# Presentation: 403545

## Recent Results from DØ 

- Recent Results from DØ

- Beyond the Standard Model: from the Tevatron to the LHC,
- Fermilab, September 15-19, 2008

- Aurelio Juste
*Fermi National Accelerator Laboratory*

## Tevatron Accelerator

- Current performance:
- Instantaneous luminosity: ~2.8x1032 cm-2s-1
- Integrated luminosity:
- 	~4.8 fb-1
- Project ~7.3-8.8 fb-1 by end of FY10

## DØ Detector

- Multipurpose detector:
- Lepton (e, , ) identification
- Jets and MET reconstruction
- Jet flavor ID via displaced tracks               and soft-leptons
- Data taking efficiency: 85-90%
- Recorded luminosity to date: ~4.2 fb-1

- Features:
- Central tracking system in a 2 T solenoidal field:
- Silicon Tracker (||<3)
- Scintillating Fiber Tracker (||<1.5)
- Central and forward preshowers
- LAr/U calorimetry (||<4.2)
- Muon system (3 layers, (||<2.0)
- Run IIb upgrades for further improved performance:
- L1 trigger: CAL, Track and CAL+Track
- Additional silicon layer (LØ) at R=1.6 cm.

- Central Tracking System

- Results presented in this talk: ~0.7 - 3.0 fb-1

## Today’s Program

- Effects from New Physics can potentially be visible over the whole spectrum of the physics program, in either precision measurements or actual searches for new particles or interactions.
- This talk will present a subset of recent results (since beginning of the year) that probe for BSM effects.
- For more information:

- http://www-d0.fnal.gov/Run2Physics/WWW/results.htm

## Dijet Angular Distributions

- Dijet angular distributions in bins of dijet mass:
- First differential cross section measurement at partonic energies >1 TeV!
- Small experimental and theoretical uncertainties.
- Sensitive to New Physics (95% CL limits):

- Compositeness (=+1): >2.6 TeV
- ADD extra-dimensions (n=4): Ms>1.6 TeV
- TeV-1 extra-dimensions: Mc>1.4 TeV

- Most restrictive limits at the Tevatron!

*y*i = jet rapidity

**0.7 fb****-1**

## CP Violation in the BS System: Recent Results

- Weak eigenstates:

- Mass eigenstates:

- Bs meson allows to probe the entire matrix:

- Time-dependent angular analysis in flavor-tagged                    Bs J/ decays
- B(Bs Ds(*)Ds(*))
- CP-violating asymmetry in semileptonic Bs decays

- Sensitive to New Physics

- Not sensitive to New Physics

- VERY sensitive to New Physics

## Asymmetry in Semileptonic Bs Decays

- Previous DØ measurements:
-                         vs.
- 	 time-integrated, no flavor tagging
-                           vs.
- 	 depends on b-fragmentation and Bd asymmetries from B factories
- Combination of both measurements:

- 1.3 fb-1, PRL 98, 151801 (2007)

- 1 fb-1, PRD 74, 092001 (2006)

## Asymmetry in Semileptonic Bs Decays

- Flavor tagging and time-dependent analysis used for Bs-mixing measurement.
- Exploits regular reversal of solenoid/toroid polarities to control systematics.

**2.8 fb****-1**

*NEW*

- Statistics-limited!

- Significant constraints on CPV phase
- expected from combination of
- measurements

## EW Physics: Recent Results

**Precision Measurements**
- AFB in Z/*ee and sin2Weff
- ...
**Diboson**
- Radiation amplitude zero and anomalous couplings in W
- Search for narrow resonances decaying to Z
- ZZ production
- ...

- arXiv:0808.0703 [hep-ex]
- arXiv:0808.0269 [hep-ex]

- PRL 100, 241805 (2008)

## AFB in Z/*e+e-

- AFB in Z/*e+e-

- Measure AFB as a function of Mee.
- Use Collins-Soper frame to reduce sensitivity to QCD effects.
- Sensitive to New Physics effects at high Mee (extend region probed by LEP2).
- Sensitive to Z-u-u and Z-d-d couplings and PDFs.
- Statistics limited.

**1.0 fb****-1**

## AFB in Z/*e+e-

- AFB in Z/*e+e-

- Measure AFB as a function of Mee.
- Use Collins-Soper frame to reduce sensitivity to QCD effects.
- Sensitive to New Physics effects at high Mee (extend region probed by LEP2).
- Sensitive to Z-u-u and Z-d-d couplings and PDFs.
- Statistics limited.

