The LHCb Silicon Tracker

The LHCb experiment is dedicated to the study of heavy flavour physics at the Large Hadron Collider (LHC). The primary goal of the experiment is to search for indirect evidence of new physics via measurements of CP violation and rare decays of beauty and charm hadrons. The LHCb detector has a large area silicon micro-strip detector located upstream of a dipole magnet, and three tracking stations with silicon micro-strip detectors in the innermost region downstream of the magnet. These two sub-detectors form the LHCb Silicon Tracker (ST). This paper gives an overview of the performance and operation of the ST during LHC Run 1. Measurements of the observed radiation damage are shown and compared to the expectation from simulation. (C) 2016 Published by Elsevier B.V.

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

Measurement of time-dependent CP violation in B0->Dpi decays and optimisation of flavour tagging algorithms at LHCb

Vincenzo Battista

This thesis presents the results of a time-dependent analysis of

B^0\to D^{\mp}\pi^{\pm}

decays using

3~\rm fb^{-1}

of proton-proton collision data collected with the LHCb detector at CERN's Large Hadron Collider during Run 1 with a centre-of-mass energy of

7

(2011) and

8

(2012) TeV. The LHCb experiment is dedicated to the study of the properties of

b

-flavoured hadrons, in particular

CP

violation in the

B

meson system. The Standard Model of Particle Physics describes very precisely the mechanism and the amount of

CP

violation expected in the Universe. However, the observed matter-antimatter asymmetry is larger by several order of magnitude compared to the predictions. This could be explained by the existence of a new source of

CP

violation, originating in New Physics beyond the Standard Model. The time-dependent analysis of

B^0\to D^{\mp}\pi^{\pm}

decays provides constraints on the angle

\gamma

of the Unitarity Triangle, one of the fundamental parameters of the Standard Model related to

CP

violation. Since no sizeable high-order Standard Model processes are expected to contribute, any deviation from the predictions would be an unambiguous signature of New Physics. The current experimental precision on

\gamma

is significantly lower than that of theoretical predictions. This motivates the effort for new experimental determinations of

\gamma

in order to reduce its uncertainty. The analysis of

\Bz\to\Dmp\pipm

decays, although not as sensitive as that obtained from decays of charged

B

mesons into

D^{(*)0}K^{(*)+}

final states, represents an independent and uncorrelated estimation of

\gamma

that contributes to the global combination of all

\gamma

measurements. The result obtained in this thesis is more precise than previous determinations from other experiments (BaBar, Belle) using

B^0\to D^{\mp}\pi^{\pm}

decays. Although based on a very large sample of about half a million signal events, it is still dominated by statistical uncertainties, indicating good prospects for future improvements in precision with more data from Run 2 and beyond. In addition to the

B^0\to D^{\mp}\pi^{\pm}

analysis, this thesis also summarizes the studies to improve the performances of the flavour tagging algorithms used by the LHCb collaboration to infer the flavour of neutral

B

mesons in time-dependent analyses. The performance of these algorithms, being correlated with the kinematics of the reconstructed particles as well as the complexity of the event (number of tracks and primary vertices), showed a significant decrease on Run 2 data (2015--2018), which were collected at a centre-of-mass energy of

13~\rm TeV

. Thanks to new implementations, these algorithms now have a performance similar to that obtained with Run 1 data.

EPFL2018

Measurement of time-dependent CP violation in B0->Dpi decays and optimisation of flavour tagging algorithms at LHCb

Vincenzo Battista

This thesis presents the results of a time-dependent analysis of

B^0\to D^{\mp}\pi^{\pm}

decays using

3~\rm fb^{-1}

of proton-proton collision data collected with the LHCb detector at CERN's Large Hadron Collider during Run 1 with a centre-of-mass energy of

7

(2011) and

8

(2012) TeV. The LHCb experiment is dedicated to the study of the properties of

b

-flavoured hadrons, in particular

CP

violation in the

B

meson system. The Standard Model of Particle Physics describes very precisely the mechanism and the amount of

CP

CP

violation, originating in New Physics beyond the Standard Model. The time-dependent analysis of

B^0\to D^{\mp}\pi^{\pm}

decays provides constraints on the angle

\gamma

of the Unitarity Triangle, one of the fundamental parameters of the Standard Model related to

CP

\gamma

is significantly lower than that of theoretical predictions. This motivates the effort for new experimental determinations of

\gamma

in order to reduce its uncertainty. The analysis of

\Bz\to\Dmp\pipm

decays, although not as sensitive as that obtained from decays of charged

B

mesons into

D^{(*)0}K^{(*)+}

final states, represents an independent and uncorrelated estimation of

\gamma

that contributes to the global combination of all

\gamma

measurements. The result obtained in this thesis is more precise than previous determinations from other experiments (BaBar, Belle) using

B^0\to D^{\mp}\pi^{\pm}

B^0\to D^{\mp}\pi^{\pm}

analysis, this thesis also summarizes the studies to improve the performances of the flavour tagging algorithms used by the LHCb collaboration to infer the flavour of neutral

B

13~\rm TeV

. Thanks to new implementations, these algorithms now have a performance similar to that obtained with Run 1 data.

EPFL2018

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

Measurement of time-dependent CP violation in B0->Dpi decays and optimisation of flavour tagging algorithms at LHCb

LHCb detector performance

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

Measurement of time-dependent CP violation in B0->Dpi decays and optimisation of flavour tagging algorithms at LHCb

LHCb detector performance