Neutrino Magnetic Moments in the Standard Model and Beyond

This thesis presents the theory describing the magnetic moments of Dirac and Majorana neutrinos, including a systematic method for extracting the neutrino magnetic moments from a given theory using electromagnetic form factors. In the standard electroweak interactions, neutrino magnetic moments are suppressed by the small neutrino masses. Theories beyond the Standard Model which overcome this suppression lead to unacceptably large loop corrections to the neutrino masses, necessitating fine-tuning of model parameters. This model building issue, and a mechanism for avoiding it using a global symmetry, are discussed. The excess in electron recoil events reported by the XENON1T collaboration may be interpreted as a neutrino magnetic moment many orders of magnitude above the Standard Model prediction. Adopting the interpretation of this excess as a transition magnetic moment from an active neutrino to a sub-MeV sterile neutrino, leptoquark models with couplings to right-chiral neutrinos are explored. A recently proposed scalar leptoquark model, which generates large magnetic moments without fine-tuning, is investigated. A vector leptoquark model is proposed to simultaneously explain a large neutrino magnetic moment and recent data on lepton flavor universality violating observables. If fine-tuning of the neutrino mass is accepted, the model can accommodate the desired observables simultaneously.Masteroppgave i fysikkPHYS399MAMN-PHY

Neutrino Magnetic Moments in the Standard Model and Beyond

This thesis presents the theory describing the magnetic moments of Dirac and Majorana neutrinos, including a systematic method for extracting the neutrino magnetic moments from a given theory using electromagnetic form factors. In the standard electroweak interactions, neutrino magnetic moments are suppressed by the small neutrino masses. Theories beyond the Standard Model which overcome this suppression lead to unacceptably large loop corrections to the neutrino masses, necessitating fine-tuning of model parameters. This model building issue, and a mechanism for avoiding it using a global symmetry, are discussed. The excess in electron recoil events reported by the XENON1T collaboration may be interpreted as a neutrino magnetic moment many orders of magnitude above the Standard Model prediction. Adopting the interpretation of this excess as a transition magnetic moment from an active neutrino to a sub-MeV sterile neutrino, leptoquark models with couplings to right-chiral neutrinos are explored. A recently proposed scalar leptoquark model, which generates large magnetic moments without fine-tuning, is investigated. A vector leptoquark model is proposed to simultaneously explain a large neutrino magnetic moment and recent data on lepton flavor universality violating observables. If fine-tuning of the neutrino mass is accepted, the model can accommodate the desired observables simultaneously

Effective impedance for the threshold of loss of Landau damping

Loss of Landau damping (LLD) in the longitudinal plane is an important intensity limitation in existing and future hadron accelerators. One of the outcomes of the recent study [I. Karpov, T. Argyropoulos, and E. Shaposhnikova. Phys. Rev. Accel. Beams, 24, 011002, 2021] is an expression to estimate an effective impedance for the evaluation of the LLD threshold. In this project, the applicability of the formula was investigated for an impedance model given by a sum of broadband and narrowband resonators. Agreement at below 70% error was achieved by using a new method for choosing the truncation point in the sum over harmonics. Applying the new method to the SPS impedance, the LLD threshold was predicted with a maximum error of 40% in a wide range of bunch lengths

Bremsstrahlung as a probe of baryon stopping in heavy-ion collisions

Abstract In collisions between heavy ions at ultra-relativistic energies the participating protons lose energy, which is converted into new particles. As the protons slow down, they emit bremsstrahlung radiation. The yield and angular distribution of the emitted radiation are sensitive probes of how much energy the incoming protons have lost. In this paper, the spectrum of bremsstrahlung radiation is calculated for different stopping scenarios, and the results are compared with the expected yield of photons from hadronic interactions

