S. Stoynev

A sample of 1.69×107 fully reconstructed π0→γe+e− decay candidates collected by the NA48/2 experiment at CERN in 2003–2004 is analyzed to search for the dark photon (A′) production in the π0→γA′ decay followed by the prompt A′→e+e− decay. No signal is observed, and an exclusion region in the plane of the dark photon mass mA′ and mixing parameter ε2 is established. The obtained upper limits on ε2 are more stringent than the previous limits in the mass range 9MeV/c2<mA′<70MeV/c2. The NA48/2 sensitivity to the dark photon production in the K±→π±A′ decay is also evaluated.

In this paper we discuss decays of the Higgs boson to quarkonia in association with a photon. We identify a new mechanism for producing such final states in Higgs decays that leads to predictions for the decay rates that differ by an order of magnitude from previous estimates. Although the branching ratios for these processes are still small, the processes are experimentally clean, and the H \to J/\psi+gamma decay should be observable at a 14 TeV LHC. We point out that quantum interference between two different production mechanisms makes the decay rates sensitive to the HQQbar couplings. Consequently, measurements of the H \to J/\psi+gamma decay rate would allow one to probe the Higgs-charm coupling directly at the LHC. We discuss the experimental prospects for the observation of these decays and for the direct measurement of the Hccbar coupling.

We show that both flavor-conserving and flavor-violating Yukawa couplings of the Higgs boson to first- and second-generation quarks can be probed by measuring rare decays of the form h->MV, where M denotes a vector meson and V indicates either gamma, W or Z. We calculate the branching ratios for these processes in both the Standard Model and its possible extensions. We discuss the experimental prospects for their observation. The possibility of accessing these Higgs couplings appears to be unique to the high-luminosity LHC and future hadron colliders, providing further motivation for those machines.

Abstract The High Luminosity Large Hadron Collider (HL-LHC) is the new flagship project of CERN. First endorsed in 2013 and approved in 2016, HL-LHC is an upgrade of the accelerator aiming to increase by a factor of ten the statistics of the LHC collisions at the horizon of 2035–2040. HL-LHC relies on cutting edge technologies: among them, large aperture superconducting magnets will replace the present hardware to allow a smaller beam size in two interaction points (IPs). The project involves the construction of about 150 magnets of six different types: the quadrupole triplet, two main dipoles and three orbit correctors. The triplet, manufactured at CERN and in the USA, will consist of 30 magnets based on Nb 3 Sn technology, with an operational peak field of 11.4 T. These will be the first quadrupole Nb 3 Sn magnets installed in a particle accelerator. The other five types of magnets, all relying on Nb–Ti technology, present non-trivial challenges in the design and construction; they will be manufactured as part of in-kind contribution under the responsibility of institutes in Japan, China, Spain, and Italy. The project is now in the phase of transition between qualification through short models and prototypes and the beginning of the series construction. In this paper we review the magnet requirements, the reasons for selecting the design, the technological challenges with respect to previous projects, and we summarize the steps that have been taken to validate the baseline.

We report the results from a study of a partial sample of ∼2.3×107 K±→π±π0π0 decays recorded by the NA48/2 experiment at the CERN SPS, showing an anomaly in the π0π0 invariant mass (M00) distribution in the region around M00=2m+, where m+ is the charged pion mass. This anomaly, never observed in previous experiments, can be interpreted as an effect due mainly to the final state charge exchange scattering process π+π−→π0π0 in K±→π±π+π− decay [N. Cabibbo, Phys. Rev. Lett. 93 (2004) 121801]. It provides a precise determination of a0−a2, the difference between the ππ scattering lengths in the isospin I=0 and I=2 states. A best fit to a rescattering model [N. Cabibbo, G. Isidori, JHEP 0503 (2005) 21] corrected for isospin symmetry breaking gives (a0−a2)m+=0.268±0.010(stat)±0.004(syst), with additional external uncertainties of ±0.013 from branching ratio and theoretical uncertainties. If the correlation between a0 and a2 predicted by chiral symmetry is taken into account, this result becomes (a0−a2)m+=0.264±0.006(stat)±0.004(syst)±0.013(ext).

We report results from the analysis of the $\mbox {$\mathrm {K}^{\pm}$}\rightarrow \pi^{+} \pi^{-} \mathrm{e}^{\pm} \nu$ ( $\mbox {$\mathrm {K}_{\mathrm {e}4}$}$ ) decay by the NA48/2 collaboration at the CERN SPS, based on the total statistics of 1.13 million decays collected in 2003–2004. The hadronic form factors in the S- and P-wave and their variation with energy are obtained. The phase difference between the S- and P-wave states of the ππ system is accurately measured and allows a precise determination of $\mbox {$a_{0}^{0}$}$ and $\mbox {$a_{0}^{2}$}$ , the I = 0 and I = 2 S-wave ππ scattering lengths: $\mbox {$a_{0}^{0}$}= 0.2220 \pm 0.0128 \mbox {$\mathrm {_{stat}}$}\pm 0.0050 \mbox {$\mathrm {_{syst}}$}\pm 0.0037\mbox {$\mathrm {_{th}}$},\mbox {$a_{0}^{2}$}= -0.0432 \pm 0.0086 \mbox {$\mathrm {_{stat}}$}\pm 0.0034 \mbox {$\mathrm {_{syst}}$}\pm 0.0028\mbox {$\mathrm {_{th}}$}$ . Combination of this result with the other NA48/2 measurement obtained in the study of $\mbox {$\mbox {$\mathrm {K}^{\pm}$}\rightarrow \mbox {$\pi ^{0}$}\mbox {$\pi ^{0}$}\mbox {$\scriptstyle \pi ^{\pm }$}$}$ decays brings an improved determination of $\mbox {$a_{0}^{0}$}$ and the first precise experimental measurement of $\mbox {$a_{0}^{2}$}$ , providing a stringent test of Chiral Perturbation Theory predictions and lattice QCD calculations. Using constraints based on analyticity and chiral symmetry, even more precise values are obtained: $\mbox {$a_{0}^{0}$}=0.2196 \pm 0.0028\mbox {$\mathrm {_{stat}}$}\pm 0.0020 \mbox {$\mathrm {_{syst}}$}$ and $\mbox {$a_{0}^{2}$}= -0.0444 \pm 0.0007 \mbox {$\mathrm {_{stat}}$}\pm 0.0005 \mbox {$\mathrm {_{syst}}$}\pm 0.0008 \mbox {$\mathrm {_{ChPT}}$}$ .

We report results from a new measurement of the Ke4 decay K±→π+π-e±ν by the NA48/2 collaboration at the CERN SPS, based on a partial sample of more than 670 000 Ke4 decays in both charged modes collected in 2003. The form factors of the hadronic current (F,G,H) and ππ phase difference (δ=δs-δp) have been measured in ten independent bins of the ππ mass spectrum to investigate their variation. A sizeable acceptance at large ππ mass, a low background and a very good resolution contribute to an improved experimental accuracy, a factor two better than in the previous measurement, when extracting the ππ scattering lengths a0 0 and a0 2. Under the assumption of isospin symmetry and using numerical solutions of the Roy equations, the following values are obtained in the plane (a0 0,a0 2): a0 0=0.233±0.016stat±0.007syst,a0 2=-0.0471±0.011stat±0.004syst. The presence of potentially large isospin effects is also considered and will allow comparison with precise predictions from Chiral Perturbation Theory.

