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Searching for New Physics at the LHC using Dijets

Searching for New Physics at the LHC using Dijets. Marco CARDACI Universiteit Antwerpen on behalf of the CMS and ATLAS collaborations Les Rencontres de Moriond, QCD, 2008 La Thuile, Valle d’Aosta, March 8-15. Outline. Introduction CMS searches ATLAS searches Conclusions.

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Searching for New Physics at the LHC using Dijets

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  1. Searching for New Physics at the LHC using Dijets Marco CARDACI Universiteit Antwerpen on behalf of the CMS and ATLAS collaborations Les Rencontres de Moriond, QCD, 2008 La Thuile, Valle d’Aosta, March 8-15

  2. Outline • Introduction • CMS searches • ATLAS searches • Conclusions Marco CARDACI,10/03/08, La Thuile

  3. Dijet Resonance s - channel • Quark compositeness (scale L): • L < √s  Narrow resonant states of excited fermions on shell • L >> √s  Effective 4 fermions Contact Interaction: Contact Interaction q, q, g q, q, g X q, q, g q, q, g Lqqqq = A (g2/2L2LL) qLgmqLqLgmqL q q L q q Short introduction • Signals are Dijet Resonances and Contact Interactions • Resonances: • Technicolor  Color Octect Technirho • Grand Unified Theory  W’ & Z’ • Superstrings & GUT  E6 diquarks • Compositeness  Excited quarks • Extra Dimensions  RS Gravitons • Extra Color  Colorons & Axigluons CMS & ATLAS use: A= +1 destructive interference sign; g2 = 4 Marco CARDACI,10/03/08, La Thuile 3

  4. Dijet Resonance q, q, g q, q, g X q, q, g q, q, g s - channel QCD q, q, g q, q, g q, q, g q, q, g mainly t - channel Motivations Starting point • CMS Physics Technical Design Report (PTDR) is the CMS baseline plan for dijet analysis • Complementary to the PTDR sensitivity estimates • Focus on 10 pb-1 , 100 pb-1 & 1OOO pb-1 luminosities • Explores how we do analysis, find optimal cuts Dijet Angular Distributions Marco CARDACI,10/03/08, La Thuile 5

  5. Analysis strategies • Use jets in the Barrel which are sensitive to New Physics • Cut on MET/SET to reject catastrophic noise/beam halo/cosmics rays • Inclusive Jet Rate vs Jet pT: Contact Interactions • Large rate compared to QCD • Dijet Rate vs Dijet Mass: Resonances • Simple bump hunting in Dijet Spectra • Dijet Ratio = N (|h|<0.7) / N (0.7<|h|<1.3 ): both searches • Simple measure of angular distribution vs dijet mass MET / SET for QCD Dijet and cut Jet Response vs h relative to Barrel |h|<1.3 |h|<1 CMS Preliminary Marco CARDACI,10/03/08, La Thuile 6

  6. Inclusive Jet pT and Contact Interactions • Contact Interactions create large rate at high pT and immediate discovery possible • Error dominated by Jet Energy Scale (10%) in early running (10 pb-1) • DE 10% not as big an effect as L+= 3 TeV for pT>1 TeV • PDF “errors” and statistical errors (10 pb-1) smaller than E scale error • With 10 pb-1 we can see new physics beyond Tevatron exclusion of L+ up to 2.7 TeV Rate of QCD and Contact Interactions Sensitivity with 10 pb-1 Sys Err. PDF Err. Marco CARDACI,10/03/08, La Thuile 7

  7. Dijet Resonances in Rate vs Dijet Mass • Measure rate vs Corrected Dijet Mass and look for resonances • Use a smooth parameterized fit or QCD prediction to model background • Strongly produced resonances can be seen • Convincing signal for a 2 TeV excited quark in 100 pb-1 • Tevatron excluded up to 0.87 TeV QCD Backgound Resonances with 100 pb-1 Marco CARDACI,10/03/08, La Thuile 8

  8. h cut and sensitivity p0+p1/M Resonances: h cut & mass resolution h cut and cross section • QCD cross section rises dramaticallywith |h| cut due to t-channel pole • Z’ signal only gradually increases with |h| cut  optimal value at low |h| • Optimal cut is at |h| < 1.3 for a 2 TeV dijet resonance • Optimization uses Pythia Z’ angular distribution for the resonance Resolution • Gaussian core of resolution for |h|<1 and |h|<1.3 is similar • Resolution for Corrected Jets • 9% at 0.7 TeV • 4.5% at 5 TeV Corrected CaloJets GenJets Natural Width Marco CARDACI,10/03/08, La Thuile 9

