Transcript G31 beta calibration

Experimental dark matter searches
Weakly Interacting Massive Particles
A WIMP c is like a massive neutrino: produced when T >> mc via annihilation
through Z (+ other channels); annihilation/pair creation maintain thermal equilibrium
If interaction rates high enough, the density drops as exp(- mc/T) as T
drops below mc: annihilation continues, production becomes suppressed
But, weakly interacting
 may freeze out
before total annihilation if
 > Gann~ nc ann v 
i.e., if annihilation too slow to keep up
with Hubble expansion
Leaves a relic abundance:
2
-27
3 -1
c h  10 cm s  ann v 

if mc and ann determined by
electroweak physics, then c ~ 1
freeze out
Detecting WIMPs
0
c
Direct detection:
WIMPs elastically scatter off nuclei  nuclear recoils
Measure recoil energy spectrum in target
v/c  10-3
m
Indirect detection:
c0
WIMPs annihilate
in halo: e+, p, g
in Sun, Earth core: high energy n’s
nm
Direct detection
WIMPs elastically scatter off nuclei in targets, producing nuclear
recoils, with nc related to ann
(same diagrams - via Z, h, H, and squarks)
Energy spectrum of recoils is exponential with E ~ 50 keV,
dependent on WIMP and target nucleus masses: Boltzmann
distribution (isothermal halo) + s-wave scattering (NR)

Ec exp  E c kT

s-wave
scattering
Elastic Scattering
Form Factors
Ge
Si
I/Xe
c
H,h,Z
~
q
q
q
WIMP flux
E c1
c
c
q
Amplitude of recoil energy spectrum, i.e. event rate,
normalized by nc, local WIMP number density, and
nucleus-dependent A2F2 (Q)
dR n c nc

expQ/ Q A2 F 2 Q
dQ
Q
Q 
2m 2c m N
2
v
2  
mc  mN 
At low Q, scattering is coherent
and ~A2. Coherence lost as Q
increases; parameterized by form factor.
mN
6  50 keV
10
c
q
WIMP nucleus cross section
In MSSM/CMSSM (neutralino):
1 event kg-1 d-1
current experiments
1 event 100 kg-1 yr-1
in general: : 10-5 between and 10-11 pb
sensitivity of current experiments: ~ 10-6 pb
testing some models, will test more models
in future as sensitivity improves
Accelerator constraints shrink SUSY bounds:
mainly constrained upper bound
g-2 can provide constraint on lower
bound if tentative disagreement due to SUSY
detectors:
low threshold
low background
large masses
good event discrimination
WIMP signatures
Annual modulation:
WIMP Isothermal Halo (assume no co-rotation) v0~ 230 km/s
WIMP wind
galactic center
Sun 230 km/s
Dec.
v0
June
log dN/dErecoil
Earth 30 km/s (15 km/s in galactic plane)
Dec
Combining earth and solar system motion around galaxy
:
 v0 
 v min  v e 
 v min  v e 
T Q 
erf
  erf

