Search for Supersymmetry with early LHC data David Stuart, UC, Santa Barbara. May 12, 2010

Search for Supersymmetry with early LHC dataDavid Stuart, UC, Santa Barbara. May 12, 2010

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Outline

What is Supersymmetry & why are we looking for it?

How do we go about searching for it?

When might we find it?

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The Standard Model, an incomplete success

Parameters unexplained: masses, mixings, couplings.

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W, Z, fermion masses could be generated by Higgs

mechanism.

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mechanism.

=> Search for Higgs at CMS

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mechanism.

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mechanism. But mass values still not explained.

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mechanism. But mass values still not explained.

And mH should diverge due to corrections:

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mechanism. Though values not explained.

And mH should diverge due to corrections.

Would cancel if fermionboson “super symmetry”.

~

~

~

~

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mechanism. Though values not explained.

And mH should diverge due to corrections.

Would cancel if fermionboson “super symmetry”.

Cancel the debt by printing more particles.~

~

~

~

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Unification would be nice.

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Unification would be nice, and corrections from the extra “SUSY” particles seem to provide it.

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The standard model does not explain dark matter.

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The standard model does not explain dark matter.

A conserved SUSY quantum number would. The LSP.

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Supersymmetry, an experimentalists dream

Many parameters to measure. Doubled mass spectrum, more mixings.

New puzzles to solve. Whence the masses and mixings?

Why is the symmetry broken?

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Supersymmetry, an experimentalists dream

Many parameters to measure. Doubled mass spectrum, more mixings.

New puzzles to solve. Whence the masses and mixings?

Why is the symmetry broken?

Supersymmetry’s variety of signatures makes it

a target representative of many new models.

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How to search for SUSY?

Produce super-partners, and

detect that we have done so.

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Massive, so need energy => LHC

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Massive, so need energy => LHC

Production via SM like diagrams.

For example...

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The same diagram that produces WZ in SM…

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…could produce Winos and Zinos.

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The cross section for weak production is small.

But squarks & gluinos would be strongly produced…

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In pairs if RP conserving.

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Cross-section is calculable given masses.

Example: 400 GeV squark and gluino

gives ≈40 pb at 7 TeV.

≈ 1/4 of top quark cross-section.

Could produce thousands this year.

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Varied signatures

Higgssector

LSP

squarks

gluino

sleptons

charginos/neutralinos

A CMS mSUGRA benchmark, LM0

Higgssector

LSP

squarks

gluino

sleptons



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Varied signatures

Higgssector

LSP

squarks

gluino

sleptons



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Varied signatures

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Many different search modes

Multijets + MET

Lepton + jets + MET

Dileptons + jets + MET

Same sign dileptons + jets + MET

Trileptons + jets + MET

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Many different search modes

Each mode has different backgrounds.

Search amounts to predicting these bkgdsand looking for an excess above prediction.

Multijets + MET Lepton + jets + MET

Dileptons + jets + MET Same sign dileptons + jets + MET

Trileptons + jets + MET

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Background cross-sections

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Background cross-sections

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Need to predict the Njet and MET tails?

But kinematic tails are hard to calculate:higher orders, pdfs, detector effects…

e.g., Z+jets

qZ

+

-

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How to predict the Njet and MET tails?

Monte Carlo predictions?

Sophisticated, higher order modeling,

e.g., ALPGEN.

Elaborate simulation of detector response.

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Monte Carlo predictions?

Sophisticated, higher order modeling,

e.g., ALPGEN.

Elaborate simulation of detector response.

Both are software…Only trust in so far as validated with data.

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Data validation challenges:

Slow.

Fit away signal?

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Data validation challenges:

Slow.

Fit away signal?

Don’t want to wait…

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Would like a quick, data-driven method to predict MET in Z+jet events.

In this case it is fake MET,

from mis-measurement.

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Missing ET in Z+jets

The Z is well measured. The MET comes from the detector’s response to the jet system.

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For each Z+jet event, find an event w/ a comparable jet system and use its MET as a prediction.

Huge QCD x-section makes such events SUSY free.

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For each Z+jet event, use a MET template measured from events with a comparable jet system in O(1) pb-1.

Templates measured in bins of NJ and JT = j ET.

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Missing ET in Z+jetsExample of template parameterization

Background predictionData distribution

For each data event...

