Improving sensitivity to the unitarity triangle angle gamma with CLEO-c CP-tagged D0 decays. (Project proposal for Responsive RA call)

Lead Research Organisation: University of Bristol
Department Name: Physics

Abstract

Precision measurements of CP violation in B mesons shed light on fundamental parameters of the Standard Model of particle physics, related to areas such as the generation of fermion masses and the predominance of matter over antimatter in the universe, and probe the Standard Model description of CP violation with a high sensitivity to New Physics. Arguably the most important goal of CP-violation measurements over the next decade will be a precise determination of the CP-violation parameter gamma. The LHCb experiment at the LHC at CERN will, for the first time, be able to perform such precision measurements. Measuring gamma will also be central to the programme of a possible Super-B factory. One of the most promising classes of gamma measurements involves the decay B+ -> DK+. In this decay chain, the D is unstable and decays further, for example to Ks pi pi. There are many intermediary states via which the D can decay to the same final state. These different decay paths interfere with each other, causing an interference pattern that can, for 3-body decays, be visualised in a 2-dimensional Dalitz plot. For 4-body decays, the visualisation is more difficult, but the same principles apply. For D mesons that originate from B+/- decays, the interference patterns are sensitive to decay parameters of the B, in particular the parameter gamma. Due to CP violation, those patterns look different depending whether the D originated from a B+ decay or a B- decay. Analysing those patterns allows in principle a very precise determination of gamma. This however requires a thorough understanding of D meson decays and the corresponding interference patterns before any B decay parameters enter. This is expected to be the limiting factor in the precision on gamma with this method. Understanding the D-decays fully requires two pieces of information for each point in the Dalitz plot: the amplitude and the phase. Usually, only one parameter can be measured, the intensity. Understanding the intensity pattern in terms of amplitudes and phases requires the use of a model for those D decays. The parameters of this model are then fitted to the intensity distribution. However, there is a dependency on the choice of model. This is the largest systematic uncertainty for the aforementioned gamma measurements. At its present value, this uncertainty will limit the use of the data accumulated at LHCb and any future Super-B facility. The CLEO-c experiment operating at Cornell University, NY, USA produces pairs of D mesons in a quantum correlated state, which is not the case at the e+e- B factories or the LHC. This data set allows, for the same final state, two independent measurements of the decay patterns of the Dalitz plot, 'CP tagged' and 'flavour tagged'. This makes it possible, in principle, to directly extract both amplitude and phase for each point in Dalitz space, without any model dependence. Even for channels where event numbers are not sufficient for a completely model-independent approach, the existing models will benefit greatly from the unique constraints imposed by the quantum-correlated data. This will significantly reduce the systematic error associated with our understanding of D decays in gamma measurement with B->DK at LHCb and elsewhere. CLEO-c however is a collaboration with very limited resources and at present there is not enough manpower to analyse many of the channels that are most important for gamma measurements at B-physics experiments. We therefore propose to join the Dalitz analysis group of CLEO-c to spearhead these studies, joining CLEO-c well before the end of data taking in spring 2008. This will put us in a position in 2008/09 to fully exploit the entire CLEO-c dataset for the proposed measurements. Our project concludes with the application of the results to gamma measurements at LHCb.
 
Description Multibody decays of D mesons at CLEO were analysed, and their phase information related to their decay amplitudes was extracted, in most cases using theoretically robust model-independent methods only viable at the charm threshold data available at CLEO-c (and nowadays also at BESIII). The key impact of these results is for the measurement of the benchmark CP-violation phase gamma in B->DK decays at the B factories and LHCb.
Impressively, we continue to publish innovative results, such as the measurement of the CP-even fraction in several multibody decay modes, and a combination of CLEO-c and LHCb data to measure the coherence factor in D->Kpipipi. These are two novel ideas, and the resulting experimental results extend the scope and precision of gamma measurements)
Exploitation Route BaBar, BELLE and LHCb already have used these result as input to their measurements of gamma. LHCb, LHCb-upgrade and BELLE-II will continue to improve the precision on gamma, making use of these results. While the key objectives have already been achieved, we continue to exploit the unique CLEO-c data set in new and innovative ways, publishing results long beyond the initial funding period, building on our previous results. Our results have been presented in many conferences (including very high profiles ones such as ICHEP) in addition to numerous peer-reviewed publications. Our recent (2015/16) results on the CP-even fraction in several multibody decay modes, and a combination of CLEO-c and LHCb data to measure the coherence factor in D->Kpipipi, are being used by LHCb to improve the precision on gamma (LHCb results not yet public).
Sectors Education,Other

