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Uncertain Dark Ma9er Status
• Annual modula,on by DAMA
• Excess of low-‐energy events by CoGeNT
• Regions excluded by XENON and CDMS
11 May 2011 Walter C. Pe9us 2
Eur. Phys. J. C (2008) 56: 333–355 337
Fig. 2 Model-independent residual rate of the single-hit scintillationevents, measured by the new DAMA/LIBRA experiment in the (2–4),(2–5) and (2–6) keV energy intervals as a function of the time. Theresiduals measured by DAMA/NaI and already published in Refs. [11,12] are also shown. The zero of the time scale is January 1st of thefirst year of data taking of the former DAMA/NaI experiment. Theexperimental points present the errors as vertical bars and the asso-ciated time bin width as horizontal bars. The superimposed curvesrepresent the cosinusoidal functions behaviors A cos!(t ! t0) with a
period T = 2"! = 1 yr, with a phase t0 = 152.5 day (June 2nd ) and
with modulation amplitudes, A, equal to the central values obtainedby best fit over the whole data, that is: (0.0215 ± 0.0026) cpd/kg/keV,(0.0176 ± 0.0020) cpd/kg/keV and (0.0129 ± 0.0016) cpd/kg/keV forthe (2–4) keV, for the (2–5) keV and for the (2–6) keV energy inter-vals, respectively. See text. The dashed vertical lines correspond to themaximum of the signal (June 2nd ), while the dotted vertical lines cor-respond to the minimum. The total exposure is 0.82 ton " yr
5
]2WIMP Mass [GeV/c6 7 8 910 20 30 40 50 100 200 300 400 1000
]2W
IMP-
Nuc
leon
Cro
ss S
ectio
n [c
m
-4510
-4410
-4310
-4210
-4110
-4010
-3910
]2WIMP Mass [GeV/c6 7 8 910 20 30 40 50 100 200 300 400 1000
]2W
IMP-
Nuc
leon
Cro
ss S
ectio
n [c
m
-4510
-4410
-4310
-4210
-4110
-4010
-3910
DAMA/I
DAMA/Na
CoGeNT
CDMS
EDELWEISS
XENON100 (2010)
XENON100 (2011) Buchmueller et al.
FIG. 5: Spin-independent elastic WIMP-nucleon cross-section
σ as function of WIMP mass mχ. The new XENON100 limit
at 90% CL, as derived with the Profile Likelihood method
taking into account all relevant systematic uncertainties, is
shown as the thick (blue) line together with the 1σ and 2σsensitivity of this run (shaded blue band). The limits from
XENON100 (2010) [7] (thin, black), EDELWEISS [6] (dotted,
orange), and CDMS [5] (dashed, orange, recalculated with
vesc = 544 km/s, v0 = 220 km/s) are also shown. Expecta-
tions from CMSSM are indicated at 68% and 95% CL (shaded
gray) [17], as well as the 90% CL areas favored by CoGeNT
(green) [18] and DAMA (light red, without channeling) [19].
and a density of ρχ = 0.3GeV/cm3. The S1 energy res-olution, governed by Poisson fluctuations, is taken intoaccount. Uncertainties in the energy scale as indicated inFig. 1 as well as uncertainties in vesc are profiled out andincorporated into the limit. The resulting 90% confidencelevel (CL) limit is shown in Fig. 5 and has a minimumσ = 7.0×10−45 cm2 at aWIMPmass ofmχ = 50GeV/c2.The impact of Leff data below 3 keVnr is negligible atmχ = 10GeV/c2. The sensitivity is the expected limit inabsence of a signal above background and is also shownin Fig. 5 as 1σ and 2σ region. Due to the presence oftwo events around 30 keVnr, the limit at higher mχ isweaker than expected. This limit is consistent with theone from the standard analysis, which calculates the limitbased only on events in the WIMP search region with anacceptance-corrected exposure, weighted with the spec-trum of a mχ = 100GeV/c2 WIMP, of 1471 kg × days.This result excludes a large fraction of previously unex-
plored WIMP parameter space, and cuts into the regionwhere supersymmetric WIMP dark matter is accessibleby the LHC [17]. Moreover, the new result challengesthe interpretation of the DAMA [19] and CoGeNT [18]results as being due to light mass WIMPs.
