searching for lightly ionizing particles. searches for lightly ionizing particles the low energy...
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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.
MACRO Collaboration (arXiv:hep-ex/042006)
MACRO 2006
Opportunity: no prior search for e/q < 6!
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.
7.6 cm
Opportunity: no prior search for e/q < 6!
LIP Search Livetimes:T2: 59.6 daysT4: 142.4 days
Relativistic, Hits all Detectors!
Relativistic, Hits all Detectors – in STRAIGHT LINE
LIPs SIGNAL NOT Signal
• Energetic, Hits all Detectors!
Only 1 Tower HitAvoids Shower
LIPs SIGNAL
NOT signal
• Only 1 Tower Hit
LIP Topology Requirement
The topology requirement decreases the Compton background by about a factor of 105.
LIP Topology: Background Reduction
Tower 2Tower 4
Relativistic, Hits all Detectors – in STRAIGHT LINE
LIPs SIGNAL NOT Signal
• Relativistic, Hits all Detectors – in STRAIGHT LINE
Plus, Basic criteria:Detector OKSignal >> Noise
• Deposit Similar Energy
Track Linearity and Energy Consistency
The energy-deposition probability is given by:
Expected LIP Energy Depositions
Where mc is the average number of collision, fn(E,v) is the n-fold convolution of the single interaction spectrum, and E is the energy deposited by a charged particle with velocity v.
Using Photo-Absorption-Ionization (PAI) modelA method to improve tracking and particle identification in TPCs and silicon detectorsHans Bichsel (Nuclear Instruments and Methods in Physics Research A 562 (2006) 154–197).
The idea: look for energy depositions consistent with a LIP with a given fractional charge, f. Repeat for the next fractional charge, etc.
Expected LIP Energy Depositions
The energy-deposition probability is then:
LIPs energy deposition in detectors INDEPENDENT
Energy Consistency
Define an energy consistency criteria, Ec, that compares the expected “distance” in cumulative probability vs that measured:
F1
F0
LIPs energy deposition in detectors INDEPENDENT
Energy Consistency
Define an energy consistency criteria, Ec, that compares the expected “distance” in cumulative probability vs that measured:
F1
F0
F1 = 0
Neighboring Surface events provide detector-resolution
LIPs pass straight, Backgrounds not!
X-location (mm)
Y-l
oca
tion
(m
m)
Neighboring Surface Events
Track Linearity
Require the reconstructed event positions to be consistent with a linear track.
Estimate xy-position resolution using events with interactions on adjacent detectors.
Perform 2 fit to tracks.
Fit LIPTrack
Fit ComptonTrack
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
No candidates observed, so we set a limit.
CDMS Collaboration (arXiv:1409.3270)
LIPs energy deposition in detectors INDEPENDENT
Future LIP Searches - Strategy
Ways to improve upon the CDMSII LIP Search
•Increase the exposure (more towers, run longer)•Improved detection efficiency for LIPs with small fractional charges
- An ultra-low threshold- A thicker detector
LIP
Mas
s (e
V)
LIP Fractional Charge, f
CDMSII
LIPs energy deposition in detectors INDEPENDENT
LIP Search – Threshold is Key
To get a feel for how small a value of f, we can probe, let’s consider the expected energy probability deposition distribution.
Note: I assumed a 3.3cm LIP path length in germanium.
CDMSII2.5keVthreshold
LIPs energy deposition in detectors INDEPENDENT
LIP Search – Threshold is Key
To get a feel for how small a value of f, we can probe, let’s consider the expected energy probability deposition distribution.
Note: I assumed a 3.3cm LIP path length in germanium.
100eVthreshold
LIPs energy deposition in detectors INDEPENDENT
LIP Search – Threshold is Key
To get a feel for how small a value of f, we can probe, let’s consider the expected energy probability deposition distribution.
Note: I assumed a 3.3cm LIP path length in germanium.
10eVthreshold
LIPs energy deposition in detectors INDEPENDENT
MINER LIP PDFs
• The expected energy depositions in Ge/Si are similar.• Difference enables 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.
LIPs energy deposition in detectors INDEPENDENT
MINER LIP Discovery Potential
Sensitivity to MUCH smaller fractional charges!
State livetime assumed.
LIPs energy deposition in detectors INDEPENDENT
MINER LIP Discovery Potential
LIP
Mas
s (e
V)
LIP Fractional Charge, f
MINER
CDMSII
