Data from the LHC at 7, 8, and 13 TeV have so far yielded no evidence for new particles beyond the 125 GeV Higgs boson; in particular, there have been no signs of SUSY. However, the complementary nature of physics with $e^+e^-$ collisions still offers many interesting scenarios in which SUSY can be discovered at the ILC. These scenarios take advantage of the capability of $e^+e^-$ collisions to observe events with missing four-momentum -- a signature not available at hadron colliders, where only transverse imbalance is observable. Due to low backgrounds and trigger-less operation, detectors at $e^+e^-$ colliders can observe events with much less visible energy than what is possible at hadron colliders. In this contribution, we will present detailed simulation studies done with the ILD concept at the ILC. These studies include simulation of the full SM background, as well as realistic accelerator conditions. We will show results both on expected discovery and exclusion reaches for the most challenging SUSY channels, such as higgsinos or winos at low mass differences. Evaluations of precision of model-parameter measurements, in case of discovery, will also be given. We also report on how such measurements can be used to put constraints on parts of the sparticle-spectrum beyond direct reach, and to discriminate between different models of SUSY breaking at high scales.
We discuss the potential of combined analyses at the Large Hadron Collider and the planned International Linear Collider to explore low-energy supersymmetry in a difficult region of the parameter space characterized by masses of the scalar SUSY particles around 2 TeV. Precision analyses of cross sections for light chargino production and forward--backward asymmetries of decay leptons and hadrons at the ILC, together with mass information on chi^0_2 and squarks from the LHC, allow us to determine the underlying fundamental gaugino/higgsino MSSM parameters and to constrain the masses of the heav…
If new phenomena beyond the Standard Model will be discovered at the LHC, the properties of the new particles could be determined with data from the High-Luminosity LHC and from a future linear collider like the ILC. We discuss the possible interplay between measurements at the two accelerators in a concrete example, namely a full SUSY model which features a small stau_1-LSP mass difference. Various channels have been studied using the Snowmass 2013 combined LHC detector implementation in the Delphes simulation package, as well as simulations of the ILD detector concept from the Technical Desi…
At the ILC, one has the possibility to search for SUSY in an model-independent way: The corner-stone of SUSY is that sparticles couple as particles. This is independent of the mechanism responsible for SUSY breaking. Any model will have one Lightest SUSY Particle (LSP), and one Next to Lightest SUSY Particle (NLSP). In models with conserved R-parity, the NLSP must decay solely to the LSP and the SM partner of the NLSP. Therefore, studying NLSP production and decay can be regarded as a "simplified model without simplification": Any SUSY model will have such a process. The NLSP could be any spar…
Once all the sleptons as well as the Bino are observed at the ILC, the Bino contribution to the muon anomalous magnetic dipole moment (muon $g-2$) in supersymmetric (SUSY) models can be reconstructed. Motivated by the recently confirmed muon $g-2$ anomaly, we examine the reconstruction accuracy at the ILC with $\sqrt{s}$ = 500 GeV. For this purpose, measurements of stau parameters are important. We quantitatively study the determination of the mass and mixing parameters of the staus at the ILC. Furthermore, we discuss the implication of the stau study to the reconstruction of the SUSY contribu…
