ISTEP2016 Project

Zprime Searches at 13TeV PP Collider

李博洋、张育飞、韩大伟、何显科、王梦真、王妙

Introduction

Various extensions of the Standard Models predict the existence of new kinds of heavy gauge bosons .

Due to their simplicity and clean signature in leptonic decay, searches for Z' and W' serve as the benchmark to examine the potential of future high energy colliders.

In this study, we are particular interested in the Sequential Standard Model

The Lagrangian of SM

'3 1 2

'1 2 3

g B W W iWg

gW iW B Wg

The gauge bosons appear in the covariant derivative

The w3 and B bosons mix ,give Z and photon A

The SSM (Sequential Standard Model)

Z' is a carbon copy of SM Z boson with the same couplings with a heavier mass

Z' is created through qqbar annihilation and decays in SM final states.

◮ ATLAS high-mass ditau: exclude Z′

SSM masses below 1.4

TeV(4.6fb−1 at√s = 7TeV) and 1.9 TeV(19.5fb−1 at

√s = 8TeV).

◮ ATLAS high-mass ditau: exclude Z′

SSM masses below 1.4

TeV(4.6fb−1 at√s = 7TeV) and 1.9 TeV(19.5fb−1 at

√s = 8TeV).

The CMS results :exclude Z′

SSM masses below 1.4 TeV(4.9fb−1 at√s = 7TeV) and 1.3 TeV(19.7fb−1 at

√s = 8TeV( in τ lepton pairs

decaying into final states with an electron and a muon)

◮ The most stringent mass limits on Z′

SSM production in the decay

channel of the Z′

to a pair of electrons or muons amount to 3.4 TeV

in the case of ATLAS and 3.2 TeV in the case of CMS,at√s = 13TeV.

Discovery research at 13 TeV @LHC

Relevant processes in our study are Drell-Yan, TTbar, Diboson, Single top, and our Zprime signal .the final states are dimuon.

Relevant Feynman diagrams:

Cross sections of bkg and signal

Background/Signal Cross section

DY 5.14615

ST 0.0361963

TT 1.04458

WW 0.178684

ZP2000 10.9372

ZP2500 2.99436

ZP3000 0.880089

ZP3500 0.28073

ZP4000 0.0968058

ZP4500 0.0371262

Inv mass distribution of bkg and signal

[GeV] μμM0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

Even

ts/b

in

2−10

1−10

1

10DYTTSTWWZprime 2000Zprime 2500Zprime 3000Zprime 3500Zprime 4000Zprime 4500

=13TeVs (mu-channel) at -1ISTEP Preliminary 1. fb

Strategy

Loop for the best cut in the inv mass range[0,5000](GeV) to find the biggest q0 and significance .

Numerical results:

