• Issue front cover thumbnail

      Volume 69, Issue 5

      November 2007,   pages  693-952e

    • Foreword

      Rohini M Godbole Atul Gurtu

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    • The LDC detector concept

      Ties Behnke LDC Concept Group

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      In preparation of the experimental program at the international linear collider (ILC), the large detector concept (LDC) is being developed. The main points of the LDC are a large volume gaseous tracking system, combined with high precision vertex detector and an extremely granular calorimeter. The main design force behind the LDC is the particle flow concept.

    • Gamma gamma technology group

      Alexander John Finch

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      The results presented at this conference in the $\gamma \gamma$ technology group are described

    • Physics overview: Introduction to international linear collider physics

      Yasuhiro Okada

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      Physics at the international linear collider (ILC) is described as an introductory talk at Linear Collider Workshop 2006 (LCWS06).

    • Physics beyond the standard model and cosmological connections: A summary from LCWS06

      K Sridhar

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      The international linear collider (ILC) is likely to provide us important insights into physics sector that may supersede our current paradigm, viz., the standard model. In anticipation of the possibility that the ILC may come up in the middle of the next decade, several groups are vigourously investigating its potential to explore this new sector of physics. The Linear Collider Workshop in Bangalore (LCWS06) had several presentations of such studies which looked at supersymmetry, extra dimensions and other exotic possibilities which the ILC may help us discover or understand. Some papers also looked at the understanding of cosmology that may emerge from studies at the ILC. This paper summarises these presentations.

    • The road towards the international linear collider: Higgs, top/quantum chromodynamics, loops

      S Heinemeyer

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      The international linear $e^{+}e$^{−}$ collider (ILC) could go into operation in the second half of the upcoming decade. Experimental analyses and theory calculations for the physics at the ILC are currently performed. We review recent progress, as presented at the LCWS06 in Bangalore, India, in the fields of Higgs boson physics and top/QCD. Also the area of loop calculations, necessary to achieve the required theory precision, is included.

    • Forward tracking detectors

      Klaus Mönig

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      Forward tracking is an essential part of a detector at the international linear collider (ILC). The requirements for forward tracking are explained and the proposed solutions in the detector concepts are shown.

    • Photon pairs: Quantum chromodynamics continuum and the Higgs boson

      Edmond L Berger

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      A new QCD calculation is summarized for the transverse momentum distribution of photon pairs produced by QCD subprocesses, including all-orders soft-gluon resummation valid at next-to-next-to-leading logarithmic accuracy. Resummation is needed to obtain reliable predictions in the range of transverse momentum where the cross-section is the largest. Results are compared with data from the Fermilab Tevatron and predictions are made for the large hadron collider. The QCD continuum is shown to have a softer spectrum than the Higgs boson signal at the LHC.

    • The standard model Higgs search at the large hadron collider

      Satyaki Bhattacharya on behalf of the CMS and the ATLAS Collaborations

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      The experiments at the large hadron collider (LHC) will probe for Higgs boson in the mass range between the lower bound on the Higgs mass set by the experiments at the large electron positron collider (LEP) and the unitarity bound ($\sim 1$ TeV). Strategies are being developed to look for signatures of Higgs boson and measure its properties. In this paper results from full detector simulation-based studies on Higgs discovery from both ATLAS and CMS experiments at the LHC will be presented. Results of simulation studies on Higgs coupling measurement at LHC will be discussed.

    • Little Higgs model effects in $\gamma \gamma \rightarrow \gamma \gamma$

      S Rai Choudhury Ashok Goyal A S Cornell Naveen Gaur

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      Though the predictions of the standard model (SM) are in excellent agreement with experiments, there are still several theoretical problems associated with the Higgs sector of the SM, where it is widely believed that some new physics will take over at the TeV scale. One beyond the SM theory which resolves these problems is the Little Higgs (LH) model. In this work we have investigated the effects of the LH model on $\gamma \gamma \rightarro \gamma \gamma$ scattering [1].

    • Charged and neutral minimal supersymmetric standard model Higgs boson decays and measurement of tan 𝛽 at the compact linear collider

      E Coniavitis A Ferrari

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      The minimal supersymmetric extension of the standard model (MSSM) predicts the existence of new charged and neutral Higgs bosons. The pair creation of these new particles at the multi-TeV $e^{+} e^{−}$ compact linear collider (CLIC), followed by decays into standard model particles, were simulated along with the corresponding background. High-energy beam–beam effects such as ISR, beamstrahlung and hadronic background were included. We have investigated the possibility of using the ratio between the number of events found in various decay channels to determine the MSSM parameter tan 𝛽 and we have derived the corresponding statistical error from the uncertainties on the measured cross-sections and Higgs boson masses.

