progress on susy particles reconstruction methods

Progress on SUSY particles reconstruction methods

Massimiliano Chiorboli

Università di Catania

31/10/2001 Massimiliano Chiorboli CMS Physics Meeting

mSUGRA Points

Proposed Post-LEP Benchmarks for Supersymmetry (hep-ph/0106204)

High total SUSY cross section

we can try to reconstruct masses with low integrated luminosity


Point B

m0 100 GeV

m1/2 250 GeV

tan 10

A0 0

sign +

g 643.3 tL 412.5

bL 522.5 tR 600.5

bR 549.7 40 379.1

qL 570 30 358.8

qR 549 20 186.8

lL 211.4 2± 379.7

lR 145.8 1± 186.0

10 = LSP 99.6

pb 41.41TOTSUSY


Decay chain and event topology

bb~

g~ pp

b~02

01

~

(26 %)

(35 %)

(0.2 %)

01

~ ~

(60 %)

p

p

g~

b~

b

b

01

~

02

~ ~

Event final state:

• 2 high pt isolated leptons OS

• 2 high pt b jets

• missing Et


Events Production

• SPYTHIA (PYTHIA 6.136)• CMSJET 4.703

-1fb 10

SUSY (10 fb-1)ll 3912

17522

g 4420

gg 42809

q 14895

qg 192400

tt 15587

qq 108849

qb 3423

bb 5959

bg 4280

Total 414056

SMtt 6.2×106 (= 10 fb-1)

Z+jet (pthat >60) 8×106 (< 10 fb-1)

W+jet (pthat >60) 3×106 (< 10 fb-1)

ZZ,WW,ZW 2×106 (> 10 fb-1)

No pile-up


Events selection

• at least 2 isolated leptons with pt>10 GeV and ||<2.5

• at least 2 b-jets with pt>15 GeV and ||<2

SUSY (10 fb-1) %ll 0

13 0.07

g 104 2.3

gg 1753 4.1

q 25 0.16

qg 3387 1.8

tt 525 3.3

qq 138 0.1

qb 90 2.6

bb 542 9.0

bg 272 6.4

SMtt 20770 (0.04 %)

Z+jet (pthat >60) 68 ( /106)

W+jet (pthat >60) 0 ( /106)

ZZ,WW,ZW 32 ( /106)


Reconstruction of 0

102

~ ~

~

GeV 32.85 M

)MM)(MM(M

~

2~

2~

2~

2~

max01

02

SUSY SM SUSY + SM

PYTHIA Signal

CMSJET


Subtracting invariant mass of OSOF pairs eliminate tt and combinatorial bkg, but not Z+jet

Other cuts

Reconstruction of 0

102

~ ~

~


GeV 50 EmissT

Reconstruction of 0

102

~ ~

~


GeV 1.64 86.00 Mmax

GeV 32.85 M

)MM)(MM(M

~

2~

2~

2~

2~

max01

02

01

02

~ ~

~Reconstruction of

Result of fit:

Generated value:


reconstruction

02

~ 01

~

~maxM

GeV 92 M GeV 75

02

~

p

M

M1p

01

02

~

~


Sbottom reconstruction

reconstructed neutralino combined with the most energetic b-jet, assuming Mknown

SUSY Signal

SUSY bkg

qg qq

gg q

g

bb tt

bg ll

qb

Cutting on Etmiss allows to suppress the SM bkg

GeV 50 EmissT


2 sbottoms

Etmiss > 100 GeV Et

miss > 150 GeV

we can’t resolve the 2 peaks

GeV 549.7 b~

GeV 522.5 b~

R

L

Sbottom reconstruction

10 fb-1


M(b) estimation

47.5

GeV 6.6509.5b)~M( 02

GeV 7.549)b~

M(

GeV 5.522)b~

M(

R

L

Result of fit:

Generated masses:


