The CMS ECAL Laser Monitoring System

The CMS detector at LHC will be equipped with a high precision lead tungstate electromagnetic calorimeter. To ensure the stability of the calorimetric response at a level of a few per mille, every channel of the detector is monitored with a laser system. This system allows to correct for fluctuations in the detector response with high precision, in particular the expected radiation induced changes of the crystal transparency, which are on the level of several per cent at nominal luminosity. Here we report results from long term tests of the system on fully equipped supermodules of the CMS ECAL which are performed after the final step of the construction but before insertion of the modules in CMS. The in‐situ monitoring strategy for the CMS ECAL is discussed in detail and the performance of the full monitoring procedure as achieved in the test beam is illustrated

Observation of B_s Production at the Y(5S) Resonance

Using the CLEO detector at the Cornell Electron Storage Ring, we have observed the B_s meson in e^+e^- annihilation at the Υ(5S) resonance. We find 14 candidates consistent with B_s decays into final states with a J/ψ or a D_s^((*)-). The probability that we have observed a background fluctuation is less than 8×10^(-10). We have established that at the energy of the Υ(5S) resonance B_s production proceeds predominantly through the creation of B_s^*B̅ _s^* pairs. We find σ(e^+e^-→B^s^*B̅ ^*)=[0.11_(-0.03)^(+0.04)(stat)±0.02(syst)]  nb, and set the following limits: σ(e^+e^-→B_sB̅ _s)/σ(e^+e^-→B_s^*B̅ _s^*)<0.16 and [σ(e^+e^-→B_sB̅ _s^*)+σ(e^+e^-→B_s*B̅ _s)]/σ(e^+e^-→B_s*B̅ _s^*)<0.16 (90% C.L.). The mass of the B_s^* meson is measured to be M_(B_s^*=[5.414±0.001(stat)±0.003(syst)]  GeV/c^2

Two-photon width of the charmonium state X_(c2)

The two-photon width of X_(c2)^3P_2 state of charmonium has been measured using 14.4 fb^(-1) of e^+e^-data taken at √s =9.46–11.30 GeV with the CLEO III detector. The yy-fusion reaction studied is e^+e^- → e^+e^-yy, → yy X_(c2) → yJ/Ψ → ye^+e^-(µ^+µ^-). We measure Г_(yy) (X_(c2))B(X_(c2)) → y J/Ψ)B(J/Ψ → e^+e^- + µ^+µ^-)= 13.2 ± 1.4(stat)± 1.1(syst) eV, and obtain Г yy(Xc2)= 559 ± 57(stat) ± 48(syst) ± 36(br) eV. This result is in excellent agreement with the result of -fusion measurement by Belle and is consistent with that of the pp → X_(c2) → yy measurement, when they are both reevaluated using the recent CLEO result for the radiative decay X_(c2) → J/Ψ

On the Usage of Precision Timing Detectors in High Rate and High Pileup Environments

High energy particle collider experiments are facing ever more challenging conditions, operating at todays accelerators capable of providing instantaneous luminosities of 10^(34)cm^(-2)s^(-1) and above. The high center of mass energy, the large number of simultaneous collision of beam particles in the experiments and the very high repetition rates of the collision events pose huge challenges. They result in extremely high particle fluxes, causing very high occupancies in the particle physics detectors operating at these machines. A precise timing information with a precision of around 10 ps and below is seen as a major aid in the reconstruction of the physics events under such challenging conditions. In this paper I discuss applications of precision timing in high pile-up conditions and review the efforts of the LHC collaborations to augment the timing performance of their detectors during future upgrade campaigns. Different detector technologies allowing precision timing measurements will be discussed and their potential benefit for a holistic event reconstruction will be illustrated

Performance of the Monitoring Light Source for the CMS Lead Tungstate Crystal Calorimeter

Light monitoring will play a crucial role in maintaining energy resolution for the CMS lead tungstate crystal calorimeter at LHC. In the last several years, a laser based monitoring light source was designed and constructed at Caltech, and was installed and commissioned at CERN. This paper presents the design of the CMS ECAL monitoring light source and its performance during beam tests. Issues related to the monitoring precision are discussed

Timing performance of the CMS electromagnetic calorimeter and prospects for the future

The CMS electromagnetic calorimeter (ECAL) is made of 75,848 scintillating lead tungstate crystals arranged in a barrel and two endcaps. The scintillation light is read out by avalanche photodiodes in the barrel and vacuum phototriodes in the endcaps, at which point the scintillation pulse is amplified and sampled at 40 MHz by the on-detector electronics. The fast signal from the crystal scintillation enables energy as well as timing measurements from the data collected in proton-proton collisions with high energy electrons and photons. The single-channel time resolution of ECAL measured at beam tests for high energy showers is better than 100 ps. The timing resolution achieved with the data collected in proton-proton collisions at the LHC is discussed. We present how precision timing is used in current physics measurements and discuss studies of subtle calorimetric effects, such as the timing response of different crystals belonging to the same electromagnetic shower. In addition, we present prospects for the high luminosity phase of the LHC (HL-LHC), where we expect an average of 140 concurrent interactions per bunch crossing (pile-up). We discuss studies on how precision time information could be exploited for pileup mitigation and for the assignment of the collision vertex for photons. In this respect, a detailed understanding of the timing performance and of the limiting factors in time resolution are areas of ongoing studies

Brecht ainda hoje?

This paper tries to find arguments for Bertolt Brecht's relevance to the present. It points out parallels between Brecht's epic theater and music, especially opera. A central point is the aesthetics of form, which was so important for Brecht and which is decisive for his modernity.Der vorliegende Aufsatz versucht, Argumente für die Aktualität Bertolt Brechts zu finden. Es werden Parallelen zwischen Brechts epischem Theater und der Musik, insbesondere der Oper, aufgezeigt. Dabei spielt die für Brecht so wichtige Ästhetik der Form eine zentrale Rolle, die entscheidend für seine Modernität ist