Coulomb and nuclear excitations of narrow resonances in 17Ne

Physics Le e s B 759 (2016) 200–205 Con en s lis s a ailable a ScienceDi ec Physics Le e s B www.else ie .com/loca e/physle b Coulomb and nuclea exci a ions o na ow esonances in 17Ne J. Ma ganieca,b,c, F. Wame s a,b,c,d, F. Aksouh b, Yu. Aksyu inab, H. Ál a ez-Pole, T. Aumann a,b, S. Becei o-No oe, C.A. Be ulani , K. Bo e zkyb, M.J.G. Bo geg, M. Cha ie h, A. Cha illonb, L.V. Chulko i,b, D. Co ina-Gile, H. Emlingb, O. E sho ab,j, L.M. F aile k, H.O.U. Fynbol, D. Gala izg, H. Geisselb, M. Heilb, D.H.H. Ho manna, J. Ho mannb, H.T. Johanssonm, B. Jonsonm,∗, C. Ka agiannisb, O.A. Kisele b, J.V. K a zn, R. Kulessao, N. Ku zb, C. Lange b,j, M. Lan zp, T. Le Bleis b,q, R. Lemmon , Yu.A. Li ino b, K. Maha ab,s, C. Mün zb, T. Nilssonm, C. Noci o ob, G. Nymanm, W. O b, V. Panina,b, S. Paschalisb,h, A. Pe eag, R. Plagb,j, R. Rei a hb,j, A. Rich e a, C. Rod iguez-Tajese, D. Rossib,u, K. Riisage l, D. Sa anc,d, G. Sch iede a, H. Simonb, J. S o hj, K. Sümme e b, O. Tengbladg, S. Typelb, H. Weickb, M. Wiesche , C. Wimme b,j aIns i u ü Ke nphysik, Technische Uni e si ä Da ms ad , DE-64289 Da ms ad , Ge many bGSI Helmhol zzen um ü Schwe ionen o schung GmbH, DE-64291 Da ms ad , Ge many cEx eMe Ma e Ins i u e EMMI and Resea ch Di ision GSI, DE-64291 Da ms ad , Ge many dF ank u Ins i u e o Ad anced S udies FIAS, DE-60438 F ank u am Main, Ge many eDepa amen o de Física de Pa ículas, Uni e sidade de San iago de Compos ela, ES-15782 San iago de Compos ela, Spain Depa men o Physics and As onomy, Texas A&M Uni e si y-Comme ce, TX 75429, USA gIns i u o de Es uc u a de la Ma e ia, CSIC, ES-28006 Mad id, Spain hDepa men o Physics, Uni e si y o Li e pool, Li e pool, L69 3BX, Uni ed Kingdom iNRC Ku cha o Ins i u e, RU-123182 Moscow, Russia jIns i u ü Angewand e Physik, Goe he Uni e si ä , DE-60438 F ank u am Main, Ge many kDepa men o A omic, Molecula and Nuclea Physics, Uni e sidad Complu ense de Mad id, ES-28040 Ma id, Spain lDepa men o Physics and As onomy, Uni e si y o Aa hus, DK-8000 Aa hus, Denma k mFysik, Chalme s Tekniska Högskola, SE-412 96 Gö ebo g, Sweden nIns i u ü Ke nchemie, Johannes Gu enbe g-Uni e si ä Mainz, DE-55122 Mainz, Ge many oIns y u Fizyki, Uniwe sy e Jagello´nski, PL-30-059 K akó , Poland pIns i u ionen ö Fysik och As onomi, Uppsala Uni e si e , SE-75120 Uppsala, Sweden qPhysik-Depa men E12, Technische Uni e si ä München, DE-85748 Ga ching, Ge many Nuclea Physics G oup, STFC Da esbu y Lab, Wa ing on, WA4 4AD, Cheshi e, UK sNuclea Physics Di ision, Bhabha A omic Resea ch Cen e, T ombay, Mumbai, 400 085, India JINA, Uni e si y o No e Dame, No e Dame, USA uNa ional Supe conduc ing Cyclo on Labo a o y, MSU, Eas Lansing, MI 48824, USA a i c l e i n o a b s a c A icle his o y: Recei ed 16 Feb ua y 2016 Recei ed in e ised o m 11 Ap il 2016 Accep ed 22 May 2016 A ailable online 25 May 2016 Edi o : V. Me ag New expe imen al da a o dissocia ion o ela i is ic 17Ne p ojec iles inciden on a ge s o lead, ca bon, and polye hylene a ge s a GSI a e p esen ed. Special a en ion is paid o he exci a ion and decay o na ow esonan s a es in 17Ne. Dis ibu ions o in e nal ene gy in he 15O +p +p h ee-body sys em ha e been de e mined oge he wi h angula and pa ial-ene gy co ela ions be ween he decay p oduc s in di e en ene gy egions. The analysis was done using exis ing expe imen al da a on 17Ne and i s mi o nucleus 17N. The isoba ic mul iple mass equa ion is used o assignmen o