Among the components to be upgraded in LHC interaction regions for the HiLumi-LHC projects are the inner triplet (or low-β) quadrupole magnets, denoted as Q1, Q2a, Q2b, and Q3. The new quadrupole magnets, called MQXF, are based on Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn superconducting magnet technology and operate at a gradient of 132.6 T/m, with a conductor peak field of 11.4 T. Q1 and Q3 are composed of magnets (called MQXFA) fabricated by the U.S. Accelerator Upgrade Project (AUP), with a magnetic length of 4.2 m. Q2a and Q2b consist of magnets (called MQXFB) fabricated by CERN, with a magnetic length of 7.15 m. After a series of short models, constructed in close collaboration by the US and CERN, the development program is now entering in the prototyping phase, with CERN on one side and BNL, FNAL, and LBNL on the other side assembling and testing their first long magnets We provide in this paper a description of the status of the MQXF program, with a summary of the short model test results, including quench performance, and mechanics, and an update on the fabrication, assembly, and test of the long prototypes.

We report the results from a study of the full sample of ∼6.031×107 K ±→π ± π 0 π 0 decays recorded by the NA48/2 experiment at the CERN SPS. As first observed in this experiment, the π 0 π 0 invariant mass (M 00) distribution shows a cusp-like anomaly in the region around M 00=2m +, where m + is the charged pion mass. This anomaly has been interpreted as an effect due mainly to the final state charge exchange scattering process π + π −→π 0 π 0 in K ±→π ± π + π − decay. Fits to the M 00 distribution using two different theoretical formulations provide the presently most precise determination of a 0−a 2, the difference between the π π S-wave scattering lengths in the isospin I=0 and I=2 states. Higher-order π π rescattering terms, included in the two formulations, allow also an independent, though less precise, determination of a 2.

A sample of 3120 K±→π±μ+μ− decay candidates with (3.3±0.7)% background contamination has been collected by the NA48/2 experiment at the CERN SPS, allowing a detailed study of the decay properties. The branching ratio was measured to be BR=(9.62±0.25)×10−8. The form factor W(z), where z=(Mμμ/MK)2, was parameterized according to several models. In particular, the slope of the linear form factor W(z)=W0(1+δz) was measured to be δ=3.11±0.57. Upper limits of 2.9×10−2 and 2.3×10−2 on possible charge asymmetry and forward–backward asymmetry were established at 90% CL. An upper limit BR(K±→π∓μ±μ±)<1.1×10−9 was established at 90% CL for the rate of the lepton number violating decay.

A sample of 7253 $K^\pm\toπ^\pm e^+e^-(γ)$ decay candidates with 1.0% background contamination has been collected by the NA48/2 experiment at the CERN SPS, allowing a precise measurement of the decay properties. The branching ratio in the full kinematic range was measured to be ${\rm BR}=(3.11\pm0.12)\times 10^{-7}$, where the uncertainty includes also the model dependence. The shape of the form factor $W(z)$, where $z=(M_{ee}/M_K)^2$, was parameterized according to several models, and, in particular, the slope $δ$ of the linear form factor $W(z)=W_0(1+δz)$ was determined to be $δ=2.32\pm0.18$. A possible CP violating asymmetry of $K^+$ and $K^-$ decay widths was investigated, and a conservative upper limit of $2.1\times 10^{-2}$ at 90% CL was established.

About one hundred magnets of six different types shall be installed in the High Luminosity LHC (HL-LHC) in the years 2026--2028 at CERN. The magnets design, construction and test are based on CERN collaborations with institutes and industrial partners in USA, Spain, Italy, Japan and China. Three types of correctors are based on Nb–Ti technology and feature conductor peak fields in the 2 to 4 T range: for all of them the protoype phase has been successfully completed. The production is well advanced for the superferric correctors, and is starting for the canted cos theta correctors and for the nested correctors. The separation and recombination Nb–Ti dipoles D1 and D2, with a 4.5-6 T bore field range, are both in the prototype phase after the completion of the short model program. The most challenging magnet, the Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn quadrupole with conductor peak field above 11 T, is in the prototype phase at CERN and halfway through the production phase in the USA. In this paper we will give, for each type of magnet, an overview of the main achievements obtained so far and we will outline the technical points still needing validation from the prototype program.

The NA48/2 experiment at CERN collected a large sample of charged kaon decays to final states with multiple charged particles in 2003–2004. A new upper limit on the rate of the lepton number violating decay K±→π∓μ±μ± is reported: B(K±→π∓μ±μ±)<8.6×10−11 at 90% CL. Searches for two-body resonances X in K±→πμμ decays (such as heavy neutral leptons N4 and inflatons χ) are also presented. In the absence of signals, upper limits are set on the products of branching fractions B(K±→μ±N4)B(N4→πμ) and B(K±→π±X)B(X→μ+μ−) for ranges of assumed resonance masses and lifetimes. The limits are in the (10−11,10−9) range for resonance lifetimes below 100 ps.

The U.S. LHC Accelerator Research Program (LARP) and CERN combined their efforts in developing Nb3Sn magnets for the high-luminosity LHC upgrade. The ultimate goal of this collaboration is to fabricate large aperture Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn quadrupoles for the LHC interaction regions. These magnets will replace the present 70-mm-aperture NbTi quadrupole triplets for expected increase of the LHC peak luminosity up to 5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">34</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> or more. Over the past decade, LARP successfully fabricated and tested short and long models of 90 and 120-mm-aperture Nb3Sn quadrupoles. Recently, the first short model of 150-mm-diameter quadrupole MQXFS was built with coils fabricated both by LARP and CERN. The magnet performance was tested at Fermilab's vertical magnet test facility. This paper reports the test results, including the quench training at 1.9 K, ramp rate and temperature dependence, as well as protection heater studies.

The development of Nb3Sn quadrupole magnets for the High-Luminosity LHC upgrade is a joint venture between the US LHC Accelerator Research Program (LARP) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">*</sup> and CERN with the goal of fabricating large aperture quadrupoles for the LHC interaction regions (IR). The inner triplet (low-β) NbTi quadrupoles in the IR will be replaced by the stronger Nb3Sn magnets boosting the LHC program of having 10-fold increase in integrated luminosity after the foreseen upgrades. Previously, LARP conducted successful tests of short and long models with up to 120 mm aperture. The first short 150 mm aperture quadrupole model MQXFS1 was assembled with coils fabricated by both CERN and LARP. The magnet demonstrated a strong performance at Fermilab's vertical magnet test facility reaching the LHC operating limits. This paper reports the latest results from MQXFS1 tests with changed prestress levels. The overall magnet performance, including quench training and memory, ramp rate, and temperature dependence, is also summarized.

Fermilab in the framework of the U.S. Magnet Development Program (MDP) has developed a Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn dipole demonstrator for a post-LHC hadron collider. The magnet uses 60-mm aperture 4-layer shell-type graded coils. The cable in the two innermost layers has 28 strands 1.0 mm in diameter and the cable in the two outermost layers has 40 strands 0.7 mm in diameter. An innovative mechanical structure based on aluminum I-clamps and a thick stainless steel skin is used to preload Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn coils and support large Lorentz forces. The maximum field for this magnet is limited by 15 T due to mechanical considerations. The first magnet assembly was done with lower coil pre-load to achieve 14 T and minimize the risk of coil damage during assembly. This paper describes the magnet design and the details of its assembly procedure, and reports the results of its cold tests.

A search for the decay KS→π0e+e− has been made by the NA48/1 experiment at the CERN SPS accelerator. Using data collected during 89 days in 2002 with a high-intensity KS beam, 7 events were found with a background of 0.15 events. The branching fraction BR(KS→π0e+e−,mee>0.165 GeV/c2)=(3.0+1.5−1.2(stat)±0.2(syst))×10−9 has been measured. Using a vector matrix element and a form factor equal to one, the measurement gives BR(KS→π0e+e−)=(5.8+2.9−2.4)×10−9.

