meg ii development of calibration methods for meg ii positron … · 2017. 9. 15. · for meg ii...

JPS Autumn Meeting 2017 (13aU33-1) MITSUTAKA NAKAO I Page: 1/20

MEG II��

Development of calibration methods for MEG II positron timing counter

Mitsutaka Nakao(The University of Tokyo)

On behalf of MEG II Collaboration


l Inter-generational mixing have not been observed only for charged lepton sector.

l Too small branching ratio is predicted in the framework of the standard model + neutrino mass.

Charged Lepton Flavour Violation

νe νμ ντ

e μ τ

d s bu c t

MEG� �

The discovery of cLFV is clear evidence for new physics

l Beyond the standard model (SUSY GUT etc) predicts that charged lepton should also mix at experimentally observable rate: O(10-11)�O(10-15)

Ⅰ Ⅱ ⅢQuark

Charged Lepton

Neutrino

Intro


MEG II Experimentl Signal (e+, γ)Ø Simultaneously emittedØ back-to-backØ same energy

µ+e+

γ

l Search for cLFV (μ+→e+γ) with unprecedented sensitivity: 4 x 10-14

Ø x10 improvement from MEG (4.2 x 10-13, 2016)

l Improve every resolution by factor 2

l All detectors will be readyin 2018

At Paul Scherrer Institutin SwitzerlandIntro


MEG II DetectorLiquid Xenon Gamma-ray Detector

Cylindrical Drift Chamber

RadiativeDecayCounter

µ+e+

γ

At Paul Scherrer Institutin Switzerland

-13aU33-1 (Lt)-13aU33-2 (nP£)-14aS36-7 (Lt)

-13aU33-3 (|�)-13aU33-7 (qj)-13aU33-9 (su)-13aU33-10 (��)

-14pS35-8 (qj)

Intro


pTC Status: Ready for Installation

Summer students from Kyusyu Univ.

Summer studentfrom KEK.

INFN Genova/Pavia

l We have completed our detector and ready for installation into experimental site.

pTC


pTC (1): Concept

Intrinsic resolution:70�80 ps

Stochastic term

Multiple scattering:~4 ps at 9 hits

Key Conceptl Improve time resolution by averaging the signal time of multiple hits.

l The total time resolution is expected to improve with and ~ 35 ps can be achieved at 9 hits.

z

φ

μ+ beam

Stopping Target

53 MeV e+(helical trajectory)

512 pixels

Constant term

2 4 6 8 10 12 14 16 18 200

0.02

0.04

0.06

0.08

0.1

0.12

l Averaged hit multiplicity for signal e+s: 9 (MC)

Number of hit pixels

Prob

abili

ty

Mean: 9

Nhit Nhit

pTC


pTC (2): Pixell Upstream (256 pixels) + Downstream (256 pixels)= 512 pixels

l Fast plastic scintillator (BC422, 40 (50) x 120 x 5 mm3)

l Readout by 6 SiPMs* with series connection (in total 6144 SiPMs) at each of both sides.

l Time calibration accuracy among pixels: < 30 ps

120 mm

Reflector (ESR2)

120 mm

50 mm6 SiPMs

…

6SiPMs…

40 mm

Optical fiber for laser calibration

*AdvanSiD, ASD-NUV3S-P High-Gain, 3x3 mm2, 50x50 μm2, Vbreakdown ~ 24 V

pTC


Time Calibrationl We have to know time offset of all 512 counters with the accuracy of 30 ps.l Radiative Muon Decay(μ→eγνν) is used for absolute calibration for relative

timing b/w e+ and gamma.l We have two complementary methods to calibrate time offset b/w

counters: laser-based method and track-based method.

pTC (3): Time CalibrationpTC


Time Calibrationl We have to know time offset of all 512 counters with the accuracy of 30 ps.l Radiative Muon Decay(μ→eγνν) is used for absolute calibration for relative

timing b/w e+ and gamma.l We have two complementary methods to calibrate time offset b/w

counters: laser-based method and track-based method.

What we did so farl We performed beam test using ¼ of pTC under the MEG II beam.l We checked the consistency b/w 2 calibration methods under a limited

situation:Ø Laser-based method: laser system was installed into 40 counters.Ø Track-based method: w/o Drift Chamber.

Purpose of This Studyl Laser-based method: extend to full laser system.l Track-based method: develop w/ Drift Chamber.

Purpose of This Study

JPS Autumn Meeting 2017 (13aU33-1) MITSUTAKA NAKAO I Page:10/20

Laser-based Method: Concept

Light switch

×8ch

HHH

Laser Controller

� �

Long Fiber10m

×8ch×8ch

Photodiodefor power monitor

Waveform DigitizerLASER Mode

ScramblerLight

Splitter

Light Splitter

1×8

Light Splitter

1×8

l PLP-10 (Hamamatsu) is used as a lightsource.

