# Presentation: 190783

## New Results From DØ Presented at DPF

** ****Fr****é****d****é****ric D****é****liot**
**CEA-Saclay**
**For the DØ Collaboration**

- Fermilab Wine and Cheese Seminar
- April 11, 2003

## DØ Integrated Luminosity

-  ~ 50 pb-1

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- F. Deliot

## DØ Detector Performance

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- F. Deliot

## New Results for DPF

-  QCD: inclusive jet cross-section
-  B Physics: Bs and b
-  Higgs: H  , background for H  WW*   
-  New Phenomena: RunI search for 3,4-body decays of stop
-  New Phenomena: Search for first generation Leptoquarks
- W/Z cross-section measurements
- Top cross-section measurement updates

-  Wine and Cheese: S. Protopopescu (March 7)
-  Wine and Cheese: B. Abbott (March 14)

-  many other new results already presented at Moriond:

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## QCD result presented at Moriond

-  Dijet mass cross-section:

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## Inclusive Jet Cross-Section

-  Jet cross-section:

-  understanding of QCD (proton structure)
-  search for new physics at high Q2

-  Data sample and selection:

-  L  34 pb-1
-  ||< 0.5, 60 < PT < 560 GeV (0.7 cone jet)
-  vertex constraints: |zvtx| < 50 cm, Ntrk > 4
-  E̸T/Ptlead jet < 0.7
-  jet quality cuts

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## Jet Energy Scale Corrections

-  Correct the measured energy:

- Offset: electronic noise, uranium noise, underlying event
- zero bias and minimum bias events (data)

- out of cone Showering:
- energy density in ring around the jet axis (data)

- Response: Emeas/Edeposit  1
- imbalance energy in  +jet events (data)

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## Jet Resolution

-  Jet PT resolution:

-  using energy asymmetry in dijet events

- parametrized as:

- N = 0.0  2.2, S = 0.902  0.045, C = 0.052  0.008

- F. Deliot

## Inclusive Jet Cross-Section

-  For each PT bin:

-  eff estimated from data
-  theory: NLO pQCD (JETRAD)
-  here data points: only statistical errors

- New

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## Data-Theory Comparison

-  ~9% for central jets, PT< 200 GeV
-  reduced statistics, extrapolation to higher PT

- error on luminosity not shown (10%)

- New

- New

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## B Physics Results Shown At Moriond

- cJ/ 

- K0s

- K

- 

- p

- BJ/ K

- BdJ/K0*

- BdJ/K0s

## B lifetimes

-  inclusive: <> = 1.561  0.024 (stat)  0.074 (sys) ps
-  charged B: <> = 1.76  0.24 (stat) ps

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## New B Physics Results

-  Another B hadron new at DØ:

-  62 fully reconstructed
-    Bs  J/ 
-  not accessible at B factories
-  golden channel for CP violation in Bs system (very small in the SM)
-  Bs oscillation (Bs  Dsl,
-     Bs  Ds)

-  DØ has improved its tracking algorithm (low pt tracks, large impact parameter)

- New

- F. Deliot

## B Physics

- Fully reconstructed
-  b  J/ 
-  not accessible at B factories
-  lifetime: discrepancy with theory for
-  mass measurement

- New

-  B baryon:

- F. Deliot

## Higgs Searches 

- high mass

- low mass

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## Low Mass Region 

-  Understand W/Z + jet production

- Jet multiplicity in Z+jets events

-  b-tagging

- d/(d)

-  impact parameter tag

- +jet events

- dijet invariant mass in W+jets events

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## High Mass Region 

-   H  WW*  l+ l-  ̅

-  Dimuon channel

-  signature: ee, e ,   + E̸T
-  background: Z/y*, WW, tt̅, W/Z+jets, and QCD

|  | Expected Background | Data |
| --- | --- | --- |
| -ID / PT > 15GeV | 1419  19 (stat) | 1414 |
| 20 < m< 75 GeV | 264  10 (stat) | 266 |
| E̸T > 20 GeV | 66.1  4.7 (stat) | 68 |
| (Jet, E̸T) > 0.5 | 60.6  4.6 (stat) | 66 |
| 50 < mT(, E̸T) < 200 Gev | 3.6  1.3 (stat) | 5 |
|  () < 2 | 0.32  0.01 (stat) | 1 |