New Analytical Criteria for Loss of Landau Damping in Longitudinal Plane

Landau damping is a very important stabilization mechanism of beams in circular hadron accelerators. In the longitudinal plane, Landau damping is lost when the coherent mode is outside of the incoherent synchrotron frequency spread. In this paper, the threshold for loss of Landau damping (LLD) for constant inductive impedance Im/ is derived using the Lebedev matrix equation (1968). The results are confirmed by direct numerical solutions of the Lebedev equation and using the Oide-Yokoya method (1990). For more realistic impedance models of the ring, new definitions of an effective impedance and the corresponding cutoff frequency are introduced which allow using the same analytic expression for the LLD threshold. We also demonstrate that this threshold is significantly overestimated by the Sacherer formalism based on the previous definition of an effective impedance using the eigenfunctions of the coherent modes

First measurement of the ∣t∣|t|-dependence of incoherent J/ψ\psi photonuclear production

International audienceThe first measurement of the cross section for incoherent photonuclear production of J/$\psi$ vector meson as a function of the Mandelstam $|t|$ variable is presented. The measurement was carried out with the ALICE detector at midrapidity, $|y|<0.8$, using ultra-peripheral collisions of Pb nuclei at a centre-of-mass energy per nucleon pair $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV. This rapidity interval corresponds to a Bjorken-$x$ range $(0.3$$-$$1.4)\times 10^{-3}$. Cross sections are reported in five $|t|$ intervals in the range $0.04<|t|<1$~GeV$^2$ and compared to the predictions of different models. Models that ignore quantum fluctuations of the gluon density in the colliding hadron predict a $|t|$-dependence of the cross section much steeper than in data. The inclusion of such fluctuations in the same models provides a better description of the data

Measurement of Non-prompt D0\rm D^0-meson Elliptic Flow in Pb-Pb Collisions at sNN\sqrt{s_{\rm NN}} = 5.02 TeV

International audienceThe elliptic flow ($v_2$) of $\rm D^0$ mesons from beauty-hadron decays (non-prompt $\rm D^0$) was measured in midcentral (30-50%) Pb-Pb collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{\rm NN}}$ = 5.02 TeV with the ALICE detector at the LHC. The $\rm D^0$ mesons were reconstructed at midrapidity ($|y|<0.8$) from their hadronic decay $\mathrm{D^0 \to K^-\pi^+}$, in the transverse momentum interval $2 < p_{\rm T} < 12$ GeV/$c$. The result indicates a positive $v_2$ for non-prompt $\rm D^0$ mesons with a significance of 2.7$\sigma$. The non-prompt $\rm D^0$-meson $v_2$ is lower than that of prompt non-strange D mesons with 3.2$\sigma$ significance in $2 < p_{\rm T} < 8$ GeV/$c$, and compatible with the $v_2$ of beauty-decay electrons. Theoretical calculations of beauty-quark transport in a hydrodynamically expanding medium describe the measurement within uncertainties

Skewness and kurtosis of mean transverse momentum fluctuations at the LHC energies

International audienceThe first measurements of skewness and kurtosis of mean transverse momentum ($\langle p_\mathrm{T}\rangle$) fluctuations are reported in Pb$-$Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV, Xe$-$Xe collisions at $\sqrt{s_\mathrm{NN}}$$=$ 5.44 TeV and pp collisions at $\sqrt{s} = 5.02$ TeV using the ALICE detector. The measurements are carried out as a function of system size $\langle \mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta\rangle_{|\eta|<0.5}^{1/3}$, using charged particles with transverse momentum ($p_\mathrm{T}$) and pseudorapidity ($\eta$), in the range $0.2 < p_\mathrm{T} < 3.0$ GeV/$c$ and $|\eta| < 0.8$, respectively. In Pb$-$Pb and Xe$-$Xe collisions, positive skewness is observed in the fluctuations of $\langle p_\mathrm{T}\rangle$ for all centralities, which is significantly larger than what would be expected in the scenario of independent particle emission. This positive skewness is considered a crucial consequence of the hydrodynamic evolution of the hot and dense nuclear matter created in heavy-ion collisions. Furthermore, similar observations of positive skewness for minimum bias pp collisions are also reported here. Kurtosis of $\langle p_\mathrm{T}\rangle$ fluctuations is found to be in good agreement with the kurtosis of Gaussian distribution, for most central Pb$-$Pb collisions. Hydrodynamic model calculations with MUSIC using Monte Carlo Glauber initial conditions are able to explain the measurements of both skewness and kurtosis qualitatively from semicentral to central collisions in Pb--Pb system. Color reconnection mechanism in PYTHIA8 model seems to play a pivotal role in capturing the qualitative behavior of the same measurements in pp collisions