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Missing ET in Z+jetsExample of template parameterization

Background predictionData distribution

For each data event,look up the appropriate template.Sum these, each withunit normalization, to get the fullbackground prediction

N JETSpT>50 GeV

sumETBin 1

sumET Bin 2

sumETBin 3

sumET Bin 4…

2

3

4…

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Missing ET in Z+jets, MC closure test

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Missing ET in Z+jets, MC closure tests

“Scaled” includes a low MET normalization, which is important for low NJ.

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Missing ET in +jets, MC closure test

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Missing ET in +jets, MC closure tests

“Scaled” includes a low MET normalization, which is important for low NJ.

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Missing ET in Z/+jets, robustness tests

Various detectoreffects could addMET tails.

Check robustnesswith MC tests,applied equally toall samples.

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• R=0.8 hole at (h,f)=(0,0)• Double gaussian smearing• Randomly add 50-100 GeV “noise jets”• Vary nJ slope by ±50%.• Jet energy scale sensitivity.

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• R=0.8 hole at (h,f)=(0,0)• Double gaussian smearing• Randomly add 50-100 GeV “noise jets”• Vary nJ slope by ±50%.• Jet energy scale sensitivity.

Now working to validate this with low ET +jets from early data.

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Missing ET in W()+jetsW

Can we predict W+jets, and ttW+jets?

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Missing ET in W()+jets

Templates can predict the fake MET in W+jet events, but we also need to predict the real MET, i.e., the pT.


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Missing ET in W(+jets

Templates can predict the fake MET in W+jet events, but we also need to predict the real MET, i.e., the pT.

But, the pT spectrum is ≈ same as the pT spectrum,

if we ignore V-A or randomize W polarization.


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Missing ET in +jets

Pretend we could detect and apply templates.

Mismatch due to b-jet dominance.

But, neutrino pT dominates MET.

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Missing ET in +jets

Combining template prediction with pT spectrum

gives a prediction for the full MET distribution.

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Missing ET in +jets

The same approach predicts W shape,

if polarization is not extreme.

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Comparison with signal

Benchmark points (LM4 and LM1) stand out with 200/pb at 14 TeV.LM4=(m0=210,m1/2=285); LM1=(60,250). tan()=10.

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But we don’t have 14 TeV.

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But we don’t have 14 TeV. So it will be a bit harder.

When will we discover SUSY with 7 TeV?

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But we don’t have 14 TeV. So it will be a bit harder.

When will we constrain SUSY with 7 TeV?

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When?

Systematic uncertainty assumed to be 50% overall.Separate tight selections for 100 pb-1 and 1 fb-1.

Expected limits in multijets + MET search

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When?Similar limits from same-sign dilepton search

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When?So far, we only have a few inverse nanobarns. But, that is a few hundred million events…

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Detector performance encouraging with first data.

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Tracking calibrated with Ks, , ,J/, D resonances.

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When?Expect 100 pb-1 by end of this year and 1 fb-1 by end of next year. Tuning up…

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www.collider.com Iron Man 2 © Paramount Pictures

http://www.collider.com/

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Summary

Potential for quick sensitivity to Supersymmetry

If we can obtain robust, data-driven background predictions

QCD based templating gives an in situ prediction of MET distribution.

Charged lepton pT predicts neutrino pT.

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Acknowledgements

MET prediction method by Victor Pavlunin. PRD81:035005 arXiv:0906.5016

Several slides borrowed from Jeff Richman

Other material from

…and references therein.

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Extra slides

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Dileptons

m(e±m) m(l +l −)

%χ20 → l +%l −; %l − → l − %χ 1

0

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Leading order cross section, tan = 3, A=0, >0

LM0

LM1

Rough limit from Tevatron

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Typical decay patterns in LM0

%b1 → %t1W

−(43%)

%t1 → %χ1

+W−(100%

%b1 → %χ20b(29%)

→ %χ1−t(24%)

%χ20 → %χ 1

0e+e− (3.3%), %χ 10μ +μ − (3.3%)

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Typical decay patterns in LM0

%g → %b1b + c.c.(54%)

%b1 → %t1W

−(43%)

%t1 → %χ1

+W−(100%

%g → %t1t + c.c.(46%)

Standard Model backgrounds to Z+jets

+ +

+q Z

e+

e-

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Search for Supersymmetry with early LHC data David Stuart, UC, Santa Barbara. May 12, 2010