obse ed esonances and hei spins and pa i ies. A combina ion o da a om he hea y and ligh a ge s yielded c oss sec ions and ansi ion p obabili ies o he Coulomb exci a ions o he na ow esonan s a es. The *Co esponding au ho . E-mail add ess: [email p o ec ed] (B. Jonson). h p://dx.doi.o g/10.1016/j.physle b.2016.05.073 0370-2693/©2016 The Au ho s. Published by Else ie B.V. This is an open access a icle unde he CC BY license (h p://c ea i ecommons.o g/licenses/by/4.0/). Funded by SCOAP3. J. Ma ganiec e al. / Physics Le e s B 759 (2016) 200–205 201 esul ing ansi ion p obabili ies p o ide in o ma ion ele an o a be e unde s anding o he 17Ne s uc u e. ©2016 The Au ho s. Published by Else ie B.V. This is an open access a icle unde he CC BY license (h p://c ea i ecommons.o g/licenses/by/4.0/). Funded by SCOAP3. The p o on d ipline nucleus 17Ne is a candida e o a wo- p o on Bo omean halo nucleus [1], wi h a 15O co e su ounded by wo alence p o ons. The p o ons a e expec ed o p edominan ly possess a mixed (1s1/2)2and (0d5/2)2configu a ion. The e is, how- e e , no eal consensus abou he ela i e s eng h o he sand d configu a ions, nei he expe imen ally no heo e ically. Es ima es based on expe imen al alues o in e ac ion c oss-sec ion and mo- men um dis ibu ions o agmen s in one-p o on knockou [2–5], he magne ic dipole momen [6], fi s - o bidden β+-decay [7,8], Coulomb ene gy di e ence be ween he mi o nuclei 17Ne and 17N[9–13], as well as pu e heo e ical in es iga ions [14–16], p o- ide widely di e ing esul s. Di e en e alua ions o he amoun o (1s1/2)2in he 17Ne g ound-s a e wa e unc ion, P(s2), ange om 15% o 100%. The e a e also s ong con adic ions be ween di e - en heo e ical models o Coulomb dissocia ion o 17Ne [17–20]. A heo e ical s udy [21] poin s o he impo ance o he de- e mina ion o elec ic ansi ion s eng hs o elucida e he wo- p o on halo p ope ies. The au ho s emphasise in pa icula he impo ance o educed elec ic ansi ion p obabili ies om he 17Ne g ound s a e o low-lying s a es as o example B(E2, 1/2−→ 3/2−)and B(E2, 1/2−→5/2−), ha could be de e mined h ough Coulomb exci a ion. This pape p esen s a new compa a i e s udy o nuclea and Coulomb exci a ion o 17Ne a ela i is ic ene gies using polye hy- lene (CH2), ca bon, and lead a ge s. The expe imen was pe o med a he GSI Helmholzzen um ü Schwe ionen o schung GmbH in Da ms ad , employing he R3B- LAND se up o measu emen s in in e se and ull kinema ics. The eac ion p oduc s, om 17Ne in e ac ion, we e fi s de ec ed in a pai o silicon-s ip de ec o s and hen sepa a ed in he magne ic field o he la ge dipole magne (ALADIN). A e he magne , wo b anches o de ec o s we e used o measu e he posi ion, ene gy- loss, and ime-o -fligh , one o hea y ions ( wo fib e de ec o s and a ToF-wall) and ano he o p o ons ( wo d i chambe s PDC and a ToF-wall). The ajec o ies o cha ged pa icles h ough he mag- ne ic field o ALADIN we e econs uc ed o pa icle iden ifica ion and de e mina ion o hei momen um ec o s. The cha ge o he pa icles was di ec ly measu ed ia hei ene gy loss in he silicon- s ip de ec o s and ToF-walls, while hei mass was ob ained om measu emen s o Bρusing he econs uc ed deflec ion angle in he ALADIN magne . This analysis is based on knowledge o he magne ic field inside and ou side he ALADIN magne , measu ed along all h ee coo dina e axes a many housands o g id poin s. The γ- ays emi ed by he de-exci ing agmen s we e de ec ed in he 4πgamma spec ome e , C ys al Ball, placed a ound he a - ge . A ske ch o he posi ions o he cha ged-pa icle de ec o s in he expe imen al se up is shown in Fig. 1 o Re . [22]. The 17Ne beam was di ec ed owa ds a seconda y 199 mg/cm lead a ge , used o induce elec omagne ic exci a ion o 17Ne. The expe imen also ook da a wi h a 370 mg/cm2ca bon a ge as well as a 213 mg/cm2polye hylene a ge , o s udy nuclea - induced b eakup. The backg ound was de e mined in uns wi h an emp y a ge . T iple coincidences be ween 15O and wo p o ons we e se- lec ed. The in insic wo-p o on de ec ion efficiency was 57.8(3.1)%. The de ec ion efficiency was de e mined om losses o wo-p o on e en s due o oo small ene gy deposi ed in he PDCs, losses du - ing he econs uc ion o p o on ajec o ies in he magne ic field o ALADIN, and losses due o he spa ial esolu ion in he PDCs. The losses due o PDC esolu ion a e inc easing wi h he dec eas- ing in e nal ene gy in he h ee-body sys em. Howe e e en a he ene gy o he 17Ne(5/2−) esonance he change in he de ec- ion efficiency was ound o be smalle han i s unce ain y. The magne ic spec ome e p o ided la ge di e ence in p o on ajec- o ies. Quad uple coincidences, including γ- ay de ec o s, showed ha con ibu ions om exci ed s a es in 15O a e negligible. The momen um ec o s o he p o ons and he 15O agmen s we e ob ained in he es ame o he beam. As in Re . [22] and i s Eq. (1), Jacobi coo dina es in he Y-sys em we e used in he analy- sis. The in e nal kine ic ene gy, E pp, in he h ee-body 15O +p +p sys em, as well as he ac ional ene gies  p =E p/E pp in he agmen -p o on subsys em and he angle θ p be ween he wo ec o s p p and pp− p, was de e mined o each e en . The anal- ysis was done in wo consecu i e loops h ough each e en , by selec ing one de ec ed p o on as he fi s one in he fi s loop and hen changing o he opposi e o de in he second loop. The da a we e co ec ed o accep ance. The o e all accep ance, including momen um cu s due o he fini e size o de ec o s and dead wi es in he p o on d i chambe s, was calcula ed in a Mon e-Ca lo sim- ula ion unde he assump ion o iso opic h ee-body decay. The accep ance unc ion on E pp is shown in Fig. 3 o Re . [22]. The expe imen al ene gy esolu ion was ound o be close o a Gaus- sian shape wi h a dispe sion σ=1.83E0.568 pp MeV. The co ela ion unc ions, o he ac ional-ene gy dis ibu- ions W( p)as well as o he angula dis ibu ions W(θ p), no - malised o uni y (1 0W()d=1 and 1 −1W(θ)dcosθ=1) we e hen cons uc ed and analysed. The expe imen al exci a ion ene gy spec a, E∗=E pp + S2p(17Ne), shown in Fig. 1, a e well desc ibed as esul ing om he con ibu ion o se e al exci ed s a es in 17Ne, supe imposed on a smoo h backg ound, shown as dashed lines. This backg ound co esponds o non- esonan dissocia ion and may also con ain con ibu ions om un esol ed esonances. Based on expe imen al esul s [25], he wid hs o he esonance s uc u es we e assumed as de e mined en i ely by he expe imen al esolu ion. A leas - squa es fi was pe o med using he unc ional minimisa ion and e o analysis code MINUIT [24]. The smoo h backg ound, shown as dashed lines in Fig. 1, co esponds o non- esonan dissocia ion and may also con ain con ibu ions om un esol ed esonances. Ex apola ion o his smoo h backg ound in o he egion o eso- nances was done by using in o ma ion om he W( p)dis ibu- ions (see Fig. 5). Fi e esonance-like s uc u es co esponding o exci a ions o na ow esonan s a es in 17Ne a e obse ed in he da a om he CH2and C a ge s, while only h ee a e iden ified in he da a