First Search for the EMC Effect and Nuclear Shadowing in Neutrino Nuclear Deep Inelastic Scattering at MINERvA

158 Pages·2017·7.296 MB·English

by  Joel Allen Mousseau (auth.)

Springer Theses
Recognizing Outstanding Ph.D. Research
Joel Allen Mousseau

First Search for
the EMC Eff ect and
Nuclear Shadowing
in Neutrino Nuclear
Deep Inelastic
Scattering at
MINERvA
Springer Theses
Recognizing Outstanding Ph.D. Research
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Joel Allen Mousseau
First Search for the EMC
Effect and Nuclear
Shadowing in Neutrino
Nuclear Deep Inelastic
Scattering at MINERvA
Doctoral Thesis accepted by University of Florida,
Gainesville, Florida
123
JoelAllenMousseau
UniversityofMichigan
AnnArbor,Michigan,USA
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ISSN2190-5053 ISSN2190-5061 (electronic)
SpringerTheses
ISBN978-3-319-44840-4 ISBN978-3-319-44841-1 (eBook)
DOI10.1007/978-3-319-44841-1
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Toallmyteachers
Foreword
Asaholisticscience,inphysicsweneedtoconsidernotonlytheindividualpieces
of a system but also how these pieces combine to form larger structures. Just as
cells group together to form complex life forms, protons and neutrons combine
to form complicated atomic nuclei. We know from many decades of research that
nucleons,anothernameforprotonsandneutrons,behaveslightlydifferentlywhen
theycombinetoformatomicnuclei.Justasthecellswhichmakeupahumanliveror
heartdiffer,thenucleonswhichmakeupacarbonatomaresubtlydifferentthanthe
nucleonsboundinsideanargonnucleus.Innuclearphysics,thedifferencesbetween
nucleonsindifferentnucleiarereferredtoas“nucleareffects.”
Inthepast,nuclearphysicistsdetectednucleareffectswithbeamsofhigh-energy
electrons.High-energybeamsallowelectronstointeractwiththequarkscontained
insidenucleonsandnuclei,atypeofinteractioncalleddeepinelasticscattering,or
DIS.Advancesinmodernphysicsnowallowphysiciststocreatehigh-intensityand
high-energy beams of neutrinos. While neutrinos interact very rarely with nuclei,
theirinteractionscanteachusmuchaboutthenatureoftheuniverse.
Usingabeamofneutrinos,thisdissertationanalyzesneutrinoDISintheenergy
rangeof5–50GeVwiththeMINER(cid:2)Adetector.Intheory,DISinteractionsbetween
neutrinos and nuclei will be different from the interactions between electrons and
nuclei. This is due to the differences in the weak nuclear force that governs the
interactions between electrons, neutrinos, and quarks inside nuclei. If the weak
nuclear forces behaves the way we believe it does, then we should see differences
inourdataandthetheoryofelectronnucleiDIS.
Neutrino DIS interactions are studied by measuring the cross section, or prob-
ability, of a neutrino interacting with quarks inside bound nucleons as a function
of a property called Bjorken-x. Bjorken-x is proportional to the momentum of the
quark that was stuck inside the nucleon. Nuclear effects are defined depending on
the region of Bjorken-x where they appear. At low Bjorken-x, nuclear shadowing
suppressesthecrosssectionofboundnucleonsrelativetothecrosssectionoffree
nucleon. At large Bjorken-x, the EMC effect likewise suppresses the bound cross
sectionrelativetothefreecrosssection.Whilethetheoryofnuclearshadowingis
vii
viii Foreword
fairly well established for electron DIS, the mechanism behind the EMC effect is
virtuallyunknownforbothelectronsandneutrinos.
The data are presented in this dissertation as ratios of carbon, iron, and lead
crosssectionstothecrosssectionofplasticscintillator.Theratioobservedindatais
comparedtoatheoreticalmodelthatassumesthenucleareffectsarethesameforall
nuclei.Wefindthereisadisagreementbetweenthedataandthisassumptioninthe
lowest Bjorken-x region for lead where shadowing is the dominate nuclear effect.
Astheratioshowsalargerdeviationfromunityinthexrange0.1–0.2thancarbon
oriron,wesaythatshadowingisenhancedinthatforlead.
As the energy and intensity of neutrino beams used in experiments increase,
theneedforprecisemeasurementsofneutrinopropertiessuchastheseintensifies.
Futureneutrinoexperimentswilluselargenucleisuchasargon,iron,andcarbonas
targetmaterialswhichhaveconsiderablenucleareffects.Iftheseexperimentsareto
meettheirgoalsanddiscovernewphysics,theymustpreciselyunderstandneutrino
interactionsanddynamicsofthoseinteractionswithinthenuclei.Thedatapresented
inthisdissertationwillbeusedtotuneandvalidatethesimulationsofthesefuture
experimentsandenablefuturephysiciststoaccuratelyanalyzetheirdata.
Likewise, these data are very valuable in validating new models of nuclear
effects. This dissertation contains the world’s only data set of neutrino DIS on
multiplenucleartargetsinthesameneutrinobeam.Thenuclearphysicscommunity
asawholewillbenefitfromhavingthisdatareadilyavailable.Itwillallowfurther
development of the EMC effect and nuclear shadowing and possibly assist in
answeringoneofthelargestquestionsinnuclearphysics.
None of this work would have been possible without the determination and
guidanceofthemembersoftheMINER(cid:2)Acollaboration.Ioweatremendousdebt
