Exploring the Unknown Universe Daniel Whiteson, UC Irvine - PowerPoint PPT Presentation

Exploring the Unknown Universe Daniel Whiteson, UC Irvine

Motivation The Standard Model Can this be right?

Outline I. Motivation II. Strategy III. Results

Searching for new physics General Specific Model Search strategy Our goals: - Maximize possibility for discovery - Learn something no matter what we see

Traditional approach General Specific Model Search strategy Bet on a specific full theory Optimize analysis to squeeze out maximal sensitivity to new physics. (param 3-N fixed at arbitrary choices) param 2 param 1

Model independent search General Specific Model Search strategy Discard the model compare data to standard model “Never listen to theorists. Just go look for it” --Aaron Pierce, Theorist

Compromise General Specific Model Search strategy Admit the need for a model New signal requires a coherent physical explanation, even trivial or effective Generalize your model Focus on the general experimental sensitivity Construct simple models that describe classes of new physics Examples Simple SM extensions: fourth generation, Z’, resonances (X->tt) etc

Effective Lagrangian A natural, compact language for communication between theory and experiment. Full Theory Full Theory Limits or Experimental measurements Full data Theory on effective Lagrangian Full parameters Theory Full Theory Full Theory

A Theorist’s dream? Unfolded cross-sections Deconvolution to remove detector effects Publish measured differential cross-sections Theorists don’t need to know/have detector description This is hard!

Outline I. Motivation II. Strategy III. Results a. Heavy resonances (Z’) b. Heavy quarks (b’, t’) c. Simplified SUSY

CDF

Dataset

High mass resonances UCI Undergrad Eddie Quinlan Z’ to di-muons

High mass dimuon res. -1 -1 CDF Run II Preliminary 4.6 fb CDF Run II Preliminary 4.6 fb (Obs’d - Exp’d )/ Exp’d 1 5 Events 10 Data 0.8 * Z/ ! 4 10 0.6 tt 3 10 0.4 WW Fakes 0.2 2 10 Cosmics 0 10 -0.2 1 -0.4 -0.6 -1 10 -0.8 -2 10 -1 200 400 600 800 1000 1200 200 400 600 800 1000 1200 2 2 M [GeV/c ] M [GeV/c ] ! ! µ µ PRL 2011, to appear

Z’ to muons PRL 2011, to appear

Z’ to muons PRL 2011, to appear

Z’ to muons -1 CDF Run II Preliminary 4.6 fb ) [pb] 95% CL limit ! Z’ ! I ! (Z’) * BR(Z’ Z’ sec Z’ N -2 10 Z’ # " Z’ $ Z’ % Z’ SM -3 10 200 300 400 500 600 700 800 900 1000 1100 2 Z’ mass [GeV/c ] PRL 2011, to appear

ATLAS Z’ Penn +other groups

Limits Penn +other groups

Limits Penn +other groups

Outline I. Motivation II. Strategy III. Results a. Heavy resonances (Z’) b. Heavy quarks (b’, t’) c. Simplified SUSY

4th generation PDG says it’s ruled out to 6 σ ....

4th generation PDG says it’s ..that’s true if the ruled out to 6 σ .... masses are degenerate [GeV] ) [%] 150 2 " 4 # ! 100 -m Prob( 10 l4 m 50 0 1 -50 -100 -1 10 -150 -150 -100 -50 0 50 100 150 m -m [GeV] projects.hepforge.org/opucem/ u4 d4

t’ UC Davis Selection 1 lepton pt>20 GeV 4 jets pt>20 GeV Missing transverse energy >20 GeV Sample 4.6/fb 28

t’ UC Davis Limit m t’ > 335 GeV 29

UCI Undergrad b’ Matt Hickman Selection 2 like-signed leptons pt>20 GeV at least one isolated 2 jets pt>20 GeV >=1 btags Missing transverse energy >20 GeV Sample 2.7/fb PRL 104 091801 (2010)

b’ Final selection 2 like-signed leptons 2 jets >=1 btags Missing transverse energy m b’ > 338 GeV PRL 104 091801 (2010)

b’ decays UCI undergrad Reza AmirArjomand If b’ -> Wt same-sign lepton selection: ~2% consider single-lepton mode 32

Signal (madgraph) CDF Run II Preliminary CDF Run II Preliminary Fraction of Events Fraction of Events 0.18 0.25 0.16 m =300 b’ m =350 b’ 0.14 m =400 0.2 b’ 0.12 0.1 0.15 0.08 0.1 0.06 0.04 0.05 0.02 0 0 0 2 4 6 8 10 0 200 400 600 800 1000 Number of jets H [GeV] T Eight hard partons, ~6 jets 33

