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Multicolor excitation is at the core of many fluorescence spectroscopy techniques such as PIE-FRET, ALEX-FRET, or FCCS. However, the influence of the multiple laser excitations on the dye photophysics is often overlooked. Here, we show that green laser pulses can surprisingly quench the fluorescence of common red dyes Alexa Fluor 647 and Atto 647N, even when the conditions leading to photobleaching are avoided. The physical origin of this phenomenon is discussed via a long-lived dark state and/or photorefractive effects. These observations are important to avoid measurement artifacts as both the fluorophore concentration and the fluorescence brightness are affected.
The recent "bullet-dwarf" model proposes that high-velocity collisions between dwarf galaxies can produce stellar systems with overluminous globular clusters (GCs) and a deficiency of dark matter, as observed in the NGC 1052 group galaxies NGC 1052-DF2 and NGC 1052-DF4. We present a possible analogue system in the outskirts of the Fornax cluster: the ultra-diffuse galaxy FCC 224 and its close companion FCC 240. Using deep VLT/MUSE integral-field spectroscopy, we characterize their stellar populations, internal kinematics, and GC systems to test this formation scenario. Both galaxies exhibit low velocity dispersions. Interpreted with a standard mass estimator at the half light radius, and allowing for the known limitations associated with flattened systems, their inner dynamics are more naturally explained by stars alone than by either cuspy or cored dark matter halos. Both systems host unusually luminous GCs, closely resembling the top-heavy GCLF of the NGC 1052 pair. Moreover, FCC 224 and FCC 240 are coeval with each other, with mass-weighted stellar ages of ~10 Gyr, and their GC populations share similarly old ages, in agreement with predictions of the formation scenario. Despite
In response to its remit, the European Strategy Group (ESG) recommended the electron-positron Future Circular Collider (FCC-ee) as the preferred option for the next flagship collider at CERN; and a descoped FCC-ee as the preferred alternative option (with reduced synchrotron radiation (SR) power, without a run at the $\rm t \bar t$ threshold, and with only two interaction regions) in the event that the preferred option turns out not to be feasible. Upon request of the ESG, a basic comparison of the physics potential of the descoped option with that of the baseline version is presented in this short note. Our first observations about the alternative proposal of a descoped FCC-ee are that (i) the same performance as the baseline, apart from $\rm t \bar t$-run related, is achieved with the longer proposed period of operation; and (ii) the top run remains essential, but can be staged at a later date. The full appraisal of the consequences of descoping and a proposal for the best way to integrate possible staging wherever feasible, and possible improvements, will need further joint studies by the physics and accelerator groups.
The Future Circular Collider (FCC) stands at the forefront of the European Strategy for Particle Physics as the future flagship project at CERN. The H$\toττ$ decay, featuring a large branching ratio, clean identification in the FCC-ee environment, and the possibility to reconstruct polarization information, is an excellent channel to measure Higgs boson properties. This work shows the expected precision for the H$\toττ$ cross-section measurement at the FCC-ee in the ZH production mechanism at $\sqrt{s}=$240 GeV and $\sqrt{s}=$365 GeV, as well as via the vector boson fusion process at $\sqrt{s}=$365 GeV. Furthermore, we explore and evaluate a set of methods for reconstructing tau decays. These techniques are critical for unlocking the full physics potential of the FCC-ee and for improving the understanding of tau-related observables in both Standard Model measurements and New Physics searches. The results obtained significantly enhance the FCC-ee outlook in the H$\toττ$ channel, improving it by at least an order of magnitude compared to the current sensitivity of measurements' performance at the LHC.
An exploratory study of the exclusive toponium production in $pp$, $pPb$ and $PbPb$ collisions at the center - of - mass energies of the Large Hadron Collider (LHC) and Future Circular Collider (FCC) is performed. Assuming that the toponium is a pseudoscalar $t\bar{t}$ state, we consider its exclusive production by photon and gluon - induced interactions. Results for the total cross - sections and associated rapidity distributions are presented, and the number of events at the LHC and FCC are estimated.