This Letter reports on a new high precision measurement of the form factors of the KL→π±μ∓νμ decay. The data sample of about 2.3×106 events was recorded in 1999 by the NA48 experiment at CERN. Studying the Dalitz plot density we measured a linear, λ+′=(20.5±2.2stat±2.4syst)×10−3, and a quadratic, λ+″=(2.6±0.9stat±1.0syst)×10−3 term in the power expansion of the vector form factor. No evidence was found for a second order term for the scalar form factor; the linear slope was determined to be λ0=(9.5±1.1stat±0.8syst)×10−3. Using a linear fit our results were: λ+=(26.7±0.6stat±0.8syst)×10−3 and λ0=(11.7±0.7stat±1.0syst)×10−3. A pole fit of the form factors yields: mV=(905±9stat±17syst)MeV/c2 and mS=(1400±46stat±53syst)MeV/c2.

The HL-LHC project aims at allowing to increase the collisions in the Large Hadron Collider by a factor ten in the decade 2025-2035.One essential element are the superconducting magnets around the interaction region points, where large aperture magnets will be installed to allow to further reduce the beam size in the interaction point.The core of this upgrade is the Nb3Sn triplet, made of 150 mm aperture quadrupoles of in the range of 7-8 m.The project is being shared between CERN and US Accelerator Upgrade Program, based on the same design, and on two strand technologies.The project is ending the short model phase, and entering the prototype construction.We will report on the main results of the short model program, including quench performance and field quality.A second important element is the 11 T dipole that replacing a standard dipole makes space for additional collimators.The magnet is also ending the model development and entering the prototype phase.A critical point in the design of this magnet is the large current density, allowing increasing the field from 8 to 11 T with the same coil cross-section as in the LHC dipoles.This is also the first two-in-one Nb3Sn magnet developed so far.We will report the main results on the test and the critical aspects.

With the successful test of the first two pre-series magnets the US HL-LHC Accelerator Upgrade Project has started production of the MQXFA magnets to be used in Q1/Q3 inner triplet elements of the HL-LHC. This good start comes after the test of two prototypes with limited performance, and it demonstrates the importance of learning from past issues. Therefore, in this paper we want to share the most important lessons learned so far, focusing on those which may be more interesting for similar projects. We will also present the status of MQXFA fabrication in the US.

A search for the decay KS→π0μ+μ− has been made by the NA48/1 Collaboration at the CERN SPS accelerator. The data were collected during 2002 with a high-intensity KS beam. Six events were found with a background expectation of 0.22−0.11+0.18 events. Using a vector matrix element and unit form factor, the measured branching ratio is B(KS→π0μ+μ−)=[2.9−1.2+1.5(stat)±0.2(syst)]×10−9.

The semileptonic decay of the neutral K meson, KL -> pi e nu (Ke3), was used to study the strangeness-changing weak interaction of hadrons. A sample of 5.6 million reconstructed events recorded by the NA48 experiment was used to measure the Dalitz plot density. Admitting all possible Lorentz-covariant couplings, the form factors for vector (f_+(q^2)), scalar (f_S) and tensor (f_T) interactions were measured. The linear slope of the vector form factor lambda_+ = 0.0284+-0.0007+-0.0013 and values for the ratios |f_S/f_+(0)| = 0.015^{+0.007}_{-0.010}+-0.012 and |f_T/f_+(0)| = 0.05^{+0.03}_{-0.04}+-0.03 were obtained. The values for f_S and f_T are consistent with zero. Assuming only Vector-Axial vector couplings, lambda_+ = 0.0288+-0.0004+-0.0011 and a good fit consistent with pure V-A couplings were obtained. Alternatively, a fit to a dipole form factor yields a pole mass of M = 859+-18 MeV, consistent with the K^*(892) mass.

We report on the measurement of the direct emission (DE) and interference (INT) terms of the K\pm -> \pi\pm\pi^0 g decay by the NA48/2 experiment at the CERN SPS. From the data collected during 2003 and 2004 about 600k such decay candidates have been selected. The relative amounts of DE and INT with respect to the internal bremsstrahlung (IB) contribution have been measured in the range 0<T*\pi<80 MeV: Frac_{DE} (0<T*\pi<80 MeV) = (3.32\pm 0.15_{stat} \pm 0.14_{sys})x10^{-2} Frac_{INT} (0<T*\pi<80 MeV) = (- 2.35\pm 0.35_{stat} \pm 0.39_{sys})x10^{-2}, where T*pi is the kinetic energy of the charged pion in the kaon rest frame. This is the first observation of an interference term in T*\pi decays. In addition, a limit on the CP violating asymmetry in the K^+ and K^- branching ratios for this channel has been determined to be less than 1.5x10^{-3} at 90% confidence level.

From 56 days of data taking in 2002, the NA48/1 experiment observed 6316 Ξ0→Σ+e−ν¯e candidates (with the subsequent Σ+→pπ0 decay) and 555 Ξ0¯→Σ+¯e+νe candidates with background contamination of 215±44 and 136±8 events, respectively. From these samples, the branching ratios BR(Ξ0→Σ+e−ν¯e)=(2.51±0.03stat±0.09syst)×10−4 and BR(Ξ0¯→Σ+¯e+νe)=(2.55±0.14stat±0.10syst)×10−4 were measured allowing the determination of the CKM matrix element |Vus|=0.209−0.028+0.023. Using the Particle Data Group average for |Vus| obtained in semileptonic kaon decays, we measured the ratio g1/f1=1.20±0.05 of the axial-vector to vector form factors.

We present a measurement of the ratio of the decay rates Gamma(KL -> pi+ pi-)/Gamma(KL -> pi e nu), denoted as Gamma(K2pi)/Gamma(Ke3). The analysis is based on data taken during a dedicated run in 1999 by the NA48 experiment at the CERN SPS. Using a sample of 47000 K2pi and five million Ke3 decays, we find Gamma(K2pi)/Gamma(Ke3) = (4.835 +- 0.022(stat) +- 0.016(syst)) x 10^-3. From this we derive the branching ratio of the CP violating decay KL -> pi+ pi- and the CP violation parameter |eta+-|. Excluding the CP conserving direct photon emission component KL -> pi+ pi- gamma, we obtain the results BR(KL -> pi+ pi-) = (1.941 +- 0.019) x 10^-3 and |eta+-| = (2.223 +- 0.012) x 10^-3.

Measured ratios of decay rates for ${\mathcal{R}}_{K e 3 / K2\pi}$ , ${\mathcal{R}}_{K \mu3 / K2\pi}$ and ${\mathcal{R}}_{K \mu3 / Ke3}$ are presented. These measurements are based on K± decays collected in a dedicated run in 2003 by the NA48/2 experiment at CERN. The results obtained are ${\mathcal{R}}_{K e 3 / K2\pi} = 0.2496\pm0.0009 ({\text{stat}})\pm0.0004 ({\text{syst}})$ and ${\mathcal{R}}_{K \mu3 / K2\pi} = 0.1637\pm0.0006 ({\text{stat}})\pm0.0003 ({\text{syst}})$ . Using the PDG average for the K±→π±π0 normalisation mode, both values are found to be larger than the current values given by the particle data book and lead to a larger magnitude of the |Vus| CKM element than previously accepted. When combined with the latest particle data book value of |Vud|, the result is in agreement with unitarity of the CKM matrix. In addition, a new measured value of ${\mathcal{R}}_{K \mu3 / Ke3} = 0.656\pm0.003({\text{stat}})\pm0.001({\text{syst}})$ is compared to the semi-empirical predictions based on the latest form factor measurements.

