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J. List
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DESY
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High Energy Physics - Experiment (37)
 
High Energy Physics - Phenomenology (27)
 
Physics - Instrumentation and Detectors (12)
 
Physics - Accelerator Physics (8)
 
Physics - Data Analysis; Statistics and Probability (2)

Publications Authored By J. List

At the ILC, the luminosity-weighted average polarization at the IP needs to be determined at the permille-level. In order to reach this goal, the combined information from the polarimeter and the collision data is required. In this study, a unified approach will be presented, which for the first time combines the cross section measurements with the expected constraints from the polarimeters. Read More

This paper addresses the question of whether the International Linear Collider has the capability of discovering new particles that have not already been discovered at the CERN Large Hadron Collider. We summarize the various paths to discovery offered by the ILC, and discuss them in the context of three different scenarios: 1. LHC does not discover any new particles, 2. Read More

Weakly Interacting Massive Particles (WIMPs, $\chi$) are candidates for Dark Matter. WIMP searches at lepton colliders are complementary to searches at hadron colliders and direct and indirect detection, since they directly probe the coupling to electrons which a priori is independent of the coupling to hadrons. Like at hadron colliders, WIMP pair production can be observed via an additional tag particle, in particular a photon from initial state radiation ($e^+e^-\rightarrow\chi\chi\gamma$). Read More

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. Read More

2016Jul
Affiliations: 1LCC Physics Working Group, 2LCC Physics Working Group, 3LCC Physics Working Group, 4LCC Physics Working Group, 5LCC Physics Working Group, 6LCC Physics Working Group, 7LCC Physics Working Group, 8LCC Physics Working Group, 9LCC Physics Working Group, 10LCC Physics Working Group, 11LCC Physics Working Group, 12LCC Physics Working Group, 13LCC Physics Working Group, 14LCC Physics Working Group, 15LCC Physics Working Group, 16LCC Physics Working Group, 17LCC Physics Working Group, 18LCC Physics Working Group, 19LCC Physics Working Group, 20LCC Physics Working Group, 21LCC Physics Working Group, 22LCC Physics Working Group, 23LCC Physics Working Group, 24LCC Physics Working Group, 25LCC Physics Working Group

If the gamma-gamma resonance at 750 GeV suggested by 2015 LHC data turns out to be a real effect, what are the implications for the physics case and upgrade path of the International Linear Collider? Whether or not the resonance is confirmed, this question provides an interesting case study testing the robustness of the ILC physics case. In this note, we address this question with two points: (1) Almost all models proposed for the new 750 GeV particle require additional new particles with electroweak couplings. The key elements of the 500 GeV ILC physics program---precision measurements of the Higgs boson, the top quark, and 4-fermion interactions---will powerfully discriminate among these models. Read More

These are the proceedings of the LHCSki 2016 workshop "A First Discussion of 13 TeV Results" that has been held at the Obergurgl Universit\"atszentrum, Tirol, Austria, April 10 - 15, 2016. In this workshop the consequences of the most recent results from the LHC have been discussed, with a focus also on the interplay with dark matter physics, flavor physics, and precision measurements. Contributions from the workshop speakers have been compiled into this document. Read More

A summary is presented of the workshop "top physics at linear colliders" that was held at IFIC Valencia from the 30th of June to the 3rd July 2015. We present an up-to-date status report of studies into the potential for top quark physics of lepton colliders with an energy reach that exceeds the top quark pair production threshold, with a focus on the linear collider projects ILC and CLIC. This summary shows that such projects can offer very competitive determinations of top quark properties (mass, width) and its interactions with other Standard Model particles, in particular electroweak gauge bosons and the Higgs boson. Read More

Supersymmetry can explain the observed dark matter relic density with a neutralino dark matter particle and a coannihilating, almost mass-degenerate sparticle. If this were the case in nature, a linear electron positron collider like the ILC could discover the two sparticles if their masses are in the kinematic reach of the collider. This contribution discusses which observations are necessary at the ILC for predicting the dark matter relic density correctly and for confirming that the observed lightest neutralino is the only kind of dark matter. Read More

