Pos(NEUTEL2015)014 Th Existing in the Interior of Our Planet

PoS(NEUTEL2015)014 http://pos.sissa.it/ Th existing in the interior of our planet. The KamLAND and Borexino 232 U and 238 ∗ [email protected] Speaker. Constraints on the Earth’s compositiontection and of on geoneutrinos, its i.e. radiogenic energy electronchains budget antineutrinos of come produced from in the beta de- decaysexperiments recently along reported the the the geoneutrino flux decay andin other different experiments countries are starting of or the planning world.spectives about We these report special here probes the of mainthe the available main Earth’s results interior. source and of Since the reactor background futurereactor antineutrinos in per- antineutrino represent geoneutrinos signals detection, for we the also differentthe experimental report most recent sites updated reactors in evaluation operational the of data. world, taking into account ∗ Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. c

XVI Workshop on Neutrino Telescopes, 2-6 March 2015 Venice, Italy B. Ricci Neutrinos from the Earth: Status and Perspectives Dipartimento di Fisica e Scienze dellaItaly Terra, Università di Ferrara and INFN-E-mail: Ferrara, I-44122, PoS(NEUTEL2015)014 ), ]. ]. 2 2 4 / 1 (1.1) B. Ricci ]. Low- ) for unit , deserve 1 4 4 4 1 H − − − ε 10 10 10 H · · · ] and Marx[ ε and 3 Th chains and of [W/Kg] ¯ ν 0.27 0.22 0.95 ε and Fig. 232 1 ] 1 7 8 7 − s 10 10 10 and sec". ¯ · · · 1 ν U and 2 ε − 238 1.62 2.32 7.46 K) are above threshold for the [Kg 40 . If assume all due to beta decay 1 − s ] pointed out the potential of Kam- 2 Q 8 42.7 51.7 − 1.311 MeV [MeV] 806 . . While on board of the Santa Fe Chief Train, 1 max 1 2.25 3.26 E − 1.311 [MeV] n ]. 2 9 + + 2 one-MeV neutrinos per cm yr] / e 9 1 8 14.0 1.28 4.47 T → [10 p ] and Rothschild et al.[ ¯ + ν 7 ¯ ν ¯ ν ), Q-value, antineutrino and heat production rates ( max He + 4e + 4 ¯ He + 6e + 6 4 ν 4 Pb +6 Pb +8 Ca +e + 208 206 40 → ] discuss in details geoneutrino properties, detection, and relevance for the Earth’s ]. In the nineties the first paper on a geophysical journal was published by Kobayashi → → 5 2.25 MeV are produced only from the uranium decay chain. Therefore the geoneutrino U Th 10 K , > The main properties of geoneutrinos. For each parent nucleus the table presents half-life (T Decay 238 232 40 9 ]. In 1998, Raghavan et al.[ 6 Such background was due to cosmic rays. Geoneutrinos are mainly produced in the decays of nuclei in the These particles have been conceived during the very first attempts of neutrino detection, per- The relevance of neutrinos for astronomical studies was realized many years ago[ In the scientific leterature, geoneutrinos were introduced in the sixties by Eder[ 1 K inside the Earth. The main geoneutrino properties, summarized in Table Table 1: antineutrino maximal energy (E mass for unit mass ofmultiplying the the isotope isotopic (the abundance), corresponding adapted values from at [ natural isotopic composition are obtained by LAND and Borexino for geoneutrino detection. 40 a few comments: 1) geoneutrinos from differentenergy elements E yield different energy spectra, e.g. geoneutrinos with classical antineutrino detection reaction, the inverse beta decay on free protons: spectrum can provide information on the2) abundances Only of a U fraction and of Th geoneutrinos separately. from U and Th (not those from Unlike the Sun, Earthreviews[ emits mainly antineutrinos, the so-called geoneutrinos. Some interesting In the eighties Krauss et al. discussedpublication[ their potential as probes of theet Earth’s interior al.[ in an extensive formed at the Hanford nuclearshowed reactor an by unexpected and Reines unexplained and background Cowan in 1953, where experimental results structure. Georg Gamow wrote to Fredcoming from Reines: high ”It energy beta-decaying justIn members occurred a of teletype to U message me by and Reines Th that influx families response your was to in background given: the the letter "Heat may crust of loss Gamow, of just from the the Earth’s first be surface estimate Earth". is of geoneutrino 50 erg cm Neutrinos from the Earth: Status and Perspectives 1. Introduction energy neutrinos have very long mean freedirect path information and neutrinos on emitted their by internal astronomical compositionneutrinos bodies and carry has structure. already Experimental provided detection valuable of information the solar on radioactive processes inside the stars[ than have only enough energy for about 10 PoS(NEUTEL2015)014 B. Ricci 10 MeV, ' Th chain (dashed- 232 : about 27% of the total reactor 2 U chain (solid black line), s later. The delayed coincidence of these two 238 µ ] 3 11 K decay (dashed blue line). The vertical dashed line shows the inverse beta decay 40 ). The IBD detection event in liquid scintillator produces two flashes of light: the ]. 