U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E faculty of science Charged-particle pseudorapidity density N part versus N coll Christian Holm Christensen Niels Bohr Institute COST Workshop on interplay of hard and soft QCD probes for collectivity in heavy–ion collisions — 27 th of February, 2019
U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E Disclaimer I am an ALICE collaborator, so many results will be from the ALICE collaboration d N ch Slide 2/30 — C.H.Christensen — — COST’19 — 2019/02/27 d η
U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E Overview 1 Measurements of d N ch d η Other measurements of interest Take-away 2 Scaling Midrapidity d N ch and total N ch d η Natural Centrality Glauber modelling 3 Summary d N ch Slide 2/30 — C.H.Christensen — — COST’19 — 2019/02/27 d η
U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E Wealth of measurements pp(pp) results η /d • From √ s = 200 GeV to ch 8 pp(p p ) collisions N ATLAS, 13TeV, INEL>1, p >100MeV d T ALICE, 13TeV, INEL>0 CMS, 13TeV, INEL ATLAS, 8TeV, INEL>1, p >100MeV 13 TeV T 7 CMS & TOTEM, 8TeV, INEL TOTEM, 8TeV, INEL>0 TOTEM, 7TeV, INEL>0 • Inelastic CMS, 7TeV, NSD ATLAS, 7TeV, INEL>1, p >100MeV T CMS, 2.36TeV, NSD 6 • with N ch > 0 CDF, 1.8TeV, MB ATLAS, 900GeV, INEL>1, p >100MeV T CMS, 900GeV, NSD • with N ch > 1 P238, 630GeV, MB CDF, 630GeV, MB 5 UA1, 540GeV, NSD PHOBOS, 410GeV, INEL • Non-single diffractive PHOBOS, 200GeV, INEL 4 • Mostly | η | < 2 3 2 1 0 − − − − 8 6 4 2 0 2 4 6 η HepData d N ch Slide 3/30 — C.H.Christensen — — COST’19 — 2019/02/27 d η
U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E Wealth of measurements AA at RHIC energies d N ch /d η Cu-Cu √ s NN = 22.4GeV 3 Cu-Cu √ s NN = 62.4Ge 3 Cu-Cu √ s NN = 200Ge 3 10 V V PHOBOS • Au–Au & Cu–Cu 2 2 2 10 0- 6% • From √ s NN = 20 GeV 6- 15% 10 10 10 to 200 GeV 15- 25% d N ch /d η Au-Au √ s NN = 19.6Ge 3 Au-Au √ s NN = 62.4GeV 3 Au-Au √ s NN = 200GeV 3 10 V • Mostly PHOBOS 25- 35% 2 2 2 10 Also results from 35- 45% BRAHMS, STAR 10 10 10 45- 55% 6 4 2 0 2 4 6 4 2 0 2 4 6 4 2 0 2 4 − − − − − − − − − η η η PRC83(2011)024913 d N ch Slide 4/30 — C.H.Christensen — — COST’19 — 2019/02/27 d η
U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E Wealth of measurements AA at LHC energies √ s NN = 2.76 TeV PLB754(2016)373-385 • Xe–Xe & Pb–Pb Pb–Pb, • From √ s NN = 2.76 TeV to 5.44 TeV √ s NN = 5.02 TeV PLB772(2017)567-577 • Here ALICE Pb–Pb, − 3.5 < η < 5 • Also ATLAS, CMS √ s NN = 5.44 TeV PLB790(2019)35 Xe–Xe, d N ch Slide 5/30 — C.H.Christensen — — COST’19 — 2019/02/27 d η
U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E Wealth of measurements d–Au & p–Pb results • From √ s NN = 200 GeV √ s NN = 200 GeV PRC83(2011)024913 d–Au, to 5.02 TeV • Here, PHOBOS & ALICE | η | < 5.3 − 5 < η < 3.5 , resp. • Also BRAHMS, ALTAS, CMS √ s NN = 5.02 TeV p-Pb √ s NN = 5 . 02TeV ( ZNA ) d N ch / d η ALICE 40 Preliminary 0- 5% 35 p–Pb, 5-10% 30 10-20% 25 20-40% 40-60% 20 60-80% 15 80-100% 10 Comb. 5 Uncorr.syst.unc. 0 Corr.syst.unc. -5 -4 -3 -2 -1 0 1 2 3 4 5 η ALI-PREL-99869 ALI-PREL-99869 ALI-PREL-99869 ALI-PREL-99869 d N ch Slide 6/30 — C.H.Christensen — — COST’19 — 2019/02/27 d η
U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E Models have room for improvement PLB754(2016)373-385 JHEP10(2018)134 • Generally OK near η = 0 • Most deviate for | η | > 0 EPJC76(2016)502 PLB790(2019)35 d N ch Slide 7/30 — C.H.Christensen — — COST’19 — 2019/02/27 d η
U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E Models have room for improvement PLB754(2016)373-385 JHEP10(2018)134 • Generally OK near η = 0 • Most deviate for | η | > 0 • Good news for EPJC76(2016)502 Lund: Pythia/Angantyr PLB790(2019)35 not the worst d N ch Slide 7/30 — C.H.Christensen — — COST’19 — 2019/02/27 d η