The NA48/2 experiment at CERN collected two data samples with minimum bias trigger conditions in 2003 and 2004. A measurement of the rate and dynamic properties of the rare decay K±→π±γγ from these data sets based on 149 decay candidates with an estimated background of 15.5±0.7 events is reported. The model-independent branching ratio in the kinematic range z=(mγγ/mK)2>0.2 is measured to be BMI(z>0.2)=(0.877±0.089)×10−6, and the branching ratio in the full kinematic range assuming a particular Chiral Perturbation Theory description to be B(Kπγγ)=(0.910±0.075)×10−6.

The U.S. LHC Accelerator Research Program (LARP) has been developing Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn quadrupoles of increasing performance for the high-luminosity upgrade of the large hadron collider. The 120-mm aperture high-field quadrupole (HQ) models are the last step in the R&D phase supporting the development of the new IR Quadrupoles (MQXF). Three series of HQ coils were fabricated and assembled in a shell-based support structure, progressively optimizing the design and fabrication process. The final set of coils consistently applied the optimized design solutions and was assembled in the HQ03a model. This paper reports a summary of the HQ03a test results, including training, mechanical performance, field quality, and quench studies.

The distribution of the K±→π±π+π− decays in the Dalitz plot has been measured by the NA48/2 experiment at the CERN SPS with a sample of 4.71×108 fully reconstructed events. With the standard Particle Data Group parameterization the following values of the slope parameters were obtained: g=(−21.134±0.017)%, h=(1.848±0.040)%, k=(−0.463±0.014)%. The quality and statistical accuracy of the data have allowed an improvement in precision by more than an order of magnitude, and are such as to warrant a more elaborate theoretical treatment, including pion–pion rescattering, which is in preparation.

Using the full data set of the NA48/2 experiment, the decay K+- -> pi+- e+ e- gamma is observed for the first time, selecting 120 candidates with 7.3 +- 1.7 estimated background events. With K+- -> pi+- pi0D as normalisation channel, the branching ratio is determined in a model-independent way to be Br(K+- -> pi+- e+ e- gamma, m_eegamma > 260 MeV/c^2) = (1.19 +- 0.12_stat +- 0.04_syst) x 10^-8. This measured value and the spectrum of the e+ e- gamma invariant mass allow a comparison with predictions of Chiral Perturbation Theory.

As first observed by the NA48/2 experiment at the CERN SPS, the π0π0 invariant mass (M00) distribution from K±→π±π0π0 decay shows a cusp-like anomaly at M00=2m+, where m+ is the charged pion mass. An analysis to extract the ππ scattering lengths in the isospin I=0 and I=2 states, a0 and a2, respectively, has been recently reported. In the present work the Dalitz plot of this decay is fitted to a new empirical parameterization suitable for practical purposes, such as Monte Carlo simulations of K±→π±π0π0 decays.

The U.S. LHC Accelerator Research Program (LARP) and CERN are developing high-gradient Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn magnets for the high luminosity LHC interaction regions. Magnetic measurements of the first 1.5-m long, 150-mm aperture model quadrupole, MQXFS1, were performed during magnet assembly at LBNL, as well as during cryogenic testing at Fermilab's Vertical Magnet Test Facility. This paper reports on the results of these magnetic characterization measurements, as well as on the performance of new probes developed for the tests.

The NA48/2 experiment at CERN reports the first observation of the K±→π±π0e+e− decay from an exposure of 1.7×1011 charged kaon decays recorded in 2003–2004. A sample of 4919 candidates with 4.9% background contamination allows the determination of the branching ratio in the full kinematic region, BR(K±→π±π0e+e−)=(4.24±0.14)×10−6. The study of the kinematic space shows evidence for a structure dependent contribution in agreement with predictions based on chiral perturbation theory. Several P- and CP-violating asymmetries are also evaluated.

FNAL has been developing multiple versions of flexible quench antennas (flex-QA), including some specially optimized for high sensitivity and/or high resolution, to characterize quench events and transients during current ramping in superconducting magnets. A fundamental feature in our use of these is the creation of grid-like structures of sensitive elements to cover coil surfaces, with the aim of getting precise localization of magnetic flux-change events. The flex-QA are coupled with fast data-acquisition, allowing comprehensive analysis of signals at the relevant fine time scales. In addition to arrays of various flex-QA types being used during cryogenic testing of superconducting magnets, we also are utilizing a newly developed room temperature test stand to better understand QA response characteristics. The data from actual superconducting magnet tests, warm test stand measurements, and simulation data on the same QA designs allows us to draw conclusions on operational feasibility and plan better for improvements of our sensors. In this paper we present data from the multiple tests performed and analysis results. Flex-QA designs are compared, and their features, options, and optimization discussed.

Superconducting magnet training is one of the accelerator related issues attracting attention due to significant operational costs and time budget associated to it. It is especially worrisome that magnets based on the next-generation Nb3Sn technology are affected by long training. While various efforts are underway to better understand and resolve the problem a parallel path could also be investigated, a path bypassing the issue. Following the concept of fast induced over-current during magnet powering, FNAL has developed an upgradable capacitor-based device to discharge through a superconducting magnet at quench detection or operator chosen time. The 0.4 F/1 kV device has been tested on a 1-m-long dipole-coil in a mirror magnet configuration and conclusive results on magnet training elimination have been observed. In this paper we discuss the main characteristics of the device, compare simulated response and actual performance, elaborate on test drivers and outcomes. Next steps and perspectives for future use are debated.

The US HL-LHC Accelerator Upgrade Project (AUP) is fabricating the MQXFA magnets to be used in the Q1 and Q3 Inner Triplet elements of the High Luminosity LHC (HL-LHC). This is the first production of Nb3Sn magnets for a particle accelerator, together with the MQXFB magnets for Q2a and Q2b. Here we show status and some results of MQXFA magnets fabrication and vertical test.

We report a measurement of the direct CP violation asymmetry parameter $A_g$ in charged kaon decays $K^\pm\to\pi^\pm\pi^+\pi^-$ by the NA48/2 experiment at the CERN SPS. The experiment has been designed not to be limited by systematics in the asymmetry measurement. Using $1.67\times 10^9$ such decays collected during the 2003 run, the charge asymmetry in the Dalitz plot linear slope parameter $g$ has been measured to be $A_g=(1.7\pm2.9)\times 10^{-4}$. The precision of the result is limited by the statistics used.

The European Organization for Nuclear Research (CERN) and U.S. LHC Accelerator Research Program (LARP) are jointly developing Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn quadrupole magnets to be installed in the LHC for its upgrade to higher luminosity. These magnets' quench protection system will include a combination of quench heaters attached to the coil surfaces and coupling-loss-induced quench (CLIQ) units electrically connected to the magnets. Different protection elements have been characterized separately and simultaneously by implementing them on two 1.2-m-long model quadrupole magnets, tested at Fermi National Acceleration Laboratory and CERN, and one 4-m-long mirror magnet tested at Brookhaven Nation Laboratory. After analyzing the test data, their performances have been positively evaluated. Furthermore, the electrothermal transients occurring after a quench have been simulated with the LEDET software and the results are compared to experimental results. The preferred quench protection system configuration relies both on heaters and CLIQ. This solution is based on electrically robust components, achieves an effective reduction of the coils hot spot temperature after a quench, and offers increased redundancy against component failures.

The decay asymmetries of the weak radiative hyperon decays Ξ0→Λγ and Ξ0→Σ0γ have been measured with high precision using data of the NA48/1 experiment at CERN. From about 52 000 Ξ0→Λγ and 15 000 Ξ0→Σ0γ decays, we obtain for the decay asymmetries αΞ0→Λγ=−0.704±0.019stat±0.064syst and αΞ0→Σ0γ=−0.729±0.030stat±0.076syst, respectively. These results are in good agreement with previous experiments, but more precise.

