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Measurement of the and polarizations in proton-proton collisions at 8 TeV
No full textThe polarizations of promptly produced χc1 and χc2 mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at s=8 TeV. The χc states are reconstructed via their radiative decays χc→J/ψγ, with the photons being measured through conversions to e+e−, which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the χc2 to χc1 yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the J/ψ→μ+μ- decay, in three bins of J/ψ transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the helicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum
The Initial State QED Corrections to
No full textWe calculate the complete initial state radiation corrections to annihilation into a neutral vector boson in a direct analytic computation without any approximation. The corrections are represented in terms of iterated incomplete (elliptic) integrals over alphabets of square--root valued letters. Performing the limit , we find discrepancies with the earlier results of Ref.~\cite{Berends:1987ab} and confirm results obtained in Ref.~\cite{Blumlein:2011mi} where the effective method of massive operator matrix elements has been used, which works for all but the power corrections in . In this way, we also confirm the validity of the factorization of massive partons in the Drell--Yan process. We add non--logarithmic terms at which have not been considered in previous calculations. The final results in the limit can be given in terms of Nielsen integrals
Measurement of the jet mass distribution and top quark mass in hadronic decays of boosted top quarks in pp collisions at 13 Te
No full textA measurement is reported of the jet mass distribution in hadronic decays of boosted top quarks produced in pp collisions at s=13 TeV. The data were collected with the CMS detector at the LHC and correspond to an integrated luminosity of 35.9 fb-1. The measurement is performed in the lepton+jets channel of tt¯ events, where the lepton is an electron or muon. The products of the hadronic top quark decay t→bW→bqq¯′ are reconstructed as a single jet with transverse momentum larger than 400 GeV. The tt¯ cross section as a function of the jet mass is unfolded at the particle level and used to extract a value of the top quark mass of 172.6±2.5 GeV. A novel jet reconstruction technique is used for the first time at the LHC, which improves the precision by a factor of 3 relative to an earlier measurement. This highlights the potential of measurements using boosted top quarks, where the new technique will enable future precision measurements
Dynamics of porous and amorphous magnesium borohydride to understand solid state Mg-ion-conductors
No full textRechargeable solid-state magnesium batteries are considered for high energy density storage and usage in mobile applications as well as to store energy from intermittent energy sources, triggering intense research for suitable electrode and electrolyte materials. Recently, magnesium borohydride, Mg(BH4)2, was found to be an effective precursor for solid-state Mg-ion conductors. During the mechanochemical synthesis of these Mg-ion conductors, amorphous Mg(BH4)2 is typically formed and it was postulated that this amorphous phase promotes the conductivity. Here, electrochemical impedance spectroscopy of as-received γ-Mg(BH4)2 and ball milled, amorphous Mg(BH4)2 confirmed that the conductivity of the latter is ~2 orders of magnitude higher than in as-received γ-Mg(BH4)2 at 353 K. Pair distribution function (PDF) analysis of the local structure shows striking similarities up to a length scale of 5.1 Å, suggesting similar conduction pathways in both the crystalline and amorphous sample. Up to 12.27 Å the PDF indicates that a 3D net of interpenetrating channels might still be present in the amorphous phase although less ordered compared to the as-received γ-phase. However, quasi elastic neutron scattering experiments (QenS) were used to study the rotational mobility of the [BH4] units, revealing a much larger fraction of activated [BH4] rotations in amorphous Mg(BH4)2. These findings suggest that the conduction process in amorphous Mg(BH4)2 is supported by stronger rotational mobility, which is proposed to be the so-called “paddle-wheel” mechanism
Measurement of Exclusive and Meson Photoproduction at HERA
No full textExclusive photoproduction of mesons is studied using the H1 detector at the collider HERA. A sample of about 900000 events is used to measure single- and double-differential cross sections for the reaction . Reactions where the proton stays intact () are statistically separated from those where the proton dissociates to a low-mass hadronic system ( GeV). The double-differential cross sections are measured as a function of the invariant mass of the decay pions and the squared -momentum transfer at the proton vertex. The measurements are presented in various bins of the photon-proton collision energy . The phase space restrictions are GeV, GeV, and GeV. Cross section measurements are presented for both elastic and proton-dissociative scattering. The observed cross section dependencies are described by analytic functions. Parametrising the \mpipi dependence with a \Soding model of photon dissociation into together with resonance production leads to a measurement of the meson mass and width at (tot) MeV and (tot) MeV, respectively. The model is used to extract the contribution to the cross sections and measure it as a function of and . In a Regge asymptotic limit in which one Regge trajectory dominates, the intercept (tot) and the slope (tot) GeV of the dependence are extracted for the case
HiggsBounds-5: Testing Higgs Sectors in the LHC 13 TeV Era
