Measuring Mass Difference at LHC using soft τ P T Slope

Jan 17, 2007

Measuring Mass Difference using soft τ PT Slope 1

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Measuring Mass Difference

at LHC using soft τ PT Slope

11~ - ~

Alfredo Gurrolain collaboration with

Richard Arnowitt, Bhaskar Dutta, Teruki Kamon,

David Toback, Abram Krislock,

Nikolay Kolev (Regina, Canada)

Jan 17, 2007


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Outline

SUSY Signature at the LHC

Analysis Methods in 2& 3 Papers

Gaugino Universality

Measuring M in a Non-Universal SUGRA model

Simultaneous measurement of model parameters to test Universality

Jan 17, 2007


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SUSY at LHC 1. , Production is dominant SUSY process at LHC ( )

2. Interested in events with or pairs

3. & Branching Ratios are ~ 97%

4. In Coannihilation Region of SUSY Parameter Space: GeV

g~ q~

Soft

Soft

p p p

g~

q~

01

~

02

~

~

q

q~q

q

~ 01

~

02

~

p

g~

q~

01

~

02

~

~

1

~

q

q~q

q

~ 01

~

Soft

Hard Hard

Hard

ggqqgqpp ~~ ,~~ ,~~02

02

021

02

01

~~ ,~~ ,~~

15 - 5 ~~~ 011

11102

~~ ~~

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Looking Back at 2 & 3 Papers 1. Use Hadronically Decaying ’s

2. Sort τ’s by ET (ET1 > ET2 > …) & use OS-LS

method to extract pairs from the decays

on a statistical basis

3. Use Counting Method (NOS-LS) & Ditau

Invariant Mass (M) to measure

mass difference

4.

5.

2~

2~

2~

2~

~

1

01

02

102

11

M

M

M

MMM end

),,( 02

~~ MMMfN gLSOS

),(

),(

0.8m~M & 2.8m~M

tyUniversali Gaugino Assume

~

~

1/2χ~1/2g~ 02

MMgM

MMfN

gend

gLSOS

hep-ph/0603128

hep-ph/0608193

02

~

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Non-Universal SUGRA

g~q~

02

~

01

~~

1

~

g~

g~

02

~

02

~

Non-Universal SUGRA

Methods used in 2 & 3 papers

depend on Gaugino Unification

Those methods can’t be used in

a Non-Universal SUGRA model

without using another observable!

How can we measure M?

SUSY Mass Hierarchy

M ~ 5 – 15 GeV

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PT STUDY

Slope of the soft PT distribution has a M dependence

hep-ph/0603128

01

~~

Slope of PT distribution contains ΔM Information.

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EVENTS WITH CORRECT FINAL STATE (2 OR 3) - 2 + 2j + ETmiss

APPLY CUTS TO REDUCE SM BACKGROUND (W+jets, …)

ETmiss > 180 GeV, ET

j1 > 100 GeV, ETj2 > 100 GeV, ET

miss + ETj1 + ET

j2 > 600 GeV

ORDER TAUS BY PT & APPLY CUTS ON TAUS: WE EXPECT A SOFT AND A HARD

PTall > 20 GeV, PT

1 > 40 GeV

LOOK AT PAIRS AND CATEGORIZE THEM AS OPPOSITE SIGN (OS) OR LIKE SIGN (LS)

OS: FILL LOW OS PT HISTOGRAM WITH PT OF SOFTER

FILL HIGH OS PT HISTOGRAM WITH PT OF HARDER

LS: FILL LOW LS PT HISTOGRAM WITH PT OF SOFTER

FILL HIGH LS PT HISTOGRAM WITH PT OF HARDER

LOW OS

HIGH OS

LOW LS

HIGH LS

LOW OS-LS

HIGH OS-LS

Extracting Pairs from Decays02

~

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PT STUDY ISAJET 7.64 to simulate our model of SUSY production

TAUOLA to re-decay the ’s

Run generated particles through detector simulator, PGS4 (author:

John Conway) using CMS parameter file

Used reconstructed jets

Used generator level ’s after being re-decayed by TAUOLA

- “visible” values of momentum and energy were used

Separate Monte Carlo routine in ROOT to simulate the effects of

identification efficiency and jet to fake rate

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OS

OS-LS

LS

GeVM

GeVM

g 831

6.10

~

ETmiss + 2j + 2Analysis: PT

soft

[1] ETmiss , at least 2 jets, at least 2 ’s with PT

vis > 20, 40 GeV

[2] = 50% , fake rate 1%

[3] Cuts: ETjet1 > 100 GeV, ET

jet2 > 100 GeV, ETmiss > 180 GeV

ETjet1 + ET

jet2 + ETmiss > 600 GeV

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Can we still see the dependence of the PT slope on M using OS-LS Method?