1.1 10 Energy spectra of geoneutrinos released in This paper is organized as follows. First we discuss the geoneutrinos detection with a particular As already mentioned, antineutrinos from the Earth are detected through inverse beta decay Really geoneutrinos represent a new probe of the Earth interior: differently from other emis- ). 1.1 attention to the main source ofNext background we due report to some antineutrino relevant producedconclusions. implications by of nuclear power available plants. experimental data. Finally we report our 2. Reactor antineutrinos background in geoneutrinos detection (IBD), see Eq. ( well beyond the endgeoneutrino point energy of window, 1.8 the - geoneutrinobetween 3.27 geoneutrino spectrum MeV and (3.27 (or reactor MeV). Low antineutrinoevents As Energy are signals, Region, registered a see in LER), consequence, Fig. the there LER. in is the an overlap annihilation flash, from electron-positron interaction,which followed is by 2.2 the MeV deuterium of formation light flash, that follows some 200 flashes of light provides the critical identification ofbackground the events antineutrino interaction a and part eliminates most theemitted background during due the to beta reactor decaysin antineutrinos, of nuclear i.e. fission power electron plants. products antineutrinos from The 235U, energy 238U, spectrum 239Pu of and reactor 241Pu antineutrinos burning extends up to 3) Antineutrinos from the Earth( are not obscured by solar neutrinos, which cannot yieldsions reaction of the planetEarth’s (e.g., interior, carrying heat to or the nobleplanet surface and, gases), information on about they the the escape radiogenic chemicalferent contribution freely composition geological to of and models terrestrial the of instantaneously heat the whole production from Earth, and see the on eg. the [ validity of dif- dotted red line) and threshold, from [ Figure 1: Neutrinos from the Earth: Status and Perspectives PoS(NEUTEL2015)014 ]. ], 9 14 B. Ricci ]. 15 ] but for the operational Load Factor of 12 free protons) and the exposure times are typically 4 32 10 ∼ target protons per year, which are practical units as liquid scin- ]. 32 12 /G between the predicted reactor signal in the Low Energy Region ] a reference worldwide model for antineutrinos from reactors has 12 LER we present our updated results on expected reactor antineutrino signal for several , the ratio R 2 2 ]. Recently in [ A schematic picture of the expected reactor signal in the Low Energy Region (LER) and in the 13 In Table Clearly several ingredients occurring in the signal calculation, spanning from nuclear physics In Table As the antineutrino detection depends on several experimental parameters (e.g. the fiducial Therefore, a careful analysis of the expected reactor antineutrino event rate at a given experi- Analyses of reactor antineutrino signals have been presented in the past, for instance see ref. ] and [ 9 and the expected geoneutrino signalcrimination can power be on considered geoneutrinos detection as at a a figure specific of location. merit for In particular, assessing with the respect dis- the We perform signal (and uncertainty) calculations as in [ corresponding to one event per 10 tillator mass is on the order of one kton ( sites in the world, compared with the prediction of geoneutrino signals calculated according tonuclear [ cores: we use here the most recent values referred to operational year 2014 [ on the order of a few years. (energy released for fission, reactormechanism, neutrino IBD spectra) cross to section), neutrinoprocedure passing (thermal properties power, through (neutrino fuel composition...) oscillation our and knowledge position . of