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Searches for Physics beyond the Standard Model
Andrey Shchukin (IHEP) on behalf of the D0 and CDF collaborations

14th Lomonosov Conference on Elementary Particle Physics. August 25, 2009. Moscow.


Tevatron collider
pp collider which provides the highest energy at present: 1.96 TeV
Hosts two multi-purpose HEP detectors: D0 and CDF Operates with excellent performance

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Run II Data
Since the beginning of Run II The Tevatron has delivered ~7 fb-1 of integrated luminosity and growing!

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D0 and CDF detectors

Typical acceptance values for the detectors:

D0 Muons Electrons Silicon tracker

||<2 ||<3 ||<3

CDF Muons Electrons Silicon tracker

||<2 ||<1.5 ||<2
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New physics searches
-A lot of interesting results! - Total number of published results is ~80! - This review will focus on the latest results - The detailed information about the results and publications can be found at: http://www-cdf.fnal.gov/physics/exotic/exotic.html (CDF) http://www-d0.fnal.gov/Run2Physics/np (D0)

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High mass resonances
- High mass resonances are sensitive to new physics Z', Randall-Sundrum graviton -Two recent CDF searches using ee and final states with 2.5 and 2.3 fb-1 respectively. ee: Phys. Rev. Lett. 102, 031801 (2009), : Phys. Rev. Lett. 102, 091805 (2009). ee inv. mass inv. mass1

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High mass resonances

Spin 1: SM coupling Z' < 966 GeV (ee) and <1030 GeV () excluded;

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Randall-Sundrum Gravitons
5th extra dimension with warped geometry; Gravity is localized on brane other than SM KK excitation have spacing of order of TeV Signature: narrow high masses resonances Two model parameters: Mass and coupling (k/Mpl) Latest CDF results in and ee excludes M < 921 GeV and M<850 GeV respectively (for k/Mpl=0.1)

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Search for b' quark
Search for 4th generation b quark - covers the models predicting heavy down-type quark and exotic T5/3 femion Produced in pairs Decays to tW CDF 2.7 fb
-1

- Same sign lepton final state - Major background is Z, di-boson, and processes with misidentified lepton from W+jets

Good agreement between data and Standard Model
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Search for b' quark

b' mass < 326 GeV and b'+T

5/3

mass < 352 GeV excluded at 95% CL

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Leptoquarks
Leptoquarks are exotic particles that have color, electric charge, lepton and baryon numbers and appear in extended gauge theories and composite models. - exist in various extensions of Standard Model; - would come in 3 different generations corresponding to the three quark and lepton generations; - can be either scalar or vector particles. At the Tevatron, leptoquarks pairs would be produced mainly through qq annihilation or gg fusion with identical leading order production cross sections.

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Leptoquarks
D0.
http://www-d0.fnal.gov/Run2Physics/WWW/results/prelim/NP/N68/ -

4 fb

-1

Search for final state with missing ET from neutrinos and two acoplanar b-jets from leptoquark. b-tagging is used to reduce SM background

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Leptoquarks
3 events remain in the data compared to an expected 3.2±0.3±0.6 events from background processes. New cross section limit is set.

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Large Extra Dimensions (LED)
Possible solution to hierarchy problem

Arkani-Hamed, Dimopoulos, Dvali model (ADD) - gravity propagates to n extra spatial dimensions; - gives massive stable Kaluza-Klein gravitons GKK; - can explain why gravity is weak: 1/G ~ M2Pl ~ Mn+2DRn

Signatures: Real graviton - high ET single photon + missing ET - monojet + missing ET Virtual graviton - high mass pair resonance: ee, ,

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LED + MET
CDF. PRL 101:181602 (2008) Data selection:
Photon ET > 50 Missing ET > 50 No jets with ET No tracks with GeV; GeV; > 15 GeV; PT > 10 GeV

CDF 2 fb-1

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LED + MET
D0.
http://www-d0.fnal.gov/Run2Physics/WWW/results/prelim/NP/N63/N63.pdf

D0 2.7 fb

-1

Data selection:
Photon ET > 90 GeV; Missing ET > 70 GeV; No jets with ET > 15 GeV; No tracks with PT > 10 GeV EM shower points to PV

At 95% CL the limits on the fundamental mass scale MD are set from 970 GeV to 816 GeV for two to eight extra dimensions