Fiber 2.5m

l Pulse laser is divided into each pixel simultaneously.

l Time offset of each pixel is measured relative to laser-synchronized pulse.

l Calibration accuracy is estimated as 24 ps by testing all parts of laser calibration system.(cited from Hamamatsu HP)

-Wavelength 405 nm-Wavelength FWHM < 10 nm

-Pulse duration typ. (max) 60 (100) ps

Synchronized pulse

Pixel

Laser


Laser Hut (Cavern) Detector Hut

Laser Box

Splitter Box

Splitter1×8

Splitter1×8

pTC (DS)

Test Installation (1)

Splitter1×2

Laser Head

Mode Scrambler

x 410 m fiber*4 in a tube

x 32

Laser Controller

Photodiode

OpticalSwitch

- By hand (now)->Optical Switch

Laser Sync.

WaveDAQ

Power Supply 24V

Laser


Test Installation (2)

Splitter Box

Splitter1×8

Splitter1×8

pTC (DS)

x 4 x 32

Laser


Status & Event Display

in 2017

l DS was checked using laser system.

l Dead/bad channels were fixed.

l Long/detail performance check from Nov. 2017.

in 2016

l A part of DS system was tested under the μ beam.

l Consistency w/ track-based calibration was checked.

Laser


Track-based Method: Conceptl Positron tracks from Michel decay (μ+→e+νν ) are used for calibration.

1. Calculate TOF values b/w adjacent counters.2. Define χ2 as the difference b/w measured time and expected time.3. Minimize χ2 using Millepede II.4. Find ΔTj.

Millepede II www.desy.de/~kleinwrt/MP2A software provided by DESY to solve the linear squares problems, such as detector alignment and calibration based on track fits.

�2 =NevX

i

NhitX

j

((Tij � (T0i + TOFij +�Tj) /�))2

Measured timeExpected time

Time offset of each pixel:What we want to know

Track


MC Setupl Generated from µ+ beam mixed at 7x107.l Time offset was set by randomly (:=Gaus(0, 100 ps)).l Evaluate the performance with the difference b/w calculated time offset

and original time offset.l Number of events: 260k.

Event Selection

Setup and Event SelectionTrack

Hit reconstruction

Clustering Matching

Drift Chamber

Propagating TOF Estimation

TOF cut (tail rejection)

• selection is not applied here in this study.

• there is room for improvements

Used for calibration

first 5 hits in a cluster which has more than 7 hits are used.


16− 14− 12− 10− 8− 6− 4− 2− 080−

60−

40−

20−

0

20

40

60

80

511 495 479 463 447 431 415 399 383 367 351 335 319 303 287 271511 495 479 463 447 431 415 399 383 367 351 335 319 303 287 271510 494 478 462 446 430 414 398 382 366 350 334 318 302 286 270

510 494 478 462 446 430 414 398 382 366 350 334 318 302 286 270509 493 477 461 445 429 413 397 381 365 349 333 317 301 285 269

509 493 477 461 445 429 413 397 381 365 349 333 317 301 285 269508 492 476 460 444 428 412 396 380 364 348 332 316 300 284 268

508 492 476 460 444 428 412 396 380 364 348 332 316 300 284 268507 491 475 459 443 427 411 395 379 363 347 331 315 299 283 267

507 491 475 459 443 427 411 395 379 363 347 331 315 299 283 267506 490 474 458 442 426 410 394 378 362 346 330 314 298 282 266

506 490 474 458 442 426 410 394 378 362 346 330 314 298 282 266505 489 473 457 441 425 409 393 377 361 345 329 313 297 281 265

505 489 473 457 441 425 409 393 377 361 345 329 313 297 281 265504 488 472 456 440 424 408 392 376 360 344 328 312 296 280 264

504 488 472 456 440 424 408 392 376 360 344 328 312 296 280 264503 487 471 455 439 423 407 391 375 359 343 327 311 295 279 263

503 487 471 455 439 423 407 391 375 359 343 327 311 295 279 263502 486 470 454 438 422 406 390 374 358 342 326 310 294 278 262

502 486 470 454 438 422 406 390 374 358 342 326 310 294 278 262501 485 469 453 437 421 405 389 373 357 341 325 309 293 277 261

501 485 469 453 437 421 405 389 373 357 341 325 309 293 277 261500 484 468 452 436 420 404 388 372 356 340 324 308 292 276 260

500 484 468 452 436 420 404 388 372 356 340 324 308 292 276 260499 483 467 451 435 419 403 387 371 355 339 323 307 291 275 259

499 483 467 451 435 419 403 387 371 355 339 323 307 291 275 259498 482 466 450 434 418 402 386 370 354 338 322 306 290 274 258

498 482 466 450 434 418 402 386 370 354 338 322 306 290 274 258497 481 465 449 433 417 401 385 369 353 337 321 305 289 273 257

497 481 465 449 433 417 401 385 369 353 337 321 305 289 273 257496 480 464 448 432 416 400 384 368 352 336 320 304 288 272 256

