# Presentation: 145438

## Search for Extra-Dimensions at D0 

- Search for Extra-Dimensions at D0

- Tevatron and D0 status
- Extra Dimensions
- Large ED
- Tev-1 ED
- Randall Sundrum Model

* **M. Jaffr**é*
*LAL Orsay*
*for the D0 Collaboration*

## Tevatron RunII Status

- New Recycler
- Higher Energy (1.96TeV)
- Higher luminosity (** **36x36 bunches)
- Design “Run IIa” : 0.8x1032 cm-2s-1
-             “Run IIb” : 2-4x1032 cm-2s-1
- Upgrades to come
- Slip stacking end 04
- Electron cooling end 05 ?
- Stacktail upgrade end 06 ?
- New helix beam separation end 06 ?
- Projected Integrated lumi. / expt:
- 2006   2fb-1
- 2009   8fb-1

**1.02 10****32 ****cm****-2 ****s****-1**

**2002**

**2003**

**2004**

- Run I record

## DØ Run II

**DØ Run II**

- Solenoid (2T)
- 4-layer Silicon Vertex  (barrels and disks)
- 16-layer Fiber Trackers
- Muon forward chamber (||<2 ), shielding
- New preshower, upgrade Calorimeter electronics
- Upgrade to Trigger and DAQ system

- For Run IIb (Fall 05)
-  Silicon layer 0
-  Trigger upgrade** **

**Notes:**
DØ Run 2a Upgrade brought:
Solenoid (2T)
4-layer Silicon Vertex and 16-layer Fiber Trackers
Muon forward chamber (||<2 ), sheilding
New preshower, upgrade Calorimeter electronics
Upgrade to Trigger and DAQ system

## Half A Femtobarn of Data!

**D0 analysis**

- Integrated Luminosity more than doubled in the last 12 months
- Efficiency >80%

## Why ED ?

- String theory is the only currently known way to incorporate gravity in Quantun Mechanics.
- ED come « naturally » with string theory (n=6 or 7)
- In short, models with ED try to address the problem of the huge hierarchy between  EW and Planck scales.
- ....
- These ideas can be tested at existing and nearly existing colliders

## Models of Extra Dimensions

- ADD Model:
- Arkani-Hamed,Dimopoulos,Dvali Phys Lett B429 (98)
- SM particles and gauge bosons are confined in D3-brane
- Only gravity propagates in n spatial ED
- Gauss law
**M****Pl** (_apparent_ 4D Planck Scale)
**M****D** (_fundamental_ Planck Scale)
- Size of ED’s (n=2-7) between ~100 m and ~1 fm

- TeV-1 Scenario:
- Dienes,Dudas,Gherghetta Nucl Phys B537 (99)
- Lowers GUT scale by changing the running of the couplings
- Only gauge bosons (g//W/Z) propagate in a single ED; gravity is not in the picture
- Size of the ED ~1 TeV-1 or ~10-19 m

- RS Model:
- Randall,Sundrum Phys Rev Lett 83 (99)
- A rigorous solution to the hierarchy problem via localization of gravity
- Gravitons (and possibly other particles) propagate in a single ED, w/ special metric
- Size of this ED as small as ~1/MPl or ~10-35 m

**M****2****Pl****  ******** M****D****n+2 **** x R****c****n**

## Kaluza-Klein Spectrum

- ADD Model:
- KK excitations with energy spacing ~1/r, i.e. 1 meV – 100 MeV
- Can’t resolve these modes – they appear as continuous spectrum

- TeV-1 Scenario:
- KK excitations with nearly equal energy spacing ~1/r, i.e. ~TeV
- Can excite individual modes at colliders or look for indirect effects

- RS Model:
- Coupling of graviton to SM fields is : k/MPl  [0.01-0.1]
- Light modes might be accessible at colliders
- Model characterized by M1 and k/MPl