om he Pb a ge (see Fig. 1 and Table 1). The le el s uc u e o 17Ne has been s udied ea lie using he h ee-neu on ans e eac ion 20Ne(3He,6He) [25]. These esul s we e used as a fi s guidance in ou in e p e a ion oge he wi h he a ailable expe imen al in o - ma ion abou he s uc u e o exci ed s a es in he mi o nucleus 17N[26]. A omic masses and ene gy le els o he A =17, T=3/2 isoba ic mul iple s aken om Re s. [27,28] we e also used o- ge he wi h he isoba ic mul iple mass equa ion (IMME) and he Thomas–Eh man shi s (TESs) o he classifica ion o he s a es. (1) The fi s peak in he spec um is due o an un esol ed double consis ing o wo na ow s a es a 1.764(12) MeV (Iπ= 5/2−) and a 1.908(15) MeV (1/2+)[25]. The ela i e con ibu- 202 J. Ma ganiec e al. / Physics Le e s B 759 (2016) 200–205 Fig. 1. Exci a ion spec a o 17Ne a e b eakup o 17Ne 500 MeV/ubeam o 15O + p +pin polye hylene, ca bon and lead a ge s. The numbe s in pa en heses e e o he esonances p esen ed in Table 1. ions o hese wo s a es we e ob ained om an analysis o he h ee-body co ela ions in he ene gy egion 0 <E pp <1.4MeV (see below). (2) The second peak a E∗=2.652 MeV (see Table 1) is close in ene gy o he obse ed exci ed s a e a 2.651(12) MeV [25]. This s a e was in e p e ed o be an Iπ=5/2+s a e. How- e e , a 5/2+s a e is unlikely o be ed in a Pb a ge by Coulomb exci a ion due o he small s eng h o he equi ed E3 o M2 ansi ions. Hence, he possibili y ha he obse ed peak is due o an un esol ed double canno be excluded. O e lapping s a es wi h he spin-pa i y, 5/2+ 1and 5/2− 2, we e p oposed (see Re . [25] and e e ences he ein). Howe e , in his case an unusually la ge Table 2 Isoba ic mul iple mass equa ion coefficien s and Thomas–Eh man shi s (keV), (TES), o A =17, T=3/2s a es. See explana ions in he ex . Iπab c χ2TES 3/2− 113025(1.2) −2844.8(1.3)219.8(3.6)0.39 −47(14) 5/2− 11349(2.5) −2825.0(3.5)210.10(4.9)0.61 20(16) 1/2+13523(3.8) −2896.4(4.7)240.28(5.5)0.00 −190(19) Assuming 5/2+ 1and 3/2− 2bo h a E∗=2.651 MeV. 5/2+ 114219(2.9) −2910.5(3.8)247.9(4.9)2.4 3/2− 214729(3.2) −2699.4(4.5)169.4(5.0)2.4 Fi o only 17F, 17Oand17Nisoba s. 5/2+ 114220(3.0) −2906.2(4.7)237.8(8.1)–−220(23) 3/2− 214730(3.2) −2706.2(6.3)179.5(8.4)– 380(16) nega i e cubic- e m coefficien is equi ed (d =−25 keV) in he isoba ic mul iple mass equa ion (IMME) o he 5/2− 2iso-qua e and u he mo e he Thomas–Eh man shi o he 5/2− 2s a e is su p isingly la ge in his case (≈1MeV). 1An al e na i e hypo he- sis is an un esol ed double o 5/2+ 1and 3/2− 2s a es. The pa abolic IMME was used in he analysis (see Table 2). The posi ion o he T=3/2, Iπ=3/2− 2s a e in 17O is no known, bu he assump- ion o a double equi es ha he posi ions o he 5/2+ 1and 3/2− 2 s a es in 17Ne a e close in ene gy, which only lea es one possibil- i y o his s a e – a na ow s a e a 14.230(2) MeV. The fi using only h ee s a es om 17N, 17O and 17F allows hen o make a p edic ion o he posi ions o s a es: 5/2+ 1a 2.614(20) MeV and 3/2− 2a 2.692(21) MeV, espec i ely. The esul ing TES(3/2− 2) = 380(16) keV, is much la ge han TES(3/2− 1) =−47(14) keV. The s uc u e o he analog s a es in he mi o nucleus 17N has shown ha he 3/2− 1and 3/2− 2s a es ha e wa e unc ions [26] wi h a 14% configu a ion wi h one alence p o on in he s-shell o 3/2− 1 and 86% o 3/2− 2[26]. A simila s uc u e is expec ed o he ana- log s a es in 17Ne. Thus a small alue o TES(3/2− 1) and a la ge o TES(3/2− 2) can be explained as a la ge asymme y in he weigh s o he configu a ion wi h