CEPC 4 IP discussions Dou Wang on behalf

CEPC 4 IP discussions Dou Wang (on behalf of CEPC AP group) CEPC day, A 419, IHEP, Aug. 16 th 2019.

Layout of CEPC 4 IP scheme Haijing Wang IP 1 • 4 IPs RF RF - Equal spacing between IPs • 4 RFs IP 4 IP 2 - RF at the midpoint of 2 IPs - shared RFs RF RF IP 3 • 2 2 collision - 2 trains/beam

Synchrotron radiation increase w. 4 IP Y. Wang U 0[a. u. ], length[km] with 2 IPs U 0[a. u. ], length[km] with 4 IPs IR 4. 4 2 3. 3 km 2 4. 4 4 3. 3 km 4 ARC 291. 6 2 81. 6 km 291. 6 2 81. 6/74. 6 km STR 0 1. 25 km 4 0 0. 25 4 for Injection RF 0 3. 4 km 2 0 (3. 4 -0. 6) 4 Total 592 100 km 638 100 km • U 0 is increased by ~7. 5% • Beam current is decreased by same amount @ H & W

Beam-beam limit

Overall consideration for parameters Ø Dynamic aperture • Keep same y* as CDR (1. 5 mm) • Same momentum acceptance as 2 IP (Oide’s talk@FCCweek 2019) • On-momentum DA of 4 IP slightly smaller than 2 IP’s (Oide’s talk@FCCweek 2019) • DA reduction due to solenoids Ø Background due to injection • Put inj. at downstream of IP Ø Beam lifetime • Bhabha lifetime (4 IP) 58% Bhabha lifetime (2 IP) • Beamstrahlung lifetime slightly longer than 2 IP • Same level of total beam lifetime

Parameter choice for 4 IP Ø Higgs • • • decrease x* (0. 36 m 0. 33 m) for smaller x (0. 018 0. 014) decrease y : 0. 11 0. 0945 Longer bunch z: 4. 4 m 4. 8 m energy acceptance requirement: 1. 35 1. 2 Luminosity/IP: 2. 93 2. 37 ( 19%) , total luminosity: 61% ØW • • decrease x* (0. 36 m 0. 3 m) for smaller x (0. 013 0. 0096) decrease y : 0. 123 0. 094 Longer bunch z: 5. 9 m 6. 1 m Luminosity/IP: 10. 1 8. 4 ( 17%) , total luminosity: 66% ØZ • • • decrease x* (0. 2 m 0. 08 m) for smaller x (0. 004 0. 0017) decrease y : 0. 06 0. 044 (3 T), 0. 079 0. 054 (2 T) Coupling: 4% (3 T), 1. 7%(2 T) Luminosity/IP: 16. 6 13. 7 (3 T) ( 17%), 32. 1 25. 4(2 T) ( 21%) Total luminosity: 65% (3 T) , 58% (2 T)

CEPC Parameters with 4 IP 20190722 Number of IPs Beam energy (Ge. V) Circumference (km) Synchrotron radiation loss/turn (Ge. V) Crossing angle at IP (mrad) Piwinski angle Number of particles/bunch Ne (1010) Bunch number (bunch spacing) Beam current (m. A) Synchrotron radiation power /beam (MW) Bending radius (km) Momentum compact (10 -5) function at IP x* / y* (m) Emittance ex/ey (nm) Beam size at IP x / y ( m) Beam-beam parameters x/ y RF voltage VRF (GV) RF frequency f RF (MHz) (harmonic) Natural bunch length z (mm) Bunch length z (mm) HOM power/cavity (2 cell) (kw) Energy spread (%) Energy acceptance requirement (%) Energy acceptance by RF (%) Photon number due to beamstrahlung Beamstruhlung lifetime /quantum lifetime* (min) Lifetime (hour) F (hour glass) Luminosity/IP L (1034 cm-2 s-1) *include beam-beam simulation and real lattice Higgs Z（3 T） W Z（2 T） 4 120 80 45. 5 100 1. 86 3. 96 15. 0 224 (0. 63 s) 16. 1 30 0. 33/0. 0015 1. 21/0. 00275 20. 0/0. 064 0. 014/0. 0945 2. 24 2. 9 4. 8 0. 4 0. 146 1. 2 1. 8 0. 075 80/80 0. 43 0. 89 2. 37 0. 37 16. 5× 2 7. 92 11. 5 1480 (0. 22 s) 81. 8 30 10. 0 1. 11 0. 3/0. 0015 0. 54/0. 0018 12. 7/0. 052 0. 0096/0. 094 0. 5 650 (216816) 3. 03 6. 1 0. 65 0. 1 0. 90 1. 46 0. 047 >400 1. 4 0. 95 8. 4 0. 038 37. 6 8. 3 12000 (25 ns+10%gap) 478. 7 18. 4 0. 08/0. 001 0. 18/0. 007 3. 7/0. 1 0. 0017/0. 044 0. 08/0. 001 0. 18/0. 003 3. 7/0. 055 0. 0017/0. 054 0. 11 2. 39 8. 5 2. 09 0. 083 0. 49 1. 8 0. 024 2. 5 2. 0 0. 99 13. 7 25. 4 7

Beam-beam simulations @Higgs Y. Zhang • Both luminosity and beam sizes agree well with the analytical estimation.

Beam-beam simulations @Higgs • DA energy acceptance requirement of 4 IP is smaller than 2 IP. Y. Zhang

IP number optimization • Cost=Accelerator + Detector*NIP+ Operation (operation=electricity + staff + repair) • L=(L 0/IP)*NIP*T_physics • Crossing at ~ 5 iab • Operation – 8 months • Physics (60%) – 5 months • Electricity: ~1 billion/year (0. 6 yuan per k. Wh) • staff +repair : ~1 billion/year

Compatibility with SPPC • Case I: 2 CEPC detectors (IP 2, IP 4) removed When SPPC is constructed. - CEPC has only beam pipe at pp IRs - No need to bypass IP 2 & IP 4 - SPPC’ design become easier • Case II: keep 4 IPs for CEPC (IP 1, IP 2, IP 3, IP 4) - Large bypass at IP 2 & IP 4 (~50 m)

Summary • First look at CEPC 4 IP possibility. New difficulties come out, but looks acceptable so far. • In the case of 4 IP instead of 2, luminosity/IP decreases by ~20%. Total luminosity increased by ~ 60%. • 4 IP will have small impact on the layout of SPPC if two CEPC detectors removed when SPPC is constructed. • 4 IP scheme is more economical if physics requirement for Higgs is larger than 5 ab-1. • Detailed design studies need to be done. - Potential risk: DA, lifetime, background…