**~M****GUT**

**E**

**...**

**M****0**

**M****i**

**~M****Pl**

**E**

**...**

**M****1**

**M****i**

## Collider Signatures: Large Extra Dimensions

- Kaluza-Klein gravitons couple to the energy-momentum tensor, and therefore contribute to most of the SM processes
- For Feynman rules for GKK see:
- Han, Lykken, Zhang, [PRD **59**, 105006 (1999)]
- Giudice, Rattazzi, Wells, [NP **B544**, 3 (1999)]
- Since graviton can propagate in the bulk, energy and momentum are not conserved in the GKK emission from the point of view of our 3+1 space-time
- Depending on whether the GKK leaves our world or remains virtual, the collider signatures include single photons/Z/jets with missing ET or fermion/vector boson pair production
- Graviton emission: direct sensitivity to the fundamental Planck scale MD
- Virtual effects: sensitive to the ultraviolet cutoff MS, expected to be ~MD (and likely < MD)
- The two processes are complementary

## Search for Monojets

- Very challenging because of instrumental background from MET mismeasurement, cosmics.
- Irreducible Physics background  from Z() + jet(s).
- Special trigger for Physics with jets and MET since spring 03 :  MHT =  pT(jets) > 30 GeV/c
-                85 pb-1 (april-august 2003)
- Calorimeter Data Quality is very important for Jet+Met analyses, since most calorimeter problems (hot cells, noise...) will increase the MET tail distribution
- Offline:  to fight mixvertexing and cosmics :
- jets have associated tracks originating from primary vertex

## Search for Monojets

- Leading jet pT > 150 GeV(||1)
- Isolated electron and muon veto
- MET > 150 GeV
- No extra jet with pT > 50 GeV
- MET separated from any jet by  30
- Signal simulation = Pythia + Lykken-Matchev code
-                              (~ 5% signal efficiency)
- Largest uncertainty is from JES and have already been much improved
*With 85 pb**-1** better than D0 Run I *
*still below CDF Run I*

- N=6
- MD = 0.7 TeV

- QCD bckg

- Mostly Z()+jets

- before MET cut

## Search for effects in high mass dilepton, diphoton events

- ED processes predict high mass di-lepton and/or di-photon events
- Study High Pt di-electron, di-muon, and di-photon mass spectra
- Main backgrounds: Drell Yan and QCD jet events where jets fake leptons and photons
- Drell-Yan: shape vs mass known from theory
- QCD: get shape from events that (just) fail particle ID cuts.
- Normalize DY and QCD to “low mass” events (typically about 50 GeV to 120 GeV) includes Z.

## LED Virtual Graviton Effects

- In the case of pair production via virtual graviton, gravity effects interfere with the SM (e.g., *l*+*l*- at hadron colliders):
- Therefore, production Xsection has three terms: SM, interference + direct gravity effects:
- where G= F/MS4
- Hewett:   F = 2/ with  = ± 1
- GRW:      F = 1
- HLZ:        F = log(MS2/s)       for n = 2                F = 2/(n-2)             for n > 2

- The sum in KK states is divergent in the effective theory, so in order to calculate the cross sections, an explicit cut-off is required
- An expected value of the cut-off MS  MD,as this is the scale at which the effective theory needs to be used to calculate production.
- There are three major conventions on how to write the effective Lagrangian:
- Hewett [PRL **82**, 4765 (1999)]
- Giudice, Rattazzi, Wells [NP **B544**, 3 (1999); revised version, hep-ph/9811291]
- Han, Lykken, Zhang [PRD **59**, 105006 (1999); revised version, hep-ph/9811350]
- Fortunately all three conventions turned out to be equivalent and only the definitions of MS are different

- cos = |cosine| of scattering angle in c.o.m frame

## diEM Selection

| min. Mass | Data | Bckg |
| --- | --- | --- |
| 300
350
400
450
480 | 14 
8
5
1
0 | 17.3
8.1
4.4
2.6 
1.9  |

- Signal G=0.6 TeV-4

-  **200 pb****-1**

** **DiEM = ee + 
- 2 EM objects ET > 25 GeV
- Track isolation
- CC : ||1.1; EC : 1.5<||2.4
- Overall ID efficiency 851% / EM

- QCD

- DY
- +
- Direct 
- +
- QCD

| Source of systematics | Uncertainty |
| --- | --- |
| K-factor
Choice of p.d.f.
Luminosity x efficiency
ET dependence of efficiency | 10%
5%
2%
5% |
| Total | 12% |