2015Oct

The ILC Technical Design Report documents the design of a 500 GeV linear collider, but does not specify the center-of-mass energy steps of operation for the collider. The ILC Parameters Joint Working Group has studied possible running scenarios, including a realistic estimate of the real time accumulation of integrated luminosity based on ramp-up and upgrade processes, and considered the evolution of the physics outcomes. These physics goals include Higgs precision measurements, top quark measurements and searches for new physics. Read More

Polarimetry with permille-level precision is essential for future electron-positron linear colliders. Compton polarimeters can reach negligible statistical uncertainties within seconds of measurement time. The dominating systematic uncertainties originate from the response and alignment of the detector which records the Compton scattered electrons. Read More

2015Aug
Affiliations: 1DESY, Hamburg, Germany, 2DESY, Hamburg, Germany, 3DESY, Hamburg, Germany, 4DESY, Hamburg, Germany, 5DESY, Hamburg, Germany, 6DESY, Hamburg, Germany, 7DESY, Hamburg, Germany, 8KIT IEKP, Karlsruhe, Germany

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 Design Report. Read More

The ILC Technical Design Report documents the design for the construction of a linear collider which can be operated at energies up to 500 GeV. This report summarizes the outcome of a study of possible running scenarios, including a realistic estimate of the real time accumulation of integrated luminosity based on ramp-up and upgrade processes. The evolution of the physics outcomes is emphasized, including running initially at 500 GeV, then at 350 GeV and 250 GeV. Read More

We summarize the physics case for the International Linear Collider (ILC). We review the key motivations for the ILC presented in the literature, updating the projected measurement uncertainties for the ILC experiments in accord with the expected schedule of operation of the accelerator and the results of the most recent simulation studies. Read More

A comprehensive review of physics at an e+e- Linear Collider in the energy range of sqrt{s}=92 GeV--3 TeV is presented in view of recent and expected LHC results, experiments from low energy as well as astroparticle physics.The report focuses in particular on Higgs boson, Top quark and electroweak precision physics, but also discusses several models of beyond the Standard Model physics such as Supersymmetry, little Higgs models and extra gauge bosons. The connection to cosmology has been analyzed as well. Read More

Precision polarimetry is essential for future e+ e- colliders and requires Compton polarimeters designed for negligible statistical uncertainties. In this paper, we discuss the design and construction of a quartz Cherenkov detector for such Compton polarimeters. The detector concept has been developed with regard to the main systematic uncertainties of the polarisation measurements, namely the linearity of the detector response and detector alignment. Read More

Polarised electron and positron beams are key ingredients to the physics programme of future linear colliders. Due to the chiral nature of weak interactions in the Standard Model - and possibly beyond - the knowledge of the luminosity-weighted average beam polarisation at the $e^+e^-$ interaction point is of similar importance as the knowledge of the luminosity and has to be controlled to permille-level precision in order to fully exploit the physics potential. The current concept to reach this challenging goal combines measurements from Laser-Compton polarimeters before and after the interaction point with measurements at the interaction point. Read More

This article is based on the talk presented at the International Workshop on Future Linear Colliders (LCWS13) which held during November 11-15, 2013 at Tokyo, Japan. We present several analyses related to the Higgs total width study at ILC based on the full detector simulation of ILD, which are \eevvH followed by \Htobb and \HtoWW. The studies show that at $\unit{250}{GeV}$ we can determine the Higgs total width with a relative precision of 11% and the $HWW$ coupling with 4. Read More

