ion-channeling in direct dm detectors · ion-channeling in direct dm detectors graciela gelmini -...
TRANSCRIPT
Ion-Channeling
in Direct DM Detectors
Graciela Gelmini - UCLA
Based on work done with Nassim Bozorgnia and Paolo Gondolo
GGI Florence, May 19, 2010
Graciela Gelmini-UCLA
Channeling and Blocking Effects in Crystalsrefer to the orientation dependence of ion penetration in crystals.
Channeling:Ions incident upon the crystal
along symmetry axis and planes
suffer a series of small-angle
scattering that maintain them in
the open“channels” and penetrate
much further (ions do not get close
to lattice sites)
Blocking:Reduction of the flux of ions
originating in lattice sites
along symmetry axis and planes
(“blocking dip”) (From D. Gemmell 1974, Rev. Mod. Phys. 46, 129)
GGI Florence, May 19, 2010 1
Graciela Gelmini-UCLA
Channeling and blocking in crystals is used in
- studies of lattice disorder
- ion implantation
- to locate dopant and impurity atoms
- studies of surfaces and interfaces
- measurement of nuclear lifetimes
- production of polarized beams... etc
- channeling is to be avoided in ion implantation in Si to make circuits:good data at ∼ 100‘s keV (and analytic models by Gerhard Hobler (ViennaUniversity of Technology)-1995)
GGI Florence, May 19, 2010 2
Graciela Gelmini-UCLA
NaI crystal
.Si or Ge crystal .
GGI Florence, May 19, 2010 3
Graciela Gelmini-UCLA
Channeling effect observed in NaI (Tl) Altman et.al 1973
GGI Florence, May 19, 2010 4
Graciela Gelmini-UCLA
Channeling effect observed in NaI (Tl) Altman et.al 1973
Sintillation output of a monochromatic 10 MeV 16O
beam through NaI(Tl) scintillator
Left peak: Not channeled ions
Right peak: higher energy channeled ions
GGI Florence, May 19, 2010 5
Graciela Gelmini-UCLA
Channeling effect observed in NaI(Tl) Altman et.al 1973
Channeled ions produce morescintillation light(because they loose most oftheir energy via electronicstopping rather than nuclearstopping)
GGI Florence, May 19, 2010 6
Graciela Gelmini-UCLA
Channeling effect in DM detection:The potential importance of the channeling effect for direct DM detection was first pointed
out in stilbene crystals by H. Sekiya et al. (2003) and
subsequently for NaI (Tl) by Drobyshevski (2007) and by the DAMA collaboration (2008).
When ions recoiling after a collision with a WIMP move along crystal axes and planes,
they give their energy to electrons, so Q = 1 instead of QI = 0.09 and QNa = 0.3
100 101 102 10310-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
MWIMP HGeVL
ΣΧpHp
bL
spin-independent CDMS I SiCDMS II Ge
XENON 10
Super-K
CoGeNT
TEXONO
CRESST I
DAMA H3Σ�90%Lwith channeling
DAMA H7Σ�5ΣLwith channeling
DAMA H3Σ�90%L
DAMA H7Σ�5ΣL
(Savage,Gelmini, Gondolo, Freese JCAP 0904:010,2009)
GGI Florence, May 19, 2010 7
Graciela Gelmini-UCLA
Daily-Modulation due to Channeling:H. Sekiya et al. (2003); Avignone, Creswick, Nussinov (2008)
• The WIMP wind comes preferentially from one direction
• When that direction is aligned with a channel, the scintillation or ionization output is
larger
• Earth’s rotation makes the WIMP wind change direction with respect to the crystal,
which produces a daily modulation in the measured recoil energy (equivalent to a
modulation of the quenching factor)
This daily modulation would be a background free DM signature!
Nassim Bosognia, Paolo Gondolo and I set out more than a year ago to do an analytic
calculation to understand channeling and blocking for DM detection, and estimate daiy
modulation amplitudes...