No full textWe describe recent developments of the public computer code HiggsBounds. In particular, these include the incorporation of LHC Higgs search results from Run 2 at a center-of-mass energy of 13 TeV, and an updated and extended framework for the theoretical input that accounts for improved Higgs cross section and branching ratio predictions and new search channels. We furthermore discuss an improved method used in HiggsBounds to approximately reconstruct the exclusion likelihood for LHC searches for non-standard Higgs bosons decaying to final states. We describe in detail the new and updated functionalities of the new version HiggsBounds-5
Oblique-incidence deposition of ferromagnetic thin films and their application in magnetoresistive sensors
No full textMagnetic field sensors can be used for compass applications, to measure electrical cur-rents or to determine position and speed of objects. Layered thin-film sensors based onthe giant or tunneling magnetoresistance (GMR or TMR) are predestined for portabledevices where their small size, high effect strength and low power consumption are crucial.Through the use of oblique-incidence deposition (OID) it is possible to tailor the magneticand magnetoresistive properties of the sensors in an easy-accessible and flexible way tothe needs of an application. The goal of this thesis is to investigate the feasibility of OIDin GMR and TMR sensors.Building on the work presented in [Sch16] with extended GMR film samples, fundamentalquestions regarding magnetic coupling and sensor stability are answered. It is shown thatmicrostructuring and the OID-characteristic wavy surface morphology do not interferewith sensor performance. Overall, around 10% GMR are achieved in microstructureddevices, making OID-GMR sensors a suitable and uncomplicated solution for a variety ofapplications.TMR sensors are based on the material combination of FeCoB and insulating MgO astunnel barrier. Upon thermal treatment, FeCoB crystallizes guided by the MgO struc-ture as template. Obliquely deposited FeCoB exhibits a sensitive balance of differentanisotropy terms that is surprisingly found to induce a rotation of the preferred magneti-zation axis by 90◦in-plane. After synchrotron-based investigations to correlate structuraland magnetic properties, a model is developed that explains the additional OID-inducedanisotropy contributions.Despite the complex transition of FeCoB and the combination of wavy interfaces witha sensitive ultra-thin tunnel barrier, the OID-approach is for the first time successfullytransferred to TMR systems. A high TMR effect strength of up to 60% is achieved inmicrostructured sensors. By changing the layer thicknesses and deposition angles, sensorparameters are tuned and novel functionalities are implemented. Overall, it is shown thatoblique-incidence deposition can be used to prepare TMR systems based on MgO andFeCoB that exhibit unique and adjustable functionalities while maintaining a high effectstrength, temperature stability and compatibility to common fabrication processes. Thispaves the way for customizable and simplified magnetoresistive sensors
Critical properties of the valence-bond-solid transition in lattice quantum electrodynamics
No full textElucidating the phase diagram of lattice gauge theories with fermionic matter in 2+1 dimensions has become a problem of considerable interest in recent years, motivated by physical problems ranging from chiral symmetry breaking in high-energy physics to fractionalized phases of strongly correlated materials in condensed matter physics. For a sufficiently large number Nf of flavors of four-component Dirac fermions, recent sign-problem-free quantum Monte Carlo studies of lattice quantum electrodynamics (QED3) on the square lattice have found evidence for a continuous quantum phase transition between a power-law correlated conformal QED3 phase and a confining valence-bond-solid phase with spontaneously broken point-group symmetries. The critical continuum theory of this transition was shown to be the O(2) QED3-Gross-Neveu model, equivalent to the gauged Nambu–Jona-Lasinio model, and critical exponents were computed to first order in the large-Nf expansion and the ε expansion. We extend these studies by computing critical exponents to second order in the large-Nf expansion and to four-loop order in the ε expansion below four spacetime dimensions. In the latter context, we also explicitly demonstrate that the discrete Z4 symmetry of the valence-bond-solid order parameter is dynamically enlarged to a continuous O(2) symmetry at criticality for all values of Nf
Thermal stability and crystallization of a Zr-based metallic glass produced by suction casting and selective laser melting
No full textThe thermal stability and crystallization mechanism of the Zr59.3Cu28.8Al10.4Nb1.5 (at%) metallic glass produced through selective laser melting SLM (from industrial grade material) was studied and compared with the same alloy produced by suction casting (from laboratory grade material of high purity). Oxygen- and Al-rich particles of a cubic phase (Fdm) with a size of up to 200 nm are detected in the as-built selective laser melted samples by transmission electron microscopy. The crystallization process of the cast and SLM samples is investigated by in-situ X-ray diffraction experiments. In the cast samples, the initial crystallization occurs via the formation of a metastable tetragonal phase (Al2Zr3), together with tetragonal CuZr2 and hexagonal Al3Zr4 type structures, while the SLM samples initially crystallize through the formation of the metastable, oxygen- and Al-rich, cubic phase already present before annealing. The main phases present at the end of the crystallization for both type of samples are the same, mainly CuZr2 and Al3Zr4. The differences in the crystallization paths are attributed to differences in the oxygen levels. In general, the higher oxygen content (∼1 at%) of the SLM samples results in a decrease of the thermal stability of the alloy and promotes the formation of an oxygen-rich, metastable cubic phase