F. Richard ILC Beijing Feb. 2007 1

How to optimize the ILC energy for measuring ZH

Philip Bambade, François Richard

LAL/Orsay

Presented at the ECFA meeting in Valencia

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: - (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:Mh=1.5 GeV in Hµµ Mh ~ 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 HZ

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

2 30 1( ) (1 ) (1 )a af x a x a x x

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How does L vary with E? L can be maintained ~constant between 350 and

230 GeV provided is taken constant:

If N is constant (particles/bunch) Pelectrical goes like Ecm

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

2²= CM

z x

NE

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The ‘needle’ plot LDC (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

Rec. Mass 350 GeVin Hµµ 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 Ejet=AEjet A=0.3 assumed (not yet realistic since

Emax=150 GeV at √s=350 GeV due to asymmetric decays)

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LHC/ILC

LHC covers a much more restricted domain and cannot measure the mass if the Higgs decays invisibly

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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), h 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

Ref below gives the details of this analysishttp://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 ZZ background

Main Inputs

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Checks on BS

Pisin Chen/ Yokoya

checked againstGuinea Pig

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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-

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Study of the processe+e- Zh l+l- X using full detector simulation and event reconstruction

M. Ohlerich, A. Raspiareza, W. Lohmann

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mrecoil = 120.245±0.0162 GeV

L = 500 fb-1

%1.2

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