URL https://indico.lal.in2p3.fr/event/1932/material/slides/0.pdf
 
Description Particle physics' key aim today is finding a more complete theory than the Standard Mode, a theory that answers open questions, e.g. related to the predominance of matter over antimatter in the universe, dark matter, dark energy, etc. Flavour physic aims to find evidence of new heavy particles using the precision study of decays that can be affected by virtual particles - a quantum mechanical affect that provides sensitivity to very heavy particle. The precision measurement of gamma is a key aim of flavour physics. Our results are a key element to such precision measurements at LHCb and have been used in that way by BaBar, BELLE and LHCb. We continue to make innovative use of CLEO-c data. For example in 2014/15/16, substantially beyond the end of the grant period, we published several results using new techniques we developed that further improve the precision on gamma.
Sector Education,Other
 
Description ERC Starter/Consolidator Grant
Amount € 1,400,000 (EUR)
Funding ID 307737 
Organisation European Research Council (ERC) 
Sector Public
Country Belgium
Start 10/2012 
End 09/2017
 
Description Rolling Grant (as Co-PI)
Amount £100,000 (GBP)
Organisation Science and Technologies Facilities Council (STFC) 
Sector Public
Country United Kingdom
Start 10/2010 
End 09/2014
 
Description CLEO 
Organisation CLEO Collaboration
Country United States 
Sector Academic/University 
PI Contribution We joined the CLEO collaboration (Wilson Lab, USA). We collaborated with CLEO colleagues, carried out research (data analysis and detector operation), published paper. Analysing CLEO data was the main aim of this research programme, and the fact that we were accepted as full members of the collaboration is a significant success.
Collaborator Contribution CLEO is a collaboration of several hundred physicists, we would not have had access to the data (and the data wouldn't exist) were it not for our colleagues at CLEO.
Impact All our CLEO publications, and continued access to valuable CLEO data that we will continue to analyse.
Start Year 2006
 
Description Nabis 
Organisation Budker Institute of Nuclear Physics (BINP)
Country Russian Federation 
Sector Academic/University 
PI Contribution Participate in workshop, organise a summer school
Collaborator Contribution Input to Dalitz analyses
Impact Workshops and a Summerschool on Dalitz Analyses
Start Year 2010
 
Description Nabis 
Organisation Durham University
Department Department of Physics
Country United Kingdom 
Sector Academic/University 
PI Contribution Participate in workshop, organise a summer school
Collaborator Contribution Input to Dalitz analyses
Impact Workshops and a Summerschool on Dalitz Analyses
Start Year 2010
 
Description Nabis 
Organisation Helmholtz Association of German Research Centres
Department GSI Helmholtz Centre for Heavy Ion Research
Country Germany 
Sector Public 
PI Contribution Participate in workshop, organise a summer school
Collaborator Contribution Input to Dalitz analyses
Impact Workshops and a Summerschool on Dalitz Analyses
Start Year 2010
 
Description Nabis 
Organisation Johannes Gutenberg University of Mainz
Department Institute for Nuclear Physics
Country Germany 
Sector Academic/University 
PI Contribution Participate in workshop, organise a summer school
Collaborator Contribution Input to Dalitz analyses
Impact Workshops and a Summerschool on Dalitz Analyses
Start Year 2010
 
Description Nabis 
Organisation Julich Research Centre
Country Germany 
Sector Academic/University 
PI Contribution Participate in workshop, organise a summer school
Collaborator Contribution Input to Dalitz analyses
Impact Workshops and a Summerschool on Dalitz Analyses
Start Year 2010
 
Description Nabis 
Organisation University of Siegen
Department Department of Physics
Country Germany 
Sector Academic/University 
PI Contribution Participate in workshop, organise a summer school
Collaborator Contribution Input to Dalitz analyses
Impact Workshops and a Summerschool on Dalitz Analyses
Start Year 2010
 
Title Mint 
Description It is a tool for notoriously difficult amplitude analysis in 3 body decays and the even in four body decays. This is being used at LHCb and CLEO-c. While there are several other tools that can be sued for 3 body amplitude analysis ("Dalitz plot analysis"), it's the only tool at LHCb and CLEO-c that is capable of analysing the substantially more complex 4-body final states. The product was never officially released (hence no open source license, yet), but made available to fellow researchers, including ca 100 CLEO-c members and 1000 LHCb members, where it is fully integrated into the s/w framework (and can thus for example be used for event generation of multibody decays, including complex interference effects, at LHCb). 
Type Of Technology Software 
Year Produced 2010 
Impact Widely used at LHCb and CLEO. 
 
Description Colloquium 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact Colloquium that is open to the public (who do participate) as well as members to the university.

n/a
Year(s) Of Engagement Activity 2010
 
Description Student Society talk 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Undergraduate students
Results and Impact o Talk to the physics student society of the University of Bristol.

n/a
Year(s) Of Engagement Activity 2010