Recent results and status of the

Transcription

1 Laboratory Underground Nuclear Astrophysics Recent results and status of the 14 N(p,γ) 15 O measurement at LUNA Heide Costantini Dipartimento di Fisica and INFN, Genova (Italy)

2 Laboratory for Underground Nuclear Astrophysics Gran Sasso National Laboratory (LNGS) Cosmic background reduction: µ: 10-6 n: He( 3 He,2p) 4 He 50 KV : ( ) d( 3 He,p) 4 He d(p,γ) 3 He 400 KV: (2000 ) 14 N(p,γ) 15 O (CNO cycle)

3 400 kv accelerator SPECIFICATIONS U max = kv I 500 µa for protons DE max = 0.07 kev Energy spread : 72eV Total uncertainty is ±300 ev between Ep= keV Present and future activity: in progress 14 N(p,γ) 15 O 4 He( 3 He, γ) 7 Be 25 Mg(p, γ) 26 Al

4 N(p,γ) 15 O and solar neutrinos 14 N(p, The rate of the CNO cycle is governed by the slowest reaction 14 N(p,γ) 15 O (Q=7.3 MeV) Borexino Homestake SuperK Sage Kamioka Gallex 13 N and 15 O neutrinos have fluxes and energy spectra comparable with those coming from 7 Be (pp chain)

5 Globular Clusters and 14 N(p,γ) 15 O reaction rate L (K)

6 14 N(p,γ) 15 O Schröder et al. (1987) Nucl. Phys A Angulo, Descouvement (2001), Nucl. Phys A S(0) = 1.55 ± 0.34 kev-b (Schröder) R/DC 0 S(0) = 0.08 ±0.06 kev-b (Angulo)

7 2 experimental approaches Gas target + BGO summing crystal Pure target Stable target total-s(e) Low resolution High efficiency E min < 100 kev Solid target angular distribution high density + HpGe detector Single γ transitions Low efficiency High resolution E min 140 kev

8 Experimental setup beam LN2 7 mm 10 mm LN2 55 o HpGe Target chamber dσ dω o ( 55 ) 1 wobbeling units target High density High stability High purity TiN deposited on Ta

9 Solid Target features TiN 14 N(p,γ) 15 O E R =278 kev yield [a.u.] = 115keV Target profile (thickness, homogeneity) Proton Energy E lab [kev] 2,00 1,80 1,60 1,40 Target stability yield [a.u.] 1,20 1,00 0,80 0,60 0,40 0,20 typical: 25 C/day 0, time[day]

10 HpGe background Yield 1,00E+00 1,00E-01 At surface 3MeV < Eγ < 8MeV counts 1,00E-02 1,00E-03 1,00E Counts/s 1,00E-05 1,00E Eγ [kev] Yield counts 1,00E+00 1,00E-01 1,00E-02 1,00E-03 1,00E-04 1,00E-05 1,00E Underground 3MeV < Eγ < 8MeV Counts/s Eγ[keV]

11 Beam induced background counts B(p,γ) 12 C 14 N(p,γ) 15 O 11 B(p,γ) 12 C E beam = 200 kev E γ [kev] E beam = 140 kev counts E γ B(p,γ) 12 C 14 N(p,γ) 15 O 11 B(p,γ) 12 C E γ [kev]

12 The experimental spectrum counts DC/6.79 DC/6.17 E p = 250 kev Q = 41.2 C T = 20 h I =570 µa 6.17 DC/ DC/0 E γ [kev]

13 Summing effect In close geometry meas. high summing effect probability cm Simulation R/dc % E-gamma(keV) cm Simulation R/dc % Summing peak E-gamma(keV)

14 278 kev resonance parameters Resonance strength present work (13.5 ± 0.4 ± 0.8) mev literature (14 ± 2) mev Branching ratios at the 278 kev resonance R/DC 0 present work 1.7±0.1 literature 3.5 ±0.5 Hebbard & Bailey (1963) R/DC ± ±0.6 R/DC ± ±0.6 R/DC ± ±0.6 Close geometry measurements Summing effect