one alence nucleon in he s-shell and he la ge spa ial ex ension o he s-wa e p o on wa e unc ion.2 (3) The exci a ion ene gy o he hi d peak, a E∗= 3.415(38) MeV, is close o he obse ed posi ion o he 9/2− s a e a E∗=3.548(20) MeV [25], bu he ene gy di e ence and he ac ha he e is no sign o a 7/2−s a e, which should ha e simila s uc u e as he 9/2−s a e [26], excludes such an assign- 1The Thomas–Eh man shi , TES(Iπ), was defined as he di e ence be ween he dis ances om 7/2− o Iπs a es in he mi o nuclei 17Ne and 17N. The 7/2−s a es we e chosen as e e ence since he Coulomb-ene gy shi s o hese s a es, ha ing h ee-body s uc u e wi h wo alence nucleons in he d-shell, a e expec ed o be small. 2No e also a la ge nega i e TES o posi i e-pa i y s a es. These s a es canno be inco po a ed in he h ee-body models gene ally used o he desc ip ion o 17Ne s uc u e and eac ions in ol ing his nucleus. An explana ion o he expe imen al pa i y-dependence o he Coulomb-ene gy shi s o he A =17 iso-qua e was sug- ges ed, e.g., in Re . [13], using a model wi h fi e alence nucleons a ound he 12C co e. Table 1 Exci a ion ene gies (MeV) and c oss sec ions (mb) wi h s a is ical e o ba s o obse ed esonance s uc u es in 17Ne exci a ion spec a. The numbe N e e s o he s uc u es shown in Fig. 1. NCH 2Ca bon Lead E∗σE∗σE∗σ (1) 1.790(5)4.89(15) 1.780(8)3.25(15) 1.813(15) 14.08(93) (2) 2.652(10)2.39(14) 2.571(37)1.17(10) 2.603(45) 7.68(74) (3) 3.422(44)1.38(12) 3.393(78)0.646(87) – – (4) 5.79(12)1.13(22) 5.40(20)0.47(19) 5.210(79) 14.4(1.7) (5) 10.06(16)2.10(35) 10.69(59)0.91(46) – – J. Ma ganiec e al. / Physics Le e s B 759 (2016) 200–205 203 Fig. 2. Na ow esonance s a es in he low-ene gy egion, 0 <E∗<4 MeV exci ed in he CH2 a ge . The hin solid lines show nega i e-pa i y s a es, dashed lines s em o posi i e-pa i y s a es and he dash-do ed line is physical backg ound. Fo ene gy egions I, II and III he ac ional ene gy spec a a e analysed as shown in Figs. 3, 4and 5, espec i ely. Table 3 Exci a ion ene gies and c oss sec ions (mb) wi h s a is ical e o s o esol ed eso- nances in 17Ne. IπE∗CH2CHPb 5/2−(i) 1.764(12) 4.04(20) 2.44(18) 0.80(14) 11.6(1.5) 1/2+(i) 1.908(15) 0.85(15) 0.81(15) <0.12.5(1.2) 5/2+2.614(20) 0.97(51) 1.14(10) <0.2 7.68(74) (3/2− 2)2.692(21) 1.40(53) <0.3 0.70(26) (5/2− 2)3.415(38) 1.37(12) 0.62(10) 0.38(8) – (3/2+)5.210(79) 1.13(22) 0.46(19) 0.33(15) 14.4(1.7) (i) Ene gies and e o s a e om Re . [25]. men . The 17Ne le el scheme is a he in ica e, which makes he analysis kno y. The h ee-neu on ans e eac ion has a selec- i i y o exci a ion o s a es wi h a defini e s uc u e and some s a es may he e o e be missed. A compa ison wi h he le el scheme o mi o nucleus, 17N, sugges s ha his s a e could be he second 5/2−s a e. The analysis gi en in Re . [26] o he 5/2− 2s a e in 17N, ga e a weigh o 72% o a configu a ion wi h a single p o on in he s-shell, a s uc u e simila o ha o he 3/2− 2s a e. The p esen alue TES(5/2− 2) =359(40) keV is close o TES(3/2− 2) =380(16) keV and is hus in suppo o he 5/2− 2 assignmen o he E∗=3.415(38) MeV s a e in 17Ne. (4)–(5) Two addi ional esonances a 5.210(79) MeV and 10.06(16) MeV we e obse ed in he p esen expe imen , he la e only o he ligh a ge s. A compa ison wi h he le els in he mi - o nucleus 17N and he ac ha he esonance a 5.210(79) MeV is s ongly exci ed wi h he lead a ge , poin s o an assignmen o Iπ=3/2+. The analysis o he na ow esonan s a es in he low ene gy egion, based on he discussion abo e, is shown in