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.