Investigation of the role of $^{10}$Li resonances in the halo structure of $^{11}$Li through the $^{11}$Li(p, d)$^{10}$Li transfer reaction

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Investigation of the role of

10

_{Li resonances in the halo}

structure of

11

_{Li through the}

11

_{Li(p, d)}

10

_{Li transfer}

reaction

A. Sanetullaev, R. Kanungo, J. Tanaka, M. Alcorta, C. Andreoiu, P. Bender,

A.A. Chen, G. Christian, B. Davids, J. Fallis, et al.

To cite this version:

A. Sanetullaev, R. Kanungo, J. Tanaka, M. Alcorta, C. Andreoiu, et al.. Investigation of the role

of

10

_{Li resonances in the halo structure of}

11

_{Li through the}

11

_{Li(p, d)}

10

_{Li transfer reaction. Physics}

Contents lists available atScienceDirect

Physics

Letters

B

www.elsevier.com/locate/physletb

Investigation

of

the

role

of

10

Li resonances

in

the

halo

structure

of

11

Li

through

the

11

Li

(

p

,

d

)

10

Li transfer

reaction

A. Sanetullaev

a

,

b

,

1

,

R. Kanungo

a

,

∗

,

J. Tanaka

c

,

M. Alcorta

b

,

C. Andreoiu

d

,

P. Bender

b

,

A.A. Chen

e

,

G. Christian

b

,

B. Davids

b

,

J. Fallis

b

,

J.P. Fortin

a

,

f

,

N. Galinski

b

,

A.T. Gallant

b

,

P.E. Garrett

g

,

G. Hackman

b

,

B. Hadinia

g

,

S. Ishimoto

h

,

M. Keefe

a

,

R. Krücken

b

,

i

,

J. Lighthall

b

,

E. McNeice

e

,

D. Miller

b

,

J. Purcell

a

,

J.S. Randhawa

a

,

T. Roger

j

,

A. Rojas

b

,

H. Savajols

j

,

A. Shotter

k

,

I. Tanihata

c

,

l

,

I.J. Thompson

m

,

C. Unsworth

b

,

P. Voss

d

,

Z. Wang

b

,

d

a_{AstronomyandPhysicsDepartment,SaintMary’sUniversity,Halifax,NSB3H3C3,Canada} b_{TRIUMF,Vancouver,BCV6T2A3,Canada}

c

RCNP,OsakaUniversity,Mihogaoka,Ibaraki,Osaka5670047,Japan

d_{DepartmentofChemistry,SimonFraserUniversity,Burnaby,BCV5A1S6,Canada} e_{DepartmentofPhysicsandAstronomy,McMasterUniversity,Hamilton,ONL8S4M1,Canada} f_{DepartmentofPhysics,UniversityofLaval,QuebecCity,QBG1V0A8,Canada}

g_{DepartmentofPhysics,UniversityofGuelph,Guelph,ONN1G2W1,Canada} h_{HighEnergyAcceleratorResearchOrganization(KEK),Ibaraki305-0801,Japan}

i_{DepartmentofPhysicsandAstronomy,UniversityofBritishColumbia,Vancouver,BCV6T1Z1,Canada} j_{GrandAccélérateurNationald’IonsLourds,CEA/DSM-CNRS/IN2P3,B.P.55027,F-14076CaenCedex5,France} k_{UniversityofEdinburgh,Edinburgh,UnitedKingdom}

l_{SchoolofPhysicsandNuclearEnergyEngineeringandIRCNPC,BeihangUniversity,Beijing100191,China} m_{LawrenceLivermoreNationalLaboratory,L-414,Livermore,CA 94551,USA}

a

r

t

i

c

l

e

i

n

f

o

a

b

s

t

r

a

c

t

Articlehistory:

Received28December2015

Receivedinrevisedform25February2016 Accepted25February2016

Availableonline2March2016 Editor:D.F.Geesaman Keywords: Halonucleus 10,11_Li Transferreaction Inversekinematics DWBA Spectroscopicfactor

Thefirstmeasurementoftheone-neutrontransferreaction11Li(p,d)10LiperformedusingtheIRISfacility atTRIUMFwitha5.7 A MeV11_{LibeaminteractingwithasolidH}

2targetisreported. The10Liresidue

was populated strongly as aresonance peakwithenergy Er=0.62±0.04 MeV havingatotalwidth

=0.33±0.07 MeV.Theangulardistributionofthisresonanceischaracterizedbyneutronoccupying the1p1/2orbital.ADWBAanalysisyieldsaspectroscopicfactorof0.67±0.12 forp1/2removalstrength

fromthegroundstateof11_{Litotheregionofthepeak.}

©2016TheAuthors.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense (http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3_.

