Muon Capture in Double Chooz Matthew Strait, on behalf of the Double Chooz collaboration University of Chicago 5 August 2015 Matthew Strait (University of Chicago) Muon Capture in Double Chooz 5 August 2015 1 / 18 Outline Introduction to Double Chooz Muon capture Search for βn isotopes produced by stopping muons Search for other isotopes produced by stopping muons Future prospects Matthew Strait (University of Chicago) Muon Capture in Double Chooz 5 August 2015 2 / 18 Double Chooz Location Double Chooz Site n Matthew Strait (University of Chicago) Muon Capture in Double Chooz 5 August 2015 3 / 18 Double Chooz Detectors Detectors Three-zone inner detector: Target, Gamma Catcher, Buffer . surrounded by an Inner Veto . and topped with an Outer Veto Matthew Strait (University of Chicago) Muon Capture in Double Chooz 5 August 2015 4 / 18 Double Chooz Neutrino Detection Reactor Neutrino Detection + Detectν ¯e via inverse beta decay:ν ¯e p ! e n Prompt positron (1{8 MeV) Delayed neutron capture on Gd (8 MeV) or H (2.2 MeV) Matthew Strait (University of Chicago) Muon Capture in Double Chooz 5 August 2015 5 / 18 Muon-induced Backgrounds Muon-induced Backgrounds 13 Hz of muons through the Target and Gamma Catcher Produce backgrounds, including 9Li βn decay Same signature asν ¯e We veto most 9Li using: Number of neutrons following µ Distance from muon to candidate Analysis assumes through-going muons. What about stopping muons? Look for correlation in time and space between stopping muons and 9Li-like events Matthew Strait (University of Chicago) Muon Capture in Double Chooz 5 August 2015 6 / 18 Stopping Muons Muon Capture Physics A stopped µ− quickly cascades to the 1s atomic orbital, then: High Z, µ− usually captures Low Z, usually decays: capture probability 7.7% for carbon In compounds, no general rule for how much each element captures µ− converts proton to neutron Hydrogen a special case: pµ neutral Often this neutron recoils enough to escape Muon gets picked off by Remaining nucleus may de-excite through γ, heavier elements n, p, deuteron, α, etc. emission So hydrocarbons can be Typically 15{20 MeV is transferred to the considered pure carbon nucleus, remaining to ν Matthew Strait (University of Chicago) Muon Capture in Double Chooz 5 August 2015 7 / 18 Stopping Muons Possible Signals In principle, signal can be as much as a seven-fold coincidence: 1 Muon track 2 Muonic x-rays: 1 ns after stop (buried in track's light) 3 Capture nuclear recoil: ∼2 µs after atomic cascade (severely quenched) 4 γ/charged particles from nuclear de-excitation: usually 1 ns after capture Gammas sometimes visible: low efficiency Protons/d/α/etc. severely quenched 5 Capture of neutrons from nuclear de-excitation: 10{100 µs after µ capture 6 β or βn decay of daughter nucleus: 10 ms{10 s after µ capture 7 Capture of neutron from βn decay: 10{100 µs after βn decay Matthew Strait (University of Chicago) Muon Capture in Double Chooz 5 August 2015 8 / 18 Analysis Stopping Muon βn Selection βn Selected Events Select βn events using pre-existing inverse beta decay analysis Require distance to stopped muon < 300 mm Possible due to high-precision muon reconstruction (NIM A764:330{339, 2014) Efficiency determined using common reaction 12C µ− ! 12B ν Double Chooz Preliminary 103 12B Background 102 10 Events/50mm 1 0 1 2 3 4 5 µ-12B distance (m) 12B production probability known to 4% (Phys.Rev, 133:B663{B675, 1964) So 12B also used to normalize capturing µ− rate ) 1:8 × 105 captures on 12C in 490 days of livetime Matthew Strait (University of Chicago) Muon Capture in Double Chooz 5 August 2015 9 / 18 Analysis Beta-n Decays Selection of βn Decays Clear excess associated with stopping muons in space and time 16 16 Double Chooz Preliminary 14 Signal 14 12 Background 12 10 10 8 8 Events/bin 6 Events/0.2s 6 4 4 2 2 0 0 0 0.1 0.2 0.3 0.4 0.5 0 0.5 1 1.5 2 2.5 3 50 100 ∆r3 (109 mm3) Time since stopping muon (s) < 0:4 s after a stopping muon < 300 mm from a stopping muon Flat background =ν ¯e events Not enough to contribute significantly toν ¯e background, but still interesting 9 What is it? Lifetime looks long for Li (t1=2 = 178:3 ms). Matthew Strait (University of Chicago) Muon Capture in Double Chooz 5 August 2015 10 / 18 Analysis Beta-n Decays How Much 9Li? Turns out there are many possible βn isotopes given 12;13C and 16;17;18O 400 kg of oxygen in acrylic vessels plus a bit more in scintillator βn isotopes Half-lives range from 8.75 ms (11Li) to 4.2 s (17N) Simultaneously fit ∆t distribution for all using an unbinned likelihood Matthew Strait (University of Chicago) Muon Capture in Double Chooz 5 August 2015 11 / 18 Analysis Beta-n Decays Fit Results Same plot as before: Zoomed in: 16 Double Chooz Preliminary Double Chooz Preliminary 10 14 Data Data, no neutrons 