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

N ovel 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 1

Introduction • 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. 2

ISR in heavy particle production at the LHC ISR jets in heavy particle productions get rather high pt. Hadronization Parton showering ˜ ˜ ˜ ˜ g g g g Hard interaction PS g g g g g g Jets from PS are soft. PS may not describe the high pt jet distribution correctly. 3

ISR in heavy particle production at the LHC ISR jets in heavy particle productions get rather high pt. Hadronization Parton showering ˜ ˜ ˜ ˜ g g g g Hard interaction ISR PS g g g g g g Jets from PS are soft. PS may not describe the high pt jet distribution correctly. 3

MT2 end points gives squark/gluino masses. ’99 Lester, Summer MT2 ’03 Barr, Lester P vis P miss T 1 T 1 pp → gluino gluino P miss T → (vis+LSP) 1 (vis+LSP) 2 p p P vis P miss T 2 T 2 Two invisible LSP in the final states and each momenta cannot measured separately. m 2 � � m 2 T ( p vis T 1 , p miss T 1 ) , m 2 T ( p vis T 2 , p miss �� T 2 ( m χ ) ≡ min max T 2 ) , p miss T 1 + p miss T 2 = p miss T i ) 2 + m 2 m 2 � p vis T i , p miss � = ( m vis � E vis T i E miss − p vis T i · p miss � χ + 2 T T i T i T i m 2 T 2 ( m χ = m χ 0 1 ) ≤ max ( m ˜ q ) g , m ˜ MT2 4

A.Barr et al, arxiv:0711.4008 B.Gripaios, arxiv:0709.2740 W.Cho et al, arxiv:0709.0288,0711.4526 Kink in MT2 endpoints g → qq χ 0 1 qq χ 0 p p → ˜ g ˜ 1 M T 2 ≤ m ˜ m χ test = m χ 0 g (GeV) 1100 1 1050 There is a kink at the true 1000 mAMSB(heavy squark) LSP mass. 950 900 ~ ) (g max 850 m T2 Gluino and the LSP masses 800 are determined 750 simultaneously from the 700 kink. 650 0 50 100 150 200 250 300 350 m � (GeV) We consider effects on MT2 from an ’07 W.Cho, K.Choi, Y.G.Kim, C.B.Park additional ISR jet. 5

MC simulation χ 0 χ 0 pp → ˜ g ˜ g + j → ( qq ˜ 1 )( qq ˜ 1 ) + j g = 685 GeV , m ˜ q = 1426 GeV , m ˜ 1 = 102 GeV , m ˜ χ 0 χ 0 B (˜ → qq ˜ 1 ) = 1 g ME/PS matching Madgraph/Madevent Detector simulation AcerDet Cross section = 2.5 pb Luminosity = 40/fb 6

How to define pvis � � M T ( p vis 1 , p T 1 χ , m test ) , M T ( p vis 2 , p T 2 χ , m test �� M T 2 = min max . χ χ p T 1 χ + p T 2 χ = p T miss simple example 1. Consider 4 highest pt jets (p1- p4). p vis 1 p 1 2. Assign p1(p2) to p1vis(p2vis) p 4 3. Assign p3,p4 to either p1vis or p p p2vis. p 3 p vis 4. take the combination which gives 2 p 2 the smallest MT2. 7

reconstructed MT2 m test = 102 GeV χ Total input gluino mass gluino+gluino+hard inclusive ISR with PS gluino+gluino exclusive N(inclusive)/N(exclusive)=1.4 Large contribution from hard ISR. 8

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 9

MT2min 1. Consider 5 (not 4) highest pt jets p vis (p1-p5). 1 p 1 2. Remove one of p1 and calculate MT2(i). p 4 p p p 3 M T 2 ( i ) = M T 2 ( p 1 , ..., p i − 1 , p i +1 , ...p 5 ) p 5 p vis 2 p 2 3. Take the minimum of MT2(i). M min T 2 ≡ min i =1 ,.. 5 ( M T 2 ( i )) . If we misidentify the ISR jet as a jet from gluino decay, MT2 tends to be large. 10

m test MT2min distribution = 102 GeV χ Reconstructed Parton f ( x ) = θ ( x − M end )[ a 1 ( x − M end ) + b ] + θ ( x − M end )[ a 2 ( x − M end ) + b ] 672 . 7 ± 3 . 5 GeV 673 . 9 ± 2 . 5 GeV 675 . 4 ± 6 . 4 GeV i min ≥ 3 input gluino mass 685 GeV 11

MT2 end points n jet ( E T ≥ 50 GeV ) ≥ 5 i min ≥ 3 MT2 end points are almost consistent with theoretical predictions. 12

Summary • 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. 13