Searcharxiv⌕ Search

arXiv subjects

L. Calibbi

Publications and source records attributed to L. Calibbi.

17 recordsLinked to original sources
arXiv2022

Mu2e-II: Muon to electron conversion with PIP-II

An observation of Charged Lepton Flavor Violation (CLFV) would be unambiguous evidence for physics beyond the Standard Model. The Mu2e and COMET experiments, under construction, are designed to push the sensitivity to CLFV in the mu to e conversion process to unprecedented levels. Whether conversion is observed or not, there is a strong case to be made for further improving sensitivity, or for examining the process on additional target materials. Mu2e-II is a proposed upgrade to Mu2e, with at least an additional order of magnitude in sensitivity to the conversion rate over Mu2e. The approach and challenges for this proposal are summarized. Mu2e-II may be regarded as the next logical step in a continued high-intensity muon program at FNAL.

hep-ex↗
arXiv2022

A New Charged Lepton Flavor Violation Program at Fermilab

The muon has played a central role in establishing the Standard Model of particle physics, and continues to provide valuable information about the nature of new physics. A new complex at Fermilab, the Advanced Muon Facility, would provide the world's most intense positive and negative muon beams by exploiting the full potential of PIP-II and the Booster upgrade. This facility would enable a broad muon physics program, including studies of charged lepton flavor violation, muonium-antimuonium transitions, a storage ring muon EDM experiment, and muon spin rotation experiments. This document describes a staged realization of this complex, together with a series of next-generation experiments to search for charged lepton flavor violation.

hep-ex↗
arXiv2020

Future Physics Programme of BESIII

There has recently been a dramatic renewal of interest in the subjects of hadron spectroscopy and charm physics. This renaissance has been driven in part by the discovery of a plethora of charmonium-like $XYZ$ states at BESIII and $B$ factories, and the observation of an intriguing proton-antiproton threshold enhancement and the possibly related $X(1835)$ meson state at BESIII, as well as the threshold measurements of charm mesons and charm baryons. We present a detailed survey of the important topics in tau-charm physics and hadron physics that can be further explored at BESIII over the remaining lifetime of BEPCII operation. This survey will help in the optimization of the data-taking plan over the coming years, and provides physics motivation for the possible upgrade of BEPCII to higher luminosity.

hep-ex↗
arXiv2012

Status of Supersymmetric Seesaw in SO(10) models

We report on the status of supersymmetric seesaw models in the light of recent experimental results on $μ\to e + γ$, $θ_{13}$ and the light Higgs mass at the LHC. SO(10)-like relations are assumed for neutrino Dirac Yukawa couplings and two cases of mixing, one large, PMNS-like, and another small, CKM-like, are considered. It is shown that for the large mixing case, only a small range of parameter space with moderate $\tan β$ is still allowed. This remaining region can be ruled out by an order of magnitude improvement in the current limit on BR($μ\to e + γ$). We also explore a model with non-universal Higgs mass boundary conditions at the high scale. It is shown that the renormalization group induced flavor violating slepton mass terms are highly sensitive to the Higgs boundary conditions. Depending on the choice of the parameters, they can either lead to strong enhancements or cancellations within the flavor violating terms. Such cancellations might relax the severe constraints imposed by lepton flavor violation compared to mSUGRA. Nevertheless for a large region of parameter space the predicted rates lie within the reach of future experiments once the light Higgs mass constraint is imposed. We also update the potential of the ongoing and future experimental searches for lepton flavor violation in constraining the supersymmetric parameter space.

hep-ph↗
arXiv2012

Flavour and Collider Interplay for SUSY at LHC7

The current 7 TeV run of the LHC experiment shall be able to probe gluino and squark masses up to values larger than 1 TeV. Assuming that hints for SUSY are found in the jets plus missing energy channel by the end of a 5 fb$^{-1}$ run, we explore the flavour constraints on three models with a CMSSM-like spectrum: the CMSSM itself, a Seesaw extension of the CMSSM, and Flavoured CMSSM. In particular, we focus on decays that might have been measured by the time the run is concluded, such as $B_s\toμμ$ and $μ\to eγ$. We also analyse constraints imposed by neutral meson bounds and electric dipole moments. The interplay between collider and flavour experiments is explored through the use of three benchmark scenarios, finding the flavour feedback useful in order to determine the model parameters and to test the consistency of the different models.