Thenuclear halo,discovered three decadesback [1,2], contin-uesto be an intriguing object of study posinga great challenge tounderstandfromfirstprinciples.Particularlyunusualstructures arethe Borromean neutronhalo nuclei, whichare weakly bound states of three components, a core nucleus plus two neutrons

*

Correspondingauthor.

E-mailaddress:ritu@triumf.ca(R. Kanungo).

1 _{Presentaddress:InhaUniversityinTashkent,Tashkent,Uzbekistan.}

[1,2]. Here anytwo sub-components taken together are neutron-unbound. Borromean two-neutron halos have been identified in 6_He, 11_Li, 14_Be, 17,19_{B [3]and}22_{C [4].The challengeto achievea} completeunderstandingoftheBorromean halorelatestothe cur-rent limited knowledge on the structure and interactions of the pair-wisesub-components.Whilethesub-componentsareneutron unbound,someofthemcanexistasresonances,suchasthe core-neutronsystems,10_Li,13_Be,16,18_{B and}21_C.

The wavefunctionof11_{Licanbe expressedby a superposition} ofdifferent resonancestatesof10Liplus a neutronthat occupies

http://dx.doi.org/10.1016/j.physletb.2016.02.060

482 A. Sanetullaev et al. / Physics Letters B 755 (2016) 481–485

therelevantmatchingorbital,intotalgivingthe11_{Ligroundstatea} spinof3

/

2−.Inordertounderstandthedominating10Listatethat constitutesthegroundstate of 11Li, we reportthe first measure-mentofaone-neutronpickupreaction11_Li(p,d)10_{Li,thattransfers} neutronfrom11Lipopulatingthestatesin10Li.

Theunboundstatesof10Lihavebeenexploredthroughvarious techniques,butmostofthesedonotrelatetothewavefunctionof 11_Li. 10_{Liisjustbeyondthedrip-lineofthe N}

₌

_{7 isotones where} it is known that the intruder 2s1/2 orbital maybe energetically lower than the 1p1/2 orbital causing a breakdown of the N

=

8 shell closure. The first observation of a 10_{Li identified through} the 9Be(9Be,8B)10Li reaction [5], found a peak at resonance en-ergy Er

=

0

.

80

±

0

.

25 MeV;



=

1

.

2

±

0

.

3 MeV (



=

full width at half maximum). Thiswas later understood not to be the ground state.A subsequentstudythroughthe11B(

π

−,9Li

+

n)preaction[6] showeda broadstructure at Er

=

0

.

15

±

0

.

15 MeV that was as-sumedtoresultfromalarges-waveamplitude.Thisassumptionis supportedby observationofan l

=

0 resonanceat0

.

1

±

0

.

1 MeV (



=

0

.

4

±

0

.

1 MeV)inthe11B(

π

−,p)10Lireaction[7].A resonant state unboundto neutrondecay by atleast100 keV, andwitha possibles-waveorp-wavestructurewasidentifiedfromastudyof the11B(7Li,8B)10Lireaction[8].

The presence of a neutron s-wave in the lowest state of 10_Li wasfurtheraffirmedfromseveralfragmentationexperiments.The relative-velocityspectrumofthe9Li-nsystemfromfragmentation of18_{O was peakedatzeroindicativeofthes-wavenature[9,10],} witha scatteringlength, as

<

−

20 fm[10].Momentum distribu-tionsofone protonandone-neutronremovalfrom11Be [11] and 11_{Li [12], respectivelywere rather narrowwhich indicates that a} neutroninthe 10_{Ligroundstatehasa strongs-wavecomponent.} The invariant mass spectrum froma 9Li-n coincidence measure-ment,following neutronremovalfrom11Li, whenanalyzed using a Breit–Wigner distribution showsthe lowest resonanceat Er

=

0

.

21

±

0

.

05 MeV;



=

0

.

12₋+₀0._.10₀₅ MeV[13].Theneutronremoval re-actionssuggestthes-wavevirtualstatetohaveascatteringlength varyingintherangeas

∼ −

22 to

−

30 fm[14,15].

Severalstudies havesuggestedthefirstexcited stateof10_Lito be ap1/2 resonance.The9Li(d,p)reaction [16] exhibitsapeak at Er

∼

0

.

