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Publication

Measurement of the CP violation parameter AG in D-0 K+ K and D-0 pi(+) pi(-) decays

Pietro Marino
2019
Journal paper

Abstract

.Asymmetries in the time-dependent rates of singly Cabibbo-suppressed D0K+K- and D0+- decays are measured in pp collision data sample collected with the LHCb detector during LHC Run 1, corresponding to an integrated luminosity of 3 fb(-1). The asymmetries in effective decay widths between D-0 and D0 decays, sensitive to indirect CP violation, are measured. These measurements show no evidence for CP violation and improve on the precision of the previous best measurements by nearly a factor of two.

Official source

https://infoscience.epfl.ch/record/266743?ln=en

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Precision measurement of neutral charm meson mixing parameters

Guillaume Max Pietrzyk

This thesis presents a measurement of the neutral charm meson mixing parameters

y_{C\!P}^{KK} - y_{C\!P}^{K\pi}

and

y_{C\!P}^{\pi\pi} - y_{C\!P}^{K\pi}

using

D^0 \rightarrow K^-K^+

D^0 \rightarrow \pi^-\pi^+

and

D^0 \rightarrow K^-\pi^+

decays. These parameters correspond to the departure from unity of the ratio of the effective decay widths of

D^0 \rightarrow K^-K^+

D^0 \rightarrow \pi^-\pi^+

decays over the effective decay width of

D^0 \rightarrow K^-\pi^+

decays. \The measurement is done with the dataset collected in the Run 2 (2015-2018) of the Large Hadron Collider (LHC) by the LHCb experiment at CERN at a centre-of-mass energy of

13 \tev

, and corresponding to an integrated luminosity of

6 \, \mathrm{fb}^{-1}

. The

D^0

mesons originate from

D^{\ast+}(2010) \rightarrow D^0 \pi^+

decays. We measure \begin{equation} \begin{split} y_{C!P}^{KK} - y_{C!P}^{K\pi} & = (7.08 \pm 0.30 \pm 0.14) \times 10^{-3}, , \ y_{C!P}^{\pi\pi} - y_{C!P}^{K\pi} & = (6.57 \pm 0.53 \pm 0.16) \times 10^{-3}, , \end{split}\end{equation}where the first uncertainty is statistical while the second is systematic. Neglecting final state dependent contributions, we obtain the combination\begin{equation} y_{C!P} - y_{C!P}^{K\pi} = (6.96 \pm 0.26 \pm 0.13) \times 10^{-3} , .\end{equation}This measurement improves by a factor of four the precision of the current world average value of

y_{C\!P} - y_{C\!P}^{K\pi}

. In addition, the results allow for an improvement of the precision on the mixing parameter

y

by a factor of two, where

y

is connected to the width difference between the neutral charm meson mass eigenstates. The new world average value of

y

is estimated to be\begin{equation} y = (6.45 \pm 0.24) \times 10^{-3} , .\end{equation}This thesis also presents the work done for the EPFL fibre mat production as part of the LHCb Scintillating Fibre (SciFi) Tracker upgrade.