15 beam Angular distribution measurements

16 2,5 Y R/DC 0 E lab = 220 kev 2 1,5 1 dσ = dω a1 P1 ( ϑ) + a2p ( ϑ) ,5 0 cos 2 (θ) -0,01 0,19 0,39 0,59 0,79 0,99 Y R/DC ,6 1,4 1,2 1 0,8 0,6 0,4 0,2 cos 2 (θ) 0-0,01 0,19 0,39 0,59 0,79 0,99 Y R/DC ,4 1,2 1 0,8 0,6 0,4 0,2 cos 2 (θ) 0-0,01 0,19 0,39 0,59 0,79 0,99 1,6 1,4 1,2 1 0,8 0,6 0,4 0,2 Y R/DC 5.18 cos 2 (θ) 0-0,01 0,19 0,39 0,59 0,79 0,99 1,6 1,4 1,2 1 0,8 0,6 0,4 0,2 Y Y Y cos 2 (θ) 0-0,01 0,19 0,39 0,59 0,79 0,99 1,2 1 0,8 0,6 0,4 0,2 cos 2 (θ) 0-0,01 0,19 0,39 0,59 0,79 0,99 1,4 1,2 1 0,8 0,6 0,4 0,2 cos 2 (θ) 0-0,01 0,19 0,39 0,59 0,79 0,99

17 Data Analysis (1) x E pi E p inc 1E-03 E γ E γ inc E pi beam 8E-04 σ Ni [a.u.] 6E-04 4E-04 E 2E-04 0E E γ [kev] N i = σ ( E ) E ( E ( E ) p i de dx γ ε γ ( E ) p i p i b j

18 Data Analysis (2) x E p E p Y 1.5 σ Y = 2 λ 2 E ϖγb de dx E R R ε ( ) j γ ( E ) r N Y i = E p [kev] ( ) de 2σ E ( ) ( ) p E p ε E E i i γ dx 2 de λ ϖγ γ dx ( ) ( R E ) R r ε E b j γ b j

19 Ground state results a = 5 fm present data Schröder (corr. for summing) a = 5.5 fm a = 6 fm S 0 gs gs = 0.25 ± 0.06 kev b

20 R/DC 6.79 results present data Schröder a = 5 fm a = 5.5 fm a = 6 fm S = 1.35 ± 0.05 kev b

21 Schröder( 87) [kev-b] 3.2 ± 0.5 Angulo ( 01) [kev-b] 1.8 ± 0.2 S 0 tot tot = 1.7 ± 0.1 kev b Paper submitted to Phys. Letter B GC age increases of Gyr CNO neutrino flux decreases a factor 2

22 Gas target set-up I max 400mA DE < 100 ev 10-7 mbar 10-6 mbar 10-4 mbar BGO Calorimeter HV kv mbar Windowless gas-target Max 10 mbar Beam: p, He

23 BGO detector Detection Efficiency 65 % Natural background ( kev) Length : 28 cm Int. hall diam.: 6 cm Thickness : 7 cm 20 c/day Beam induced background E beam =210 kev E beam = 130 kev 19 F(p,αγ) 16 O 11 B(p,γ) 12 C 13 C(p,γ) 14 N D(p,γ) 3 He 13 C(p,γ) 14 N

24

25 Data analysis(1) Thin target N γ ( E ) z = N N σ η targ proj cm Extended gas target Detector efficiency N t arg ( z) P = ν ( z) kt de dx ( ) = E dz E z beam z 0 N γ = N proj ν kt L 0 P ( z) σ ( E( z) ) η( z)dz

26 Data analysis(2) Effective cross section σ eff ( E ) effcm = L N proj ν kt N 0 γ P ( z) η( z) dz N = proj Q Beam e Monte Carlo E z Eff de = EBeam d ( ρx) ρ( z dz Eff ) 0 L 0 P( z) η( z) dz Pressure profile along the target

27 Beam heating effect measurement The particle beam heats the gas changing the local density. Movable Lead Shielded NaI detector (1 x 1 ) The 278 kev 14 N(p,γ) 15 O resonance is positioned in front of the detector. The beam energy loss is proportional to the gas density.