U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E The (not-so) transparent glass d N ch /d( y , η ) Pb-Pb √ s NN = 5.02 Te V 0 − 5% P hys.Lett. B523 (2001)79 -87 Pb -Pb √ s NN = 2.76 Te 3000 3000 V 0 − 5% CGC exp. CGC d N ch /d η fit 0.95 C.L. Au -Au √ s NN = 200 GeV 0 − 6% • Fit CGC λ 0.95 C.L. Au -Au √ s NN = 130 GeV 0 − 6% expression 2000 2000 PLB523(2001)79-87 • Good fit of d N ch 1000 1000 d η • λ parameter off 0 0 6 4 2 0 2 4 6 0.25 0.3 0.35 − − − y , η λ However . . . d N ch Slide 8/30 — C.H.Christensen — — COST’19 — 2019/02/27 d η
U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E The (not-so) transparent glass d N ch /d( y , η ) Pb-Pb √ s NN = 5.02 Te V 0 − 5% P hys.Lett. B523 (2001)79 -87 Pb -Pb √ s NN = 2.76 Te 3000 3000 V 0 − 5% CGC exp. CGC d N ch /d η fit 0.95 C.L. Au -Au √ s NN = 200 GeV 0 − 6% • Fit CGC λ 0.95 C.L. CGC d N ch /d y from d N ch /d η Au -Au √ s NN = 130 GeV 0 − 6% expression 2000 2000 PLB523(2001)79-87 • Good fit of d N ch 1000 1000 d η • λ parameter off 0 0 6 4 2 0 2 4 6 0.25 0.3 0.35 − − − y , η λ However . . . • Sharp peak in d N ch at y = 0 d y Caveat: older paper, but mechanism the same AFAIK d N ch Slide 8/30 — C.H.Christensen — — COST’19 — 2019/02/27 d η
U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E Normality and transparency BRAHMS Results: (a) 300 + π d N π , K • ∼ N [ 0, σ ] - π √ s NN = 200 GeV d y Au–Au, 0 − 10% + K - ( 4) PRL94(2005)032301 × K ( 4) dN/dy × 200 similar for p • Small decrease in � p T � 100 y beam over y > [GeV/c] (b) similar for p,p 0.8 0.6 T 0.4 <p 0 1 2 3 4 5 y d N ch Slide 9/30 — C.H.Christensen — — COST’19 — 2019/02/27 d η
U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E Normality and transparency BRAHMS Results: (a) 300 + π d N π , K • ∼ N [ 0, σ ] - π √ s NN = 200 GeV d y Au–Au, 0 − 10% + K - ( 4) PRL94(2005)032301 × K ( 4) dN/dy × 200 similar for p • Small decrease in � p T � 100 y beam over y > [GeV/c] (b) similar for p,p 0.8 0.6 • Small rapidity loss � δ y � T 0.4 <p over SPS energies 0 1 2 3 4 5 y Increased transparency for 3.5 60 √ s NN � 17 GeV 50 Au–Au,Pb–Pb, central 40 3 y> 30 20 PLB677(2009)267-271 10 net-baryons 62.4 GeV δ 2.5 0 Rapidity loss < 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 2 1.5 E917 1 E802/E866 NA49 (PbPb) 0.5 BRAHMS 62.4 GeV BRAHMS 200 GeV 0 0 1 2 3 4 5 6 7 8 9 10 y p d N ch Slide 9/30 — C.H.Christensen — — COST’19 — 2019/02/27 d η
U N I V E R S I T Y O F C O P E N H A G E N N I E L S B O H R I N S T I T U T E Normality and transparency BRAHMS Results: (a) 300 + π d N π , K • ∼ N [ 0, σ ] - π √ s NN = 200 GeV d y Au–Au, 0 − 10% + K - ( 4) PRL94(2005)032301 × K ( 4) dN/dy × 200 similar for p • Small decrease in � p T � 100 y beam over y > [GeV/c] (b) similar for p,p 0.8 0.6 • Small rapidity loss � δ y � T 0.4 <p over SPS energies 0 1 2 3 4 5 y Increased transparency for 3.5 60 √ s NN � 17 GeV 50 Au–Au,Pb–Pb, central 40 3 y> 30 20 PLB677(2009)267-271 10 net-baryons 62.4 GeV δ 0.6 2.5 (GeV/c) 0 Rapidity loss < 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 ISR INEL UA1 NSD | η | < 2.5 〉 CMS NSD | η | < 2.4 T p 2 0.55 CDF | η | < 1.0 • Slow � p T � 〈 E735 NSD | η | < 3.25 ALICE INEL | η | < 0.8 ALICE NSD | η | < 0.8 1.5 0.5 increase with E917 √ s 1 E802/E866 0.45 NA49 (PbPb) 0.5 BRAHMS 62.4 GeV 0.4 BRAHMS 200 GeV 0 PLB693(2010)53-68 0 1 2 3 4 5 6 7 8 9 10 0.35 10 2 10 3 y s (GeV) p d N ch Slide 9/30 — C.H.Christensen — — COST’19 — 2019/02/27 d η
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