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LED /ee
D0. PRL 102:051601 (2008) -Combine ee and channels to maximize sensitivity - 2D-fit in mass and cos * - assume BR(GKK)/BR(GKKee)=2

D0 1.1 fb

-1

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SUperSYmmetry searches
- Spinbased symmetry between fermions and bosons - Can be a solution to many outstanding problems · Provides a natural solution to the hierarchy problem · Allows to unify gauge couplings at GUT scale · Provides a dark matter candidate (R = (1)3(BL)+2s) · No SuperPartners are seen: SUSY is broken

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Stop searches
-Lightest stop might be lighter than top quark, it leads to interesting decay modes - Final state signature (Rparity): 2 leptons, 2 bjets, MET Main background ttbar production

- Challenge can be potentially soft jets (leptons)
D0. PLB 675, 289 (2009) e, CDF. http://www-cdf.fnal.gov/physics/exotic/r2a/20090319.

stop_dilepton/cdf9775_stop_in_dilep_pub.pdf

e, ,ee

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Stop searches
CDF.

CDF 2.7 fb

-1

http://www-cdf.fnal.gov/physics/new/top/2008/tprop/Stop/images2_7InvFb_may20_09/stopDilPublicNote_may20_09.pdf

- b-tagging is used - Good agreement between data and SM is observed.

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Trileptons
- Assuming R-parity supersimmetry can be discovered in trilepton final state and missing ET - Clean signature -Largest source of background are diboson processes - Leptons can be soft and depend on m

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Trileptons
CDF. http://www-cdf.fnal.gov/physics/exotic/r2a/20090521.trilepton_3fb/cdf9817_susy_trilep_pub. D0. http://www-d0.fnal.gov/Run2Physics/WWW/results/final/NP/N09A/N09A.pdf - 2.3 fb-1
pdf

- 3.2 fb

-1

CDF · 5 categories of leptons and tracks combinations · pT thresholds 5-20 GeV · MET > 20 GeV Background Trilepton Lepton+Track 1.5±0.2 9.4±1.4 Data 1 6 Low-pT High-pT

D0 · Combination of l, l, el, , and eel · Optimization of highpT and lowpT criteria · MET > 20 GeV

Background 5.4±0.6 3.3±0.4

Data 9 4

No evidence for SUSY is observed
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CDF

Trileptons
New limits are set

D0

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~ Search for



If R-parity is not conserved then single production of super partner is possible

Search for isolated high pT lepton pairs

Assume ~ is LSP Assume all RPV couplings are zero except '311, 321= 312 Latest D0 result uses 4.1 fb-1 data

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~ Search for
D0.


-

http://www-d0.fnal.gov/Run2Physics/WWW/results/prelim/NP/N64/N64.pdf

4.1 fb

-1

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SUSY with Hidden Valleys
SUSY with Hidden Valleys is important class of Hidden Valleys models - Motivated by recent results from PAMELA, ATIC, EGRET, HESS, Fermi/LAT - Many phenomenological problems can be explained - If R-parity is conserved superpartners are produced in pairs and decay to the SM particles and the lightest superpartner

Very distinct final state which never was explored: -Missing ET (from darkino) - Photon - Two spatially close leptons

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SUSY with Hidden Valleys
D0. PRL 103, 081802 (2009) - 4.1 fb
-1

Major sources of background are: - QCD events with real or fake photons and mismeasured MET. These contain jets or photon conversions faking the dark photon - W l plus real or fake photon. The dark photon is faked by a accidental overlap of a high pT track with the lepton

The data is consistent with background.
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SUSY with Hidden Valleys
-No evidence for dark photon events is found; For dark photon masses of 0.2, 0.782, and 1.5 GeV chargino masses of 230, 142, and 200 GeV, respectively, are excluded.

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Summary
It 's a very good time to make high energy physics searches at Tevatron! - ~7 fb-1 of integrated luminosity (and growing!); - well understood detectors; - powerful analysis tools; Most of presented results use 1-4 fb-1 datasets - with growing integrated luminosity there can be many promising updates There are a lot of interesting results which are not covered in this talk Please check web pages: http://www-cdf.fnal.gov/physics/exotic/exotic.html (CDF) http://www-d0.fnal.gov/Run2Physics/np (D0)

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