  9. h = -1.3 - 0.7 0.7 1.3 Jet 1 Numerator Sensitive to New Physics |cos q*| ~ 0 z Jet 2 Denominator Dominated by QCD |cos q*| ~ 0.7, usually Jet 1 z or Jet 2 (rare) Jet 2 L+ (TeV) 3 5 10 QCD Dijet Ratio from QCD & Contact Interactions • Dijet Ratio = N(|h|<0.7) / N(0.7<|h|<1.3): • Number of events in which each leading jet has |h|<0.7divided by the number ofevents in which each leading jet has 0.7<|h|<1.3 • Dijet Ratio is a simple measure of the dijet angular distribution vs Dijet Mass • Numerator is sensitive to New Physics, denominator is dominated by QCD • QCD background has flat dijet ratio = 0.5 up to Dijet Mass = 6 TeV • Contact interactions increase the Dijet Ratio at high mass • CMS can discover L+= 4, 7 & 10 TeV with 10, 100 & 1000 pb-1 Dijet Ratio Marco CARDACI,10/03/08, La Thuile 10

  10. Dijet Resonances with Dijet Ratio Dijet Ratio vs Mass • Spin ½ (q*), spin 1 (Z’), and spin 2 (RS Graviton)resonances are more isotropic than QCD in dN / dcosq* • Resonances Dijet Ratio larger than for QCD because numerator mainly low cos q*anddenominator mainly high cos q* • Dijet Ratio from signal + QCD compared to statistical errors for QCD • Resonances normalized with q* cross section for |h|<1.3 to see effect of spin • Convincing signal for 2 TeV strongresonance in 100 pb-1 regardless of spin • Technique for discovery, confirmation and eventually spin measurement Dijet Ratio for Spin ½, 1, 2 Marco CARDACI,10/03/08, La Thuile 11

  11. Rdist optimization 3 TeV ATLAS Preliminary 5 TeV L=20fb-1 10 TeV 20 TeV ET0 40 TeV ET (GeV) Analysis strategies • Inclusive Jet Rate vs Jet pT • To characterize the excess of high pT events:R(L) = ( N(ET > ET0 )/N(ET < ET0) ) |L • To quantify the distance: Rdist = (R(L) – R(SM)) / √ s2R(L) + s2R(SM) • ET0 1100 GeV to optimize Rdist • Dijet angular distribution •  = e| 1 - 2 | • R(L) = ( N(c < cO )/N(c > cO) ) |L • Sensitivity: R1 = (Rc(L) – Rc(SM)) / √ s2Rc(L) + s2Rc(SM) • c0 2.8 to optimize R1 13 Marco CARDACI,10/03/08, La Thuile

  12. L=30 fb-1 3 TeV 5 TeV 15 TeV 10 TeV 20 TeV QCD +1,2,3% QCD QCD -1,2,3% ATLAS Preliminary Inclusivejet production Inclusive leading Dijet pT spectra (QCD+CI) Fractional Difference from QCD L=30fb-1 • 1% uncertainty in Energy Scale is enough to hide L = 20 TeV Integrated Luminosities to achieve Rdist = 3 • =3, 5, 10 TeV might be ruled out or verified with first tens of pb-1 of good data Rdist values for L = 300 fb-1 • No systematics is included (PDF, calorimeter non linearity, …), therefore the required L will be larger, in case of  = 40 TeV the discovery is still unclear 14 Marco CARDACI,10/03/08, La Thuile

  13. N Rdist Rdist N CTEQ6M errors 10 TeV100 fb-1 CTEQ6M errors 10 TeV10 fb-1 CTEQ6M central CTEQ6M central =10 TeV L=30 fb-1 ATLAS Preliminary central PDF error PDF uncertainties studies Fractional Difference + PDF error • CTEQ6M PDFs based on NLO calculations fitted to DIS • 20 parametric global fit, 40 error PDFs (+ one central value) used to obtain right-hand plot • PDF uncertainty studies done with Pythia 6.326, pT > 1 TeV • Systematic error due to PDF uncertainties in this case PDF(Rdist)= 1.40To be compared with to Rdist(=40TeV, 300 fb-1) = 3.40 15 Marco CARDACI,10/03/08, La Thuile

  14. R1 20 fb-1 pT > 350 GeV 3 TeV 5 TeV 10 TeV 20 TeV 40 TeV pT > 350 GeV Mjj > 4 TeV Dijet angular distribution Dijet mass cut optimization pT cut optimization Inclusive leading Dijet angular distribution • R1 optimization • pT > 350 GeV increase the sensitivity • Dijet invariant mass cut optimized for each L 16 Marco CARDACI,10/03/08, La Thuile