Pt distribution before inv mass cut

ptMu1/GeV0 200 400 600 800 1000 1200 1400 1600 1800 2000

even

ts/fb

-1

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

bkgptMu1_ZP2000_bkg

Entries 135230Mean 419.1RMS 149.4

signalbkg

bkg

ptMu1/GeV0 200 400 600 800 1000 1200 1400 1600 1800 2000

even

ts/fb

-1

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

bkgptMu1_ZP2500_bkg

Entries 135230Mean 419.1RMS 149.4

signalbkg

bkg

ptMu1/GeV0 200 400 600 800 1000 1200 1400 1600 1800 2000

even

ts/fb

-1

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

bkgptMu1_ZP3000_bkg

Entries 135230Mean 419.1RMS 149.4

signalbkg

bkg

ptMu1/GeV0 200 400 600 800 1000 1200 1400 1600 1800 2000

even

ts/fb

-1

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

bkgptMu1_ZP3500_bkg

Entries 135230Mean 419.1RMS 149.4

signalbkg

bkg

ptMu1/GeV0 200 400 600 800 1000 1200 1400 1600 1800 2000

even

ts/fb

-1

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

bkgptMu1_ZP4000_bkg

Entries 135230Mean 419.1RMS 149.4

signalbkg

bkg

ptMu1/GeV0 200 400 600 800 1000 1200 1400 1600 1800 2000

even

ts/fb

-1

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

bkgptMu1_ZP4500_bkg

Entries 135230Mean 419.1RMS 149.4

signalbkg

bkg

Pt distribution after inv mass cut

ptMu1/GeV0 200 400 600 800 1000 1200 1400 1600 1800 2000

even

ts/fb

-1

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

bkgptMu1_ZP2000_bkg

Entries 6790Mean 714.5RMS 223.2

signalbkg

bkg

ptMu1/GeV0 200 400 600 800 1000 1200 1400 1600 1800 2000

even

ts/fb

-1

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

bkgptMu1_ZP2500_bkg

Entries 1943Mean 851.1RMS 251.7

signalbkg

bkg

ptMu1/GeV0 200 400 600 800 1000 1200 1400 1600 1800 2000

even

ts/fb

-1

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

bkgptMu1_ZP3000_bkg

Entries 529Mean 962.4RMS 281.2

signalbkg

bkg

ptMu1/GeV0 200 400 600 800 1000 1200 1400 1600 1800 2000

even

ts/fb

-1

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

bkgptMu1_ZP3500_bkg

Entries 125Mean 1056RMS 341.9

signalbkg

bkg

ptMu1/GeV0 200 400 600 800 1000 1200 1400 1600 1800 2000

even

ts/fb

-1

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

bkgptMu1_ZP4000_bkg

Entries 62Mean 1066RMS 380.7

signalbkg

bkg

ptMu1/GeV0 200 400 600 800 1000 1200 1400 1600 1800 2000

even

ts/fb

-1

0

0.02

0.04

0.06

0.08

0.1

0.12

bkgptMu1_ZP4500_bkg

Entries 18Mean 1345RMS 339

signalbkg

bkg

Two dimentional distribution of pt and mll

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

-310×

mll(GeV)0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

(GeV

)m

u1pt

0

200

400

600

800

1000

1200

1400

TTmll_TT

Entries 54978Mean x 1143Mean y 423.8RMS x 287.6RMS y 146.7

TT0

0.000

0.001

0.001

0.002

0.002

0.003

0.003

mll(GeV)0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

(GeV

)m

u1pt

0

200

400

600

800

1000

1200

1400

DYmll_DY

Entries 55039Mean x 1143Mean y 423.7RMS x 288.2RMS y 147

DY

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

mll(GeV)0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

(GeV

)m

u1pt

0

200

400

600

800

1000

1200

1400

ZP2000mll_ZP2000

Entries 7020Mean x 1925Mean y 685.1RMS x 268.5RMS y 207.5

ZP2000

0

0.000

0.000

0.000

0.000

0.001

0.001

0.001

0.001

0.001

mll(GeV)0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

(GeV

)m

u1pt

0

200

400

600

800

1000

1200

1400

ZP2500mll_ZP2500

Entries 6581Mean x 2361Mean y 810.7RMS x 384.2RMS y 263.1

ZP2500

Probability Distribution function of BDT inputs for MZ’ =2000GeV

mll [GeV]

1000 2000 3000 4000 5000

128

GeV

/ (1

/N) d

N

0

0.0005

0.001

0.0015

0.002

0.0025

0.003SignalBackground

U/O

-flo

w (S

,B):

(0.0

, 0.0

)% /

(0.0

, 0.0

)%

Input variable: mll

ptll [GeV]

200 400 600 800 1000

29.1

GeV

/ (1

/N) d

N

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.009

U/O

-flo

w (S

,B):

(0.0

, 0.0

)% /

(0.1

, 0.0

)%

Input variable: ptll

ptMu1 [GeV]

200400 60080010001200140016001800200022002400

58.9

GeV

/ (1

/N) d

N

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

U/O

-flo

w (S

,B):

(0.0

, 0.0

)% /

(0.0

, 0.0

)%

Input variable: ptMu1

ptMu2 [GeV]200 400 600 800 1000 12001400 16001800

44.7

GeV

/ (1

/N) d

N

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0.0035

U/O

-flo

w (S

,B):

(0.0

, 0.0

)% /

(0.0

, 0.0

)%Input variable: ptMu2

detall

0.5 1 1.5 2 2.5 3 3.5 4 4.5

0.12

2 /

(1/N

) dN

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

U/O

-flo

w (S

,B):

(0.0

, 0.0

)% /

(0.0

, 0.0

)%

Input variable: detall

dphill1.6 1.8 2 2.2 2.4 2.6 2.8 3

0.04

12

/ (1

/N) d

N

0

2

4

6

8

10

12

U/O

-flo

w (S

,B):

(0.2

, 0.2

)% /

(0.0

, 0.0

)%

Input variable: dphill

Correlation matrices of bkg and signal

BDT output of signal and bkg

BDTG response0.8− 0.6− 0.4− 0.2− 0 0.2 0.4 0.6 0.8

dx / (1/

N) dN

0

2

4

6

8

10

12

14

16

18SignalBackground

U/O-

flow

(S,B

): (0.

0, 0.0

)% / (

0.0, 0

.0)%

TMVA response for classifier: BDTG

Best cut on BDT and the significance

Summary

• We have analyzed the discovery significance of a new neutral gauge boson

• The BDT method is the best way to separate the signal and bkg .The significance obtained in such a way is higher than the traditional methods such as those based on the single inv mass cut.

Outlook

• suppress TTbar bkg

• We considered WW but not WZ or ZZ for the diboson contributions .the bkg from WZ or ZZ process.

• Shape Analysis instead of Cut/counting

工作量

• 李博洋(写code)

• 张育飞(算法，理论，PPT制作)

• 韩大伟(PPT制作)

• 何显科(图片后期处理)

• 王梦真(PPT制作)

• 王妙(文献查找)

Thank�You