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Searching for Lightly Ionizing Particles

This study focuses on the search for energetic Lightly Ionizing Particles (LIPs) produced by cosmogenic processes, with a low energy threshold. The aim is to find LIPs with a fractional charge less than 6e/q, providing an opportunity to discover previously unsearched particles.

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Searching for Lightly Ionizing Particles

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  1. Searching for Lightly Ionizing Particles

  2. 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 Perl, Lee, and Loomba, Annu. Rev. Nucl. Part. Sci. 59, 47 (2009). MACRO Collaboration (arXiv:hep-ex/042006)

  3. Searches for Lightly Ionizing Particles 7.6 cm 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! LIP Search Livetimes: T2: 59.6 days T4: 142.4 days

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

  5. LIP Topology: Background Reduction The topology requirement decreases the Compton background by about a factor of 105. Tower 2 Tower 4

  6. Track Linearity and Energy Consistency • Relativistic, Hits all Detectors – in STRAIGHT LINE • Relativistic, Hits all Detectors – in STRAIGHT LINE • Deposit Similar Energy LIPs SIGNAL NOT Signal • Plus, Basic criteria: • Detector OK • Signal >> Noise

  7. Expected LIP Energy Depositions The energy-deposition probability is given by: 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) 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).

  8. 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.

  9. 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:

  10. 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:

  11. Fit Compton Track Fit LIP Track 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 c2 fit to tracks. • LIPs pass straight, Backgrounds not! • Neighboring Surface events • provide detector-resolution Neighboring Surface Events Y-location (mm) X-location (mm)

  12. Combined LIP Background Rejection Tower 4: f = 1/15

  13. Combined CDMSII LIP Results Tower 4: f = 1/15 No candidates observed, so we set a limit.

  14. LIP Limits CDMS Collaboration (arXiv:1409.3270) No candidates observed, so we set a limit.

  15. 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 • LIPs energy deposition in detectors INDEPENDENT CDMSII LIP Mass (eV) LIP Fractional Charge, f

  16. 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. • LIPs energy deposition in detectors INDEPENDENT CDMSII 2.5keV threshold Note: I assumed a 3.3cm LIP path length in germanium.

  17. 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. • LIPs energy deposition in detectors INDEPENDENT 100eV threshold Note: I assumed a 3.3cm LIP path length in germanium.

  18. 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. • LIPs energy deposition in detectors INDEPENDENT 10eV threshold Note: I assumed a 3.3cm LIP path length in germanium.

  19. MINER LIP PDFs • The expected energy depositions in Ge/Si are similar. • Difference enables cross-checking of any potential signal. • LIPs energy deposition in detectors INDEPENDENT

  20. MINER Strategy Tower 4: f = 1/15 Energy Consistency powerful. More detectors = more power. Tracking less powerful and harder.

  21. MINER LIP Discovery Potential Sensitivity to MUCH smaller fractional charges! • LIPs energy deposition in detectors INDEPENDENT State livetime assumed.

  22. MINER LIP Discovery Potential • LIPs energy deposition in detectors INDEPENDENT CDMSII MINER LIP Mass (eV) LIP Fractional Charge, f

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