GGI Florence, May 19, 2010 8
Graciela Gelmini-UCLA
Our calculation of the fraction of recoils that arechanneled as function of recoil energy and direction:
• Use classical analytic models of the 60’s and 70’s, in particular Lindhard’s model(Lindhard
1965, Morgan & Van Vliet 1971, Dearnaley 1973, Gemmell 1974, Appleton & Foti 1977, Hobler 1995)
• Continuum string and plane model, in which
the screened Thomas-Fermi potential is averaged
over a direction parallel to a row/plane (took just one)
0.00 0.05 0.10 0.15 0.200.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
DistanceHnmL
UHk
eVL
100 Channel, Si ions
aSiSi
Planar
Axial
• In the direction perpendicular the row or plane, the
“transverse energy” is conservedEperp = Eφ2
i + Ui
vperp = v sinφ ≃ vφ
and Eperp = Mv2perp/2
GGI Florence, May 19, 2010 9
Graciela Gelmini-UCLA
Axial and planar channelsρmin: min. distance of approach - ψ: angle far away from row or plane(Fig. from D. Gemmell 1974, Rev. Mod. Phys. 46, 129)
Eperp = Eφ2i + Ui
= U(ρmin)= Eψ2 + Umiddle
Umiddle: at middle of channel,
far from row/plane,
angle there is
ψ =
q
[U(ρmin)−Umiddle)]E
Channeling requiresρmin > ρcwhich amounts toψ ≤ ψc
GGI Florence, May 19, 2010 10
Graciela Gelmini-UCLA
Axial and planar channels can be understood as interference of Coulomb
shadow cones, ρmin > ρc and ψ < ψc
(Fig. from Hiroshi Kudo, 2001)
GGI Florence, May 19, 2010 11
Graciela Gelmini-UCLA
Channeling requires (Lindhard 1965, Morgan & Van Vliet 1971, Hobler 1995)
• Min. distance of approach to row or plane larger than a critical value:
ρmin > ρc(E,T ) =
√
ρ2c(E) + [c u1(T )]2
ρc(E): for perfect-rigid-lattice decreases with E
u1(T ): 1-dim. amplitude of thermal fluctuations
. (used Debye model) increases with T, e.g. in Si0 200 400 600 800
0.006
0.008
0.010
0.012
0.014
Crystal TemperatureHKL
HnmL
aSiSi
u1
c: found through data/simulations, 1 < c < 2
• Angle far from the row/plane smaller than a critical angle:
ψ ≤ ψc =√
[U(ρc)−U(rch)]E
If ρc(E, T ) ≥ the radius of thechannel rch = dch/2, ψc = 0:NO CHANNELING POSSIBLE
GGI Florence, May 19, 2010 12
Graciela Gelmini-UCLA
Si ion in Si crystal, c = 1 (i.e. rc → u1(T ) at high E)(Bozorgnia, Gelmiin, Gondolo 2010)
dach � 2
u1
Static lattice
293 K600 °C900 °C
40 mK
1 10 100 1000 1040.002
0.005
0.01
0.02
0.05
0.1
0.2
E HkeVL
r cHn
mL
<100> axial channel, Si ions, c=1
Static lattice
40 mK
293 K600 °C
900 °C
1 10 100 1000 1040.2
0.5
1.
2.
5.
E HkeVLΨ
cHd
egL
<100> axial channel, Si ions, c=1
GGI Florence, May 19, 2010 13
Graciela Gelmini-UCLA
Si ion in Si crystal, c = 2 (i.e. rc → 2 u1(T ) at high E)(Bozorgnia, Gelmiin, Gondolo 2010)
dach � 2
2 u1
40 mK293 K600 °C900 °C
Static lattice
1 10 100 1000 1040.002
0.005
0.01
0.02
0.05
0.1
0.2
E HkeVL
r cHn
mL
<100> axial channel, Si ions, c=2
Static lattice40 mK
293 K
600 °C
900 °C
1 10 100 1000 1040.2
0.5
1.
2.
5.