As the particle physics community has explored most of the conventional avenues for new physics, the more elusive areas are becoming increasingly appealing. One such potential region, where new physics might be hiding, involves light and weakly interacting long-lived particles (LLPs). To probe deeper into this region, where the possibility of highly displaced scenarios weakens the role of general-purpose collider detectors, dedicated LLP detectors are our best option. However, their potential can only be fully realized if we optimize their position and dimensions to suit our physics goals. This is possible at the upcoming Future Circular Collider (FCC) facility, where the feasibility and design studies are still ongoing and can accommodate new proposals focused specifically on LLP searches. We propose optimized dedicated detectors in both the transverse and forward directions, DELIGHT and FOREHUNT, significantly enhancing the sensitivity to previously uncharted regions of the new physics parameter space. Our proposed DELIGHT detector can additionally serve as a shared transverse detector during both the FCC-ee and FCC-hh runs. The concept of a shared transverse detector is novel an
The Future Circular Lepton Collider (FCC-ee) presents challenges for a longitudinal bunch profile monitor due to its wide range of bunch lengths and charge densities across its four distinct operational modes. For commissioning, monitoring the top-up injection, and energy calibration, the FCC-ee requires non-destructive, single-shot measurements of the bunch length and profile. This contribution proposes an in-vacuum electro-optical (EO) longitudinal bunch profile monitor for single-shot measurements at high repetition rates, building on the successful EO monitor at the Karlsruhe Research Accelerator (KARA) at the Karlsruhe Institute of Technology. A novel single-pass conceptual design for the in-vacuum holder of the electro-optical crystal is presented, utilizing prisms instead of a mirror to guide the laser through the crystal, which additionally allows measurements of the long bunches foreseen for FCC-ee operation mode at the Z-pole energy. A first prototype has been constructed and tested at the in-air test stand of the CERN Linear Electron Accelerator for Research (CLEAR). Results from the prototype tests are presented, demonstrating the proof of principle for the single-pass
Following in the footsteps of the LHC, the Future Circular Collider (FCC) plans to be the next multi-generational collider project. In the first stage, FCC-ee will collide intense beams of electrons and positrons at centre of mass energies between 88 and 365 GeV, making it an electroweak, flavour, Higgs and top factory. The unprecedented statistical precision requires FCC-ee experiments to limit their systematic uncertainties to the very minimum. The precise reconstruction of the interaction vertices is central to most measurements at FCC-ee, such as rare flavour physics processes and the measurement of Higgs and Z decays to bottom and charm quarks and taus. This contribution will discuss the requirements of FCC-ee vertex detectors, from the necessary impact parameter resolution via the challenging collision environment at the Z pole to the tight requirement on the material budget, which should be kept below 0.3% of a radiation length per detection layer. Next, the proposed vertex detector designs for FCC-ee are shortly presented, and an outlook is given on novel detector designs and features. The requirements for the vertexing performance translate into requirements for the sensor
The electron-positron stage of the Future Circular Collider (FCC-ee) provides exciting opportunities that are enabled by next generation particle physics detectors. This contribution presents IDEA, a detector concept optimised for FCC-ee and composed of a vertex detector based on MAPS, a very light drift chamber, a silicon wrapper, a high resolution dual-readout crystal electromagnetic calorimeter, an HTS based superconducting solenoid, a dual-readout fibre calorimeter, and three layers of muon chambers embedded in the magnet flux return yoke. In particular, the physics requirements and the technical solutions chosen in the various sub-systems to address them are discussed. This is followed by a description of the detector R&D currently in progress, test-beam results, and the expected performance on some key physics benchmarks.
Single Higgs production at FCC-ee probes the Higgs self-coupling at next-to-leading order (NLO). Extracting a bound requires a global analysis accounting for other possible new physics contributions up to NLO. We determine the FCC-ee sensitivity to Higgs self-coupling modifications $δκ_λ$ within the Standard Model Effective Field Theory (SMEFT) framework, including for the first time flavour, LEP, LHC, and FCC-ee observables in a global analysis with all leading NLO effects via one-loop renormalisation group evolution, as well as incorporating finite NLO contributions to electroweak precision and $ZH$ observables. The global sensitivity to $δκ_λ$ is estimated by marginalising over the effects of all other operators, bringing flavour considerations to the fore. We find that, under reasonable assumptions, FCC-ee sensitivity to $δκ_λ$ can exceed that of the HL-LHC.
SuperKEKB has achieved significantly higher specific luminosity than its predecessor KEKB, and it has proven a much more sustainable machine. It has successfully demonstrated several key design elements of FCC-ee. The design luminosity has not yet been reached, however. This observation is often (mistakenly) used to put into question the reliability of the FCC-ee design luminosity. In this note we review the accomplishments, challenges and obstacles of SuperKEKB, and compare these with the FCC-ee design.
The purpose of this paper is to calculate the longitudinal and transverse wakefields of the FCC collimators by using the electromagnetic codes ECHO3D and IW2D. We cross-checked our results using CST particle studio for long bunches, and found them to be in good agreement. The obtained results show that the collimators give one of the highest contributions to the overall FCC-ee wake potentials. Using the code PyHEADTAIL, we have found that the presence of the geometric wakefield of the collimators leads to the occurrence of transverse mode coupling instability (TMCI) at a significantly lower bunch population as compared to that of all other contributions and solutions to reduce this geometric term must be found.
Recent advances in $b$, $c$, and $s$ quark tagging coupled with novel statistical analysis techniques will allow future high energy and high statistics electron-positron colliders, such as the FCC-ee, to place phenomenologically relevant bounds on flavor violating Higgs and $Z$ decays to quarks. We assess the FCC-ee reach for $Z/h\to bs, cu$ decays as a function of jet tagging performance. We also update the SM predictions for the corresponding branching ratios, as well as the indirect constraints on the flavor violating Higgs and $Z$ couplings to quarks. Using type III two Higgs doublet model as an example of beyond the standard model physics, we show that the searches for $h\to bs, cu$ decays at FCC-ee can probe new parameter space not excluded by indirect searches. We also reinterpret the FCC-ee reach for $Z\to bs , cu$ in terms of the constraints on models with vectorlike quarks.
