Ion-Channeling in Direct DM Detectors Graciela Gelmini - UCLA - - PowerPoint PPT Presentation

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Ion-Channeling in Direct DM Detectors Graciela Gelmini - UCLA - - PowerPoint PPT Presentation

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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 Crystals refer to the orientation

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Ion-Channeling in Direct DM Detectors

Graciela Gelmini - UCLA

Based on work done with Nassim Bozorgnia and Paolo Gondolo

GGI Florence, May 19, 2010

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Graciela Gelmini-UCLA

Channeling and Blocking Effects in Crystals

refer to the orientation dependence of ion penetration in crystals.

Channeling:

Ions incident upon the crystal along symmetry axis and planes suffer a series

  • f

small-angle scattering that maintain them in the open“channels” and penetrate much further (ions do not get close to lattice sites)

Blocking:

Reduction

  • f

the flux

  • f

ions

  • riginating

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

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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 (Vienna University of Technology)-1995)

GGI Florence, May 19, 2010 2

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Graciela Gelmini-UCLA

NaI crystal .Si or Ge crystal .

GGI Florence, May 19, 2010 3

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Graciela Gelmini-UCLA

Channeling effect observed in NaI (Tl) Altman et.al 1973

GGI Florence, May 19, 2010 4

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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

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Graciela Gelmini-UCLA

Channeling effect observed in NaI(Tl) Altman et.al 1973

Channeled ions produce more scintillation light (because they loose most of their energy via electronic stopping rather than nuclear stopping)

GGI Florence, May 19, 2010 6

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Graciela Gelmini-UCLA

Channeling effect in DM detection:

The potential importance of the channeling effect for direct DM detection was first pointed

  • ut 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

100 101 102 103 108 107 106 105 104 103 102 101 100

MWIMP GeV ΣΧp pb spinindependent

CDMS I Si CDMS II Ge XENON 10 SuperK CoGeNT TEXONO CRESST I DAMA 3Σ90 with channeling DAMA 7Σ5Σ with channeling DAMA 3Σ90 DAMA 7Σ5Σ

(Savage,Gelmini, Gondolo, Freese JCAP 0904:010,2009) GGI Florence, May 19, 2010 7

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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

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Graciela Gelmini-UCLA

Our calculation

  • f

the fraction

  • f

recoils that are channeled 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

  • ver a direction parallel to a row/plane (took just one)

0.00 0.05 0.10 0.15 0.20 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Distance nm U keV 100 Channel, Si ions

aSiSi Planar Axial

  • In the direction perpendicular the row or plane, the

“transverse energy” is conserved Eperp = Eφ2

i + Ui

vperp = v sin φ ≃ vφ and Eperp = Mv2

perp/2 GGI Florence, May 19, 2010 9

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Graciela Gelmini-UCLA

Axial and planar channels

ρmin: min. distance of approach - ψ: angle far away from row or plane

(Fig. from D. Gemmell 1974, Rev. Mod. Phys. 46, 129)

Eperp = Eφ2

i + Ui

= U(ρmin) = Eψ2 + Umiddle

Umiddle: at middle of channel, far from row/plane, angle there is ψ = q [U(ρmin)−Umiddle)]

E

Channeling requires ρmin > ρc which amounts to ψ ≤ ψc

GGI Florence, May 19, 2010 10

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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

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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) =

  • ρ2

c(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 Si

200 400 600 800 0.006 0.008 0.010 0.012 0.014 Crystal Temperature K nm

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 the channel rch = dch/2, ψc = 0: NO CHANNELING POSSIBLE

GGI Florence, May 19, 2010 12

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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 K 600 °C 900 °C 40 mK

1 10 100 1000 104 0.002 0.005 0.01 0.02 0.05 0.1 0.2 E keV rc nm

100 axial channel, Si ions, c1

Static lattice 40 mK 293 K 600 °C 900 °C

1 10 100 1000 104 0.2 0.5 1. 2. 5. E keV Ψc deg

100 axial channel, Si ions, c1

GGI Florence, May 19, 2010 13

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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 mK 293 K 600 °C 900 °C Static lattice

1 10 100 1000 104 0.002 0.005 0.01 0.02 0.05 0.1 0.2 E keV rc nm

100 axial channel, Si ions, c2

Static lattice 40 mK 293 K 600 °C 900 °C

1 10 100 1000 104 0.2 0.5 1. 2. 5. E keV Ψc deg

100 axial channel, Si ions, c2

GGI Florence, May 19, 2010 14

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Graciela Gelmini-UCLA

Data B and P ion in Si crystal fitted with c = 2 (data from Hobler-1995)

(Bozorgnia, Gelmiin, Gondolo 2010)

  • <100>

{110} {100}

100 200 300 400 500 600 0.0 0.5 1.0 1.5 2.0 E keV Ψc deg

B in Si, c1c22

  • <100>

{110} {100}

100 200 300 400 500 600 0.0 0.5 1.0 1.5 2.0 E keV Ψc deg

P in Si, c1c22 GGI Florence, May 19, 2010 15

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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) fraction

