledge of the electroweak sector is highlighted. Finally, the prospects for new measurements using the full dataset collected by CMS at 13 TeV by the end of 2018 are briefly discussed as well

    Herd Behavior in a Laboratory Financial Market

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    We study herd behavior in a laboratory Þnancial market where a sequence of subjects trades an asset whose value is unknown. In two treatments the price is updated according to a deterministic rule based on the order ßow, and in another it is updated by experimental participants. Theory predicts that agents should never herd. Our experimental results are in line with this prediction. Nevertheless, we observe a phenomenon that cannot be accounted for by the theory. In some cases, subjects decide not to use their private information and choose not to trade. In other cases, they ignore their private information to trade against the market (contrarian behavior). (JEL C92, D8, G14)

    Herd Behavior in Financial Markets: An Experiment with Financial Market Professionals

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    We study herd behavior in a laboratory financial market with financial market professionals. An important novelty of the experimental design is the use of a strategy-like method. This allows us to detect herd behavior directly by observing subjects’ decisions for all realizations of their private signal. In the paper, we compare two treatments: one in which the price adjusts to the order flow in such a way that herding should never occur, and one in which the presence of event uncertainty makes herding possible. In the first treatment, subjects herd seldom, in accordance with both the theory and previous experimental evidence on student subjects. A proportion of sub jects, however, engage in contrarianism, something not accounted for by the theory. In the second treatment, the proportion of herding decisions increases, but not as much as the theory would suggest. Moreover, contrarianism disappears altogether. In both treatments, in contrast with what theory predicts, subjects sometimes prefer to abstain from trading, which affects the process of price discovery negatively.Herding, Contrarianism, Financial Market Professionals

    Herd Behavior in Financial Markets: An Experiment with Financial Market Professionals

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    We study herd behavior in a laboratory ?nancial market with ?- nancial market professionals. An important novelty of the experi- mental design is the use of a strategy-like method. This allows us to detect herd behavior directly by observing subjects?decisions for all realizations of their private signal. In the paper, we compare two treatments - one in which the price adjusts to the order ?ow in such a way that herding should never occur, and one in which the presence of event uncertainty makes herding possible. In the ?rst treatment, traders herd seldom, in accordance with both the theory and previous experimental evidence on student subjects. A proportion of traders, however, engage in contrarianism, something not accounted for by the theory. In the second treatment, on the one hand, the proportion of herding decisions increases, but not as much as the theory would sug- gest; on the other hand, contrarianism disappears altogether. In both treatments, in contrast with what theory predicts, subjects sometimes prefer to abstain from trading, which a¤ects the process of price discovery negatively.

    Volatility in International Financial Market Issuance: The Role of the Financial Center

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    We study the pattern of volatility of gross issuance in international capital markets since 1980. We find several short-lived episodes of high volatility. Over the long run, however, volatility has declined, suggesting that international financial integration has not made financial markets more erratic. We use VAR analysis to examine the determinants of the time-varying pattern of volatility, focusing in particular on the role of financial centers. Our results suggest that a significant portion of the decline in volatility of issuance in international capital markets can be explained by the reduction in the volatility of U.S. interest rates.

    Measurement of the helicity of the W boson with the CMS experiment

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    This thesis describes the measurement of the helicity of W bosons as a function of the W-boson rapidity in the WμνW\rightarrow\mu\nu and WeνW\rightarrow e\nu decay channels. The analysis is based on a dataset of 35.9\,fb1\mathrm{fb^{-1}} at s\sqrt{s} = 13\,TeV collected in 2016 by the CMS experiment at the LHC. The thesis also presents the measurement of the W-boson double-differential cross section as a function of the transverse momentum and pseudorapidity of the decay charged lepton unfolded to stable-particle level. Both measurements are carried out for each W-boson charge through a simultaneous fit and are complemented by the measurement of the charge asymmetry of W bosons produced at the LHC. All these measurements are performed using an innovative method that allows to unfold the cross section and charge asymmetry directly as a function of stable-particle-level quantities. The measurement of the W-boson helicity and rapidity distribution provides stringent tests of the parton distribution functions, and has been developed with the aim of reducing the theoretical systematic uncertainties that currently limit the precision of the W-boson mass measurement at the LHC. Therefore, some prospects regarding this topic are discussed as well

    Detrital events within pelagic deposits of the Umbria-Marche basin (Northern Apennines, Italy). Further evidence of Early Cretaceous tectonics

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    Re-sedimented deposits characterize different stratigraphical intervals in the pelagic successions of the Umbria-Marche-Sabina Domain (Central and Northern Apennines, Italy). Three stratigraphic sections of the Maiolica and Marne a Fucoidi Formations, characterized by breccias and calcarenites embedded in pelagic sediments, were sampled across the Mt. Primo area (Umbria- Marche Ridge, Northern Apennines). Facies analysis indicates a gravity-driven origin for the clastic levels, interpreted as debris-flows, or turbidity flows. The massive lensoid-to-tabular levels are composed of loose shallow-water benthic material, sourced from an unknown carbonate platform, associated with: i) lithoclasts made of Lower Jurassic and Lower Cretaceous shallow-water carbonates; ii) Jurassic mudstones and wackestones referable to the pelagic succession; iii) calpionellid/radiolarian-rich soft pebbles (Maiolica-type facies). The compositional features of the studied detrital deposits imply submarine exposure and dismantling of portions of the stratigraphic succession older than the Barremian/Aptian, which had to be buried in the late Early Cretaceous. Such evidence led us to refer the investigated clastic event to an extensional tectonic phase. Our interpretation well fits with data coming from different geological settings of Italy, strongly suggesting the occurrence of a widespread extensional phase in the late Early Cretaceous
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