- ee and e channels

- L  48 pb-1

- New

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## H  WW*  + -  ̅

-  () cut

- L  48 pb-1

- ()

- before selection cuts

-  Higgs: spin correlation: ll parallel
-  Z/y and QCD: ll back to back

- m = 52.5 GeV/c2

-  1 candidate:

-  PT(=33.7 GeV, PT(=23.7 GeV, E̸T = 45.7 GeV
-  () = 1.84, m() = 52.5 GeV, mT = 60.3 GeV

- after selection cuts

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## H  

-  Branching ratio in  :

-  in SM, very low: ~ 10-3-10-4
-  enhance in extensions like Fermiphobic, Topcolor Higgs

- Br (h  ) = 1

-  Search for Topcolor Higgs:

-  L  52 pb-1
-  2 isolated EM, ET > 25 GeV, no track matched, mass window cut
-  SM background: Z/,
-     QCD

- approaching region of interest

- New

- M = 202 GeV

- F. Deliot

## Searches for New Phenomena 

-  Deviations from  SM:

-  Supersymmetry:
-  e,  + E̸T: 3,4-body decays of the stop (RunI)
-  Jets + E̸T
-  Di-Trilepton (eel, ,  channels, ...)
-  GMSB:  + E̸T
-  Exotics
-  first generation leptoquarks (ee +jets)
-  second generation leptoquarks ( +jets)
-  Extra-dimensions:
-  Dielectrons and Diphotons
-  Dimuons

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## Search for 3,4-Body Decays of the Stop at RunI

-  MSSM:

-  due to the high top mass, the *scalar top* can naturally be lighter than the other squarks
-  produce by pairs

-  Stop decay:

-  if heavy enough:     b +1
-  moderate mass:      c 01,    b ff’01 (via virtual +1)

-  Signature:

-  assume 4-body decay dominant (low tan)
-  channel: electron + muon + E̸T

- W exchange

- l+

- 

- light

- 

- l

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## Data Selection

-  Event selection:

-  Background:

-  QCD (fake, heavy flavor)
-  Z  , WW, tt̅

-  electron Et > 15 GeV within || < 2.5
-  muon PT() > 15 GeV within || < 1.7
-  E̸T > 20 GeV
-  |e + | < 2,  15o < |e - | < 165 o
-  leptons separated from jets (if any)

- m(t̃) = 120 GeV
- m(01) = 60 GeV

- F. Deliot

## Results

-  Event selection:

| QCD | 4.3  0.3 |
| --- | --- |
| Z   | 0.5  0.1 |
| WW | 2.8  0.3 |
| tt̅ | 0.4  0.1 |
| Total expected | 8.0  0.8 |
| Observed events | 6 |

- light   scenario

-  new scenario allows to complete the
-         c 01 result
-  for light   , exclude up to m(  )=140GeV
-  need more luminosity for W exchange scenario

- F. Deliot

## Search for first generation Leptoquarks 

-  Leptoquarks:

-  couple directly leptons and quarks
-  scalar or vector
-  carry color, fractional charge, baryonic and leptonic numbers

-  3 generations but limits on FCNC: no intergeneration decays
-  first generation: LQ  eq or q  search for ee+2jets final states

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## Dielectron + Dijet Channel 

- Dielectron + Dijet Channel

-  Background:

-  Drell-Yan/Z + jets, QCD (with 2 fakes EM), tt̅

|  | Expected Background | Data |
| --- | --- | --- |
| 2 EM Et > 15 GeV / one track | 1989  172 | 2093 |
| 2 jets Et> 20 GeV / R>0.5 | 39  10 | 37 |
| Z veto (Mee< 75 GeV, Mee> 105 GeV) | 5.0  1.1 | 6 |
| ST=  Et(e,jets) > 300 | 0.34  0.06 | 0 |

