html5-img
1 / 32

Highlights of SMU Work + Latest on Monopole Production at ATLAS

Highlights of SMU Work + Latest on Monopole Production at ATLAS. Daniel Goldin. Standard Model Higgs. In Standard Model, Higgs boson(s) necessary as evidence of Higgs field. Higgs field responsible for giving masses to particles.

cain-cardenas
Download Presentation

Highlights of SMU Work + Latest on Monopole Production at ATLAS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Highlights of SMU Work + Latest on MonopoleProduction at ATLAS Daniel Goldin

  2. Standard Model Higgs • In Standard Model, Higgs boson(s) necessary as evidence of Higgs field. Higgs field responsible for giving masses to particles. • LEP experiments excluded Higgs mass up to 114 GeV/c2 , Tevatron (this year’s result) between 160 and 170 GeV/c2. • Higgs mass chosen in this work set at 170 GeV/c2.

  3. Jets in Physics Signals: VBF H → WW → lnjj Process VBF Higgs Production q VBF jet } p W W,Z W jets H q W,Z l W p n VBF jet q p W W,Z H q q q q q W,Z l W p n • H → WW decay mode is one of main Higgs discovery channels at LHC and WW or ZZ fusion (VBF fusion) is one of the main modes of Higgs production. Higgs Branching Ratios 160GeV BR • Might be possible to see a few signal events early on (~10-100 pb-1). large BR

  4. Jets in a Physics Signal:H →WW through Vector Boson Fusion Particle-Level Jets: W and VBF Jet Eta VBF Jets W Jets h • The H→WW → lnjj channel has following advantages over fully leptonic H→WW → lnln: • Unlike lnln channel, missing ET from only one neutrino in lnqq allows for Higgs mass determination • Branching ratio for lnjj is 5.5 times that of lnln (with l = e±, m± ) • Color coherence of the valence quarks → jets from VBF process tend to be rather forward. Jets from the hadronically decaying W (W jets) tend to be more central. • However,mixing between VBF and W jets makes W mass (⇒Higgs mass) determination challenging.

  5. Jet Energy Scale (JES) from Hadronic W True jet energy Measured jet energy Parton energy For calibration with physics channels at ATLAS we can also use Absolute scale factor Parton-true jet scale factor • E = jet energy • = h coordinate of the jet vertex s = detector resolution • DR = cone size • L = luminosity } Kabs Set to constant here Kpart

  6. Jet Energy Scale from VBF H→WW: “Pure” and Reconstructed W Jets • “Best case scenario” of pure W jets and reco jets matched to quarks: Kabs = Etruejet/Ereco jet = 1.112 ± 0.007 • Pure W jets and quarks yield the parton scale Kpart: : Kpart = Equark/Etrue jet = 1.029 ± 0.002 • Can determine the total JES by matching reconstructed jets to quarks: Ktot = Equark/Ereco jet = 1.109 ± 0.002 • Since these jets are of highest purity, the 3% deviation from unity represents out-of-cone correction. Total Calibration Scale (Ktot) Equark/Erecojet True Jet to Partons (Kpart) Reconstructed Jet to True Jet (Kabs) Equark/Etruejet Etrue jet/Erecojet

  7. Jet Energy Scale from VBF H→WW: “Mixed” and Reconstructed W Jets • Majority of jets from W are mixed and yield: Kabs = Etrue jet/Ereco jet = 1.162 ± 0.002 Kpart = Equark/Etrue jet = 0.965 ± 0.001 Ktot = Equark/Ereco jet = 1.117 ± 0.002 • Kabs for mixed jets is 5% higher for mixed jets than for pure jets. • There is a 5% difference between Kpart between pure and mixed jets. Explained by the contamination of mixed jets by particles from the interaction region. Total Calibration Scale (Ktot) Ktot = Equark/Erecojet True Jet to Partons (Kpart) Reconstructed Jet to True Jet (Kabs) Etrue jet/Erecojet Equark/Etruejet

  8. Jet Energy Scale from VBF H→WW: Summary • From values of Kpart conclude that Cone 0.7 algorithm is adequate in describing hadronic W decays in VBF H→WW signal. • From Kabs conclude that TowerJet method might not be most optimal for reconstructing jets in calorimeter. JES rising with energy. Average Kabs > 1. • Possible improvement: TopoClusters.