38 MeV interpretedas this resonance.This peak is much lower in energy than that in Ref. [5]. 10_Be(12_C, 12_N)10_{Li is the} onlyothermeasurement[17]whichshowedanevenlowerenergy peakat0

.

24

±

0

.

04 MeV togetherwithapeakat0

.

53

±

0

.

06 MeV which are both l

=

1 resonances. The latter resonance energy seemsconsistentwiththeobservationfromthe 9Be(9Be,8B) reac-tionreportinganl

=

1 resonanceat0

.

50

±

0

.

06 MeV[18],butnot consistentwiththe 0.8 MeVstate inRef. [5].Theresonances ob-servedat0

.

54

±

0

.

06 MeV inthe 11B(7Li,8B)10Lireaction [8],and at0

.

7

±

0

.

2 MeV inthe11B(

π

−,p)reaction[7],arealsoin agree-ment with the above. The two-proton removal from 12_{B reports} threepositiveparityresonancesat0

.

1

±

0

.

04 MeV,0

.

5

±

0

.

1 MeV and1

.

1

±

0

.

1 MeV[19].The decayspectrumisdominatedbythe 0

.

5

±

0

.

1 MeV resonanceexhibitingapeakbuttheothertwo com-ponentswererequiredinordertofittherisingandtrailingedges ofthe spectrum.Recently, stopped

π

− absorption reactions with 14_{C target reported peaks for} 10_{Liat E}

r

=

0

.

70

±

0

.

05 MeV and 0

.

78

±

0

.

15 MeV[20].

Whileall ofthe abovementioned reactions canprobethe ex-cited resonance spectrum of 10Li, they do not convey informa-tionontheroleoftheseresonances inthegroundstatestructure of 11Li. This can be investigated via neutron removal orneutron transferreactionsfrom11Li.Severalneutronremovalreactions ex-hibitedpeaksatEr

=

0

.

61

±

0

.

10 MeV[13],0

.

68

±

0

.

10 MeV[23], 0

.

510

±

0

.

044 MeV [15] and 0

.

566

±

0

.

014 MeV [14]. The reso-nanceenergieswere obtainedfromBreit–Wigner fitsofthe9Li-n decayenergyspectra,withasumofcontributionsfromresonances

Fig. 1. (a)Aschematiclayoutoftheexperiment.Theparticleidentificationusingthe (b)YY1-CsI(Tl)array(c)S3E−E array.

whose widthsdepend on thedecay energyandangular momen-tum.Thisledtoanunderstandingofthel

=

1 natureofthepeak whilethelowerenergyspectrumshowsastrongandnarrow con-tributionfromthel

=

0 virtualstate.Thesemeasurementshowever donotprovideanyinformationonthespectroscopicfactorthatis necessarytodefinethegroundstateof11Li.A neutrontransfer re-actionisadecisivewaytoascertainboththeangularmomentum andthe spectroscopicstrengthfromthemeasured angular distri-bution. The mainmotivation ofthe investigationreported inthis articleis tostudytheneutronpickup reaction 11Li(p,d)10Li, since nosuchstudyhasyetbeenperformed.

The first measurement of this one-neutron transfer from 11_Li using the IRISfacility [21] atTRIUMF, Canada isreported inthis letter.The11_{Libeamwithanaverageintensityof2800 pps,} accel-erated toan energyof6 A MeV using thesuperconducting LINAC attheISACIIfacility,interactedwithasolid H2 targetatIRIS.The beamintensitywasdeterminedusingalow-pressure transmission-type ionizationchamber operatedwithisobutanegasat19.5 Torr placedbefore theH2 target.Theenergy-lossspectrum ofthe ion-izationchamberalsorevealedthattherewerenoisobaric contam-inantsinthebeam.

The solid H2 target was formed by spraying H2 gas onto a 5.4 μmthickcooledAgfoil.Thefoiladherestoacoppertargetcell framecooled to4 K.Thetargetthicknesswas measuredusingthe Ag(11_Li,11_{Li)Ag elastic scattering peak energy of} 11_{Li detected in} theS3siliconarray.Thiswas donesimultaneously while measur-ingthe(p,d)reaction.Thedifferenceinenergyofthiselasticpeak withoutandwithH2 providesameasureofthesolidH2thickness fromtheenergylosswithinit.Itwascrucialtohaveacontinuous thicknessdeterminationbecausethetargetwasfoundtogradually evaporateafterseveralhours.A continuousthicknessmeasurement thereforeallowed usunambiguous determinationofcross section usingthethicknessmeasuredateachinstanttogetherwiththe re-spectivenumberof reactionevents.When thethickness dropped below a certain level the target was re-furbished by adding H2. The average thickness was