12 Fit with 1σ error 8 Fit with 1σ error 10 6 8 Events/0.2s 6 Events/0.05s 4 4 2 2 0 0 0 0.5 1 1.5 2 2.5 3 50 100 0 0.1 0.2 0.3 0.4 0.5 Time since stopping muon (s) Time since stopping muon (s) Overall βn significance 5.0σ 2.9σ evidence of 8He (119 ms) and/or 9Li (178 ms) 8 9 +0:9 −4 No power to separate He/ Li. Probability/capture: (2:4−0:8 ± 0:1) × 10 No evidence of shorter-lived isotopes Long-lived isotopes included as nuisance parameters with pull terms Data does not significantly move their input values. Matthew Strait (University of Chicago) Muon Capture in Double Chooz 5 August 2015 12 / 18 Analysis Beta-n Decays 9Li with a Neutron Originally reasoned that 9Li should be produced with a neutron Requiring a neutron capture dramatically reduces the background Post-muon neutron efficiency is 75%, so expect about 10 9Li events 16 Double Chooz Preliminary 14 Data, 1 neutron 12 Fit with 1σ error 10 8 Events/s 6 4 2 0 0 0.5 1 1.5 2 2.5 3 50 100 Time since stopping muon (s) Instead find about2 (consistent with zero) Plus a longer-lived component, probably 17N Matthew Strait (University of Chicago) Muon Capture in Double Chooz 5 August 2015 13 / 18 Analysis Beta-n Decays 9Li from 13C What happened? 13C(µ−; να)9Li In retrospect, more reasonable than 12C(µ−; ν p n)9Li 13 +0:9 So probability/capture on C: (2:4−0:8 ± 0:2)% Interpretation is not definitive, but is in line with other measured isotopes: Isotope P(µ−; να) 12C 0:59 ± 0:05% Later in this talk 13C2 :4 ± 0:9 % 23Na 1:10 ± 0:15% Nucl.Phys.A 294 (1978) 278 27Al 0:76 ± 0:11% Nucl.Phys.A 294 (1978) 278 Matthew Strait (University of Chicago) Muon Capture in Double Chooz 5 August 2015 14 / 18 Analysis Plain Beta Isotopes Other Isotopes: 8Li With this analysis framework, it is easy to extract other results These are only mildly interesting as ν backgrounds, more so as nuclear physics Double Chooz Preliminary 250 Data, 0 neutrons 200 Fit with 1σ error 150 8 Events/0.5s 100 Li 12B 16N 50 0 2 4 6 8 10 12 14 Time since stopping muon (s) Flat background is accidental single events 12C(µ−; να)8Li probability: (0:59 ± 0:04 ± 0:03)% Never before measured, as far as I can tell In fact, not much at all measured in carbon Inconvenient for beam experiments. Low capture rate means backgrounds in small detectors are a serious problem. Matthew Strait (University of Chicago) Muon Capture in Double Chooz 5 August 2015 15 / 18 Analysis Plain Beta Isotopes Long-lived Isotopes: 15C, 16N, 11Be Half-lives of 2.4 s, 7.1 s and 13.8 s Major uncorrelated background: 12C(n,p)12B caused by through-going muons Reduced 40% using likelihood analysis, adapting method used for 9Li 16O(µ−; ν)16N probability already measured (11 ± 1%). Used as input. Solid line is fit with only 16N. No evidence for 15C or 11Be. Double Chooz Preliminary Double Chooz Preliminary 140 0.4 Data Best fit Fit without 11Be, 15C 120 0.3 68% CL Fit with 11Be, 15C Be (%) 11 90% CL 100 0.2 Events/4s 80 0.1 60 Probability of 8Li 40 0 10 20 30 40 50 60 70 80 90 100 0 2 4 6 8 10 12 14 16 Time since stopping muon (s) Probability of 15C (%) Matthew Strait (University of Chicago) Muon Capture in Double Chooz 5 August 2015 16 / 18 Conclusions Results Table { Preliminary Parent Daughters Probability/capture 12C 6He, 0nX < 0:45% 12C 6He, 1nX < 0:49% 12C 6He, 2nX < 0:08% 12C 6He, 3nX < 0:09% 12C 8B, 4n < 3:4 × 10−5 12C 8Li, α (0:59 ± 0:04(stat) ± 0:03(syst))% 12C 11Be, p < 0:23% natC 8He, X < 7 × 10−4 nat 9 +0:9 −4 C Li, X (2:4−0:8(stat) ± 0:1(syst)) × 10 13 8 +1:1 C Li, nα (5:3−1:0(stat) ± 0:4(syst))% 13 9 +0:9 C Li, α (2:4−0:8(stat) ± 0:2(syst))% 13C 11Li, 2p < 0:6% 13C 12Be, p < 0:24% 13C 12B, n (47 ± 2(stat) ± 4(syst))% 13C 13B < 75% 14N 9C, 5n < 3:7% 16O 14B, 2p < 0:44% 16O 9C, p6n < 0:10% 16O 15C, p < 9% 16O 12N, 4n < 9 × 10−4 Matthew Strait (University of Chicago) Muon Capture in Double Chooz 5 August 2015 17 / 18 Conclusions Conclusions Discovered βn-isotope (probably 9Li) production by stopping µ− Many other reactions with no previous data also investigated Results useful for: Understanding neutrino backgrounds Tests of nuclear models Analysis improvements in the pipeline: Use new measurements of our 13C fraction Decouple from 1964 12B analysis Analysis of gamma lines from 12B excited states Paper in preparation Double Chooz near detector, now online, will collect stopping muons at 20× the rate of the far detector Matthew Strait (University of Chicago) Muon Capture in Double Chooz 5 August 2015 18 / 18 Backup Backups Matthew Strait (University of Chicago) Muon Capture in Double Chooz 5 August 2015 19 / 18 Backup Comparison of Experiments Reactor Inner Scint Overburden PMTs/ Power Mass (m.w.e.) detector 140 near Double Chooz 8.4 GWth 2 × 27 t 300 far 390 120 near RENO 16.4 GWth 2 × 30 t 450 far 354 250 near 192 + Daya Bay 17.4 GWth 8