A search for direct CP-violation in K±→π±π0π0 decay based on 47.14 million events has been performed by the NA48/2 experiment at the CERN SPS. The asymmetry in the Dalitz plot linear slopes Ag=(g+−g−)/(g++g−) is measured to be Ag=(1.8±2.6)×10−4. The design of the experiment and the method of analysis provide good control of instrumental charge asymmetries in this measurement. The precision of the result is limited by statistics and is almost one order of magnitude better than that of previous measurements by other experiments.

A sample of 65210 K ± → π 0 π 0 e ± ν (K e4 00 ) decay candidates with 1% background contamination has been collected in 2003-2004 by the NA48/2 collaboration at the CERN SPS. A study of the differential rate provides the first measurement of the hadronic form factor variation in the plane (M 2 , M 2 ) and brings evidence for a cusp-like structure in the distribution of the squared π 0 π 0 invariant mass around $$ 4{m}_{\pi^{+}}^2 $$ . Exploiting a model independent description of this form factor, the branching ratio, inclusive of radiative decays, is obtained using the K ± → π 0 π 0 π ± decay mode as normalization. It is measured to be BR(K e4 00 ) = (2.552 ± 0.010stat ± 0.010syst ± 0.032ext) × 10−5, which improves the current world average precision by an order of magnitude while the 1.4% relative precision is dominated by the external uncertainty from the normalization mode. A comparison with the properties of the corresponding mode involving a π + π − pair (K e4 + − ) is also presented.

A bstract A measurement of the form factors of charged kaon semileptonic decays is presented, based on 4.4 × 10 6 K ± → π 0 e ± ν e ( K e 3 ± ) and 2.3 × 10 6 K ± → π 0 μ ± ν μ ( K μ 3 ± ) decays collected in 2004 by the NA48/2 experiment. The results are obtained with improved precision as compared to earlier measurements. The combination of measurements in the K e 3 ± and K μ 3 ± modes is also presented.

In the past ten years, Fermilab has been executing an intensive R&D program on accelerator magnets based on Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn superconductor technology. This R&D effort includes dipole and quadrupole models for different programs, such as LARP and 11 T dipoles for the LHC high-luminosity upgrade. Before the Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn R&D program, Fermilab was involved in the production of the low-beta quadrupole magnets for LHC based on the NbTi superconductor. Additionally, during the 2003-2005 campaign to optimize the operation of the Tevatron, a large number of Tevatron magnets were remeasured. As a result of this field analysis, a systematic study of the persistent current decay and snapback effect in these magnets was performed. This paper summarizes the result of this study and presents a comparison between Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn and NbTi dipoles and quadrupoles.

A 2-m-long single-aperture dipole demonstrator and two 1-m-long single-aperture models based on Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn superconductor have been built and tested at FNAL. The two 1-m-long collared coils were then assembled in a twin-aperture Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn dipole demonstrator compatible with the LHC main dipole and tested in two thermal cycles. This paper summarizes the quench performance of the FNAL twin-aperture Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn 11 T dipole in the temperature range of 1.9-4.5 K. The results of magnetic measurements for one of the two apertures are also presented. Test results are compared to the performance of coils in a single-aperture configuration. A summary of quench propagation studies in both apertures is given.

FNAL and CERN are developing a twin-aperture 11 T $$Nb_{3}Sn$$ dipole suitable for installation in the LHC. A single-aperture 2-m long dipole demonstrator and two 1-m long dipole models have been fabricated and tested at FNAL in 2012-2014. The two 1 m long collared coils were then assembled into the first twin-aperture $$Nb_{3}Sn$$ demonstrator dipole and tested. Test results of this twin-aperture $$Nb_{3}Sn$$ dipole model are reported and discussed.

In the framework of the U.S. Magnet Development Program (MDP), Fermilab has developed and tested a high-field Nb 3 Sn dipole demonstrator MDPCT1 for a post-LHC Hadron Collider.The magnet was first assembled with a lower coil pre-load to minimize the risk of coil damage during assembly and test.In the first test the magnet reached its test goal producing a world record field of 14.1 T at 4.5 K. Next the magnet was reassembled with nominal pre-load to achieve its design field limit of 15 T.This paper describes the details of MDPCT1 inspection, design modifications and reassembly.The magnet quench performance, including training, ramp rate and temperature dependences in the temperature range of 1.9-4.5 K, is presented and discussed.

The NA48 Collaboration has measured the amplitude of the CP-conserving component of the decay KS0→π+π−π0 relative to KL0→π+π−π0. For the characteristic parameter λ, the values Reλ=0.038±0.010 and Imλ=−0.013±0.007 have been extracted. These values agree with earlier measurements and with theoretical predictions from chiral perturbation theory.

We present a measurement of the relative branching ratio of the decay K0→π±e±νγ (Ke3γ) with respect to K0→π±e±ν (Ke3+Ke3γ) decay. The result is based on observation of 19 000 Ke3γ and 5.6×106 Ke3 decays. The value of the branching ratio is Br(Ke3γ0,Eγ*>30MeV, θeγ*>20°)/Br(Ke30)=(0.964±0.008−0.009+0.011)%. This result agrees with theoretical predictions but is at variance with a recently published result.

The weak radiative decay Ξ0→Λe+e− has been detected for the first time. We find 412 candidates in the signal region, with an estimated background of 15±5 events. We determine the branching fraction B(Ξ0→Λe+e−)=[7.6±0.4(stat)±0.4(syst)±0.2(norm)]×10−6, consistent with an internal bremsstrahlung process, and the decay asymmetry parameter αΞΛee=−0.8±0.2, consistent with that of Ξ0→Λγ. The charge conjugate reaction Ξ0¯→Λ¯e+e− has also been observed.

The decay rate of KS→πeν relative to the rate of KL→πeν has been measured by the NA48 Collaboration in a neutral kaon beam originating from 400 GeV proton-Be interactions at the CERN SPS. The result is 0.993±0.026stat±0.022syst, compatible with 1 in agreement with the Standard Model prediction at tree level. It implies BR(KS→πeν)=(7.05±0.18stat±0.16syst)×10−4.

The KS→π+π−e+e− decay mode was investigated using the data collected in 2002 by the NA48/1 Collaboration. With about 23 k KS→π+π−e+e− events and 59 k KL→π+π−πD0 normalization decays, the KS→π+π−e+e− branching ratio relative to the KL→π+π−πD0 one was determined to be BR(KS→π+π−e+e−)/BR(KL→π+π−πD0)=(3.28±0.06stat±0.04syst)×10−2. This result was used to set the upper limit |gE1/gBR|<3.0 at 90% CL on the presence, in the decay amplitude, of an E1 direct emission (gE1) term relative to the dominant inner bremsstrahlung (gBR) term. The CP-violating asymmetry Aϕ in the sinϕcosϕ distribution of KS→π+π−e+e− events, where ϕ is the angle between the π+π− and the e+e− decay planes in the kaon centre of mass, was found to be Aϕ=(−0.4±0.8)%, consistent with zero. These results are in good agreement with a description of the KS→π+π−e+e− decay amplitude dominated by the CP-even inner bremsstrahlung process.

Abstract A sample of more than one million K ± → π + π − e ± ν ( K e 4 ) decay candidates with less than one percent background contamination has been collected by the NA48/2 experiment at the CERN SPS in 2003–2004, allowing a detailed study of the decay properties. The branching ratio, inclusive of K e 4 γ decays, is measured to be BR ( K e 4 ) = ( 4.257 ± 0.016 exp ± 0.031 ext ) × 10 − 5 with a total relative error of 0.8 % . This measurement complements the study of S- and P-wave hadronic form factors by assigning absolute values to the relative hadronic form factors obtained earlier in a simultaneous analysis of the ππ scattering lengths conducted on the same data sample. The overall form factor normalization f s = 5.705 ± 0.017 exp ± 0.031 ext is obtained with a total relative precision of 0.6 % .

