Status of GMSB studies

Status of GMSB studies

Shilei Zang

University of Colorado, Boulder

CU CMS Meeting, 28th Apr. 2008

2

Outline

• Invariant mass of neutralino

• De-convolution method

G~~0

1

3

G~

01

~

01

~

p p

q

q

q

q ~…

…

jet

jet

jet

jet

G~

~

• MET distribution is used to get signal yield, but we have two gravitinos.

21 METMETMET

MET

4

• MET distribution is used to get signal yield. Simple variable; powerful separation; largely used• 1) It’s crowded at small MET region for both signal and

background.• 2) Shapes are different for signal and each bkg.• 3) Vector addition of the two gravitinos.• 4) MET resolution is difficult to estimate.• 5) Can not get mass from MET MET is not a much sensitive variable; bkg studies are

difficult; not directly relate with mass

Can we use the invariant mass of photon+gravitino?

5

)]())()(()))(()([(2

))]~

()~

(())()((

))~

()~

())(()([(24

2121

2121

21212

METppMETEE

GpGppp

GEGEEEmass

TT

2/)]())()(()))(()([(~ 2121 METppMETEEmass TT

G~~0

1 )]

~()()

~()([2

);~

(),~

();(),(:~);

~(),

~();(),(:~

2

22220

1

11110

1

GppGEEmass

GpGEpE

GpGEpE

6

• MET

• Pt2>0GeV

• Peak=157 GeV

• MET

• Pt1>90GeV; Pt2>30GeV

• Peak=160.4 GeV;

MET

7

• Pt2>0GeV

• Peak=185GeV

• Sig=77GeV

• Pt1>90GeV; Pt2>30GeV; MET>130GeV

• Peak=223GeV; sig=61GeV


• Pt1>90GeV; Pt2>30GeV;

• Peak=196GeV

Invariant mass of neutralino

8

two gravitinos.photon and gravitino.

photon1 and gravitino2 photon2 and gravitino1

• Cos(theta) from MC Truth G~~0

1

9

• Cos(theta) of and .)()( 21 TT pp

MET


10

• Ratio = (-cos(theta))/cos(theta)


2/)]())()(()))(()([(~2 2121 METppMETEEmass TT

-cos(theta)

cos(theta)

-cos(theta)

cos(theta)

11

mass mass2

mass2 weighted

mass minus

mass2 weighted

• mass = CB Line; mass2weighted = CB Line + Polynomial

• mass = mass2weighted for background

12

Variables for GMSB analysis

I. MET

II. Rough mass of neutralino

III. Edge of MT2 distribution

IV. Edges of some invariant masses

V. Accurate calculation with cross-events for long decay chain

VI. Long-lived neutralinos: photon timing, cluster shapes, decay chain, .. (CDF, ATLAS, CMS)

VII. Deconvolution method accurate mass of neutralino; accurate ctau of neutralino

hep-ph/9906349

CMS Note1997/079

arXiv:0802.4290v1

13


2/)]())()((|)()([|~ 2121 METppMETppPmass TTTT

)]())()((2/)))(()([(~ 2121 METppMETEEmassB TT

Rough mass of neutralino

• Many questions on mass: Not accurate; Bias? Shape? Backgrounds?

• Signal can be fitted with CB Line?• Bkg shapes are expected to be similar (CB Line +

Polynomial functions) can study all backgrounds together?

• mass2weighted can be used for bkg study or as a cross check.

14

De-convolution Method

• Convolution: b

adtgftgf )()())((

dtgtfttgf

gbfafgbfgaf

fffggf

)()())((

)(

;

00

2121 linear

shift-invariant

f(mass)

(mass)gf

system: g(mass)

hgnrb )(• Mass:

Briet-Wigner

(Delta)Resolution

(Gaussian)

noise

(Argus)

transfer

rough

mass

15

gfh • Rough mass in Data:

• Accurate mass in Data : nrbf

• Rough mass in signal MC:

• Accurate mass in signal MC:

gfh

rbf • Suppose we know h and f for signal MC;

• We can determine the transfer function g by deconvolution using signal MC.

• In Fourier space: FGHgfh • h, f H, F G g (signal MC)

• h, g H, G F f (Data)

16

Gaussian f

(mean=mass0

rough sigma)

? =

Signal MC: GM1b~1g

RooFit

system: g

• h• Peak=196

• RMS=112

17

hgfgnrb )(

• signal MC:

• Data :

hgfgrb

)()0(

)()(

)0(

)0(0 masshmassmassg

massgbmassgrb

r

massb

• h0

• Peak=175

• RMS=89

• h• Peak=196

• RMS=112)0(massb

• Peak=196.8GeV

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• g• Mean=1GeV

• RMS=89

• h• Mean=235

• Peak=196

• RMS=112

• f• Mean=196GeV

• RMS=70

hgf

)()0( 0 masshmassmassg

Signal MC:

GM1e

Gold deconvolution

algorithm

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• Convolution is largely used in: Statistics; Astronomy; Meteorology; Geophysics; Optics; Digital image; Spectroscopy; …; but not in Particle physics as I know.

• Deconvolution can be used to recover the missing information. MET, resolution, … mass, width, …

• A shadow is the convolution of the shape of the light source that is casting the shadow and the object whose shadow is being cast

• An out-of-focus photograph is the convolution of the sharp image with the shape of the iris diaphragm.

• An echo is the convolution of the original sound with a function representing the various objects that are reflecting it.

• ……

wikipedia

http://en.wikipedia.org/wiki/Shape

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• We can use mass to get signal yield, CB Line functions. Same methods as in MET for bkg studies; or bkg studies are simple.

• We can use mass-mass2weighted as a cross check of the result.

• De-convolution method is introduced, which is expected to be useful in experimental particle physics.

• Test the invariant mass and the de-convolution method with all GMSB points and all backgrounds.

• Study the QCD control samples:

• Correlation between shower shape/isolation and MET/mass need to be studied.

• Can shower shape/isolation get enough control sample? Do we need photon Pt, MET, number of jets, or jets’ pt for control sample?

Summary

Thank you!

21

MT2

• hep-ph/9906349

• Left edge is known; use the right edge to get the mass.

• Enough signal events close to the right edge?

• Edge is not sharp; shape? Background?

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Edge of invariant mass

Jet+photon

2 leptons

2 leptons+1photon

• CMS Note 1997/079

• Kinematics reasons

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Accurate calculation with cross-events

• 6 constraints; 8 unknowns for one event.

• 6+10 constrains; 16 unknowns for two events. solve the equations

• Need long decay chain.

• Wrong combinations are large.

• Bias? Shape? ill equations? measure uncertainties? ...

• arXiv:0802.4290v1

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Long-lived neutralino

• arXiv:0804.1043v1 Search for heavy, long-lived neutralinos that decay to photons at CDF II using photon timing

• arXiv:0704.0760v1 Search for heavy, long-lived particles that decay to photons at CDF II

• arXiv:0710.2647v1 Search for GMSB NLSPs at LHC

• PRD 69, 035003 (2004) Study of the gauge mediation signal with nonpointing photons at the CERN LHC

• ……

Documents

Status of GMSB studies