Fourth Tropical Workshop on Particle Physics and Cosmology

FLAVOUR PHYSICS AND PRECISION COSMOLOGY 9-13 June 2003, Cairns, Queensland, Australia

CP Violation, Dark Matter and Extra Dimensionsin the D-Zero experiment at the Tevatron ?

Peter RatoffLancaster University

The Tevatron

p-p collisions at s = 1.96 TeV_

The DØ Detector in Run 2

+ New Software(OO C++)+ STT displaced track

trigger, Summer’03

Tevatron operating parameters

396 – 132 ns

2 x 1032 cm-1 s-1

1.96 TeV

6.5 – 11 fb-1

2001 - 2009

Run 2

396 ns3.5 sBunch spacing

4.5 x 1031 cm-2 s-1

2 x 1031 cm-2 s-1Luminosity

1.96 TeV1.8 TeVc.m. energy

~200 pb110 pb-1Integrated Luminosity

20031992 – 1996Date

NowRun 1

Run 2 Luminosity Performance

Physics in Run 2

W: mass, width, gauge couplings

Top: mass, cross-section, branching ratios

Electroweak

Jet cross-section, shapes multijet events

QCD

Higgs, SUSY, extra

dimensions, leptoquarks compositeness, etc.

Searches

Lifetimes, cross-section, Bc, B, Bs studies, CP violation, xs

Heavy flavour

# events in 1 fb-1

1014

1011

104

107

Detector Performance: electrons and muons

Electrons:

Muons

D0:10% Lumierror

Detector Performance: Jets

Dominant systematic error: Jet energy scale (will improve with statistics)

Detector Performance: b’s and B’s

Signed IPJet

TrackInteraction vertex

Golden modefor CP viol’n(Sin2)

Detector Performance: TausEvidence for Z Z ++- - eehh

(similar study in Z (similar study in Z hh))

Isolated electron opposite to narrow, single track jet.Signal enhanced using NN:

(New at DØ)

Putting everything together: the top !3 observation

X-section:

B Physics at the Tevatron?• Large Cross Section!

• Produce bottom mesons with all flavor combinations as well as bottom baryons– Bd, Bu, Bc, Bs, b, b, ...

• DØ is a multipurpose detector capable of reconstructing many B final states

• Rich B physics program– Cross-sections

– Bs mixing

– B lifetime

– CP violation in Bd and Bs

– Rare decays

(pp bb ) 150b at 2 TeV (15 kHz! )0Zat 7)( nbbbee

(4S)at 1)( nbBBee

b

Bs

Bd

B Physics Triggers• Have to go down from 2.5 MHz crossing rate to 50 Hz

writing to disk (0.25 MB/event)– Sophisticated 3-level trigger system

• Most useful triggers for B physics so far: dimuon triggers (simple and unprescaled)– Central (||<1): pT>3.5 GeV

– Forward (1<||<2): pT>2-2.5 GeV

• But can also do physics with single muon trigger ...

• Coming soon (this summer):– L2 track trigger (track match to /e)

– L2 (STT) silicon track trigger (displaced vertices)

T

+jet

• Begin with in jet cross section• Extract b content via fit to pT

rel distribution

• Unfold jet energy resolution (unsmearing)• Dominant error: jet energy scale corrections

Inclusive b cross-section

J/ data sample• Exploit J/ +– mode• Results based on 40 pb-1 collected data (75k J/)• Calibration not finalized, mass not in good agreement with PDG

Charged B lifetimeFull reconstruction (B± J/ K ±): no hadronization or momentum uncertainties

<B> = 1.76 0.24(stat) ps (PDG : 1.674 0.018)

cB = Lxy M B / pT B

Semi-leptonic B meson decay 2% of currentRun II data !

• single muon trigger works!• abundance of SL B decays• other decay channels to follow:

• B D*X• B D+X• B Ds X

• excellent opportunities for various B measurements (mixing, CP viol)• good source of B hadrons for technical studies (trigger, b-tagging)

: efficiency for a tag =

D: Dilution =

B mixing - flavour tagging status

3.3 1.8 %2.4 1.7%

D=-3.7 19.2%D=2.4 4.1%

= 8.5 1.6 %= 65.8 2.4%

D=44.4 21.1%D=15.8 8.3 %

= 8.3 1.9%= 63.0 3.6%

Jet tag Muon tag

Signalregion

Sidebands

D2 for signal

NNN

NN

notagwrongcorrrect

wrongcorrect

NN

NN

wrongcorrect

wrongcorrect

Tagging power: D2

Significance of a mixing measurement is proportional to D2

Muon tag: Charge of highest pT muon in the event (excluding those from reconstructed B) gives (opposite-side) b-tagJet tag: Q= qi pTi / pTi, count events with |Q|>0.2

Taggingperformancemeasured inB+ J/K+- close to simulationexpectations

CP violation in B hadron decays

• Able to reconstruct “golden’’ channels for CP violation measurements• High statistics measurements with BS only possible at hadron colliders

B physics prospects

(with 2fb-1)

Bs mixing: Bs Ds(Ds) (xs up to 60, with xd meas. one side of U.T.)

