Particle Interferometry for Hydrodynamics and Event Generators - PowerPoint PPT Presentation

Particle Interferometry for Hydrodynamics and Event Generators Christopher J. Plumberg with Leif Lönnblad, Torbjörn Sjöstrand, and Gösta Gustafson COST Workshop, Lund University February 28, 2019

The Big Question: How do we know when we’ve created the QGP? Christopher J. Plumberg Particle Interferometry from Hydrodynamics and Event Generators

The Big Question: How do we know when we’ve created the QGP? Some broad options (not mutually exclusive): ◮ Look for collectivity ◮ Anisotropic flow ◮ The ridge Christopher J. Plumberg Particle Interferometry from Hydrodynamics and Event Generators

The Big Question: How do we know when we’ve created the QGP? Some broad options (not mutually exclusive): ◮ Look for collectivity ◮ Anisotropic flow ◮ The ridge ◮ Look for chemistry ◮ J/ ψ abundances ◮ Strangeness enhancement Christopher J. Plumberg Particle Interferometry from Hydrodynamics and Event Generators

The Big Question: How do we know when we’ve created the QGP? Some broad options (not mutually exclusive): ◮ Look for collectivity ◮ Anisotropic flow ◮ The ridge ◮ Look for chemistry ◮ J/ ψ abundances ◮ Strangeness enhancement ◮ Look for quenching But why haven’t we seen jet quenching in small systems? Christopher J. Plumberg Particle Interferometry from Hydrodynamics and Event Generators

The Big Question: How do we know when we’ve created the QGP? Some broad options (not mutually exclusive): ◮ Look for collectivity ◮ Anisotropic flow ◮ The ridge ◮ Look for chemistry ◮ J/ ψ abundances ◮ Strangeness enhancement ◮ Look for quenching But why haven’t we seen jet quenching in small systems? Consider the space-time geometry! Christopher J. Plumberg Particle Interferometry from Hydrodynamics and Event Generators

short long Fig credit: Ulrich Heinz and Scott Moreland Christopher J. Plumberg Particle Interferometry from Hydrodynamics and Event Generators

short long Freeze-out volume constant, but space-time volume changes significantly! Fig credit: Ulrich Heinz and Scott Moreland Christopher J. Plumberg Particle Interferometry from Hydrodynamics and Event Generators

How can we probe the space-time geometry? 1 HBT ≡ Hanbury Brown-Twiss Christopher J. Plumberg Particle Interferometry from Hydrodynamics and Event Generators

How can we probe the space-time geometry? → HBT 1 particle interferometry is ideal for this 1 HBT ≡ Hanbury Brown-Twiss Christopher J. Plumberg Particle Interferometry from Hydrodynamics and Event Generators

How can we probe the space-time geometry? → HBT 1 particle interferometry is ideal for this Today: ◮ Particle interferometry: basics ◮ Particle interferometry with hydrodynamics ◮ Particle interferometry with Pythia 8 1 HBT ≡ Hanbury Brown-Twiss Christopher J. Plumberg Particle Interferometry from Hydrodynamics and Event Generators

Correlation functions and HBT radii d 6 N d 3 N d 3 N � � C ( � p 1 , � p 2 ) ≡ E p 1 E p 2 / E p 1 E p 2 d 3 p 1 d 3 p 2 d 3 p 1 d 3 p 2 Christopher J. Plumberg Particle Interferometry from Hydrodynamics and Event Generators

Correlation functions and HBT radii d 6 N d 3 N d 3 N � � C ( � p 1 , � p 2 ) ≡ E p 1 E p 2 / E p 1 E p 2 d 3 p 1 d 3 p 2 d 3 p 1 d 3 p 2   q, � � ij ( � R 2 → C fit ( � K ) ≡ 1 + λ exp  − K ) q i q j  i,j = o,s,l K ≡ 1 p 2 , � � q ≡ � p 1 − � 2 ( � p 1 + � p 2 ) Christopher J. Plumberg Particle Interferometry from Hydrodynamics and Event Generators

