Bulk observables vs. hard probes bulk high- p T probes Only few - PowerPoint PPT Presentation

Bulk observables vs. hard probes bulk high- p T probes Only few particles with high transverse momenta (or containing heavy quarks), but their production mechanism is a priori better understood (perturbative QCD) can probe their environment ≡ the “bulk”. STAR Collaboration, Phys. Rev. Lett. 91 (2003) 172302

QCD Lagrangian L classical = − 1 µ ν F µ ν � 4 F A A + q a (i � D − m ) ab q b ¯ flavors F A µ ν = ∂ µ A A ν − ∂ ν A A µ − gf ABC A B µ A C ν ( D µ ) ab = ∂ µ δ ab + i g ( t C A A µ ) ab [ t A , t B ] = i f ABC t C 2 a , b = 1 … N c 3; A , B , C = 1 … N c = - 1 = 8 α s ≡ g 2 Effective coupling: 4 π

Running of α s Q 2 ∂α s ∂ Q 2 = β ( α s ) ≡ − b α 2 1 + b ′ α s + b ′′ α 2 s + O ( α 3 � � s ) s � � b = 11 C A − 2 N f ≡ β 0 12 π 4 π plot from Bethke, Prog. Part. Nucl. Phys. 58 (2007) 351

Jets in heavy-ion collisions […] …

Jets in heavy-ion collisions (unfortunately, effect overestimated by a factor ≈ 100) […] …

Time evolution of a heavy-ion collision time space

Time evolution of a heavy-ion collision γ time – QQ hard parton hard scatterings space

Time evolution of a heavy-ion collision γ μ ± e ± time n o i s n a – p x QQ e few fm/ - Quark-Gluon Plasma c hard scatterings space

Time evolution of a heavy-ion collision p J/ ψ , Υ ? γ μ ± K Λ e ± jet π time hadronization n o i s n a – p x QQ e few fm/ - Quark-Gluon Plasma c hard scatterings space

Time evolution of a heavy-ion collision p stolen from Steffen Bass J/ ψ , Υ ? γ μ ± K Λ e ± jet π & John Harris time freeze-out hadronization n o i s n a – p x QQ e few fm/ - Quark-Gluon Plasma c hard scatterings space

“Jet quenching”: basic picture A fast parton propagating through a dense medium will “lose” part of its energy. The resulting jet of hadrons (if any!) is distorted: “quenching”. in vacuum in medium

Hadrons at large p T at RHIC d N h AB 1 d p T d y Nuclear modification factor R h AB ≡ � N AB d N h coll � pp d p T d y (=1 if AA collision is a superposition of independent NN collisions ) * uncertainty � N AB coll � PHENIX Coll., Phys. Rev. Lett. 101 (2008) 232301 In central Au+Au collisions at = 200 GeV , one misses 80% of the √ s NN high-transverse-momentum hadrons! * up to isospin corrections…

Hadrons at large p T at RHIC d N h AB 1 d p T d y Nuclear modification factor R h AB ≡ � N AB d N h coll � pp d p T d y (=1 if AA collision is a superposition of independent NN collisions ) * uncertainty � N AB coll � uncertainty on pp-normalization PHENIX Coll., Phys. Rev. Lett. 101 (2008) 232301 In central Au+Au collisions at = 200 GeV , one misses 80% of the √ s NN high-transverse-momentum hadrons! * up to isospin corrections…

Hadrons at large p T at RHIC Photons should not dissipate energy like colored particles : R AA ≈ 1 * * yet photon production is modified: Bremsstrahlung, photons from parton fragmentation…

Hadrons at large p T at RHIC Photons should not dissipate energy like colored particles : R AA ≈ 1 * computations of are not off N coll by a factor 5! * yet photon production is modified: Bremsstrahlung, photons from parton fragmentation…

Hadrons at large p T at RHIC Photons should not dissipate energy like colored particles : R AA ≈ 1 * deviation from 1 not unexpected (isospin…) computations of are not off N coll by a factor 5! * yet photon production is modified: Bremsstrahlung, photons from parton fragmentation…

Hadrons at large p T at RHIC Photons should not dissipate energy like colored particles : R AA ≈ 1 * deviation from 1 not unexpected (isospin…) computations of embarrassingly are not off N coll close to the by a factor 5! pion value? * yet photon production is modified: Bremsstrahlung, photons from parton fragmentation…

Hadrons at large p T at RHIC more quenching d 2 N AA d P T d y d P T d y d 2 N pp N coll 1 ≡ R AA less quenching PHENIX Coll., Phys. Rev. Lett. 101 (2008) 232301

Hadrons at large p T at RHIC The scaled yield of high- p T hadrons decreases with growing centrality: increasing quenching PHENIX Coll., Phys. Rev. Lett. 101 (2008) 232301

Hadrons at large p T at RHIC taken from A.Sickles’ talk at QM’09

Hadrons at large p T at RHIC “Azimuthal correlation” between a “trigger” particle (4 < p T,trig < 6 GeV / c ) and “associated” particles (2 < p T < p T,trig ).

Hadrons at large p T at RHIC “Azimuthal correlation” between a “trigger” particle (4 < p T,trig < 6 GeV / c ) and “associated” particles (2 < p T < p T,trig ). In central collisions, the “back jet” (= peak at 180° from the trigger particle) disappears.

Hadrons at large p T at RHIC Trigger particle: 4 < p T,trig < 6 GeV / c ; associated particles: 2 < p T < p T,trig . STAR Coll., Phys. Rev. Lett. 91 (2003) 072304

Hadrons at large p T at RHIC The “back jet” reappears when one changes the momentum cuts... STAR Coll., Phys. Rev. Lett. 97 (2006) 162301

Hadrons at large p T at RHIC Trigger particle: 8 < p T,trig < 15 GeV / c . The “back jet” reappears when one changes the momentum cuts... STAR Coll., Phys. Rev. Lett. 97 (2006) 162301

Jets? UA2, ca.1982 DELPHI, 1991 pictures taken from T.Ullrich’ s student lecture at QM’09

Jets? CDF D0, ca.2003 pictures taken from T.Ullrich’ s student lecture at QM’09

Observing jets in heavy-ion collisions Needle in a haystack… About 8000 hadrons in a central Au+Au collision at = 200 GeV: √ s NN

Jets in Au-Au collisions at RHIC Audaces fortuna juvat… very preliminary “results” ≃ 22 GeV /c /c) p T per grid cell (GeV η φ talks by J.Putschke & S.Salur @ Hard Probes 2008

Jets in Au-Au collisions at RHIC Audaces fortuna juvat… very preliminary “results” (with cone or k T reconstruction algorithms) ≃ 47 GeV /c ≃ 22 GeV /c /c) /c) p T per grid cell (GeV p T per grid cell (GeV η η φ φ talks by J.Putschke & S.Salur @ Hard Probes 2008