the nuclear plant operation volume), expressing both geoneutrino and reactor antineutrinodent signals quantities in allows terms of the detector comparison indepen- offrom signals different measured sources. at different Therefore, experiments event and rates originating are quoted in Terrestrial Neutrino Units (TNU) [ High Energy Region (HER), from [ been published, including uncertainties related to reactordetection antineutrino processes, production, estimated propagation, using and a Monte Carlo-based approach. Figure 2: mental site is mandatory. Insignal particular, the in comparison the between LER the andcess predicted the the reactor expected potentiality antineutrino geoneutrino of signal a can geoneutrinochanges be according detector. considered to Note the an also different important reactor that operational tool theis, conditions, to reactor in while ac- contribution principle, the to geoneutrino time component the independent. signal [ Neutrinos from the Earth: Status and Perspectives PoS(NEUTEL2015)014 /G LER B. Ricci ]. These /G ], LENA ) obtained ] and new 20 kt), the 27 21 0.6 1.1 0.2 1.4 5.0 0.1 0.4 5.4 1.7 3.0 0.7 1.0 0.2 0.2 LER 27 LER ' , R ]. The R ] demonstrated 26 14 C.L [ 26 3 8 5 3 9 1 5 2 1 9 9 9 3 9 4 1 6 4 8 3 0 6 3 9 7 4 ...... σ 7 6 7 5 7 6 4 4 6 5 6 4 6 5 6 4 6 5 7 6 7 6 7 5 8 6 7 6 . . 0 0 + − + − + − + − + − + − + − + − + − + − + − + − + − + − 3 4 5 7 3 5 2 0 8 1 4 7 2 ...... 12 ], RENO-50 [ 40 45 31 39 38 45 39 40 42 45 43 48 47 G [TNU] 20 ] in year 2020 the ratio will ]. 12 0 5 6 5 7 5 0 7 5 5 . . 5 6 0 1 ...... 2 2 2 2 16 76 72 28 27 . . . . 5 5 ...... 02 02 0 0 1 1 3 2 0 0 22 20 10 10 we report the location of existing 1 1 1 1 . . 0 0 0 0 0 0 0 0 − + 0 0 + − + − + − + − + − + − + − + − 3 + − + − + − + − [TNU] − + 7.4 8.5 190 210 0.9 67.7 42.2 22.9 48.8 53.9 18.0 31.3 9.96 LER 129.1 R ) and in the Low Energy Region (R ]. In Fig. 6 4 5 7 7 8 . . 7 5 . . . . 0 8 6 6 8 7 25 . . 7 6 9 8 ...... 11 10 4 2 4 2 FER . . . . 75 72 29 30 6 5 07 08 3 3 10 11 2 1 0 0 0 0 . . 1 1 0 0 + − − − + + + − + − + − 0 0 + − − + + − + − + − 5 + − + − /G. As reported in [ [TNU] − + 237 LER 69.5 37.4 3.4 85.2 27.4 31.8 1176 1056 154.8 FER 214.4 193.9 114.9 558.1 R ] and Baksan [ 24 ] one can observe that: JUNO SNO+ LENA LENA LENA LENA LENA LENA 12 Borexino RENO-50 Hanohano Experiment KamLAND ], Homestake [ 23 ], or proposed to the scientific community, such as Juno [ 19 For current and proposed neutrino experimental sites we report the redicted antineutrino signals SLANIC SIEROSZOWICE HOMESTAKE BAKSAN HAWAII PHYASALMI BOULBY CANFRANC FREJUS GRAN SASSO SUDBURY KAMIOKA DONGKENG GUEMSEONG Sites The first observation of geoneutrinos in 2005 by KamLAND experiment [ ], Hanohano [ 22 [ increase of about one ordercollection of of a magnitude. high statistic But couldthe nevertheless provide temporary due switching interesting to off results the for on ordinary huge geoneutrinos, plants in mass maintenance, particular ( see during [ 3. Geo-neutrinos measurements and implications that geoneutrino detection wasservation possible. of geoneutrinos In at 2010 Granachievements Borexino Sasso were National collaboration the consequence Laboratory presented of with two the fundamental more developments:neutrino first than extremely-low-background detectors ob- 4 and progress onexperiments the updated understanding their neutrino first results propagation. withmeasurements larger In statistics of the and geoneutrino last lower fluxes years background are [ both highlyas awaited SNO+ from [ experiments entering operation, such from nuclear power plants in thewith Full Energy 2014 Region reactor (R operational data,ratios is together also with shown. the expected geoneutrino signals (G) [ previous results reported in [ 1) In year 2014 KamLAND experiment reachedfact a during very this high year sensitivity in all geoneutrino nuclearpower detection. power for In plant the were third closed time down,will in leaving provide Japan 40 new without interesting years. any measurements nuclear on We2)Conversely, geoneutrino expect in flux. that China near the nuclear in power theerative, plant providing future near an KamLAND JUNO increase collaboration site of are the becoming ratio more R and more op- Table 2: Neutrinos from the Earth: Status and Perspectives PoS(NEUTEL2015)014 the 4 B. Ricci ] and the 12 /G signal all over observed events in LER 28 27 + − 4.4 geoneutrino events in 1353 days for ± 7 TNU respectively. Let us see how these is obtained with 2013 reactors operational data. ± LER 6 ], one can extract the radiogenic heat power from U and 10 ]. The red and blue lines contain the region of all possibile , 10 12 TNU and to 30 17 ± , 9 ] is shown. Note that R ]. 