Higgs pair production

in a Photon ColliderTohru Takahashi

Hiroshima Universityfor S.Kawada, N.Maeda, K.Ikematsu, K.Fujii,Y.Kurihara ,,,

1LCWS12 Arlington, TX

Higgs selfcoupling• A Higgs like particle found at LHC!• Higgs?, SM Higgs or ….

– coupling to fermions, gauge bosons• mass generation

– selfcoupling• symmetry breaking

T.Takahashi Hiroshima

How can the PLC do ?

even tough with the e+e-

2 4( )V

17th General Meeting @ KEK 3

This study

)1( SM

Self-coupling constant in the SM

Parameter of deviation from the SM

Final goal: Study of Higgs self-coupling

See feasibility of the measurement of Higgs pair creation in PLC.

how may events expected?

possible to suppress background?

S.Kawada.. et.al, Phys. Rev. D 85, 113009 (2012)

Sensitivity vs energy

T.Takahashi Hiroshima

BB

SM

obs

SM

L

L

N

NNysensitivit

GeVmH 120

η=η’=1,ηB=0

)(GeVs

11000 fbLdt

120hm GeV

Beam parameters (based on TESLA optimistic)

T.Takahashi Hiroshima

x3.7 x4.8Ee[GeV] 210 195n(1010) 2 2sz(mm) 0.35 0.35gex/y[m rad] 2.5/0.03 2.5/0.03bx/y[mm]@IP 1.5/0.3 1.5/0.3sx/y[nm] 96/4.7 99/5.5lL[nm] 1054 770x 3.76 4.8Pulse Energy[J] 10 10Lgeo(e-e-) [1034cm-2s-

1]8.7 8.1

Lpeak(gg) [1034cm-2s-

1]1.2 0.7

Ltot(gg)[1034cm-2s-1] 12.6 5.88

( ) ~ 270s peak GeV

Luminosity Distribution(CAIN)x=3.76

dLN s ds dtds

][106.12 1234 scmLdt

][102.1

)260(1234

scm

GeVLpeak

10

1

10-1

10-2

10-3

[ ]pb100

[ ]s GeV

Signal backgrounds

7

270GeV

gg->ZZ

tt

gg->WW

10-4 ( )HH bbbb

Signal & Backgrounds

• gg->WW 1.462*107events/year)

• gg->ZZ 1.187*104events/year

Signal

gg->HH( －＞ bbbb) 16.4events/year

Backgrounds

• gg->bbbb 1.187*104events/year

Assumption for the study integrated luminosity of 5 years of PLC run

106

dLs ds dtds

9

Event generation and Detector simulation

• detector simulation

• MC events• HH• WW• zz• bbbb

7.2 dead

45 1077.5 10

61 1061 10

!

10

Analysis• Signal

–gg->HH->bbbb• Kinematics and flavor information

– Jet clustering• forced 4 Jets

– Jet pairing– b tagging

• Event selection– pre-selection to reduced number of events– optimization with Neural Net

11

jet paring

22

22

22

212

j

H

j

HH

MMMM

The jet of the least χ2 was chosen to be the most probable combination.

M1, M2 ： reconstructed mass

MH ： Higgs mass

2W

2Z

2bb are defined the same way

(Mbb=10GeV)

12

Analysis ~ b tagging~

• impact parameter <- simple !

Nsig: Number of displaced tracks in a jet

nsigL

L

L

13

Selection (1)

99.0cos,05.0 # Jet w/ more 0 off-vertex(>3s) tracks > 3

# Jet w/ more than 1 off-vertex(>3s) tracks > 2 b-tagging

β ： Lorentz factor of a particle

θ ： Angle between a particle and the beam

HH WW ZZ bbbb

Total 80 7.3×107 59400 260000

Pre-selecttion 47.7 81300 51270 80000

pre-selection: cut tacks to forward/backward region loose b- tagging

14

Selection (2) --- Neural Network (NN)• parameters ：

– χH2 , χZ

2, χbb2

– transverse (longitudinal) momentum,– # of jets with displaced vertex jets, – visible energy, – Ycut value of jet clustering, – # of tracks

• Maximize statistical significance *

* *Sig Sig

stat

Sig Sig BG BG

NS

N N

N: # of events occurring in 5 years

η: selection efficiency

Sig: signal

BG: background

15

Example parameters For WW

2H (( 2))Njets Noff

WWHH

WWHH

Example of parameters for 4b

16

max[cos ]jet# tracks

bbbbHH

bbbbHH

17

example parameters for ZZ

2H

2Z

ZZHH

ZZHH

17th General Meeting @ KEK 18

Cut statictics

0.92SigJADE

total

NS

N

HH WW ZZ bbbbTotal 80 7.3×107 59400 260000

Pre-selecttion 47.7 81300 51270 80000

WW filter 12.3 24 234 380

ZZ filter 5.90 2 59 13

bbbb filter 3.77±0.08 0+1.8 5.4±0.6 7±1

jet clustering

17th General Meeting @ KEK 19

Ideal clusteringideal clustering usingcolor singlet information

for HH, WW,ZZ

not for bbbb as color singlet is nottrivial ( )jjm GeV

HHZZ

( )jjm GeV

H or zｂ

ｂ

17th General Meeting @ KEK 20

Cut statictics

HH WW ZZ bbbb

Total 80 7.3×107 59400 260000Pre-selecttion 47.7 55800 4170 77800WW filter 40 8 46 1826ZZ filter 36 8 19 8

bbbb filter 34.7±0.2 5±2 5.2±0.6 6±1

4.9SigIdeal

total

NS

N

21

Summary• We tried to see gg -> HH in a photon collider

based on TESLA optimistic parameters.• gg CM energy of 270GeV is optimum for mh

=120GeV• It is possible to suppress backgrounds with

improved jet clustering technique.– statistical significance of 4.9 with integrated luminosity

corresonds to 5 years of PLC run

22

Backup slide

17th General Meeting @ KEK 23

Ideal clustering

4.9SigIdeal

total

NS

N