CP violation in B-meson decays

Charmless three-body B decays

Last Update: Feb. 5, 2017

At LAPE we are studying the difference between matter and antimatter through the phenomenon of CP violation in the decays of B mesons. CP violation can be measured via the difference in decay rates between positive and negative B mesons to three light mesons (kaons and pions). We explore these and other properties of B mesons by analysing data collected by the LHCb experiment.


About the Analysis

Decays of B mesons to three-body charmless final states offer a good environment to study CP violation phenomena. They also provide important insight into the dynamics of hadronic B decays.

The LHCb Bu→hhh Rio Group has been studying charmless three-body B decays since the beginning of LHCb data taking in 2009. The first analysis was a measurement of the relative branching fractions of B±→K±K±K- and B±→ppK± decays with respect to the reference mode B±→K±π±π-. The analysis was performed using 34 pb-1 of 2010 data, and was reported in the public note LHCb-CONF-2011-059. The branching ratios relative to B±→K±π±π- are found to be

  • ℬℛ(B±→K±K±K-)ℬℛ(B±→K±π±π-)= 0.52 ± 0.003(stat) ± 0.01(syst)
  • ℬℛ(B±→ppK±)ℬℛ(B±→K±π±π-) = 0.19 ± 0.02(stat) ± 0.02(syst)

With the larger dataset of 3 fb-1 of data collected by LHCb in 2011 and 2012, we measured the direct CP asymmetries of four charmless decay modes. We found for the the first evidences of CP violation in these modes, as well as localised asymmetries much larger than the integrated ones in some regions of phase space. The results are listed below in the LHCb Collaboration Results. The inclusive CP asymmetries (ACP) of these modes are measured to be

  • ACP(B±→K±π±π-) = +0.025 ± 0.004 ± 0.004 ± 0.007
  • ACP(B±→K±K±K-) = -0.036 ± 0.004 ± 0.002 ± 0.007
  • ACP(B±→π±π±π-) = +0.058 ± 0.008 ± 0.009 ± 0.007
  • ACP(B±→K±K±π-) = -0.123 ± 0.017 ± 0.012 ± 0.007

In addition, a measurement of the forward-backward asymmetry (AFB) of the light meson in the pp rest frame are measured to be

  • AFB(ppK+, mpp < 2.85 GeV/c2) = 0.495 ± 0.012(stat) ± 0.007(syst)
  • AFB(ppπ+, mpp < 2.85 GeV/c2) = -0.409 ± 0.033(stat) ± 0.006(syst)

and the branching fraction of the decay B+Λ(1520)p is measured to be

  • ℬℛ (B+Λ(1520)p) = (3.15 ± 0.48(stat) ± 0.07(syst) ± 0.26(BF))×10-7

where BF denotes the uncertainty on secondary branching fractions.

The phase space of three-body decays is the Dalitz plot, and its complete understanding is achieved by a complex amplitude analysis. However, such an amplitude analysis is model dependent. The CBPF group proposed in 2009 a model-independent method for a CP anisotropy measurement in the Dalitz plot. This “Mirandizing” method performs a direct measurement of the diference between particles and antiparticles in the Dalitz plot. Although qualitative, the method can be used as a guide to locate the decay channels and the Dalitz plot regions with large asymmetry, thus aiding the choice of a future amplitude analysis model.

In addition to the Mirandizing analysis, we are now working on a full Dalitz plot amplitude analysis within the framework of existing theoretical models.


Irina Nasteva and Fernando Rodrigues
Last update: August 11, 2017

 

LHCb Collaboration Results
A list of all the LHCb public results that the Bu→hhh Rio Group directly participated.

Results from LHCb Run I dataset (2009 → 2012)

About the Bu→hhh Group

Current members from UFRJ:

Jose Helder, Juan Otalora, Irina Nasteva, Fernando Rodrigues

in collaboration with:

Centro Brasileiro de Pesquisas Físicas: Ignacio Bediaga, Jussara Miranda, Alberto Reis, Patricia Magalhães, Melissa Cruz, Ana Cavalcante, Lais Soares

Universidade Católica do Rio de Janeiro: Carla Gobel, Valdir Salustino

Universidade Federal do Triângulo Mineiro: Alvaro Gomes

University of Bristol: Jeremy Dalseno, Jonas Rademacker

University of Warwick: Thomas Latham, Timothy Gershon, John Back, Daniel O’Hanlon

Group meeting

Wednesday at 15:00 (BRT/BRST) — Vidyo or WebRTC

 

LHCb Twikis and Workspace
Twikis and workspaces restricted to LHCb members.

  • Charged Charmless Bu→hhh Analysis Page(main page)[TWiki]
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  • Rio Group Bu→hhh Analysis Page (group page)[TWiki]
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  • Analysis under development

 

Conferences & Workshops