hep-ph↗
arXiv2011

SUSY Flavour at LHC7

The current 7 TeV run of the LHC experiment shall be able to probe gluino and squark masses up to values of about 1 TeV. Assuming that hints for SUSY are found by the end of a 2 fb$^{-1}$ run, we explore the flavour constraints on the parameter space of the CMSSM, with and without massive neutrinos. In particular, we focus on decays that might have been measured by the time the run is concluded, such as $B_s\toμμ$ and $μ\to eγ$. We also briefly show the impact such a collider--flavour interplay would have on a Flavoured CMSSM.

hep-ph↗
arXiv2009

FCNC and CP Violation Observables in a SU(3)-flavoured MSSM

A non-Abelian flavour symmetry in a minimal supersymmetric standard model can explain the flavour structures in the Yukawa couplings and simultaneously solve the SUSY flavour problem. Similarly the SUSY CP problem can be solved if CP is spontaneously broken in the flavour sector. In this work, we present an explicit example of these statements with a SU(3) flavour symmetry and spontaneous CP violation. In addition, we show that it is still possible to find some significant deviation from the SM expectations as far as FCNC and CP violation are concerned. We find that large contributions can be expected in lepton flavour violating decays, as $μ\to e γ$ and $τ\to μγ$, electric dipole moments, $d_e$ and $d_n$ and kaon CP violating processes as $ε_K$. Thus, these flavoured MSSM realizations are phenomenologically sensitive to the experimental searches in the realm of flavor and CP vioation physics.

hep-ph↗
arXiv2009

SU(3) Flavour Symmetries and CP Violation

In order to satisfy current FCNC and CP violation bounds, SUSY flavour structures cannot be generic. An interesting solution to these SUSY Flavour and CP Problems lies on the use of an SU(3) family symmetry which spontaneously breaks CP symmetry. Typical observables of such a model are electric dipole moments and LFV processes. In addition, these models can give contributions to CP violation in neutral meson mixing. We show how the latter can be used to restrict the allowed SUSY parameter space, and induce correlations between LFV and EDM predictions.

hep-ph↗
arXiv2009

Consequences of a unified, anarchical model of fermion masses and mixings

We show that most features of the mass and mixing pattern of the second and third SM fermion families can be accounted for without making use of flavour symmetries or other types of flavour dynamics. We discuss the implications for flavour phenomenology, in particular for the $τ\toμγ$ decay rate, and comment on LFV effects at colliders. We show that the model can be embedded in a full SO(10) supersymmetric GUT in 5 dimensions that preserves the successful MSSM gauge coupling unification prediction for $α_s$. Interesting features of this embedding are i) the connection of one of the hierarchy parameters with the strong coupling assumption, ii) the absence of KK threshold effects on the $α_s$ prediction at one loop, and iii) the shift of the GUT scale up to about $10^{17}\GeV$. Proton decay is under control, also due to the larger GUT scale. A large atmospheric angle for normal hierarchical neutrinos is obtained in an unusual way.

hep-ph↗
arXiv2009

Gauge coupling unification, the GUT scale, and magic fields

We consider field sets that do not form complete SU(5) multiplets, but exactly preserve the one-loop MSSM prediction for $α_3(M_Z)$ independently of the value of their mass. Such fields can raise the unification scale in different ways, through a delayed convergence of the gauge couplings, a fake unified running below the GUT scale, or a postponed unification after a hoax crossing at a lower scale. The $α_3(M_Z)$ prediction is independent of the mass of the new fields, while the GUT scale often is not, which allows to vary the GUT scale. Such "magic" fields represent a useful tool in GUT model building. For example, they can be used to fix gauge coupling unification in certain two step breakings of the unified group, to suppress large KK thresholds in models with extra dimensions, or they can be interpreted as messengers of supersymmetry breaking in GMSB models.

hep-ph↗
arXiv2008

Electric dipole moments from flavoured CP violation in SUSY

The so-called supersymmetric flavour and CP problems are deeply related to the origin of flavour and hence to the origin of the SM Yukawa couplings themselves. We show that realistic SU(3) flavour symmetries with spontaneous CP violation reproducing correctly the SM Yukawa matrices can simultaneously solve both problems without ad hoc modifications of the SUSY model. We analyze the leptonic electric dipole moments and lepton flavour violation processes in these models. We show that the electron EDM and the decay mu -> e gamma are naturally within reach of the proposed experiments if the sfermion masses are measurable at the LHC.