Iodine recoils Sodium recoils

10

  • 3

10

  • 2

10

  • 1

1 10 20 30 40 50 60

GGI Florence, May 19, 2010 16

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Graciela Gelmini-UCLA

Reproduced DAMA calculations of channeled fraction

We used HEALPix (Hierarchical Equal Area iso Latitude Pixelisation) method to compute the integral over all directions. Dechanneling due to Tl doping (only first interaction and no rechanneling)

(Bozorgnia, Gelmiin, Gondolo 2010)

10 20 30 40 50 60 0.001 0.005 0.01 0.05 0.1 0.5 1. E keV Fraction Incident ions

NaDAMA IDAMA Na,dech I,dech Na I

GGI Florence, May 19, 2010 17

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SLIDE 19

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! Collision

may happen when nucleus is somewhat within the channel, with prob. g(ρ) = ρ

u2

1e(−ρ2/2u2 1) thus PCh =

∞

ρi,min drg(ρ) = e(−ρ2

i,min/2u2 1)

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 increases channneling prob.- but rc also increases with T what decreases the prob.

GGI Florence, May 19, 2010 18

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Graciela Gelmini-UCLA

Channeling probability of ions ejected from lattice sites: Si

No dechanneling included (Bozorgnia, Gelmiin, Gondolo 2010)

900 °C 600 °C 293 K 40 mK

5 10 50 100 5001000 1104 2104 5104 0.001 0.002 0.005 0.01 E keV Fraction

Si ions, c1c21

40 mK 900 °C 600 °C 293 K

10 20 50 100 200 5001000 0.0001 0.001 0.0005 0.0002 0.0003 0.00015 0.0015 0.0007 E keV Fraction

Si ions, c1c22

Upper bound (static lattice)

900 °C 600 °C 293 K 40 mK

5 10 50 100 5001000 1104 5104 0.001 0.005 0.01 E keV Fraction

Si ions, Static lattice

GGI Florence, May 19, 2010 19

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Graciela Gelmini-UCLA

Channeling probability of ions ejected from lattice sites: Ge

No dechanneling included (Bozorgnia, Gelmiin, Gondolo 2010)

900 °C 600 °C 293 K 40 mK

50 100 5001000 5000 1104 2104 5104 0.001 0.002 0.005 0.01 E keV Fraction

Ge ions, c1c21

900 °C 600 °C 293 K 40 mK

50 100 5001000 5000 0.0001 0.0005 0.0002 0.0003 0.00015 0.0007 E keV Fraction

Ge ions, c1c22

Upper bound (static lattice)

900 °C 600 °C 293 K 40 mK

50 100 5001000 5000 1104 5104 0.001 0.005 0.01 E keV Fraction

Ge ions, Static lattice

GGI Florence, May 19, 2010 20

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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 104 1104 5104 0.001 0.005 0.01 0.05 0.1 E keV Fraction

Static lattice

Na, 600 °C I, 600 °C Na, 293 K I, 293 K Na, 77.2 K I, 77.2 K

1 2 5 10 20 50 108 106 104 0.01 E keV Fraction

Static lattice, dechanneling GGI Florence, May 19, 2010 21

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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 = 1 Na, c = 2 I, c = 2

1 10 100 1000 104 105 104 0.001 0.01 E keV Fraction

T293 K

Na, c = 1 I, c = 1 Na, c = 2 I, c = 2

1 10 100 1000 104 105 104 0.001 0.01 E keV Fraction

T293 K, dechanneling GGI Florence, May 19, 2010 22

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Graciela Gelmini-UCLA

Compatibility of DAMA/LIBRA with other experiments

Then (Savage, Gelmini, Gondolo, Freese JCAP 0904:010,2009)

100 101 102 103 108 107 106 105 104 103 102 101 100

MWIMP GeV ΣΧp pb spinindependent

CDMS I Si CDMS II Ge XENON 10 SuperK CoGeNT TEXONO CRESST I DAMA 3Σ90 with channeling DAMA 7Σ5Σ with channeling DAMA 3Σ90 DAMA 7Σ5Σ

and now (diff. at 7σ)(Savage,Gelmini, Gondolo 2010)

GGI Florence, May 19, 2010 23

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Graciela Gelmini-UCLA

Compatibility of DAMA/LIBRA with other experiments

If 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

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SLIDE 26

Graciela Gelmini-UCLA

Compatibility of DAMA/LIBRA with other experiments

If 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

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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 recoil nuclei: the channeled fraction of recoils is smaller and it is strongly temperature dependent (so it is negligible at mK).

  • Channeling in crystaline detectors can lead to a daily modulation of

a WIMP signal, a DM signature without any background (Avignone, Creswell & Nussinov 2008) (with small amplitudes- but larger for halo components with small velocity dispersion)

  • Analytic models give good qualitative results but need data/simulations

to get good quantitative results (not available or NaI). Montecarlo simulations may be needed to settle these issues (many are used in other applications of channeling).

GGI Florence, May 19, 2010 26

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Graciela Gelmini-UCLA GGI Florence, May 19, 2010 27

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Graciela Gelmini-UCLA GGI Florence, May 19, 2010 28

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Graciela Gelmini-UCLA GGI Florence, May 19, 2010 29