We gratefully acknowledge support from NSF, DOE,SNF, Volkswagen Foundation, FCT, Region des Pays dela Loire, STCSM, DFG, and Weizmann Institute of Sci-ence. We are grateful to LNGS for hosting and support-ing XENON.
∗Electronic address: [email protected]
†Electronic address: [email protected]
[1] G. Steigman and M. S. Turner, Nucl. Phys. B253, 375(1985); G. Jungman, M. Kamionkowski, and K. Griest,
Phys. Rept. 267, 195 (1996).
[2] N. Jarosik et al., Astrophys. J. Suppl. 192, 14 (2011);
K. Nakamura et al. (Particle Data Group), J. Phys. G37,075021 (2010).
[3] M. W. Goodman and E. Witten, Phys. Rev. D31, 3059(1985).
[4] J. D. Lewin and P. F. Smith, Astropart. Phys. 6, 87
(1996).
[5] Z. Ahmed et al. (CDMS), Science 327, 1619 (2010).
[6] E. Armengaud et al. (EDELWEISS) (2011),
arXiv:1103.4070.[7] E. Aprile et al. (XENON100), Phys. Rev. Lett. 105,
131302 (2010).
[8] E. Aprile et al. (XENON100) (2011), arXiv:1103.5831.[9] E. Aprile et al., Phys. Rev. C79, 045807 (2009).
[10] E. Aprile et al. (XENON100) (2011), accepted by PRD,
arXiv:1101.3866.[11] E. Aprile and T. Doke, Rev. Mod. Phys. 82, 2053 (2010).
[12] G. Plante et al. (2011), submitted to PRD and arXiv.
[13] F. Arneodo et al., Nucl. Instrum. Meth. A449, 147
(2000); D. Akimov et al., Phys. Lett. B524, 245 (2002);
R. Bernabei et al., Eur. Phys. J. direct C3, 11 (2001).
E. Aprile et al., Phys. Rev. D72, 072006 (2005). V. Che-
pel et al., Astropart. Phys. 26, 58 (2006). A. Manzur
et al., Phys. Rev. C81, 025808 (2010).
[14] E. Aprile et al., Phys. Rev. Lett. 97, 081302 (2006).
[15] E. Aprile et al. (XENON100) (2011), arXiv:1103.0303.[16] S. Yellin, Phys. Rev. D66, 032005 (2002).
[17] O. Buchmueller et al. (2011), arXiv:1102.4585.[18] C. E. Aalseth et al. (CoGeNT), Phys. Rev. Lett. 106,
131301 (2011).
[19] C. Savage et al., JCAP 0904, 010 (2009).
E. Aprile et al. arXiv:1104.2549v2
R. Bernabei et al. J. Phys.: Conf. Ser. 203 (2010) 012003
DM-‐Ice Experiment
11 May 2011 Walter C. Pe9us 3
• Expect the same DM signal • Opposite muon rate – Tagging of muons by IceCube/DeepCore
• Drilling to 2500m in ice established – No temperature fluctua,on – Ice is rela,vely radiopure • No radon • ppt of U/Th, ppb 40K
– Ice as a neutron moderator • Infrastructure at Amundsen-‐Sco9 South Pole Sta,on
Cosmogenic Ac,va,on
• Spalla,on
• Capture
11 May 2011 Walter C. Pe9us 4
€
ZA X n,γ( ) Z
A +1X
ZA X p,n( )Z +1
AY
ZA X µ−,ν( )Z −1AY
Produc,on Rate
11 May 2011 Walter C. Pe9us 5
€
R ∝ dE φx E( )∫ σ E( )
! Rates presented in [2] are again compatible with our estimateswithin a factor "2, except for 58Co, with an enormous produc-tion much higher than in any other estimate.