∼

60 μm varying from

∼

30 μm to

∼

130 μm with time. In order to restrict the radiative heating ofthe H2 target, the target cell is surrounded by a copper heat shieldwhichiscooled to

∼

30 K.The openingoftheheat shield forthescatteredparticlesledtoanangledependentgeometric ef-ficiencyforthe Yd1-CsI(Tl)detectorarray since the shieldmasks partsofthisarray.Thisgeometricefficiencywasdeterminedby a Monte Carlosimulation.ThebackgroundreactionsfromtheAgfoil emittingdeuteronswere negligiblysmallasfoundfrom measure-ment without the H2 layer. The beam energy atmid-target was 5

.

7 A MeV.

Fig. 2a shows the measured energy-angle scatter plot of deuteronsbytheYY1-CsI(Tl)telescope.Forenergiesbelow4.5 MeV, the deuterons stop in the silicon layer and therefore cannot be identifiedbytheprocedurementionedabove.Thoseeventsplotted below4.5 MeVincludeallparticlesstoppedintheYY1detectorin coincidencewith9LiintheS3telescope(Fig. 2a).Inorderto min-imizethenon-resonant backgroundtheazimuthal anglebetween thedeuteronsandthe9_{Liwasrestrictedto180}◦

_±

₆₀◦_.Theregion outsidethisselectiondoesnotexhibitanyresonancepeak.

Theresonanceenergyspectrum (Fig. 2b)of10Liisconstructed in the missing mass technique using the measured energy and scattering angle of the deuterons. A very prominent resonance peakis seenat Er

=

0

.

62

±

0

.

04 MeV andfull width



=

0

.

33

±

0

.

07 MeV isobtainedfromfittingthespectrumwithaVoigt func-tionwithan energydependent Breit–Wignerfunctionwidth[22]. Theaverage(Gaussian)excitationenergyresolutionovertherange of angles used in this fit is

σ

∼

0

.

31 MeV based on simulation thatreproduceselasticscatteringpeak width.Theresonancepeak width extracted is consistent throughout the angular range. The resonance energy is consistent with that reported in Refs. [7,8, 14,15,17,19,23].The intrinsicwidthofthe peakis ingood agree-ment with observations from multinucleon transfer reactions [8, 17,18]andconsistentwithin large uncertainties withneutron re-movalreactions [15,14]. The widths reportedin Refs. [13,23] are muchlargerandthatinRef.[7]ismuchsmaller.

The spectrum does not exhibit any other resonance peak(s) such as at Er

=

0

.

24 MeV [17], 0.35 MeV [16] although they wouldbe within the detectoracceptance. A higher energy reso-nancesuch as Er

∼=

1

.

49 MeV discussed in [15] is also within thedetectoracceptancebutitsabsencesuggeststhatitcouldonly bea smallcomponentinthegroundstate of11_{Li.The remaining} partofthe spectrumis estimatedwithnon-resonant background fromthethree-body phase space of11Li

+

p

→

d

+

9Li

+

n consid-eringanisotropic emissionof theproducts inthecenter-of-mass (cm) frame. The simulated shape of this non-resonant contribu-tionfoldedwiththe (Gaussian)experimental resolutionisshown by the dotted (red)curve inFig. 2b. This simulatedcontribution describes fairly well the spectrum with energy higher than the peak region. In addition, there can be background from mixing ofother particles for eventsstopping in the YY1 detectorwhich

Fig. 2. (a)Thecorrelationofenergyofdeuteronsasafunctionoflaboratory scat-teringangle.Theblackcurveshowsthecalculatedkinematiclocusfor10_Liatthe 9_{Li+n threshold(i.e. for E}

r=0 MeV).The regionbelow the dashed horizontal

lineareeventsthatstopintheYY1detector.(b) Theresonanceenergyspectrum reconstructedfromenergyandscatteringanglemeasuredforthe deuterons.The dottedcurveshowsthecalculated9_{Li+n+dthree-bodynon-resonantphasespace.}

Thesolid(red)lineshowsthelinearbackgroundshapeconsideredinthecross sec-tionevaluation.ThepinkcurveisthefittothepeakusingBreit–Wignerresonance foldedwithexperimentalresolutionandthelinearbackground.(Forinterpretation ofthereferencestocolorinthisfigurelegend,thereaderisreferredtotheweb versionofthisarticle.)