From the 2002 data taking with a neutral kaon beam extracted from the CERN-SPS, the NA48/1 experiment observed 97 $\Xi^{0}\rightarrow \Sigma^{+} \mu^{-} \bar{\nu}_{\mu}$ candidates with a background contamination of $30.8 \pm 4.2$ events. From this sample, the BR($\Xi^{0}\rightarrow \Sigma^{+} \mu^{-} \bar{\nu}_{\mu}$) is measured to be $(2.17 \pm 0.32_{\mathrm{stat}}\pm 0.17_{\mathrm{syst}})\times10^{-6}$.

Within the U.S. magnet development program, Fermilab is developing a 15-T Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn dipole demonstrator. Prior to the construction of the real magnet model, short sections and the whole structure were instrumented with strain gauges and assembled to validate the results of structural analysis, check tooling, and to gain experience with the assembly of the real magnet components. This paper summarizes the lessons learned from these mechanical models and compares the measured data with the finite-element analysis.

Flexible printed-circuit-board-based quench antenna arrays have been developed at FNAL since 2017. They proved to be low-noise, low-cost, sensitive, and non-invasive sensors for quench characterization in superconducting magnets, having the potential to extend even to quench detection. Starting with applications of small area sensors of this type, we have explored feasibility for operations at high pressure, and have invested in multi-channel quench antenna arrays covering the complete area of the innermost magnet layer of the conductor. We've also tested and optimized sensor geometry and relative orientations to increase sensitivity and spatial resolution. Beyond developments of warm and cold bore antennas, we've progressed to concepts which attach quench antennas to the conductor surfaces of accelerator magnets. Multiple programs and projects at FNAL and collaborating institutions benefited from this work already and our plans target further extensions of capabilities and applicability of these devices. In this paper we present the logic behind the development steps taken so far, status of our work and direction of near-term research on quench antennas at Fermilab.

LQXFA/B production series cryogenic assemblies are being built for the LHC upgrade by the HL-LHC Accelerator Upgrade Project (AUP). These contain a pair of MQXFA quadrupole magnets combined as a cold mass within a vacuum vessel, and are to be installed in the IR regions of the LHC. The LQXFA/B are being tested at 1.9 K to assess alignment and magnetic performance at Fermilab's horizontal test facility. The ~10 m - long assembly must meet stringent specifications for quadrupole strength and harmonic field integrals determination, magnetic axis location, and for variations in axis position and local field profile. A multi-probe, PCB-based rotating coil and Single Stretched Wire system are employed for these measurements. To accurately determine rotating coil location and angles within the cold mass, a laser tracker is utilized to record multiple targets at one end of the probe. This paper describes the measurements, probes/equipment, and techniques used to perform the necessary characterization of the cold mass.

Abstract We report the results from a study of a partial sample of ∼ 2.3 × 10 7 K ± → π ± π 0 π 0 decays recorded by the NA48/2 experiment at the CERN SPS, showing an anomaly in the π 0 π 0 invariant mass ( M 00 ) distribution in the region around M 00 = 2 m + , where m + is the charged pion mass. This anomaly, never observed in previous experiments, can be interpreted as an effect due mainly to the final state charge exchange scattering process π + π − → π 0 π 0 in K ± → π ± π + π − decay [N. Cabibbo, Phys. Rev. Lett. 93 (2004) 121801]. It provides a precise determination of a 0 − a 2 , the difference between the ππ scattering lengths in the isospin I = 0 and I = 2 states. A best fit to a rescattering model [N. Cabibbo, G. Isidori, JHEP 0503 (2005) 21] corrected for isospin symmetry breaking gives ( a 0 − a 2 ) m + = 0.268 ± 0.010 ( stat ) ± 0.004 ( syst ) , with additional external uncertainties of ±0.013 from branching ratio and theoretical uncertainties. If the correlation between a 0 and a 2 predicted by chiral symmetry is taken into account, this result becomes ( a 0 − a 2 ) m + = 0.264 ± 0.006 ( stat ) ± 0.004 ( syst ) ± 0.013 ( ext ) .

The HL-LHC interaction region magnet triplets (Q1, Q2, and Q3) will be composed of superconducting Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn quadrupoles. The MQXF quadrupole protection system is based on CLIQ (Coupling-Loss Induced Quench system) and outer layer quench heaters. This paper reports a summary of quench heaters to coil high voltage tests performed on MQXF short and long coils in air after fabrication, and in air and He gas after magnet training. Breakdown voltage values demonstrate good margin with respect to the Electrical design criteria for the HL-LHC inner triplet magnets. A modification in the quench heater installation- with an extra layer of fiber glass between the coil and the quench heater trace- has been proposed and tested in a mirror magnet to further increase electrical margins. Results demonstrated improvements of high voltage margin at the expense of a clear increase of hot spot temperature. The baseline heater to coil insulation was assessed to be able to guarantee safe operation for the Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn quadrupole magnets for the interaction regions of HL-LHC.

In the Compact Muon Solenoid (CMS) experiment, muon detection in the forward direction is accomplished by cathode strip chambers (CSC). These detectors identify muons, provide a fast muon trigger, and give a precise measurement of the muon trajectory. There are 468 six-plane CSCs in the system. The efficiency of finding muon trigger primitives (muon track segments) was studied using 36 CMS CSCs and cosmic ray muons during the Magnet Test and Cosmic Challenge (MTCC) exercise conducted by the CMS experiment in 2006. In contrast to earlier studies that used muon beams to illuminate a very small chamber area (<0.01m2), results presented in this paper were obtained by many installed CSCs operating in situ over an area of ≈23m2 as a part of the CMS experiment. The efficiency of finding two-dimensional trigger primitives within six-layer chambers was found to be 99.93±0.03%. These segments, found by the CSC electronics within 800 ns after the passing of a muon through the chambers, are the input information for the Level-1 muon trigger and, also, are a necessary condition for chambers to be read out by the Data Acquisition System.

FNAL has been developing multiple versions of flexible quench antennas (flex-QA), including some specially optimized for high sensitivity and/or high resolution, to characterize quench events and transients during current ramping in superconducting magnets. A fundamental feature in our use of these is the creation of grid-like structures of sensitive elements to cover coil surfaces, with the aim of getting precise localization of magnetic flux-change events. The flex-QA are coupled with fast data-acquisition, allowing comprehensive analysis of signals at the relevant fine time scales. In addition to arrays of various flex-QA types being used during cryogenic testing of superconducting magnets, we also are utilizing a newly developed room temperature test stand to better understand QA response characteristics. The data from actual superconducting magnet tests, warm test stand measurements, and simulation data on the same QA designs allows us to draw conclusions on operational feasibility and plan better for improvements of our sensors. In this paper we present data from the multiple tests performed and analysis results. Flex-QA designs are compared, and their features, options, and optimization discussed.

Controlled mechanical oscillations are not part of superconducting magnet toolkit except for diagnostics/quench detection purposes. However, significant potential exists to use them to affect operational conditions in magnets. There is also the possibility to explore them in terms of magnet protection. As none of these is known to had been investigated in past an effort is made here to address viability, use cases and benefits of such developments. Both appear to be valid and promising subjects and the magnet community can only gain with further investigations.

in the winding pack, (4) local pressure in the winding pack. Fiber-optic based isolation systems are used to remove high common-mode magnet voltages and eliminate ground loops. The data acquisition and fault-detection systems are computer based. The design of the local I&C system incorporates redundant, fault-tolerant, and/or fail-safe features at all component levels. As part of a quench detection R&D plan, a Quench Detection Model Coil has been proposed to test all detection methods. Initial cost estimates and schedule for the local I&C system are presented.