From the comparison of production rates in Tables 3 and 4, theeffect of enrichment on activation can be studied. Only the enrich-ment percentage usual for DBD germanium detectors has been ta-ken into consideration. In general, production rates in enrichedcrystals are reduced to several tenths of the rates as in the naturalones. This is due to the suppression of the germanium isotopeshaving the lowest mass number and the highest productioncross-sections. However, according to our estimates, neither for60Co nor 63Ni production rates are reduced in enriched material;in [13] for these two isotopes the reduction of production ratesin enriched material is much lower than for the others. This behav-
ior for 60Co is corroborated by the available measured cross-sec-tions on individual germanium, as stated before.
One interesting point is to know which is the energy range ofnucleons giving the largest activation yields. Comparing the contri-butions to the production rates of HMS-ALICE below 150 MeV andYIELDX above 150 MeV in Tables 3 and 4, it is seen that for many ofthe induced nuclides high energy neutrons are the most relevantfor activation. But when considering natural germanium, this isnot true for 65Zn, and specially for 68Ge, for which"85% of the yieldcomes from neutrons below 150 MeV.
In the context of experiments searching for the neutrinolessDBD of 76Ge, the important production of 60Co and specially 68Gecould be a serious hazard. Fortunately, events entangled with theexpected signal in the region of interest are produced by variousenergy deposits and can be very efficiently rejected by means of
0.01
0.1
1
10
100
00001000100101 Energy (MeV)
Prod
uctio
n cr
oss
sect
ion
(mb)
Michel'86 Michel'97 Michel'95 Michel'89 Aleksandrov'90Aleksandrov'96 Greenwood'84 Mills'92 Grutter'82 MENDL(p)YIELDX MENDL(n) Kim'99(n)
Fig. 15. Comparison of excitation functions for 59Fe in natural copper by nucleons.
0.001
0.01
0.1
1
10
100
00001000100101 Energy (MeV)
Prod
uctio
n cr
oss
sect
ion
(mb)
Michel'95 Michel'89 Michel'97 Cumming'74 Orth'76Kozma'90 Mills'92 Greenwood'84 Yashima'03 Grutter'82MENDL(p) MENDL(n) YIELDX
Fig. 16. Comparison of excitation functions for 54Mn in natural copper by nucleons.
S. Cebrián et al. / Astroparticle Physics 33 (2010) 316–329 325
S Cebrian et al. Astropar,cle Phys. 33 (2010) 316-‐329.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
J. Ziegler. IBM J. of R&D. 42 (1998) 117-‐139
Loca,on and Cosmic Ray Flux
• Contours of “geomagne,c rigidity”:
• Flux varia,on with rigidity:
• Up to a factor of two varia,on in flux
11 May 2011 Walter C. Pe9us 6
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
J. Ziegler. IBM J. of R&D. 42 (1998) 117-‐139
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Al,tude and Cosmic Ray Flux
• Exponen,al decay of nucleon flux with atmospheric depth:
• No spectral distor,on, just a9enua,on:
11 May 2011 Walter C. Pe9us 7
24. Cosmic rays 255
!
!"
!""
! !" !"" !"""#$%&'())*+%,-
!. "#$"!)*+%,
/ $01/) 2)2&3-
Figure 24.2: Di!erential spectrum of electrons plus positronsmultiplied by E3 (data from [15–22]) . The line shows theproton spectrum multiplied by 0.01.
p/p ratio also shows a strong dependence on the phase and polarityof the solar cycle [26] in the opposite sense to that of the positronfraction. There is at this time no evidence for a significant primarycomponent either of positrons or of antiprotons. No antihelium orantideuteron has been found in the cosmic radiation. The best currentmeasured upper limit on the ratio antihelium/helium is approximately7 ! 10!7 [27]. The upper limit on the flux of antideuterons around 1GeV/nucleon is approximately 2 ! 10!4 m2 s sr GeV/nucleon [28].
