Phenomenology of heavy-ion collisions How can one characterize what - - PowerPoint PPT Presentation

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Phenomenology of heavy-ion collisions How can one characterize what - - PowerPoint PPT Presentation

Oct 24, 2022 635 likes •881 views

Phenomenology of heavy-ion collisions How can one characterize what is created in a heavy-ion collision? Focus on collective phenomena present in nucleus-nucleus collisions, but absent in pp collisions (condensed matter physics of

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Phenomenology of heavy-ion collisions

How can one characterize what is created in a heavy-ion collision? Focus on “collective phenomena” present in nucleus-nucleus collisions, but absent in pp collisions (“condensed matter physics of QCD”) Establish a reference, in which collective effects are absent. Quantify the deviation from these benchmarks in nucleus-nucleus collisions. Analyze the origin of these deviations.

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First measurement: multiplicity

number Nch of charged particles ∝

PHOBOS Collaboration, Phys. Rev. Lett. 85 (2000) 3100

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First measurement: multiplicity

number Nch of charged particles ∝

PHOBOS Collaboration, Phys. Rev. Lett. 85 (2000) 3100

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Nucleon-nucleon cross-section

taken from Miller, Reygers, Sanders & Steinberg, Ann. Rev. Nucl. Part. Sci. 57 (2007) 205

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Multiplicity distribution

Vary the equivalent number of nucleon-nucleon collisions between and : Probability P (n,b) to find a multiplicity n in a particular A-B collision at impact parameter b: Gaussian around , with some dispersion; given by a Monte-Carlo simulation. event-multiplicity distribution:

              

probability that an inelastic process occur ¯ NAB(b) = 1 − x 2 ¯ N AB

part(b) + x ¯

N AB

coll (b)

  • ¯

NNN ¯ N AB

part(b)

¯ N AB

coll (b)

¯ NAB(b) dNevts dn =

  • db P(n, b)
  • 1 −
  • 1 − σinel

NNTAB(b)

AB

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SLIDE 6

taken from Miller, Reygers, Sanders & Steinberg, Ann. Rev. Nucl. Part. Sci. 57 (2007) 205

Multiplicity distribution

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Multiplicity distribution

dNevts dn =

  • db P(n, b)
  • 1 −
  • 1 − σinel

NNTAB(b)

AB

figure from Kharzeev & Nardi, Phys. Lett. B 507 (2001) 121

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Multiplicity vs. geometry

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taken from Miller, Reygers, Sanders & Steinberg, Ann. Rev. Nucl. Part. Sci. 57 (2007) 205

Multiplicity vs. geometry

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taken from Miller, Reygers, Sanders & Steinberg, Ann. Rev. Nucl. Part. Sci. 57 (2007) 205

Cross-checking Glauber theory

Multiplicity at projectile rapidity vs. at midrapidity

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data from PHOBOS Collaboration Phys. Rev. C 74 (2006) 021901(R)

Pseudorapidity distributions

figure taken from Miller, Reygers, Sanders & Steinberg, Ann. Rev. Nucl. Part. Sci. 57 (2007) 205

Collision centralities: 0-6%, 6-15%, 15-25%, 25-35%, 35-45%, 45-55% (missing / not shown at the lower two energies)

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SLIDE 12

taken from BRAHMS Collaboration, Phys. Rev. Lett. 94 (2005) 162301

Rapidity distributions

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Multiplicity at mid-rapidity

Beware: in fact, at η=0, not y=0!

taken from PHOBOS Collaboration Phys. Rev. C 74 (2006) 021901(R)

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data from PHOBOS Collaboration Phys. Rev. C 74 (2006) 021901(R)

Charged hadron multiplicity

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data from PHOBOS Collaboration Phys. Rev. C 74 (2006) 021901(R)

We boost everything to the rest frame of one nucleus (“projectile”) universal “limiting fragmentation”

Charged hadron multiplicity

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data from PHOBOS Collaboration Phys. Rev. C 74 (2006) 021901(R)

We boost everything to the rest frame of one nucleus (“projectile”) universal “limiting fragmentation” ln √sNN grows like

Charged hadron multiplicity

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We boost everything to the rest frame of one nucleus (“projectile”) universal “limiting fragmentation”

Charged hadron multiplicity

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We boost everything to the rest frame of one nucleus (“projectile”) universal “limiting fragmentation” −ybeam @ LHC

Charged hadron multiplicity

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We boost everything to the rest frame of one nucleus (“projectile”) universal “limiting fragmentation” ln √sNN grows like −ybeam @ LHC

Busza 2004; N.B. & Wiedemann 2008

Charged hadron multiplicity

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The naive extrapolation of RHIC data yields at

  • increase, in opposition to conventional power-law rise

dN ch dη ≈ 1100 η = 0 ln √sNN

Charged hadron multiplicity

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The naive extrapolation of RHIC data yields at

  • increase, in opposition to conventional power-law rise

dN ch dη ≈ 1100 η = 0 ln √sNN

  • rganized by

N.Armesto, N.B., S.Jeon & U.A.Wiedemann

Hijing + baryon junctions: 3500 EPOS (multiple scattering): 2500 pQCD minijets + saturation (EKRT) of produced gluons: 2570 AMPT (Hijing+ZPC): ≈2500 Percolating strings: DMPJET III: ≈1900 Pajares et al.: 1500-1600 2-component + shadowing: ≈1700 “Geometric scaling” (Armesto, Salgado, Wiedemann): 1700-1900 Gluon saturation (Kharzeev, Levin, Nardi 2000-05): 1800-2100 B-K eq.+ running coupling (Albacete, Kovchegov): ≈1400 “CGC” (Gelis, Stasto, Venugopalan): 1000-1400 ALCOR (quark-antiquark plasma + recombination): 1250-1830 =

dN ch dy

Charged hadron multiplicity

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taken from BRAHMS Collaboration, Phys. Rev. Lett. 93 (2004) 102301

Net baryon-number density

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bulk: “soft particles” high-pT particles

Transverse-momentum spectrum

∝ ¯ N AB

coll (b)

∝ ¯ N AB

part(b)