    • Power losses in the international linear collider 20 mrad extraction line at 1 TeV

      A Ferrari Yuri Nosochkov

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      We have performed a detailed study of the power losses in the post-collision extraction line of a TeV $e^{+}e^{−}$ collider with a crossing angle of 20 mrad at the interaction point. Five cases were considered: four luminosity configurations for ILC and one for CLIC. For all of them, the strong beam–beam effects at the interaction point lead to an emittance growth for the outgoing beam, as well as to the production of beamstrahlung photons and $e^{+}e^{−}$ coherent pairs. The power losses along the extraction line, which are due to energy deposition by a fraction of the disrupted beam, of the beamstrahlung photons and of the coherent pairs, were estimated in the case of ideal collisions, as well as with a vertical position or angular offset at the interaction point.

    • Probing CP-violating Higgs contributions in $\gamma \gamma \rightarrow f\bar{f}$

      Rohini M Godbole Sabine Kraml Saurabh D Rindani Ritesh K Singh

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      We discuss the use of fermion polarization for studying neutral Higgs bosons at a photon collider. To this aim we construct polarization asymmetries which can isolate the contribution of a Higgs boson 𝜙 in $\gamma \gamma \rightarrow f\bar{f}$, $f = \tau/t$, from that of the QED continuum. This can help in getting information on the $\gamma \gamma \phi$ coupling in case 𝜙 is a CP eigenstate. We also construct CP-violating asymmetries which can probe CP mixing in case 𝜙 has indeterminate CP. Furthermore, we take the MSSM with CP violation as an example to demonstrate the potential of these asymmetries in a numerical analysis. We find that these asymmetries are sensitive to the presence of a Higgs boson as well as its CP properties over a wide range of MSSM parameters.

    • Anomalous $V V H$ interactions at a linear collider

      Sudhansu S Biswal Debajyoti Choudhury Rohini M Godbole Ritesh K Singh

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      We examine, in a model independent way, the sensitivity of a linear collider to the couplings of a light Higgs boson to a pair of gauge bosons, including the possibility of CP violation. We construct several observables that probe the various possible anomalous couplings. For an intermediate mass Higgs, a collider operating at a center of mass energy of 500 GeV and with an integrated luminosity of 500 fb-1 is shown to be able to constrain the $ZZH$ vertex at the few per cent level, with even higher sensitivity for some of the couplings. However, lack of sufficient number of observables as well as contamination from the $ZZH$ vertex limits the precision to which anomalous part of the $W W H$ coupling can be probed.

    • Testing the minimal supersymmetric standard model with the mass of the 𝑊 boson

      S Heinemeyer W Hollik D Stöckinger A M Weber G weiglein

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      We review the currently most accurate evaluation of the 𝑊 boson mass, $M_{W}$, in the minimal supersymmetric standard model (MSSM). It consists of a full one-loop calculation, including the complex phase dependence, all available MSSM two-loop corrections as well as the full standard model result. We analyse the impact of the phases in the scalar quark sector on $M_{W}$ and compare the prediction for $M_{W}$ based on all known higher-order contributions with the experimental results.

    • Partially composite two-Higgs doublet model

      Dong-Won Jung

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      In the extra dimensional scenarios with gauge fields in the bulk, the Kaluza-Klein (KK) gauge bosons can induce Nambu-Jona-Lasinio (NJL) type attractive four-fermion interactions, which can break electroweak symmetry dynamically with accompanying composite Higgs fields. We consider a possibility that electroweak symmetry breaking (EWSB) is triggered by both a fundamental Higgs and a composite Higgs arising in a dynamical symmetry breaking mechanism induced by a new strong dynamics. The resulting Higgs sector is a partially composite two-Higgs doublet model with specific boundary conditions on the coupling and mass parameters originating at a compositeness scale 𝛬. The phenomenology of this model is discussed including the collider phenomenology at LHC and ILC.

    • Probing anomalous Higgs couplings at an $e\gamma$ collider using unpolarised beams

      Debajyoti Choudhury Mamta

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      We examine the sensitivity of $e \gamma$ colliders (based on $e^{+} e^{-}$ linear colliders of c.m. energy 500 GeV) to the anomalous couplings of the Higgs to 𝑊-boson via the process $e^{-} \gamma \rightarrow \nu WH$. This has the advantage over $e^{+} e^{-}$ collider in being able to dissociate $WWH$ vertex from $ZZH$. We are able to construct several dynamical variables which may be used to constrain the various couplings in the $WWH$ vertex.