Correlation functions and HBT radii d 6 N d 3 N d 3 N � � C ( � p 1 , � p 2 ) ≡ E p 1 E p 2 / E p 1 E p 2 d 3 p 1 d 3 p 2 d 3 p 1 d 3 p 2   q, � � ij ( � R 2 → C fit ( � K ) ≡ 1 + λ exp  − K ) q i q j  i,j = o,s,l K ≡ 1 p 2 , � � q ≡ � p 1 − � 2 ( � p 1 + � p 2 ) 2 � d 4 x S ( x, K ) e iq · x � � q, � � � C th ( � K ) ≈ 1 + � � � d 4 x S ( x, K ) � � Christopher J. Plumberg Particle Interferometry from Hydrodynamics and Event Generators

Correlation functions and HBT radii d 6 N d 3 N d 3 N � � C ( � p 1 , � p 2 ) ≡ E p 1 E p 2 / E p 1 E p 2 d 3 p 1 d 3 p 2 d 3 p 1 d 3 p 2   q, � � ij ( � R 2 → C fit ( � K ) ≡ 1 + λ exp  − K ) q i q j  i,j = o,s,l K ≡ 1 p 2 , � � q ≡ � p 1 − � 2 ( � p 1 + � p 2 ) 2 � d 4 x S ( x, K ) e iq · x � � q, � � � C th ( � K ) ≈ 1 + � � � d 4 x S ( x, K ) � � For Gaussian sources: ij ( � ⇒ R 2 x i − β i ˜ x j − β j ˜ � � = K ) ≡ (˜ t )(˜ t ) S , � d 4 x f ( x ) S ( x, K ) � f ( x ) � S ≡ � d 4 x S ( x, K ) x i − � x i � S , ˜ t ≡ t − � t � S , � β ≡ � K/K 0 x i ˜ ≡ Christopher J. Plumberg Particle Interferometry from Hydrodynamics and Event Generators

Space-time evolution in Hydrodynamics 14 20 Pb-Pb, T =100 MeV Pb-Pb, T =100 MeV Pb-Pb, T =155 MeV Pb-Pb, T =155 MeV 12 Pb-Pb, T =200 MeV Pb-Pb, T =200 MeV p-Pb, T =100 MeV p-Pb, T =100 MeV 15 p-Pb, T =155 MeV p-Pb, T =155 MeV 10 p-Pb, T =200 MeV p-Pb, T =200 MeV s; 0 (fm 2 ) o; 0 (fm 2 ) p-p, T =100 MeV p-p, T =100 MeV 8 p-p, T =155 MeV p-p, T =155 MeV p-p, T =200 MeV p-p, T =200 MeV 10 6 R 2 R 2 4 5 2 0 0 0.2 0.4 0.6 0.8 1.0 0.2 0.4 0.6 0.8 1.0 K T (GeV) K T (GeV) Steeper scaling at large K T Christopher J. Plumberg Particle Interferometry from Hydrodynamics and Event Generators

Space-time evolution in Hydrodynamics 14 20 Pb-Pb, T =100 MeV Pb-Pb, T =100 MeV Pb-Pb, T =155 MeV Pb-Pb, T =155 MeV 12 Pb-Pb, T =200 MeV Pb-Pb, T =200 MeV p-Pb, T =100 MeV p-Pb, T =100 MeV 15 p-Pb, T =155 MeV p-Pb, T =155 MeV 10 p-Pb, T =200 MeV p-Pb, T =200 MeV s; 0 (fm 2 ) o; 0 (fm 2 ) p-p, T =100 MeV p-p, T =100 MeV 8 p-p, T =155 MeV p-p, T =155 MeV p-p, T =200 MeV p-p, T =200 MeV 10 6 R 2 R 2 4 5 2 0 0 0.2 0.4 0.6 0.8 1.0 0.2 0.4 0.6 0.8 1.0 K T (GeV) K T (GeV) Steeper scaling at large K T ⇒ pp has more flow than pPb or PbPb! = Christopher J. Plumberg Particle Interferometry from Hydrodynamics and Event Generators