Angle : B0 J/ Ks (refine CDF Run1 meas. up to (sin2) 0.05)

CP violation, angle : B0 (K), Bs KK(K)

Angle s and s/ s : Bs J/ (probe for New Physics)

Precise Lifetimes, Masses, BR for all B-hadrons: Bs, Bc, b … (CDF observed: Bc J/ e(). Now hadronic channels Bc Bs X can be explored)

Cross sections

Stringent tests of SM … or evidence for new physics !!

Both competitive and complementary to B -factories

SUSY models

– SUSY is the best motivated scenario today for physics beyond the Standard Model• doesn’t contradict precise Electroweak data• predicts light Higgs• unification of gauge couplings at GUT scale• essential element of String Theories• … provides explanation of Cold Dark Matter in the Universe!

– SUSY must be broken symmetry (otherwise MSUSY = MSM)• variety of models proposed - differ mainly in the nature of the “messenger interactions”• most experimental results obtained in the context of the SUGRA and GMSB models

SUSY productionSUSY production

• Neutralinos/charginos- trilepton channel

- dilepton channel

• squarks/gluinos (dominant)– jets + mET

stop and sbottom

b1 b 20

10 e+ e-~

~ ~

pp ˜ i˜ j

, ˜ i0 ˜ j

, ˜ i0 ˜ j

0, ˜ q ̃ q , ˜ q ̃ g , ˜ g ̃ g , ˜ l ̃ l

~ squarks and gluinos are quite heavy decay via multi-step cascades:

many high Pt jets and leptons plus large missing transverse energy

0

1

0

2

~ ~

Z q q q q q q g

SUGRA models

• SUSY breaking is communicated to the physical sector by gravitational interactions

• GUT scale parameters + RGE’s low-scale phenomenologyM0 = common scalar massM1/2 = common gaugino massA0 = common trilinear coupling valuetanratio of the V.E.V. of the two Higgs doubletssign of = Higgsino mass parameter

LSP is lightest neutralino - a neutral WIMP excellent CDM candidate

Highly constrained

minimal SUGRA

GMSB models

• ‘Messenger’ sector couples to source of SUSY-breaking and physical sector of MSSM (through gauge interactions)

• The identity of the NLSP and its lifetime determine the phenomenology

~ ~ GSMT CFT CAL

Tracks as we know Kinks Large dE/dx

Hot cell c

Photons as we know Impact

parameter

~ ~ 10 G

slepton

llG

c

NLSP

neutralino

G

Current DØ searches for new phenomena

Model Independent• e + X

Supersymmetry:• SUGRA-inspired Jets + Missing ET (Squarks) Trileptons (Gauginos)• GMSB Diphotons + Missing ET

Leptoquarks •1st and 2nd generations

New Gauge Bosons• Dielectrons

Large Extra Dimensions• Dielectrons + Diphotons• Dimuons

Jets + missing ET

Generic signature for squarks and gluinos which, in SUGRA inspired models,cascade decay to (quarks and gluons jets) + (two LSP’s missing ET)

“Proof of existence” with ~ 4 pb-1•Select events with at least one jet with pT > 100 GeV

•Apply topological cuts (e.g., on jet- missing ET angles)

•Simulate physics backgrounds (with real missing ET)

•Estimate the large instrumental QCD background from the data (empirical fit)

No surprise:For missing ET > 100 GeV: 3 events observed vs. (2.7 1.8) expected

Backgrounds Data

313210 GeV < M(ee) < 70 GeV 721

123

3

0

pT(e1) > 15 GeV, pT(e2) > 10 GeV 3216 ± 43.2660.2 ± 19.1

MT > 15 GeV 96.4 ± 8.1Add. Isolated Track, pT > 5 GeV 3.2 ± 2.3Missing ET > 15 GeV 0.0 ± 2.0