The requirement of electroweak naturalness in simple supersymmetric models implies the existence of a cluster of four light higgsinos with mass $\sim 100-300$\,GeV, the lighter the better. While such light compressed spectra may be challenging to observe at LHC, the International Linear $e^+e^-$ Collider (ILC) with $\sqrt{s}>2m_{\rm higgsino}$ would serve as both a SUSY discovery machine and a precision microscope. We study higgsino pair production signatures at the ILC based on full, \texttt{Geant4-}based simulation of the ILD detector concept. We examine several benchmark scenarios that may …
The direct pair-production of the superpartner of the $τ$-lepton, the $\widetildeτ$, is one of the most interesting channels to search for SUSY in. First of all, the $\widetildeτ$ is likely to be the lightest of the scalar leptons. Secondly the signature of $\widetildeτ$ pair production signal events is one of the experimentally most difficult ones, thereby constituting the "worst" possible scenario for SUSY searches. The current model-independent $\widetildeτ$ limits comes from analyses performed at LEP but they suffer from the limited energy of this facility. Limits obtained at the LHC do ex…
We study the possibility to determine the supersymmetric (SUSY) contribution to the muon anomalous magnetic dipole moment by using ILC measurements of the properties of superparticles. Assuming that the contribution is as large as the current discrepancy between the result of the Brookhaven E821 experiment and the standard-model prediction, we discuss how and how accurately the SUSY contribution can be reconstructed. We will show that, in a sample point, the reconstruction can be performed with the accuracy of ~ 13 % with the center-of-mass energy 500 GeV and the integrated luminosity ~ 500-10…
A core prediction of natural Supersymmetry is the existence of four light higgsinos not too far above the mass of the $Z$ boson. The small mass splittings amongst the higgsinos -- typically 5-20\,GeV -- imply very little visible energy release from decays of heavier higgsinos. In particular, if other SUSY particles are quite heavy, as can be the case in SUSY with radiatively-driven naturalness, the higgsinos are extremely hard to detect at hadron colliders. The clean environment of electron-positron colliders with $\sqrt{s} > 2m_{\mathrm{higgsino}}$, however, would allow for a decisive search …
Supersymmetry (SUSY) with bilinearly broken R parity (bRPV) offers an attractive possibility to explain the origin of neutrino masses and mixings. In such scenarios, the study of neutralino decays at colliders gives access to neutrino sector parameters. The ILC offers a very clean environment to study the neutralino properties as well as its subsequent decays, which typically involve a $W$ or $Z$ boson and a lepton. This study is based on ILC beam parameters according to the Technical Design Report for a center of mass energy of $500\,\mathrm{GeV}$. A full detector simulation of the Internatio…
The LHC experiments have searched for and excluded many proposed Beyond the Standard Model (BSM) theories. However, there are many scenarios where LHC has little or no sensitivity. Electron-positron colliders offers a different avenue for searches for such phenomena.In this talk, we will review the expectations for searches for number of BSM models at the International Linear Collider (ILC). We will discuss new Higgs-like scalars, indirect BSM via Standard Model Effective Field Theory (SMEFT) fits, mono-photons, and SUSY in strongly or moderately compressed models.
Although the LHC experiments have searched for and excluded many proposed new particles up to masses close to 1 TeV, there are many scenarios that are difficult to address at a hadron collider. This talk will review a number of these scenarios and present the expectations for searches at an electron-positron collider such as the International Linear Collider. The cases discussed include the light Higgsino, the \stau~ slepton in the coannihilation region relevant to dark matter, as well as other SUSY signatures. he studies are based on the ILD concept at the ILC.