E HkeVLΨ
cHd
egL
<100> axial channel, Si ions, c=2
GGI Florence, May 19, 2010 14
Graciela Gelmini-UCLA
Data B and P ion in Si crystal fitted with c = 2 (data from Hobler-1995)(Bozorgnia, Gelmiin, Gondolo 2010)
æ
æ
æ
æ
æ
æ
æ
æ
æ
<100>
{110}
{100}
0 100 200 300 400 500 6000.0
0.5
1.0
1.5
2.0
E HkeVL
ΨcHd
egL
B in Si, c1=c2=2
æ
æ
æ
æ
æ
æ
æ
æ
æ
<100>
{110}
{100}
0 100 200 300 400 500 6000.0
0.5
1.0
1.5
2.0
E HkeVL
ΨcHd
egL
P in Si,c1=c2=2
GGI Florence, May 19, 2010 15
Graciela Gelmini-UCLA
In NaI, no data or modeling available at low energies
DAMA channeling fraction:Calculated as if ions start from the middle of the channel(DAMA- Eur. Phys. J. C 53, 205-2313, 2008)
ER (keV)
frac
tion
Iodine recoils
Sodium recoils
10-3
10-2
10-1
1
0 10 20 30 40 50 60
GGI Florence, May 19, 2010 16
Graciela Gelmini-UCLA
Reproduced DAMA calculations of channeled fractionWe used HEALPix (Hierarchical Equal Area iso Latitude Pixelisation)method to compute the integral over all directions. Dechanneling dueto Tl doping (only first interaction and no rechanneling)(Bozorgnia, Gelmiin, Gondolo 2010)
0 10 20 30 40 50 600.001
0.0050.01
0.050.1
0.51.
E HkeVL
Fra
ctio
n
Incident ions
NaDAMA
IDAMA
Na,dech
I,dech
Na
I
GGI Florence, May 19, 2010 17
Graciela Gelmini-UCLA
Channeling probability of ions ejected from lattice sites
• Recoiling nuclei start at or close to lattice sites
• Blocking effects are important
• In a perfect lattice no recoil would be channeled (“rule of reversibility”).
• However, there are channeled recoils due to lattice vibrations! Collisionmay happen when nucleus is somewhat within the channel, with prob.
g(ρ) = ρ
u21e(−ρ
2/2u21) thus PCh =
∫
∞
ρi,mindrg(ρ) = e(−ρ
2i,min/2u
21)
and ρi,min is given by ρc (uncertainty in ρc is exponentiated in PCh)
• Recoiling nucleus leaves an empty lattice site.
Two main T effects: amplitude u1(T ) increases with T which increaseschannneling prob.- but rc also increases with T what decreases the prob.
GGI Florence, May 19, 2010 18
Graciela Gelmini-UCLA
Channeling probability of ions ejected from lattice sites: SiNo dechanneling included (Bozorgnia, Gelmiin, Gondolo 2010)
900 °C
600 °C
293 K
40 mK
5 10 50 100 50010001´10-42´10-4
5´10-40.0010.002
0.0050.01
E HkeVL
Fra
ctio
n
Si ions,c1=c2=1
40 mK
900 °C
600 °C 293 K
10 20 50 100200 50010000.0001
0.001
0.0005
0.00020.0003
0.00015
0.0015
0.0007
E HkeVL
Fra
ctio
n
Si ions,c1=c2=2
Upper bound (static lattice)
900 °C
600 °C
293 K40 mK
5 10 50 100 50010001´10-4
5´10-40.001
0.0050.01
E HkeVL
Fra
ctio
n
Si ions, Static lattice
GGI Florence, May 19, 2010 19
Graciela Gelmini-UCLA
Channeling probability of ions ejected from lattice sites: GeNo dechanneling included (Bozorgnia, Gelmiin, Gondolo 2010)
900 °C
600 °C293 K
40 mK
50 100 5001000 50001´10-42´10-4
5´10-40.0010.002
0.0050.01
E HkeVL
Fra
ctio
n
Ge ions,c1=c2=1
900 °C
600 °C293 K
40 mK
50 100 5001000 50000.0001
0.0005
0.0002
0.0003
0.00015
0.0007
E HkeVL
Fra
ctio
n
Ge ions,c1=c2=2
Upper bound (static lattice)
900 °C
600 °C
293 K
40 mK
50 100 5001000 50001´10-4
5´10-40.001
0.0050.01
E HkeVL
Fra
ctio
n
Ge ions, Static lattice
GGI Florence, May 19, 2010 20
Graciela Gelmini-UCLA
Channeling probability of ions ejected from lattice sites: NaI(Tl)Upper bound: T-dep. static lattice.