Fig. 2 and he esul s a e gi en in Table 3. C oss sec ions o exci a ion o en- e gy le els in he 1H(17Ne(g.s.),17Ne(Iπ)) eac ion we e ob ained om he ela ion: σ(CH2) =σ(C) +2σ(H). The da a demons a e di e en selec i i y o he di e en a ge s. Thus, o he hyd o- gen a ge , posi i e-pa i y s a es ha e lowe exci a ion p obabili y compa ed o hose wi h nega i e-pa i y. The pa ial decay scheme wi h domina ing decay b anches is shown in Fig. 6. In o de o ex ac mo e in o ma ion om he da a, he low- ene gy pa o he E pp spec um was di ided in o h ee sepa a e egions, as show in Fig. 2, whe e he ac ional ene gy spec um W( p)and he angula dis ibu ion W(θ p)we e cons uc ed and analysed. A sequen ial decay ia an in e media e na ow esonance in 16F a  =E /E pp appea s in he W(E p)dis ibu ion as wo peaks a  and 1 − . A 2He decay, o dip o on emission, would Fig. 3. F ac ional ene gy spec a W( p)in he Y-sys em o he egion o 15O + p +pin e nal ene gy 0 ≤E pp ≤1.4MeV om he CH2 a ge (a) and Pb a ge (b). The dis ibu ions s em om he un esol ed esonances 17Ne(5/2−) and 17Ne(1/2+) decaying o he 16F g ound s a e. A fi wi h only one ee pa ame e gi es hei ela i e con ibu ions. Fig. 4. F ac ional ene gy spec a W( p)in he Y-sys em o he egion o 15O + p +pin e nal ene gy 1.4 ≤E pp ≤2.2MeV om he CH2 a ge (a) and Pb a - ge (b). Thin solid and hick dashed lines show decays h ough he in e media e 16F(2−) and 16F(3−) s a es, espec i ely. These s a es ha e he s uc u e o 15O wi h one p o on in he d-shell. The dashed lines ep esen decays o he 16F(0−) s a e wi h he s uc u e 15O wi h one p o on in he s-shell. Fig. 5. F ac ional ene gy spec a in he Y-sys em W( p) o he egion o 15O + p +pin e nal ene gy 2.2 ≤E pp ≤3.0MeV om he CH2 a ge (a) and Pb a - ge (b). The hin solid lines show decays o 16F(2−and 3−) s a es and he dashed lines ep esen decays o 16F(0−and 1−) s a es. be cha ac e ised by an asymme ic angula W(θ p)dis ibu ion, inc easing when θ p ge s close o 180◦. In he p esen analysis W(θ p)was ound o be close o iso opic, wi hin s a is ical un- ce ain ies, which excludes a significan 2He emission. The shapes o he W( p)dis ibu ions a e well desc ibed by assuming se- quen ial decays h ough he fi s ou exci ed s a es in 16F. The pa ame e s o hese s a es we e aken om Re . [23]. The pa ial W( p)shapes a e s ongly influenced by he expe imen al esolu- ion and we e calcula ed in Mon e-Ca lo simula ions. The MINUIT 204 J. Ma ganiec e al. / Physics Le e s B 759 (2016) 200–205 Fig. 6. Na ow esonance s a es abo e he wo-p o on sepa a ion ene gy in 17Ne. The dominan decay b anches o he esonan s a es o 15O +2p, ia in e media e esonan s a es in 16F, a e shown. Posi i e-pa i y s a es a e colou ed in ed online. Resonances shown as dashed lines a e om Re . [25] and a e no popula ed in he p esen expe imen . code was used o he leas -squa e fi s o he measu ed W( p) spec a. The ac ional ene gy spec a o he lowes ene gy bin, 0 ≤ E pp ≤1.4MeV, a e shown in Fig. 3. The panels (a) and (b) show leas -squa e fi s o he W( p)dis ibu ions assuming sequen ial decay om s a es a exci a ion ene gies 1.764 MeV (5/2−) and 1.908 MeV (1/2+)[25] h ough he in e media e 16F(0−) s a e. The dis ibu ions W( p)a e no malised o uni y and in he fi he ela i e in ensi y was he only ee pa ame e used. Fo he CH2 a ge he fi gi es a 17.5(3.2)% con ibu ion om he 1/2+decay, o C 25.0(4.3)% (no shown), and o Pb 17.6(8.7)%, wi h s a is ical e o s. A double wi h 5/2+and 3/2− 2s a es was iden ified in he ene gy egion 1.4 ≤E pp ≤2.2 MeV ( egion II in Fig. 2). The di e - ence in exci a ion ene gy o hese wo s a es is much smalle han he expe imen al esolu ion and he di e ence in shape o W( p) o he decay b anches is ma ginal. The pene abili y h ough he Coulomb and cen i ugal ba ie s o he decay o 5/2+ o 3−is abou 20 imes smalle han ha o he decay o he 2−s a e. Fu he , his a io is a ound 1000 o he decay o 3/2− 2s a e. The main decay b anches o bo h s a es a e he e o e expec ed o p o- ceed ia he 16F(2−) s a e. The analysis o W( p) om a ca bon a ge ga e a decay b anch o 86(2)% while he es can be a - ibu ed o he eeding o he 16F(3−) s a e. The W( p) om CH2 and Pb a ge s we e fi ed wi h an assump ion ha he 17Ne(5/2+) and 17Ne(3/2− 2) s a es decay p edominan ly h ough 16F(2−) and 16F(0−) s a es. Con ibu ions om he 16F(2−) b anch we e 74(2)% o CH2and 41(4)% o Pb a ge s, see Fig. 4. The es can be a ibu ed o eeding mainly o he 16F(0−) s a e wi h a small con- ibu ion om he 16F(3−) b anch. In he case o he Pb a ge , he main pa o he 16F(0−) b anch is coming om a con inuous E pp spec um. In he ene gy egion 2.2 ≤E pp ≤3.0MeVa con ibu ion om he 17Ne(5/2− 2) s a e is expec ed. The decay b anches om his esonance should p oceed mainly by emission o  =0p o ons, eeding dominan ly 2−and 3−s a es in 16F. The popula ion o 0−and 1−s a es in he esonance decay equi es emission o  =2p o ons and is expec ed o be small due o pene abili y ac o s. S ill he e a e sizeable con ibu ions in he W( p)dis i- bu ion om eeding o hese s a es, especially p onounced o he Pb a ge , as shown in Fig. 5. These pa s o he dis ibu ions we e ea ed as a physical backg ound. The a io be ween he eedings σ(2−)/σ(3−) ≈1was ob ained o bo h he CH2and he C a ge . Fo he Pb a ge , keeping his a io fixed, he W( p)canno be ep oduced, which shows ha hese e en s canno be conside ed as ha ing hei o igin in he decay o he 5/2− 2s a e. They we e he e o e also conside ed as coming om a con inuous E pp spec um. The dis ibu ion was well fi ed wi h only h ee decay b anched o he 0−, 1−and 2− s a es in 16F. The c oss sec ions o Coulomb exci a ion o esonan s a es, σC, we e ob ained by sub ac ing he nuclea con ibu ion om he c oss sec ions measu ed wi h he lead a ge scaled wi h a ac o 1.84(20). The scaling ac o was de e mined expe imen ally. I was assumed ha Coulomb dissocia ion o 14O has a e y small, i no ze o, c oss sec ion and he scaling ac o was de e mined as he a io o (17Ne,14O) c oss sec ions ob ained wi h Pb and C a ge s. The scaling ac o is close o he a io be ween nuclea adii o p o- jec ile and a ge , (A1/3 Ne +A1/3 Pb )/(A1/3 Ne +A1/3 C), eflec ing ha he nuclea disin eg a ion is o su ace cha ac e . In his analysis i was assumed ha he 5/2+s a e is no Coulomb exci ed. Exci a ion o his s a e wi h a la ge c oss sec ion by a M2 o E3 ansi ion o in a mul i-s ep p ocess is unlikely. C oss sec ions o Coulomb exci a- ion o he iden ified na ow esonances a e gi en in Table 1. Fo he s a e a E∗=5.210(79) MeV and a lead a ge he exci a ion s ems dominan ly om Coulomb in e ac ion. The ansi ion p obabili ies B(πλ) om he g ound o an ex- ci ed s a e in he p ojec ile, whe e π=Eo Ms ands o an elec ic o magne ic ansi ion wi h mul ipola i y λ, we e calcu- la ed by he i ual-pho on me hod o in e media e ene gies [29, 30]. The c oss sec ion o Coulomb exci a ion o a na ow eso- nance a E∗is σπλ C(E∗)=(2π)3(λ +1) λ[(2λ+1)!!]2E∗ ¯ hc 2λ−1N(πλ) E∗B(πλ), (1) whe e N(πλ) is he numbe o i ual pho ons a exci a ion en- e gy E∗. This exp