Transcript Slides

Searching for Lightly Ionizing
Particles
Searches for Lightly Ionizing Particles
The low energy threshold allows us to search for energetic Lightly
Ionizing Particles (LIPs) produced by cosmogenic processes.
Opportunity: no prior search for e/q < 6!
MACRO 2006
MACRO Collaboration (arXiv:hep-ex/042006)
Perl, Lee, and Loomba,
Annu. Rev. Nucl. Part. Sci. 59, 47 (2009).
Searches for Lightly Ionizing Particles
The low energy threshold allows us to search for energetic Lightly
Ionizing Particles (LIPs) produced by cosmogenic processes.
Opportunity: no prior search for e/q < 6!
7.6 cm
LIP Search Livetimes:
T2: 59.6 days
T4: 142.4 days
LIP Topology Requirement
Hits
all Detectors!
•Relativistic,
Energetic, Hits
all Detectors!
• Only 1 Tower Hit
Relativistic, Hits all Detectors – in STRAIGHT LINE
LIPs SIGNAL
Only 1 Tower Hit
Avoids Shower
LIPs SIGNAL
NOT signal
NOT Signal
LIP Topology: Background Reduction
The topology requirement decreases the Compton background
by about a factor of 105.
Tower 2
Tower 4
Track Linearity and Energy Consistency
Hitsallall
Detectors
in STRAIGHT
•Relativistic,
Relativistic, Hits
Detectors
– in–STRAIGHT
LINE LINE
• Deposit Similar Energy
LIPs SIGNAL
Plus, Basic criteria:
Detector OK
Signal >> Noise
NOT Signal
Expected LIP Energy Depositions
The energy-deposition probability is given by:
Where mc is the average number of collision, fn(E,v) is the nfold convolution of the single interaction spectrum, and E is
the energy deposited by a charged particle with velocity v.
Using Photo-Absorption-Ionization (PAI) model
A method to improve tracking and particle identification in TPCs and silicon detectors
Hans Bichsel (Nuclear Instruments and Methods in Physics Research A 562 (2006) 154–197).
Expected LIP Energy Depositions
The energy-deposition probability is then:
The idea: look for energy depositions consistent with a LIP with a
given fractional charge, f. Repeat for the next fractional charge, etc.
Energy Consistency
LIPs energy deposition in detectors INDEPENDENT
DF1
DF0
Define an energy consistency criteria, Ec,
that compares the expected “distance” in
cumulative probability vs that measured:
Energy Consistency
DF1 = 0
LIPs energy deposition in detectors INDEPENDENT
DF1
DF0
Define an energy consistency criteria, Ec,
that compares the expected “distance” in
cumulative probability vs that measured:
Track Linearity
Require the reconstructed event positions to be consistent with a linear track.
LIPs pass straight, Backgrounds not!
Estimate xy-position resolution using events with interactions on adjacent
detectors.
Neighboring Surface events
2 fit to tracks.
Perform
c
provide detector-resolution
Fit LIP
Track
Neighboring Surface Events
Y-location (mm)
Fit Compton
Track
X-location (mm)
Combined LIP Background Rejection
Tower 4: f = 1/15
Combined CDMSII LIP Results
Tower 4: f = 1/15
No candidates observed, so we set a limit.
LIP Limits
CDMS Collaboration (arXiv:1409.3270)
No candidates observed, so we set a limit.
Future LIP Searches - Strategy
Ways to improve upon the CDMSII LIP Search
LIPs energy deposition in detectors INDEPENDENT
• Increase the exposure (more towers, run longer)
• Improved detection efficiency for LIPs with small fractional
charges
CDMSII
An ultra-low threshold
A thicker detector
LIP Mass (eV)
-
LIP Fractional Charge, f
LIP Search – Threshold is Key
To get a feel for how small a value of f, we can probe, let’s consider
LIPs
energyenergy
deposition
in detectors
INDEPENDENT
the expected
probability
deposition
distribution.
CDMSII
2.5keV
threshold
Note: I assumed a 3.3cm LIP path length in germanium.
LIP Search – Threshold is Key
To get a feel for how small a value of f, we can probe, let’s consider
LIPs
energyenergy
deposition
in detectors
INDEPENDENT
the expected
probability
deposition
distribution.
100eV
threshold
Note: I assumed a 3.3cm LIP path length in germanium.
LIP Search – Threshold is Key
To get a feel for how small a value of f, we can probe, let’s consider
LIPs
energyenergy
deposition
in detectors
INDEPENDENT
the expected
probability
deposition
distribution.
10eV
threshold
Note: I assumed a 3.3cm LIP path length in germanium.
MINER LIP PDFs
• The expected energy depositions in Ge/Si are similar.
LIPs
energyenables
deposition
in detectors
INDEPENDENT
• Difference
cross-checking
of any
potential signal.
MINER Strategy
Tower 4: f = 1/15
Energy Consistency powerful. More detectors = more power.
Tracking less powerful and harder.
MINER LIP Discovery Potential
Sensitivity to MUCH smaller fractional charges!
LIPs energy deposition in detectors INDEPENDENT
State livetime assumed.
MINER LIP Discovery Potential
LIP Fractional Charge, f
CDMSII
MINER
LIP Mass (eV)
LIPs energy deposition in detectors INDEPENDENT