    • Search for Higgs boson in beyond standard model scenarios at large hadron collider

      Kajari Mazumdar on behalf of the ATLAS and CMS Collaborations

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      The principal physics motivation of the LHC experiments is to search for the Higgs boson and to probe the physics of TeV energy scale. Potential of discovery for Higgs bosons in various scenarios beyond standard model have been estimated for both CMS and ATLAS experiments through detailed detector simulations. Main results from the recently published studies of CMS collaboration are only included in this write-up.

    • Associated single photons and doubly-charged scalars at linear $e^{-} e^{-}$ colliders

      Biswarup Mukhopadhyaya Santosh Kumar Rai

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      Doubly-charged scalars, predicted in many models having exotic Higgs representations, can in general have lepton-number violating (LFV) couplings. We show that by using an associated monoenergetic final state photon seen at a future linear $e^{-} e^{-}$ collider, we can have a clear and distinct signature for a doubly-charged resonance. The strength of the $\Delta L = 2$ coupling can also be probed quite effectively as a function of the recoil mass of the doubly-charged scalar.

    • Identifying new physics contributions in the Higgs sector at linear $e^{+} e^{-}$ colliders

      Santosh Kumar Rai

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      Loop-driven decay modes of the Higgs are sensitive to new physics contributions because of new particles in the loops. To highlight this we look at the dilepton-dijet signal in the dominant Higgs production channel at a linear $e^{+} e^{-}$ collider. We show that by taking a simple ratio between cross-sections of two different final states such contributions can be very easily identified.

    • Higgs self-coupling in the fusion channel at the international linear collider

      K Moeing A Rosca

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      We investigate the Higgs pair production process at the international linear collider (ILC), focusing on the measurement of the trilinear self-coupling of the Higgs boson in the fusion channel. The sensitivity of this measurement is discussed in the Higgs mass range 140-200 GeV at a center-of-mass energy between 1 TeV and 1.5 TeV.

    • Phenomenology of non-universal gaugino masses and implications for the Higgs boson decay

      K Huitu J Laamanen P N Pandita Sourov Roy

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      Grand unified theories (GUTs) can lead to non-universal gaugino masses at the unification scale. We study the implications of such non-universal gaugino masses for the composition of the lightest neutralino in supersymmetric (SUSY) theories based on $SU(5)$ gauge group. We also consider the phenomenological implications of non-universal gaugino masses for the phenomenology of Higgs bosons in the context of large hadron collider.

    • Low-scale gravity mediation in warped extra dimension and collider phenomenology on hidden sector

      H Itoh N Okada T Yamashita

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      We propose a new scenario of gravity-mediated supersymmetry breaking (gravity mediation) in a supersymmetric Randall-Sundrum model, where the gravity mediation takes place at a low scale due to the warped metric. We investigate collider phenomenology involving the hidden sector field, and find a possibility that the hidden sector field can be produced at the LHC and the ILC. The hidden sector may no longer be hidden.

    • Model-independent approach for dark matter phenomenology: Signatures in linear colliders and cosmic positron experiments

      Shigeki Matsumoto Nobuchika Okada

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      We have studied the phenomenology of dark matter at the ILC and cosmic positron experiments based on model-independent approach. We have found a strong correlation between dark matter signatures at the ILC and those in the indirect detection experiments of dark matter. Once the dark matter is discovered in the positron experiments such as the PAMELA, its nature will be investigated in detail at the ILC.

    • Top squark and neutralino decays in a 𝑅-parity violating model constrained by neutrino oscillation data

      Sujoy Poddar

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      In a 𝑅-parity violating (RPV) model of neutrino mass with three bilinear couplings $\mu_{i}$ and three trilinear couplings $\lambda_{i33}^{'}$, where 𝑖 is the lepton index, we find six generic scenarios each with a distinctive pattern of the trilinear couplings consistent with the neutrino oscillation data. These patterns may be reflected in direct RPV decays of the lighter top squark or in the RPV decays of the lightest superparticle, assumed to be the lightest neutralino. Typical signal sizes at the Tevatron RUN II and the LHC have been estimated and the results turn out to be encouraging.

    • Testing the supersymmetric QCD Yukawa coupling in a combined LHC/ILC analysis

      A Freitas P Z Skands

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      In order to establish supersymmetry (SUSY) at future colliders, the identity of gauge couplings and the corresponding Yukawa couplings between gauginos, sfermions and fermions needs to be verified. A first phenomenological study for determining the Yukawa coupling of the SUSY-QCD sector is presented here, using a method which combines information from LHC and ILC.

