Abstract
A good knowledge of the luminosity spectrum is mandatory for many measurements at future e+e- colliders. As the beam-parameters determining the luminosity spectrum cannot be measured precisely, the luminosity spectrum has to be measured through a gauge process with the detector. The measured distributions, used to reconstruct the spectrum, depend on Initial State Radiation, cross-section, and Final State Radiation. To extract the basic luminosity spectrum, a parametric model of the luminosity spectrum is created, in this case the spectrum at the 3 TeV Compact Linear Collider (CLIC). The model is used within a reweighting technique to extract the luminosity spectrum from measured Bhabha event observables, taking all relevant effects into account. The centre-of-mass energy spectrum is reconstructed within 5% over the full validity range of the model. The reconstructed spectrum does not result in a significant bias or systematic uncertainty in the exemplary physics benchmark process of smuon pair production.
Highlights
The knowledge of the shape of this luminosity spectrum is mandatory for the precision measurements in which a crosssection has to be known
The luminosity spectrum distribution can be seen as a convolution of the beam-energy spread, which is inherent to the accelerator, and the Beamstrahlung due to the Beam–Beam effects
Three observables, which can be extracted from the final state electrons, are used for the reconstruction of the luminosity spectrum: the relative centre-of-mass energy calculated from positron stahcoel /p√olsanroma,ngthleesenoef rgthye outgoing electron of the electron E1, and and the energy of the positron E2
Summary
The knowledge of the shape of this luminosity spectrum is mandatory for the precision measurements in which a crosssection has to be known. The distributions used for the reconstruction of the luminosity spectrum are dependent on the cross-section of the process, and initial and final state radiation (FSR). Shibata et al [7] proposed to calculate the distribution of the four-vectors of the Bhabha electrons and extract the luminosity spectrum with the iterative Expectation–Maximisation algorithm They have, considered neither detector resolutions, nor Initial and Final State Radiation. The acollinearity and the energies of the electrons measured in the calorimeter were used in a reweighting fit to reconstruct the luminosity spectrum. Bhabha scattering is the process of choice for luminosity measurements It can be calculated with high precision and has a large cross-section. Because cross-sections σx s depend on the centre-ofmass energy, any process used to reconstruct the basic luminosity spectrum will inherently contain a scaled luminosity spectrum. The scattered particles are recorded in the detector, where their properties are reconstructed within the limits of the resolution of the respective sub-detectors
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