Search for New Physics in the MET Channel at DØ

Stelios Kesisoglou Alex Melnitchouk

for the DØ collaboration

APS-DPF 2003 Conference, Philadelphia

Stelios Kesisoglou, Alex Melnitchouk APS-DPF

conference 2003

2

An alternative to gravity mediated SUSY: introduce new gauge fields (“messengers”) which propagate SUSY-breaking interactions and couple to ordinary and SUSY particles Phenomenology:

Gravitino is very light (<<MeV) and is LSPNLSP can be a neutralino or a sleptonNLSP lifetime is a free parameter

May yield non-prompt photons in the decay

In case of the neutralino NLSP:Final state always has two photons

Do inclusive search for MET + X

Gauge-Mediated SUSY

Stelios Kesisoglou, Alex Melnitchouk APS-DPF

conference 2003

3

Previous SearchesCDF has found an intriguing event eeMET

In the GMSB framework CDF set lower limit on the neutralino mass at M(0) > 65 GeV

LEP SUSY WG

DØ PRL(80) 1998

eeMET

CDF Run 1

DØ found no high ET

diphoton+MET events and set lower limit on the neutralino mass at M(0) > 75 GeV

LEP2 recently set lower limit on 1

0 ~ 95 GeV

Stelios Kesisoglou, Alex Melnitchouk APS-DPF

conference 2003

4

Data Selection ~40 pb-1 (September 2002 - January 2003) Trigger:

One EM object over the threshold ORTwo EM objects over the (lower) threshold

Off-line: events with two photonsIsolation

Shower shape consistent with photonNo matching tracks|| < 1.1 (since looking for heavy objects)

ET>20 GeV

to be above trigger turn-on: Trigger=0.98±0.02

to be able to rely on EM ID efficiency from Z decays

MET is calculated summing all calorimeter cells and corrected for EM and jet energy scales

0.150.2)(RE

0.2)(RE0.4)(RE

EM

EMTOT

EM ID = 0.85±0.06

Stelios Kesisoglou, Alex Melnitchouk APS-DPF

conference 2003

5

MET Resolution Tails of MET distribution are most important (region of expected signal) Can be caused by mis-measured jets discard events in which ET is collinear with a jet

Red – EM energyRed – EM energyYellow – direction of MEYellow – direction of MET T

Blue – hadronic Blue – hadronic energyenergy

Z+jet event:Both EM have tracksMass consistent with Z

MET has the same azimuthal angle as the jet!

Stelios Kesisoglou, Alex Melnitchouk APS-DPF

conference 2003

6

Backgrounds without true MET

QCD: , +j, j+j (jet is “faking” ) Drell-Yan (lost tracks)

with true MET (from )

W e & Wj ej (lost track, fake )

Z ee +X ( lost tracks )tt ee + X ( lost tracks )WW, WZ, …

Largest backgrounds

if a jet ”fakes” an isolated EM object, it’s mainly because it’s fragmented into a leading 0 and therefore its energy resolution is similar to the EM energy resolution MET resolution is similar for

, +jet, e+jet, ee, etc…

0

Quark or

gluon

hadrons

(leading particle)

Stelios Kesisoglou, Alex Melnitchouk APS-DPF

conference 2003

7

Predicting Backgrounds QCD (, +j, j+j)

require at least one of the isolated EM clusters to fail the shower shape cut “QCD Sample”Assume that events in the sample with small MET are dominated by QCD use MET<20 GeV region for normalizing QCD sample

W e & Wj ej require exactly one cluster to have a track match subtract QCD contribution multiply by (1-track)/track

MET>25 >30 >35 data 3 1 0

QCD contribution 6.0 ± 0.8 2.5 ± 0.5 1.6 ± 0.4e,ej contribution

0.6 ± 0.4 0.2 ± 0.2 0.0 ± 0.2

Stelios Kesisoglou, Alex Melnitchouk APS-DPF

conference 2003

8

Signal Efficiency

MET, GeV

QCD

MET, GeV

Run 2 preliminary

, TeV

, pb

Acceptance, %

ET>25

ET>30

ET>35

35 10.3 4.6 3.8 2.7

40 4.06 8.3 6.9 5.5

45 2.07 12.1 10.8 9.0

50 1.17 15.1 13.7 12.3

55 0.70 16.8 15.3 14.0

60 0.45 18.6 17.4 16.3

= 55 TeV = 45 TeV = 35 TeV

/ / /

A

AIDEMvtxtrigSUSY

09.066.0

2

Snowmass Slope E: mGMSB()

M=2; Nmess=1; tan=15; >0

( )

Stelios Kesisoglou, Alex Melnitchouk APS-DPF

conference 2003

9

Upper Limit Calculation Bayesian approach

Cut on MET should depend on - for now 30 GeV is conservative

95% CL90% CL

95% CL limit

>25 >30 >35

35 10.3 3.82 3.87 4.36

40 4.06 2.11 2.12 2.14

45 2.07 1.45 1.36 1.30

50 1.17 1.16 1.07 0.95

55 0.70 1.04 0.95 0.84

60 0.45 0.94 0.85 0.72CLGeVm

CLTeV

%95@66

%95@51

01

theory

Stelios Kesisoglou, Alex Melnitchouk APS-DPF

conference 2003

10

Prospects for Diphotons

Prompt decays:m(1

+) discovery up to 300 GeV with 2 fb-1

J. Qian, hep-ph/9903548

Similar model to Snowmass Slope, but tg = 2.5

Non-prompt decays:Sensitivity drops as NLSP leaves the detectorIn the limit of large lifetime we are back to jets+METIntermediate lifetime – ask for one photon plus jets plus MET

R calo

Stelios Kesisoglou, Alex Melnitchouk APS-DPF

conference 2003

11

A search for the Gauge-Mediated SUSY signal was carried out in the inclusive MET + X channelMET distribution is well understood and does not have significant non-Gaussian tailsObserved MET data are in good agreement with the Standard Model predictions With 40 pb-1 neutralino mass limit has been set at 66 GeV (sensitivity approaches that in Run I) More data are being accumulated Search for non-prompt photons is underwayStay tuned - new results will be coming soon

Conclusions

Stelios Kesisoglou, Alex Melnitchouk APS-DPF

conference 2003

12

5/20/2002 6

Photon PointingPreshowers give a very precise

position measurement – fit shower axis!

ZEMVTX

EM ShowerEM4EM3EM2EM1

Central Calorimeter

EndCalorimeterSolenoid

Central Fiber Tracker

Central: R = 1.4 cm Z = 2.2 cmForward: R = 1.2 cm Z = 2.8 cm

Preshowers are still in commissioning –pointing not used now. MC estimates are

Photon Pointing

Use calorimeter and preshower detectors to reconstruct displaced vertices in MET

events