Signal (madgraph) HT CDF Run II Preliminary CDF Run II Preliminary Scalar sum of transverse Fraction of Events Fraction of Events 0.18 energy in the event 0.25 0.16 m =300 b’ m =350 b’ 0.14 m =400 0.2 b’ 0.12 Includes jets, lepton and 0.1 0.15 0.08 missing transverse energy 0.1 0.06 0.04 0.05 0.02 Captures soft recoil and 0 0 0 2 4 6 8 10 0 200 400 600 800 1000 Number of jets unclustered jets H [GeV] T 34

top quark pair background tt + 0,1,2,3p p = udscb Madgraph+Pythia MLM matching 35

Analysis technique CDF Run II Preliminary Events Events 2 10 heavy and jetty Backgrounds 5j b’, m =350 b’ 6j 10 7j+ Analysis variable 1 -1 10 -2 10 0 1000 2000 3000 Jet-H T normalized to 5/fb 36

Data, >=1 b-tag 5j 6j 7j+ 37

The numbers 38

The limits 39

Direct searches replace m b’ > 372 GeV m t’ > 335 GeV

Direct searches b’ l+j m b’ > 372 GeV m t’ > 335 GeV If BR(b’ → Wt)=100% If BR(t’ → Wq)=100%

b’ and t’ UCI postdoc UCI undergrad Matt Kelly Christian Flacco If m t’ > m b’ u c t t’ d s b b’ PRL 2010, PRD 2011

b’ and t’ PRL 2010, PRD 2011

b’ and t’ CDF limits u c t t’ d s b b’ PRL 2010, PRD 2011

b’ and t’ No direct limits! PRL 2010, PRD 2011

t’ and b’ m t’ = m b’ + 50 m t’ = m b’ + 100 PRL 2010, PRD 2011

Limits 290 300 V34 V44 PRL 2010, PRD 2011

heavy quarks If the lifetime is short enough so the decay is in the central detector: m Q’ > 290 GeV PRL 2010, PRD 2011

ATLAS t’ UCI grad student Michael Werth Selection 2 OS leptons pt>20 GeV 2 jets pt>20 GeV Missing transverse energy >20 GeV Sample 35/pb

topology b b t t W W Boosted tops

topology b b t t W W b b t’ t’ W W Boosted Ws!

Lepton-neutrino angles SM top Heavy t’ More W p T means smaller W opening angle

Mass reconstruction Assume lepton and neutrino are ~collinear

Data No sign of heavy quarks...

Limit Limit m t’ > 275 GeV

Limit s t i m h i l c ’ r t a C e s H n L o t s t p r i e F l i d ’ t t s r i F Limit m t’ > 275 GeV

Dark Matter Need long lived dark matter X

Dark Matter Need long lived dark matter X Give it some dark charge that is conserved (eg R-parity for susy LSP) SM Particles Dark Matter X SM Charges Dark Charge

Dark Matter Need long lived dark matter X Give it some dark charge that is conserved (eg R-parity for susy LSP) SM Particles Dark Matter X SM Charges Dark Charge X can’t be light (~< 10 GeV) and carry SM charges to be consistent with relic density.

Dark Matter Need long lived dark matter X Connector Y SM Charges Dark Charge SM Particles Dark Matter X SM Charges Dark Charge Produce Y, decay as Y -> f X

Dark Matter+4th gen UCI grad student Kanishka Rao Look for ttbar + invisible X T’ -> t+X stop -> t + LSP

Transverse mass

Limits

Outline I. Motivation II. Strategy III. Results a. Heavy resonances (Z’) b. Heavy quarks (b’, t’) c. Simplified SUSY

SUSY Goal Set limits on SUSY-like processes in as general a fashion as possible Approach Use effective lagrangian, explicitly set particle masses (EW scale): simple to handle, easy to interpret Set limits as functions of these masses, not parameters of specific models: can be easily translated into arbitrary models

How? How many particles & parameters needed? Want leptons needs Ws and Zs, so chargino/neutralinos and sleptons Want strong production so squarks and gluinos R-Parity conserving need LSP Large sections of this space are 3 or 4-dimensional

SUSY simplified UCI postdoc Ning Zhou

SS SUSY simplified UCI postdoc Ning Zhou

CDF Still producing world-class physics ATLAS Working well, much more to come