  9. VBF H→WW: Optimizing Jet Selection Cuts • VBF H→WW signal discovery potential and the potential cuts have been previously considered by the collaboration. • Among (quite a few) CSC jet cuts: • Select jets pT > 30 GeV/c • 2 jets closest to PDG W mass are selected → W jet pair candidates. Of the remaining jets select 2 jets with highest jet Pt’s →tag jet pair candidates. • Require that the leading tag jet pT > 50 GeV/c. • Opposite hemisphere requirement: hj1×hj2< 0. • Pseudorapidity separation: |hj1-hj2| < 4.4. • Invariant mass of pair of tag jets > 1500 GeV/c2. • Central Jet Veto: no jets other than W jet pair with pT > 30 GeV/c and |h| < 3.2. • b jet veto • … • We propose a new set of cuts that (ATLAS Note: ATLAS-COM-2008-168). • improves the W jet candidate purity • no need to require (as the CSC note does) hadronic W be on mass shell. • if W does happen to be on mass shell, the proposed selection should lead to less biased W mass determination. • are likely to enhance signal-to-background ratio across most of background events. • Considered signal and one of leading backgrounds: t-tbar…

  10. Pt Balance Cut VBF jet } q W jets W W,Z H q W,Z l W n VBF jet q p W W,Z H q q q q q W,Z l W p n VBF Higgs Production • Apply the pT < 25 GeV/c balance cut to improve W jet candidate selection. The cut leaves 29% signal and 2.7% of the background events. • pT balance: S 2 tag jet pT’s + Higgs pT = S 2 tag jet pT’s + S pT (lnqq) p p t-tbar background: pT Balance Distribution VBF HWW signal: pT Balance Distribution Cut pT < 25 GeV/c Cut pT < 25 GeV/c Selection (5): pT balance cut

  11. Applying Results to Higgs Mass Invariant Mass of 2 W-Tagged Jets • Selection above, as opposed to taking jet pairs, whose invariant mass is closest to the PDG value, results in a higher purity W jets ⇒ more precise W mass determination ⇒more precise Higgs mass determination. • Selection steps above lead to unbiased W mass estimate, not tied to previously measured value. Invariant Higgs Mass from 2 Reco Jets + Truth Leptons + Truth Neutrino

  12. Conclusions for HWW Studies • We have focused on the jet selection for the VBF H→WW →lnqq signal and the ttbar background. • Estimated Jet Energy Scale for signal, i.e. how accurately physics events reconstructed in calorimeter. • Cone algorithm with DR = 0.7 describes parton events well. • TowerJet reconstruction may be improved by considering TopoClusters • Presented a set of selection cuts, some of which have been proposed previously, while others were new. Combined selection should result in: • improved significance of the VBF H→WW discovery. • better purity (precision) of W mass determination. • Utilized custom-built package to assess effectiveness of W jet/tag jet separation of the signal. After cuts: factor of 37 reduction of background acceptance, with factor of 3.3 for signal. • To be done: • Rest of backgrounds need to be obtained from real data. • Cuts need to be optimized using multivariate analysis. • Would like to look at jet-charge track association to improve purity of W selection for VBF H→WW signal. • This work shelved for now by ATLAS until data comes in and we get better handle on W+jet and muiltijet backgrounds.

  13. Dirac Monopole • Searched, but not discovered, by many experiments, such as accelerators and cosmic detectors. • Theoretically: Dirac Quantization Condition (1931) Dirac Unit Charge where Huge! • Motivation: • Explains quantization of electric charges. • Symmetrization (duality) of Maxwell’s Equations: unit electric charge → unit magnetic charge. • Predicted by GUT theories.

  14. Monopole Production with Colliders m m Diphoton Fusion through elastic pp collision Drell-Yan a p m amm m mm amm a p • Shown today • Already modeled for ATLAS at SMU (ATLAS int. note: Ana et al.) • Diphoton fusion has not yet been searched for at hadronic colliders. But calculated cross-sections already exist. • Elastic collisions easiest (fastest) to implement. Shown today. • Semi-elastic and inelastic collisions also possible (to be done later?), but generation more complex.

  15. Monopole Production Cross-Section through Elastic Diphoton Fusion For n=1 (spin=1/2) monopole: Dz. Shoukavy et al., Mod. Phys. Lett. A 21, 2873 (2006) T.Dougall and S.D. Wick, Eur. Phys. J. A39, 213 (2009) Compare M.Drees et al, Phys. Rev. D 50, 2335 (1994) Using duality and Rutherford scattering: J.Schwinger et al., Annals Phys. 101, 451 (1976) K.Milton, Rept. Prog. Phys. 69, 1637 (2006) (68.5 e)2

  16. MadGraph-Generated Diagrams • Cross-section pp → mm obtained using Weizsacker-Williams approximation (selectable in MadGraph): photon distr. inside proton u-channel u = -2p2 ( 1 + cosq ) t-channel t = -2p2 (1 – cosq )

  17. Monopole Cross-section vs. Mass from MadGraph Agreement Elastic diphoton Elastic diphoton Drell-Yan Drell-Yan T.Dougall and S.D. Wick, Eur. Phys. J. A39, 213 (2009) X-section vs. Mass for massive leptons with regular QED couplings Compare [Phys.Rev.D50:2335-2338,1994]

  18. Monopoles in Uniform Magnetic Field • Monopole’s trajectory in constant magnetic field is like that of electron in constant electric field (duality). • In ATLAS Bz (= 2 T), then equations of motion in r-z plane: • Lead to time-dependent trajectory: • Trajectory: catenary. Non-relativistic limit: parabola.

