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 days T4: days

 Relativistic, Hits all Detectors!  Relativistic, Hits all Detectors – in STRAIGHT LINE LIPs SIGNALNOT Signal Energetic, Hits all Detectors!  Only 1 Tower Hit  Avoids Shower LIPs SIGNAL NOT signal Only 1 Tower Hit LIP Topology Requirement

The topology requirement decreases the Compton background by about a factor of LIP Topology: Background Reduction Tower 2 Tower 4

 Relativistic, Hits all Detectors – in STRAIGHT LINE LIPs SIGNALNOT Signal Relativistic, Hits all Detectors – in STRAIGHT LINE  Plus, Basic criteria:  Detector OK  Signal >> Noise Deposit Similar Energy Track Linearity and Energy Consistency

The energy-deposition probability is given by: Expected LIP Energy Depositions Where m c is the average number of collision, f n (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) 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).

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 SIGNAL BACKGROUND Energy Consistency Define an energy consistency criteria, E c, that compares the expected “distance” in cumulative probability vs that measured: F1F1 F0F0

 LIPs energy deposition in detectors INDEPENDENT Energy Consistency Define an energy consistency criteria, E c, that compares the expected “distance” in cumulative probability vs that measured: F1F1 F0F0

 LIPs energy deposition in detectors INDEPENDENT Energy Consistency Define an energy consistency criteria, E c, that compares the expected “distance” in cumulative probability vs that measured: F1F1 F0F0

 LIPs energy deposition in detectors INDEPENDENT Energy Consistency Define an energy consistency criteria, E c, that compares the expected “distance” in cumulative probability vs that measured: F1F1 F0F0  F 1 = 0

 Neighboring Surface events provide detector-resolution  LIPs pass straight, Backgrounds not! X-location (mm) Y-location (mm) 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 LIP Track Fit Compton Track

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: )

 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 Mass (eV) LIP Fractional Charge, f CDMSII

 LIPs energy deposition in detectors INDEPENDENT Future LIP Searches – Number of Interactions To get a feel for how small a value of f, we can probe, let’s consider the expected number of LIP interactions in 3.3cm of Ge.

 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. CDMSII 2.5keV threshold

 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. 100eV threshold

 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. 10eV threshold

 LIPs energy deposition in detectors INDEPENDENT LIP Search – Threshold is Key Universal PDF for small f, so “some” sensitivity to even the smallest LIP! Note: I assumed a 3.3cm LIP path length in germanium.

 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 Mass (eV) LIP Fractional Charge, f MINERCDMSII