Search

The Fermilab E989 Muon g-2 experiment's goal is to measure the anomalous magnetic dipole moment of the muon, $a_\mu$ with a precision of 140 ppb to test the prediction of $a_\mu$ in the Standard Model (SM) of subatomic physics. The Brookhaven National Laboratory (BNL) experiment E821, the most recent previous muon g-2 measurement, produced a result in 2005 with a precision of 0.54 ppm, that differed by 3.5 to 3.7 $\sigma$ from the SM prediction. After more than 10 years, Fermilab E989 continued the BNL measurement, taking the first physics data in 2018. At the time of this writing, Run 6 is ongoing and measurements of Runs 1 through Run 5 are completed. The targeted 4-fold improvement in precision would yield an above 5 sigma tension assuming the central values don't change, opening the possibility of discovery of physics beyond the Standard Model. To reach the goal of 140 ppb, E989 aims for 100 ppb statistical and 100 ppb systematical uncertainties. In order to measure $a_\mu$, there are two major observables needed: $\omega_a$, the anomalous precession frequency, and $\Tilde{\omega}'_p$, the average magnetic field weighted by the muon distribution around the 14-meter diameter storage ring, determined at a 70 ppb level. The field is precisely mapped using a field mapper, which carries 17 NMR probes, running around the muon storage region every 2 or 3 days. Calibration of these 17 NMR probes to the absolute probe, in-situ water-based calibration probe, is crucial for accurate measurements. The field's drift between the field maps is tracked using 378 NMR probes installed at fixed positions around the outside of the muon storage ring. The result of the Run 1 dataset was published in April 2021 and agreed with the BNL experiment. Analysis of Run 2 and 3 data is nearing completion as of this writing. This dissertation discusses the experiment, and detailed methods applied in evaluating the systematic uncertainties for the magnetic field measurement with a focus on Run 2 and 3.

We study an attractive scenario, "Sleptonic SUSY", which reconciles the $125$ GeV Higgs scalar and the non-observation of superpartners thus far with potentially pivotal roles for slepton phenomenology: providing viable ongoing targets for LHC discovery, incorporating a co-annihilation partner for detectable thermal relic dark matter, and capable of mediating the potential muon $g-2$ anomaly. This is accomplished by a modestly hierarchical spectrum, with sub-TeV sleptons and electroweakinos and with multi-TeV masses for the other new states. We study new elements in the UV MSSM realization of Sleptonic SUSY based on higher-dimensional sequestering and the synergy between the resulting gaugino-mediation, hypercharge $D$-term mediation and Higgs-mediation of SUSY-breaking, so as to more fully capture the range of possibilities. This framework stands out by harmoniously solving the flavor, CP and $\mu - B\mu$ problems of the supersymmetric paradigm. We discuss its extension to orbifold GUTs, including gauge-coupling and $b$-tau unification. We also develop a non-minimal model with extra Higgs fields, in which the electroweak vacuum is more readily cosmologically stable against decay to a charge-breaking vacuum, allowing a broader range of sleptonic spectra than in the MSSM alone. We survey the rich set of signals possible at the LHC and future colliders, covering both $R$-parity conservation and violation, as well as for dark matter detection. While the multi-TeV squarks imply a Little Hierarchy Problem, intriguingly, small changes in parameter space to improve naturalness result in dramatic phase transitions to either electroweak-preservation or charge-breaking. In a Multiverse setting, the modest unnaturalness may then be explained by the "principle of living dangerously"., Comment: 56 pages, 4 figures. v3: journal version

Since the heavy neutrinos of the inverse seesaw mechanism mix largely with the standard ones, the charged currents formed with them and the muons have the potential of generating robust and positive contribution to the anomalous magnetic moment of the muon. However, bounds from the non-unitary in the leptonic mixing matrix may restrict so severely the parameters of the mechanism that, depending on the framework under which the mechanism is implemented, may render it unable to explain the recent muon g-2 result. In this paper we show that this happens when we implement the mechanism into the standard model and into two versions of the 3-3-1 models.