## Search for LED in diEM channel

- Combine diphotons and dielectrons into “di-EM objects” to maximize efficiency
- Sensitivity is dominated by the diphoton channel (spin 2 graviton   1 + 1)

- Data agree well with the SM predictions; proceed with setting limits on large ED: alone or in combination with published Run I result [PRL **86**, 1156 (2001)]:
- G95% =  0.292 TeV-4
- Translated into the following mass limits
- RunII result
- Combined RunI + RunII result
- These are the most stringent constraints on large ED for n > 2 to date, among all the experiments

**200 pb****-1**

|       Hewett |  | GRW |                        HLZ         (TeV, @95% CL) |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- |
| = +1 | = 1 |  | n = 2 | n = 3 | n = 4 | n = 5 | n = 6 | n = 7 |
| 1.22 | 1.10 | 1.36 | 1.56 | 1.61 | 1.36 | 1.23 | 1.14 | 1.08 |
| 1.28 | 1.16 | 1.43 | 1.67 | 1.70 | 1.43 | 1.29 | 1.20 | 1.14 |

| 170 m | 1.5 nm | 5.7 pm | 0.2 pm | 21 fm | 4.2 fm |
| --- | --- | --- | --- | --- | --- |

**r****max**

- MS = 1 TeVn=6

- See these 2 evts in next slide

## Interesting Candidate Events

-  Mee = 475 GeV, cos* = 0.01

- M = 436 GeV, cos* = 0.03

## Search for LED in diMuon channel

-  isolated, ||<2.0
-  for M > 300 GeV:             Nexp = 6.40.8 and Nobs = 5
-  Systematics: ~ 13%

|       Hewett |  | GRW |                        HLZ         (TeV, @95% CL) |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- |
| l = +1 | l = -1 |  | n=2 | n =3 | n=4 | n =5 | n=6 | n=7 |
| 0.97 | 0.95 | 1.09 | 1.00 | 1.29 | 1.09 | 0.98 | 0.91 | 0.86 |

- Fit the 2D distributions as for diEM
-   G95% = 0.72 TeV-4 (Bayesian)

- 250pb-1

## Apply the same 2D-technique as for LED search.
        Z/ KK states effects parameterized by
                        C=2/3MC2
Data agree with the SM predictions, which resulted in the following limit on their size: 
MC > 1.12 TeV @ 95% CL
r < 1.75 x 10-19 m

Well below indirect contraints from EW measurement (6 TeV)

-         Z/ KK states effects parameterized by
-                         C=2/3MC2
- Data agree with the SM predictions, which resulted in the following limit on their size:
- MC > 1.12 TeV @ 95% CL
- r < 1.75 x 10-19 m
- Well below indirect contraints from EW measurement (6 TeV)

- Search for TeV-1 ED

- signal for
- C = 5 TeV-2

- Di-electron channel  200 pb-1
- QCD fake bckg much reduced compare to diEM

**CC-CC**

- Note the negative interference

## DØ Search for RS Gravitons

- Analysis based on 200 pb-1 of e+e- and  data – the same data set as used for searches for LED
- Search window size has been optimized to yield maximum signal significance;
-  G(1)  is narrow compare to the mass resolution

**300 GeV RS signal**

- QCD

- DY+direct + QCD

## DØ Limits in the ee+ Channel

- Already better limits than the sensitivity for Run II, as predicted by theorists!

- Assume fixed *K*-factor of 1.3 for the signal

- Masses up to 785 GeV are excluded for *k*/*M**Pl* = 0.1

- The tightest limits on RS gravitonsto date

**D****Ø Run II Preliminary, 200 pb****-1**

**D****Ø Run II Preliminary, 200 pb****-1**

## Conclusion - Outlook

- The data agree well with the Standard Model
- New limits from D0 on Extra Dimensions
- Twice the statistics is available,
-        ... more will come soon
- Expect to increase the mass limits for LED models up to 2TeV before the LHC startup

| Topic | Prelim. Results |
| --- | --- |
| LED : ee + 
          :  | MS >1.43 TeV (GRW Run 1&2)
MS > 1.09 GeV |
| TeV-1 ‘longitudinal’ ED: ee | Mc > 1.12 TeV |
| RS: ee +  | M(G(1)) > 785 GeV for k/MPl=0.1 |