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Optimizing ILC Energy for Accurate Measurements of the Higgs Boson at the ECFA Meeting

At the ECFA meeting in Valencia, Philip Bambade and François Richard presented a detailed analysis on optimizing the International Linear Collider (ILC) energy levels to enhance measurement precision for the Higgs boson. They argue that operating at approximately ( sqrt{s} sim MH + 110 ) GeV, rather than strictly at the top threshold, provides significantly better recoil mass resolution. The discussion highlights energy configurations at 350 GeV and 230 GeV, addressing challenges like beam energy requirements and beamstrahlung effects to maximize experimental potential in discovering phenomena like invisible decays.

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Optimizing ILC Energy for Accurate Measurements of the Higgs Boson at the ECFA Meeting

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  1. Presented at the ECFA meeting in Valencia How to optimize the ILC energy for measuring ZH Philip Bambade, François Richard LAL/Orsay F. Richard ILC Beijing Feb. 2007

  2. Introduction • TESLA scenario for ZH(120): 500 fb-1 at √s=350 GeV (the top threshold) • Here we suggest that running at √s~MH+110 is more adequate since one has: - s(HZ) twice larger if MH=120 GeV - the recoil mass resolution for Hµµ is 4 times better • Also, while it seems much more useful to operate at √s=500 GeV for ttH, ZHH and new physics, this energy seems inadequate for measuring Higgs mass and branching ratios F. Richard ILC Beijing Feb. 2007

  3. Running at 350 GeV • TESLA TDR at 350 GeV: sMh=1.5 GeV in Hµµ • sMh ~ p(2ECMp-Mz²) p=momentum of the muon • At 230 GeV ~4 times better • Similar gains are observed in the hadronic mode F. Richard ILC Beijing Feb. 2007

  4. Running at 230 GeV • Fast rising of sHZ Objections: • Undulator requires beam energy>150 GeV ? To be checked • How does L vary with s ? • Beamstrahlung F. Richard ILC Beijing Feb. 2007

  5. Beamstrahlung • Formula where x=E/E0 at the beam level • There is a ‘hard-core’ with a0 ~0.5 at 500 GeV a0 increases at lower energy • -> With a better momentum resolution there is always improvement F. Richard ILC Beijing Feb. 2007

  6. How does L vary with E? • L can be maintained ~constant between 350 and 230 GeV provided d is taken constant: • If N is constant (particles/bunch) Pelectrical goes like Ecm • d constant means more focusing in x and/or shorter bunches • Seems possible, but is it optimum for recoil mass? • The answer is yes optimizing on L(a0)² F. Richard ILC Beijing Feb. 2007

  7. The ‘needle’ plot Rec. Mass 350 GeV in Hµµ 230 GeV • LDC d(1/p)<510-5 GeV-1 • BS, ISR, FSR included • Same BS for both Ecm • NB: Eb stability <1-210-4 needed 350(230) GeV F. Richard ILC Beijing Feb. 2007

  8. Invisible decays • Present in many BSM scenarios: SUSY, Higher dimensions etc… • Very large discovery potential for ILC • Best sensitivity using recoil to Zhad • DEjet=AEjet A=0.3 assumed (not yet realistic since Emax=150 GeV at √s=350 GeV due to asymmetric decays) F. Richard ILC Beijing Feb. 2007

  9. LHC/ILC • LHC covers a much more restricted domain and cannot measure the mass if the Higgs decays invisibly F. Richard ILC Beijing Feb. 2007

  10. Conclusions If Mh=120 GeV, there are many good reasons to run at ~230 GeV: • Maximum cross section • Best possible precision on Mh (the ‘needle’ plot), Gh and BRinv • We should therefore see what are the limitations on the Machine side • Detector performances are essential F. Richard ILC Beijing Feb. 2007

  11. Main Inputs • Ref below gives the details of this analysis http://esgard.lal.in2p3.fr/Project/Activities/Current/ Networking/N2/ELAN/Documents/2007/ • Use of Chen/Yokoya parametrization checked against Guinea Pig • Use of an BS spectrum at 230 GeV with twice more focusing in x and 1.5 shorter bunches • Use an LDC momentum resolution and take into account asymmetric decays • Use a realistic ZZg background F. Richard ILC Beijing Feb. 2007

  12. Checks on BS Pisin Chen/ Yokoya checked against Guinea Pig F. Richard ILC Beijing Feb. 2007

  13. Control of systematics for Hµµ • Beam Energy /E<10-3 stability <210-4 • Twice tighter at 350 GeV • Momentum calibration at Z pole • BS through acollinear e+e- F. Richard ILC Beijing Feb. 2007

  14. Study of the processe+e- Zh l+l- X using full detector simulation and event reconstruction M. Ohlerich, A. Raspiareza, W. Lohmann F. Richard ILC Beijing Feb. 2007

  15. L = 500 fb-1 mrecoil = 120.245±0.0162 GeV F. Richard ILC Beijing Feb. 2007

  16. F. Richard ILC Beijing Feb. 2007

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