We explore a class of models which can provide a common origin for the recently observed evidence for lepton flavor universality violation in b→sl+l− decays, the dark matter (DM) problem, and the long-standing muon (g−2) anomaly. In particular, both anomalies in the B meson decays and the muon (g−2) can be explained by the additional one-loop diagrams with DM candidates. We first classify several simple models according to the new fields’ quantum numbers. We then focus on a specific promising model and perform a detailed study of both DM and flavor physics. A random scan over the relevant parameter space reveals that there is indeed a large parameter space which can explain the three new physics phenomena simultaneously, while satisfying all other flavor and DM constraints. Finally, we discuss some of the possible new physics signatures at the Large Hadron Collider.

The Muon g –2 experiment at Fermilab (E989) plans to measure the muon anomalous magnetic moment to a precision of 140 parts per billion (ppb), which corresponds to a total uncertainty of 1 . 6 × 1 0 − 10 . To achieve this level of precision the experiment must detect more than 1 . 8 × 1 0 11 decay positrons by using the 24 calorimeters distributed around the muon storage ring. Each calorimeter consists of 54 Pb F 2 crystals read out by SiPMs. The response of each of the 1296 channels must be calibrated and monitored to keep uncertainties due to gain fluctuations at the sub-per mil level in the time interval corresponding to one beam fill ( 700 μ s ) and at the sub-percent level on longer time scales. These requirements are much more demanding than those needed by most high energy physics experiments. This paper presents a novel laser-based calibration system that distributes light to all calorimeter cells, while allowing one to correct for laser intensity fluctuations and to monitor the distribution chain stability at unprecedented levels of accuracy. Results on the system performance during the first few months of stored muon operation in 2018 are also presented.

In this thesis we use effective field thory methods and models for low energy QCD in two different contexts. One is direct calculation of contributions to the anomalous magnetic moment of the muon, muon g-2. The other is estimates of systematic sources of uncertainty in lattice QCD simulations. The work is presented in five papers. Papers II, IV and V describe calculations for muon g-2 and papers I, III and V contain estimates of various systematic effects in lattice QCD simulations.Paper I deals with the use of twisted boundary conditions. Using chpt we calculate one loop effects of twisted boundary conditions for a number of different observables. Furthermore, we show how the direction dependence of masses, which shows up when using twisted boundary conditions, should be taken into account in order to fulfill Ward identities.Twisted boundary conditions together with other effects are considered in papers III and V as well. In paper V we use partially twisted partially quenched chpt at two loops to estimate the systematic uncertainties in hadronic vacuum polarization which is relevant for muon g-2. In paper III we estimate systematic uncertainties for Kl3 decays, which are relevant for the CKM matrix element Vus, using partially twisted partially quenched rooted staggered chpt at one loop. In paper II we use several different models to compute the pion loop contribution to hadronic light-by-light scattering. Most models are inspired by vector meson dominance but we try to go beyond that and include also the lightest axial vector meson, a1. We also present an estimate of the ratio of disconnected to connected contributions to hadronic light-by-light scattering relevant for lattice QCD. In paper IV we use chpt to estimate the ratio between disconnected and connected contributions to hadronic vacuum polarization. This was studied in earlier work at one loop. We give an underlying reason for their result and show that the ratio holds for a large part of the higher loop corrections. We also discuss corrections to the ratio.

We present a frequentist analysis of the parameter space of the pMSSM10, in which the following 10 soft SUSY-breaking parameters are specified independently at the mean scalar top mass scale Msusy = Sqrt[M_stop1 M_stop2]: the gaugino masses M_{1,2,3}, the 1st-and 2nd-generation squark masses M_squ1 = M_squ2, the third-generation squark mass M_squ3, a common slepton mass M_slep and a common trilinear mixing parameter A, the Higgs mixing parameter mu, the pseudoscalar Higgs mass M_A and tan beta. We use the MultiNest sampling algorithm with 1.2 x 10^9 points to sample the pMSSM10 parameter space. A dedicated study shows that the sensitivities to strongly-interacting SUSY masses of ATLAS and CMS searches for jets, leptons + MET signals depend only weakly on many of the other pMSSM10 parameters. With the aid of the Atom and Scorpion codes, we also implement the LHC searches for EW-interacting sparticles and light stops, so as to confront the pMSSM10 parameter space with all relevant SUSY searches. In addition, our analysis includes Higgs mass and rate measurements using the HiggsSignals code, SUSY Higgs exclusion bounds, the measurements B-physics observables, EW precision observables, the CDM density and searches for spin-independent DM scattering. We show that the pMSSM10 is able to provide a SUSY interpretation of (g-2)_mu, unlike the CMSSM, NUHM1 and NUHM2. As a result, we find (omitting Higgs rates) that the minimum chi^2/dof = 20.5/18 in the pMSSM10, corresponding to a chi^2 probability of 30.8 %, to be compared with chi^2/dof = 32.8/24 (31.1/23) (30.3/22) in the CMSSM (NUHM1) (NUHM2). We display 1-dimensional likelihood functions for SUSY masses, and show that they may be significantly lighter in the pMSSM10 than in the CMSSM, NUHM1 and NUHM2. We discuss the discovery potential of future LHC runs, e+e- colliders and direct detection experiments., Comment: 47 pages, 29 figures

