1. Design of Time zero(T0) counter contents Characteristic of p+p collision Time of Flight method Systematic scintillator performance Scintillator selection PMT selection Simulation of T0 counter Schematic design of T0 counter Background by T0 counter Last modified 2000/10/03 Univ. of Tsukuba Hiroshi Tsuruoka, Masaya Ono

2. What’s different in p+p collision ? p+p １００ GeV(JAM) Au+Au 100AGeV(JAM) Charged dn/dy distribution dn c /dy Low multiplicity(≈1/200 of Au+Au collision). rapidity p+p １００ GeV(FRITIOF)

3. Mean=1.2 〔 particles/event 〕 Beam-Beam Counter(BB) in p+p collisions. No.of hits%σ BBC [ps] 041― 12387 21760 31050 4543 5339 6135 Hit Multiplicity of Beam Beam Counter No.of hits% 084 114 22 Hit Multiplicity of Time-of-Flight detector region (67 ° <θ<113°,0 ° <φ<45° ） Mean=0.18 〔 particles/event 〕 Few charged particles hit Time of Flight. Need “Trigger” for efficient measurement. ～ 40 ％ No Hit at BBC ～ 84 ％ No Hit at ToF BBC can’t be used as start counter.

4. Purpose of T0 Time zero(T0) counter Covered Time-of-Flight detector region. Time resolution <50ps Purpose Provides trigger for hadron measurement and start timing for TOF measurements BBC can’t be used as start counter. Few charged particles hit Time of Flight. Need “Trigger” for efficient measurement. TRIGER=CLOCK×T0(×TOF) preferable

5. Time of Flight method resolution Required 100ps for 4σ Stop counter (Time-of-Flight detector) resolution. <80ps Start counter resolution For Au+Au collision start counter= Beam Beam Counter ΔT stop =60ps achieved ∴ ΔT start required 50~60 ps Time of Flight (ToF) resolution

6. How to measure the start, stop Time PMT2PMT1 Charged particle x L-x t0t0 Measured timeObtain hit time t 0, hit position X Resolution t 0, x Resolution t 1, t 2 N: Number of photo- electron Time resolution has been found to be dominated by Number of photo-electron.

7. Systematic scintillator performance (ref M.Kurata et al. / NIM A 349(1994)447-45) 1.Light yield (proportional photo-electron) Light yield is decrease exponentially with the distance from PMT λ LA is proportional scintillator’s cross section λ LA :light attenuation length 2.PMT’s time resolution λ TD :time degradation length ΔT degrades exponentially with the distance from the PMT Large cross section scintillater has small ΔT. BC404 scintillator

8. Scintillator selection BC404 plastic scintillator Physical constant value Light output(%anthracene)68 Wavelength of maximum emission408nm Decay constant of main component1.8ns Bulk light attenuation length160cm Refractive index1.58 Radiation length42.5cm Required performanse 1.for good ΔT large light yield ⇒ thicker scintillator 2.a little background effect for backyard detectors a little conversion probability ⇒ thiner scintillator Where do we compromise?

9. Top : http://www.phenix.bnl.gov/phenix/project_info/integration/config_management/envelope_control Bottom : PHENIX Conseptual Design Report, Chapter4 Magnets (1993) PMT for strong magnetic field ( ～ 4000 gauss) Hide PMT from charged particle B Effect of magnetic field

10. ※ HAMAMATSU PHOTONICS K.K. R5924 fine mesh PMT Operate in high magnetic field High gain ～ 400μA ( cf. R3809 MCP type ～ 1 ０ μA ) Rise Time ‥‥‥ 2.5 nsec T.T.S ‥‥‥ 440psec Anode Effective Area ‥‥‥ Φ39mm (min) Current Amplification at 0 Tesla at 0.5 Tesla at 1.0 Tesla PMT selection

11. Monte Carlo Calculation

12. Cross section Scintillator face 2cm×8cm PMT scintillator PMT face 4cm×4cm ① inside ② outside 100 % ? % L cm Few difference between inside rod and outside and get many photon when L=10cm Light Guide

13. Cross section scintillator inside outside 100 % ? % L cm PMT Scintillator face 2cm×8cm PMT face 4cm×4cm ① no reflection ② rectangle ③ fish tail ④ rectangle + fish tail 4cm L [cm] Light Guide(detail)

14. cross section 2cm×2cm ×42cm×8cm ‥‥ ① outside ‥‥‥ ‥‥･② inside ‥‥‥･ ③ PMT scintillator x [cm] ・ Scintillator should be divided into four. Expected Time Degradation

15. PMT Light guide charged particle scintillator ⊿TL⊿TL ⊿TR⊿TR x [cm] T0 resolution : (x=50cm) Expected T0 Resolution

16. Proposed Design 1

17. Proposed Design 2

18. φcoverage of T0 counter Pt(MeV/c)Max degree Min degree Required φcoverage(Δφ) 1set coverage of T0 is 10° 200248°118°130° 300235°136°100° 400230°145°85° *Max degree ・・・ The maximum degree that plus charged particles can hit Time-of-Flight detector.(particles also through drift,pad chamber) *Min degree ・・・ The minimum degree that minus charged particles can hit Time-of-Flight detector.(particles also through drift,pad chamber) Time-of-Flight detector covers φ=168° ～ 213° e+:Pt=400MeV e+:Pt=300MeV e+:Pt=200MeV e-:Pt=400MeV e-:Pt=300MeV e-:Pt=200MeV T0 counter Time-of-Flight detector Ｘ y φ

19. Background by T0 (conversion) GEANT simulation Generate γray which have (π0 ⇒ 2γ ） momentum ThicknessConversion Probability(GEANT) From Radiation length(λ rad =43cm) 2.0cm 2.5 ％ 2.4 ％ 2.5cm 2.8 ％ 3.0 ％ 3.0cm 3.4 ％ 3.5 ％ Charged Multiplicity =primary +secondary =0.18+0.004(JAM) =0.26+0.006(FRITIOF)