Some surprises in pp, pA and AA high energy collisions
Grigory Feofilov St.- Petersburg State University, Faculty of Physics,
V.Fock Institute for Physics, Laboratory of Ultra-High Energy Physics
“In Search of Fundamental Symmetries”, International Conference dedicated to the Novozhilov's 90-th anniversary. Saint-Petersburg, December 2-5, 2014
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CONTENT
1. A bit of history
2. Surprises or…what?
-- new phenomena in pp collisions at the LHC
-- some studies of Pb-Pb collisions with ALICE
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A bit of history1998 -- YuV is chairing a ceremony at the SPbSU
of Doctor Honoris Causa for Luciano Maiani
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Yu.V. Novozhilov, L.Maiani and L.A.Verbitskaya
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A bit of history:SPbSU in AMPIR collaboration at Moscow
Meson Factory – 1987-19921) A.A.Andrianov, A.A.Bolokhov, G.A.Feofilov, V.V.Vereschagin, M.V.loffe,
S.N.Manida, M.V.Polyakov, S.G.Sherman, Perspectives of Inelastic Pion - Nucleon Scattering Studies at the Detector AMPIR , INES-89, The Proceedings of Internationa1 Seminar оп Intermediate Energy Physics (USSR, Moscow, 1989, Nov.27-30), vо1.1, рр. 231-236, Moscow, 1990.
2) AMPIR collaboration (INR RAS, Kurchatov, SРЬ University), Rare Pion-Nucleon, Pion-Nucleus and {Photonuclear Reaction: Program of Physical Studies at the AMPIR Spectrometer (препринт) Preprint Institut fur Theoretiche Physik Freie Universitat Berlin, FUB-HEP/921, 1990, 21 pages.
3) The Program of investigations of Rare pion-Nucleon reactions and status of AMPIR spectrometer, The Proceedings от Internationa1 Workshop оп Pions in Nuc1ei, Spain, 3-8 June 1991, Singapour, 1992, рр.98-103.
….
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A bit of history: SPbSU in ALICE at the LHC -- since August 1992
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Surprise No.1 – HIGGS!
ЦЕРН, 4 июля 2012 !
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Standard Model Higgs boson decay branching ratios
https://twiki.cern.ch/twiki/bin/view/LHCPhysics/CrossSections#Higgs_cross_sections_and_decay_b
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Signal strengths in the main Higgs analysis channels (see review of data in [1])
[1] http://pdg.lbl.gov/2013/reviews/rpp2013-rev-higgs-boson.pdf
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What about other things@LHC?
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Основные эксперименты на Большом адронном коллайдере
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Surprise No.2: “Ridge” in pp collisions@LHC
Two-particle correlation function:
CERN-PH-EP/2010-031 2010/09/21
Signal:
Background:
Here <N> - number of tracks per event averaged over the multiplicty bin
Δ
Trigger
Associated
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CMS: Observation of Long-Range, Near-Side Angular Correlations in
Proton-Proton Collisions at the LHC
Figure 7: 2-D two-particle correlation functions for 7 TeV pp (a) minimum bias events with pT > 0.1 GeV/c, (b) minimum bias events with 1 < pT < 3 GeV/c, (c) high multiplicity (Noffline trk 110) events with pT > 0.1 GeV/c and (d) high multiplicity (Noffline trk 110) events with 1 < pT < 3 GeV/c. The sharp near-side peak from jet correlations is cut off in order to better illustrate the structure outside that region.
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CMC: “Unexplained long-range correlations
observed in pPb collisions”
http://cms.web.cern.ch/news/unexplained-long-range-correlations-observed-ppb-collisions
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Ridge phenomenon in pp and pPb collisions is still unexplained…
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16K. Aamodt et al. (ALICE), JINST, 3 , S08002 (2008)
1721.04.23 17
Photo: © ALICE: the Inner Tracking System (ITS) - the Heart of installation (January 2007)
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23 ноября 2009: первое событие в ALICE на LHC!The very 1st LHC physics paper:
“First proton–proton collisions at the LHC as observed with the ALICE detector:measurement of the charged-particle pseudorapidity density at √s = 900 GeV“
Eur. Phys. J. C (2010) 65: 111–125
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Pb-Pb collisions at the LHC
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Charged particle pseudo-rapidity density per participant pair for central nucleus-nucleus and non-single diffractive pp (pp) collisions , as a function of √sNN
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an increase of about a factor 1.9 relative to pp collisions at similar collision energies, an increase of about a factor 2.2 to central Au-Au collisions at √sNN = 0. 2 TeV !
arXiv:1011.3916 [nucl-ex]. Phys. Rev. Lett. 105 (2010) 252301
Faster growth with √sNN in AA than in pp! Logarythmic extrapolation is rulled out Important constraint for the models!