24.2. Cosmic rays in the atmosphere
Figure 24.3 shows the vertical fluxes of the major cosmic raycomponents in the atmosphere in the energy region where the particlesare most numerous (except for electrons, which are most numerousnear their critical energy, which is about 81 MeV in air). Except forprotons and electrons near the top of the atmosphere, all particles areproduced in interactions of the primary cosmic rays in the air. Muonsand neutrinos are products of the decay of charged mesons, whileelectrons and photons originate in decays of neutral mesons.
Most measurements are made at ground level or near the top of theatmosphere, but there are also measurements of muons and electronsfrom airplanes and balloons. Fig. 24.3 includes recent measurementsof negative muons [29–32]. Since µ+(µ!) are produced in associationwith !µ(!µ), the measurement of muons near the maximum of theintensity curve for the parent pions serves to calibrate the atmospheric!µ beam [33]. Because muons typically lose almost two GeV inpassing through the atmosphere, the comparison near the productionaltitude is important for the sub-GeV range of !µ(!µ) energies.
The flux of cosmic rays through the atmosphere is described bya set of coupled cascade equations with boundary conditions at thetop of the atmosphere to match the primary spectrum. Numerical orMonte Carlo calculations are needed to account accurately for decayand energy-loss processes, and for the energy-dependences of the crosssections and of the primary spectral index ". Approximate analyticsolutions are, however, useful in limited regions of energy [34,35]. Forexample, the vertical intensity of nucleons at depth X (g cm!2) in theatmosphere is given by
IN (E, X) " IN (E, 0) e!X/! , (24.3)
where " is the attenuation length of nucleons in air.The corresponding expression for the vertical intensity of charged
pions with energy E! # #! = 115 GeV is
I!(E!, X) " ZN!
$NIN (E!, 0) e!X/! X E!
#!. (24.4)
15 10 5 3 2 1 0
0 200 400 600 800 10000.01
0.1
1
10
100
1000
10000
Atmospheric depth [g cm–2]
Ver
tica
l flu
x [m
–2 s
–1 s
r–1 ]
Altitude (km)
µ+ + µ!
"+ + "!
e+ + e!
p + n
#µ + #µ_
Figure 24.3: Vertical fluxes of cosmic rays in the atmospherewith E > 1 GeV estimated from the nucleon flux of Eq. (24.2).The points show measurements of negative muons withEµ > 1 GeV [29–32].
This expression has a maximum at X = " "121±4 g cm!2 [36],which corresponds to an altitude of 15 kilometers. The quantityZN! is the spectrum-weighted moment of the inclusive distribution ofcharged pions in interactions of nucleons with nuclei of the atmosphere.The intensity of low-energy pions is much less than that of nucleonsbecause ZN! " 0.079 is small and because most pions with energymuch less than the critical energy #! decay rather than interact.
24.3. Cosmic rays at the surface
24.3.1. Muons : Muons are the most numerous charged particlesat sea level (see Fig. 24.3). Most muons are produced high in theatmosphere (typically 15 km) and lose about 2 GeV to ionizationbefore reaching the ground. Their energy and angular distributionreflect a convolution of production spectrum, energy loss in theatmosphere, and decay. For example, 2.4 GeV muons have a decaylength of 15 km, which is reduced to 8.7 km by energy loss. Themean energy of muons at the ground is " 4 GeV. For GeV muonsthere is also a solar activity and a latitude e!ect that results from thegeomagnetic e!ects. These two e!ects a!ect the GeV muon flux at the10% level. The energy spectrum is almost flat below 1 GeV, steepensgradually to reflect the primary spectrum in the 10–100 GeV range,and steepens further at higher energies because pions with E! > #!tend to interact in the atmosphere before they decay. Asymptotically(Eµ $ 1 TeV), the energy spectrum of atmospheric muons is onepower steeper than the primary spectrum. The integral intensity ofvertical muons above 1 GeV/c at sea level is " 70 m!2s!1sr!1 [37,38],with recent measurements [39–41] tending to give lower normalizationby 10-15%. Experimentalists are familiar with this number in theform I " 1 cm!2 min!1 for horizontal detectors.