We make a frequentist analysis of the parameter space of the NUHM2, in which the soft supersymmetry (SUSY)-breaking contributions to the masses of the two Higgs multiplets, $m^2_{H_{u,d}}$, vary independently from the universal soft SUSY-breaking contributions $m^2_0$ to the masses of squarks and sleptons. Our analysis uses the MultiNest sampling algorithm with over $4 \times 10^8$ points to sample the NUHM2 parameter space. It includes the ATLAS and CMS Higgs mass measurements as well as their searches for supersymmetric jets + MET signals using the full LHC Run~1 data, the measurements of $B_s \to \mu^+ \mu^-$ by LHCb and CMS together with other B-physics observables, electroweak precision observables and the XENON100 and LUX searches for spin-independent dark matter scattering. We find that the preferred regions of the NUHM2 parameter space have negative SUSY-breaking scalar masses squared for squarks and sleptons, $m_0^2 < 0$, as well as $m^2_{H_u} < m^2_{H_d} < 0$. The tension present in the CMSSM and NUHM1 between the supersymmetric interpretation of $g_\mu - 2$ and the absence to date of SUSY at the LHC is not significantly alleviated in the NUHM2. We find that the minimum $\chi^2 = 32.5$ with 21 degrees of freedom (dof) in the NUHM2, to be compared with $\chi^2/{\rm dof} = 35.0/23$ in the CMSSM, and $\chi^2/{\rm dof} = 32.7/22$ in the NUHM1. We find that the one-dimensional likelihood functions for sparticle masses and other observables are similar to those found previously in the CMSSM and NUHM1. We make a frequentist analysis of the parameter space of the NUHM2, in which the soft supersymmetry (SUSY)-breaking contributions to the masses of the two Higgs multiplets, $m^2_{H_{u,d}}$ , vary independently from the universal soft SUSY-breaking contributions $m^2_0$ to the masses of squarks and sleptons. Our analysis uses the MultiNest sampling algorithm with over $4 \times 10^8$ points to sample the NUHM2 parameter space. It includes the ATLAS and CMS Higgs mass measurements as well as the ATLAS search for supersymmetric jets + ${/\!\!E}_T$ signals using the full LHC Run 1 data, the measurements of $\mathrm{BR}(B_s \rightarrow \mu ^+\mu ^-)$ by LHCb and CMS together with other B-physics observables, electroweak precision observables and the XENON100 and LUX searches for spin-independent dark-matter scattering. We find that the preferred regions of the NUHM2 parameter space have negative SUSY-breaking scalar masses squared at the GUT scale for squarks and sleptons, $m_0^2 < 0$ , as well as $m^2_{H_u} < m^2_{H_d} < 0$ . The tension present in the CMSSM and NUHM1 between the supersymmetric interpretation of $(g-2)_\mu $ and the absence to date of SUSY at the LHC is not significantly alleviated in the NUHM2. We find that the minimum $\chi ^2 = 32.5$ with 21 degrees of freedom (dof) in the NUHM2, to be compared with $\chi ^2/\mathrm{dof} = 35.0/23$ in the CMSSM, and $\chi ^2/\mathrm{dof} = 32.7/22$ in the NUHM1. We find that the one-dimensional likelihood functions for sparticle masses and other observables are similar to those found previously in the CMSSM and NUHM1. We make a frequentist analysis of the parameter space of the NUHM2, in which the soft supersymmetry (SUSY)-breaking contributions to the masses of the two Higgs multiplets, $m^2_{H_{u,d}}$, vary independently from the universal soft SUSY-breaking contributions $m^2_0$ to the masses of squarks and sleptons. Our analysis uses the MultiNest sampling algorithm with over $4 \times 10^8$ points to sample the NUHM2 parameter space. It includes the ATLAS and CMS Higgs mass measurements as well as their searches for supersymmetric jets + MET signals using the full LHC Run~1 data, the measurements of $B_s \to \mu^+ \mu^-$ by LHCb and CMS together with other B-physics observables, electroweak precision observables and the XENON100 and LUX searches for spin-independent dark matter scattering. We find that the preferred regions of the NUHM2 parameter space have negative SUSY-breaking scalar masses squared for squarks and sleptons, $m_0^2 < 0$, as well as $m^2_{H_u} < m^2_{H_d} < 0$. The tension present in the CMSSM and NUHM1 between the supersymmetric interpretation of $g_\mu - 2$ and the absence to date of SUSY at the LHC is not significantly alleviated in the NUHM2. We find that the minimum $\chi^2 = 32.5$ with 21 degrees of freedom (dof) in the NUHM2, to be compared with $\chi^2/{\rm dof} = 35.0/23$ in the CMSSM, and $\chi^2/{\rm dof} = 32.7/22$ in the NUHM1. We find that the one-dimensional likelihood functions for sparticle masses and other observables are similar to those found previously in the CMSSM and NUHM1.

