Polarization and CP Violation Measurements: Angular Analysis of B -> ϕK* Decays and Search for CP Violation at the Belle Experiment

111 Pages·2014·7.62 MB·English

by  Michael Prim (auth.)

Springer Theses
Recognizing Outstanding Ph.D. Research
Michael Prim

Polarization
and CP Violation
Measurements
Angular Analysis of B  K*
Decays and Search for CP
Violation at the Belle
Experiment
Springer Theses
Recognizing Outstanding Ph.D. Research
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Michael Prim
Polarization and CP
Violation Measurements
Angular Analysis of B ! /K(cid:2)
Decays and Search for CP Violation
at the Belle Experiment
Doctoral Thesis accepted by
Karlsruhe Institute of Technology, Germany
123
Author Supervisor
Dr. Michael Prim Prof.Michael Feindt
InstituteforExperimental Nuclear Physics InstituteforExperimental Nuclear Physics
Karlsruhe Instituteof Technology Karlsruhe Instituteof Technology
Karlsruhe Karlsruhe
Germany Germany
ISSN 2190-5053 ISSN 2190-5061 (electronic)
ISBN 978-3-319-05755-2 ISBN 978-3-319-05756-9 (eBook)
DOI 10.1007/978-3-319-05756-9
Springer ChamHeidelberg New YorkDordrecht London
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(cid:2)SpringerInternationalPublishingSwitzerland2014
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Supervisor’s Foreword
The discoveryofCP violation effects inB meson decaysat B factories has ledto
the Nobel Prize in Physics in 2008 for its explanation in the Standard Model of
particlephysics.Meanwhile,precisionmeasurementsofsucheffectsinspecialrare
decaysareapowerfulwaytosearchforNewPhysicseffectsbeyondtheStandard
Model, complementary to the direct search at the LHC.
MichaelPrimdescribesathoroughdataanalysisoftherareBmesondecayinto
Phi K(cid:2) on data taken by the Belle Collaboration at the B-meson factory KEKB
over 10 years. This reaction is interesting, because it in principle allows the
observationoflargeCPviolationeffects. IntheStandardModel,however,noCP
violationisexpected.AnobservationofCPasymmetriesthusimmediatelyimplies
new physics.
MichaelPrimhadtoreconstructthedecaysfromfourchargedparticles.Forthis
complex analysis he developed and made publicly available several generally
usefulnewanalysistools,particularlyforquantifyingmultivariatedependence.He
also developed a fast numerical evaluation procedure for acceptance integrals in
the amplitude likelihood fit using some master integrals. Although not new, the
particle physics community seems to have forgotten this technique over the last
two decades. Exploiting this method, Michael Prim could accelerate systematic
uncertainty calculations by several orders of magnitude. Also, this software he
made publicly available.
From the 5-fold differential cross-section he altogether determined 26 param-
eters, all of them are either first or world-best measurements. Some of the final
results are surprising. These findings now await theoretical explanation in low
energy-QCD models. However, independently of these details, the observation of
largestrongphasesprovesalargesensitivitytonewphysicseffects,butnosignsof
CP violationare observed.Thus,this work reinforces the validity of the Standard
Model.
The thesis is well written and may serve as a textbook example of how to
explore highest energies on the basis of low energy precision experiments and
modern statistical data analysis exploiting quantum mechanical interference
effects.
Karlsruhe, December 2013 Prof. Michael Feindt
v
Abstract
The Standard Model of particle physics describes the properties and fundamental
interactions ofmatter. Thetheoryhas been tested bycountlessmeasurements and
has proven to be a robust model. Yet, there exist hints on physics beyond the
Standard Model. Deviations between experimental measurements and theoretical
predictions or observations like the within the Standard Model unexplainable
matter–antimatter asymmetry inthe universe demand moreprecisemeasurements
and searches.
The constituents of matter are leptons and quarks, the latter form bound states
called hadrons such as the proton, neutron, or mesons. In this thesis, a measure-
ment of the decay of a neutral B meson into a / meson and an exited K(cid:2) meson
(cid:2)B0 ! /K(cid:2)(cid:3)ispresented.IntheStandardModelthistransitionisdescribedviaa
single one-loop diagram, a higher order amplitude in the perturbation theory.