PT STUDY

GeVM

GeVM

GeVM

GeVM

GeVM g

0.15

6.10

7.5

286.260

831

02

~

~

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PT STUDY: ETmiss + 2j + 2

What is the dependence of PT slope on mass & mass?02

~g~

Luminosity = 40 fb-1

GeVM

GeVM

g 831

6.10

~

GeVM

GeVM

286.260

6.10

02

~

PT Slope is insensitive to mass & mass!!02

~g~

What is the dependence on M?

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Measuring M from the PT Slope


Luminosity = 40 fb-1

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How accurately can M be measured for our reference point?

Considering only the statistical uncertainty:

We can measure M to ~ 6% accuracy at 40 fb-1 & ~ 12% accuracy at 10 fb-1 for mass

of 831 GeV.

g~


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Can parameterize the our observables as functions of M, , &

NOS-LS , to first order, does not depend on mass. A large increase or decrease

in mass is needed to obtain a point that lies outside the error bars Cross-Section is dominated by the gluino mass

02

~02

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Simultaneous Measurement of Model Parameters

gM ~ 02

~M

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Simultaneous Measurement of Model Parameters

2~

2~

2~

2~

~

1

01

02

102

11

M

M

M

MMM end

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Testing Gaugino Unification

CONTOURS OF CONSTANT VALUES ( L = 40 fb-1 )

• Intersection of the central contours

provides the measurement of M,

, &

• Auxilary lines determine the 1

region

• 1st order test on Universality

gM ~ 02

~M

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SUMMARY

Soft PT distribution is sensitive to M

PT slope is independent of gluino mass and neutralino mass

M can measured to ~ 12% accuracy at 10 fb-1 for our reference point

Methods used in 2 and 3 papers can’t be used in a Non-Universal

SUGRA model

We can combine counting method, ditau invariant mass measurement

and PT slope to test the idea of gaugino unification to first order

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PROBLEM: OS-LS method does NOT give the “true” slope

PT STUDY

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PT STUDY – Method I How accurately can we measure M with this method? Assuming the theoretical dependence (‘True’ Fit) of M on Slope:

We can measure M to ~ 8-9% accuracy at 40 fb-1 for mass of 831 GeV.g~

Slope does NOT change

with ~ 10% change in

gluino mass, but the

uncertainty changes due

to change in NOS-LS

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PT STUDY

BACKGROUND: SM, SUSY, soft ’sfrom the ’s from the is the dominant background!

How can the slope be corrected?

02

~

GeV 22002

~ M

02

~

What causes this difference?

GeV 26002

~ M

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Correcting the Slope: Method I Defining the measured PT slope by and the theoretical (“true” identification) PT slope by ,

the mean statistical uncertainty on the slope is with the mean

statistical uncertainty of . The shift S due to background effects is given by the mean difference

of the theoretical slope and the measured slope:

The root-mean-square uncertainty is

With these definitions, the CORRECTED measured Slope is

Mim T

im

N

iN 1

Mi

Mstat m

1m

Mim

Mim

N

iN 1

Mi

Ti )m(m

1S

N

iNS

1

2Mi

Ti S)m(m

1

)m( S)(m m Mi

Mi

correctedi S

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.003166

S .008900

.002032

Mstatm

S

A plot of the distribution of the

shift S between theoretical and

measured values. The shift S is

fairly close to being constant.

A summary of the calculated uncertainties

and shift in GeV.

Correcting the Slope: Method I

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Correcting the Slope: Method II Soft ’s from is the dominant background By increasing the second PT cut, this source of background can be reduced Other Background (SM & other SUSY Background) is reduced

02

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GeV 40

GeV 201

T

allT

P

P

GeV 80

GeV 201

T

allT

P

P

GeV 22002

~ M

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Correcting the Slope: Method II

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Optimizing PT Cut

Optimized Cut would be ~ 70 – 80 GeV for M = 10.6 GeV

Jan 17, 2007


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GeV 20702

~ M

GeV 27402

~ M

Measuring Mass Difference at LHC using soft τ P T Slope

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