Higgs pair production at photon collider
ILC Physics WG general meeting21.November 2009
Hiroshima UniversityNozomi Maeda
Introduction
Photon Linear Collider (PLC) is gamma-gamma collision option in ILC.
We study feasibility of measurement of Higgs self-coupling constant =SM(1+) by ->HH
This process occurs at low energy(than e+e-). contribution to cross section is different.
Energy optimization
BB
SM
obs
SM
LL
NNN
ysensitivit
L:Luminosity(assume 1000fb-1) :detection efficiency :cross section B:background suppression
Higgs mass=120GeV
SMLysensitivit
=-1
=+1
Background
large background : ->WW ( ~ 90pb) cf.) Signal: = 0.044fb0.044fb/90pb = 4.9×10-7
10-7 background suppression is necessary.
(+,+), (-,-)
Luminosity spectrum
total luminosity of photon collision = 1.26×1035cm-2s-1
effective Xsec(Signal) = 0.013fb → 16event/yeareffective Xsec(BG) = 11,600fb → 1.467×107event/yearB<10-6 is required.
Simulation by CAIN.
Analysis ->HH H -> bb or WW* or gg …
H->bb mode has the largest Branching Ratio (when Higgs mass = 120GeV, B.R.=67.8%).
Signal:HH->4bBackground:WW->4quark
reconstruct particles from jet pairs that has the smallest 2.
22
22
22
212
jj
MMMM
M1, M2 = reconstructed particle mass M = MH or MW 2j = 2jets mass resolution
->WW rejuction
• pre-Selection :
use Neural Net(JetNet) to separate ->HH from ->WW.
input = 9, hidden = 18, output = 1# of loose b-tagged jets > 2 & # of tight b-tagged jets > 1 (loose : nsig=3.0, noffv=1 tight : nsig=3.0,
noffv=2)- >HH - >WWNo Cut 5.00E+04 7.50E+07pre- Selection 3.04E+04 8.62E+04
Signal = 5.00×104 BG = 7.50×107
• # of generated events :
• # of nodes :
NN output• input parameters :
2H, 2
W, # of tracks, momentum(transverse, longtidunal), Visible Energy, ycut, # of b-tagged jets(loose, tight) (loose : nsig=3.5, noffv=1 tight : nsig=3.5,
noffv=2)black:BG blue:Signal
87 1033.5
105.74
BG
156.0100.5
78054
Sig
NNout > 0.98
If PLC runs for 5years... Signal : 16×5×Sig ≒ 12.5 Background : 1.467×107×5×BG ≒ 3.9 significance =
3.1
0102030405060708090
100
0.15 0.2 0.25 0.3 0.35 0.4sqrt(s_AA)
Xsec
->ZZ background
->ZZ Xsec ≒ 50fb@300GeVphoton helicity = (+1, +1)
Integrate over 8deg<<172deg
(generated by Gounaris’s gamgamZZ code: hep-ph/0610085. offered by Tsumura-san.)
02468
101214
0.2 0.25 0.3 0.35 0.4 0.45
->ZZ background
->ZZ effective Xsec ≒ 9.6fb→1.2×104events/yearIntegrate over
8deg<<172deg (generated by Gounaris’s gamgamZZ code: hep-ph/0610085. offered by Tsumura-san.)
x=3.76
->ZZ->4f event generatorZZ decay modes are ... q = light
quark
→ develop ->ZZ->4f event generator
bbbb……be background source .
bbqq (12.9%), ccqq (10.3%), qqqq (18.3%), bbbb (2.28%), bbcc (3.62%), cccc (1.44%)
Z
Z
f
ff
fgamgamZZ code HELAS
use gamgamZZ code and HELAS for calculating helicity amplitude.
→ simulate ->ZZ event, and study how to reject ->ZZ.
->ZZ event generator
Z
ZXsec distribution
(not includes Z decay mode and Luminosity)
total Xsec = 49.8fb (consistent with gamgamZZ code)
Summary We study feasibility of measurement of Higgs
self-coupling constant at PLC. ->WW background is 106 times larger than
->HH signal. Neural Net with b-tagging and kinematics can
reject almost all ->WW background. ->ZZ event generator developing in progress. Next plan is including Z decay mode and
Luminosity spectrum to ->ZZ event generator.
->4b background
+ and other diagrams
Xsec(not convolute luminosity) = 2.81fb@optimum energy
b-tagging cannot reject ->4b too.