M e a su rem en t o f Solar p p -n e u trin o flux w ith B orex in o : re su lts an d im p lic a tio n s
0 Y u S m ir n o v 1,29, M A g o s t in i2, S A p p e l2, G B e llin i3, J B e n z ig e r 4, D B ic k 5, G B o n fin i6, D B r a v o 7, B C a c c ia n ig a 3, F C a la p r ic e 8, A C a m in a ta 9, P C a v a lc a n te 6, A C h e p u r n o v 10, D D ’A n g e lo 3, S D a v in i11, A D e r b in 12, L D i N o t o 9, I D r a c h n e v 11, A E t e n k o 13, K F o m e n k o 1, D F r a n c o 14, F G a b r ie le 6, C G a lb ia ti8, C G h ia n o 9, M G ia m m a r c h i3, M G o e g e r -N e ff2 , A G o r e t t i8, M G r o m o v 10, C H a g n e r 5, E H u n g e r fo r d 15, A ld o I a n n i6, A n d r e a Ia n n i8,
K J e d r z e jc z a k 17, M K a is e r 5, V K o b y c h e v 18, D K o r a b le v 1, G K o r g a 6, D K r y n 14, M L a u b e n s te in 6, B L e h n e r t 19, E L it v in o v ic h 13,20,
F L o m b a r d i6, P L o m b a r d i3, L L u d h o v a 3, G L u k y a n c h e n k o 13,20,
1 M a c h u lin 13,20, S M a n e c k i7, W M a n e s c h g 22, S M a r c o c c i11, E M e r o n i3, M M e y e r 5, L M ir a m o n ti3, M M is ia s z e k 17,6, M M o n tu s c h i23,
P M o s te ir o 8, V M u r a to v a 12, B N e u m a ir 2, L O b e r a u e r 2,
M O b o le n s k y 14, F O r tic a 24, M P a lla v ic in i9, L P a p p 2, L P e r a s s o 9, A P o c a r 26, G R a n u c c i3, A R a z e t o 6, A R e 3, A R o m a n i24, R R o n c in 6 14, N R o s s i6, S S c h o n e r t2, D S e m e n o v 12, H S im g e n 22,
M S k o r o k h v a to v 13,20, A S o tn ik o v 1, S S u k h o t in 13, Y S u v o r o v 27,13, R T a r ta g lia 6, G T e s te r a 9, J T h u r n 19, M T o r o p o v a 13, E U n z h a k o v 12, A V is h n e v a 1, R B V o g e la a r 7, F v o n F e ilitz s c h 2, H W a n g 27, S W e in z 28, J W in te r 28, M W o jc ik 17, M W u r m 28, Z Y o k le y 7, O Z a im id o r o g a 1, S Z a v a ta r e lli9, K Z u b e r 19a n d G Z u z e l17(B o r e x in o C o lla b o r a tio n ) 1 Jo in t In stitu te for N uclear Research, 141980 D ubna, R ussia
2 P h ysik-D epartm ent and Excellence C luster Universe, Technische U niversitat M iinchen, 85748 G arching, G erm any
3 D ip artim en to di Fisica, U niversita degli Studi e IN FN , 20133 M ilano, Italy
4 C hem ical E ngineering D ep artm en t, P rin c eto n University, P rinceton, N J 08544, USA
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6 IN FN L ab o rato ri N azionali del G ran Sasso, 67010 Assergi (AQ), Italy
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9 D ip artim en to di Fisica, U niversita degli Studi e IN FN , G enova 16146, Italy
10 Lomonosov Moscow S tate U niversity Skobeltsyn I n s titu te of N uclear Physics, 119234 Moscow, R ussia
11 G ra n Sasso Science In stitu te (IN FN ), 67100 L ’A quila, Italy
12 St. P etersb u rg N uclear Physics In stitu te NRC K urchatov In stitu te , 188350 G atchina, R ussia
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17 M. Smoluchowski In stitu te of Physics, Jagiellonian University, 30059 Krakow, Poland
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19 D ep a rtm en t of Physics, Technische U niversitat D resden, 01062 D resden, G erm any
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E-m ail: o s m irn o v @ jin r.ru
A b s t r a c t . M easurem ent of th e Solar pp-n eu trin o flux com pleted th e m easurem ent of Solar neu trin o fluxes from th e pp-chain of reactions in Borexino experim ent. T he result is in agreem ent w ith th e p rediction of th e S tan d a rd Solar M odel and th e M S W /L M A oscillation scenario. A com parison of th e to ta l n eutrino flux from th e Sun w ith Solar lum inosity in photons provides a te st of th e stab ility of th e Sun on th e 105 years tim e scale, and sets a strong lim it on th e power pro d u ctio n by th e unknow n energy sources in th e Sun.
