searches for di-lepton and di-photon resonances at atlas

OCPA7, Yanwen Liu/USTC 1

Searches for di-lepton and di-photon resonances at ATLAS

Yanwen Liu

University of Science and Technology of China(USTC)

On behalf of the ATLAS collaboration

Aug 4, 2011. Kaohsiung


Outline• LHC and ATLAS

• Searches with photon pairs– Higgs

– Gravitons

• Searches with lepton pairs– Gravitons – Z’– R-parity violating sneutrino

• Summary



Experiments at LHC

Aug 4, 2011. Kaohsiung+LHCf, TOTEM


Inner detector (B=2 T)• Si pixels and strips• Transition Radiation Detector (e/ separation)• s/pT ~ 0.05% pT(GeV)0.1%; • |h| < 2.5, B=2 T(central solenoid)

Hadron Calorimeter• Fe/scintillator (central), Cu/W-LAr (fwd)• s/E ~ 50%/√E(GeV)3%• |h|<3

Muon spectrometer• air-core toroids, MDT+RPC+TGC+CSC

• s/pT ~ 2-7 %• |h| < 2.7, |h|<2.5 ( precision phys.)

EM Calorimetry • Pb-LAr• s/E ~ 10%/√E(GeV)1%• |h|<3.2, |h| < 2.5 (fine granularity)

Length: ~ 46 m Radius : ~ 12 m Weight : ~ 7000 tonsChannels: ~ 108 Lcable: ~ 3000 kmCost: 541M CHF



Data collection


7 TeV

2010: Exponential ramping up of luminosity

data-taking efficiency ~95% Peak luminosity : 1.75x1033 cm-2s-1

2011: steadily delivering !


Search for Higgs in di-photons


arxiv: 1107.0975v1 http://cern.ch/gfitter

Low mass Higgs is favored by the global electroweak fitting. γγ is one of the most promising channels at low mass.


Analysis overview• Two photon candidates PT

1>40 GeV, PT2>25 GeV, 1.52<|η|<2.37 and |η|<1.37

• Background : γγ(~70%), γj +jj (~28%) and ee(~2%, relevant near Z pole)

• Events are divided into 5 non-overlapping categories for different signal/background and resolutions


No significant excessmH =120 GeV, expect ~18 events


The ATLAS picture on Higgs


Dominating systematic uncertainties for γγ channel:• signal normalization: photon ID efficiency (11%)• mass resolution : 14% in total.


Randall-Sundrum gravitons


A possible “explanation” to the hierarchy problemOne extra dimension of finite size(rc), φ : 0 -> π.“Warped” metric:

K-K excitation of gravitons observable at hadron colliders Two model parameters: k/Mpl, mG

PRL83(1999)3370


RS limits from 2010 data


2011 data analysis in progress. Mass > 920 (545) GeV for k/Mpl=0.1(0.02)

Excludedat 95%CL


Search Di-lepton resonances


e+e- μ+μ-

Two isolated electrons with ET>25 GeV. |η|<1.37 and 1.52<|η|<2.47For 1500 GeV Z’, acceptance ~65%

Two isolated muons with PT>25 GeVFor 1500 GeV Z’, acceptance ~40%

Background estimated using MC simulations.Normalized to data using 70 GeV<M<110 GeV(scaling factor differs from 1 by less than 1%)


Constraints on RS gravitons and Z’


0.7 TeVfor k/Mpl= 0.01 1.63 TeV

for k/Mpl = 0.1 1.83 TeVSSM

RS gravitons, spin=2

Two benchmark modelsSequential Standard Model (SSM)E6 : SU(5)xU(1)xU(1)The two U(1) fields can mix


Search for e+μ resonances


Example models:Lepton-Flavor-Violating Z’

R-parity violating sneutrino.

For 0.7 TeV Z’,σ(pp->Z’+X)*Br(Z’->eμ) < 10.7 fb

λ311’, λ312 ≠ 0

All other couplings = 0


Summary• No discoveries in 1fb-1.• We will have much

more data soon


0.01

0.10

1.00

10.00

100.00

1000.00

0.0E+00

2.0E+33

4.0E+33

6.0E+33

8.0E+33

1.0E+34

1.2E+34

2010

2011

2012

2013

2014

2015

2016

2017

2018

2019

2020

2021

Inte

grat

ed lu

min

osity

[fb-1

]

Peak

Lum

inos

ity [c

m-2

s-1]

Peak lumi Int. lumi

Shut

dow

n

Shut

dow

n

One of the projections presented at EPS 2011. Not validated by LHC Machine Committee.

Stay tuned!

log scale!


THANKS!



BACK-UP


Some slides are borrowed from EPS 2011 talks

OCPA7, Yanwen Liu/USTC 17Aug 4, 2011. Kaohsiung


ATLAS Higgs-> γγ categories



CMS Higgs status



HggLow sensitivity, high resolution (1-2 GeV today but further improvements possible), tiny signal on a smoothly falling background; challenges: vertexing with PU, calibrations and transparency corrections for the crystals.

CMS PAS-HIG-11-011 CMS PAS-HIG-11-010



CDF Higgs status



Tevatron Higgs status



Tevatron Combination



High pT di-leptons

Z’m+m-

1940 GeV for the Sequential Standard Model Z′SSM, 1620 GeV for Super-String inspired models, Z′ψ. 1450-1780 GeV for RS Kaluza-Klein Gravitons for (k/MPl) 0.05-0.1.

Z’/GKK

q

q +l

l

We study in detail the high mass tail of the Z. Since spectra are consistent with known SM processes we extract 95% CL limits.

CMS-PAS-EXO-11-019.

Z’e+e- Z’e+e- or m+m-



LHC 2011 schedule


searches for di-lepton and di-photon resonances at atlas

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