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Charged-particle multiplicity density at mid-rapidity
in central Pb-Pb collisions at √sNN = 2.76 TeV
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is essential to estimate the initial energy density and it is the 1st important constraint for the models!
arXiv:1011.3916 [nucl-ex]. Phys. Rev. Lett. 105 (2010) 252301
Comparison of ALICE measurement with model predictions.
Bjorken energy density: 2.8 x RHIC for 5% of most central collisions
tmdy
dN
AV
E
0
1)(
Multiplicity:
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Charged-particle multiplicity density at mid-rapidity
in central Pb-Pb collisions at √sNN = 2.76 TeV: :
22arXiv:1011.3916 [nucl-ex]. Phys. Rev. Lett. 105 (2010) 252301
ALICE measurement and model predictions
Empirical extrapolation
pQCD-inspired MC
Initial-state gluon density saturation models
Some other approaches
]
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Centrality dependence of the charged-particle multiplicity densityat mid-rapidity in Pb–Pb collisions at √sNN =2.76 TeV
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arXiv:1012.1657 [nucl-ex], 4 Feb 2011; Phys.Rev.Lett. 106 (2011) 032301
Important constraint for the models!
Strong competition between the models!Saturation models {Kharzeev et al.} are looking better …
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Эллиптический поток в Pb-Pb столкновениях при энергии √sNN =2.76 TeV:
24arXiv:1011.3914v1 [nucl-ex] 17 Nov 2010; Phys. Rev. Lett. 105 (2010) 252302
Tannebaum’ 06
2- and 4-particle cumulant methods: v 2{2} and v 2{4}
Excentricity:
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Surprise: Elliptic flow of charged particles in Pb-Pb collisions at √sNN =2.76 TeV:
25arXiv:1011.3914v1 [nucl-ex] 17 Nov 2010; Phys. Rev. Lett. 105 (2010) 252302
the value ofv2(pt) does not change within uncertainties from RHIC to LHC
Qualitatively similarfor all 3 centrality classes.
Integrated elliptic flow vs. centrality
Differential elliptic flow vs. pt
CERN Press release, November 26, 2010:“…confirms that the much hotter plasma produced at the LHC behaves as a very low viscosity liquid (a perfect fluid)…”
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Elliptic flow of charged particles in Pb-Pb collisions at √sNN =2.76 TeV:
26arXiv:1011.3914v1 [nucl-ex] 17 Nov 2010; Phys. Rev. Lett. 105 (2010) 252302
There is a continuous increase in the magnitude of integrated elliptic flow measured in the 20-30% centrality class from RHIC to LHC energies.
This increase is higher than current predictions from ideal hydrodynamic models
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Surprise: Higher harmonic anisotropic flow measurements
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Initial geometry fluctuations, a mean-free-path (lmf p) and higher harmonics, see: P.Sorensen,”The rise and fall of the ridge”, Nuclear Physics A 855 (2011) 229–232
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Higher harmonic anisotropic flow measurements of charged particles in Pb-Pb collisions at √sNN = 2.76 TeV: Intergrated v2, v3 and v4 vs. centrality
28arXiv:1105.3865 ; CERN-PH-EP-2011-073. - 2011
behavior of higher harmonics is different from that of v2{2} !