- L  43 pb-1

- Bkg

-     Data

- mLQ = 200 GeV

- mLQ = 140 GeV

- New

- ST = 213 GeV

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## Scalar LQ Search Results 

-  Data consistent with SM Background:

-  (LQ) < 0.47pb @ 95% CL
-  for Br(LQ1eq) = 1:
-      mLQ1 > 179 GeV

- approaching RunI limit: mLQ1 > 225 GeV

-  for Br(LQ2q) = 1:
-      mLQ2 > 157 GeV

- 1st generation

- 2nd generation

- New

- F. Deliot

## Electroweak Physics 

-  W/Z production

-  W can be used to determine the luminosity
-  tune algorithms and triggers
-  test of the SM, precision EW measurement
-  W + jets: background for Top and Higgs signals

-  Signal:

-  dominant production via qq̅ annihilation
-  signature: high PT e or  + E̸T (W)
-          high PT dilepton (Z)
-  background: QCD (fake leptons)

- Run2, 2fb-1

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## Electron Channel 

-  Selection:

-  EM cluster with Et > 25 GeV (isolated, large EM fraction, with shower shape consistent with MC expectation)
-  || < 1.1
-  W: E̸T > 25 GeV, track match
-  Z: 70 < Mee < 110 GeV

-  Efficiencies:

-  evaluated on data: tot(Z) = 9.3 %, tot(W) = 15.7 %

- pass shower shape cut

- fail shower shape cut

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## Zee signal 

-  Signal extraction:

-  background removed by fitting a scaled shape
-  contribution from Drell-Yan events: 1.7%

- L  42 pb-1

-  Number of Z(ee) candidates: 1139  42

- New

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## Background estimation 

-  W e:

-  QCD background evaluated from data
-  W  (MC), Z  ee (negligible)

-  “Matrix method”:

- 1 additional requirement

-  for W e: additional requirement = track match

- using QCD EM/jet events:
- f = 2.3  1 %

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## W e signal 

- ET (GeV)

-  Number of W(e) candidates: 27370  898

- E̸T (GeV)

- mT (GeV)

- L  42 pb-1

- New

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## Muon Channel 

-  W selection:

-  PT() > 20 GeV isolated and matched with a track
-  E̸T > 20 GeV (corrected from the muon Pt)
-  Z veto

-  Efficiencies:

-  evaluated on data: tot(W) = 13.2 %

- tracking*matching efficiency

- trk = 81.50.6%

- iso = 90.61.5%

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## Background estimation 

-  W :

-  bb̅ background evaluated from data
-  W , Z   (MC/data)

-  “Matrix method”:

- 1 additional requirement

-  for W : additional requirement = isolation (calorimeter+tracker)
-  Nb of candidates: 7352  154

- F. Deliot

## W signal

- L  17 pb-1

- New

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## Z signal

-  Number of Z() candidates: 1585  40

-  Z selection:

-  2 opposite charged muons PT > 15 GeV
-  one isolated (calorimeter+tracker)
-  separated in (,)

- L  32 pb-1

- tot(Z) = 16.3 %

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## W/Z Cross-Sections Summary

- (W) Br(We) = 3054  100 (NW)  86 (sys)  305 (lumi) pb
- (Z) Br(Zee) = 294  11 (Nz)  8 (sys)  29 (lumi) pb
- (W) Br(W) = 3226  128 (stat)  100 (sys)  323 (lumi) pb
- (Z) Br(Z) = 264  7 (stat)  17 (sys)  26 (lumi) pb

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## W/Z Cross-Sections at Tevatron

- theoretical prediction: C. R. Hamberg, W.L. van Neerven and T. Matsuura, Nucl. Phys. B359 (1991) 343, CTEQ4M PDF

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## Top Production Cross-Section Measurement 

-  Production and decays:

-  produced mostly in pairs: (tt̅) 7pb, ~ 30% higher cross-section than at Run I
-  decay: Br(tWb) = 100%