  15. R1 CTEQ6M errors 10 TeV100 fb-1 CTEQ6M central CTEQ5L Discovery limits Integrated luminosities to achieve R1 = 3 • R1 from Pythia (2 partons with highest pT),  = 10 TeV, mjj = 4 TeV, pT > 1 TeV • Systematic error due to PDF uncertainties in this case PDF(R1)= 0.88, which is comparable to R1(=40TeV, 30 fb-1) = 0.80 • Preliminary to say R1 is less sensitive than Rdist R1 values for L = 300 fb-1 • Also in this case no systematics are included (PDF, calorimeter non linearity, …) = 40 TeV the discovery is unclear R1 CTEQ6M errors 10 TeV10 fb-1 CTEQ6M central CTEQ5L 17 Marco CARDACI,10/03/08, La Thuile

  16. Conclusions • Inclusive jet pT analysis gives a convincing signal for a Contact Interactionscale L+ = 3 TeV in 10 pb-1 • Rate vs. Dijet mass gives a convincing signal for a 2 TeV q* with 100 pb-1 • Dijet Ratio can discover L+ 4, 7 and 10 TeV for 10 pb-1, 100 pb-1, and 1 fb-1 • Dijet Ratio can discover or confirm a dijet resonance,and eventually measure its spin • Early limits: +  3, 5,10 TeV might be discovered or rulled outwith first tens of pb-1 of good data • +  20 TeV still should be visible with larger integrated luminosity • Discovering +  40 TeV still unclear • Systematic errors studies in progress Marco CARDACI,10/03/08, La Thuile 18

  17. Thanks to Dijet group in CMS:A. Bhatti, B. Bollen, M. C., F. Chlebana, S. Esen, R. Harris, K. Kousouris, M. Jha, D. Mason and M. Zielinski ATLAS: S. Ferrag, L. Přibyl

  18. BACKUP SLIDES

  19. (qq, gg  A or C; qq  Z’, q1q2 W’ )dN/d cosq* 1 + cos2q* (qq  G  qq) dN/d cosq* 1 – 3 cos2q* + 4 cos4q* (gg  G  gg) dN/d cosq* 1 + 6 cos2q* + cos4q* (qq  G  gg, gg  G  qq)dN/d cosq* 1– cos4q* Resonances properties Spin ½ (qg  q*) dN/d cosq* 1 + cosq* Spin 1 Spin 2 (QCD) dN/d cosq* 1/(1 – cosq*)2 21

  20. CDF current limits Limits on production of new particles decaying into dijets Mass exclusion • Preliminary results just released • Best limits on dijet resonances • Thanks to Ken Hatakeyama 22

  21. Preliminary Results Just Released Best limits on dijet resonances Thanks to Ken Hatakeyama ! CDF Dijet Resonance Search in Run II 23

  22. Model details 24

  23. Detectors characteristics 25

  24. Detectors 26

  25. Particle detection in CMS 27

  26. Jet 2 Jet 1 Calorimeter Simulation ET h f -1 0 1 Dijet Mass = 900 GeV Dijet event CMS Barrel & Endcap Calorimeters h=0 h=1 h=-1 Jet 1 Transverse f q proton proton Jet 2 • Dijets are easy to find • Two jets with highest pTin the calorimeter • A jet is the sum of calorimeterenergy in a cone of radius 28

  27. Standard jet reconstruction • Cone algorithm R=0.5 • Midpoint & iterative cone indistinguishable at high pT • Standard jet kinematics • Jet E = SEi, Jet p=Spi • q = tan-1(py/px) • ET = E sinq, pT=√px2+py2 • Standard MC jet corrections • Scales Jet (E,px,py,pz) by • ~1.5 at ET = 70 GeV • ~1.1 at ET = 3 TeV for jets in barrel region • Dijet is two leading jets. • m= √(E1+E2)2 –(p1+p2)2 Dijet Balance Barrel Jet (|h|<1.3) Probe Jet (any h) Hcal towers and h cuts h = 1 h = 1.3 HB HE Transition Region Jet response vs h relative to | h | < 1.3 |h|<1.3 |h|<1 CMS Preliminary Jet Reconstruction & Correction in CMS • Barrel jets have uniform response & sensitive to new physics • Jet response changes smoothly and slowly up to | jet h | = 1.3 • CaloTowers with | h | < 1.3 are in barrel with uniform construction. • CaloTowers with 1.3< | h | < 1.5 are in barrel / endcap transition region • Some of our analyses use | jet h | < 1.3, others still use | jet h | < 1 • All are migrating to | jet h | < 1.3 which is optimal for dijet resonances • Measure relative response vs. jet h in data with dijet balance • Data will tell us what is the region of response we can trust 29