International audience; These pages, based on my talk at the Montpellier 14th International Conference in QCD, provide us with a short update of the Standard Model contributions to the Muon Anomalous Magnetic Moment.

The muon g-2 experiment at Brookhaven National Laboratory has the goal of determining the muon anomalous g-value a(mu) ( = (g - 2)/2) to the very high precision of 0.35 parts per million and thus requires a storage ring magnet with great stability and homogeniety. A superferric storage ring with a radius of 7.11 m and a magnetic field of 1.45 T has been constructed in which the field quality is largely determined by the iron, and the excitation is provided by superconducting coils operating at a current of 5200 A. The storage ring has been constructed with maximum attention to azimuthal symmetry and to tight mechanical tolerances and with many features to allow obtaining a homogenous magnetic field. The fabrication of the storage ring, its cryogenics and quench protection systems, and its initial testing and operation are described. (C) 2001 Elsevier Science B.V. All rights reserved.

The Muon $g-2$ experiment, E989, is currently taking data at Fermilab with the aim of reducing the experimental error on the muon anomaly by a factor of four and possibly clarifying the current discrepancy with the theoretical prediction. A central component of this four-fold improvement in precision is the laser calibration system of the calorimeters, which has to monitor the gain variations of the photo-sensors with a 0.04\% precision on the short-term ($\sim 1\,$ms). This is about one order of magnitude better than what has ever been achieved for the calibration of a particle physics calorimeter. The system is designed to monitor also long-term gain variations, mostly due to temperature effects, with a precision below the per mille level. This article reviews the design, the implementation and the performance of the Muon $g-2$ laser calibration system, showing how the experimental requirements have been met., 33 pages,24 figures. Matches the published version

The recent measurement of the muon $g$-2 at Fermilab confirms the previous Brookhaven result. The leading hadronic vacuum polarization (HVP) contribution to the muon $g$-2 represents a crucial ingredient to establish if the Standard Model prediction differs from the experimental value. A recent lattice QCD result by the BMW collaboration shows a tension with the low-energy $e^+e^- \to \text{hadrons}$ data which are currently used to determine the HVP contribution. We refer to this tension as the new muon $g$-2 puzzle. In this Letter we consider the possibility that new physics contributes to the $e^+e^- \to \text{hadrons}$ cross-section. This scenario could, in principle, solve the new muon $g$-2 puzzle. However, we show that this solution is excluded by a number of experimental constraints., 6 pages, 4 figures. Version to appear in Physics Letters B