496 480 464 448 432 416 400 384 368 352 336 320 304 288 272 256

US

0 2 4 6 8 10 12 14 1680−

60−

40−

20−

0

20

40

60

80

15 31 47 63 79 95 111 127 143 159 175 191 207 223 239 25515 31 47 63 79 95 111 127 143 159 175 191 207 223 239 255

14 30 46 62 78 94 110 126 142 158 174 190 206 222 238 25414 30 46 62 78 94 110 126 142 158 174 190 206 222 238 254

13 29 45 61 77 93 109 125 141 157 173 189 205 221 237 25313 29 45 61 77 93 109 125 141 157 173 189 205 221 237 253

12 28 44 60 76 92 108 124 140 156 172 188 204 220 236 25212 28 44 60 76 92 108 124 140 156 172 188 204 220 236 252

11 27 43 59 75 91 107 123 139 155 171 187 203 219 235 25111 27 43 59 75 91 107 123 139 155 171 187 203 219 235 251

10 26 42 58 74 90 106 122 138 154 170 186 202 218 234 25010 26 42 58 74 90 106 122 138 154 170 186 202 218 234 250

9 25 41 57 73 89 105 121 137 153 169 185 201 217 233 2499 25 41 57 73 89 105 121 137 153 169 185 201 217 233 249

8 24 40 56 72 88 104 120 136 152 168 184 200 216 232 2488 24 40 56 72 88 104 120 136 152 168 184 200 216 232 248

7 23 39 55 71 87 103 119 135 151 167 183 199 215 231 2477 23 39 55 71 87 103 119 135 151 167 183 199 215 231 247

6 22 38 54 70 86 102 118 134 150 166 182 198 214 230 2466 22 38 54 70 86 102 118 134 150 166 182 198 214 230 246

5 21 37 53 69 85 101 117 133 149 165 181 197 213 229 2455 21 37 53 69 85 101 117 133 149 165 181 197 213 229 245

4 20 36 52 68 84 100 116 132 148 164 180 196 212 228 2444 20 36 52 68 84 100 116 132 148 164 180 196 212 228 244

3 19 35 51 67 83 99 115 131 147 163 179 195 211 227 2433 19 35 51 67 83 99 115 131 147 163 179 195 211 227 243

2 18 34 50 66 82 98 114 130 146 162 178 194 210 226 2422 18 34 50 66 82 98 114 130 146 162 178 194 210 226 242

1 17 33 49 65 81 97 113 129 145 161 177 193 209 225 2411 17 33 49 65 81 97 113 129 145 161 177 193 209 225 24116 32 48 64 80 96 112 128 144 160 176 192 208 224 24016 32 48 64 80 96 112 128 144 160 176 192 208 224 240

DS

PositionID0 100 200 300 400 500

[ps]

100−

80−

60−

40−

20−

020406080100

calculated Toffset - true Toffset

l First results w/ Drift Chamber.

l Bias depending on counter position was observed.Ø TOF calculation in propagation.Ø Position dependence of statistics.

l Accuracy of < ~22 ps was achieved.Ø Needs further improvements.

Results

Downstream: σ~20 ps Upstream: σ~22 ps

0

25515

240496

271511

256

phi

z

e+ track

↓Calculated time offset – true time offset / ↑its position dependence

Track

~70 ps


Prospects

2017

2018

l Pilot Run 2017Ø pixelated Timing Counter, Liquid Xenon Gamma-ray

Detector, Radiative Decay Counter will be installed.Ø ~7 weeks of combined detector DAQ is planned under

the MEG II environment.Ø Laser-based and track-based calibration will be applied

for full pTC.Ø Performance check of full pTC using μ beam is planned.

l Installation of all detectorsØ Maintenance after Pilot Run 2017.Ø Including Drift Chamber.

l Engineering RunØ 6 months of performance data-taking.Ø This run may evolve into physics run if things get ready.Ø Inter-detector calibrations.

l Physics RunØ Start searching for μ+→e+γ with unprecedented sensitivity.

Nov.

Jul.

Key months


Consistency Check b/w 2 Methods

2017

2018



the MEG II environment.Ø Laser-based and tracked-based calibration will be

applied for full pTC.Ø Performance check of full pTC using μ beam is planned.




Nov.

Jul.

Key months


Prospects

2017

2018



the MEG II environment.Ø Laser-based and track-based calibration will be applied

for full pTC.Ø Performance check of full pTC using μ beam is planned.




Nov.

Jul.

Key months


l We have developed and constructed 2 complementary methods for time calibration.

l Laser-based method:Ø extended to full laser system.Ø ready for long-term and detail performance check from Nov. 2017.

l Track-based method:Ø first results w/ Drift Chamber was presented.Ø accuracy of 22 ps was achieved, but have some bias.Ø it needs improvements at each step of analysis chain.

l Beam test w/pTC, LXe and RDC is planned from Nov. 2017 (Pilot Run 2017).

Summary

meg ii development of calibration methods for meg ii positron … · 2017. 9. 15. · for meg ii...

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