a search for new physics in the high mass dilepton spectrum at cdf

Tracey Pratt DIS 2002, Poland April 02

•CDF Detector

•Drell-Yan Signatures and New Physics

•Run I Limits and Run II reaches

•First Run II Data

•Near Future

A Search for New Physics in the High Mass Dilepton spectrum at CDF

Tracey Pratt, Oxford UniversityRepresenting the CDF collaboration


CDF at Fermilab

CDF CDF

D0

Tevatron

Main Injector

pp collisions


CDF Run I and Run II overview

Run I ran from 1992 until 95

In total 110pb-1 of data was collected

Centre of mass energy 1.8 TeV

Since the shutdown in 1996, the Tevatron and CDF have undergone major upgrades

Run II started in spring 2001

Centre of mass energy 2 TeV


CDF detector – what’s new?Muon System

COT

Plug Calorimeter

Time-of-Flight

Central Calorimeters

Solenoid

Silicon Tracker

New

Partially New

Old


Cosmic Ray event in CDF

-6 4 2 0 2 4300 200 100 0

2

0

Et


Z candidate

46.3 GeV

44.8 GeV

Invariant Mass 90.0 GeV


Drell-Yan (DY)

Low background at high dilepton invariant massDistinctive signatures:

•two oppositely charged leptons produced •have a high transverse momentum •are isolated•originate from a single interaction point

qq */ Z l+l-

p p

l+ l-

*/ Z

q q


New Physics Searches with Dileptons

New Gauge Bosons (Z')

Extra Dimensions

Quark-lepton Compositeness

Technicolor (T,T)

Looking for deviations to the Standard Model at high invariant mass


Run I Drell-Yan (DY)

•AFB smaller than SM

• AFB dips beyond 200 GeV/c2

X 88/89 CDF dileptons (ee+ 4pb-1)

o 92-95 CDF dimuons (107.4pb-1)

Invariant Mass in GeV/c2

0 100 200 300 400

101

100

10-1

10-2

10-3

10-4

Z and

only

d2/dMdy

CDF Collaboration, F.Abe et al., Phys. Rev. D 59, 052001 (1999)


Run 1 Z' limitsset limits for Z' ll, in both dielectron and dimuon channels

CDF Run I (110pb-1), for MZ > 600 GeV/c2 (Z ).BR(Z ->ll) is 40 fb.

which excludes MZ with Standard Model coupling < 690 GeV/c2

(Phys. Rev. Lett.79: 2192-2197, 1997))


Extrapolating from Run I, with 2 fb-1, if no candidates events in the high mass region are found, then predicted Z' mass reach could be extended to

1000 GeV/c2 with s =2.0 TeV

1200

1000

800

600

400

200

0

Integrated Luminosity (fb-1)

95 % CL Mass Reach (GeV/c2)

W'e (1.8TeV)

Z'll (2.0 TeV)

W' dijet (1.8TeV)

Z' dijet (1.8TeV)

10-2 10-1 1 10 102

Searches for New Gauge Bosons at Fermilab

Run II Reaches


ADD modelIn which the fundamental Planck scale (MPl) can brought down to the TeV range, by allowing for a large compactified dimensions at the TeV scale.The SM fields are confined to a 3-D braneMassless gravitons propagate in the full 4+n dimensional space G

RS modelMPl is determined by the higher-dimensional curvature rather than the size of the extra dimension. There is one additional dimension.Gravity can be localised near a brane. Kaluza-Klein states can be produced separately on resonance,and produce potentially observable spin 2 resonances.The cleanest signal for graviton resonance production is either an excess in Drell-Yan,or in the dijet channel.L.Randall and R.Sundrum, Phys. Rev. Lett. 83,3370 (1999), Phys. Rev. Lett. 83,4690 (1999)

G

Gravitons can be detected by 1) Graviton Emission - gravitons radiate into the bulk appearing as missing energy2) Graviton Exchange - deviations in the cross-section from SM predictionN. Arkani-Hamed et el., Phys. Lett. B 429, 263 (1998), I. Antoniadis et al., Phys Lett. B 436, 257 (1998)

Extra Dimensions


Extra DimensionsGraviton Exchange - modifies the rate and angular distribution of high-mass Drell-Yan events

Gg

g

l-

l+

Gq

q

l-

l+

+

+

• The SM exchange of a or Z boson interferes with the exchange of a graviton

• There is also a gluon-gluon initiated graviton exchange process which has no SM analogue.

/Z0 l-

l+

q

q


ADD model and RS model limits

SM predictionQuantum Gravity Model for Ms valuesCDF results for dimuon samples

Effective Planck Scale lower limit (95% C.L.)0.9-1.5 TeV Run I1.3-2.5 TeV Run IIa, 1.7-3.5 TeV LHCRange corresponds to number of extra dimensions n=7-2. (hep-ph/9904234, hep-ph/9909218)

Compactification scales R-1 (TeV) 0.9 Run 1 at 95% C.L., 1.2 Run II, 6.7 LHC(hep-ph/9905311)

Run I

Mll (GeV)

RS model

10 -2

10 -4

10 –6

10 -8

200 400 600 800 1000 1200

d/dM (pb/GeV) 1

0.70.50.30.20.1

700 GeV KK graviton K/MPl

Mll (GeV)


CompositenessQuark-lepton contact interaction was searched for in Run I in the dimuon and dielectron channels, by looking for an excess of dileptons compared to the Drell-Yan prediction.

Run Ib dielectron data set the limits on the compositeness scale to - > 3.8 TeV and + > 2.6 TeV.

In Run II we expect to be able to explore up to limits of approximately 5 TeV.

(Where +/- corresponds to the constructive / destructive interference with the dominant up-quark contribution to the cross-section.)

(Phys. Rev. Lett.79: 2198-2203, 1997))


TechnicolourIntegrated plots of dielectron mass distributions of D0 120 pb-1data and expected background

No signal above background found. T and T with masses < 225 GeV/c2 are ruled out for M( T) and M(T) < MW

B(

T

T e

+e- )*

(pb

)

100 200 300 400 500Mass (GeV)

1

10-1

10-295 % C.L. theoretical limits for T T e+e-

MT = 100 GeV

M, - M = 60 GeV

M, - M = 100 GeV

D0 Run I data

CC-CC

CC-EC

• Run I Data Background

100 200 300 400Minimum Mee (GeV)

Num

ber

of E

vent

s

103

102

101

1

103

102

101

1

*,Z*q

q

l-

l+T0,T

0


Run IIRun II started in spring 2001

CDF Upgrade improvements for Drell-Yan measurements•Dielectron channel New plug calorimeter •Dimuon channel Increased muon chamber coverage Better background rejection using Time-of-Flight detector to remove cosmic rays


Time-Of-Flight (ToF) Detector in CDF

216 scintillator bars located just outside the COT

Expected time resolution is 100 ps.


ToF Cosmic-Ray Rejection

~ 2L/c for CR dimuons ~ 0 for interaction ee and

Removal of the cosmic ray background is important for high mass dimuon sample

Above plots are from uncalibrated ToF. Calibration work is in progress.

Move Cosmic Rays with a cut requiring Tupper – Tlower > -5 ns

Cosmic Ray

Sample

Z ee

Tupper – Tlower


Run II Drell-Yan spectrumDielectron Dimuon


Future Plans

It is hoped that approximately 50-70 pb-1 data will be collected by Summer 2002

And 150 pb-1 by end of 2002.

We hope to find new physics or set new limits using the dilepton channels.


The End !

a search for new physics in the high mass dilepton spectrum at cdf

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