We demonstrate that the eight multipole parameters describing the spin state of the
Z
boson are able to disentangle known
Z
production mechanisms and signals from new physics at the LHC. They can be ...extracted from appropriate asymmetries in the angular distribution of lepton pairs from the
Z
boson decay. The power of this analysis is illustrated by (1) the production of
Z
boson plus jets; (2)
Z
boson plus missing transverse energy; (3)
W
and
Z
bosons originating from the two-body decay of a heavy resonance.
. Background events are one of the most relevant contributions to image degradation in Compton camera imaging for hadron therapy treatment monitoring. A study of the background and its contribution ...to image degradation is important to define future strategies to reduce the background in the system.
. In this simulation study, the percentage of different kinds of events and their contribution to the reconstructed image in a two-layer Compton camera have been evaluated. To this end, GATE v8.2 simulations of a proton beam impinging on a PMMA phantom have been carried out, for different proton beam energies and at different beam intensities.
. For a simulated Compton camera made of Lanthanum (III) Bromide monolithic crystals, coincidences caused by neutrons arriving from the phantom are the most common type of background produced by secondary radiations in the Compton camera, causing between 13% and 33% of the detected coincidences, depending on the beam energy. Results also show that random coincidences are a significant cause of image degradation at high beam intensities, and their influence in the reconstructed images is studied for values of the time coincidence windows from 500 ps to 100 ns.
. Results indicate the timing capabilities required to retrieve the fall-off position with good precision. Still, the noise observed in the image when no randoms are considered make us consider further background rejection methods.
Massive neutrinos demand to ask whether they are Dirac or Majorana particles. Majorana neutrinos are an irrefutable proof of physics beyond the Standard Model. Neutrinoless double electron capture is ...not a process but a virtual ΔL = 2 mixing between a parent AZ atom and a daughter A(Z - 2) excited atom with two electron holes. As a mixing between two neutral atoms and the observable signal in terms of emitted two-hole X-rays, the strategy, experimental signature and background are different from neutrinoless double beta decay. The mixing is resonantly enhanced for almost degeneracy and, under these conditions, there is no irreducible background from the standard two-neutrino channel. We reconstruct the natural time history of a nominally stable parent atom since its production either by nature or in the laboratory. After the time periods of atom oscillations and the decay of the short-lived daughter atom, at observable times the relevant "stationary" states are the mixed metastable long-lived state and the short-lived excited state, as well as the ground state of the daughter atom. Their natural population inversion is most appropriate for exploiting the bosonic nature of the observed X-rays by means of stimulating X-ray beams. Among different observables of the atom Majorana mixing, we include the enhanced rate of stimulated X-ray emission from the long-lived metastable state by a high-intensity X-ray beam. A gain factor of 100 can be envisaged in a facility like European XFEL.
The proposed high-luminosity B/flavor factories offer new opportunities for the improved determination of the fundamental physical parameters of standard heavy leptons. Compared to the electron or ...the muon case, the magnetic properties of the
τ lepton are largely unexplored. We show that the electromagnetic properties of the
τ, and in particular its magnetic form factor, may be measured competitively in these facilities, using unpolarized or polarized electron beams. Various observables of the
τ's produced on top of the
ϒ resonances, such as cross-section and normal polarization for unpolarized electrons or longitudinal and transverse asymmetries for polarized beams, can be combined in order to increase the sensitivity on the magnetic moment form factor. In the case of polarized electrons, we identify a special combination of transverse and longitudinal
τ polarizations able to disentangle this anomalous magnetic form factor from both the charge form factor and the interference with the
Z-mediating amplitude. For an integrated luminosity of
15
×
10
18
b
−1
one could achieve a sensitivity of about 10
−6, which is several orders of magnitude below any other existing high- or low-energy bound on the magnetic moment. Thus one may obtain a QED test of this fundamental quantity to a few % precision.
We derive predictions for the Nadir angle (
θ
n
) dependence of the ratio
N
μ
/
N
e
of the rates of the
μ-like and
e-like multi-GeV events measured in water-Čerenkov detectors in the case of ...3-neutrino oscillations of the atmospheric
ν
e
(
ν
̄
e
) and
ν
μ
(
ν
̄
μ
), driven by one neutrino mass squared difference, |Δ
m
2
31|∼(2.5–3.0)×10
−3 eV
2⪢Δ
m
2
21. This ratio is particularly sensitive to the Earth matter effects in the atmospheric neutrino oscillations, and thus to the values of sin
2
θ
13 and sin
2
θ
23,
θ
13 and
θ
23 being the neutrino mixing angle limited by CHOOZ and Palo Verde experiments and that responsible for the dominant atmospheric
ν
μ
→
ν
τ
(
ν
̄
μ→
ν
̄
τ
) oscillations. It is also sensitive to the type of neutrino mass spectrum which can be with normal (Δ
m
2
31>0) or with inverted (Δ
m
2
31<0) hierarchy. We show that for sin
2
θ
13≳0.01, sin
2
θ
23≳0.5 and at cos
θ
n
≳0.4, the Earth matter effects modify substantially the
θ
n
-dependence of the ratio
N
μ
/
N
e
and in a way which cannot be reproduced with sin
2
θ
13=0 and a different value of sin
2
θ
23. For normal hierarchy the effects can be as large as ∼25% for cos
θ
n
∼(0.5–0.8), can reach ∼35% in the Earth core bin cos
θ
n
∼(0.84–1.0), and might be observable. They are typically by ∼10% smaller in the inverted hierarchy case. An observation of the Earth matter effects in the Nadir angle distribution of the ratio
N
μ
/
N
e
would clearly indicate that sin
2
θ
13≳0.01 and sin
2
θ
23≳0.50.
We calculate the density matrix for the decay of a polarised top quark into a polarised
W boson and a massive
b quark, for the most general
Wtb vertex arising from dimension-six gauge-invariant ...effective operators. We show that, in addition to the well-known
W helicity fractions, for polarised top decays it is worth defining and studying the transverse and normal
W polarisation fractions, that is, the
W polarisation along two directions orthogonal to its momentum. In particular, a rather simple forward–backward asymmetry in the normal direction is found to be very sensitive to complex phases in one of the
Wtb anomalous couplings. This asymmetry, which indicates a normal
W polarisation, can be generated for example by a P-odd, T-odd transition electric dipole moment. We also investigate the angular distribution of decay products in the top quark rest frame, calculating the spin analysing powers for a general
Wtb vertex. Finally we show that, using a combined fit to top decay observables and the
tW cross section, at LHC it will be possible to obtain model-independent measurements of all the (complex)
Wtb couplings as well as the single top polarisation. Implications for spin correlations in top pair production are also discussed.
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