6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"1 Development of an Aerogel-based Photon Detector T. Nomura (Kyoto Univ.)

6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"2 Motivation, Challenge, and Solution A part of veto detector in rare K L experiment Aerogel-based photon detector Located in intense neutral beam

6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"3 Motivation Necessary in K L   0 measurement Importance of K L   0 CP violating process Branching ratio proportional to |Im(V td )| 2, BR~ Very small theoretical uncertainty (~1%)  Play an important role to explore BSM (like SUSY) Difficulty of K L   0 experiment All neutrals in initial and final states Event signature: 2  (from  0 )+ nothing (2 )  We have to prove “nothing” in order to suppress backgrounds: K L   0  0  0 ( BR 21% ),  0  +  - ( BR 13% ),  0  0 ( BR ), …

6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"4 “2  (from  0 )+ nothing” K L   0 Signature ： To prove “nothing”, we needs Hermetic veto system Need to catch photons escaping through the beam-hole What we want to develop !! Motivation           Main Photon Detector signal Background Escaping  through beam-hole veto Surrounding Veto

6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"5 Challenge “In-beam” environment High intensity neutral beam (necessary to observe >100 K L   events in 2-3 years) –A vast amount of neutrons (a few~10GHz)  Produce protons, pions, (  and e + /e - ) in the detector –Most K L s survive after decay region (~100MHz)  Decay into , ,e + /e - in the detector  These secondary particles fire the counter and disturb its primary function !!

6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"6 Solution Utilize Cherenkov radiation Aerogel (low refractive index ~1.05) radiator  Avoid detection of slow particles from neutron interactions Slow , p and other hadrons cannot emit lights. Use direction information Segment the detector into many modules and require coincidence along the beam direction  Catch forward photons only Reduce fake signal due to  from secondary  0 (neutron interaction and K L decay in the detector)

6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"7 γ e+e+ e-e- Design of In-Beam Photon Detector Module –Pb (  converter) & Aerogel (Cherenkov radiator) –Light collection with Flat mirror & Winston cone Sparse “sandwich” detector –modules’ array  red: e + /e -, blue: photon Example of  event (MC) Plan view Require coincidence along forward direction

6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"8 Proof of Principle (I) We’ve made three generations of prototypes Prototype 1 (2001-2) –Simple structure 11cm x 11cm tiles Flat mirror Read by 5-inch PMT –Exercise to use aerogel detector light yield PT1

6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"9 Proof of Principle (II) Prototype 2 (2002-3) –Sophisticated optics 11cm x 11cm tiles 2-axis parabolic mirror Read by 5-inch PMT light yield response to proton (as substitute for neutron) PT2

6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"10 What we learned from Prototype 2 Response to Proton (analogous to neutron’s) –Single module efficiency  Find N 2 gas scintillation (problematic in 1p.e. region) –Two layers’ coincidence  Good agreement with MC M1*(M2+M3+M4) thres. = 2pe

6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"11 Proof of Principle (III) Prototype 3 (2004-5) –Base design 30cm x 30cm area (3x3 of 10cm sq. aerogel tiles) Flat mirror Winston cone Read by 5-inch PMT light yield position / angular dependence PT3

6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"12 30cm 48cm 3 x-sectionals, jointed here Elements of Prototype 3 Elements –3x3 10cm sq tiles, stacked 5 layers –Winston cone made by thin Al Al+SiO 2 evaporated on inner surface 30cm Made by Yokohama-Kiko 45 Tiles made by Matsushita

6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"13 What we learned from Prototype 3 (i) Position dependence –Global structure, reproduced well by MC –Edge effect between tiles surface deterioration by trimming process (water jet) By Winston cone entrance (x=6cm) By tiles’ edge effect (x=5cm)

6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"14 What we learned from Prototype 3 (ii) Angular dependence –Global structure, reproduced well by MC –Winston cone deformed stressed by joint or support By cone deformation (  =5 deg) By cone’s acceptance (  =7 deg) Reflection angle measured by laser

6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"15 Practice in KEK E391a experiment E391a-III had run with this Prototype 3 called “APC” (Aerogel Photon Catcher)  Used as in-beam  tagger APC BA BA (Beam Anti) E391a in-beam detector PWO & Quartz sandwich