eel + X

~~~~ 01

021 leeppSignal:

Start from dielectron sample (~40 pb-1)

Typical mSUGRA selection efficiency:3 to 4% at the edge of the excluded region

Sensitivity still about a factor 7 away from extending the excluded domain

“Golden channel”: very low backgrounds, but large statistics will be needed

allows for h

Similar analysis in the el channel

GMSB - diphotonsIn GMSB, the LSP is a light gravitinoWith a “bino” NLSP, the signature is therefore two photons with missing ET: Require two isolated photons with pT > 20 GeVApply topological cuts

Determine the instrumental QCD background from the data(inversion of photon quality cuts)

G~~0

1

Theory = "Snowmass“ slope:M = 2, N

5 = 1, tan = 15, > 0

With ~50 pb-1, the Run I limit is approached

Large Extra DimensionsSearch for the effects of KK graviton exchange in the ee, and final states:

Two discriminating variables are used:• the dilepton/diphoton mass• the scattering angle in the rest frame

2int

2

cosM GKKGSM fffdd

d

4F SG Mwhere

Ms is the fundamental Planck scale. To solve the hierarchy problem, one can have Ms in the TeV scale for n > 2 extra dimensions (n=1 is ruled out and n=2 is tightly constrained).

LED in the ee/ channelsRequire • 2 EM objects with pT > 25 GeV • and missing ET < 25 GeV

Fit G => MS > 1.12 TeV in GRW formalism

Determine• Physics backgrounds from simulation• Instrumental backgrounds from data

(with ~50 pb-1: close to Run I, similar to LEP)MEM-EM = 394 GeV

cos * = 0.49

LED in the channel

M = 347 GeV

Require• 2 opposite sign muons with pT > 15 GeV• and M > 40 GeV

Determine• Drell-Yan background from simulation• QCD background from data

With ~ 30 pb-1: MS > 0.79 TeV in GRW formalism

(New channel at the Tevatron, similar to LEP)

• Fit the distributions in the Mll - cos* plane to

determine the value of G ( G = 0 in SM)

Di-EM analysis: G = 0.0 0.27 TeV-4

Di-Muon analysis: G = 0.02 1.35 TeV-4

• Extract 95% CL upper limits on G

• Translate to 95% CL lower limits on Planck scale MS ,

in TeV, using different formalisms for F

Large Extra Dimensions Search: ResultsLarge Extra Dimensions Search: Results

Di-EM limit close to Run I Di-Muon (new)

Formalism GRW HLZ for n=: 2 7

Hewett = 1

di-EM (~50 pb-1) 1.12 1.16 0.89 1.00

di-MU (~30 pb-1) 0.79 0.68 0.63 0.71

Summary and Conclusions

• DØ is almost fully operational following major upgrades for Run II (some trigger improvements to come e.g STT)• The Run I data sample has now been exceeded and physics results are emerging from the first 40-50 pb-1• The B physics potential of DØ has been established • Good lepton, photon, jet and missing ET detection enables DØ to perform many new physics searches • Measurements of cosmological significance can be expected in the coming few years with data samples > 5 fb-1

• CP violation (unitary triangle angles, beyond the SM?)• dark matter candidates/limits (e.g. neutralino LSP)• large extra dimensions/limits

SUSY Particle ZooSUSY Particle Zoo

pp ˜ i˜ j

, ˜ i0 ˜ j

, ˜ i0 ˜ j

0, ˜ q ̃ q , ˜ q ̃ g , ˜ g ̃ g , ˜ l ̃ l

Where we are standing: Run I vs Run IIWhere we are standing: Run I vs Run II

Run IIRun I (120 pb-1) SUSY search

x BR< 2.2 pb (42 pb-1)

M(0)=62 GeV

mET >15 GeV

x BR< 0.3 pb

M(0)60 GeV

mET >10-15 GeV

lll+mET (Run I)

eel+mET (Run II)

A x <0.1 pb (33 pb-1)mET >45 GeV

?e +mET

x < 4.2 pb (4.1 pb-1)mET >70 GeV

---------Jets +mET (new)

Where we are standing: Run I vs Run IIWhere we are standing: Run I vs Run II

MLQ > 179 (43 pb-1)MLQ > 225 GeV1st LQ 2 e + 2 jets

Run IIRun I (120 pb-1) Analysis

MS> 1.0 (50 pb-1)MS> 1.1 TeVLED 2em

M(0) > 66 (40 pb-1)M(0) > 75 GeVSUSY 2 + mET

MLQ > 157 (30 pb-1)MLQ > 200 GeV2nd LQ 2 + 2 jets

MS> 0.71 (30 pb-1)-------LED 2 (new)

A lot of another analyses are going on: gauge interactions search, SUGRA particles search with the different jets & leptons & mET signatures … etc