28 NaI detector Interaction chamber position Lead Shield Brass Pipe

29 Pressure profile L 0 Pt ( z ) η ( z ) dz Pressure (mbar) Z (cm)

30 Cross Section preliminary data gas target data solid target data 71 kev

31 Ebeam = 80 kev

32 ωγ measurement(1) BGO Resonance Scan at 2 mbar (77 µa) Pressure 2.0 mbar ωγ (mev) 13.6 ± 0.8 Solid Target: 13.5 ± 0.4 ± 0.8 Other Works 14 ± 1

33 ωγ measurement(1) BGO Resonance Scan at 2 mbar (77 µa) Pressure 2.0 mbar 1.0 mbar 0.5 mbar ωγ (mev) 13.6 ± ± ± 0.6 Solid Target: 13.5 ± 0.4 ± 0.8 Other Works 14 ± 1

34 ωγ measurement(2) Y ( E σ 0 b, ρ) = N Q Assuming η and ρ as constants d = L 0 σ ( E( z)) ρ( z) η( z) dz η de d( ρx) Eb Eb σ ( E) de Because Amplitude energy dependence is negligible: bw ( E) de IF = 2 λ ωγ 2 >6Γ ωγ = 2 λ 2 Y max M + m M η de d( ρx)

35 ωγ measurement(3) P % σ BW (E) (mbar) integral Experimental ratio Γ Γ Γ No appreciable systematic effects but Further scans at 1.5 and 3 mbar

36 Future perspectives(1) 4 He( 3 He,γ) 7 Be Φ B depends on nuclear physics and astrophysics inputs Φ B = Φ (SSM) B s s s 1 17 s -1 e7 s -2.7 pp com 1.4 opa 2.6 dif 0.34 lum 7.2 These give flux variation with respect to the SSM calculation when the input X is changed by x = X/X (SSM). Can learn astrophysics if nuclear physics is known well enough. Nuclear physics uncertainties, particularly on S 34, dominate over the present observational accuracy Φ Β /Φ Β =7%. The foreseeable accuracy Φ Β /Φ Β =3% could illuminate about solar physics if a significant improvement on S 34 is obtained Source S33 S34 S17 Se7 Spp Com Opa Dif Lum X/X (1σ) ? Φ Β /Φ Β (1σ)

37 4 He( 3 He,γ) 7 Be Mainly 3 γ-transitions: Eγ =1585 kev + E cm (DC 0); Eγ = 1157 kev + E cm and Eγ = 429 kev (DC 0.429; )

38 Past measurements 0,8 on-line γ-measurements activation measurements 0,7 Hilgemeier et. al S(0) [kev b] 0,6 0,5 Nagatani et. al Osborne et. al Hilgemeier et. al on-line γ -meas. average Osborne et. al Robertson et. al Volk et. al activation average 0,4 Parker et. al Kräwinkel et. al Alexander et. al ,3

39 Target chamber design (1) gas target Pb Pb W Pb Cu HpGe Cu Pb

40 Target chamber design Movable silicon detector for I*ρ meas. Removable calorimeter cap for off-line 7 Beactivity measurement

41 Expected counting rate P = 1 mbar; I = 200 µa counts/day 10000, ,00 100,00 10,00 1, MeV 1.2 MeV BCK HpGe 0,10 0,01 0,00 0,00 50,00 100,00 150,00 200,00 E cm [kev]

42 Future perspectives(2) 25 Mg(p,γ) 26 Al 25 Mg(p,γ) is the main production mechanism for 26 Al in astrophysical scenarios

43 E lab p (kev) ωγ (ev) < (3±1) (1±0.3) (3±1) < E γ = 6436 kev E γ = 6398 kev Resonance strengths calculated from the 25 Mg( 3 He,d) 26 Al reaction (Iliadis et al 1996) BGO background spectrum Time = d

44 Conclusions N(p,γ) 15 O has been studied with a solid target set-up down to E cm =135 kev 14 N(p, Present work improves the experimental information concerning the R/DC 0 transition Using a gas target set-up the 14 N(p,γ) 15 O total cross-section is presently studied at LUNA down to E cm =70 kev Future measurements are : 4 He( 3 He, γ) 7 Be 25 Mg(p, γ) 26 Al (gas target) (solid target)