TESLA Collider Research Articles

Measurement of the top-Higgs Yukawa coupling at a linear e+e- collider

Understanding the mechanism of electroweak symmetry breaking and the origin of boson and fermion masses is among the most pressing questions raised in contemporary particle physics. If these issues involve one (several) Higgs boson(s), a precise measurement of all its (their) properties will be of prime importance. Among those, the Higgs coupling to matter fermions (the Yukawa coupling). At a linear collider, the process e+e-→tt̄H will allow a direct measurement of the top-Higgs Yukawa coupling. We present a realistic feasibility study of the measurement in the context of the TESLA collider. Four channels are studied and the analysis is repeated for several Higgs mass values within the range 120–200 GeV/c 2.

New results on DEPFET pixel detectors for radiation imaging and high energy particle detection

DEPFET pixel detectors are unique devices in terms of energy and spatial resolution because very low noise operation can be obtained (ENC=2.2e/sup -/ at room temperature) by implementing the amplifying transistor in the pixel cell itself. Full DEPFET pixel matrices have been built and operated for autoradiographical imaging with imaging resolutions of 4.3/spl plusmn/0.8 /spl mu/m at 22 keV. For applications in low energy X-ray astronomy the high energy resolution of DEPFET detectors is attractive. For particle physics, DEPFET pixels are interesting as low mass detectors with high spatial resolution. For a linear collider detector the readout must be very fast. New readout chips have been designed and produced for the development of a DEPFET module for a pixel detector at the proposed TESLA collider, containing 520/spl times/4000 pixels, with 50 MHz line rate and 25 kHz frame rate. The circuitry contains current memory cells and current hit scanners for fast pedestal subtraction and sparsified readout. The imaging performance of DEPFET devices as well as present achievements toward a DEPFET vertex detector for a linear collider are presented.

Computation of higher order modes in TESLA structures

This paper presents results on the computation of Higher Order Modes (shortly HOMs) in the designs for the accelerating structures which have already been built in into the TESLA (1) Test Facility (TTF) or are presently being studied as final design for the TESLA collider. Depending on the complexity of the studied arrangement different computational strategies are followed: 1. the use of commercial software packages like MAFIA (2) or CST Microwave Studio (MWS) (2) on workstations, and 2. a recently implemented tool for Coupled S-Parameter Calculation (CSC) which easily allows to calculate the scattering properties of rf-sections connected to each other with arbitrary topology or to determine eigenmodes of resonating structures.

Study of a flavor-changing neutral top-pion production processe+e−→tc¯Πt0

We study a flavor-changing top-pion production process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}t\overline{c}{\ensuremath{\Pi}}_{t}^{0}$ in the top-color-assisted technicolor (TC2) model. The studies show that, with the high center of mass energy in the DESY TESLA collider, the production cross section of ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}t\overline{c}{\ensuremath{\Pi}}_{t}^{0}$ is at the order of magnitude 0.1 fb in most parameter regions of the TC2 model and a few tens of events of a top-pion production can be produced each year. The resonance effect can enhance the cross section to a few fb when the top-pion mass is small. With a clean background, the top-pion events can possibly be detected at the TESLA collider. On the other hand, we find that there exists a narrow peak near ${m}_{t}\ensuremath{-}{m}_{c}$ in the top-pion--charm invariant mass distribution which could be clearly detected. Therefore, such a top-pion production process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}t\overline{c}{\ensuremath{\Pi}}_{t}^{0}$ provides a unique chance to detect top-pion events and test the TC2 model.

Heavy quark production at the TESLA collider and its sensitivity to the gluon content in the photon

Heavy quark production is studied at the TESLA high energy linear $e^+e^-$ collider (LC) both in its nominal and photon collider (PC) mode. Leading order cross-sections are calculated for the production of heavy quarks, $e^+e^- \rightarrow e^+e^- Q(\bar{Q}) X$ , at high transverse momenta. The sensitivity of this process to the gluon content in the photon is studied.

Effective Lagrangian description of the lepton flavor violating decaysZ→li∓lj±

A comprehensive analysis of the lepton flavor violating (LFV) decays Z-->li lj is presented within the effective Lagrangian approach. Both the decoupling and nondecoupling scenarios are explored. The experimental constraints from li --> lj lk \bar{lk} and li -->lj gamma as well as some relationships arising from the gauge invariance of the effective Lagrangian are used to put constraints on Z-->li lj. It is found that while current experimental data impose very strong constraints on Z-->mu e, the channel Z --> tau mu (e)still may be at the reach of the planned TESLA collider.

M øller scattering polarimetry for high energy e +e − linear colliders

The general features of the M øller scattering and its use as an electron polarimeter are described and studied in view of the planned future high energy e +e − linear colliders. In particular the study concentrates on the TESLA collider which is planned to operate with longitudinal polarised beams at a centre of mass energy of the order of 0.5 TeV with a luminosity of 3.4×10 34 cm −2 s −1 .

A fast CCD vertex detector for the future linear collider: some recent developments

Experiments at a future e +e − linear collider will require a high-performance vertex detector to identify heavy quarks in multi-jet final states. The SLD experiment at SLAC has successfully demonstrated that charge-coupled devices (CCDs) are ideal candidates for this role, offering excellent two-dimensional spatial resolution with extremely low mass.This paper discusses recent R&D studies aimed at further reducing the vertex detector material budget and significantly increasing the CCD readout speed, in order to extend the physics reach of the future linear collider. A radical new CCD architecture is described, which would enable a CCD-based vertex detector to be used in the extremely challenging environment of the superconducting TESLA collider.

Superconducting superstructure for the TESLA collider: A concept

We discuss the new layout of a cavity chain (superstructure) allowing, we hope, significant cost reduction of the RF system of both linacs of the TESLA linear collider. The proposed scheme increases the fill factor and thus makes an effective gradient of an accelerator higher. We present mainly computations we have performed up to now and which encouraged us to order the copper model of the scheme, still keeping in mind that experiments with a beam will be necessary to prove if the proposed solution can be used for the acceleration.

Design considerations and analysis of potential applications of a high power ultraviolet FEL at the TESLA test facility at DESY

A possibility of constructing a high power ultraviolet free electron laser at the TESLA test facility at DESY is discussed. The proposed facility consists of a tunable master oscillator (P av ∼10 mW, P peak ∼10 kW, λ≃200–350 nm) and an FEL amplifier with a tapered undulator. The average and peak radiation power at the exit of the FEL amplifier is about 7 kW and 220 GW, respectively. Installation of such a facility can significantly extend scientific potential of the TESLA test facility. The UV free electron laser can be used to construct a polarized, monochromatic gamma-source with the ultimate yield up to 10 12 gamma-quanta per second and the maximal energy of about 100 MeV. An intensive gamma-source can also form the base for constructing the test facility for the TESLA positron generation system. Another accelerator application of the proposed facility is verification of the main technical solutions for the laser and the optical system to be used in the gamma–gamma option of the TESLA collider. A high average power UV laser is also promising for industrial applications.