The NA48/2 experiment at CERN reports the first observation of the $K^{\pm} \rightarrow \pi^{0} \pi^{0} \mu^{\pm} \nu$ decay based on a sample of 2437 candidates with 15% background contamination collected in 2003--2004. The decay branching ratio in the kinematic region of the squared dilepton mass above $0.03$~GeV$^2/c^4$ is measured to be $(0.65 \pm 0.03) \times 10^{-6}$. The extrapolation to the full kinematic space, using a specific model, is found to be $(3.45 \pm 0.16) \times 10^{-6}$, in agreement with chiral perturbation theory predictions.

Recently a new type of device, capacitor-based, aiming to eliminate or reduce superconducting magnet training was developed and tested at FNAL. I’ll review its main characteristics and principles of operation, make relevant comparisons and conclusions. Separately, I’ll discuss somewhat similar concepts based on induced vibrations in magnets, but I’ll extend this topic to cover both training reduction and quench protection. Those will be discussed at conceptual level, arguing about feasibility of such an approach and the need for more focused research on the topic, including simulations.

MQXFA production series quadrupole magnets are being built for the Hi-Lumi (HL) LHC upgrade by the US Accelerator Upgrade Project (US-HL-LHC AUP). These magnets are being placed in pairs, as a cold mass, within cryostats at Fermilab, and are being tested to assess alignment and magnetic performance at Fermilab's horizontal test stand facility. The ~10 m - long assembly must meet stringent specifications for quadrupole strength and harmonic field integrals determination, magnetic axis position, and for magnet variations in positioning and local field profile. This paper describes the results of the magnetic and alignment measurements which characterize the first LQXFA/B assembly.

The scope of the proposal outlined in this white paper is the development and demonstration of the technology needed for next generation of Nb_3Sn accelerator magnets in the 12-14 T range. The main goal is to cut magnet cold-mass cost by a factor 2 or higher with respect to the Nb_3Sn magnets produced by the US Accelerator Upgrade Project (AUP) for the High-Luminosity Large Hadron Collider (HL-LHC). This goal will be achieved by significant reduction of labor hours, higher operating point, and improved performance uniformity. A key factor will be automation that will be achieved through industry involvement and benefitting from the experience gained in US national laboratories through the production of the AUP magnets. This partnership will enable the development of a technology that will be easily transferable to industry for mid- and large-scale production of Nb_3Sn accelerator magnets in the 12-14 T range. This step is essential to enable next generation of colliders such as the FNAL-proposed Muon Collider, FCC and other HEP hadron colliders. This is a Directed R&D where direction is given by the field range and industry involvement for high-automation and industry-ready technology. The plan includes ten milestones, to be achieved in 6-8 years at the cost of 5-7 $M/year.

Future colliders will operate at increasingly high magnetic fields pushing limits of electromagnetic and mechanical stress on the conductor [1]. Understanding factors affecting superconducting (SC) magnet performance in challenging conditions of high mechanical stress and cryogenic temperatures is only possible with the use of advanced magnet diagnostics. Diagnostics provide a unique observation window into mechanical and electromagnetic processes associated with magnet operation, and give essential feedback to magnet design, simulations and material research activities. Development of novel diagnostic capabilities is therefore an integral part of next-generation magnet development. In this paper, we summarize diagnostics development needs from a prospective of the US Magnet Development Program (MDP), and define main research directions that could shape this field in the near future.

horn power supply is expected to last the lifetime of the project, 30 years. A resonant, half sine wave pulser was used for NuMI and BNB and has many practical advantages. The system has impedance limited fault currents by design, albeit large ones. That along with the resonant behavior means that thyristor switches are well suited. Many fault modes of the system have also been calculated. Several circuit changes were incorporated so that a single fault can be tolerated. The supply must be reversable to enable both neutrinos and anti-neutrinos to be produced. These reversal requirements required a significant amount of mechanical design and consideration to allow for quick reversal of all the semiconductors.

A sample of more than one million K±→π+π−e±ν ( Ke4 ) decay candidates with less than one percent background contamination has been collected by the NA48/2 experiment at the CERN SPS in 2003–2004, allowing a detailed study of the decay properties. The branching ratio, inclusive of Ke4γ decays, is measured to be BR(Ke4)=(4.257±0.016exp±0.031ext)×10−5 with a total relative error of 0.8% . This measurement complements the study of S- and P-wave hadronic form factors by assigning absolute values to the relative hadronic form factors obtained earlier in a simultaneous analysis of the ππ scattering lengths conducted on the same data sample. The overall form factor normalization fs=5.705±0.017exp±0.031ext is obtained with a total relative precision of 0.6% .

The production, installation, and testing of 468 cathode strip chambers for the endcap muon system of the CMS experiment played a critical role in the preparation of the endcap muon system for the final commissioning. Common testing procedures and sets of standard equipment were used at 5 international assembly centers. The chambers were then thoroughly retested after shipment to CERN. Final testing was performed after chamber installation on the steel disks in the CMS detector assembly building. The structure of the detector quality control procedure is presented along with the results of chamber performance validation tests.

Fermilab, in collaboration with CERN, has developed a double-aperture 11-T Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn dipole suitable for the high-luminosity LHC upgrade. During 2012-2014, a 2-m-long single-aperture dipole demonstrator and three 1-m-long single-aperture dipole models were fabricated by FNAL and tested at its Vertical Magnet Test Facility. Collared coils from two of the 1-m-long models were then used to assemble the first double-aperture dipole demonstrator. This magnet had extensive testing in 2015-2016, including quench performance, quench protection, and field quality studies. This paper reports the results of measurements of dynamic effects in the single-aperture and double-aperture 11-T Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn dipoles and compares them with similar measurements in previous NbTi magnets.

In an earlier paper [1], the background for Ke3 was over estimated due to an erroneous calculation of the electron identification efficiency. The correct ratios of the partial widths involving this channel are $\mathcal{R}_{K e 3 / K2\pi} = 0.2470\pm0.0009\, ({\text{stat}})\pm0.0004\, ({\text{syst}})$ and $\mathcal{R}_{K \mu3 / Ke3} = 0.663\pm0.003\,({\text{stat}})\pm0.001\,({\text{syst}})$ . Assuming the PDG value [2] for the K2π branching ratio, the measured branching fraction of Br (Ke3) continues to exceed the current PDG value [2]. The extracted value of |Vus|f+(0) is in agreement with the CKM unitary prediction; thus, our conclusions in [1] do not change.

beams of low or moderate emittance, electron cooling excels. The realization of electron cooling for 8 GeV antiprotons requires major extension of existing practice in electron energy and length of the cooling interaction region. It will require 4.3 MeV dc electron beam maintaining high quality and precise collinearity with the antiprotons over a 66 m straight section. The initial goal of the R and D project is 200 mA electron current in about three years; the plan is to reach 2 A over the following three years.

Magnetic fields interact with biological cells affecting them in variety of ways which are usually hard to predict. Among them, it was observed that strong fields can align dividing cells in a preferred direction. It was also demonstrated that dividing cancer cells are effectively destroyed by applying electric fields in vivo with a success rate dependent on the cell-to-field orientation. Based on these facts, the present note aims to suggest the use of magnetic and electric fields for improved cancer treatment. Several possibilities of generating the electric fields inside the magnetic field volume are reviewed, main tentative approaches are described and discussed. Most if not all of them require special magnet configuration research which can be based on existing magnet systems in operation or in development.