Righ: extreme dechanneling due to Tl, with no re-channeling considered.
(Bozorgnia, Gelmiin, Gondolo 2010)
Na, 600 °C
I, 600 °C
Na, 293 K
I, 293 K
Na, 77.2 K I, 77.2 K
1 10 100 1000 1041´10-4
5´10-40.001
0.0050.01
0.050.1
E HkeVL
Fra
ctio
n
Static lattice
Na, 600 °CI, 600 °C
Na, 293 K
I, 293 K
Na, 77.2 K I, 77.2 K
1 2 5 10 20 5010-8
10-6
10-4
0.01
E HkeVL
Fra
ctio
n
Static lattice, dechanneling
GGI Florence, May 19, 2010 21
Graciela Gelmini-UCLA
Channeling probability of ions ejected from lattice sites: NaI (Tl)More reasonable upper bounds at 20 K with lattice oscillations included
- Right: extreme dechanneling due to Tl with no re-channeling considered.
(Bozorgnia, Gelmiin, Gondolo 2010)
Na, c = 1
I, c = 1Na, c = 2
I, c = 2
1 10 100 1000 10410-5
10-4
0.001
0.01
E HkeVL
Fra
ctio
n
T=293 K
Na, c = 1
I, c = 1
Na, c = 2
I, c = 2
1 10 100 1000 10410-5
10-4
0.001
0.01
E HkeVL
Fra
ctio
n
T=293 K, dechanneling
GGI Florence, May 19, 2010 22
Graciela Gelmini-UCLA
Compatibility of DAMA/LIBRA with other experimentsThen (Savage, Gelmini, Gondolo, Freese JCAP 0904:010,2009)
100 101 102 10310-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
MWIMP HGeVL
ΣΧpHp
bL
spin-independent CDMS I SiCDMS II Ge
XENON 10
Super-K
CoGeNT
TEXONO
CRESST I
DAMA H3Σ�90%Lwith channeling
DAMA H7Σ�5ΣLwith channeling
DAMA H3Σ�90%L
DAMA H7Σ�5ΣL
and now (diff. at 7σ)(Savage,Gelmini, Gondolo 2010)
GGI Florence, May 19, 2010 23
Graciela Gelmini-UCLA
Compatibility of DAMA/LIBRA with other experimentsIf Leff extrapolated as a constant below 4 keVnr (band: how the 90%CL bound changes
with 1σ change in Leff)
(Savage,Gelmini, Gondolo 2010)
GGI Florence, May 19, 2010 24
Graciela Gelmini-UCLA
Compatibility of DAMA/LIBRA with other experimentsIf Leff extrapolated linearly to zero as E decreases below 4 keVnr (band: how the 90%CL
bound changes with 1σ change in Leff from Manzur (2010) data set)
(Savage, Gelmini, Gondolo 2010)
GGI Florence, May 19, 2010 25
Graciela Gelmini-UCLA
Conclusions:• The channeling of recoiling lattice ions and incident ions is different. The
effect of blocking is important to understand the channeling of recoilnuclei: the channeled fraction of recoils is smaller and it is stronglytemperature dependent (so it is negligible at mK).
• Channeling in crystaline detectors can lead to a daily modulation ofa WIMP signal, a DM signature without any background (Avignone,Creswell & Nussinov 2008) (with small amplitudes- but larger for halocomponents with small velocity dispersion)
• Analytic models give good qualitative results but need data/simulationsto get good quantitative results (not available or NaI).Montecarlo simulations may be needed to settle these issues (many areused in other applications of channeling).
GGI Florence, May 19, 2010 26
Graciela Gelmini-UCLA
GGI Florence, May 19, 2010 27
Graciela Gelmini-UCLA
GGI Florence, May 19, 2010 28
Graciela Gelmini-UCLA
GGI Florence, May 19, 2010 29