Direct searches for superpartners and precision measurements of the properties of the $\sim 126$ GeV Higgs boson lead to important inter-dependent constraints on the underlying parameter space of the MSSM. The 19/20-parameter p(henomenological)MSSM offers a flexible framework for the study of a wide variety of both Higgs and SUSY phenomena at the LHC and elsewhere. Within this scenario we address the following questions: `What will potentially null searches for SUSY at the LHC tell us about the possible properties of the Higgs boson?' and, conversely, `What do precision measurements of the pro…
The International Linear Collider (ILC) has recently proven its technical maturity with the publication of a Technical Design Report, and there is a strong interest in Japan to host such a machine. We summarize key aspects of the Beyond the Standard Model physics case for the ILC in this contribution to the US High Energy Physics strategy process. On top of the strong guaranteed physics case in the detailed exploration of the recently discovered Higgs boson, the top quark and electroweak precision measurements, the ILC will offer unique opportunities which are complementary to the LHC program …
We study the potential of International Linear Collider (ILC) at sqrt(s) = 500 GeV to probe new dark matter motivated scenario where the bottom squark (sbottom) is the next to lightest supersymmetric particle. For this scenario, which is virtually impossible for the LHC to test, the ILC has a potential to cover a large fraction of the parameter space. The challenge is due to a very low energy of jets, below 20-30 GeV, which pushes the jet clustering and flavour tagging algorithms to their limits. The process of sbottom pair production was studied within the SiD detector concept. We demonstrate…
Special calorimeters are needed to instrument the very forward region of an ILC detector. These devices will improve the hermeticity being important for new particle searches. A luminometer is foreseen to measure the rate of low angle Bhabha scattering with a precision better than 10-3. A calorimeter adjacent to the beam-pipe will be hit by a large amount of beamstrahlung remnants. The amount and shape of these depositions will allow a fast luminosity estimate and the determination of beam parameters. However, the sensors must be extremely radiation hard. Finely segmented and very compact calo…
Impact of quark flavor violating SUSY on h(125) decays at future lepton colliders
Institut für Hochenergiephysik der Österreichischen Akademie der Wissenschaften（奥地利科学院高能物理研究所）；Department of Physics, Tokyo Gakugei University（东京学艺大学物理系）
The CERN Large Hadron Collider (LHC) is scheduled to commence operation in 2008 and inclusive searches for supersymmetry (SUSY) will be one of our primary tasks in the first days of LHC operation. It is certain that the final state of multijets + missing transverse energy will provide a superior performance in SUSY searches. Strategies to understand the instrumental background and to understand the Standard Model (SM) background are still under development and are urgent issues for the coming data. We describe the strategy for early SUSY searches at the ATLAS experiment using the fist data cor…
The performance of the ILD detector at the ILC for the analysis of $μ$ and $τ$ channels at the SUSY benchmark-point SPS1a' has been studied with full detector simulation. It is concluded that if 500 fb$^{-1}$ is delivered to the experiment, $Δ(\MXN{1}) = 920 \MeVcc$, $Δ(\msmul) = 100 \MeVcc$, $Δ(\MXN{2}) = 1.38 ~\GeVcc$, and $Δ(σ(\eeto \smul \smul))$ = 1.35 fb can be achieved from the $μ$ channels alone. The preliminary results from the $\stau$ channels, indicates that $Δ(P_τ) = 13 $ % is also achievable.
The precision measurements envisaged at the International Linear Collider (ILC) depend on excellent instrumentation and reconstruction software. The correct identification of heavy flavour jets, placing unprecedented requirements on the quality of the vertex detector, will be central for the ILC programme. This paper describes the LCFIVertex software, which provides tools for vertex finding and for identification of the flavour and charge of the leading hadron in heavy flavour jets. These tools are essential for the ongoing optimisation of the vertex detector design for linear colliders such a…
Two finely segmented and very compact calorimeters are foreseen for the instrumentation of the very forward region of the ILC and the CLIC detectors; a luminometer to measure the rate of low angle Bhabha scattering events with a precision better than $10^{-3}$ and, at lower polar angles, a detector for fast luminosity estimate. Both devices will improve the hermeticity of the detector in searches for new particles. Due to the expected high occupancy, fast front-end electronics is needed. The calorimeter closest to the beampipe will be hit by a large amount of beamstrahlung remnants, so that ra…
Construction of the cubic-kilometer neutrino detector IceCube at the South Pole has been completed in December 2010. It forms a lattice of 5160 photomultiplier tubes monitoring a gigaton of the deep Antarctic ice for particle induced photons. The telescope is primarily designed to detect neutrinos with energies greater than 100 GeV from astrophysical sources. Beyond this astrophysical motivation IceCube is also a discovery instrument for the search for physics beyond the Standard Model. Owing to subfreezing ice temperatures, the photomultiplier dark noise rates are particularly low which opens…