6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"16 Application To K L   0 experiment at JPARC To KOPIO experiment at BNL

6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"17 Signal 2  Barrel Veto Main (endcap) Photon Detector Planned K L   0 experiment at BNL (Construction 2006-, Run 2010-) –High intensity proton beam 100 TP/spill –Soft K L beam GeV/c –Horizontally wide beam 4mrad x 90mrad –Measure  direction as well as energy –Sensitivity: 40 SM events (S/N~2), or 200 SM events (S/N~0.3) KOPIO experiment Terminated (2005 August)

6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"18 KOPIO detector & Beam Catcher

6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"19 KOPIO In-beam Photon Detector In-beam Aerogel Detector Module size: 30cm x 30cm Module array –Number of modules: 420 –12-21 in horizontal with beam divergence –25 layers along beam (8.3 X 0 in total) –Z gap between layers: 35cm Top view 12m downstream of main detector Beam envelope

6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"20 Expected Performance by MC (1) Photon Efficiency 300MeV Photon efficiency –Soft K L in KOPIO  Relatively low energy   Relatively small shower  Low threshold Coincidence condition: 4 p.e in A, 2 p.e. in B In KOPIO case

6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"21 Expected Performance by MC (2) Hit probability for Neutrons 800MeV Hit probability for K L s Dominated by decays in the detector In KOPIO case

6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"22 K L   0 experiment plan at J-Parc –30GeV proton, 100 TP/spill –Small production angle, relatively hard K L beam –Pencil beam ( a few ~ 10 )  str, ~10cm  at the detector –Step 1 with (modified) KEK E391a detector  ~10 SM events, Discovery phase –Step 2 with new, optimized detector  Precision measurement, ~100 SM events Application to Experiment at J-Parc

6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"23 In-beam Detector for J-Parc experiment In contrast with KOPIO case –Pencil beam  A series of modules along beam direction –Relatively high energy  (neutrons)  Detection threshold can be (has to be) higher  3 consecutive hits, 4~24 p.e. 25 modules(8.3X 0 ), 35cm pitch  ~9m long Beam 30cmx30cm

6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"24 Expected Performance Neutron Hit probability –Level of 4.0GeV/c Photon efficiency –90% –99% –At high energy limit, inefficiency ~ O(10 -3 ) red: e + /e -, blue: photon Example of photon event (MC) Example of neutron event (MC) dot-chain: neutral hadron In J-Parc case

6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"25 Expected Performance In J-Parc case Inefficiency for Photon ~10% 1GeV ~1% 2GeV Hit probability for Neutrons O( GeV/c With various threshold

6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"26 Summary We’ve developed Aerogel-based Photon Detector to use in intense neutral beam –One of the key detectors in K L   0 experiment to explore physics beyond the SM –New concept Pb (converter) + Aerogel (Cherenkov radiator) Sparse “sandwich” detector –Proof-of-Principle done with 3 generations of prototypes Originally, it was designed for KOPIO experiment. Now, we are considering to use this detector at J-PARC

6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"27 Signal Loss due to False Hit Accidental hit due to neutrons may kill K   signal Total false hit probability was found ~ 0.4 events /  -bunch –Integrated over the duration consistent with the arrival time of  from our signal K L If we set the time window to be 3ns, signal loss due to false hit will be 4.6% –Calculation based on random effect –Detailed studies by MC under way Neutron rate False hit (rate x hit prob.) False hit rate due to neutron Apply timing cut… In KOPIO case

6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"28 Accidental hit due to neutrons (In case Step 1) –Integrate over neutron momentum  Enough low rate (~1MHz) even with lowest thres. False Hit Rate due to neutron (Step1) In J-Parc case Neutron rate False hit (rate x hit prob.) False hit rate due to neutron

6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"29 Accidental hit due to neutrons (In case Step 2)  Very high rate (~10MHz) even with highest thres. False Hit Rate due to neutron (Step2) In J-Parc case Neutron rate False hit (rate x hit prob.) False hit rate due to neutron

6-8 March, 2006T. Workshop on "Mass Origin and Supersymmetry Physics"30 To gain background rejection power  Prefer lower threshold To prevent acceptance loss due to false veto  Prefer high threshold Signal / Background (Step2) In J-Parc case