EPFL2022

Observation of CP Violation in Charm Decays

Jian Wang, Olivier Schneider, Yiming Li, Yi Zhang, Aurelio Bay, Guido Haefeli, Christoph Frei, Frédéric Blanc, Tatsuya Nakada, Michel De Cian, Luca Pescatore, François Fleuret, Elena Graverini, Chitsanu Khurewathanakul, Renato Quagliani, Maria Vieites Diaz, Federico Betti, Andrea Merli, Aravindhan Venkateswaran, Luis Miguel Garcia Martin, Vitalii Lisovskyi, Katharina Müller, Sebastian Schulte, Veronica Sølund Kirsebom, Mingkui Wang, Zhirui Xu, Lei Zhang, Ho Ling Li, Mark Tobin, Minh Tâm Tran, Niko Neufeld, Matthew Needham, Marc-Olivier Bettler, Greig Alan Cowan, Maurizio Martinelli, Vladislav Balagura, Donal Patrick Hill, Liang Sun, Pietro Marino, Mirco Dorigo, Xiaoxue Han, Liupan An, Federico Leo Redi, Plamen Hristov Hopchev, Thibaud Humair, Maxime Schubiger, Hang Yin, Guido Andreassi, Violaine Bellée, Olivier Göran Girard, Axel Kuonen, Preema Rennee Pais, Pavol Stefko, Tara Nanut, Maria Elena Stramaglia, Tommaso Colombo, Vladimir Macko, Guillaume Max Pietrzyk, Albert Puig Navarro, Evgenii Shmanin, Lino Ferreira Lopes, Dipanwita Dutta, Zheng Wang, Yi Wang, Hans Dijkstra, Gerhard Raven, Peter Clarke, Frédéric Teubert, Giovanni Carboni, Victor Coco, Adam Davis, Paolo Durante, Yu Zheng, Anton Petrov, Maxim Borisyak, Feng Jiang, Chen Chen, Zhipeng Tang, Luis Alberto Granado Cardoso, Xuan Li

A search for charge-parity (CP) violation in D-0 -> K-K+ and D-0 -> pi(-)pi(+) decays is reported, using pp collision data corresponding to an integrated luminosity of 5.9 fb(-1) collected at a center-of-mass energy of 13 TeV with the LHCb detector. The flavor of the charm meson is inferred from the charge of the pion in D* (2010)(+) -> D-0 pi(+) decays or from the charge of the muon in (B) over bar -> D-0 mu(-)(nu) over bar X-mu decays. The difference between the CP asymmetries in D-0 -> K-K+ and D-0 -> pi(-)pi(+) decays is measured to be Delta A(CP) = [-18.2 +/- 3.2(stat) +/- 0.9(syst)] x 10(-4) for pi-tagged and Delta A(CP) = [-9 +/- 8(stat) +/- 5(syst)] x 10(-4) for mu-tagged D-0 mesons. Combining these with previous LHCb results leads to Delta A(CP) = (-15.4 +/- 2.9) x 10(-4), where the uncertainty includes both statistical and systematic contributions. The measured value differs from zero by more than 5 standard deviations. This is the first observation of CP violation in the decay of charm hadrons.

2019

This thesis presents a search for

CP

violation in the

D^0\rightarrow K^+K^-\pi^+\pi^-

Cabibbo-suppressed decay mode using an amplitude analysis. New sources of

CP

violation have to be discovered in order to explain the matter-antimatter imbalance observed in the universe today.

CP

violation has not been observed in charm decays up to now, where it is predicted by the Standard Model to be very small. This provides a clean environment to look for physics beyond the Standard Model, which could enhance

CP

violation in charm decays with, for example, the contribution of new particles entering through loop diagrams. This analysis is performed with a sample of proton-proton collisions recorded by LHCb during 2011 and 2012 at centre-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3.0 fb

^{-1}

. LHCb is one of the four main experiments at CERN's Large Hadron Collider in Geneva in Switzerland. It is specialised in the study of

CP

violation in

b

- and

c

-hadron decays. The

D^0

candidates are selected from semileptonic

b

-hadron decays into

D^0\mu^- X

final states. More than 160000 signal decays are studied, resulting in the most precise amplitude model of this decay to date. This amplitude model, built assuming

CP

conservation, is used to perform a search for

CP

violation. The result is compatible with no

CP

violation, with a sensitivity ranging from 1% to 15% on each amplitude. This result is compatible with the Standard Model predictions and is ruling out any large contribution from New Physics processes in the

D^0\rightarrow K^+K^-\pi^+\pi^-

decay mode. The

CP

violation measurements presented here are statistically limited and will benefit from the addition of the Run 2 sample collected between 2015 and 2018 at a centre-of-mass energy of 13 TeV, which is expected to correspond to an integrated luminosity of

\sim6

^{-1}

. Beyond the additional luminosity, the increase in energy as well as various tracking and trigger improvements make this dataset much more powerful than the Run 1 sample. This thesis also presents one of the improvements made for Run 2, which is a more accurate description of the magnetic field of the dipole magnet through the development of a new field map.

EPFL2018