CPviolation,anasymmetryinthebehaviorofmatterandantimatter,isaresult
ofinterferenceeffectsandrequiresatleasttwocontributingamplitudes.Therefore,
noCPviolationisexpectedwithintheStandardModelinB0 ! /K(cid:2) transitions.
AnypotentialphysicsbeyondtheStandardModelcould,however,contributewith
a second amplitude to the transition that could result in a measurable deviation
fromtheexpectation.MeasuringasymmetriesthataresensitivetoCPviolationin
the decay probes the Standard Model and indirectly constrains the possible
parameter space for physics beyond the Standard Model.
In the B0 ! /K(cid:2) system, K(cid:2) denotes contributions from scalar (S-wave, spin
J ¼0), vector (P-wave, J ¼1), and tensor (D-wave, J ¼2) components from
ðKpÞ(cid:2), K(cid:2)ð892Þ0, and K(cid:2)ð1430Þ0, respectively. As the / is a vector meson, the
0 2
pseudoscalarB0decaysintoavector–scalar,vector–vector,orvector–tensorstate.
Conservation of angular momentum results in up to three polarizations (longitu-
dinal, parallel, and perpendicular) for these decays, thus providing several quan-
tities that are potentially sensitive to deviations from the Standard Model
expectation. Using a partial wave analysis, which exploits the different angular
distributions of the S-, P-, and D-wave component, the branching fraction B , the
J
longitudinal (perpendicular) polarization fraction f ðf Þ, the relative phase of
LJ ?J
theparallel(perpendicular)amplitude/ ð/ Þtothelongitudinalamplitude,the
kJ ?J
strong phase differences d between the S-wave and the P- and D-wave, and a
0J
vii
viii Abstract
number of parameters related to direct CP violation in all these quantities are
measured. In total, 26 parameters are measured.
The analysis was performed using the full Belle data sample, consisting of an
integratedluminosityof711 fb-1containing ð772(cid:3)11Þ(cid:4)106BBpairs collected
at the !ð4SÞ resonance at the KEKB asymmetric-energy eþe(cid:5) collider. The
!ð4SÞ resonance decays into a B meson pair and the subsequent decay products
are detected and recorded by the Belle detector.
Severalnewandimprovedmethodshavebeenappliedwithrespecttoprevious
Bellemeasurements.Neuralnetworkshavebeenemployedtoobtainanobservable
that discriminates between signal and the dominating background from eþe(cid:5) !
qqðq 2fu,d,s,cgÞ events. A nine-dimensional maximum likelihood fit was used
toperformthefinalparameterextraction.Forthisfit,atoolhasbeendevelopedto
obtain a reliable measure of dependence among the observables in multivariate
data sets. Furthermore, a method that can improve the computation time of
numeric integrations in partial wave analysis and amplitude analyses, in general,
by orders of magnitude was developed.
The obtained results are summarized in Table 1 and supersede all previous
Belle results for the P-wave component B0 ! /K(cid:2)ð892Þ0. The analysis also
provides the first measurement related to the S- and D-wave components B0 !