    • Probing space-time structure of new physics with polarized beams at the international linear collider

      B Ananthanarayan

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      At the international linear collider large beam polarization of both the electron and positron beams will enhance the signature of physics due to interactions that are beyond the standard model. Here we review our recently obtained results on a general model-independent method of determining for an arbitary one-particle inclusive state the space-time structure of such new physics through the beam polarization dependence and angular distribution of the final state particle.

    • Signals of universal extra dimension at the international linear collider

      Biplob Bhattacherjee

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      In the minimal universal extra dimension model, single production of $n = 2$ gauge bosons provides a unique discriminating feature from supersymmetry. We discuss how the proposed international linear collider can act as a $n = 2$ factory, much in the same vein as LEP.

    • Higher-order corrected Higgs bosons in FeynHiggs2.4

      T Hahn S Heinemeyer W Hollik H Rzehak G Weiglein K Williams

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      Large higher-order corrections enter the Higgs boson sector of the MSSM via Higgs-boson self-energies. Their effects have to be taken into account for the correct treatment of loop-corrected Higgs-boson mass eigenstates as external (on-shell) or internal particles in Feynman diagrams. We review how the loop corrections, including momentum dependence and imaginary contributions, are correctly taken into account for external (on-shell) Higgs boson and how effective couplings can be derived. The procedures are implemented in the code FeynHiggs2.4.

    • Extra dimension searches at hadron colliders to next-to-leading order-QCD

      M C Kumar Prakash Mathewes V Ravindran

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      The quantitative impact of NLO-QCD corrections for searches of large and warped extra dimensions at hadron colliders are investigated for the Drell-Yan process. The K-factor for various observables at hadron colliders are presented. Factorisation, renormalisation scale dependence and uncertainties due to various parton distribution functions are studied. Uncertainties arising from the error on experimental data are estimated using the MRST parton distribution functions.

    • Distinguishing new physics scenarios with polarized electron and positron beams

      A A Pankov N Paver A V Tsytrinov

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      Contact-like nonstandard interactions can be revealed only through deviations of observables from the standard model (SM) predictions. We consider a number of such nonstandard scenarios, and discuss their identification as sources of deviations in fermion-pair production processes at the international linear collider (ILC), if they were observed. We emphasize the role of $e^{-}$ and $e^{+}$ polarization in enhancing the identification reaches.

    • Transverse polarization in $\gamma Z; H Z$ production

      Saurabh D Rindani

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      With the use of transverse polarization (TP), a CP-odd and T-odd observable can be constructed when the final-state particles are self-conjugate. In the case of $H Z$ production, this observable can be used to probe a certain effective four-point $e^{+} e^{-} Z H$ CP-violating coupling, not accessible without TP. Effective CP-violating $Z Z H$ coupling does not contribute to this observable. A similar observable in $\gamma Z$ production can be used to probe $e^{+} e^{-} \gamma Z$ four-point couplings.

    • Higher curvature effects in Arkani-Hamed-Dimopoulos-Dvali and Randall-Sundrum models

      T G Rizzo

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      We explore the collider phenomenology of terascale extra-dimensional models with gravitational actions that contain higher curvature terms. In particular, we examine how the classic collider signatures of the models of Arkani-Hamed, Dimopoulos and Dvali (ADD) and of Randall and Sundrum (RS) are altered by these modifications to the usual Einstein-Hilbert (EH) action. Not only are the detailed signatures for gravitationally induced processes altered but new contributions are found to arise due to the existence of additional scalar Kaluza-Klein (KK) states in the spectrum.

    • Event-shape of dileptons plus missing energy at a linear collider as a supersymmetry/Arkani-Hamed-Dimopoulos-Dvali discriminant

      Pabir Roy

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      An event-shape analysis of the dileptons in the process $e^{+} e^{-} \rightarrow \ell^{+} \ell^{-} Ɇ$, studied in ILC or CLIC, can clearly discriminate between a supersymmetric or a large extra dimensional (ADD) production mechanism.

    • Probing universal extra dimension at the international linear collider

      Gautam Bhattacharyya

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      We consider the UED scenario and study the detectability of the first KK electron-positron pair at the ILC. A few hundred GeV KK electron decays into a nearly degenerate KK photon, which carries away missing energy, and the standard electron. The mass splitting between the KK electron and KK photon is controlled by the bulk- and brane-induced radiative corrections. We look for the signal event $e^{+} e^{-} +$ large missingenergy for $\sqrt{s} = 1$ TeV and observe that with a few hundred fb-1 luminosity the signal can be deciphered from the standard model background. We briefly outline how the UED signals may be distinguished from the supersymmetric signals.

