Beam test results of a prototype sensor for the Belle SVD upgrade

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

The Belle SVD Group 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

Outline • Belle SVD (Silicon Vertex Detector)1 Belle SVD upgrade2 Prototype sensor • Beam test for the prototype sensor 1 Setup2 Measurement Spatial resolution and Hit-finding efficiency • Summary

KEKBThe highest luminosity in the world Belle detector Located in Tsukuba, Japan 3.5 GeV e+ 8.0 GeV e- SVD

Silicon Vertex Detector (SVD) SVD Ladder Charged track • Consist of 4 layers of silicon sensors • Find decay vertex of B mesons (resolution ~100m) B-decay vertex Charged track

Double-sided Silicon Strip Detector (DSSD) P-side Floating strip P+strip readout chip N-side P-stop N+strip readout chip

Layer1 Layer2 Hit-finding Efficiency Layer3 Layer4 Occupancy (B.G. level) SVD upgrade Improvement of accelerators Larger beam background Higher occupancy Too many strips will give signal at the same time Solution Employment of readout chip “APV25” with faster peaking time Peaking time: 800ns50nsOccupancy:  1/16

Necessity of capacitance reduction • Present sensorLarge strip-width = Large detector capacitance • Faster peaking time <APV25> Larger NCapacitance  S/N reduction Spatial resolution and efficiency will become worse Noise = NCapacitance ( )  NLeakage-current( ) (C: detector Capacitance, L: Leakage-current, Tp: peaking time) Ncapacitance Noise NLeakage-current Faster peaking time We have already prepared 5 configurations of prototypes. To evaluate the performance of them with APV25, we did beam test. Peaking Time

Test-sensor (N-side SSD) P-stop gap strip pitch strip width Test-sensor N N P P N N P N N P P P S75-2 S75-3 S75-4 N P P N N P P N S100-3 S100-5

Beam Test Property of the Beam • KEK / PS π2 Beam (4GeVπ-) • Perpendicular incidence • Multiple-scattering contribution to spatial resolution~ 1.3 m (GEANT4 simulation) Z-direction (~Beam line) Test-sensor with APV25(Z=8mm) DSSD-1 with VA1TA (Z0mm) DSSD-2 with VA1TA (Z=17mm) DSSD-3 with VA1TA (Z=40mm)

Analysis Process Test-sensor(APV system) Telescope (VA1 system) Data sparsification & clustering Data sparsification & clustering X DSSD X Test-sensor Reconstructionof track DSSD X Calculate residual on Test sensor DSSD X Spatial resolution, Efficiency

Good track selection Cluster width distribution 1 Find good hit-positions of DSSD Cluster width < 4 2 Tracking (minimize χ2 ) Entries 3 Select good tract χ2 (each event) < 3 χ2 distribution Cluster width DSSD I Test sensor I Uncertainty of estimated position tracking ~ 6.3 m Entries DSSD I DSSD I χ2

Spatial resolution Spatial resolution Test-sensor = S75-3 S75-2 S75-4 Entries Entries Entries Residual (m) Residual (m) Residual (m) S100-3 S100-5 Entries Entries Residual (m) Residual (m)

Results - Spatial resolution spatial resolution Spatial resolution (m) S100-3 S75-2 S75-3 Spatial resolution Wider P-stop gap Better resolution S75-4 S100-5 ● strip-pitch 75(m) ● strip-pitch 100(m) P-stop gap (m) Better N N P P N N P N N P P P S75-2 S75-3 S75-4 N P P N N P P N S100-3 S100-5

Large P-stop gap  Charge is well-shared Charge sharing S75-3 S75-2 S75-4 Hit position (m) Hit position (m) Hit position (m) Estimated position (m) Estimated position (m) Estimated position (m) S100-3 S100-5 Effect of floating strips Hit position (m) Hit position (m) Effect of bonded strips It looks like floating strip (but not floating) Estimated position (m) Estimated position (m) N P P N N P P S75-4 N P P N P P N S100-3

Hit-finding efficiency <Denominator> : Entries of tracks come in <Numerator> : Number of hits (test-sensor)in search area : | Y track-estimated – Y hits| < 3σresidual Y Track Bonded strip Floating strip expected position by track

Results – Hit-finding efficiency Hit-finding efficiency S75-2 Efficiency S75-3 S100-3 S75-4 S100-5 • Hit-finding Efficiency • At all configurations • ~ 99% ● strip-pitch 75(m) ● strip-pitch 100(m) P-stop gap (m) Better N N P P N N P N N P P P S75-2 S75-3 S75-4 N P P N N P P N S100-3 S100-5

Summary • To evaluate the performance of prototype N-side SSD with APV25, we did a beam test. Hit-finding efficiency: Independent of parameters Spatial Resolution : Wider P-Stop gap gives better one

That's all for today

Back up

APV25 • Input: 128ch • Internal clock : 40MHz • Peaking time :50ns • Multi-peak mode • ⇒Waveform sampling Multi-peak mode output • I analyzed the data of 12-peak mode, • and selected the most highest peak. APV25 : 4 chips

System of beam test

Beam incidence Incidence direction Angle Z axis

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

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

tracking ZDSSD1,2,3 = {0mm,17mm,40mm} ,  tracking( Z(Test-sensor)=8mm ) = 6.98 m

Beam test results of a prototype sensor for the Belle SVD upgrade