**1.0 fb****-1**

## Top Physics: Recent Results

- Limits on anomalous *tbW* couplings   from single top production
- Model-independent measurement of the W helicity fraction in top quark decays
- Search for tt resonances
- Search for W’tb
- Search for H± tb
- Limits on H± in top quark decays

## Top Pair Cross Section and New Physics

**1.0 fb****-1**

- Combine tt cross section measurements                                 in lepton+jets, dilepton and lepton+tau                    (14 independent channels).
- Precise measurements in different channels allows to place constraints              on New Physics.
- tH+b: channels affected differently depending on H+ decay modes.
- 	Tauonic: B(H+)=1
- disappearance of l+jets, dilepton
- appearance of l+
- 	Leptophobic: B(H+cs)=1
- disappearance of l+jets, dilepton                 and l+

- Using top as a tool to look for New Physics

## tbW Interaction: Single Top

- Top couplings to the W boson very interesting!
- Single top production directly sensitive to the *tbW* interaction: rate and kinematics.
- 	SM (f1L=1, rest=0):  ~ 2.9 pb
- 	f2L(R)=1, rest=0     :  ~ 10.4 pb
- Use same multivariate analysis technique as for the single top production evidence.

- arXiv:0807.1692 [hep-ex]

- First direct constraints on *tbW* tensor couplings

*tbW* Interaction: Single Top

**0.9 fb****-1**

## tbW Interaction: W Helicity

- W helicity polarizations in top quark decays:
- Lepton+jets and dilepton final states.
- Reconstruct lepton helicity angle.
- Model independent measurement:

- SM:

*tbW* Interaction: W Helicity

**2.7 fb****-1**

- Most precise measurement!
- Further constraints on *tbW* couplings to follow

*NEW*

- 1

- 

## New Phenomena Searches: Recent Results

- Scalar top pair production
- Leptoquarks (1st, 2nd, 3rd generation)
- T-odd quarks in Little Higgs models
- Large extra-dimensions in mono-photon
- Large extra-dimensions in di-EM and dijets
- Long-lived particles decaying into ee, 
- Charged massive stable particles
- Excited electrons
- 

## Scalar Leptoquarks (3rd Generation)

- Predicted by a variety of New Physics models (GUTs, Compositeness, etc).
- Couple directly to a quark and a lepton:
- Consider 3rd gen scalar LQ with charge 2/3 or 4/3: LQ+b

- 1 isolated , pT>15 GeV
- 1  candidate, pT>15-20 GeV
- 2 jet, pT>25(20) GeV; 1 and 2 b-tags

- 1+2 tags

-  ~ B(LQl+q)

- arXiv:0806.3527 [hep-ex]

**1.0 fb****-1**

- Most restrictive limits in this decay channel!

## Acoplanar Jets+MET

- 2 jets, pT>15 GeV
- (jet1,jet2) >165o
- MET>75 GeV
- Optimized cuts on MET and HT

- 1- = B(LQq)

**2.5 fb****-1**

- Most restrictive direct limits!

- arXiv:0808.0446 [hep-ex]

## Large Extra-Dimensions: ee, 

- Tower of Kaluza-Klein gravitons GKK (massive, stable, non-interacting).

- Di-EM (ee,) final state signature.
- Exploit di-EM mass and cos(*) distributions.

- Large Extra-Dimensions: ee, 

**1.0 fb****-1**

- Interference!

- Most restrictive limits at the Tevatron!

- BR(GKK) = 2 BR(GKKee)

## Long-lived Particles Decaying into e+e-/

- Long-lived Particles Decaying into e+e-/

**1.1 fb****-1**

- Quasi-model independent search for long-lived particles decaying into e+e-/, e.g.
- b’Z+b
- 10 Z+G (GMSB models)
- ve+e- (Hidden-Valley models)

- ~

- ~

- b’Z+b

- “EM pointing”

- 1 m!!

## Long-lived Particles Decaying into e+e-/

- Long-lived Particles Decaying into e+e-/

**1.1 fb****-1**

- Quasi-model independent search for long-lived particles decaying into e+e-/, e.g.
- b’Z+b
- 10 Z+G (GMSB models)
- ve+e- (Hidden-Valley models)

- ~

- ~

- b’Z+b

- 1 m!!

## Charged Massive Stable Particles

- Charged: leaves track in detector
- 	Massive: long time-of-flight, heavily ionizing
- 	“Stable” = long-lived  signal in muon system
- Search for dimuon-like signature with long time-of-flight. Exploit timing information from muon scintillator system (resolution: ~2.5 ns)

**1.1 fb****-1**

- Most restrictive limits at the Tevatron

- DØ Run II Preliminary

- DØ Run II Preliminary

## Higgs Searches Beyond the SM

- Many extended models of EWSB possess a limit in which they are indistinguishable from the SM (“decoupling limit”): e.g. 2HDM, extra dimensions, composite models, etc.
- 	 SM-like Higgs searches provide useful information.
- Within a generic (Type II) 2HDM:
- u and d couple respectively to up- and down-type fermions; tan=vu/vd.
- After EWSB: four massive scalars (h0,H0,H±) and one pseudo-scalar (A0)
- MSSM at large tan:
- 0={h0/H0,A0} nearly degenerated in mass
- Coupling to b,  enhanced (tan)
- b(b)+0bbb(b)
- b(b)+0hadb(b)
- 0

- Significant increase in production rate: +X  2 x tan2
- 	BR(0bb)~90%, BR(0+-)~10%

*NEW*

*NEW*

*NEW*

## b(b)+0bbb(b)

- Experimental signature:
- 3, 4 or 5 jets; 3 b-tags
- Select on likelihood discriminant (mass information not used).
- Invariant mass of leading two jets peaks                at M
- Backgrounds dominated by heavy flavor-enriched QCD multijets:
- Shape extracted from 2-tag sample
- Rate normalized outside the “signal region”
- Run IIb preliminary result combined with Run IIa (1 fb-1) publication.