were notidentifiedasdeuterons.Suchbackgroundeventsand ef-fects of the experimental resolution contribute to the spectrum extendingbelowEr

=

0 MeV.Inordertoestimatetheuncertainty duetothe assumedbackgroundprofilewe havealsoused a sec-ond method where the spectrum was fitted by a Breit–Wigner peak folded with the resolution plus a linear background shape (solid red line, Fig. 2b) around the peak region. The uncertainty inbackgrounddeterminationfromthesedifferentmethodsis20% andisincludedinthetotaluncertaintyoftheangulardistribution data. The background countsunder the resonance peak are sub-tractedinordertoget thenumberofscattereddeuterons forthe 11_Li(p,d)10_Li∗ _{reaction.The cross section data presentedbelow is}

fromlinearbackgroundsubtractionincludingeffectsofthe three-bodyphasespacebackgroundas20%uncertainty.

484 A. Sanetullaev et al. / Physics Letters B 755 (2016) 481–485

Table 1

Opticalpotentialparametersfor11_{Li+pfromafitofelasticscattering.}

V0 (MeV) r0 (fm) a0 (fm) WV (MeV) rI (fm) aI (fm) WD (MeV) rD (fm) aD (fm) Vso (MeV) rso (fm) aso (fm) 95.93 1.00 1.10 15.00 0.65 0.50 11.90 0.67 1.1 10.70 0.80 0.75

Fig. 3. Theelasticscatteringangulardistributiondatafor11_Li(p,p)11_Li

gs.Thecurve

showsopticalmodelcalculationswiththebestfitopticalpotentialparameters. crosssection an additional20% uncertainty fromthebackground estimationisincluded.

Fig.4showstheangulardistributionforthe11_Li(p,d)10_Li reac-tion.ThedetectionefficiencyshownintheinsetofFig. 4isbased on simulation with the 10Li resonance decaying isotropically in its cm frame into 9Liand neutron. It includes the geometric ef-fect of the heat shield of the target as well as the coincidence efficiencyof d and9_{Li detectionforthe forward}

_θ

cm angles.The curves in Fig. 4 are DWBA calculations using FRESCO [24]. The exit channel optical potential was considered to be the same as that extracted from the 11Li(d,d) elastic scattering [25]. The sin-gleparticleformfactorshaveaneutronboundtotheprotonina Woods–Saxonpotential. The potentialis chosen to reproducethe bindingenergy,rootmeansquareradius,andD0 ofthedeuteron. TheparametersforthepotentialareV0

=

165

.

54 MeV,r0

=

0

.

4 fm anda0

=

0

.

6 fm. Theseare thequantities that affectthetransfer crosssections.A Woods SaxonformfactorhasbeenusedinDWBA calculationsinRefs.[26,27].A comparisonofthisformfactorwith aReidSoftcorepotentialformfactoryields

∼

5% changein spec-troscopicfactorforthe11_Li(p,d)10_Lireaction.11_{Liisdescribedasa} boundstateofa10_Listate

₊

_{aneutronwithaWoods–Saxon} bind-ingpotentialwheretheeffectiveseparationenergyis

=

0

.

98 MeV. Thepotential hasarealandspin–orbitpartwithsamegeometry, r0

=

1

.

15 fm anda0

=

0

.

6 fm.Thedepthofthespin–orbitpartis Vso

=

6 MeV whilethedepthoftherealpartisV0

=

49

.

6 MeV for a1p1/2neutron.

IntheDWBAcalculations,weconsiderthreedifferent possibil-ities ofneutron configurationof 11_{Liforthe resonance observed.} The solid (red) curve (Fig. 4) showsneutron transfer with angu-larmomentuml

=

1.Thedistributionhassameshapefortransfer fromthe1p1/2 or1p3/2 orbital.Weconsiderthisneutrontransfer tobedominatedbytransferfromthe1p1/2 forthediscussion be-low.ThisconsiderationissupportedbypredictionsfromtheTensor OptimizedShellModelframeworkthatsuggestsonly2.5% compo-nent of

(

p3/2

)

2 neutrons in 11Li[28].Neutron transfers fromthe 2s1/2 orbital and 1d5/2 orbital in 11Li are shown by the dotted (black) and dashed (blue) curves, respectively (Fig. 4). The data clearlydemonstratethattheresonancepeakobservedisassociated withneutron transfer from the 1p1/2 orbital. The

χ

min2 value for

Fig. 4. Theangulardistributiondatafor11_Li(p,d)10_Li

Er=0.62 MeV.Thecurvesshow

the DWBA calculations.The solid(red)curve/dashed (blue)curve/dotted (black) curverepresentsoneneutrontransferfromthe1p1/2/1d5/2/2s1/2orbital.The

in-setshowsthedetectionefficiency.

thep-orbital is

∼

0

.

