Luminosity

Summary

Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a star, galaxy, or other astronomical objects. In SI units, luminosity is measured in joules per second, or watts. In astronomy, values for luminosity are often given in the terms of the luminosity of the Sun, L⊙. Luminosity can also be given in terms of the astronomical magnitude system: the absolute bolometric magnitude (Mbol) of an object is a logarithmic measure of its total energy emission rate, while absolute magnitude is a logarithmic measure of the luminosity within some specific wavelength range or filter band. In contrast, the term brightness in astronomy is generally used to refer to an object's apparent brightness: that is, how bright an object appears to an observer. Apparent brightness depends on both the luminosity of the object and

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The High Luminosity Large Hadron Collider (HL-LHC) upgrade aims for a tenfold increase in integrated luminosity compared to the nominal Large Hadron Collider (LHC), and for operation at a leveled luminosity five times higher than the nominal LHC peak luminosity. In order to compensate the geometric luminosity loss due to the increased crossing angle, crab cavities will be used to transversely rotate the beam bunches, allowing quasi head-on collisions at the experiments. Crab cavity failures can be very fast, having time constants similar to the reaction time of the machine protection system. In such a scenario the beams cannot be immediately extracted, making the protection of the machine fully rely on passive protection devices such as the collimation system. At the same time the energy stored in the HL-LHC beams will be doubled with respect to the LHC to more than 700 MJ, which increases the risk of damaging the machine and the experiments in case of failure. Crab cavity failures have the potential to displace the beam core and create considerable particle losses around the machine, posing a machine protection challenge. Any increase in failure rates will be difficult to compensate, affecting the performance of the HL-LHC and therefore the integrated luminosity goal. This is why it is important to correctly interlock the machine and make sure that certain types of failure never happen. In order to do this advanced simulations are needed well before the crab cavity prototypes can be tested in real operating conditions. This thesis analyzes different failure scenarios for crab cavities installed around the ATLAS and CMS experiments. The selected failure scenarios are later simulated with the tracking code SixTrack thanks to a newly developed functionality. The distribution of the particle losses in space and time are analyzed for the different failure cases and a quantitative estimate of the impact in the collimation system is given. The results are analyzed from a machine protection point of view, where the time for the beam abort trigger is calculated for each failure case and mitigation techniques are proposed. These results allow identifying corner cases corresponding to the most dangerous crab cavity failure scenarios, serving as input for the design of the future interlocking system.

EPFL2018

This thesis describes the wide subject of the luminosity leveling and its requirements for the LHC and the HL-LHC. We discuss the advantages and disadvantages of different leveling methods focusing the thesis on the beta star leveling technique. We review the beams offset build--up due to the environmental (i.e. natural ground motion) and mechanical (i.e. moving quadrupole) sources. We quantify the instrumentation requirements for the reliable and reproducible operation with small offsets at the interaction points. Last but not least, we propose a novel method for the beam offset stabilization at the collision point based on the feedback from the luminosity.

EPFL2016

Model-independent measurement of charm mixing parameters in D0 -> K0S pi+ pi- decays

Surapat Ek-In

This thesis presents a measurement of charm mixing and CP-violation parameters using D0 -> K0S pi+ pi- decays. These mixing parameters include the mass and decay-width differences of the mass eigenstates of the D0-D0bar system. A search for Charge-Parity violation is performed through measurements of D0-D0b mixing and of the interference between mixing and decay amplitudes. The dataset consists of events reconstructed in proton-proton collisions collected by the LHCb experiment during theoperation of the Large Hadron Collider (LHC) from 2016 to 2018. This sample corresponds to an integrated luminosity of 5.4 fb^-1. The D0 decays are selected in semileptonically decays of b hadrons. The results are expressed in terms of the CP-averaged mixing parameters and CP-violating differences asx_cp= (+4.29 +/- 1.48 (stat) +/- 0.26 (syst)) x 10^{-3}y_cp= (+12.61 +/- 3.12 (stat) +/- 0.83 (syst)) x 10^{-3}delta x= (-0.77 +/- 0.93 (stat) +/- 0.28 (syst)) x 10^{-3}delta y= (+3.01 +/- 1.92 (stat) +/- 0.26 (syst)) x 10^{-3}where the first uncertainty is statistical and the second is systematic. They correspond to the mixing and CP-violation parameters x = 0.46^{+0.15}{-0.16} x 10^{-2} y = 1.24^{+0.32}{-0.33} x 10^{-2} |q/p| = 1.21^{+0.21}{-0.15} \phi = -0.132^{+0.088}{-0.120} rad.The value of x deviates from zero with a significance of almost 3 sigma.These results are complementary to and consistent with previous measurements and with the current world-average values.They represent an independent and complementary knowledge of the charm-mixing parameters.A combination with the recent LHCb analysis of Dstar -> D0 (->K0S pi+ pi-) pi decays is also reported.

EPFL2022