Gluino/squarks will be produced copiously at the LHC if the masses - - PowerPoint PPT Presentation

Novel reconstruction technique for

new physics with ISR

Yasuhiro Shimizu( IIAIR, Tohoku)

J.Alwall, K.Hiramatsu, M.M.Nojiri, Y.S, PRL:103(2009)151802 2010/5/10-13@Madison,WI

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• Gluino/squarks will be produced copiously at the LHC if the masses

are less than 1 TeV.

• Gluino/squark mass reconstruction is very important issue.
• For heavy particle productions, initial state radiation (ISR) jets are

rather hard.

• The hard ISR jets become serious BG for SUSY mass

reconstruction.

• We propose a new method to remove the ISR BG using MT2.

Introduction

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ISR in heavy particle production at the LHC

Hadronization Parton showering Hard interaction

g g g

˜ g ˜ g

ISR jets in heavy particle productions get rather high pt.

PS may not describe the high pt jet distribution correctly. Jets from PS are soft.

g g g

˜ g ˜ g

PS

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ISR in heavy particle production at the LHC

Hadronization Parton showering Hard interaction

g g g

˜ g ˜ g

ISR

ISR jets in heavy particle productions get rather high pt.

PS may not describe the high pt jet distribution correctly. Jets from PS are soft.

g g g

˜ g ˜ g

PS

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MT2

m2

T

• pvis

T i , pmiss T i

• = (mvis

i )2 + m2 χ + 2

• Evis

T i Emiss T i

− pvis

T i · pmiss T i

• m2

T 2(mχ = mχ0

1) ≤ max(m˜

g, m˜ q)

MT2 end points gives squark/gluino masses.

’99 Lester, Summer ’03 Barr, Lester

pp→gluino gluino →(vis+LSP)1 (vis+LSP) 2

Two invisible LSP in the final states and each momenta cannot measured separately.

MT2

P miss

T

P miss

T 1

P miss

T 2

P vis

T 2

P vis

T 1

m2

T 2(mχ) ≡

min

pmiss

T 1 +pmiss T 2 =pmiss T

• max
• m2

T (pvis T 1, pmiss T 1 ), m2 T (pvis T 2, pmiss T 2 )

• ,

p p

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Kink in MT2 endpoints

650 700 750 800 850 900 950 1000 1050 1100 50 100 150 200 250 300 350

(GeV) m (GeV)

mT2

max

(g

~)

mAMSB(heavy squark)

p p → ˜ g ˜ g → qqχ0

1 qqχ0 1

’07 W.Cho, K.Choi, Y.G.Kim, C.B.Park

There is a kink at the true LSP mass.

MT 2 ≤ m˜

g

mχtest = mχ0

1

We consider effects on MT2 from an additional ISR jet.

W.Cho et al, arxiv:0709.0288,0711.4526 B.Gripaios, arxiv:0709.2740 A.Barr et al, arxiv:0711.4008

Gluino and the LSP masses are determined simultaneously from the kink.

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MC simulation

pp → ˜ g˜ g + j → (qq ˜ χ0

1)(qq ˜

χ0

1) + j m˜

g = 685 GeV, m˜ q = 1426 GeV, m˜ χ0

1 = 102 GeV,

ME/PS matching

Madgraph/Madevent

Detector simulation AcerDet Cross section = 2.5 pb Luminosity = 40/fb

B(˜ g → qq ˜ χ0

1) = 1

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p p

How to define pvis

p1

p2

p3 p4

pvis

1

pvis

2

MT 2 = min

pT

1χ+pT 2χ=pT miss

• max
• MT (pvis

1 , pT 1χ, mtest χ

), MT (pvis

2 , pT 2χ, mtest χ

• .
• 1. Consider 4 highest pt jets (p1-

p4).

• 2. Assign p1(p2) to p1vis(p2vis)
• 3. Assign p3,p4 to either p1vis or

p2vis.

• 4. take the combination which gives

the smallest MT2.

simple example

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reconstructed MT2

mtest

χ

= 102 GeV

N(inclusive)/N(exclusive)=1.4

Large contribution from hard ISR.

Total inclusive exclusive input gluino mass

gluino+gluino gluino+gluino+hard ISR with PS

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pt order of ISR parton among five parton

ISR parton is the 5th softest parton: only 22 %

high probability to misidentify the jets from gluino decay

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MT2min

MT 2(i) = MT 2(p1, ..., pi−1, pi+1, ...p5)

M min

T 2 ≡ min i=1,..5(MT 2(i)).

p p p1

p2

p3 p4

pvis

1

pvis

2

p5

• 1. Consider 5 (not 4) highest pt jets

(p1-p5).

• 2. Remove one of p1 and calculate

MT2(i).

• 3. Take the minimum of MT2(i).

If we misidentify the ISR jet as a jet from gluino decay, MT2 tends to be large.

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f(x) = θ(x − M end)[a1(x − M end) + b] + θ(x − M end)[a2(x − M end) + b]

Reconstructed Parton

672.7 ± 3.5 GeV 675.4 ± 6.4 GeV imin ≥ 3

673.9 ± 2.5 GeV

MT2min distribution

mtest

χ

= 102 GeV

input gluino mass 685 GeV

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MT2 end points MT2 end points are almost consistent with theoretical predictions.

njet(ET ≥ 50GeV ) ≥ 5

imin ≥ 3

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• ISR is rather hard for heavy gluino productions.
• The hard ISR is included with ME/PS matching by Magraph/

Madevent.

• We defined the MT2min variable by minimizing MT2

variables for all combinations.

• ISR can be removed by cuts to MT2min and MT2min end

points become clearer.

Summary

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