4 ve   v0 
v


0
~3% effect
Erecoil
June

 2  t  t 
p

where v e  v 0 1.05 0.07cos


 1 yr 
t p  June 2  1.3 days
Annual Modulation
Not distinguish between WIMP signal and background directly
From the amplitude of the modulation, we can calculate the
underlying WIMP interaction rate
125
105
100
103
101
WIMP Signal
75
±2%
99
50
Background
25
0
97
95
-0.5
Dec
-0.1
0.3
June
0.7
Dec
1.1
1.5
June
-0.5
Dec
-0.1
0.3
June
0.7
Dec
1.1
June
1.5
WIMP signatures
Diurnal modulation:
v0: solar motion
WIMPs
WIMP
WIMP
42o
vo
a
Nuclear recoil
The mean recoil direction rotates over
one sidereal day
The distribution of the angle a between the
solar motion and recoil directions:
peaks at a=180o
WIMP signatures
Material dependence:
WIMPs: Ge has ~6x higher interaction rate per kg than Si
neutrons: Si has ~2x higher interaction rate per kg than Ge
WIMPS 40 GeV
Background neutrons
Direct detection techniques
CRESST
ROSEBUD
CUORICINO
Phonons
CRESST II
ROSEBUD
CDMS
EDELWEISS
ER
HDMS
GENIUS
IGEX
MAJORANA
DRIFT (TPC)
Ionization
Scintillation
XENON
ZEPLIN II,III,IV
Large spread of technologies:
varies the systematic errors, important if positive signal!
All techniques have equally aggressive projections for future performance
But different methods for improving sensitivity
DAMA
ZEPLIN I
UKDM NaI
LIBRA
Where do we stand?
DAMA 3
CDMS
EDELWEISS
ZEPLIN I
~ 1 event/kg/day
Most advanced experiments
start to test the predicted
SUSY parameter space
One evidence for a positive
WIMP signal
Not confirmed by other
experiments
Predictions: Ellis, Baltz & Gondolo, Mandic & all
The DAMA/LIBRA experiment
LIBRA
At LNGS (3800 mwe)
9 x 9.7 kg low activity NaI crystals,
each viewed by 2 PMs
2 methods of backgrd discr:
PS; annual modulation
-> positive signal (4 )
What next?
update to LIBRA (250 kg)
improved backround (~few)
improved light yield
Installation completed;
analyze additional 3 yr
of DAMA data (finished Jan 02)
Day 1 = Jan 1, 1995
DAMA
The CDMS II experiment
At SUF (16 mwe) /Soudan (2030 mwe)
uses advanced athermal phonon (TES)
measuring charge and phonons
discrimination
position resolution
surface event rejection
neutrons
gammas
gamma source
neutron source
electrons
The CDMS II experiment
1 tower of 4 Ge and 2 Si ZIPs
operated at SUF 2001-2002; > 120 livedays
> 99.98 % rejection of bulk electron recoils: 5-100 keV
> 99 % rejection of surface events: 10-100 keV
n background x 2.3 lower due to inner poly (as expctd);
20 Ge recoil single scatters, 2 Si single scatters,
2 triple scatter, 1 nnn double scatter; consistent
with all single scatters caused by neutrons
FET cards
SQUID cards
first results submitted to PRL, hep-ex/0306001
Si
Ge
Ge
Ge
Ge
Si
Ge
Muon anticoincident background
Si
CDMS and DAMA
assumptions of standard halo,
standard WIMP interactions
predicted WIMP
modulation
CDMS results incompatible with
DAMA model-independent annualmodulation data (left) at > 99.8%
CL even if all low-energy events
were WIMPs
Best simultaneous fit to CDMS and
DAMA predicts too little annual
modulation in DAMA, too many
events in CDMS (even for no
neutron background)
predicted WIMP
spectrum alone
CDMS
data
neutron spectrum fit
The CDMS II experiment
first 2 towers at the Soudan mine (2030mwe)
m-flux reduced by 104, n-flux by ~ 300
first dark April 03!
goal: 5 towers, 4 kg Ge, 1.5 kg Si
