“ Sensitivity to Dijet Resonances at CMS ”

1. “Sensitivity to Dijet Resonances at CMS” APS April meeting 24 April 2006 Kazım Gümüş and Nural Akchurin Texas Tech University Selda Esen and Robert M. Harris Fermilab

2. q,qbar,g Resonance q,qbar,g Z’, etc q,qbar,g s - channel q,qbar,g Motivation • We search for narrow resonances decaying to dijets at CMS. (inclusive) Feynman Diagram for a dijet resonance • There are many models of new particles which decay to dijets. (See next slide) • The fact that LHC is a proton-proton collider makes this channel important because resonances made from partons will decay to partons, giving jets.

3. Resonance Cross Sections & Constraints • Resonances produced via color force, or from valence quarks in the proton, have the highest cross sections. • Published Limits in Dijet Channel: • q* > 0.78 TeV (D0) • Axi or Col > 0.98 TeV (CDF) • E6 Diquark > 0.42 TeV (CDF) • rT8 > 0.48 TeV (CDF) • W ’ > 0.8 TeV (D0) • Z ’ > 0.6 TeV (D0) CDF: hep-ex/9702004 D0: hep-ex/0308033

4. Analysis • Simulation Samples • Signal : Z’ g Dijets for M = 0.7, 2.0 and 5.0 TeV. • Background : QCD dijet sample. • Jet Reconstruction & Correction • Iterative cone jet algorithm with R=0.5. • Correct jets back to particles in jet cone before pileup. • Event Selection • Find the two jets in the event with highest PT (leading jets). • Require each leading jet have | h | < 1. • Enhances sensitivity to new physics which is produced at low | h |. • Dijet mass: • Rates and Cross Section • Plot dijet mass in bins equal to mass resolution: bin size increases with mass. • Divide rate by integrated luminosity and bin width: differential cross section. This analysis was done for 100 pb-1 (pilot run), 1 fb-1 (1st physics run) and 10 fb-1(high luminosity run).

5. Narrow Resonance Shape in CMS • Model narrow resonance line shape at CMS with Z’ Simulation. • All resonances with a width significantly less than our resolution look like this in the CMS detector. • Corrected dijet mass peaks around generated value • Gaussian core with resolution • Long tail to low mass caused by QCD radiation. • Data here is in bins equal to the measured mass resolution above.

6. Signal and Background • QCD cross section falls smoothly as a function of dijet mass. • Resonances produce mass bumps we can see if xsec is big enough. QCD QCD q* Z’

7. Many resonances give obvious signals above the QCD error bars • Resonances produced via color force • Excited quark (shown) • Axigluon • Coloron • Color Octet rT • Resonances produced from valence quarks of each proton • E6 Diquark (shown) • Others may be at the edge of our sensitivity.

8. 0.7 TeV 2 TeV Statistical Sensitivity to Dijet Resonances • Sensitivity estimates • Statistical likelihoods done for both discovery and exclusion • 5s Discovery • We see a resonance with 5s significance • 1 chance in 2 million of effect being due to QCD. • 95% CL Exclusion • We don’t see anything but QCD • Exclude resonances at 95% CL. • Plots show resonances at 5s and 95% CL • Compared to statistical error bars from QCD. 5 TeV 2 TeV 0.7 TeV

9. Systematic Uncertainties • Uncertainty on QCD Background • Dominated by jet energy uncertainty (±5%). • Trigger prescale edge effect • Jet energy uncertainty has large effect at mass values just above where trigger prescale changes. • Resolution Effect on Resonance Shape • Bounded by difference between particle level jets and calorimeter level jets. • Radiation effect on Resonance Shape • Long tail to low mass which comes mainly from final state radiation. • Luminosity • We include all these systematic uncertainties in our likelihood distributions.

10. Sensitivity to Resonance Cross Section • Cross Section for Discovery or Exclusion • Shown here for 1 fb-1 • Also for 100 pb-1, 10 fb-1 • Compared to cross section for 7 models • CMS expects to have sufficient sensitivity to • Discover with 5s significance any model above solid black curve • Exclude with 95% CL any model above the dashed black curve. • Can discover resonances produced via color force, or from valence quarks.

11. 95% CL Sensitivity to Dijet Resonances 5s Sensitivity to Dijet Resonances CMS 100 pb-1 CMS 1 fb-1 CMS 10 fb-1 Published Exclusion (Dijets) CMS 100 pb-1 CMS 1 fb-1 CMS 10 fb-1 E6 Diquark Excited Quark Axigluon or Coloron Color Octet Technirho E6 Diquark Excited Quark Axigluon or Coloron Color Octet Technirho W ’ R S Graviton Z ’ 0 1 2 3 4 5 Mass (TeV) 0 1 2 3 4 5 6 Sensitivity to Dijet Resonance Models • CMS can exclude each of the models in some mass range. • CMS can discover the strongly produced models up to many TeV. Mass (TeV) Mass (TeV)

12. Conclusions • We have estimated CMS sensitivity to narrow dijet resonances. • Including estimates of both statistical and systematic uncertainties. • For samples of 100 pb-1, 1 fb-1 and 10 fb-1. • Signal cross sections that CMS can expect to discover (5s) or exclude (95% CL). • CMS can discover a strongly produced dijet resonance up to many TeV. • Axigluon, Coloron, Excited Quark, Color Octet Technirho or E6 Diquark • These are produced via the color force, or from the valence quarks of each proton. • CMS can exclude at 95% CL all models considered for some range of mass. • Including the lower cross section particles W’, Z’ and Randall-Sundrum Gravitons