Beam test results of a prototype sensor for

Beam test results of a prototype sensor for the Belle SVD upgrade 31 October 2006 Nobuhiro Tani for Belle SVD group 1

The Belle SVD Group Frankfurt U. , U. Hawaii, Jozef Stefan Inst. , Kanagawa U. , KEK, Krakow INP, U. Melbourne, National Taiwan U. , Niigata U. , Nihon Dental U. , Nova Gorica U. , Osaka U. , Princeton U. , U. Sydney, Tohoku U. , U. Tokyo, Tokyo Inst. Tech. , Tokyo Metropolitan U. , Toyama NCMT, Vienna IHEP ~100 people 2

Outline Belle Silicon Vertex Detector (SVD) 1 Belle SVD upgrade 2 Prototype sensor l Beam test for the prototype sensor 1 Setup 2 Measurement 　　Spatial resolution l Hit-finding efficiency l Summary 3

Belle detector KEKB e+e- collider in Tsukuba, Japan The highest luminosity in the world 8. 0 Ge. V e- SVD 3. 5 Ge. V e+ 4

Silicon Vertex Detector (SVD) SVD Ladder Consists of 4 layers of silicon sensors l To measure decay vertex of B mesons (Resolution ~100 m) Charged track l Charged track decay vertex of B mesons 5

Double-sided Silicon Strip Detector (DSSD) P-side Floating strip P+strip N-side Hole Electron Layer readout chip Layer 1~3 Side P-side N-side Sensor size (mm 3) 79. 6 x 28. 4 x 0. 3 Active area (mm 2) 76. 8 x 25. 6 Layer 4 P-side N-side P-stop 76. 4 x 34. 9 x 0. 3 73. 8 x 33. 3 Strip pitch ( m) 75 50 73 65 Readout pitch ( m) 150 50 146 65 Strip width ( m) 50 10 55 12 Readout electrode width ( m) 56 10 61 10 Number of strips 1024 512 N+strip readout chip 6

SVD upgrade Too many strips will give signal at the same time Hit-finding Efficiency With the improvement of accelerators Larger beam background Higher occupancy Innermost Layer Introduction of “APV 25” Readout chip with faster peaking time comparing present readout chip Peaking time: 800 ns 50 ns Occupancy: 1/16 Occupancy (B. G. level)7

Necessity of capacitance reduction • Present sensor Large strip-width = Large detector capacitance Noise = NCapacitance ( ) NLeakage-current ( ) • APV 25 with faster peaking time Larger NCapacitance Degrade sensor performance To reduce detector capacitance, Wider P-stop gap is necessary. Prototype sensor 5 different strip-configurations Noise (C: detector Capacitance, I: Leakage-current, Tp: peaking time) NCapacitance NLeakage-current Faster peaking time Tp (Peaking Time) We did a beam test to evaluate the performance of the prototype sensor with APV 25 readout. 8

Prototype-sensor (N-side SSD) P-stop gap strip pitch strip width Prototype-sensor N N P P N S 75 -2 P P S 100 -3 N N S 75 -2 N P S 75 -3 P S 100 -5 S 75 -3 S 75 -4 N P P S 75 -4 P N N S 100 -3 S 100 -5 Strip pitch ( m) 75 100 Readout pitch ( m) 150 100 Strip width ( m) 32 23 12 12 12 P-stop gap ( m) 7 15 37 6 56 9

Beam test 4 Ge. Vπ- (KEK / PS π2 Beam) l Perpendicular incidence l (GEANT 4 simulation) Multiple-scattering contribution to spatial resolution ~ 1. 3 m l Z-direction (~Beam line) Prototype-sensor with APV 25 (Z=8 mm) Telescope-sensors DSSD-1 with VA 1 TA (Z 0 mm) DSSD-2 with VA 1 TA (Z=17 mm) DSSD-3 with VA 1 TA (Z=40 mm) 10

Analysis Procedure X DSSD X X DSSD Telescope (VA 1 system) Data sparsification & clustering Prototype-sensor X DSSD Prototype-sensor (APV system) Calculate residual on Prototype-sensor Reconstruction of track Spatial resolution, Hit-finding efficiency 11