Conclusion : particle interferometry may help constrain the system’s geometry in relation to jet quenching, but quantitative studies are still needed. So how do we do this with event generators? Christopher J. Plumberg Particle Interferometry from Hydrodynamics and Event Generators

HBT and Pythia8 Method 1 : momentum-space modifications ◮ The idea: modify pairwise correlations in particle momenta to emulate Bose-Einstein (BE) enhancement 2 The precise form depends on the algorithm being used Christopher J. Plumberg Particle Interferometry from Hydrodynamics and Event Generators

HBT and Pythia8 Method 1 : momentum-space modifications ◮ The idea: modify pairwise correlations in particle momenta to emulate Bose-Einstein (BE) enhancement ◮ Strategy: perturb final-state momenta of identical particle pairs by some amount δQ , where � Q � Q + δQ q 2 dq q 2 dq = f 2 ( q ) q 2 + 4 m q 2 + 4 m � � 0 0 � − Q 2 R 2 � is the Bose-Einstein enhancement factor, 2 and f 2 ( Q ) ∼ 1 + λ exp and λ and R are (user-defined) coherence and radius parameters, respectively, and Q 2 = − ( p 1 − p 2 ) 2 2 The precise form depends on the algorithm being used Christopher J. Plumberg Particle Interferometry from Hydrodynamics and Event Generators

HBT and Pythia8 Method 1 : momentum-space modifications ◮ The idea: modify pairwise correlations in particle momenta to emulate Bose-Einstein (BE) enhancement ◮ Strategy: perturb final-state momenta of identical particle pairs by some amount δQ , where � Q � Q + δQ q 2 dq q 2 dq = f 2 ( q ) q 2 + 4 m q 2 + 4 m � � 0 0 � − Q 2 R 2 � is the Bose-Einstein enhancement factor, 2 and f 2 ( Q ) ∼ 1 + λ exp and λ and R are (user-defined) coherence and radius parameters, respectively, and Q 2 = − ( p 1 − p 2 ) 2 ◮ Net shift for a hadron is vector sum of shifts in all pairs it belongs to ◮ Implements BE correlations directly into spectra; all space-time information contained in R 2 The precise form depends on the algorithm being used Christopher J. Plumberg Particle Interferometry from Hydrodynamics and Event Generators

HBT and Pythia8 Method 1 : momentum-space modifications ◮ The idea: modify pairwise correlations in particle momenta to emulate Bose-Einstein (BE) enhancement ◮ Strategy: perturb final-state momenta of identical particle pairs by some amount δQ , where � Q � Q + δQ q 2 dq q 2 dq = f 2 ( q ) q 2 + 4 m q 2 + 4 m � � 0 0 � − Q 2 R 2 � is the Bose-Einstein enhancement factor, 2 and f 2 ( Q ) ∼ 1 + λ exp and λ and R are (user-defined) coherence and radius parameters, respectively, and Q 2 = − ( p 1 − p 2 ) 2 ◮ Net shift for a hadron is vector sum of shifts in all pairs it belongs to ◮ Implements BE correlations directly into spectra; all space-time information contained in R Output : List of particle momenta with BE effects included 2 The precise form depends on the algorithm being used Christopher J. Plumberg Particle Interferometry from Hydrodynamics and Event Generators

HBT and Pythia8 Method 2 : space-time vertex tracking 3 ◮ Assume q ¯ q string with linear confinement potential, for simplicity ◮ Hadrons formed by multiple string breaks 3 S. Ferreres-Sol´ e and T. Sj¨ ostrand, Eur. Phys. J. C 78 , 983 (2018). Christopher J. Plumberg Particle Interferometry from Hydrodynamics and Event Generators