AA->HH Study-Current status of AA->4b BG-

Shin-ichi Kawada(AdSM, Hiroshima University)

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AA->HH subgroup : Experiment

Outline• Introduction• Previous results• Current issues --- Calculation of AA->4b BG• Results– Cross-section of AA->4b BG– Histograms

• Summary & Next plan

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Introduction• Photon Linear Collider (PLC) has been

proposed as one of the options of ILC.• It is expected that we can observe the Higgs

self-coupling in PLC.• Feasibility study of Higgs pair creation in PLC is

needed.

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About PLC

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Electrons

Backward Compton scattering

Gamma-gamma collision

ILC : e+ e- collision PLC : gamma gamma collision

Reaction in gamma-gamma collision

• Signal : AA->HH->4b• Many backgrounds– AA->WW, ZZ, 4b, etc…

• Analysis of background reduction is necessary.– We assumed that Higgs mass equals to 120GeV in

this study.

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4b = b b-bar b b-bar

Previous results (1)• Main backgrounds– AA->WW (~11.6pb, 1.5*107 events/year)– AA->ZZ (~9.42fb, 1.2*104 events/year)

• Analysis with Neural Network– We can observe Higgs pair creation if we can

develop good b-tagging method and jet clustering.

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BG usual cheatAA->WW 2.69 5.85AA->ZZ 1.61 5.85

Previous results (2)• Other background (AA->4b)– Calculate the cross-section of AA->4b with using

GRACE and BASES.– Total cross-section = 960fb (√s = 270GeV, no cuts)– Making histograms• cos_theta, invariant mass, energy, etc…

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Calculation of the cross-section of AA->4b

• Tried to calculate the cross-section with several conditions as below.– √s = 270GeV with cuts• cos_theta of quarks, 2-jet invariant mass

– convolute luminosity distribution– convolute luminosity distribution with cuts

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Cut criteria

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γ

γ

b

b-bar

b

b-bar

g*

B

A

Both invariant mass of A (MA) and that of B (MB) would be small.

If (MA < Mcut) and (MB < Mcut), then cut that events.

Mcut : Cut value for 2-jet invariant mass (GeV)

Main reaction of AA->4b

Cut results

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|cos_theta| cut Mcut cut √s = 270GeV (fb) with lumi. (fb)None None 960 109None 20GeV 778 77.1None 40GeV 404 27.8

<=0.99 None 102 34.6<=0.99 20GeV 100 24.7<=0.99 40GeV 80.1 8.57<=0.80 40GeV 4.11 0.577

cf :Total cross-section of signal : 0.19fbEffective cross-section of signal : 0.013fb

σsignal < σBG!!!

Discussion --- Cut results• Try to more cuts– Now using : cos_theta of quarks, 2-jet invariant

mass• Can we use other physical values as the cut

parameters?– Energy of 2-jet• Energy of 2-jet of 4b BG is near to the energy of initial

photon beam.

– Cos_theta of lowest 2-jet invariant mass– And more…?

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Histograms• Making 2-D and 3-D histograms between

signal and 4b BG– 2-D : 2-jet invariant mass (lowest & that’s pair)– 3-D : 2-jet invariant mass & cos_theta of lowest 2-

jet invariant mass

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LowINV

2-je

t inv

. mas

s of

pa

ir of

Low

INV

LowINV

2-jet inv. mass of

pair of LowINVco

s_th

eta

of

Low

INV

LowINV = lowest 2-jet inv. mass2-D

3-D

Results (2-D)

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Signal

4b BG(√s = 270GeV)

4b BG(with luminosity)

LowINV

2-je

t inv

. mas

s of

pa

ir of

Low

INV

Results (3-D)

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Signal

4b BG(with luminosity)

LowINV

2-jet inv. mass of

pair of LowINV

cos_

thet

a of

Lo

wIN

V

4b BG(√s = 270GeV)

Discussion --- Histograms• Event distribution is different between signal

and 4b BG.– 2-jet invariant mass• Signal : peak @ ~120GeV• 4b BG : peak @ <50GeV

– Cos_theta of lowest 2-jet invariant mass• Signal : flat• 4b BG : peak @ |cos_theta|~1

• These parameters could be used as the cut parameter.

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Summary• Calculation of AA->4b BG cross-section– 960fb (√s = 270GeV)– 109fb (with luminosity)– Applied some cuts, but σsignal < σBG!!!– Other physical values could be used as the cut

parameter.• Making histograms of 2-jet invariant mass and

cos_theta– Event distribution is different between signal and

4b BG.

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Next plan• Try to calculate AA->4b cross-section with

other cuts.– Now running…

• Creating AA->4b event generator– Now creating with SPRING.

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Backup slide

Luminosity distribution