8 whilethoseforthed- ands-orbital are

∼

4

.

5 and

∼

6

.

7,respectivelyforthe bestfitnormalizationto thedata. The magnitude of the measured cross section compared to the DWBAcalculationprovidesthespectroscopicfactor(S)ofthis con-figuration tobe 0

.

67

±

0

.

12 with

(

d

σ

/

d

)

ex

=

S

× (

d

σ

/

d

)

DWBA. Here, the spectroscopic factor value refers to that of two neu-trons. Assuming that the resonance peak observed includes the complete

(

1p1/2

)

2 strength andhence an overlap ofthe 1+ and 2+ states of 10_{Li, the probability fraction of the}

₍

_1p1

/2

)

2 com-ponent in the wavefunction of 11Li is S

/

2

=

0

.

33

±

0

.

12, where sum of all components is unity. This is consistent with the pre-dictionsinRef.[28].Alternatively,ifthe resonancepeak observed is only one of 1+ or 2+ states of 10_{Li with half the p-wave} strength, then the total probability fraction of the 1p1/2 compo-nent is2

×

S

/

2

=

0

.

67

±

0

.

12.Weconsider theformercasetobe themorelikelysituationbecausethefragmentationreactionsalso reportoneresonancepeakforthel

=

1 component[14,15].In ad-dition,anequallystrongsecondresonancewellseparatedfromthe presentpeakandwithinthisexcitationenergyrangeshouldhave beenobservedinthisexperiment.

If all the remaining component was only

(

2s1/2

)

2, then this probability fraction would be

∼

0

.

67

±

0

.

12. Recently, 11(2)% of d-waveprobabilityhasbeenfoundinthegroundstateof11_Li[29]. Therefore,considering thed-wave,thes-waveprobabilityfraction could be reduced to

∼

0

.

56

±

0

.

12. Fragmentation studies had pointedtoans-waveprobabilityfractionof0

.

4

±

0

.

1[30].The an-gular distribution of(p,t)two-neutron transferreaction from11_Li was best explained by wavefunctionmodels withs-wave proba-bility fraction in the range of 0.31–0.45 [31]. The small

(

p1/2

)

2 probability observedthrough the 10Liresonance andhence large

three-body model [33] finds that the B(E1) value from Coulomb dissociationis explained by a rather small s-wave probability of 25% while the charge radius was explained using a higher value of50%.Thelatterseems tobe consistentwiththeobservationin thiswork. Theoreticaldevelopmentsincludingmulti-stepreaction mechanismswouldbeusefultoinvestigateinfuture.

Insummary,thefirstmeasurementoftheone-neutrontransfer reaction11_Li(p,d)10_LiatE

_/

_A

₌

₅

_.

_{7 MeV isreported.Theexcitation} spectrumofthe10_{Liresidueisdominatedby astrongpopulation} ofa resonance peak at Er

=

0

.

62

±

0

.

04 MeV witha width



=

0

.

33

±

0

.

07 MeV.The angulardistribution ofthisresonance ana-lyzedina one-stepDWBAframeworkconfirms ithavingan l

=

1 character i.e. with the neutron occupying the 1p1/2 orbital. The measuredcrosssectionyieldsa spectroscopic factor

=

0

.

67

±

0

.

12 forthe

(

1p1/2

)

2 component. This defines relatively small

(

p1/2

)

2 fractionin11_Li

gs associatedwiththis10Liresonancepeak consid-eredto contain the complete

(

p1/2

)

2 strength. Assuming the re-mainingprobabilityfractiontobes- andd-waves,a large

(

2s1/2

)

2 probabilityfraction

≥

44% isdeducedforthegroundstateof11Li. Thepresentobservationwillserveasguidancefortheoretical mod-elscalculatingmoreaccuratewavefunctionsfor11_Li.

The authors express sincere thanks to the TRIUMF beam de-liveryteam. Thesupport fromCanada Foundation forInnovation, NSERC,NovaScotiaResearchandInnovationTrust isgratefully ac-knowledged.Thisworkissupportedbythegrant-in-aidprogramof JapaneseGovernment under the contractnumber 23224008.This workwasperformedundertheauspicesoftheU.S.Departmentof EnergybyLawrenceLivermoreNationalLaboratoryunderContract DE-AC52-07NA27344.

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