Overview of SPring-8 Beam Test Manabu MORITSU ( Osaka University ) 11 Sep., 2015 COMET Collaboration Meeting 17 Paris, France 1 COMET-CDC

Preface 2 This is the first talk of a series of reports on the SPring-8 beam test. I will talk about an overview of the beam test. Analysis status is reported by the following speaker, Sam.

Purpose of the experiment 3 Purpose of the test experiment is to study gas mixtures for COMET-CDC.

Gas parameters 4 For the 100-MeV electrons, multiple scattering is more important than spatial resolution. Low-density gas is better.  He:iC 4 H 10 (=90:10) was the base design so far. Based on the simulation result #, sensitivity is not so different.  It is worth revisiting other gas selections. (Belle/Belle-II)(KLOE) # CM16 talk by H. Sakamoto [Ref.] CM16 talk by MM

Prototype-4 chamber The prototype-4, partial copy of the real CDC, was constructed to demonstrate the performance in the real situation. – 7 sense layers + 2 guard layers – ~±4 deg tilted layer by layer – Sense wire =  25 um, Field wire =  126 um 5

Beam test campaign at SPring-8 6 July 8—12th, 2015 SPring-8: Largest synchrotron radiation facility with 8-GeV electron storage ring LEPS: Leaser Electron Photon Experiment at Spring-8 MEMBERS: N.T. Hoai 1, Y. Kuno 1, M. Moritsu 1, Y. Nakazawa 1, M. Okada 1, H. Sakamoto 1, A. Sato 1, M.L. Wong 1, T.S. Wong 1, C. Wu 2,3, T. Yamane 1, H. Yoshida 1, J. Zhang 2* 1 Osaka Univ., Japan, 2 IHEP, China, 3 Nanjing Univ. China * remote help Hyogo, Japan Spring-8

e+e+ e-e- Convertor (Pb) DC P4 Drift chamber (Prototype-4) Scintillator (S2) (S1) Setup of the experiment < 3.0 GeV 100—200 kHz

Setup of beam test e - beam ~530 mm

9 e - beam RECBE x 2 Setup of beam test

Noise & signal check 10 He:C2H6 (50:50) 2300 V He:iC4H10 (90:10) 1800 V Cosmic ray signal He:CH4 (80:20) 2000 V Noise level < 10 mV Cosmic ray signal

RECBE Experimental area Counting area Protorype-4 chamber Scintillator S1 Scintillator S2 PMT RECBE DAQ NIM Logic Power supply LEPS TRG (Start timing) Trigger HV Gas Data Data acquisition 11 Data were acquired by using our independent system controlled by DAQ-middleware. FCT-GRIB system was not used in this exp.

Measurement Measured points: – HV: every 100 or 50 V – Threshold: every 5 mV – Gas: He:C 2 H 6 (50:50), He:iC 4 H 10 (90:10), He:CH 4 (80:20) Amount of data – Typical trigger rate = 4.5 kHz – ~800k events per data-point + several longer runs  We can obtain systematic data. Efficiency, spatial resolution, drift velocity etc. will be examined. 12

Online monitor 13 run3018: He:C2H6(50:50), HV = 2300 V, Th = 25 mV

ns 290 ns 330 ns TDC distributions The width of TDC distribution are consistent to the maximum drift time in a 8-mm cell for each gas mixtures.

Summary We are reconsidering the best gas mixture for COMET CDC. The beam test was carried out at SPring-8/LEPS. Data-taking was successfully carried out for 3 types of gas mixtures. Analysis status is reported by the next speaker. 15 Merci beaucoup

Backup 16

648 (DC) 78 (HV) 273 (RO Board)

18 Setup with finger scintillators Finger Scintillator We took data with finger scintillators as a trigger in order to make analysis easier.

19 e - beam Setup for 18-deg inclined data

Information about the beam test 20

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Data of He:C2H6=50:50 23

Data of He:iC4H10=90:10 24

Data of He:CH4=80:20 25

Environmental monitor 26

Backward Compton scattering  27 Now, they use 266-nm laser.   Energy < 3.0 GeV  100—200 kHz BCS  rate. BCS 

Photon conversion 28 e+e- pair creation dominate.  = ~50 barn (  ≈ Z^2  Pb convertor )

Pair creation 29 [Ref.] R.C. Fernow, “Introduction to experimental particle physics”, Cambridge Press (1986), Sec Fraction of total available kinetic energy taken by e+ e+/e- do not have the same energy and are produced with any allowed energy. Approximate mean production angle of e+/e- Around 3 GeV,  ~ 0.  Straight beam !! Then, e- are horizontally spread out by D- magnet depending on their momentum, but not spread vertically !!  e- are only on the beam height !!

Distribution of electrons 30 Horizontal position at TOF wall [Caution] In the current laser setting, the rate will be 1/2. From N. Tomida, Master thesis, Kyoto Univ. (2012). Our trigger counter size is 30 x 9 cm2. If we can set the chamber around 300—400 mm, trigger rate of 1 kHz will be achieved.

Visiting SPring-8 31 Our space

32 Slide by H. Yoshida

Beam time schedule July 9 th 10:00 – 12 th 10: Beam commissioning & detector check (4h) Data taking with He:C 2 H 6 (11h) + backup (3h) Gas replacement from He:C 2 H 6 to iso-C 4 H 10 (14h) + overhead (1h) Data taking with iso-C 4 H 10 (11h) + backup (1h) Gas replacement from He:iso-C 4 H 10 to He:CH 4 (14 h) + overhead (1h) Data taking with He:CH 4 (11h) + backup (1h) Total: 72 h 7/9 7/10 7/11

34 Gasrun#HV [V]Threshold [mV] He:C2H6=50: He:CH4=80: H2:iC4H10=90: [Note] Using root-preview files (first 1GB of data) TDC[18]: maybe central region of chamber Only plot the first hit to make the plot easy to understand