1. Nov 27th, 2007 Yuekun Heng (hengyk@mail.ihep.ac.cn) IHEP
PID detector on BESIII
Nov 27th, 2007
Yuekun Heng
IHEP
Now I will introduce the TOF detector on BESIII.

2. Outline Physics requirements for PID Present TOF design
Upgrade to MRPC??
Upgrade to Internally reflecting Cherenkov detector:
CCT
TOP
Focusing DIRC
Summary and discussion

3. 1. Physics requirements for PID

4. K/πmomentum on BESIII Momentum distribution for hadrons at J/psi
BEPCII: 2.0~4.2GeV
BESIII:
Charm physics:J/Psi, Psi’, Psi’’
Tau Physics
K/π seperation:
0.9GeV is generally OK
1.2GeV is needed of some topics
1.5GeV is good enough
Present TOF: 0.9GeV(2sigma,95%)
Momentum distribution for hadrons at J/psi

5. Searching for D0D0 Mixing
By Kπchannel:
Big challenge to PID Main backgrounds come from the double miss-PID
By semi-leptonic decay: difficulty with 2 missing neutrino (hard to reduce background contribution to 10-4)
Monte Carlo study with different PID (TOF resolution)
(by He Kanglin )

6. 2. Present TOF Design

7. Present TOF: 90 ps 90 ps: almost the limits for scin. for 2m length
Table. TOF based on scin.
Exp.
year
Scin.
L X W X T(cm)
PMT
Reso.(ps)
DELPHI
1990
NE110
350 X 20 X 2
EMI19902KB
1200
NNbar
1992
( ) X 21 X 2
XP2020
300
CLEOII
BC408
280 X 10 X 5
139
OBELIX
1995
300 X 9.3 X 4
170
NA49
2000
(12-48)X(1-1.25)
X(1.5–2.4)
R3478 80
DIRAC
2002
BC420
40 X 7 X 2.2 R
123
BELLE
255 X 6 X 4
R6680
90ps
CDFII
2003
279 X 4 X 4
R7761
100
HARP
2004
( ) X 21 X 2.5
160

8. Capability of separation
Why two layers?
Capability of separation
of Kaon and Pion
Much uncertainty from NON TOF contribution like bunch length and time etc.
Time reso. For Kaon and pion is worse than muon
Time reso. Of two layers totally is from 100ps to 110ps for kaon and pion.
That time reso. Can separate kaon/pion of 0.9GeV in the middle of barrel.
Contribution
Time reso. For 1GeV Muon
Time reso. For
Kaon/pion
Non TOF
60ps
One layer of scin. Intrinsic
80-90ps
One layer of
Scin. Totally ps
110ps-130ps
Two layers,
Totally
100ps-110ps

9. Beam tests of Prototype
TOF prototype :
scin.、PMT
preamp、18m cable and electronics
Particles:
π, p, e
Analysis：
position correction,
time walk correction
double particles
Pion:104±11ps proton:70±2ps Electron:94±3ps
图. 束流实验框图

10. Installation just finished
图. 安装后信号：噪声<10mV、前沿～5ns
图. 安装过程示意图

11. 3. Upgrade to MRPC??

12. Target for MRPC with long pad: 60ps
TOF of MRPC: 60ps.
totally time reso. <80ps to get 1.2GeV separation of K/pi,
Non-TOF is 60ps,
ALICE’s and STAR’s MRPC with small pad: <60ps.
Long-strip MRPC needs much more studies.
Example 1. Italian EEE project:

13. Example 2. 75ps HV: 10kV/mm GAS: 85% C2H2F4 5% iso- C4H10 10%SF6，
4 gaps, 0.3mm/gap
HV: 10kV/mm
GAS: 85% C2H2F % iso- C4H10
10%SF6，
Results: 75ps

14. Manufacture of MRPC with long pad
Bakelite type:
made and tested and canceled
reason: un-uniformity of 1mm bakelite influence electronic field much
Glass type:
T(1mm) by L(1m)
Components of China-made glass
图. MRPC结构
图. 制作过程非常繁琐：测试清洁玻璃、制作电极、PCB板粘接到蜂窝板、安装尼龙柱、绕钓鱼线、安装高压电极、安装玻璃、安装高压电极、安装信号引出等等10多项步骤。

15. Preliminary results from cosmic ray tests
Eff.>95%, Reso.～100ps
Fig. Eff. VS HV
Fig. Time resolution.
Fig.Time reso.VS HV
Fig. Single Rate VS HV

16. 4. Internally reflecting Cherenkov detector

17. 3 options (refers to Honscheid ,Ohshima, Vavra,)
CCT(Cherenkov Correlated Timing )
1D Timing only
a) Time is related to cherenkov angle

18. CCT simulation (by Chunxiu Liu)
Charged particle
87cm
By SLAC
MCP-PMT( )
Photocathode square
2 in
Spectra Range nm
Rise Time
0.3 ns
Pulse Width (FWHM)
1.8 ns
Transit Time
3 ns
Transit Time Spread
30 ~ 50 ps
Model Gain
0.6106
By Nogoya Univ.

19. PMT Response time response for SPE Time of Photoelectron
rise time=0.3ns
time response for SPE
Signal of Single PE
Pe number
Time of Photoelectron
Time(ns)
PMT signal pulse
Voltage(mV)
Time(ns)

20. Threshold :40mV~5photonelectron
CCT: Seperation of K/ 
Threshold :40mV~5photonelectron
1.0GeV
0.8GeV
1.2GeV
1.5GeV
K/  seperation(3)
K/  seperation(2)
cos
Time Diff of k/  (ns)
CCT (intrinsic)

21. 5. Summary Physics requirements for K/  separation on BESIII:
0.9GeV is general OK
1.2GeV is needed for some topics
1.5GeV is good enough
Present TOF:
90ps is reached from beam tests and almost the limit of scintillator TOF.
BESIII is made of two layers of TOF.
MRPC with long-pad,
target: 60ps;
Prototype is made
Preliminary result: 100ps.
Internally reflecting Cherenkov detector:
CCT has good potential for the upgrade. Simulation show it can give 1.2 GeV K/  separation
TOP is another option, refer to PID upgrade for BELLE.
Focusing DIRC needs more space, impossible for BESIII

22. The End
Thanks a lot!

23. K/Pi difference of cherekov light