ession is used o calcula e he ansi ion p oba- bili y based on he measu ed c oss sec ion σπλ C(E∗)(in m2). The o malism desc ibed in Re s. [29,30] is used o calcula e N(πλ). In Re . [30] he e ec o s ong abso p ion is inco po a ed om he ou se (see Eqs. (13)–(15)), while a minimal impac pa- ame e Bcu has o be used when he analy ical semi-classical me hod om Re . [29] (Eqs. (2.5.5)) is applied. Calcula ions using he semi-classical me hod wi h Bcu =10.8 mgi e he same e- sul as Eqs. (13)–(15) in Re . [30]. The esul ing N(πλ) and B(πλ) alues a e gi en in Table 4. The Coulomb exci a ion o he fi s wo exci ed s a es in 17Ne was s udied ea lie [31] and he ansi ion p obabili y B(E2, 1/2−→5/2−) =24 e2 m4was deduced. Howe e , in he B(E2)calcula ions he au ho s included an ex a ac o e2in Eq. (1), which means ha he ob ained B(E2) alues a e in uni s o m4and should hus be mul iplied wi h a ac o 1.44. The co - ec ed alue o B(E2, 1/2−→5/2−)is gi en in he las ow in Table 4. The B(E2) alues om Re . [31] wi hou his co ec ion ac- o we e, howe e , used in Re s. [21,32] as a confi ma ion o he p oposed 17Ne wa e unc ion. The co ec ed alue B(E2, 1/2−→ 5/2−)is abou wice la ge han ha ob ained in he p esen ex- pe imen . This migh be connec ed wi h he assump ion, made in Re . [31], ha he de ec ed e en s we e om pu e Coulomb exci a- ion. In he p esen expe imen i is shown ha nuclea exci a ion con ibu es o he c oss sec ion wi h abou 50%, see Tables 3 and 4. J. Ma ganiec e al. / Physics Le e s B 759 (2016) 200–205 205 Table 4 Coulomb exci a ion c oss sec ions, σC, in mb, o na ow esonan s a es in 17Ne, i ual-pho on numbe s and ansi ion p obabili ies B(πλ) in (e2 m2λ). The lowes ow gi es B(E2) o 5/2− esonance calcula ed wi h Eq. (1) using σCand N(E2) om Table I in Re . [31]. IπE∗σCπλN(πλ) B(πλ) 5/2−1.764 7.13(1.5)E2 11868 90(18) 1/2+1.908 <2.4E1 121.43 <0.007 (3/2− 2) 2.692 5.57(76)E2 5180.4 69(10) (3/2+)5.141 13.6(1.7)E1 68.68 0.071(9) 5/2−1.764 29.9(4.4)E2 24990 179(26) Fig. 7. T ansi ion p obabili ies B(E2, 1/2−→5/2−)as a unc ion o he s-shell oc- cupa ion, P(s2), in 17Ne(g.s.). The solid line gi es expe imen al B(E2) alue and he ha ched zone shows he 1σde ia ion om his alue. The dashed line ep esen s calcula ions om Re . [21]. A compa ison be ween he B(E2, 1/2−→5/2−) alues de- duced om he p esen expe imen and heo e ical calcula ions om [21] is shown in Fig. 7. The mos p obable alue o he s2oc- cupancy would be ei he P(s2) =23% o P(s2) =53%. The ha ched zones in Fig. 7 show he 1σde ia ions om hese alues. In conclusion, new expe imen al da a on dissocia ion o 17Ne in o 15O +2ps udied a GSI wi h a ela i is ic 17Ne beam im- pinging on lead, ca bon, and polye hylene a ge s a e p esen ed. The main a en ion is paid o he exci a ion and decay o na ow esonan s a es in 17Ne, o which c oss sec ions we e measu ed. Th ee-body co ela ions we e used o de e mine he ela i e con- ibu ions o un esol ed esonances. The da a ob ained om lead and ca bon a ge s allowed he de e mina ion o c oss sec ions and ansi ion p obabili ies o Coulomb exci a ion. The educed elec ic quad upole ansi ion p obabili y B(E2, 1/2−→5/2−) = 90(18) e2 m4was de i ed by using he i ual-pho on me hod. The measu ed B(E2) alue was compa ed o he model calcula ions. Finally, he obse a ion o a esonance a E∗=5.210(79) MeV en- a i ely in e p e ed as 3/2+s a e, mainly Coulomb exci ed, is o special in e es and should be a subjec o u he in es iga ions. 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