Photoproduction of K+^{+}K−^{-} pairs in ultra-peripheral collisions

International audienceK$^{+}$K$^{-}$ pairs may be produced in photonuclear collisions, either from the decays of photoproduced $\phi (1020)$ mesons, or directly as non-resonant K$^{+}$K$^{-}$ pairs. Measurements of K$^{+}$K$^{-}$ photoproduction probe the couplings between the $\phi (1020)$ and charged kaons with photons and nuclear targets. We present the first measurement of coherent photoproduction of K$^{+}$K$^{-}$ pairs on lead ions in ultra-peripheral collisions using the ALICE detector, including the first investigation of direct K$^{+}$K$^{-}$ production. There is significant K$^{+}$K$^{-}$ production at low transverse momentum, consistent with coherent photoproduction on lead targets. In the mass range $1.1 < M_{\rm{KK}} < 1.4$ GeV/$c^2$ above the $\phi (1020)$ resonance, for rapidity $|y_{\rm{KK}}|<0.8$ and $p_{\rm T,KK} < 0.1$ GeV/$c$, the measured coherent photoproduction cross section is $\mathrm{d}\sigma/\mathrm{d}y$ = 3.37 $\pm\ 0.61$ (stat.) $\pm\ 0.15$ (syst.) mb. The centre-of-mass energy per nucleon of the photon-nucleus (Pb) system $W_{\gamma \mathrm{Pb, n}}$ ranges from 33 to 188 GeV, far higher than previous measurements on heavy-nucleus targets. The cross section is larger than expected for $\phi (1020)$ photoproduction alone. The mass spectrum is fit to a cocktail consisting of $\phi (1020)$ decays, direct K$^{+}$K$^{-}$ photoproduction, and interference between the two. The confidence regions for the amplitude and relative phase angle for direct K$^{+}$K$^{-}$ photoproduction are presented

Photoproduction of K+^{+}K−^{-} pairs in ultra-peripheral collisions

International audienceK$^{+}$K$^{-}$ pairs may be produced in photonuclear collisions, either from the decays of photoproduced $\phi (1020)$ mesons, or directly as non-resonant K$^{+}$K$^{-}$ pairs. Measurements of K$^{+}$K$^{-}$ photoproduction probe the couplings between the $\phi (1020)$ and charged kaons with photons and nuclear targets. We present the first measurement of coherent photoproduction of K$^{+}$K$^{-}$ pairs on lead ions in ultra-peripheral collisions using the ALICE detector, including the first investigation of direct K$^{+}$K$^{-}$ production. There is significant K$^{+}$K$^{-}$ production at low transverse momentum, consistent with coherent photoproduction on lead targets. In the mass range $1.1 < M_{\rm{KK}} < 1.4$ GeV/$c^2$ above the $\phi (1020)$ resonance, for rapidity $|y_{\rm{KK}}|<0.8$ and $p_{\rm T,KK} < 0.1$ GeV/$c$, the measured coherent photoproduction cross section is $\mathrm{d}\sigma/\mathrm{d}y$ = 3.37 $\pm\ 0.61$ (stat.) $\pm\ 0.15$ (syst.) mb. The centre-of-mass energy per nucleon of the photon-nucleus (Pb) system $W_{\gamma \mathrm{Pb, n}}$ ranges from 33 to 188 GeV, far higher than previous measurements on heavy-nucleus targets. The cross section is larger than expected for $\phi (1020)$ photoproduction alone. The mass spectrum is fit to a cocktail consisting of $\phi (1020)$ decays, direct K$^{+}$K$^{-}$ photoproduction, and interference between the two. The confidence regions for the amplitude and relative phase angle for direct K$^{+}$K$^{-}$ photoproduction are presented