Download BDMPS Model for Jet Quenching and Energy Loss in Nuclear Medium and more Papers Health sciences in PDF only on Docsity! Dec 7, 2006 Qualifying Examination University of Texas at Austin Department of Physics, Austin, TX Matthew T. Haley Committee Members: Charles Chiu Duane Dicus Christina Markert George Sudarshan Energy Loss in Nuclear Medium through Radiation 2 Introduction I. Background on jet quenching in QGP II. BDMPS model for multiple scattering and emission Multiple scattering amplitude Multiple scattering with emission amplitude Coherence regimes III. Evaluation of R AA using obtained spectra Estimate of R AA Integration over coherence regimes Discussion of R AA plots IV. Conclusion A brief glance at a contemporary model (AMY) Possible future directions 5 Background—Medium effects as evidence for QGP High p T suppression observed in RHIC heavy ion collisions The nuclear modification factor—an indicator of medium effects from BRAHMS White Paper 6 Introducing the BDMPS method If jet quenching is the “smoking gun” of QGP, we need to put it on solid theoretical ground Find the radiative energy loss induced by successive scatterings in the medium 1) find the matrix element for successive scatterings 2) then find the matrix element for scattering induced emission 3) show that 2) factorizes into 1) times a radiation term 7 BDMPS—Multiple scattering Parton collides with N scattering centers: Need to find the S-matrix for this process Assumptions Well separated (scattering centers are distinct) Eikonal approximation—transverse recoil is very small Nearly collinear photons Soft photons 10 BDMPS—multiple scattering S-matrix The S-matrix will Conserve energy Have N-1 propagators Have N scattering potentials Integrating over longitudinal momenta, we pick up poles But the res due from the red pole is negligible, since it goes as , and the scattering centers are well separated. 11 BDMPS—Multiple Scattering Phase The phase will moderate between coherence regimes To evaluate phase, decompose vectors into longitudinal and transverse directions. z i is the longitudinal position of the ith scatterer. Averaging over scattering centers, 12 BDMPS—Multiple scattering induced radiation Parton again collides with N scattering centers but now also emits a photon between x j and x j+1 The orange term can be easily shown to be the difference of propagators using on shell conditions 15 BDMPS—Appearance of radiation regimes To get a feel for the opposite limits of the Bethe- Heitler and factorization regimes, 1) 2) Incoherent regime (Bethe-Heitler) If the phase difference between emission at i and emission at j is very large, this term washes out Totally coherent regime (factorization) If the phase difference is very small, this term cancels Recall 16 BDMPS—discussion of regimes How do we know which regime we're in? Depends on Mean free path Coherence length Size of medium Bethe-Heitler regime occurs when Factorization regime occurs when A third regime, the Landau-Pomeranchuk-Migdal (LPM), occurs when 17 BDMPS—Approximate radiation intensities QCD is similar to QED. QCD results are: Bethe-Heitler limit intensity LPM intensity Factorization limit intensity 20 Plots of R AA Assumptions: E LPM =1 GeV T=400 MeV =1 fm L=4 fm 15 20 25 30 35 40 pTT 0.2 0.4 0.6 0.8 1 RAA 50 100 500 1000 5000 10000 pT T 0.2 0.4 0.6 0.8 1 RAA Red—with absorption Blue—without absorption from PHENIX White Paper 21 A brief glance at a contemporary model-AMY In AMY approach, calculate Wightman current-current correlator Convenient to put the two “rails” together, like so Involves interference between terms like 22 AMY advantages Fully thermal calculation Other formalisms assume static scatterers AMY has temperature dependence built in No assumption about where Bethe-Heitler “stops” and LPM regime “begins”