Magnetic fields interact with biological cells affecting them in variety of ways which are usually hard to predict. Among them, it was observed that strong fields can align dividing cells in a preferred direction. It was also demonstrated that dividing cancer cells are effectively destroyed by applying electric fields in vivo with a success rate dependent on the cell-to-field orientation. Based on these facts, the present note aims to suggest the use of magnetic and electric fields for improved cancer treatment. Several possibilities of generating the electric fields inside the magnetic field volume are reviewed, main tentative approaches are described and discussed. Most if not all of them require special magnet configuration research which can be based on existing magnet systems in operation or in development.

The Drell-Yan differential cross section is measured in pp collisions at sqrt(s) = 7 TeV, from a data sample collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 36 pb^{-1}. The cross section measurement, normalized to the measured cross section in the Z region, is reported for both the dimuon and dielectron channels in the dilepton invariant mass range 15-600 GeV. The normalized cross section values are quoted both in the full phase space and within the detector acceptance. The effect of final state radiation is also identified. The results are found to agree with theoretical predictions.

A total of 368 415 Ξ0→Λπ0 and 31 171 Ξ0¯→Λ¯π0 were selected from data recorded in the NA48/1 experiment during 2002 data taking. From this sample, the polarization of Ξ0 and Ξ0¯ hyperons was measured to be PΞ0=−0.102±0.012(stat)±0.008(syst) and PΞ0¯=−0.01±0.04(stat)±0.008(syst). The dependence of PΞ0 on the Ξ0 transverse momentum with respect to the primary proton beam is also presented. With the same data sample, the ratio of Ξ0¯ and Ξ0 fluxes in proton collisions at 400GeV/c on a beryllium target was measured.

A sample of 7253 K± → π±e+e−(γ) decay candidates with 1.0% background contamination has been collected by the NA48/2 experiment at the CERN SPS, which allowed a precise measurement of the decay properties. The branching ratio in the full kinematic range was measured to be BR = (3.11 ± 0.12) × 10−7, where the uncertainty includes also the model dependence. The shape of the form factor W (z), where z = (Mee/MK), was parameterized according to several models, and, in particular, the slope δ of the linear form factorW (z) = W0(1+δz) was determined to be δ = 2.32 ± 0.18. A possible CP violating asymmetry of K+ and K− decay widths was investigated, and a conservative upper limit of 2.1 × 10−2 at 90% CL was established.

The scope of the proposal outlined in this white paper is the development and demonstration of the technology needed for next generation of Nb_3Sn accelerator magnets in the 12-14 T range. The main goal is to cut magnet cold-mass cost by a factor 2 or higher with respect to the Nb_3Sn magnets produced by the US Accelerator Upgrade Project (AUP) for the High-Luminosity Large Hadron Collider (HL-LHC). This goal will be achieved by significant reduction of labor hours, higher operating point, and improved performance uniformity. A key factor will be automation that will be achieved through industry involvement and benefitting from the experience gained in US national laboratories through the production of the AUP magnets. This partnership will enable the development of a technology that will be easily transferable to industry for mid- and large-scale production of Nb_3Sn accelerator magnets in the 12-14 T range. This step is essential to enable next generation of colliders such as the FNAL-proposed Muon Collider, FCC and other HEP hadron colliders. This is a Directed R&D where direction is given by the field range and industry involvement for high-automation and industry-ready technology. The plan includes ten milestones, to be achieved in 6-8 years at the cost of 5-7 $M/year.

LHC still does not operate at full energy due to training features in magnets. Higher field practical superconductors (Nb3Sn) show much worse training behavior than NbTi. Most magnet performance issues relate to quenching, and it is this phenomenon and its dependencies that need to be understood for us to succeed addressing them in magnets. For pragmatic and scientific reasons underlying mechanisms are hard to investigate in real magnets. Available data suggest that emulating local conditions at quench location may be enough to arrive at a good understanding of what drives observed behavior. "Local" conditions imply emulation by small samples of cables/"stacks" powered within a facility with controllable conditions, including external magnetic and force fields. This paper argues about the necessity of this approach, while reminding current understanding and directions of quench studies, and pointing out inadequacy of available techniques. Improved facilities and change of perspective are required for consistent and affordable development.

LHC still does not operate at full energy due to training features in magnets. Higher field practical superconductors (Nb3Sn) show much worse training behavior than NbTi. Most magnet performance issues relate to quenching, and it is this phenomenon and its dependencies that need to be understood for us to succeed addressing them in magnets. For pragmatic and scientific reasons underlying mechanisms are hard to investigate in real magnets. Available data suggest that emulating local conditions at quench location may be enough to arrive at a good understanding of what drives observed behavior. "Local" conditions imply emulation by small samples of cables/"stacks" powered within a facility with controllable conditions, including external magnetic and force fields. This paper argues about the necessity of this approach, while reminding current understanding and directions of quench studies, and pointing out inadequacy of available techniques. Improved facilities and change of perspective are required for consistent and affordable development.

Particle accelerators rely on superconducting magnets to guide particles in circular trajectories. These magnets can undergo quenching, a process in which a portion of the magnet’s coils experience a loss in superconductivity, thus causing a shift to a normal (resistive) state. Consequently, a current redistribution towards other wires in the coil occurs, which is detectable by relevant sensors. Quenches are irreversible, and it takes significant resources for the magnet to recover (e.g., additional liquid helium for the cryogenic magnet bath). Thus, understanding the causes of any given quench is vital. Our research introduces a Python-based tool used to visualize and process data from sensors surrounding superconducting magnets as they quench. We leverage a standalone back end, responsible for interacting with the data stored in TDMS files, and a front end in the form of a Graphical User Interface (GUI) built with Tkinter, which facilitates no-code interaction with the back end. The tool is designed to normalize units across the dataset, zero the data relative to the time of the quench to enable cross-sensor analysis, and also introduces various data handling tools important for user analysis. It used some functionality developed by Kiernan 2021, but it is the first tool attempting to be a modular package featuring easy use and upgrades. Future research shall leverage our tool to better understand the specific causes for a particular quench, with the ultimate goal of preventing them altogether.

Presents corrections to author information for the above named paper.

The MQXFA quadrupoles have 150 mm aperture, 4.2 m magnetic length, nominal gradient of 132.2 T/m, and coil peak field of 11.3 T. They use Nb_3Sn conductor and a support structure made of segmented aluminum shells pre-loaded by using bladders and keys. This report presents the final design of the MQXFA quadrupole magnets.

In order to progress on various research points related to superconducting magnets, we suggest performing series of tests with induced and natural quenches on a mirror magnet, probably using a “11 T” coil. The “mirror” is to have voltage taps instrumented on half the strands, on both coil ends. It is to be instrumented with multiple spot-heaters, of the order of ten, in designated pole-turn areas. Instrumentation is to include quench antenna array facing the inner coil surface, as well as acoustic sensors on the inner layer pole. Further, acoustic sensors at the magnet ends and an acoustic calibration transducer are to be installed. Thus, we are to test sensitivity and precision of acoustic and quench antenna (QA) array sensors, both at close proximity to the coil, and we are to test and commission acoustic on-magnet real-time “calibration”. New or extended DAQ will be tested as well. In addition to diagnostic development, the purpose of the magnet experiment is to investigate current redistribution in the coil, both during quenching and in operating conditions; to assess voltage build up across strands and in the coil segments during quenching, to explore voltage signature differentiation between different type of quenches; to improve modeling of processes during quenching and for magnet design purposes. In this experiment, we expect to be able to characterize the processes during a quench in unprecedented details.