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

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

8. F. Richard ILC Beijing Feb. 2007
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. F. Richard ILC Beijing Feb. 2007
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. F. Richard ILC Beijing Feb. 2007
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. F. Richard ILC Beijing Feb. 2007
Main Inputs
Ref below gives the details of this analysis
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. F. Richard ILC Beijing Feb. 2007
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. M. Ohlerich, A. Raspiareza, W. Lohmann
Study of the process e+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. F. Richard ILC Beijing Feb. 2007
L = 500 fb-1
mrecoil = ± GeV
F. Richard ILC Beijing Feb. 2007

16. F. Richard ILC Beijing Feb. 2007