  28. Inclusive Jet pT • Inclusive jet pT is a QCD measurement that is sensitive to new physics • Counts all jets inside a pT bin and h interval, and divides by bin width and luminosity • Corrected CaloJets agree reasonably well with GenJets • CaloJets jets before corrections shifted to lower ET than GenJets • Ratio between corrected CaloJets and GenJets is “resolution smearing”: small at high pT • Simple correction for resolution smearing in real data is to divide rate by this ratio Resolution Smearing Inclusive Jet Cross Section 30

  29. Event Selection CMS Detector 4 x 107 Hz L1 Trigger 1 x 105 Hz HLT Trigger 1.5 x 102 Hz Saved for Analysis Trigger and Luminosity • Collision rate at LHC is expected to be 40 MHz • 40 million events every second • CMS cannot read out and save that many • Trigger chooses which events to save • Two levels of trigger are used to reduce rate in steps • Level 1 (L1) reduces rate by a factor of 400 • High Level Trigger (HLT) reduces rate by a factor of 700 • Trigger tables are intended for specific luminosities • We’ve specificied a jet trigger table for three luminosities • L = 1032 cm-2 s-1. Integrated luminosity  100 pb-1 • LHC schedule projects this after 1 months running • L = 1033 cm-2 s-1. Integrated luminosity  1 fb-1 • LHC schedule projects these after  1 year of running • L = 1034 cm-2 s-1. Integrated luminosity  10 fb-1 • One months running at design luminosity 31

  30. Add New Threshold (Ultra) - Increase Prescales by 10 L = 1033 1 fb-1 Add New Threshold (Super) - Increase Prescales by 10 L = 1034 10 fb-1 CMS Jet Trigger Table and Dijet Mass Analysis • CMS jet trigger saves all high ET jets & pre-scales the lower ET jets Mass values are efficient for each trigger, measured with prior trigger L = 1032 100 pb-1 As luminosity increases new trigger paths are added Each with new unprescaled threshold. 32

  31. Dijet Ratio and Systematic Uncertainties • Systematics (red) are small • They cancel in the ratio • Relative Energy Scale • Energy scale in center vs edge of barrel in h • Estimate +/- 0.5 % is achievable in barrel • Determined with dijet balance • Parton Distributions • We’ve used CTEQ6.1 uncertainties P T D R 33

  32. 5s Sensitivity to Dijet Resonances CMS 100 pb-1 CMS 1 fb-1 CMS 10 fb-1 E6 Diquark Excited Quark Axigluon or Coloron Color Octet Technirho 0 1 2 3 4 5 Mass (TeV) Rate: Discovery Sensitivity to Models • Resonances produced by the valence quarks of each proton • Large cross section from higher probability of quarks in the initial state at high x • E6 diquarks (ud  D  ud) can be discovered up to 3.7 TeV for 1 fb-1 • Resonances produced by color force • Large cross sections from strong force • With just 1 fb-1 CMS can discover • Excited Quarks up to 3.4 TeV • Axigluons or Colorons up to 3.3 TeV • Color Octet Technirhos up to 2.2 TeV • Discoveries possible with only 100 pb-1 • Large discovery potential with 10 fb-1 P T D R 34

  33. Rate: Exclusion Sensitivity to Models 95% CL Sensitivity to Dijet Resonances • Resonances produced via color interaction or valence quarks • Wide exclusion possibility connecting up with many exclusions at Tevatron • CMS can extend to lower mass to fill gaps • Resonances produced weakly are harder • But CMS has some sensitivity to each model with sufficient luminosity • Z’ is particularly hard • Weak coupling and requires an anti-quark in the proton at high x Tevatron Exclusion (Dijets) CMS 100 pb-1 CMS 1 fb-1 CMS 10 fb-1 E6 Diquark Excited Quark Axigluon or Coloron Color Octet Technirho W ’ R S Graviton Z ’ 0 1 2 3 4 5 6 P T D R Mass (TeV) 35

  34. Discovery and Exclusion sensitivity to CI Before |h| cut optimization After |h| cut optimization Senstivity to contact interactions with 10 pb-1, 100 pb-1, and 1 fb-1 Estimates include statistical uncertainties only 36

  35. QCD b = 0.045, 2% @ 2TeV pT (GeV) Inclusivejets – calorimeter nonlinearity • What effect a calorimeter nonlinearity will make? • To parametrize nonlinearity of ATLAS hadronic calorimeter (simple method): • e/h - noncompensation, b – nonlinearity (smaller values achievable by e.g. weighting method) • c makes nonlin. and lin. spectra equal at 500 GeV =10 TeV 37

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