to all the men and women who worked to make MINER(cid:2)A a reality behind the
scenes, as well as those who helped tirelessly develop the neutrino reconstruction
andanalysis.Icouldnotaskforagreatergroupofcolleaguesandpeersthanthose
at Fermilab. Completing my graduate work at a national laboratory was the best
decisionIhaveevermadeprofessionally.Iencourageallstudentstoseekoutactive
researchcommunitieslikethosebasedatnationallabs.Theeducationandexpertise
youwillreceivewillbeinvaluable.
Supervisor’s Foreword
The analysis presented in this thesis is the world’s first and highly anticipated
measurementofthemuonneutrinocharged-currentdeepinelasticscattering(DIS)
cross section using neutrinos with energy from 5 to 50GeV. While neutrino
cross sections have been studied for many years, our current picture of neutrino
and antineutrino charged-current (CC) interactions is cloudy. There exists tension
between existing CC exclusive measurements from different experiments, and
between measurements and theory. It is suspected that nuclear effects and inter-
actionsarekeytounderstandingthesediscrepancies.
OnesuchareaofintrigueisfoundintheCCDISevents.NucleareffectsinDIS
havebeenthoroughlystudiedusingbeamsofchargedleptons(muonsandelectrons)
as a function of Bjorken-x, the fractional momentum carried by the struck quark.
Chargedleptonnucleareffectshavebeenextensivelycharacterizedforthepast50
years. However, nuclear effects in neutrino scattering have not yet been directly
measured and are not well constrained by global fits to scattering data. We expect
nuclear effects presentinneutrino DISmaydifferfromthosefound inleptonDIS
duetotheadditionalpresenceoftheaxial-vectorcurrentinneutrinoscattering,and
because neutral neutrinos probe the quarks in a way that charged leptons do not;
differentnucleareffectsmayarisefromneutrinointeractionswiththevalenceand
seaquarks.
TheMINER(cid:2)AexperimentisuniqueinthatitwillproduceDIScrosssectionand
structure function measurements across a wide range of nuclear material within a
single data set and with a single neutrino beam. All previous measurements have
been performed with a single nuclear target within a detector. This will allow
MINER(cid:2)AtocompletelydescribeDISinlowZmaterialtohighZmaterial,without
thedifficultiesassociatedwithcombiningmultipledatasetsacrossdifferentexperi-
ments.Theworkpresentedinthispublicationisthefirstanalysistomeasureratios
ofdifferentialcrosssectionsandabsolutecrosssectionsoncarbon,scintillator,iron,
andleadasafunctionofneutrinoenergyandBjorken-x.
ix
x Supervisor’sForeword
AbstractofDissertationPresentedtotheGraduateSchool
oftheUniversityofFloridainPartialFulfillmentofthe
RequirementsfortheDegreeofDoctorofPhilosophy
FirstSearchfortheEMCEffectandNuclearShadowinginNeutrinoNucleusDeep
InelasticScatteringatMINER(cid:2)A
By
JoelA.Mousseau
August2015
Chair:HeatherRay
Major:Physics
Decades of research in electron-nucleus deep inelastic scattering (DIS) have
providedaclearpictureofnuclearphysicsathighmomentumtransfer.Whilethese
effects have been clearly demonstrated by experiment, the theoretical explanation
oftheirorigininsomekinematicregionshasbeenlacking.Particularly,theeffects
in the intermediate regions of Bjorken-x, anti-shadowing, and the EMC effect
have no universally accepted quantum mechanical explanation. In addition, these
effectshavenotbeenmeasuredsystematicallywithneutrino-nucleusdeepinelastic
scattering,duetoexperimentslackingmultipleheavytargets.
The MINER(cid:2)A (Main Injector Experiment (cid:2)-A) experiment, located in the
Neutrinos at the Main Injector (NuMI) facility at Fermilab, is designed explicitly
to measure these kind of effects with neutrinos. MINER(cid:2)A is equipped with
solid targets of graphite, iron, lead, and plastic scintillator. The plastic scintillator
region provides excellent particle-tracking capabilities, and the MINOS (Main
Injector Neutrino Oscillation Search) near detector is used as a downstream muon
spectrometer.Theexposureofmultiplenucleartargetstoanidenticalneutrinobeam
allowsforasystematicstudyofthesenucleareffects.
An analysis of the MINER(cid:2)A DIS data on carbon, iron, lead, and plastic
scintillator has been conducted in the energy region 5 (cid:2) E(cid:2) < 50GeV and
(cid:3)(cid:4) < 17ı. The data are presented as ratios of the total cross section ((cid:5).E(cid:2)/) as
well as the differential cross section with respect to Bjorken-x (d(cid:5) ) of carbon,
dxbj
iron, and lead to scintillator. The total cross section data is useful for deciphering
gross nuclear effects which effect neutrino energy reconstruction. No significant
differences between simulation and MINER(cid:2)A DIS data are observed in the total
cross section. The ratios of the x differential ratios, however, may provide clues
bj
for decoding long-standing questions about the EMC effect. The MINER(cid:2)A data
tendtosupportnodifferenceinthestrengthoftheEMCeffectfromchargedlepton
scattering.Thereisasuggestionofadditionalnuclearshadowing,notpredictedby
simulation,intheratioofleadtoscintillator.