T. Gaisser and T. Stanev. PDG
€
ʹ′ I = I e A − ʹ′ A ( ) /λ
GORDON et al.: MEASUREMENT OF THE FLUX AND ENERGY SPECTRUM OF COSMIC-RAY INDUCED NEUTRONS ON THE GROUND 3431
TABLE IDATA RELATING TO THE MEASUREMENT LOCATIONS
where is a normalization factor, and and depend on pres-sure (depth) and solar modulation. Values of these parametersfor solar minimum and maximum ( and ) were de-rived by BSY, and are given in the Appendix, along with a tableof values of for sea level and mid-value solar mod-ulation, normalized so . fits theobserved cutoff dependence and monthly-averaged solar modu-lation of the rates of many neutron monitors reasonably well forall the observed solar cycles except for the extremely low ratesbetween 1989 and 1991.
To compare our measurements at the different locations, fit(4) to them, and determine the best value for , we used theflux integrated above 10 MeV, because neutrons at lower ener-gies come partly from scatter in local materials which variedfrom site to site. The measured high-energy flux was divided by
at the cutoff and depth of each location. Our measure-ment with the most data, the one at Yorktown Heights, was doneat a time (November 2002) when neutron monitor count rateswere about 20% of the way from their typical minimum values,at , to their maximum values, at . Since we have pa-rameters from BSY only for and , we obtainedfor the time of the measurement by interpolating 20% of the wayfrom to .
Since the data from the 5 measurements presented herespanned a period of about 9 months, there was a slight changein the flux between measurements due to changes in solarmodulation. To compensate, the ratio of a neutron monitorcount rate at the time of each measurement relative to the timeof the Yorktown Heights measurement, , was used as ameasure of solar modulation, and this ratio was multiplied by
for the cutoff and depth of each measurement locationto obtain a solar modulation factor. This correction was 1% orless. Any neutron monitor could be used; we used data fromthe one in Newark, Delaware [30].
Table I shows data relating to each of the measurementlocations, including altitude, atmospheric depth, cutoff,
for November 2002, the solar modulation factor,and the value of resulting from a fit of (4) to thecorrected high-energy fluxes. The high energy flux data werecorrected by dividing by and the solar modulationfactor. The corrected data and the fit are shown in Fig. 5.
Fig. 5. Neutron flux above 10 MeV at 5 measurement locations as a function ofatmospheric depth (points). The data have been corrected for location-dependentgeomagnetic cutoff and variations in solar modulation as described in the textand fit with (4) (line).
Fig. 6. Measured neutron spectra for all five sites. Each spectrum has beenscaled to sea level at the cutoff of New York City and solar modulation forNovember 2002, as described in the text.
From the least-squares fit shown in Fig. 5, the neutron atten-uation length was determined to be . Thelargest fit residual occurred for the twodata points near sea level (Yorktown Heights and Houston) andamounted to 2.35%. If the measured flux had not been cor-rected for , the fitted attenuation length would have been135.0 and the fit to the data would not have been as good,with residuals of up to 4.2% and 4.9%.
