Commissioning studies of the CMS hadron calorimeter have identified sporadic uncharacteristic noise and a small number of malfunctioning calorimeter channels. Algorithms have been developed to identify and address these problems in the data. The methods have been tested on cosmic ray muon data, calorimeter noise data, and single beam data collected with CMS in 2008. The noise rejection algorithms can be applied to LHC collision data at the trigger level or in the offline analysis. The application of the algorithms at the trigger level is shown to remove 90% of noise events with fake missing transverse energy above 100 GeV, which is sufficient for the CMS physics trigger operation.

In the heavy-fermion metal CePdAl long-range antiferromagnetic order coexists with geometric frustration of one third of the Ce moments. At low temperatures the Kondo effect tends to screen the frustrated moments. We use magnetic fields B to suppress the Kondo screening and study the magnetic phase diagram and the evolution of the entropy with B employing thermodynamic probes. We estimate the frustration by introducing a definition of the frustration parameter based on the enhanced entropy, a fundamental feature of frustrated systems. In the field range where the Kondo screening is suppressed the liberated moments tend to maximize the magnetic entropy and strongly enhance the frustration. Based on our experiments, this field range may be a promising candidate to search for a quantum spin liquid.If competing exchange interactions prevent magnetic systems from developing long-range order, the frustrated magnetic moments can form fluid-like states of matter, so-called spin liquids (SLs) [1]. If the moments act as effective spin-1/2 particles, quantum fluctuations dominate and impede the moments from freezing or ordering at low temperatures T [2]. The ground states of these quantum SLs are characterized by massive many-body entanglement rendering them particularly attractive for investigations of new types of quantum matter. Ever since the first notion of SLs was advertised, there has been continual effort to search for materials that might host SLs, mainly in geometrically frustrated magnets [3][4][5][6][7]. Up to now only very few candidates for metallic SLs have been discovered [2, 8].CePdAl belongs to a class of heavy-fermion (HF) metals with ZrNiAl-type crystal structure (space group P62m) that display geometric frustration owing to the fact that the Ce ions form a distorted kagomé network in the hexagonal ab plane [9][10][11]. In HF compounds the magnetic moments are formed by nearly localized 4f or 5f states. Magnetic correlations are enabled by the Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction which competes with the Kondo effect tending to screen the moments at low T . The presence of a Kondo effect in CePdAl is manifest through a logarithmic increase of the resistivity with decreasing T [12, 13] and an extremum of the thermopower at low T [14-16].CePdAl stands out due to the coexistence of geometric frustration with antiferromagnetic (AF) order below T N = 2.7 K [9, 14]. Neutron diffraction experiments [9] and 27 Al NMR measurements [17] reveal that one third of the Ce moments do not participate in the longrange order down to 30 mK. Theoretical models considering a quasi-two-dimensional magnetic structure based on the neutron experiments performed on polycrystals [9] suggest that the Ce moments of the hexagonal basal plane order in ferromagnetic chains which are antiferromagnetically coupled and separated from each other by the frustrated, interjacent moments [inset of Fig. 1(b)] [18, 19]. In the c direction this structure is repeated with an incommensurate AF modulation. Due to the crystal-electric...

In contrast with the simultaneous structural and magnetic first order phase transition T0 previously reported, our detailed investigation on an underdoped Ba(0.84)K(0.16)Fe2As2 single crystal unambiguously revealed that the transitions are not concomitant. The tetragonal (τ: I4/mmm)-orthorhombic (ϑ: Fmmm) structural transition occurs at T(S)≃110 K, followed by an adjacent long-range antiferromagnetic (AFM) transition at T(N)≃102 K. Hysteresis and coexistence of the τ and ϑ phases over a finite temperature range observed by NMR experiments confirm the first order character of the τ-ϑ transition and provide evidence that both T(S) and T(N) are strongly correlated. Our data also show that superconductivity develops in the ϑ phase below T(c)=20 K and coexists with AFM. This new observation, T(S)≠T(N), firmly establishes another similarity between the hole-doped BaFe2As2 and the electron-doped iron-arsenide superconductors.

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The operation and general performance of the CMS electromagnetic calorimeter using cosmic-ray muons are described. These muons were recorded after the closure of the CMS detector in late 2008. The calorimeter is made of lead tungstate crystals and the overall status of the 75 848 channels corresponding to the barrel and endcap detectors is reported. The stability of crucial operational parameters, such as high voltage, temperature and electronic noise, is summarised and the performance of the light monitoring system is presented.