Select good track 2 Tracking (least χ2 method) Cluster width distribution Entries 1 Find good hit-positions of DSSD Cluster width < 4 3 Select good track χ2 (each event) < 3 χ2 distribution DSSD I Entries Cluster width I χ2 I DSSD Test sensor Uncertainty of estimated position by the tracking ~ 6. 3 m 12

Residual distribution S 75 -3 Entries S 75 -4 Entries S 75 -2 residual ~ 19. 4 m residual ~ 17. 5 m Residual ( m) S 100 -5 Entries residual ~ 24. 5 m Residual ( m) Spatial resolution Prototype-sensor = Residual ( m) Entries Residual ( m) S 100 -3 residual ~ 12. 3 m residual ~ 11. 9 m Residual ( m) tracking ~ 6. 3 m multi-scattering ~ 1. 3 m 13

Spatial resolution ( m) P-sop gap dependence S 100 -3 S 75 -2 S 75 -3 S 75 -4 Wider P-stop gap Better resolution S 100 -5 ● strip-pitch 75 ( m) ● strip-pitch 100 ( m) P-stop gap ( m) N P P S 75 -2 N N N P P S 75 -3 P P N S 100 -3 N Better N P S 100 -5 P S 75 -4 N P N 14

Estimated position ( m) S 100 -3 Estimated position ( m) S 75 -4 Hit position ( m) S 75 -2 Hit position ( m) Charge sharing Estimated position ( m) S 100 -5 Floating strip Bonded strip Estimated position ( m) The wide P-stop gap sensor behaves as if it has a floating strip 15

Guess P-stop pitch Narrow Wide Electric field near the boundary Strong Weak Charge collection On one side Equally Charged particle N P P ● Electron Electric field N N Charged particle P P N 16

Hit-finding efficiency <Denominator> : Entries of tracks come in <Numerator> : Number of hits (Prototype-sensor) in search window | Residual (= YEstimated – YHits)| < 3 residual Y Type Entries Efficiency(%) S 75 -2 1240 / 1245 99. 6 ± 0. 2 % S 75 -3 1333 / 1349 98. 8 ± 0. 3 % S 75 -4 1349 / 1371 98. 4 ± 0. 3 % S 100 -3 1891 / 1902 99. 4 ± 0. 2 % S 100 -5 2662 / 2699 98. 6 ± 0. 2 % ~ 99% for all configurations Bonded strip Floating strip Estimated position by track 17

Summary We did a beam test to evaluate the performance of a prototype N-side SSD with APV 25 readout. l We confirmed the good hit-finding efficiency for all configurations. l Better spatial resolution is obtained with wider P-stop gap. l Type S 75 -2 S 75 -3 Strip-pitch Strip-width (Read-pitch) ( m) 75 (150) S 75 -4 S 100 -3 S 100 -5 100 (100) P-stop gap Spatial Hit-finding ( m) resolution ( m) efficiency (%) 32 7 18. 2 ± 0. 4 99. 6 ± 0. 2 23 15 16. 2 ± 0. 4 98. 8 ± 0. 3 12 37 10. 4 ± 0. 3 98. 4 ± 0. 3 12 6 23. 6 ± 0. 4 99. 4 ± 0. 2 12 56 10. 0 ± 0. 2 98. 6 ± 0. 2 18

Back up 19

APV 25 • Input: 128 ch • Internal clock : 40 MHz • Peaking time : 　50 ns • Multi-peak mode ⇒Waveform sampling Multi-peak mode output APV 25 : 4 chips • I analyzed the data of 12 -peak mode, and selected the most highest peak. 20

System of beam test 21

Clustering 1, Define “Cluster-Seed” if Sstrip / Nstrip > 5 2, Define “Cluster-Strip” if neighboring strip of “cluster seed” implements Sstrip / Nstrip > 3 Sstrip : Signal ADC count on the strip Nstrip : RMS of random noise on the strip 1 2 Cluster-Seed (S/N > 5) , Cluster-Strip (S/N > 3) Apply Scluster / Ncluster < 10 22

Align 3 -DSSD system Minimize the of residual X Test sensor X X X DSSD (reference) DSSD (object of alignment) Tracking Select the track with minimum χ2 in all possible ones X X X 23

tracking ZDSSD 1, 2, 3 = {0 mm, 17 mm, 40 mm} , tracking( Z(Test-sensor)=8 mm ) = 6. 98 m 24