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
OCPA7, Yanwen Liu/USTC 2
Outline• LHC and ATLAS
• Searches with photon pairs– Higgs
– Gravitons
• Searches with lepton pairs– Gravitons – Z’– R-parity violating sneutrino
• Summary
Aug 4, 2011. Kaohsiung
OCPA7, Yanwen Liu/USTC 3
Experiments at LHC
Aug 4, 2011. Kaohsiung+LHCf, TOTEM
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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
Aug 4, 2011. Kaohsiung
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Data collection
Aug 4, 2011. Kaohsiung
7 TeV
2010: Exponential ramping up of luminosity
data-taking efficiency ~95% Peak luminosity : 1.75x1033 cm-2s-1
2011: steadily delivering !
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Search for Higgs in di-photons
Aug 4, 2011. Kaohsiung
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.
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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
Aug 4, 2011. Kaohsiung
No significant excessmH =120 GeV, expect ~18 events
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The ATLAS picture on Higgs
Aug 4, 2011. Kaohsiung
Dominating systematic uncertainties for γγ channel:• signal normalization: photon ID efficiency (11%)• mass resolution : 14% in total.
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Randall-Sundrum gravitons
Aug 4, 2011. Kaohsiung
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
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RS limits from 2010 data
Aug 4, 2011. Kaohsiung
2011 data analysis in progress. Mass > 920 (545) GeV for k/Mpl=0.1(0.02)
Excludedat 95%CL
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Search Di-lepton resonances
Aug 4, 2011. Kaohsiung
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%)
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Constraints on RS gravitons and Z’
Aug 4, 2011. Kaohsiung
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
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Search for e+μ resonances
Aug 4, 2011. Kaohsiung
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
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Summary• No discoveries in 1fb-1.• We will have much
more data soon
Aug 4, 2011. Kaohsiung
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!
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THANKS!
Aug 4, 2011. Kaohsiung
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BACK-UP
Aug 4, 2011. Kaohsiung
Some slides are borrowed from EPS 2011 talks
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ATLAS Higgs-> γγ categories
Aug 4, 2011. Kaohsiung
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CMS Higgs status
Aug 4, 2011. Kaohsiung
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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
Aug 4, 2011. Kaohsiung
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CDF Higgs status
Aug 4, 2011. Kaohsiung
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Tevatron Higgs status
Aug 4, 2011. Kaohsiung
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Tevatron Combination
Aug 4, 2011. Kaohsiung
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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-
Aug 4, 2011. Kaohsiung
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LHC 2011 schedule
Aug 4, 2011. Kaohsiung