Radiator study status Y. Horii, Y. Koga, N. Kiribe, … (Nagoya University, Japan) 1 B2GM, 6 th July

Introduction 2  Performance of TOP shown in TDR  Problem arising from the beam test in 2010: Very effective for many modes including K ± /  ± while it is challenging to achieve this performance. (M. Thesis by Y. Arita) difference of the time distributions from TDC between simulation and data. Simulation Data Time Radiator study is important for investigating the reason.

Radiators 3  Radiator for beam test in 2010  Two “Suprasil-P20” bars and mirror, surface polished by Okamoto.  Radiator for beam test in 2011 (backup for Belle II TOP?)  One “Suprasil-P710” bar polished by Okamoto and one “Corning-7980” bar polished by Zygo.  Mirror and wedge will also be glued. glue mirror Already glued and there are restrictions for the checks… Will receive the Suprasil-P710 in the middle of July. mirror wedge Today we will show the status of the quality check for the Corning Suprasil-P20 Suprasil-P710 Corning-7980

Photon paths and their effects 4 Position difference ~ 1mm Time difference ~ 1 mm / c ~ 3 psec PMT resolution: ~40 psec channel size: ~5 x 5 mm 2 Striae and surface non-flatness of quartz and mirror could change the paths of the photons. If this change is large compared to the PMT SPEC, effect on the K/  separation could be significant. 1 mrad change at ~1m before arriving at PMT produces Finally we need to estimate the effect by the simulation but at least the variance of O(0.1) mrad will be safe.

Check of the photon paths 5 Laser (405 nm) Data taken by CCD. Example of the images at the CCD: Bit map file is transferred to a histogram and fitted with 2-D Gaussian (signal) + 2-D linear function (BG). DataFitted PDF Striae and surface non-flatness effect on position and size of the spot. Only Blue is used from RGB.

Check of the photon paths 6 Scanned incident points at x=2.5 cm. x y Laser CCD y [mm]  y [mm]  y [mm]  x [mm]  x [mm] y >15 mm: through air. y <15 mm: through bar. (Thickness of the bar in y axis is 2 cm, and length of the bar in x axis is 45 cm.) Variance is obtained for y = 14 mm. (Variance due to non-zero incident angle.) (Could be the lens effect from the bar.)

Scan for x axis 7  As a further check, we take data also for x = 12.5, 22.5, 32.5, and x y y [mm]  y [mm] y [mm]  y [mm] y [mm]  y [mm] y [mm]  y [mm] We show the position (mean of Gaussian) in y axis for each x value. x = 12.5 cm x = 22.5 cmx = 32.5 cmx = 42.5 cm Quite similar results are obtained for all y points. Obtained variances correspond to 1 mrad shift of the photon direction.

Surface flatness of the bar 8  Surface flatness of the bar is measured by Zygo. Flatness for vertical (y) axis. Flatness for horizontal (x) axis. 1 mrad shift of the photon direction can be made by the non-flatness of the surface. Then we conclude that the effect of striae on the measurements in page 6 and 7 are lower than (or in a similar level to) the effect of the non-flatness. x y

Another check: bulk transmission 9 Laser (405 nm) I1I1 x y I0I0 I2I2 I3I3 I 0 and I 1 measured by PD. I 2 and I 3 calculated by Fresnel equation. Scanned incident position for x and y. Systematic error is not estimated yet but it will be around 0.01 (PD efficiency). Bulk transmission (per meter) is measured to be around Photon retainment after 10 m is 80%-90% (safe).

Similar measurements for Suprasil-P20 10  While the bars are already glued for Suprasil-P20, we measure the change of photon direction and bulk transmission similarly by using the laser from the side. glue mirror LaserCCD, PD 40 cm y [mm]  x [mm] y [mm]  x [mm] y [mm]  y [mm] y [mm]  y [mm] Change of photon direction is O(0.1) mrad. (Effect of striae is smaller than the one of non-flatness.) Bulk transmission is 1.00±0.01 (safely large).

Summary and plan 11  Effects of the striae and the non-flatness of the surface are estimated by measuring laser light by CCD.  No significant effect of striae is obtained for the Corning-7980 and Suprasil-P20 bars for now.  We will receive the Suprasil-P710 bar in the middle of July. Need to check the quality soon after that.  We need to make a decision on the bar in this summer for ordering the mass production for Belle II.

Backup slides 12

Plan 13 Week 1 Week 2 Week 3 Week 4 July Joint the quartz bars. Busy with BGM/B2GM Joint the mock-up (glass) bars. Quartz quality check.

Issues 14  Bulk  Bulk transmission (  photon retainment)  Mean and width of the laser spot (  mean and width at PMT)  Surface  Surface reflectivity (  photon retainment)  Mean and width of the reflected spot (  mean and width at PMT)  Mirror  Reflectivity (  photon retainment)  Mean and width of the reflected spot (  mean and width at PMT)  Glue  Refraction index (reflections at glue joints provide backgrounds)  Position dependence for all measurements.  Numerical estimation of the effect of each source to PID power.

Light path in the bar 15 Striae and surface irregularities of quartz and mirror could change the paths of the photons. mirror images of the bar Want to know the effects on position and timing at PMT. Light path

Naïve estimation 16 1 m 1 mrad Position difference ~ 1mm Time difference ~ 1 mm / c ~ 3 psec PMT resolution: ~40 psec channel size: ~5 x 5 mm 2

Bitmap  Text 17  Order is “BGR.” Reported on 23 rd May (Mon).

Text file  Root file 18  The text file is converted to a root file which includes three TH2I objects (histograms for blue, green, and red). bluegreenred Since the wavelength of the laser is 405 nm, we obtain the highest peak for blue.

2-D fit for the blue histogram 19 Hist. for blueFitted PDF PDF Signal: Gauss(x) x Gauss(y) BG: Linear(x) x Linear(y) Proj. for xProj. for y Small values of  2 /ndf indicate good quality of the fit.  2 /ndf = 0.63  2 /ndf = 0.19

More projections 20 Slightly enhanced for lower x. Effect of the light from outside of the clean room? (Anyway, is it not significant for now.)

Bulk Transmission DIRC(Babar) results 99.9±0.1%/m (442nm) 98.9±0.1%/m (325nm) 21PID Upgrade Meeting, 27th May 40cm ・ Using the photo diode, measure the intensity for I 1 and I 2. ・ We can calculate I 3 and I 4 from Fresnel theory. n 1 =1.47 (405nm) n 0 = nm ・ Then obtain the ratio = I 2 / ( I 1 – 2 I 3 )

Setup PD Laser 22PID Upgrade Meeting, 27th May

Results mirror x(mm) I 1 = 57.28±0.133 μA I 2 (Average)=53.13 μA 23PID Upgrade Meeting, 27th May DIRC(Babar) results 99.9±0.1%/m (442nm) 98.9±0.1%/m (325nm) Theoretical value of surface reflection ratio R=3.62 ％ (α=0) Bulk Transmission 100.0±0.3 ％（ 40cm ） 100.0±0.8(%/m)

Suprasil-P20 24 Local roughness is O(1) Å. Global flatness is O(1)  m.