hep-ph↗
arXiv2008

Flavour physics of leptons and dipole moments

This chapter of the report of the ``Flavour in the era of the LHC'' Workshop discusses the theoretical, phenomenological and experimental issues related to flavour phenomena in the charged lepton sector and in flavour-conserving CP-violating processes. We review the current experimental limits and the main theoretical models for the flavour structure of fundamental particles. We analyze the phenomenological consequences of the available data, setting constraints on explicit models beyond the Standard Model, presenting benchmarks for the discovery potential of forthcoming measurements both at the LHC and at low energy, and exploring options for possible future experiments.

hep-ph↗
arXiv2007

Distinguishing SUSY scenarios using τpolarisation and \tildeχ^0_1 Dark Matter

We discuss first a method of measuring $τ$ polarisation at the ILC using the 1--prong hadronic decays of the $τ$. We then show in this contribution how a study of the $\tilde τ$ sector and particularly use of decay $τ$ polarisation can offer a very good handle for distinguishing between mSUGRA and a SUSY-GUT scenario, both of which can give rise to appropriate Dark Matter.

hep-ph↗
arXiv2007

SUSY-GUTs, SUSY-Seesaw and the Neutralino Dark Matter

We will consider a SUSY-SU(5) with one right-handed neutrino with a large top like Yukawa coupling. Assuming universal soft masses at high scale we compute the low-energy spectrum and subsequently the neutralino LSP relic density taking also into consideration SU(5) as well as the see-saw running effects above the gauge coupling unification scale. We found that there exists no viable region in parameter space for $\tanβ\ler ~35$. The $\tildeτ$ coannihilation process starts becoming efficient for $\tanβ\ger 35-40$. However, this process is significantly constrained by the limited range in which the stau is lighter than the neutralino. In fact, for a given $\tanβ$ we find that there exists an upper bound on the lightest neutralino mass ($M_{χ_1^0}$) in this region. The A-pole funnel region appears at very large $\tanβ\simeq 45-50$, while the focus-point region does not make an appearance till large ($m_0,M_{1/2}$), namely a few TeV. Large $A_0$ terms at high scale can lead to extended regions consistent with WMAP constraints and remove the upper bounds in the stau coannihilation regions.

hep-ph↗
arXiv2007

Running $U_{e3}$ and BR($μ\to e +γ$) in SUSY-GUTs

In supersymmetric seesaw models based on SUSY-GUTs, it could happen that the neutrino PMNS mixing angles are related to the lepton flavour violating decay rates. In particular SO(10) frameworks, the smallest mixing angle would get directly correlated with the $μ\to e + γ$ decay amplitude. Here we study this correlation in detail considering $U_{e3}$ as a free parameter between 0 and $U_{e3}$(CHOOZ). Large radiative corrections to $U_{e3}$ present in these models, typically of the order ~$ΔU_{e3} ~\sim ~10^{-3}$ (peculiar to hierarchial neutrinos), can play a major role in enhancing the Br($μ\to e +γ$), especially when $U_{e3} \ler 10^{-3}$. For large tan$β$, even such small enhancements are sufficient to bring the associated Br($μ\to e + γ$) into realm of MEG experiment as long as SUSY spectrum lies within the range probed by LHC. On the other hand, for some (negative) values of $U_{e3}$, suppressions can occur in the branching ratio, due to cancellations among different contributions. From a top-down perspective such low values of $U_{e3}$ at the weak scale might require some partial/full cancellations between the high scale parameters of the model and the radiative corrections unless $U_{e3}$ is purely of radiative origin at the high scale. We further emphasize that in Grand Unified theories there exist additional LFV effects related to the running above the GUT scale, that are also independent on the low energy value of $U_{e3}$. These new contributions can become competitive and even dominant in some regions of the parameter space.

hep-ph↗
arXiv2006

Lepton Flavour Violation from SUSY--GUTs: Where do we stand for MEG, PRISM/PRIME and a Super Flavour factory

We analyse the complementarity between Lepton Flavour Violation (LFV) and LHC experiments in probing the Supersymmetric (SUSY) Grand Unified Theories (GUT) when neutrinos got a mass via the see--saw mechanism. Our analysis is performed in an SO(10) framework, where at least one neutrino Yukawa coupling is necessarily as large as the top Yukawa coupling. Our study thoroughly takes into account the whole RG running, including the GUT and the right handed neutrino mass scales, as well as the running of the observable neutrino spectrum. We find that the upcoming (MEG, SuperKEKB) and future (PRISM/PRIME, Super Flavour factory) LFV experiments will be able to test such SUSY framework for SUSY masses to be explored at the LHC and, in some cases, even beyond the LHC sensitivity reach.

hep-ph↗