QCD Factorization for Top Quark Mass Reconstruction Andr

QCD Factorization for Top Quark Mass Reconstruction André H. Hoang Max-Planck-Institute for Physics Munich Based on: S. Fleming, S. Mantry, I. W. Stewart, AHH, hep-ph/0703207 I. W. Stewart, AHH, ar. Xiv: 0709. 3519 S. Fleming, S. Mantry, I. W. Stewart, AHH, ar. Xiv: 0709. 2079 Euro. Flavor 07, Orsay , Nov 14 -16, 2007

Outline • Why do we want a precision • Methods for top mass determinations • Factorization theorem for ? What kind of precision. and -positron annihilation ( l l • invariant mass distribution in electron ) EFT derivation of Factorization at LO in Top mass determination to better than Which top mass is (not) measured ? NLL order analysis Summary 2 Euro. Flavor 07, Orsay , Nov 14 -16, 2007

Top Quark is Special ! • Heaviest known quark (related to SSB? ) • Important for quantum effects affecting many observables • Very unstable, decays “before hadronization” ( ) 1% precision ! How shall we theorists judge the error ? What is theoretical error ? What mass is it ? 3 Euro. Flavor 07, Orsay , Nov 14 -16, 2007

Need for a precise Top mass Fit to electroweak precision observables causes half of error in predicted 4 Euro. Flavor 07, Orsay , Nov 14 -16, 2007

Need for a precise Top mass Mass of Lightest MSSM Higgs Boson 5 Higgs bosons: • How to reduce theoretical and experimental errors? • What mass scheme does the central value refer to? 5 Euro. Flavor 07, Orsay , Nov 14 -16, 2007

Methods at Tevatron Template Method Not easy to address both issues: • complicated mass dependence • systematics (expansion scheme) unclear Dynamics Method • effects of radiative corrections (NLO) • might or might not be numerically relevant • kinematics yet unresolved conceptual problem from Aurelio Juste (theoretically) 6 Euro. Flavor 07, Orsay , Nov 14 -16, 2007

Basic Methods Threshold Scan ILC Miquel, Martinez; Boogert, Gounaris “threshold masses” Invariant Mass Reconstruction • • • Tev +LHC + ILC data available soon measures different top mass ? uncertainties (much) more involved many different methods available error around 1 Ge. V challenging 7 Euro. Flavor 07, Orsay , Nov 14 -16, 2007

Reconstruction Methods Plain Method: Kinematic Fit: • • W reconstruction + b tagging Inv. mass from • • • reconstruct entire event impose constraints ( e. g. vary unknows freely Lepton + Jets Atlas study: Borjanovic etal Major error sources: o b jet energy scale: 100. 000 events after cuts ) o FSR jets: o b jet energy scale: o FSR jets: Continuous Jet Definition: • • • Large Events: • • • 8 plain method for varying cone size: take weighted average FSR error reduced event shape-like ! select events with top pair back-to-back decay products in different hemispheres large cone size around top/antitop jet axes: and from in-cone momenta o UE: strong sensitivity to soft jets + Underlying Events Mass scale calibrations (W mass) o calibration Euro. Flavor 07, Orsay , Nov 14 -16, 2007

ILC: Ideal Study Case • No beam remnant : all soft radiation can be assigned to top or antitop Resonance region: ILC at large c. m. energy: • • • Dijet limit: QCD factorization á la Korchemsky/Sterman • unstable particle effective theory method (Fadin, Khoze; Beenaker etal, Beneke etal, Reisser, AH) related to thrust and heavy jet mass event shapes set up similar to Chekanov/Morgunov experimental analysis (based on k_T jet algorithm) 9 Euro. Flavor 07, Orsay , Nov 14 -16, 2007

Factorization Theorem Fleming, Mantry, Stewart, AH hep-ph/0703207 SOFT QCD JET SCET b. HQET SOFT LO factorization theorem JET 10 JET SOFT Euro. Flavor 07, Orsay , Nov 14 -16, 2007

Step 1: Factorization in SCET Integrate out Q Invariant mass fluctuations Jet functions still contain large logs in peak region: top decay products (b, W) still appear as explicit d. o. f. applicable to massless jet event shapes (thrust, etc. ) 11 Euro. Flavor 07, Orsay , Nov 14 -16, 2007

Soft-Collinear Effective Theory Degrees of freedom Light-cone coordinates quark fields gluon fields Leading order Lagrangian (n-collinear) massive SCET: Leibovich etal, Boos, Feldmann, Mannel etal 12 Euro. Flavor 07, Orsay , Nov 14 -16, 2007

Soft-Collinear Effective Theory Top pair production current one-loop matching • • agrees with massless SCET known to Kramer, Lampe ’ 87 Matsuura, v. d. March, v. Neerven ’ 88, ‘ 89 Gehrmann, Huber, Maitre ‘ 05 13 Euro. Flavor 07, Orsay , Nov 14 -16, 2007

Soft-Collinear Effective Theory QCD Cross Section Integrate out hard fluctuations at Q SCET Cross Section (LO in m/Q) factorization of asymptotic final states 14 Euro. Flavor 07, Orsay , Nov 14 -16, 2007

Soft-Collinear Effective Theory Factorization: soft-collinear decoupling Factorization and Soft field redefinition: soft-collinear decoupling Hemisphere mass constraint 15 Euro. Flavor 07, Orsay , Nov 14 -16, 2007