1. I n tr o d u c tio n
T he solar ph oton lum inosity L© = 3.846 x 1026 W is m easured for a precision of 0.4% [1, 2]. T he energy lost by neutrinos adds L v = 0.023 ■ L© to th is value [3]. T he solar lum inosity co n strain t on th e solar neu trin o fluxes can be w ritte n as [4]:
4n(la© u.)2 = ^ (1)
w here 1 a.u. is th e average E a rth -S u n distance, th e coefficient a is th e am ount of energy provided to th e s ta r by nuclear fusion reactions associated w ith each of th e im p o rta n t solar n eu trin o fluxes, Tj. T he num erical values of th e a ’s are d eterm ined to an accuracy of 10-4 and b e tte r.
T he estim ated u n c e rtain ty in th e lum inosity of th e Sun corresponds to less th a n 3%
u n certain ty in to ta l solar n eu trin o flux.
Because of th e relation (1) betw een th e solar p ho ton and neu trin o luminosity, th e m easurem ent of th e to ta l n eu trin o lum inosity will provide a te st of th e stab ility of th e Sun at th e tim e scale of 40000 years [5], th e tim e needed for th e rad iatio n born at th e center of th e Sun to arrive to its surface. F inding a disagreem ent betw een L© and L v would have significant long te rm envirom ental im plications, and in th e case of an agreem ent betw een th e two m easurem ents it would be possible to lim it th e unknow n sources of th e solar energy, different from th e known th erm on u clear fusion of light elem ents in th e pp-chain and CNO-cycle.
T he m ain n eu trin o sources in th e Sun are th e pp- and 7Be reactions, providing roughly 91 and 7% of th e to ta l n eu trin o flux respectively. B orexino alread y m easured th e 7Be neu trin o
flux w ith 5% precision [6], b u t till recent tim e th e pp -n eu trin o flux was derived in a differential m easurem ent using solar d etecto rs d a ta .
A num ber of projects aim ing to perform pp -n eu trin o d etectio n have been p u t forw ard in p ast two decades, b u t w ith all th e tim e passed since th e proposals, none of th em s ta rte d th e op eratio n facing th e technical problem s w ith realization. A possibility to use u ltra p u re liquid organic scintillator as a low energy solar neu trin o d e te c to r for a first tim e was discussed in [7, 8].
T h e au th o rs come to th e conclusion th a t a liquid scin tillator d e te c to r w ith an active volum e of 10 tons is an a p p ro p riate tool to register th e solar p p-n eu trin o if o p erated at th e ta rg e t level of rad io p u rity for B orexino and good energy resolution (5% a t 200 keV) is achieved.
2. S o la r p p -n e u tr in o flu x m e a s u r e m e n t w it h B o r e x in o d e t e c t o r
T he low-energy range, nam ely 165-590 keV, of th e B orexino experim ental sp ectru m has been carefully analyzed w ith th e purpose of th e p p -neu trino flux e x tra ctio n [9]. T he d a ta were acquired from Ja n u a ry 2012 to M ay 2013 and correspond to 408 live days of d a ta taking.
T he m ain features of th e experim ental spectrum , as can be seen in in figure 1, are: a m ain co n trib u tio n from th e 14C decays a t low energies (below 200 keV) and th e m onoenergetic peak corresponding to 5.3 MeV a —particles from 210P o decay. T he sta tistic s in th e first bins used in th e analysis is very high, of th e order of 5 x 105events, dem anding th e developm ent of a very precise m odel for th e studies - th e allowed system atic precision a t low energy p a rt should be com parable to th e sta tistic a l fluctuations of 0.14%. T he developm ent of such a precise m odel was a m ain goal of th e analysis.
As one can see from figure 1 th e shapes of co ntribution s to th e sp ectru m from 14C and o th er background com ponents are quite different from th e co n trib u tio n from th e expected co n trib u tio n of th e electron recoil sp ectrum from th e Solar pp-neutrino. This fact allows th e e x tractio n of th e Solar pp -n eu trin o c o n trib u tio n from th e d a ta .
T he stab ility and robustness of th e m easured pp n eu trin o in teractio n ra te was verified by perform ing fits varying initial conditions, including fit energy range, m ethod of pile-up con stru ctio n, and energy estim ato r. T he d istrib u tio n of th e central values for pp-neu trino in teractio n rates o b tain ed for all these fit conditions was th e n used as an e stim ate of th e m axim al system atic erro r (p artial correlations betw een different factors are not excluded).
3. R e s u lt s a n d I m p lic a tio n s
T he solar pp neu trin o in teractio n ra te m easured by B orexino is pp = 144 ± 13(stat) ± 10(syst) c p d /1 0 0 t, com patible w ith th e expected ra te of ppt h e o r = 131 ± 2 cp d /1 0 0 t. T he corresponding to ta l solar p p -n eu trin o flux is ^p p( Bo r e x ) = (6.6 ± 0.7) x 1010 cm - 2 s- 1 , in a good agreem ent w ith th e com bined best fit value of th e radiochem ical and o th er solar experim ents
$p p(other) = (6.14 ± 0.61) x 1010 cm - 2 s-1 [10]. B o th are in agreem ent w ith th e expected value of 6.0 x (1.000 ± 0.006) x 1010 cm - 2 s- 1 .