- t
- t̅

- W+
- b

- W-
- b̅

- qq’
- l

- +X
- X

- qq’
- l

-  dileptons (ee, e, )
-  lepton + jets (e or  +  4 jets)
-  lepton + jets with soft muon tag (e or  +  3 jets + SLT)

-  7 channels presented:

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## Dielectron Channel 

-  Background:

-  physics: Z   (MC), WW  ee (MC), Z/  ee (Data)
-  instrumental: heavy flavor QCD, W + jets with fake electrons (Data)

-  2 electrons Et > 20 GeV matched with a track
-  E̸T > 25 GeV (> 40 GeV in Z mass region)
-  2 jets PT > 20 GeV
-  HT = (PTjet + Ete) > 120 GeV

-  Event selection:

|  | ee + E̸T  | + 2 jets | + HT |
| --- | --- | --- | --- |
| physical background | 8.29 | 1.16 | 0.98 |
| fakes | 0.42 | 0.02 | 0.02 |
| Expected tt̅ signal | 0.40  0.04 | 0.26  0.02 | 0.25  0.02 |
| Total expected | 9.11  1.09 | 1.44  0.47 | 1.25  0.48 |
| Observed events | 9 | 4 | 4 |

- L  48 pb-1

- New

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## Dilepton Channel 

-  dilepton combined:

-  DØ RunII Preliminary

|  | ee | e |  |
| --- | --- | --- | --- |
| L (pb-1) | 48 | 33 | 43 |
| Total Background | 1.00  0.49 | 0.07  0.01 | 0.60  0.30 |
| Expected tt̅ signal | 0.25  0.02 | 0.50  0.01 | 0.3  0.04 |
| Observed events | 4 | 1 | 2 |

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## Lepton+Jets Channel 

-  Background:

-  sample enriched in W (e,  PT > 20GeV,
-     E̸T > 20 GeV, soft  veto)
-  estimate QCD background as a function of the number of jets
-  evaluate W+4jets using scaling law
-  topological cuts (4 jets, HT, aplanarity)

-  Event selection:

-  +jets: heavy flavor QCD with semi-leptonic decays
-  e+jets: QCD with fake electron
-  both evaluated on data using the matrix method

-  = 0.1450.02

-  = 0.1640.02

- W+jets

- W+jets

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## Lepton+Jets Channel 

|  | e+jets | +jets |
| --- | --- | --- |
| L (pb-1) | 50 | 40 |
| Total Background | 2.7  0.6 | 2.7  1.1 |
| Expected tt̅ signal | 1.8 | 2.4 |
| Observed events | 4 | 4 |

**e**

- E̸ T

-  b-tagged jet

- 5 jets:
-    PT1 = 100.9 GeV, PT2 = 71.7 GeV,
-    PT3 = 70.3 GeV, PT4 = 69.6 GeV,
-    PT5 = 54.8 GeV (tagged)
- PT(e) = 34.2 GeV, E̸T = 32.1 GeV
- HT = 422.6 GeV, aplanarity = 0.17

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## Lepton+Jets Channel with Soft Muon Tag

-  same preselection as lepton+jets
-  at least 3 jets
-  estimate QCD background with the matrix method
-  softer topological cuts
-  soft muon tag

-  Event selection:

|  | e+jets | +jets |
| --- | --- | --- |
| L (pb-1) | 50 | 40 |
| Total Background | 0.2  0.1 | 0.7  0.4 |
| Expected tt̅ signal | 0.5 | 0.8 |
| Observed events | 2 | 0 |

- jet PT (GeV)

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## Lepton+Jets Channel Combined

- lepton+jets combined:

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## DØ Run 2 Top Production Cross-Section Combined

-  all channels combined:

-  theoretical prediction at 1.96 TeV:

- (tt̅)  6.7 to 7.5 pb

-  DØ RunII Preliminary

- DØ Run 2 Top Production Cross-Section Combined

- F. Deliot

## Conclusion

-  A lot of DØ Run 2 analyses in progress:

-  re-establishing signals
-  searches already approach Run I limits and will break new grounds soon

-  Many more results to come:

-  with improved detector understanding
-  with improved object ID efficiencies
-  with increased statistics

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- F. Deliot