SCET Cross Section SCET factorization formula a la Korchemsky, Sterman including top mass and width effects Jet functions: • • • perturbative depends on insensitive to hemisphere constraints Soft function: • • 16 non-perturbative renormalized due to UV divergences governs massless dijet thrust and jet mass distributions depends on hemisph. constr. Euro. Flavor 07, Orsay , Nov 14 -16, 2007

Step 2: Factorization in boosted HQET integrate out the top mass Jet functions without large logs in peak region: top decay “integrated out” (unstable particle EFT) soft function S unchanged 17 Euro. Flavor 07, Orsay , Nov 14 -16, 2007

boosted HQET b. HQET Lagrangian: two copies of HQET (top+antitop) residual mass term: for pole mass total top width: - Inclusive treatment of top decay - wrong mass assignment -suppressed Jet functions: one-loop matching of jet functions 18 Euro. Flavor 07, Orsay , Nov 14 -16, 2007

Factorization Theorem Jet functions: • • • perturbative, any mass scheme depends on Breit-Wigner at tree level Soft function: • • • non-perturbative renormalized due to UV divergences also governs massless dijet thrust and jet mass event distributions 19 Korshemsky, Sterman, etal. Bauer, Manohar, Wise, Lee Short distance top mass can (in principle) be determined to better than. Euro. Flavor 07, Orsay , Nov 14 -16, 2007

Summation of Logs § Wilson coefficients 20 and sum local double logs Euro. Flavor 07, Orsay , Nov 14 -16, 2007

Summation of Logs § § low energy scales of jet functions and soft function differ RG-evolution of jet and soft functions individually involve plus functions 21 Euro. Flavor 07, Orsay , Nov 14 -16, 2007

Soft Function Model beyond LL Stewart, AH ar. Xiv: 0709. 3519 partonic soft function: • • soft function non-perturbative (distribution in the peak region) model function partonic contributions required for OPE for moments and predictions in the tail → → absorb partonic information fully into model parameters Korchemsky, Sterman, Tafat ‘ 00 glue partonic tail to model function (absorbs partonic information partially into ) Bosch, Lange, Neubert, Paz ‘ 04 23 Euro. Flavor 07, Orsay , Nov 14 -16, 2007

Soft Function Model beyond LL Stewart, AH ar. Xiv: 0709. 3519 partonic soft function: soft function model: normalized model function • • consistent OPE for predictions of moments or in the tail has renormalon: ambiguity in partonic zero-point Gardi ‘ 00 affects first power correction 24 Euro. Flavor 07, Orsay , Nov 14 -16, 2007

Soft Function Model beyond LL Stewart, AH ar. Xiv: 0709. 3519 partonic soft function: soft function model: normalized model function → gapped soft model: → renormalon subtraction scheme: 25 Euro. Flavor 07, Orsay , Nov 14 -16, 2007

Soft Function Model beyond LL Stewart, AH ar. Xiv: 0709. 3519 first moment renormalon-free with renormalon subtraction without renormalon subtraction 26 Euro. Flavor 07, Orsay , Nov 14 -16, 2007

Can one measure the Pole Mass ? Message: The pole mass is not accessible ! 27 Euro. Flavor 07, Orsay , Nov 14 -16, 2007

Short-distance Top Jet Mass • • • Top Jet mass is a scheme where we expect that a pert. analysis contains the least theoretical uncertainties. 29 One-loop: shift in the pole scheme 250 Me. V shift in the pole scheme contains renormalon jet mass scheme: defined such that peak located at the mass to all orders 2 -loop analysis talk by I. Scimemi Euro. Flavor 07, Orsay , Nov 14 -16, 2007

NLL Numerical Analysis Soft function model: Fit to heavy jet mass distribution Korchemsky, Tafat hep-ph/0007005 30 Euro. Flavor 07, Orsay , Nov 14 -16, 2007

NLL Numerical Analysis Double differential invariant mass distribution: Non-perturbative effects shift the peak by +2. 4 Ge. V and broaden the distribution. 31 Euro. Flavor 07, Orsay , Nov 14 -16, 2007

NLL Numerical Analysis LL vs. NLL distribution • • Jet vs. Pole mass scheme NLL corrections large for normalization NLL corr. reduce scale-dependence 32 Euro. Flavor 07, Orsay , Nov 14 -16, 2007

NLL Numerical Analysis Scale-dependence of peak position • • 33 Jet mass scheme: significanly better perturbative behavior. Renormalon problem of pole scheme already evident at NLL. Euro. Flavor 07, Orsay , Nov 14 -16, 2007

NLL Numerical Analysis Q-dependence of peak position different soft models different treatment for soft particles between jets Fairly precise determination of jet mass from determination of Qdependence of the peak position and extrapolation Q to zero 34 Euro. Flavor 07, Orsay , Nov 14 -16, 2007

NLL Predictions for Thrust NLL thrust distribution for massive quark jets top (bottom) mass from event shape distributions 35 Euro. Flavor 07, Orsay , Nov 14 -16, 2007

Summary & Outlook established factorization theorem for invariant mass distributions: separation of perturbative and non-perturbative effects for the ILC applicable for many other systems and setups (e. g. squarks) exact and systematic relation of peak to a Lagrangian mass: What mass is measured ? “Jet-mass” resummation of large logarithms NNLL analysis on the way extension to LHC other applications: → massless/massive event shapes (electron-positron) → hadron collider event shapes → …. . 37 Euro. Flavor 07, Orsay , Nov 14 -16, 2007