2013Oct

This report summarizes the work of the Energy Frontier Higgs Boson working group of the 2013 Community Summer Study (Snowmass). We identify the key elements of a precision Higgs physics program and document the physics potential of future experimental facilities as elucidated during the Snowmass study. We study Higgs couplings to gauge boson and fermion pairs, double Higgs production for the Higgs self-coupling, its quantum numbers and $CP$-mixing in Higgs couplings, the Higgs mass and total width, and prospects for direct searches for additional Higgs bosons in extensions of the Standard Model. Read More

2013Sep
Affiliations: 1DESY, 2University of Pittsburgh, 3DESY, 4University of California, San Diego, 5University of Arizona, 6University of Tokyo

We make a systematic and comparative study for the LHC and ILC for the electroweakino searches in the Minimal Supersymmetric Standard Model. We adopt a general bottom-up approach and scan over the parameter regions for all the three cases of the lightest supersymmetric particle being Bino-, Wino-, and Higgsino-like. The electroweakino signal from pair production and subsequent decay to Wh (h to b\bar b) final state may yield a sensitivity of 95% C. Read More

Simplified models have become a widely used and important tool to cover the more diverse phenomenology beyond constrained SUSY models. However, they come with a substantial number of caveats themselves, and great care needs to be taken when drawing conclusions from limits based on the simplified approach. To illustrate this issue with a concrete example, we examine the applicability of simplified model results to a series of full SUSY model points which all feature a small stau-LSP mass difference, and are compatible with electroweak and flavor precision observables as well as current LHC results. Read More

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 of the next decade. Read More

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. Read More

In supersymmetric extensions of the Standard Model, higgsino-like charginos and neutralinos are preferred to have masses of the order of the electroweak scale by naturalness arguments. Such light $\widetilde{\chi}^0_1$, $\widetilde{\chi}^0_2$ and $\widetilde{\chi}^{\pm}_1$ states can be almost mass degenerate, and their decays are then difficult to observe at colliders. In addition to the generic naturalness argument, light higgsinos are well motivated from a top-down perspective. Read More

We re-evaluate prospects for supersymmetry at the proposed International Linear e^+e^- Collider (ILC) in light of the first two years of serious data taking at LHC: LHC7 with ~5 fb^{-1} of pp collisions at sqrt{s}=7 TeV and LHC8 with ~20 fb^{-1} at \sqrt{s}=8 TeV. Strong new limits from LHC8 SUSY searches, along with the discovery of a Higgs boson with m_h~125 GeV, suggest a paradigm shift from previously popular models to ones with new and compelling signatures. After a review of the current status of supersymmetry, we present a variety of new ILC benchmark models, including: natural SUSY, radiatively-driven natural SUSY (RNS), NUHM2 with low m_A, a focus point case from mSUGRA/CMSSM, non-universal gaugino mass (NUGM) model, stau-coannihilation, Kallosh-Linde/spread SUSY model, mixed gauge-gravity mediation, normal scalar mass hierarchy (NMH), and one example with the recently discovered Higgs boson being the heavy CP-even state H. Read More

2013Jun
Affiliations: 1University of Oklahoma, Department of Physics and Astronomy, 2SLAC, 3KEK, 4TUHEP, 5Universität Wien, Theoretische Physik, 6University of Toyama, Department of Physics, 7DESY, 8Carleton University, Department of Physics, 9University of Oxford, Particle Physics Department, 10Cornell University, Laboratory for Elementary-Particle Physics, 11SLAC, 12LAL, 13DESY, 14DESY, 15APC, CNRS/IN2P3, 16CERN, 17University of California, Department of Physics and Astronomy, 18University of Texas, Center for Accelerator Science and Technology

The International Linear Collider Technical Design Report (TDR) describes in four volumes the physics case and the design of a 500 GeV centre-of-mass energy linear electron-positron collider based on superconducting radio-frequency technology using Niobium cavities as the accelerating structures. The accelerator can be extended to 1 TeV and also run as a Higgs factory at around 250 GeV and on the Z0 pole. A comprehensive value estimate of the accelerator is give, together with associated uncertainties. Read More