    • Littlest Higgs model and 𝑊 pair production at international linear collider

      P Poulose

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      Among the viable alternatives to the standard Higgs mechanism is the recently proposed Little Higgs model. The advantage here is that the model has an elementary light neutral scalar particle, which arises dynamically as against its ad hoc introduction in the standard model. The model also avoids hierarchy problem. We have investigated the 𝑊 pair production at ILC to study the littlest Higgs model using different observables. Specifically, polarization fraction of 𝑊 boson is expected to be measured very accurately at ILC. We use this to put limit on the scale parameter, 𝑓, in the model.

    • Lepton distribution in top decay: A probe of new physics and top-polarization

      Rohini M Godbole Saurabh D Raindani Ritesh K Singh

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      We investigate the possibilities of studying new physics in various processes of 𝑡-quark production using kinematical distributions of the secondary lepton coming from decay of 𝑡 quarks. We show that the angular distributions of the secondary lepton are insensitive to the anomalous $tbW$ vertex and hence are pure probes of new physics in a generic process of 𝑡-quark production. The effects of 𝑡 polarization on the distributions of the decay lepton are demonstrated for top-pair production process at a $\gamma \gamma$-collider mediated by a heavy Higgs boson.

    • Scalar top study: Detector optimization

      C Milsténe A Sopczak

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      A vertex detector concept of the linear collider flavour identification (LCFI) collaboration, which studies pixel detectors for heavy quark flavour identification, has been implemented in simulations for 𝑐-quark tagging in scalar top studies. The production and decay of scalar top quarks (stops) is particularly interesting for the development of the vertex detector as only two 𝑐-quarks and missing energy (from undetected neutralinos) are produced for light stops. Previous studies investigated the vertex detector design in scenarios with large mass differences between stop and neutralino, corresponding to large visible energy in the detector. In this study we investigate the tagging performance dependence on the vertex detector design in a scenario with small visible energy for the international linear collider (ILC).

    • Measuring Higgs CP properties through top quark production at a photon collider

      Eri Asakawa

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      We study resonant effects of heavy Higgs bosons on the top-pair production process at a photon linear collider. Observables which can be obtained by circular polarization of colliding photons and polarization measurement through the angular distribution of the top quark decays are useful not only for measuring the Higgs CP parity but also for resolving degeneracy of Higgs bosons.

    • Heavy neutral MSSM Higgs bosons at the photon linear collider - a comparison of two analyses

      M Spira P Nieżurawski M Krawczyk A F Żarnecki

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      Measurement of the heavy neutral MSSM Higgs bosons 𝐻 and 𝐴 production in the process $\gamma \gamma \rightarrow A/H \rightarrow b\bar{b}$ at the Photon Linear Collider [1,2] has been considered in two independent analyses for the parameter range corresponding to the so-called `LHC wedge'. Significantly different conclusions were obtained; signal-to-background ratio 36 vs. 2. Here assumptions and results of these two analyses are compared. We have found that differences in the final results are mainly due to different assumptions on $\gamma \gamma$-luminosity spectra, jet definitions and selection cuts.

    • Photon collider beam simulation with CAIN

      Aleksander Filip Żarnecki

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      The CAIN simulation program was used to study the outgoing beam profile for the photon collider at ILC. The main aim of the analysis was to verify the feasibility of the photon linear collider running with 20 mrad electron beam crossing angle. The main problem is the distorted electron beam, which has to be removed from the interaction region. It is shown that with a new design of the final dipole, it should be possible to avoid large energy losses at the face of the magnet.

    • Results from GRACE/SUSY at one-loop

      J Fujimoto T Ishikawa M Jimbo T Kaneko T Kon Y kurihara M Kuroda Y Shimizu Y Yasui

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      We report the recent development on the SUSY calculations with the help of GRACE system. GRACE/SUSY/1LOOP is the computer code which can generate Feynman diagrams in the MSSM automatically and compute one-loop amplitudes in the numerical way. We present new results of various two-body decay widths and chargino pair production at ILC (international linear collider) at one-loop level.

    • Electroweak precision data and gravitino dark matter

      S Heinemeyer

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      Electroweak precision measurements can provide indirect information about the possible scale of supersymmetry already at the present level of accuracy. We review present day sensitivities of precision data in mSUGRA-type models with the gravitino as the lightest supersymmetric particle (LSP). The $\chi^{2}$ fit is based on $M_{W}$, sin2 $\theta_{\text{eff}}$, $(g - 2)_{\mu}$ BR($b \rightattow s\gamma$) and the lightest MSSM Higgs boson mass, $M_{h}$. We find indications for relatively light soft supersymmetry-breaking masses, offering good prospects for the LHC and the ILC, and in some cases also for the Tevatron.

    • List of Participants

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    • International Advisory Committee

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