**2.6 fb****-1**

- Most restrictive limits at the Tevatron!

## 0

- Typical experimental signature (had):
- 1 isolated , pT>10 GeV
- 1  candidate, pT>15(20) GeV
- Main background: Z+-
-  Visible mass:
-  Combination of four channels:
- Run IIa (1.0 fb-1): had, ehad, e
- Run IIb (1.2 fb-1) : had

- 0

**2.2 fb****-1**

- Work ongoing to combine the three analyses

## SM Higgs Searches: Recent Results

- Major effort underway to continue to improve sensitivity:
- Adding channels,
- Optimized object identification/resolution
- Optimized selections and signal-to-bckg discrimination, and of course,
- Adding more luminosity!
- WHlbb
- WHbb
- ZHllbb
- ttHlbjjbbb
- H
- HWW
- Search in as many channels as possible also opens a window of sensitivity to BSM effects:
- Non-SM Higgs (e.g. hf)
- 4th Generation quarks (e.g. HWW
- ...

- Added for the first time

- ...and more!

## DØ Higgs Combination

- A total of 21 channels.
- Many improvements underway:
- Adding more data
- Adding more channels
- Increase acceptance                 (e.g. lepton ID)
- More sensitive multivariate analysis techniques (e.g. include ME discriminants)
- Reduce systematics
- 	and particularly at low mass:
- Better b-tagging (e.g. b/c discrimination, soft-lepton tagging,..)
- Improved dijet mass resolution
- And combine with CDF!

- At mH = 160 GeV:
- Expected limit: 2.1 x SM
- Observed limit: 3.0 x SM

- At mH = 115 GeV:
- Expected limit: 4.6 x SM
- Observed limit: 5.3 x SM

**1.1-3.0 fb****-1**

## Tevatron Higgs Combination

- First direct exclusion since LEP II.
- Limits continued to scale ~linearly with luminosity between Moriond’08 and ICHEP’08.
- Expect to exclude wide mass range by Moriond’09.

**1.1-3.0 fb****-1**

- Excluded mH = 170 GeV @ 95% CL

## Conclusions

- Have discussed a subset of recent DØ results probing for New Physics effects.
- The large expected datasets, well-understood detectors and highly developed analysis techniques open a window of opportunity for discoveries before first LHC physics results, especially in those channels where the Tevatron may have an advantage.
- Also, there is potential for synergy between both machines, where one could feed relevant information to the other, which may help make faster progress in performing/interpreting discoveries.
- Experimentalists at both the Tevatron and the LHC are eager to receive your feedback!!

## Backup

## Large Extra-Dimensions: mono-photon

- Tower of Kaluza-Klein gravitons GKK (massive, stable, non-interacting).

- qq   + GKK  monophoton signature
- pT()>90 GeV, MET>70 GeV
- Backgrounds:
- Z(),..
- Non-collision                                            (cosmics, beam-halo)
- Exploit fine granularity of the                                                                                       EM calorimeter and central                                  preshower detector to                                   do “photon pointing”.

**2.7 fb****-1**

## Large Extra-Dimensions: mono-photon

- Tower of Kaluza-Klein gravitons GKK (massive, stable, non-interacting).

**2.7 fb****-1**

- Improve upon LEP limits for nd>4

- qq   + GKK  monophoton signature
- pT()>90 GeV, MET>70 GeV
- Backgrounds:
- Z(),..
- Non-collision                                            (cosmics, beam-halo)
- Exploit fine granularity of the                                                                                        EM calorimeter and central                                  preshower detector to                                   do “photon pointing”.

## b(b)+0hadb(b)

- b(b)+0hadb(b)

**1.2 fb****-1**

- Experimental signature (had):
- 1 isolated , pT>12 GeV
- 1  candidate, pT>10(15) GeV
- 	[NN-based ID]
- 1 jet, pT>15 GeV; 1 b-tag
- Main background: tt, multijets
- 	Discriminate using multivariate techniques.
- High sensitivity to 0  near/at the Z resonance:
- 	 complementary to 0 search

- Combination of the three searches underway

## Fermiophobic Higgs: hf()+X

- Fermiophobic Higgs: hf()+X

**1.1 fb****-1**

- B(h ) can be large in some BSM models.
- Preferentially select vector-boson fusion and associated production by requiring qT>35 GeV (reduces background).
- Background dominated by  (~70%).