We investigate the prospects for detecting and measuring the parameters of WIMP dark matter in a model independent way at the International Linear Collider. The signal under study is direct WIMP pair production with associated initial state radiation $e^+e^- \rightarrow \chi\chi\gamma$. The analysis accounts for the beam energy spectrum of the ILC and the dominant machine induced backgrounds. Read More

We re-evaluate prospects for supersymmetry at the proposed International Linear $e^+e^-$ Collider (ILC) in light of the first year of serious data taking at LHC with $\sqrt{s}=7$ TeV and $\sim 5$ fb$^{-1}$ of $pp$ collisions (LHC7). Strong new limits from LHC SUSY searches, along with a hint of a Higgs boson signal around $m_h\sim 125$ GeV, suggest a paradigm shift from previously popular models to ones with new and compelling signatures. We present a variety of new ILC benchmark models, including: natural SUSY, hidden SUSY, NUHM2 with low $m_A$, non-universal gaugino mass (NUGM) model, pMSSM, Kallosh-Linde model, Br\"ummer-Buchm\"uller model, normal scalar mass hierarchy (NMH) plus one surviving case from mSUGRA/CMSSM in the far focus point region. Read More

The prospects of measuring the parameters of WIMP dark matter in a model independent way at the International Linear Collider are investigated. The signal under study is direct WIMP pair production with associated initial state radiation. The analysis is performed in full simulation of the ILD detector concept. Read More

We perform the first experimental study with full detector simulation for the radiative production of neutralinos at the linear collider, at sqrt{s} = 500 GeV and realistic beam polarizations. We consider all relevant backgrounds, like the Standard Model background from radiative neutrino production. The longitudinal polarized beams enhance the signal and simultaneously reduce the background, such that statistical errors are significantly reduced. Read More

Future linear colliders plan to collide polarised beams and the planned physics reach requires knowledge of the state of polarisation as precisely as possible. The polarised beams can undergo depolarisation due to various mechanisms. In order to quantify the uncertainty due to depolarisation, spin tracking simulations in the International Linear Collider (ILC) Beam Delivery System (BDS) and at the Interaction Point (IP) have been performed. Read More

This paper describes the design and construction of a Cherenkov detector conceived with regard to high energy Compton polarimeters for the International Linear Collider, where beam diagnostic systems of unprecedented precision must complement the interaction region detectors to pursue an ambitious physics programme. Besides the design of a prototype Cherenkov detector, detailed simulation studies are presented. Results of a first testbeam campaign with the main objective of validating the simulation in terms of the light distribution inside the channels and the channel response are presented. Read More

In this study the ILC's capabilities for detecting WIMPs and measure their properties are investigated. The signal events are detected by associated production of Initial State Radiation (ISR). A model independent formulation of the signal cross section is used. Read More

Kinematic fitting is an important tool to improve the resolution in high-energy physics experiments. At future e+e- colliders, photon radiation parallel to the beam carrying away large amounts of energy and momentum will become a challenge for kinematic fitting. A photon with longitudinal momentum pz({\eta}) is introduced, which is parametrized such that {\eta} follows a normal distribution. Read More

Precise knowledge of all beam parameters is crucial to fully exploit the physics potential of the International Linear Collider (ILC). A sufficiently accurate measurement of the beam polarisation can only be achieved using dedicated high energy Compton polarimeters combined with well-designed arrays of Cherenkov detectors. This note focuses on the design and detailed simulation of a suitable Cherenkov detector prototype and provides an overview of first results from a highly successful beam test period. Read More

Kinematic fitting, where constraints such as energy and momentum conservation are imposed on measured four-vectors of jets and leptons, is an important tool to improve the resolution in high-energy physics experiments. At future e+ e- colliders, photon radiation parallel to the beam carrying away large amounts of energy and momentum will become a challenge for kinematic fitting. A photon with longitudinal momentum p_z^\gamma (\eta) is introduced, which is parametrized such that \eta ~follows a normal distribution. Read More

