Particle identification —TOF detector of BESIII Heng Yuekun hengyk@mail.ihep.ac.cn Now I will introduce the TOF detector on BESIII.

Outline Functions and target Structure and dimension Detector design TOF+TOF TOF+CCT CCT Experiment plan My report mainly include 4 parts, that is ……..

Functions of TOF Particle ID Give a fast trigger (Level-1) Reject cosmic ray background The most important function of TOF is Particle ID , Also it should give a fast trigger and reject cosmic ray background.

PID Target Time Res.: Target: Upper limit of K/ separation(2) : 1.1GeV/c The capability of Particle ID of TOF is dependent to its time resolution. The time resolution is mainly determined by itself performance and the beam bunch length of BEPCII. For the new TOF, we hope its intrinsic time resolution will be about 60ps. Considering the beam bunch length (about 1 cm) , the total time resolution will be 65ps. So the upper limit for /K separation will be about 1.1 GeV/c.

Detector design Two layers, two independent time: Two options: TOF+TOF TOF+CCT PMT connected directly To get so high time resolution, the barrel TOF will be made up of two layers and each layer can give a independent time measurement. Here two options are considered: one is double TOF, the other is one layer of TOF and one layer of CCT(Cherenkov Correlated Timing Detector). In both options, the PMT will be connected directly with the scintillator or CCT material.

Dimension Length: 1906mm Coverage:~83% Pieces: 80 /layer Place: Space: 105mm Reserved: 7mm Thickness: 49mm /layer The length of the scintillator is the same of the MDC outer layer, and solid angle coverage is about 80 percent. Each layer will have 80 pieces of scitillator. TOF will be placed between MDC and EMC. There will be totally 105mm space in r-direction. About 7mm space should be reserved for its support and installation. Each layer of TOF will be 49mm thick.

Scintillator and PMT Scintillator:BC404 PMT: R5924 The scintillator will use BC404, produced by BICRON company. The PMT will use R5924, manufactured by hamammasu company. Both of them have good time performances. Here is the comparison of TOF between BESII, BELLE and our new TOF.

CCT introduction Cherenkov Correlated Timing Proposed in 1994 by K.Honscheid, M.Selen, M.Sivertz Beam test in 1996 no detector apply it need more researches Now I’d like to introduce the CCT detector. CCT means Cherenkov Correlatec Timing. It is a new Particle ID technique proposed in 1994 by Honscheid, Selen and Sivertz. In 1996, a CCT beam test is done successfully. But until now no detetor has apply this method. So we need more researches.

CCT Principle & advantages Cherenkov radiation: Improve PID Greater mass, Smaller angle, Longer time Cheap Simple It is known that the Cherenkov radiation can happen at certain angle when a charge particle pass through material with enough high speed. Considering two particles with same momentum, the particle with greater mass has smaller angle and longer transit time, so this will improve the capability of particle ID. The other advantages of CCT is its cheap cost and simple structure.

Comparison of K/ sep. TOF+TOF TOF+CCT This is the comparison of K/pi separation for Double TOF or TOF plus CCT. For double TOF, the upper limit is over 1.1 GeV. While for the TOF plus CCT detector, the limit is over 1.2GeV, and almost to 1.3GeV

CCT threshold Why threshold? Cherenkov radiation & Full reflection: Under threshold, no signal TOF layer give trigger signal CCT detector has a momentum threshold for any particles, because both Cherenkov radiation and full reflection must happen. If the momentum is under the threshold, CCT can’t give a signal. Thus the other TOF layer must give trigger signal.

CCT Material Quartz is best, but expensive Plastic: 50-100ps BC480: Atte. Length:4.5m Cher/Scin.: 10/1 According to the beam experiment at KEK, quartz is best CCT material but it’s expensive. It is found that the plastic material can give a time resolution of 50-100 ps. So we plan to use the plastic BC480 produced by BICON company, it has long attenuation length. Its cherenkov light is ten times bigger than scintillating light

Preliminary Simulation The Cher. light production and transit in BC480 by Geant4 Fig. Under the different hitting angle, the number of photon received by PMT. Fig. The histogram of the time when the photons hitting the PMT. Using Geant 4, we simulate the cherenkov light production and transition, when a particle passed through the CCT. The left figure shows the photon number received by PMT while a 640 MeV pion passing through CCT under different angle. The right figure is the time histogram when photon arrive at PMT. From the two figures we can see the Cherenkov light can be used to measure the time.

CCT Experiment Plan Cosmic ray Lead: Two Scin.: Two CCT: T1-T2: Coin. & Trig. Collimation Two CCT: T1-T2: Scin. PMT T0, Trig. PMT T1 PMT T2 Lead We have no experience with CCT. So we must do some research. This is our experiment plan. We use cosmic ray as source, use some lead to select high momentum cosmic ray, use two scintillator to give trigger, use two CCT to give time measurement. From the difference of the two time, we can get the time resolution. Scin. PMT T0,Trig. Cosmic ray

Summary Target: 65ps, >1.1GeV Structure: 2 layers, 2 timing Two options: TOF+TOF: experienced TOF+CCT: better PID, more research CCT Experiments plan Now let me give a summary.