Color coherence Measurement at CMS Feb 11 2011

재방송. . 심광숙교수님 정년퇴임 기념 헌정 워크 Color coherence Measurement at CMS Feb. 11, 2011 Inkyu PARK, Chawon PARK, Sangnam PARK Dept. of Physics, University of Seoul Les Parks

Introduction: Color coherence q Interference between particles radiated from color connected partons in the parton fragmentation process. – CDF : Phys. Rev. D 50, 5562 (1994) – DO : Phys. Lett. B 414, 419 (1997) q Simple MC with incoherent parton shower model could not reproduce the observed effects q MC with the coherence effect on by the AO assumption, such as PYTHIA, could successfully described the data. – AO (Angular Ordering): angles between mother and offspring partons decreases along the fragmentation step 2 Les Parks

Typical analysis & obsevable q Select “Y” shape 3 -jet events, then define Jet 1, Jet 2, Jet 3 – E(Jet 1) > E(Jet 2) > E(Jet 3) q Jet 3 are most likely color connected with Jet 2 – Enhancement of Jet 3 along the event plane, and suppression in the out of plane are expected. q Ideally, e+ e- collider is the best place to do the measurement. J 3 – No color interference from the initial state q In pp, both initial and final states have color constituents J 2 b f Φ – Complicate the signatures – Comparison with MC is crucial J 1 η h 3 Les Parks

1. 8 Te. V measurements at Tevatron D 0 Collaboration, Phys. Lett. B 414 419 (1997) 4 Les Parks

Motivation q Conservative follow the coherence measurement – Measure the strength of coherence in LHC – Provide MC tuning q Adventurous explore with some new observables – Track beta in di-jet events (assuming 2. 5 jet events) • Profit high statistics, correlate with other di-jet analyses – Transverse shape correlation between jets • jet 2 d-thrust axis angular correlation & thrust value dependence J 2 5 J 3 Les Parks

Data Samples q Used Data – The run range: 141956 -144114 • /Jet. MET/Run 2010 A-Nov 4 Re. Reco_v 1/RECO • Total Integrated Luminosity: 2. 9 pb-1 • The Nov 4 Re. Reco and JSON file used: Cert_136033149442_7 Te. V_Nov 4 Re. Reco_Collisions 10_JSON. txt • The trigger: HLT_Jet 50 U q MC Sample • Pythia 6 D 6 T Spring 10: QCDDi. Jet_Ptxxtoxx/Spring 10 START 3 X_V 26_S 09 -v 1/GEN-SIM-RECO (AO turned on) 6 Les Parks

Event selection q Analysis with CMSSW_3_8_7 q Jets were reconstructed by using the antikt (R=0. 5) clustering algorithm q Track jet : Default Jet energy correction q Calo jet was corrected for energy loss and effects due to nonlinear calorimeter response • Relative (corrects for eta dependence) • Absolute (corrects for the PT dependence) • Residual corrections only for Data q Online Selection • Technical bit “ 0” • select events with HLT single Jet triggers: HLT Jet 50 U q Offline Selection • Primary Vertex & Jet selection: PT > 10 Ge. V & “Loose” Jet ID • Mj 1 j 2 > 100 Ge. V 7 Les Parks

Classical measurement q follow the coherence measurement – define two polar variables R & β • The location of third jet in a search disk of R 23 < 1. 5 around 2 nd jet in η-φ plane • All the results are very preliminary J 3 b φ J 2 Φ J 1 η η 8 Les Parks

§ Divide |η 2| region 1/N d. N/dβ β distributions for Data and MC Central: |η 2| < 0. 9 Forward: 0. 9 < |η 2| < 2. 0 Forward Ratio(Data/MC) Central p 0 0 p § Data show an enhancement of events compared with Pythia 6(AO On) near the event plane (| b| = 0, p). § Depletion in the transverse plane(| b| = p/2) 9 Les Parks

β ratio (Data/MC) • Ratio(Data/MC) • Enhancement on Data compared with Pythia 6(AO On) is shown near the event plane (|b| = 0, p). Depletion in the transverse plane(| b| = p/2) Ratio(Data/MC) § For both algorithm, see the similar tendency ak 5 Track. Jet ak 5 Calo. Jet p 0 10 0 p Les Parks

New variable: βT distribution affected by fake tracks & tracking efficiency as a function of eta Ratio(Data/MC) § Promising observable § BUT, probably it is 1/N d. N/dβ § Track beta in di-jet events (assuming 2. 5 jet events) § situation follows the case of β § enhance at event plane, deplete at transverse plane 11 Les Parks

Conclusion & Remarks q We reviewed the DZero measurement on Color coherence with CMS 7 Te. V data collected in 2010 – Much stronger coherence effect exists at LHC – MC having coherence effect, such as PYTHIA with AO, does not describe the strength of coherence in Data q We can extend this measurement with di-jet events by looking at the track distribution nearby jet 2. – Tracking efficiency & fake tracks should be under control q Plan: – Examine more MC with/without coherence effects • We do need help on this!) – Use more Data statistics – Explore new variables • Track b. T distribution in dijet • 2 D-thrust axis correlation, thrust value dependence on R 23 12 Les Parks

Back-up slides 13 Les Parks

Back-up Ratio(Data/MC) 1/N d. N/dη Normalized d. N/dη distribution at ak 5 Calo. Jet 14 Les Parks