2010Apr
Affiliations: 1Deutsches Elektronen-Synchrotron DESY, 2Laser Zentrum Hannover, 3Deutsches Elektronen-Synchrotron DESY, 4Laser Zentrum Hannover, 5Deutsches Elektronen-Synchrotron DESY, 6Laser Zentrum Hannover, 7Deutsches Elektronen-Synchrotron DESY, 8Deutsches Elektronen-Synchrotron DESY, 9Max-Planck-Institute for Gravitational Physics, Albert-Einstein-Institute, and Institut für Gravitationsphysik, Leibniz Universität, Hannover, 10Deutsches Elektronen-Synchrotron DESY, 11Deutsches Elektronen-Synchrotron DESY, 12Deutsches Elektronen-Synchrotron DESY, 13Deutsches Elektronen-Synchrotron DESY, 14Hamburger Sternwarte, 15Max-Planck-Institute for Gravitational Physics, Albert-Einstein-Institute, and Institut für Gravitationsphysik, Leibniz Universität, Hannover

The ALPS collaboration runs a "Light Shining through a Wall" (LSW) experiment to search for photon oscillations into "Weakly Interacting Sub-eV Particles" (WISPs) often predicted by extensions of the Standard Model. The experiment is set up around a superconducting HERA dipole magnet at the site of DESY. Due to several upgrades of the experiment we are able to place limits on the probability of photon-WISP-photon conversions of a few 10^{-25}. Read More

The precision physics program of the ILC requires precise knowledge of the state of beam polarisation. In fact the Compton polarimeters intended for the ILC will have to measure the polarisation with error a factor of 2 smaller than the previous best measurement at the SLAC SLD experiment. In order to further reduce measurement error, spin tracking simulations in the ILC Beam Delivery System subject to ground motion induced misalignment have been performed and the expected variation in polarisation has been quantified. Read More

The prospects for the analysis of tau channels at the SUSY benchmark point SPS1a', especially from e+e- -> stau_1 stau_1 and e+e- -> stau_2 stau_2, have been studied in full simulation of the ILD detector concept forseen for the International Linear Collider. All accessible SUSY channels as well as all Standard Model backgrounds were generated at a centre-of-mass energy E_CMS=500 GeV, including the beam energy spectrum and beam backgrounds expected for nominal ILC beam parameters. With an integrated luminosity of 500 fb-1 delivered to the experiment, the masses of the stau_1 and stau_2 can be measured to 107. Read More

One of the benchmark processes for the optimisation of the detector concepts proposed for the International Linear Collider is Chargino and Neutralino pair production in an mSugra scenario where Chargino-1 and Neutralino-2 are mass degenerate and decay into W+Neutralino-1 and Z+Neutralino-1, respectively. In this case the separation of both processes in the fully hadronic decay mode is very sensitive to the jet energy resolution and thus to the particle flow performance. The mass resolutions and cross-section uncertainties achievable with the ILD detector concept are studied in full simulation at a center of mass energy of 500 GeV, an integrated luminosity of 500 fb-1 and beam polarisations of P(e+,e-) = (30%, -80%). Read More

2009May
Affiliations: 1Deutsches Elektronen-Synchrotron DESY, 2Laser Zentrum Hannover, 3Deutsches Elektronen-Synchrotron DESY, 4Laser Zentrum Hannover, 5Deutsches Elektronen-Synchrotron DESY, 6Laser Zentrum Hannover, 7Deutsches Elektronen-Synchrotron DESY, 8Deutsches Elektronen-Synchrotron DESY, 9Max-Planck-Institute for Gravitational Physics, Albert-Einstein-Institute, and Institut für Gravitationsphysik, Leibniz Universität, Hannover, 10Deutsches Elektronen-Synchrotron DESY, 11Deutsches Elektronen-Synchrotron DESY, 12Deutsches Elektronen-Synchrotron DESY, 13Deutsches Elektronen-Synchrotron DESY, 14Hamburger Sternwarte, 15Max-Planck-Institute for Gravitational Physics, Albert-Einstein-Institute, and Institut für Gravitationsphysik, Leibniz Universität, Hannover

