WW Threshold scan runs and Z pole runs

WW Threshold scan runs and Z pole runs in CEPC Zhijun Liang IHEP, CAS 1

Introduction • Some discussion about CEPC Z pole running. – http: //indico. ihep. ac. cn/event/7709/ – Two possibility: • L=1. 6 X 1035 cm-2 s-1, solenoid field = 3 T • L=3. 2 X 1035 cm-2 s-1, solenoid field = 2 T • Two year running proposed by accelerator team • WW threshold scan – Proposal from accelerator team – One year running, Total luminosity 3. 2 ab-1 2

WW threshold scan Vs luminosity • • WW threshold scan need to scan 3~5 mass points – Especially need to cover 158. 5 Ge. V, 161. 2 Ge. V, 162. 4 Ge. V In CEPC Pre-CDR, we assume 0. 5 ab-1 for W threshold scan – W width measurement is totally limited by statistics – W mass measurement suffers a bit from statistics Assume we run one year WW threshold to collect 3. 2 ab-1 data. – W width measurement is still limited by statistics, but much better than pre-CDR If running for two years with 6. 4 fb-1 – W width measurement is not limited by statistics any more Observable Systematics L=0. 5 ab-1 (3 points scan, 0. 16 ab-1 per run) L=3. 2 ab-1 (3 points scan, 1 ab-1 per run) L=6. 4 ab-1 (3 points scan, 2 ab-1 per run) Major uncertainty Mw 2 Me. V 0. 8 Me. V 0. 6 Me. V E beam cali. ΔE < 1 Me. V GW 2 Me. V 6 Me. V 2. 4 Me. V 1. 7 Me. V Statistics 3

The parameters of CEPC Higgs Number of IPs Energy (Ge. V) Circumference (km) SR loss/turn (Ge. V) Half crossing angle (mrad) Piwinski angle Ne/bunch (1010) Bunch number (bunch spacing) Beam current (m. A) SR power /beam (MW) Bending radius (km) Momentum compaction (10 -5) IP x/y (m) Emittance x/y (nm) Transverse IP (um) x/ y/IP VRF (GV) f RF (MHz) (harmonic) Nature bunch length z (mm) Bunch length z (mm) HOM power/cavity (kw) Energy spread (%) 2. 58 15 2 80 100 0. 34 16. 5 7. 74 15 242 (0. 68 us) 1220 (0. 27 us) 17. 4 30 87. 9 30 10. 6 120 1. 73 0. 36/0. 0015 1. 21/0. 0031 20. 9/0. 068 0. 031/0. 109 2. 17 2. 72 3. 26 0. 54 (2 cell) 0. 1 Energy acceptance requirement (%) 1. 35 Energy acceptance by RF (%) Photon number due to beamstrahlung 2. 06 0. 29 Lifetime _simulation (min) 100 Lifetime (hour) F (hour glass) Lmax/IP (1034 cm-2 s-1) W 0. 67 (40 min) 0. 89 2. 93 1. 11 0. 36/0. 0015 0. 54/0. 0016 13. 9/0. 049 0. 013/0. 12 0. 47 650 (216816) 2. 98 6. 53 0. 87(2 cell) 0. 066 Z 45. 5 0. 036 23. 8 8. 0 12000 (25 ns+10%gap) 461 16. 5 0. 2/0. 0015 0. 17/0. 004 5. 9/0. 078 0. 0041/0. 056 0. 1 3 T 2 T 0. 2/0. 00 1 0. 17/0. 0015 2. 42 8. 5 1. 94(2 cell) 0. 038 1. 47 0. 44 1. 7 0. 55 2 0. 94 11. 5 4 0. 99 16. 6 32

Z pole electroweak physics Vs lumiosity • Assuming Z pole runs last for 180 days, Z cross section 60 nb • L=1 e 34, about 1010 Z Ø Ø Ø Observable Systematics L=1 e 34 (stat unc. ) 3 T, L=1. 6 e 35 (stat unc. ) L=3. 2 e 35 (stat unc. ) Key Mz. GZ 0. 5 Me. V 0. 2 Me. V 0. 05 Me. V 0. 035 Me. V E beam cali. ΔE < 500 ke. V R l =Gh/Gl 0. 01% 0. 0025% 0. 0018% Statistics Rb 0. 05% 0. 04% 0. 01% 0. 007% Statistics + small Rin ALR NA NA Beam polarization AFB lept. 0. 1% 0. 08% 0. 02% 0. 014% Forward acceptance From 1 e 34 to 1. 6 e 35 , large improvement in stat. uncertainty From 1. 6 e 35 to 3. 2 e 35 , improvement is not big From 3 T to 2 T, Momentum resolution degraded to 50%, higher Bk. G. (no major impact ) Key issue for Z pole physics, beam momentum systematics need to be smaller than 500 ke. V Beam polarization is needed for beam momentum measurement and ALR 5

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Cross section Vs W mass or W width • df 7

W mass stat uncertainty single energy point (500 fb-1) • df From Peixun and Gang 8

W width stat uncertainty single energy point (500 fb-1) • df width From Peixun and Gang 9

Start from detector solenoid 3. 0 T From Chenghui βy* Vs. coupling @ Z Limitation of the luminosity improvement by reducing the βy*

Start from detector solenoid 3. 0 T Coupling=1. 7% + 0. 3~0. 5% Large beam size & serious bunch lengthening Coupling Vs. Luminosity @ Z From Chenghui For the 2 Cell cavity operation, if the coupling lose control L L 0/2 ~ L 0/4