Searches for New Physics in Photonic Final States at the LHC with CMS

1

APS April Meeting

Denver CO, May 03, 2009

Andy Yen California Inst. of Technology

CMS Collaboration

The CMS Detector

• CMS is general purpose detector with good sensitivity towards Higgs and other New Physics signatures.

• High precision crystal ECAL is the source of much of its discovery potential.

2Andy Yen (Caltech/CMS)

The CMS ECAL (76k PbWO4 crystals, 90 tons)

• Capable of energy resolution of < 0.5% for ~100 GeV photons (testbeams).

• Goal is to achieve and maintain this resolution in situ at the LHC.

3Andy Yen (Caltech/CMS)

Barrel Crystals

EndCap(s)

Barrel: 61,200 crystals in 170 φ-

rings of 360 (|η| < 1.48)

Two Endcaps: 7,324 crystals each

(1.48<|η| < 3)

Searching for Higgs at CMS

• H→γγ is the most promising decay channel at CMS.

• Direct Signal

• Relatively low SM background.

4Andy Yen (Caltech/CMS)

Combined LEP, CDF and D∅, Mar 09

MH < 160 GeV (95% CL)

BR ~ 2 x 10-3

115 – 140 GeV

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H Signal and Backgrounds

g

g

gq

q q

q

SIGNAL (NLO) 2 Isolated, High ET Photons

Gluon Fusion

Vector Boson Fusion

Associated Production

with Z, W, tt

BACKGROUND ‘Irreducible’ backgrounds

(two real photons)

qq→ γγ (born diagram)

gg→ γγ (box diagram)

‘Reducible’ backgrounds

(at least one fake photon

pp→ g +jets or isolated π0

pp→ jets (2 fake g)

pp→ ee (Drell Yan), e’s

mis-ided as photons

box born brem

Andy Yen (Caltech/CMS)

6

CMS: Optimized H Analysis

• We see that photon energy resolution is very important in this analysis.

• Photon ID is also key.• Diphoton QCD background will need to be measured when

first data become available.

mH (GeV) L fb-1

115 8.5

120 7.7

130 11

140 16

150 ~30

Integrated luminosity for 5s discovery

(CMS NOTE-2006/112)

Higgs Signal and Backgrounds

Andy Yen (Caltech/CMS)

Gravity scale = MPl exp(-krc) ~TeV;

for krc ~11-12, no hierarchy problem

Graviton resonances mn = xn k exp(-krc), J1(xn)=0

Two parameters control graviton couplings and widths:

mass mG and constant c=k/MPl

Signals: Narrow, high-mass resonance states in

di-lepton and di-photon systems

7

Search for RS Gravitons G/e+e-

Andy Yen (Caltech/CMS)

8

Fully Simulated with Backgrounds;

ECAL Saturation Corrected (for E > 2 TeV)

Discovery Reach10 fb-1: MG > 3.14 TeV for c=0.1; MG > 1.32 TeV for c=0.0130 fb-1: MG > 3.54 TeV for c=0.1; MG > 1.59 TeV for c=0.01

Bkgds: QCD Jets, Direct

Photons, Drell-Yan

Can Directly Measure the

Width

RS Gravitons G

Andy Yen (Caltech/CMS)

CMS NOTE-2006/051

ADD Graviton Emission in γ+MET Channel

9Andy Yen (Caltech/CMS)

Signature:

A single high-pT photon in the

central η region.

High missing pT back-to-back with

the photon in the azimuthal plane

MD= 1 – 1.5 TeV for 1 fb-1

2- 2.5 TeV for 10 fb-1

The γ+(Z → νν)

background can be

estimated by studying

the γ+(Z→μμ) process

CMS NOTE-2006/129

L=60 fb-1

ECAL Calibration

• For early CMS runs, using π⁰ mass peaks is optimal.

• L=2x1033 gives

average π0γγ rate

of 1.5 kHz or 2,100

π0/crystal/day

10Andy Yen (Caltech/CMS)

Barrel Pi0 Callibration(Work in Progress)

11Andy Yen (Caltech/CMS)

• Good results after correcting for ECAL cracks and pileup π⁰’s• Calibration algorithm converges rapidly.• Can calibrate most of ECAL to 0.5% in under 100 hours.

Data after L1 Trigger Online Farm p0 Calibration

>10 kHz~1 kHz

Effect of ECAL Calibration

12January 09, 2008

Crystals Pulse Amplitudes

in a clustering algorithmParticle EnergyCalibration

Achieving a precise in situ crystal-by-crystal calibration of the CMS

ECAL will be crucial for the Hγγ search (CMS NOTE-2006/021)

Calibration Target

Andy Yen (Caltech/CMS)

Conclusion

• Photonic events also serve as a useful test of SM QCD predictions.

• Only a small sampling of CMS physics with photonic final states presented.

• Many early discovery opportunities.

• Detector performance, especially achieving ECAL calibration will be crucial to success of CMS physics program.

• Jet fake rates and Photon ID are also very important due to the large SM backgrounds.

13andyyen@hep.caltech.edu

The most exciting times

are just beginning!

Extra Slides Follow

G Discovery Potential

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CMS NOTE-2006/051

Andy Yen (Caltech/CMS)

Excited Leptons(Preliminary Results)

• e* and μ* can be produced copiously at the LHC (via contact interactions), and then decay via contact and electroweak interactions into ordinary photons and leptons

• Analysis benefits from good resolution of ECAL

• Discovery Potential (1 fb-1): Me* to ~2 TeV, Λ up to ~10 TeV

16Andy Yen (Caltech/CMS)

qq ee* ee qq μμ* μμ