0.1 events/kg/keV/yr
EDELWEISS
CDMS 03
SUSY gm-2
Baltz&Gondolo,
PRL 86 (2001) 5004
CDMS Soudan
No SUSY gm-2
Baltz&Gondolo,
PRL 86 (2001) 5004
CMSSM
Ellis et al. (2001)
PRD 63, 065016
entrance to the mine
The EDELWEISS experiment
In Frejus UL (4800 mwe); 320 g Ge crystals
measure thermal phonons + charge
EDELWEISS I: 1 kg stage
fall 2000, first semester 2002,
October 2002 - March 2003
total exposure:
13.8 kg  day @ Erec > 20 keV,
30.5 kg  day @ Erec > 30 keV
Incompatibility with DAMA candidate
(99.8% C.L.) confirmed with three different
detectors and extended exposure
G. Chardin 2003
The EDELWEISS experiment
New run started: improved energy threshold
≈100% detection efficiency at 10 keV ER
September 2003:
end EDELWEISS-I run
install EDELWEISS-II
21  320 g Ge-NTD detectors
7 thin film (NbSi) 200 g Ge detectors
Achieve factor 100 improvement
in sensitivity
100 l dilution
cryostat for up to
120 detectors (36 kg Ge)
The ZEPLIN I experiment
Operating at the Boulby mine (~3000 mwe)
Single phase, scintillation in LiXe, PSD
3.7 kg liquid Xe (3.1 kg fid vol)
1 ton liquid scintillator veto
75 d livetime, 230 kg d of data
1
1
Gamma source
0.1
0.01
0.01
10-20keV
0.001
0.001
0.0001
0.0001
0.00001
0.00001
0.1
Neutron source
0.1
1
10
100
1
10
100
pulse time constant ns
pulse time constant (ns)
data
0.01
gamma cal
Background:
40 dru @ 100keV implies
85Kr < 10-17 atoms/atom
(standard Xe used)
GD f it
0.001
0.0001
0.00001
1
10
fitted time constant ns
100
Fiducial
Volume
cut
The ZEPLIN experiment
ZEPLIN II at RAL, UK
ZEPLIN I
ER
Ionisation
Xe+
+Xe
Excitation
Xe2+
+e-
Xe*
Xe**+ Xe
+Xe
Xe2*
175nm
Triplet
27ns
2Xe
175nm
Singlet
3ns
2Xe
Future ZEPLIN I:
more data, low Kr Xenon
ZEPLIN II/III:
Ionization + scintillation, 2 phase Xe;
30 kg, 6kg high field
II: tested at RAL, UK, PMs being produced
to be installed at Boulby in 2003
The DRIFT experiment
Scattered
WIMP
In the Boulby mine (3000 mwe)
Resolve ionization tracks in a gas
TPC filled with low-pressure EN gas (CS2)
Endcap sense-planes: determination of range,
orientation & energy (via ionization)
e--capture by CS2 suppresses diffusion
during charge-drift
operates at ~40 torr , 140 g target mass
discrimination through dE/dx measrmnt
CS
Recoil
Atom
Electric
Field
Future: DRIFT-II
scaled-up DRIFT-I with full 3D readout
& x50 sensitivity
gamma
region
Gamma
Region
R&D: higher-resolution readout,
higher-pressure operation
cathode-readout of positive ions
allowing event localization away
from wire planes
2
Drift
direction
Cathode
Neutron Region
neutron
region
overlapRegion
Overlap
Rec
oil
Electro
n
MWPC
Readout
Plane
CS2
The ‘far’ future
1 event/kg d: EDELWEISS, CDMS, ZEPLIN
1 event/kg yr: CDMSII, CRESSTII, EDELWEISSII,
ZEPLINII
1 event/100 kg yr: future projects!
Predictions: Bottino, Ellis, Gondolo
1 ton is needed in order to detect
10 events per year at  = 10-46 cm2
The ‘far’ future
Project
Discrimin
Type
Mass
Location
CryoArray
Yes
Ge/Si
phonon/ioniz
1 ton
NUSEL
CRESST/
EDELWEISS
Yes
Ge, CaWO4?
phonon/ion/scint
100 kg - 1t
Gran Sasso?
Zeplin IV
Yes
LiXe ioniz/scint
2 phase
1 ton
Boulby
XENON
Yes
LiXe ioniz/scint
2 phase
1 ton
(10 x 100 kg)
NUSEL
DRIFT3
Yes + direction
TPC (CS2)
negative ion
100 kg
Boulby
GENIUS
No
Ge ionization in LiN
100 kg -1 ton
Gran Sasso
Majorana
No
Ge ionization
500 kg
NUSEL