/ðKpÞ(cid:2) and B0 ! /K(cid:2)ð1430Þ0, respectively, at Belle. The results are consistent
0 2
with other measurements from the BaBar collaboration and improve the uncer-
tainties on all parameters related to the S- and P-wave components. Naive
expectations predict a dominant longitudinal polarization in the decay, which is
confirmedinB0 ! /K(cid:2)ð1430Þ0 decaysbutinconflictwiththeresultobtainedin
2
B0 ! /K(cid:2)ð892Þ0 decays.AllparametersrelatedtoCPviolation,whicharelisted
Table1 Summaryofthe26parametersmeasuredintheB0 ! /K(cid:2) system
Parameter /ðKpÞ(cid:2) /K(cid:2)ð892Þ0 /K(cid:2)ð1430Þ0
0 2
J¼0 J¼1 J¼2
BJ(cid:2)10(cid:5)6(cid:3) 4:3(cid:3)0:4(cid:3)0:4 10:4(cid:3)0:5(cid:3)0:6 5:5(cid:5)þ00::79(cid:3)1:0
fLJ (cid:6)(cid:6)(cid:6) 0:499(cid:3)0:030(cid:3)0:018 0:918(cid:5)þ00::006209(cid:3)0:012
f?J (cid:6)(cid:6)(cid:6) 0:238(cid:3)0:026(cid:3)0:008 0:056(cid:5)þ00::003550(cid:3)0:009
/ ðradÞ (cid:6)(cid:6)(cid:6) 2:23(cid:3)0:10(cid:3)0:02 3:76(cid:3)2:88(cid:3)1:32
kJ
/?JðradÞ (cid:6)(cid:6)(cid:6) 2:37(cid:3)0:10(cid:3)0:04 4:45þ(cid:5)00::4338(cid:3)0:13
d0JðradÞ (cid:6)(cid:6)(cid:6) 2:91(cid:3)0:10(cid:3)0:08 3:53(cid:3)0:11(cid:3)0:19
ACPJ 0:093(cid:3)0:094(cid:3)0:017 (cid:5)0:007(cid:3)0:048(cid:3)0:021 (cid:5)0:155(cid:5)þ00::113532(cid:3)0:033
A0 (cid:6)(cid:6)(cid:6) (cid:5)0:030(cid:3)0:061(cid:3)0:007 (cid:5)0:016þ0:066(cid:3)0:008
CPJ (cid:5)0:051
A? (cid:6)(cid:6)(cid:6) (cid:5)0:14(cid:3)0:11(cid:3)0:01 (cid:5)0:01þ0:85(cid:3)0:09
CPJ (cid:5)0:67
D/ ðradÞ (cid:6)(cid:6)(cid:6) (cid:5)0:02(cid:3)0:10(cid:3)0:01 (cid:5)0:02(cid:3)1:08(cid:3)1:01
kJ
D/ ðradÞ (cid:6)(cid:6)(cid:6) 0:05(cid:3)0:10(cid:3)0:02 (cid:5)0:19(cid:3)0:42(cid:3)0:11
?J
Dd0J ðradÞ (cid:6)(cid:6)(cid:6) 0:08(cid:3)0:10(cid:3)0:01 0:06(cid:3)0:11(cid:3)0:02
Thefirsterrorisstatisticalandthesecondduetosystematicuncertainties
Abstract ix
in the bottom half of the table, are consistent with zero and the absence of CP
violation.
The results of the measurement in B0 !/K(cid:2) decays have been published in
M. Prim et al. (Belle Collaboration), ‘‘Angular analysis of B0 !/K(cid:2) decays and
search for CP violation at Belle,’’ Physical Review D 88, 072004 (2013).
Thetoolformeasuringdependenceinmultivariatedatasetshasbeenpublishedin
M.FeindtandM.Prim,‘‘Analgorithmforquantifyingdependenceinmultivariate
data sets,’’ Nuclear Instruments and Methods in Physics Research A 698, 84
(2013).
Acknowledgments
First of all I thank my doctoral advisor Prof. Michael Feindt for instructive dis-
cussions, advice, support, and the possibility to carry out this research in his
working group.
I thank Prof. Dr. Günter Quast for being the second reviewer of this thesis.
I thank Dr. Thomas Kuhr and Dr. Anzˇe Zupanc for their excellent supervision
during my entire Ph.D.
I thank further Christian Pulvermacher, Bastian Kronenbitter, Dr. Benjamin
Fuchs, and again Dr. Thomas Kuhr and Dr. Anzˇe Zupanc for proofreading this
thesis at different stages.
I thank the entire working group and the remaining Institute of Experimental
Nuclear Physics for 4 years of excellent working atmosphere.
I thank the research training group ‘‘Hochenergiephysik und Teilchenastro-
physik’’ of the German Research Foundation and the ‘‘Studienstiftung des
Deutschen Volkes’’ for supporting and funding of my graduate studies and
research.
Finally, I thank my parents Christine and Thomas Prim for their unconditional
support in all circumstances.
xi