To compare the shapes of the measured spectra at the 5 loca-tions, the spectra were scaled by applying the same correctionsused for the fit shown in Fig. 5 and then divided by foreach location (the last column of Table I). The resulting spectraare shown in Fig. 6. Above a few MeV, the spectra practicallylie on top of one another, justifying the assumption in (3) thatone spectral shape can be used at various locations, at leastfor the limited range of cutoffs covered by our measurements
M. Gordon et al. IEEE Trans Nuc. Sci. 51 (2004) 3427-‐3434.
Flux Adjustment
• Flux scales with al,tude (h), rigidity (Rc), and solar cycle:
– Al,tude dependence (rela,ve to sea level):
• Requires conversion from al,tude (H) to barometric pressure (h):
– Loca,on dependence:
• Normaliza,on factor (N) varies with solar intensity (I) and rigidity (Rc)
11 May 2011 Walter C. Pe9us 8
€
h = 9.8025 ×10−4( ) 1033.7 − 0.03648( )H + 4.26 ×10−7( )H 2( )€
φ = φ0 *Falt (h) *FBSYD(Rc,h,I)
€
Falt = e hSL −h( ) /λ
€
FBSYD = N Rc,I( ) 1− exp −αRck
⎛
⎝ ⎜
⎞
⎠ ⎟
⎡
⎣ ⎢
⎤
⎦ ⎥
€
α = exp 1.89 + 0.12h − 0.14exp −5.6h( )[ ]k =1.36 − 0.53h + 0.21exp −9.2h( )
Ac,va,on Targets
• 125 kg NaI(Tl) – 23Na and 127I
• 850 kg OFHC Cu – 63Cu (69%), 65Cu (31%)
• 450 kg SS 2205 – 67% Fe (54, 56, 57, 58) – 22% Cr (50, 52, 53, 54) – 5% Ni (58, 60, 61, 62, 64) – 3.2% Mo (92, 94-‐98, 100) – 2% Mn, 1% Si, 0.18% N, 0.030% C, 0.030% P, 0.015% S
11 May 2011 Walter C. Pe9us 9
Table 3: Radioactive daughter isotopes of crystal elements
Isotope Half-Life Decay Mode Production Channel(s)
3H 12.31 y β− 23
Na(n,21Ne)
3H,
127I(n,
125Te)
3H
22Na 2.60 y β+
24Na 14.96 h β− 23
Na(n,γ)24Na,23Na(n,γ)24mNa
125I 59.40 d EC
129I 1.57x10
7y β−
Table 4: Comprehensive list of daughter isotopes
Isotope Half-Life Production Channel(s)
3H 12.31 y
23Na(n,
21Ne)
3H,
127I(n,
125Te)
3H
24Na 14.96 h
23Na(n,γ)24Na, 23
Na(n,γ)24mNa
46Sc 83.79 d Spallation
48V 15.9735 d Spallation
54Mn 312.12 d Spallation
56Co 77.27 d Spallation
57Co 271.79 d Spallation
58Co 70.82 d Spallation
59Fe 44.503 d Spallation
60Co 5.2714 y Spallation
65Zn 244.26 d
65Cu(p,n)
65Zn
7Be 53.2 d Spallation
54Mn 312.2 d
56Fe(n,p2n),
56Fe(µ−
,ν2n)58Co 70.9 d
60Ni(n,p2n),
60Ni(µ−
,ν2n), 58Ni(n,p)
56Co 77.236 d
58Ni(n,p2n),
58Ni(µ−
,ν2n)46Sc 83.8 d Spallation on Fe
48V 16.0 d
52Cr(n,p4n),
50Cr(n,p2n),
50Cr(µ−
,ν2n)51Cr 27.70 d
52Cr(n,2n),
50Cr(n,γ)
52Mn 5.59 d
56Fe(n,p4n),
54Fe(n,p2n)
56Ni 6.1 d
58Ni(n,3n)
95Nb 34.99 d
95Mo(n,p),
96−98Mo(n,p1-3n)
4
Es,ma,ng Ac,va,on
• Obtain reference ac,va,on rate (/kg/day) – Standard is sea level, New York City
• Scale to component mass
• Scale reference rate by appropriate al,tude, loca,on factors
• Scale to exposure ,me for each stage
11 May 2011 Walter C. Pe9us 10
€
R = Rref * Falt (h)Falt, ref (h)
* FBSYD(Rc,h,I)FBSYD, ref (Rc,h,I)
Height Profile