T he survival p ro b ab ility for electron neu trin o from pp-reaction is Pe e( Bo r e x ) = 0.64 ± 0.12.
Taking into account th a t B orexino and o th er experim ents m easurem ents are independent, th e results can be combined:
(pp p = (6.37 ± 0.46) x 1010cm - 2 s - 1 .
T he electron n eu trin o survival p rob ability m easured in all solar b u t B orexino experim ent is Pe e(o t h er ) = 0.56 ± 0 .08, com bining it w ith B orexino one we obtain:
Pe e = 0.60 ± 0.07,
well com patible w ith th eo retical p rediction of th e M S W /L M A m odel 0 .5 6 1 -°;°3°.
F ig u r e 1. Borexino energy spectru m betw een 165 and 590 keV (in black). T he pp n eu trin o com ponent is shown in red, th e 14C sp ectru m in d ark purple and th e synth etic pile-up in light purple. T he large green peak is 210Po a-decays. 7Be (dark blue), pep and CNO (light blue) solar n eutrinos, and 210Bi (orange) sp e ctra are alm ost flat in this energy region.
T a b le 1. T he S ta n d ard Solar M odel predictions (for high m etallicity and low m etallicity abundances) and curren t ex perim ental s ta tu s of th e Solar neu trin o fluxes m easurem ent. T he lim its are given for 90% C.L.. T he corresponding energy release is calculated in th e last colum n.
R e ac tio n GS98 [11] A G S09 [12] U n its
— 2 — 1 cm 2 s 1
M easu rem e n t M e V /1 v L
x 1 0 26 W -s- 1 6.14 ± 0.61 [10]
PP 5.98 ± 0.04 6.03 ± 0.04 x 1 0 10 6.6 ± 0.7 [13]
6.37 ± 0.46
13.10
3.76 ± 0.28 P eP 1.44 ± 0.012 1.47 ± 0.012 x 1 0 8 1 .6 ± 0 .3 [14] 11.92 0.009 ± 0.002 7 Be 5.00 ± 0.07 4.56 ± 0.07 x 1 0 9 4.87 ± 0.24 [6] 12.60 0.276 ± 0.014 8 B 5.58 ± 0.14 4.59 ± 0.14 x 1 0 6 5.25 ± 0.16 [15] 6.63 1.57 ± 0.05
x 1 0 - 4
hep 8.0 ± 2.4 8.3 ± 2.5 x 1 0 3 < 23[16]
13 N 2.96 ± 0.14 2.17 ± 0.14 X i—1 o00
CNO : 15 o 2.23 ± 0.15 1.56 ± 0.15 x 1 0 8 < 7.4[14]
17 F 5.52 ± 0.17 3.40 ± 0.16 x 1 0 6
All available m easurem ents of th e solar neu trin o fluxes are shown in tab le 1. T he to ta l energy pro d u ctio n in th e solar reactions observed till now (by detectin g corresponding n eu trin o fluxes)
is (4.04 ± 0.28) x 1026 W -s-1 in a good agreem ent w ith a to ta l m easured L© = 3.846 x 1026 W -s- 1 . T here is not m uch space left for th e unknow n energy sources, th e 90% C.L. lower lim it for th e to ta l energy p ro d u ctio n (conservatively assum ing zero co n trib u tio n from th e not-observed reactions) is L tot = 3.68 x 1026 W -s- 1 . If one assum es th a t such an unknow n source exists, its to ta l power w ith 90% p rob ability c a n ’t exceed 0.15 x 1026 W -s- 1 . In o th er words no m ore th a n 4% of th e to ta l energy p ro d uctio n in th e Sun is left for th e unknow n energy sources, confirm ing th a t th e Sun shines due to th e th erm o n uclear fusion reactions.
4. C o n c lu s io n
B orexino provided an in dependent m easurem ent of th e Solar p p -n eutrino flux, which can be com bined w ith m easurem ents from o th er solar experim ents. A com parison of th e n eu trin o flux from th e Sun w ith Solar lum inosity in photons provides a test of th e stab ility of th e Sun on th e 105 years tim e scale, and allows to set a lim it of no m ore th a n 4% of th e to ta l power pro du ction for th e unknow n energy sources in th e Sun a t 90% C.L..
A c k n o w le d g m e n ts
T he Borexino program is m ade possible by funding from IN FN (Italy ), N SF (USA), BM B F, D FG , and M PG (G erm any), R F B R : G ran ts 14-22-03031 and 13-02-12140, R F B R -A S P E R A - 13-02-92440 (R ussia), and N C N P oland (U M O -2 0 1 2 /0 6 /M /S T 2 /0 0 4 2 6 ). We acknowledge th e generous su p p o rt and h o sp itality of th e L ab o rato ri N azionali del G ran Sasso (LNG S). R ussian colleagues from M E P h I acknowledge p a rtial su p p o rt from M E P h I Academ ic Excellence P ro je c t (con tract No. 02.a03.21.0005, 27.08.2013).
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