14 12 /G between the predicted reactor signal in the Low Energy Region [ LER The ratio R ]. Combining the present day surface flux and independent estimates of the radiogenic heat 28 Up until now the debate about the terrestrial heat flow is still open: estimates over the last 40 As widely described in [ At the moment the available geoneutrino experimental results are: 116 2 [ years for the Earth’s surface heat± flow are between 30 and 50 TW, with recent estimates being 47 Borexino, corresponding to 39 experimental results can help in the knowledgegeological of models, the Earth in interior, the in the particular in determinationthe testing of distribution different the of radiogenic radioactive heat power elementsand and inside we in remand our understanding to planet the cited references (we for summary extensive here analysis). the main highlights a total live-time of 2991 days for KamLAND and 14.3 Th decays, H(T+U), fromActually, geoneutrino the measured experimental geoneutrino data, signal does althoughof not it U depend is and only on Th, not the butpower so absolute also extracted mass straightforward. on abundances from their a distributionexpected measured throughout geoneutrino geoneutrino the signal signal Earth. in isof Borexino Therefore, Earth-model the (left) the dependent. produced and radiogenic radiogenic KamLAND heat signals, In heat (right) [ Fig. taking are into shown, account as the a errors function in the prediction of the signal due to U and Th existing production allows one to estimate the amount of primordial heat remaining in the Earth. Figure 3: The location of existing andJUNO, RENO-50, some KamLAND future (from experiments west are to est). also shown (withe triangles): SNO+, Borexino, experiments and some future plannedthe experiments, world, together adapted with from the [ ratio R Neutrinos from the Earth: Status and Perspectives expected geoneutrino signal [ PoS(NEUTEL2015)014 σ B. Ricci ] gives : H(U+Th)= ], using KamLAND 10 ]. 10 26 ] in the hypothesis that U 30 ], while the mantle contribution 29 , 14 represent the predictions of three main classes 4 7 8.1 TNU. In Gando et al. 2013 [ ± one can see that H(U+Th) consistent with present Borexino (Kam- ] together with the calculation of the contribution from the Rest Of ], from Borexino data a mantle geoneutrino signal of S(Mantle)=15.4 4 29 27 7.9 TW [112]. ± 9 TW). Such determinations will be constrained in the future by new experimental ]. In particular, the crustal contribution to the geoneutrino signal can be inferred ]. Furthermore, the Borexino and KamLAND results have been combined, by as- ± 9 14 The expected geoneutrino signal in Borexino (left panel) and KamLAND (right panel) from U ]. The horizontal lines represent the 2013 results of Borexino and KamLAND. At 1 18 In addition, geoneutrinos are a real time probe of the Earth’s distribution of U and Th natu- Furthermore, from Fig. 14 TW (13 ] for details. The three filled areas in Fig. 2.8) TNU, this last obtained by combining the study of the Local Crust in the region around the ± 12.3 TN has been extracted, by considering the geoneutrino signal from the crust S(Crust) = (23.4 10 the Crust of [ suming a homogeneous mantle and thus thesurface, same resulting signal into from the S(Mantle)=14.1 mantle geoneutrinos2013 on data the and Earth subtracting outand Th the are crust uniformly distributed contribution throughout determined theis mantle, by calculated the [ to total mantle be radiogenic 11.2 heat production rally present in the crustradioisotopes and [ in the mantle, which are thought to be the main reservoirs of these ± ± Gran Sasso laboratory of [ data and surely represent a valuable determination of the radiogenic heat flux. from direct geochemical and geophysical surveys, see e.g. [ into the Earth’s crust, as[ well as different Uof and Earth Th models: distributions through cosmochemical, geochemical, thefrom and Earth’s [ geodynamical, mantle, according see to thelevel classification the geodynamical models seem disfavoredcompatible by with KamLAND all results, the whereas models. Borexino data are Land) results, lies in the interval 13–45 TW23 (8–25 TW). More refined analysis [ is totally model-dependent. Hence from thesubtracting experimental the determination crustal of geoneutrinos contribution, signal, oneway. by can In derive Bellini the et al the 2013 mantle [ contribution in an independent Figure 4: and Th as a function ofdelimit, radiogenic from heat the released left in to radioactive2013 decays Borexino the of and right, U KamLAND the results and cosmochemical, are Th. indicated geochemical The by three and the filled geodynamical horizontal regions lines; Earth from models. [ The Neutrinos from the Earth: Status and Perspectives PoS(NEUTEL2015)014 B. Ricci km each other, measure a geoneu- 4 , Budapest No. 48 (1960). , 819-862 (2003). 75 8 Rev. Mod. Phys. Mitteilungen der Sternwarte , 1471 (1969). B19 , 657 (1966). 78 J. Phys Nucl. Phys. , to F. Mantovani for suggestions and for providing me some useful pictures, to J. Mandula 2 Really geoneutrinos represent a new probe of the Earth interior: they escape freely and in- At the moment two independent experiments, far about 10 All of these measurements need further confirmations and refinements, which can be achieved One of the most exciting question is the measurement of the geoneutrino signal from the At Sudbury, SNO+ experiment will have excellent opportunities to determine the uranium For the very long term future, one can speculate about completely new detectors, capable We are extremely grateful to M. Baldoncini for the support in the numerical calculations of [3] G. Eder, [4] G. Marx, Czech. [2] K. Langanke and G. Martinez-Pinedo, [1] G. Marx and N. Menyhfird, in for information on Powercomments Reactor from I. Information Callegari, System G. Fiorentini,by database. MIUR V. Strati (Ministero and dell’Istruzione, We G. dell’Università also e Xhixha. della acknowledge This Ricerca) work useful under is PRIN2012 partly project. supported References stantaneously from the Earth’s interiorquantities carrying such to as the the surface radiogenic preciousand contribution Th information inside to on the terrestrial important Earth, heat and production, on the the validity abundances of of different geological U models of the Earth. Neutrinos from the Earth: Status and Perspectives 4. Conclusions and perspectives with an increase of statistical significance.even In bigger this than respect the future current geoneutrino ones detectors, are like really JUNO, suitable. mantle: a geoneutrino detectorsignal is placed minimal in and easily Hawaii, estimated,of where can improve the the our mantle. crustal knowledge on contribution the Furthermorecan radioactive to due composition be geoneutrino to measured the with absence smallterrestrial of heat errors, nearby generation. allowing power a reactors, better the discrimination geoneutrino among signal different modelsmass for in the crust, whichimportant accounts test for about about models 80% for the of Earth’s the crust. geo-neutrino signal. Thisof will providing provide an (moderately) directionaldifferent information. geo-neutrino sources (crust, These mantle should and possibly allow core) the in identification the Earth. of the Acknowledgments Table trino signal essentially in agreementwith with the the big effort expectations. inknowledge These geoneutrino of experimental signal the results, calulation backgrounds accomplished together dueestimate in to the the antineutrinos last amount produced years by of and reactorinaccessible. radioactive to power elements plant, a in allow better the us to most deeper region of our planet, otherwise PoS(NEUTEL2015)014 (2013) B. Ricci 88 Phys. Rev. D (2013) 1-34. (2010) 299; G. Bellini et al. (Borexino 73 , 117-172 (2007). (2015) 5 687 2 , 499-503 (2005) ; S. Abe et al. (KamLAND 453 , 633 (1991). 436 (2011) 2271. 18 (2014) 2003 9 75 (2012) 1324 . (2005) 69. 14 (2007). , 1083 (1998). (2010) 5. 37 68 Nature Phys. Rep. 1 Phys. Lett. B 25 (2013) 361. (2012) 033004 258 , 635 (1998). 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