• PSL, Stoughton, WI – 30 days of tes,ng (876 n)
• Shipment to Christchurch, NZ (high flight) – 20 + 10 hrs (35,000 n)
• Christchurch, NZ – 30 days processing (123 n)
• Shipment to Pole (low flight) – 10 hrs (21,000 n)
• South Pole, Antarc,ca – 30 days tes,ng (9,000 n)
11 May 2011 Walter C. Pe9us 11
Ac,va,on Es,mate
• Ac,va,on at South Pole dominates (> 50%) followed by high flight (>25%)
11 May 2011 Walter C. Pe9us 12
Table 7: Total Activation for trip(atoms)
Isotope Stoughton, WI Christchurch South Pole High Flight Low Flight Total
7Be 7524282 5136528 57765200 31093993 6306526 107826529
46Sc 433911 296214 331213 1793133 363686 6218157
48V 1050765 717315 8066902 4342272 880705 15057959
51Cr 4518862 3084847 34692074 18674134 3787513 64757431
52Mn 570210 389260 4377599 2356385 477925 8171379
54Mn 4670366 3188273 35855199 19300224 3914497 66928560
56Co 536101 365975 4115737 2215429 449336 7682577
56Ni 132074 90162 1013958 545796 110699 1892690
57Co 2707149 1848063 20783247 11187257 2269014 38794730
58Co 2957021 2018641 22701559 12219851 2478447 42375519
59Fe 684307 467149 5253543 2827890 573556 9806446
60Co 3158341 2156074 24247121 13051799 2647184 45260518
in Physics Research Section B: Beam Interactions with Materials andAtoms, 251(1):115 – 120, 2006.
[3] R. Bernabei, P. Belli, A. Bussolotti, F. Cappella, R. Cerulli, C.J. Dai,
A. d’Angelo, H.L. He, A. Incicchitti, H.H. Kuang, J.M. Ma, A. Mattei,
F. Montecchia, F. Nozzoli, D. Prosperi, X.D. Sheng, and Z.P. Ye. The
dama/libra apparatus. Nuclear Instruments and Methods in Physics Re-search Section A: Accelerators, Spectrometers, Detectors and AssociatedEquipment, 592(3):297 – 315, 2008.
[4] S. Cebrian, H. Gomez, G. Luzon, J. Morales, A. Tomas, and J.A. Villar.
Cosmogenic activation in germanium and copper for rare event searches.
Astroparticle Physics, 33(5-6):316 – 329, 2010.
[5] T. K. Gaisser. Cosmic Rays and Particle Physics. Cambridge University
Press, New York, 1990.
[6] M.S. Gordon, P. Goldhagen, K.P. Rodbell, T.H. Zabel, H.H.K. Tang,
J.M. Clem, and P. Bailey. Measurement of the flux and energy spectrum
of cosmic-ray induced neutrons on the ground. Nuclear Science, IEEETransactions on, 51(6):3427 – 3434, dec. 2004.
6
Conclusions & Extensions
• Unshielded storage at the South Pole will lead to a dominant contribu,on to cosmogenic ac,va,on of the detector
• Based on given exposures, expected cosmogenic background decay rate is ~68 Hz
11 May 2011 Walter C. Pe9us 13
Further Work
• Ac,va,on in the crystal was not calculated because produc,on rates were unavailable – Only 24Na and 3H expected
• Consider effect of shielding the detector under ice at the South Pole – What thickness of ice would be needed?
• Produce plots of ac,vity vs ,me for full pre-‐deployment schedule
11 May 2011 Walter C. Pe9us 14