  19. Monopole Energy Loss I = • Adapt Bethe-Bloch energy loss to monopole (à la G. Bauer et al, Nucl. Instrum. Meth. A 545, 503 (2005)): neglect: bg ~10 duality: z/b→ng/e • Thus, for monopole: 1 • Note: more precise E-loss treatment (based on Ahlen) in our Drell-Yan int. note. S.P. Ahlen, Phys. Rev. D17, 17 (1978)

  20. Event Samples and Simulation • Simulated 20k monopole events with MadGraph for Mmono = 400 GeV/c2 and 1200 GeV/c2. • Rest of the simulation ROOT-based: • Simulated (roughly) detector volumes up to EM barrel calorimeter inner wall. • Propagated monopoles (anti-monopoles) using trajectory equations. • If monopole traversed subdetector volume, energy loss was calculated, and new kinematics were taken into account at exit of volume. • Assumptions: • E-loss formula adapted from standard one, with exception of charge replacement and ionization potential. • Only barrel and central tracking region simulated (h < 1.4), no endcaps. • Detector volumes simulated as uniform “barrels” (no gaps, surface imperfections, etc.) • Only the active materials simulated (e.g., for TRT: Xe gas, but no polyamide tubing) • No support structures simulated. • B-field assumed uniform (2 T).

  21. Energy Loss in Water: Implementation Cross-check dE/dx (GeV/cm) dE/dx (GeV/cm) g b Compare S.P. Ahlen, Phys. Rev. D17, 17 (1978)

  22. Putting It All Together: Trajectory + ATLAS Geometry + Eloss Sample 10 monopole tracks in ATLAS: mass = 400 GeV/c2 Barrel EM calorimeter Solenoid (Al) TRT (Xe) “low” |P| (= 318 GeV/c): mono trapped in solenoid coil B = 2T Tracker (Si) Beam pipe (Be)

  23. Energy Losses in Detector Volumes Eloss in Magnet (Mmono = 400 GeV/c2) Eloss in Si Tracker (Mmono = 400 GeV/c2) Eloss in Si Tracker (Mmono = 1200 GeV/c2) Eloss in Magnet (Mmono = 1200 GeV/c2)

  24. Acceptance Statistics (20k Events) Monos Trapped in Det. Volumes (Mmono = 400 GeV/c2) Monos Out of Acceptance Region (Mmono = 400 GeV/c2) TRT Si tracker magnet beam pipe Monos Out of Acceptance Region (Mmono= 1200 GeV/c2) Monos Trapped in Det. Volumes (Mmono = 1200 GeV/c2) TRT magnet Si tracker beam pipe

  25. Acceptance Plots (Mmono = 400 GeV/c2) 10k events

  26. Acceptance Plots (Mmono = 1200 GeV/c2) 1k events

  27. Monopole Summary Monopole acceptances for 20k diphoton events with 1fb-1 luminosity We could get plenty of monopoles (if they exist)!

  28. Summary • Worked on a few topics while at SMU: • Calorimeter calibration • Feasibility of producing Higgs in association with W,Z • H→WW cut optimization and jet energy scale • Jet energy scale with t-tbar events • Monopoles • Really enjoyed my time here, at SMU! • Thanks very much to everybody I worked with!

  29. Extras

  30. Tower vs. TopoCluster Jets • Advantages of TopoCluster over Tower method: • Built-in noise suppression • Clusters can span more than one area of calorimeter, even across gap regions • e/h is corrected at detector level, without use of specific jet algorithm noise cells (no true signal) σnoise (GeV) Tower jets Tower jets snoise(GeV) Cluster jets Cluster jets

  31. Jet Algorithms collinear sensitivity (1) (signal split into two towers below threshold) infrared sensitivity (artificial split in absence of soft gluon radiation) collinear sensitivity (2) (sensitive to Et ordering of seeds) Jet requirements: • Detector independence • Need for best possible Jet Energy Scale. • Infrared-safety: infrared instabilities undermine the claim of a jet algorithm to be telling us about the short distance physics. • Adding an arbitrarily soft gluon to the event should not change the jets. • Collinear safety • Appropriate ET threshold must be chosen (case 1) • Case 2 taken care of by seedless algorithm.

  32. Signal Events: W Jet Purity Cuts Particle-Level Jets: W and VBF Jet Eta • Cut at number of constituents for the mixed W jet: Nb. of constit. < 22. • There is less correlation between inv. mass and fractional contamination as evidenced by slope of the 2D fit and fewer number of high mass jets (M > 100 GeV) • Peak’s mean shifted toward pure W jet value. High mass tail is almost gone. • For the reconstructed jets may be able to correlate the constituent cut with the number of charged tracks Mixed W Jets Invariant Mass after Constituent Cut Pure W Jets: Invariant Mass High mass tail disappeared

More Related