The ALPS collaboration runs a light-shining-through-walls (LSW) experiment to search for photon oscillations into "weakly interacting sub-eV particles" (WISPs) inside of a superconducting HERA dipole magnet at the site of DESY. In this paper we report on the first successful integration of a large-scale optical cavity to boost the available power for WISP production in this type of experiments. The key elements are a frequency tunable narrow line-width continuous wave laser acting as the primary light source and an electronic feed-back control loop to stabilize the power build-up. Read More

Any future high energy e+e- linear collider aims at precision measurements of Standard Model quantities as well as of new, not yet discovered phenomena. In order to pursue this physics programme, excellent detectors at the interaction region have to be complemented by beam diagnostics of unprecedented precision. This article gives an overview of current plans and issues for polarimeters and energy spectrometers at the International Linear Collider, which have been designed to fulfill the precision goals at a large range of beam energies from 45. Read More

In this contribution accelerator solutions for polarized beams and their impact on physics measurements are discussed. Focus are physics requirements for precision polarimetry near the interaction point and their realization with polarized sources. Based on the ILC baseline programme as described in the Reference Design Report (RDR), recent developments are discussed and evaluated taking into account physics runs at beam energies between 100 GeV and 250 GeV, as well as calibration runs on the Z-pole and options as the 1TeV upgrade and GigaZ. Read More

In order to fully exploit the physics potential of the ILC, it will be necessary to measure (and control) beam parameters to a permille level precision. In case of the beam polarisation, this can only be achieved with dedicated high energy Compton polarimeters and by improving the detector linearity, as well as the calibration of the analyzing power. This note summarises results of an early testbeam period with the Cherenkov detector of the SLD polarimeter, linearity measurements of readout electronics and photodetectors and compares simulation results of the SLD Cherenkov detector with those of a new `U-shaped' prototype. Read More

The physics programme of the ILC requires polarimetry with yet unprecedented precision. This note focusses on aspects of the upstream polarimeter as described in the ILC Reference Design Report which are not compatible with the extraordinary precision goals. In conclusion, recommendations for improving the design are given. Read More

In this note the ILC's capabilities for detecting WIMPs and measuring their properties are studied. The expected signal cross section is derived in a model-independent way from the observed relic density of Dark Matter. Signal events are detected by means of initial state radiation (ISR). Read More

The fully hadronic final states of two signal processes from an mSUGRA inspired scenario (SUSY-P5) are studied within a full simulation of the LDC' detector model. These are chargino pair and neutralino pair production, i.e. Read More

Kinematic fitting is a well-established tool to improve jet energy and invariant mass resolutions by fitting the measured values under constraints (e.g. energy conservation). Read More

The International Linear Collider (ILC) will collide polarised electrons and positrons at beam energies of 45.6 GeV to 250 GeV and optionally up to 500 GeV. To fully exploit the physics potential of this machine, not only the luminosity and beam energy have to be known precisely, but also the polarisation of the particles has to be measured with an unprecedented precision of dP/P ~ 0. Read More

This note summarizes the results of the "Workshop on Polarisation and Beam Energy Measurements at the ILC", held at DESY (Zeuthen) April 9-11 2008. The topics for the workshop included (i) physics requirements, (ii) polarised sources and low energy polarimetry, (iii) BDS polarimeters, (iv) BDS energy spectrometers, and (v) physics-based measurements of beam polarisation and beam energy from collider data. Discussions focused on the current ILC baseline programme as described in the Reference Design Report (RDR), which includes physics runs at beam energies between 100 and 250 GeV, as well as calibration runs on the Z-pole. Read More