We report on the Future Circular Collider (FCC) Feasibility Study, the mid-term review in autumn 2023, and the longer term timeline.
With the LHC about to start its last data-taking period before being upgraded to the High-Luminosity LHC, it is time for the international high energy physics community to define the future of collider particle physics. The European Strategy for Particle Physics highlights an electron-positron Higgs boson factory as the main priority and as a first step towards a very high-energy future hadron collider. A staged Future Circular Collider (FCC), consisting of a luminosity-frontier highest-energy electron-positron collider (FCC-ee) followed by an energy-frontier hadron collider (FCC-hh), promises the most far-reaching physics program for the post-LHC era. FCC-ee is a precision instrument to study the Z, W, Higgs and top particles, and offers unprecedented sensitivity to signs of new physics. Most of the FCC-ee infrastructure can later be reused for the subsequent hadron collider, FCC-hh. The FCC-hh provides proton-proton collisions at a centre-of-mass energy of 100 TeV and can directly produce new particles with masses of up to several tens of TeV. This collider will also measure the Higgs self-coupling and explore the dynamics of electroweak symmetry breaking. Thermal dark matter can
The worldwide High Energy Physics community widely agrees that the next collider should be a Higgs factory. Acknowledging this priority, in 2021 CERN has launched the international Future Circular Collider (FCC) Feasibility Study (FS). The FCC Integrated Project foresees, in a first stage, a high-luminosity high-energy electron-positron collider, serving as Higgs, top and electroweak factory, and, in a second stage, an energy frontier hadron collider, with a centre-of-mass energy of at least 100 TeV. In this paper, we address a few key elements of the FCC-ee accelerator design, its performance reach, and underlying technologies, as requested by the Snowmass process. The Conceptual Design Report for the FCC, published in 2019, serves as our primary reference. We also summarize a few recent changes and improvements.
The Future Circular Collider (FCC-hh) is a proposed successor of the Large Hadron Collider (LHC). FCC-hh would push both the energy and intensity frontiers of searches for new physics particles. In particular, due to higher energy and luminosity than at the LHC, at FCC-hh there would be produced around $\simeq\!30$ times larger amount of $B$ mesons and $\simeq 120$ times of $W$ bosons, which then may decay into feebly interacting particles. In this paper we demonstrate the potential of FCC-hh by studying its sensitivity to heavy neutral leptons (HNLs) with masses $m_{N}<m_{B}$. We consider various locations of a displaced decay volume embedded in the planned infrastructure of FCC-hh. We demonstrate that FCC-hh may substantially improve the reach of the parameter space of HNLs as compared to the searches proposed at the LHC.
The proposed electron-proton collider experiments LHeC and FCC-eh at CERN are the highest resolution microscopes that can be realised in the present century and they would represent a really unique research facility. We exploit simulated neutral-current and charged-current deep-inelastic scattering data of the LHeC and the FCC-eh and examine their sensitivity for precision physics in the Electroweak sector of the Standard Model (SM), like the effective weak mixing angle $\sin^2θ_{\textrm{W},\ell}^\textrm{eff}$, or the light-quark weak-neutral-current couplings. Unique measurements are further feasible at high precision for the running of the weak mixing angle, as well as for electroweak effects in charged current interactions. The sensitivity to beyond SM effects is studied using the generic $S$, $T$ and $U$ parameterization. The report summarizes previous studies about the LHeC and presents new prospects for the FCC-eh.
The Future Circular Collider (FCC) study was launched as a world-wide international collaboration hosted by CERN. Its goal is to push the field to the next energy frontier beyond LHC, increasing by an order of magnitude the mass of particles that could be directly produced, and decreasing by an order of magnitude the subatomic distances to be studied. The FCC study covers two accelerators, namely, an energy-frontier hadron collider (FCC-hh) and a highest luminosity, high-energy lepton collider (FCC-ee). Both rings are hosted in the same 100 km tunnel infrastructure, replicating the CERN strategy for LEP and LHC, i.e. developing a lepton and a hadron ring sharing the same tunnel. This paper is devoted to the FCC-hh and summarizes the key features of the FCC-hh accelerator design, performance reach, and underlying technologies. The material presented in this paper builds on the conceptual design report published in 2019, and extends it, including also the progress made and the results achieved since then.
Jet-flavour identification algorithms are of paramount importance to maximise the physics potential of the Future Circular Collider (FCC). Out of the extensive FCC-ee physics program, flavour tagging is crucial for the Higgs physics program, given the dominance of hadronic decays of the Higgs boson. Highly efficient discrimination of $b$-, $c$-, $s$-, and gluon jets allows access to novel decay modes that cannot be identified at the LHC, adding quantitatively new dimensions to the Higgs physics programme. This contribution presents new jet flavour identification algorithms based on advanced machine-learning techniques that exploit particle-level information. Beyond an excellent performance of $b$- and $c$-quark tagging, they are also able to discriminate jets from strange quark hadronisation, opening the way to improve the sensitivity of the Higgs to strange quark coupling. The impact of different detector design assumptions on the flavour tagging performance is assessed using one of the baseline detector concepts for FCC-ee, IDEA.