Estimation of Mllbmax

02

~01

~

~b~

b

PYTHIA Signal

total

Lb~

Rb~


GeV 38.11.364Mmaxb

GeV 12.844 M

)MM)(MM(M

02

01

02

02L

~

2~

2~

2~

2

b~

max

b

GeV 37.504 M

)MM)(MM(M

02

01

02

02R

~

2~

2~

2~

2

b~

max

b

Estimation of Mllbmax

GeV 50EmissT

Result of fit:


Gluino Reconstruction

SUSY Signal

SUSY bkg

qg qq

gg q

g

bg tt

ll

bb

qb

Another b-jet is associated to the recostructed sbottom

b)b~

( angle

the b-jet closest in angle to the

reconstructed sbottom is chosen



Etmiss > 50 GeV Et

miss > 100 GeV Etmiss > 150 GeV


66.6

GeV 9.2611.2bb)~M( 02


Result of fit:

GeV 3.643)g~M( Generated mass:


Combinatorial suppression

b)b~

( angle


Gluino after angle cut

4.0cos

8.0cos

71.0

GeV 9.6604.6bb)~M( 02

66.9

GeV 13.3597.4bb)~M( 02

10 fb-1


Sbottom after angle cut

4.0cos

8.0cos

50.5

GeV 8.5502.4b)~M( 02

56.9

GeV 8.6511.8b)~M( 02

10 fb-1


Estimation of

4.0cos

doesn’t depend on M(10) !

GeV 30)~M( 01

)b~

M(-)g~M(

)b~

M(-)g~M(


30.8

GeV 5.80.78b)~M(bb)~M( 02

02

4.0cos

GeV 6.93)b~

M(-)g~M(

GeV 8.120)b~

M(-)g~M(

R

L

Estimation of )b~

M(-)g~M(

Result of fit:

From the model:


Sbottom and Gluino reconstruction With 40 fb-1

49.7

GeV 3.9514.5b)~M( 02

68.2

GeV 5.4615.4bb)~M( 02

No angle cutssbottom gluino

Only SUSYEtmiss > 150 GeV

GeV 3. 643 ) g~ M(GeV 7.549)b

~M(

GeV 5.522)b~

M(

R

L


With 40 fb-1

4.0cos

8.0cos

53.4

GeV 4.4506.6b)~M( 02

50.4

GeV 8.3519.3b)~M( 02

sbottom

GeV 7.549)b~

M(

GeV 5.522)b~

M(

R

L

Generated values


With 40 fb-1

4.0cos

8.0cos

70.4

GeV 5.6607.8bb)~M( 02

72.8

GeV 9.1611.2bb)~M( 02

gluino

Generated value GeV 3. 643 ) g~ M(


With 40 fb-1

1.72

GeV 2.11.69b)~M(bb)~M( 02

02

.542

GeV 3.90.94b)~M(bb)~M( 02

02

no cut 4.0cos )b~

M(-)g~M(


Point G

+sign

0A0

20tan

375 GeVm1/2

120 GeVm0

152.510 = LSP

294.51±193.4lR

546.12±299.6lL

294.820780qR

532.430814qL

545.340771.3bR

800.8tR723.0bL

589.4tL919.8g

pb 6.00TOTSUSY


Point G

bb~

g~ pp

b~02

(26 %)

(44 %)

01

~ ~

(8.8 %)

GeV 140 M GeV 100

GeV 300 E

fb 60missT

-1


Conclusions

• estimation of M(l+l-)max

• estimation of M(l+l-b)max

• sbottom reconstruction with Resol. ~ 10 %, but 2 sbottoms not resolved

• gluino reconstruction with Resol. ~ 12 %

• M(g) - M(b) estimation, independent from M(10), with Err ~ 7 %

Point B, with 10 fb-1

Point G, with 60 fb-1

• No sbottom reconstruction, needs more investigation

~2~

2~

2~

2~ M)MM)(MM( 0

102

02

01

02

02R

~2~

2~

2~

2

b~ M)MM)(MM(

progress on susy particles reconstruction methods

Documents

peaks10 fb

angle cut10 fb

energetic bjet

z jet pthat

w jet pthat

bmax sbottom reconstruction

generated masses

high pt b jets