{2}
{2}
{2}
{4}
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Higher harmonic anisotropic flow measurements of charged particles in Pb-Pb collisions at √sNN =2.76 TeV: ν2 ,ν3 , ν4 , ν5 vs. pt
29arXiv:1105.3865 ; CERN-PH-EP-2011-073. - 2011
behavior of ν3 changes dramatically
for very central collisionshydrodynamic prediction for v3(pt) with ƞ/s = 0.08better than ƞ/s = 0.0 no hydro calculation (yet) describing
simultaneously data on v2 and v3 …
…analysis of the viscosity effects is in progress…
30-40% centrality
0-5% centrality
ν3
ν3
ν2
ν2
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Suppression of charged particle production at large pTin central Pb-Pb collisions at √sNN =2.76 TeV: RAA vs. Pt
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arXiv:1012.1004v1 [nucl-ex], 5 Dec 2010; Phys. Lett. B 696 (2011) 30-39
Data driven interpolation900 GeV & 7 TeV
or from NLO7 TeV * NLO (2.76 TeV)/NLO(7 TeV)
Nuclear modification factor RAA:
RAA =1 if no nuclear effects
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Suppression of charged particle production at large pTin central Pb-Pb collisions at √sNN =2.76 TeV:
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arXiv:1012.1004v1 [nucl-ex], 5 Dec 2010; Phys. Lett. B 696 (2011) 30-39
Strong centrality dependence Small losses for peripheral collisions Minimum (~0.12) is reached at pT ≈ 6-7 GeV/c Strong rise above 6 GeV/c
0.9 TeV * NLO (2.76 TeV)/NLO(0.9 TeV)
from 0.9 TeV * NLO (2.76 TeV)/NLO(0.9 TeV)
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Suppression of charged particle production at large pt
in central Pb-Pb collisions at √sNN =2.76 TeV:
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arXiv:1012.1004v1 [nucl-ex], 5 Dec 2010; Phys. Lett. B 696 (2011) 30-39
results are qulitatively similar to the STAR and PHENIX datamore “dramatic” behaviour the medium formed in central Pb-Pb collisions is denser than at RHIC
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Two-pion Bose--Einstein correlations in central Pb-Pb collisions at √sNN =2.76 TeV:
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Homogeneity-region volume 2 x RHIC (~ dNch/d)
arXiv:1012.4035v2 [nucl-ex]; Phys. Lett. B 696 ( 2011) 328-337
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Two-pion Bose--Einstein correlationsin central Pb-Pb collisions at √sNN =2.76 TeV:
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arXiv:1012.4035v2 [nucl-ex]; Phys. Lett. B 696 ( 2011) 328-337
Decoupling time f (~ Rlong)1.4 x RHIC (~ (dNch/d)1/3)
f(central PbPb) ~ 10–11 fm/c
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Ongoing analyses : J/psi supression (?)in Pb-Pb collisions at √sNN =2.76 TeV (preliminary)
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J/psi production is suppressed (factor ~2) independently on centrality
J/psi behavior is still a puzzle …!?
3621.04.23 36
(c) Женевское озеро и Альпы, Фото: П.А.Науменко
Научная программа СПбГУ в эксперименте ALICE
• Слияние кварк-глонных струн и дальние корреляции [1,2]• Коллективные явления в АА, и pPb (?) и в рр(?) столкновениях• Барионный заряд, странность, Net chаrge и дальние корреляции• Флуктуации и модель Глаубера, • Партонно-струнная модель, • Мультипомеронный обмен и колективные эффекты
[1] reported by G.Feofilov et al. at the ISHEPP VII, , Dubna, 2002; P.A.Bolokhov, M.A.Braun, G.A.Feofilov, V.P.Kondratiev, V.V.Vechernin, Internal Note/PHY.ALICE-INT-2002-20(2002)16p;[2] ALICE collaboration “ALICE: Physics Performance Report, Volume II”, J. Phys. G: Nucl. Part. Phys. 32 (2006) 1295-2040 (Section: 6.5.15 - Long-range correlations, p.1749)
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Summary and outlook
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The medium produced in Pb-Pb collisions at √sNN =2.76 TeV at the LHC has in comparison to 200 GeV data at RHIC:~ 3 times larger energy density~ 2 times larger volume of homogenity region~ Larger lifetime ≈ +20% (≈ 10 fm/c)It shows the properties of almost ideal liquid (like at RHIC) It appears to be denser than at RHIC (suppression of high- pt particles is stronger) J/psi production is suppressed (factor ~2) - still a puzzle…?“Ridge” structures in long-range azimuthal 2-particle correlations - another puzzle…?
We are entering a new and unexplored territory!
...все самое интересное только начинается!
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BACK-UP slides:
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“Charged-particle multiplicity measurement in proton–protoncollisions at √s = 7 TeV with ALICE at LHC”
Fig. 2 Charged-particle pseudorapidity density in the central pseudorapidity region |η| < 0.5 for inelastic and non-single-diffractive collisions [4, 16–25], and in |η| < 1 for inelastic collisions with at least one charged particle in that region (INEL > 0|η|<1), as a function of the centre-of-mass energy. The lines indicate the fit using a power-la dependence on energy. Note that data points at the same energy have been slightly shifted horizontally for visibility
Eur. Phys. J. C (2010) 68: 345–354
Fig. 1 Relative increase of the charged-particle pseudorapidity density,for inelastic collisions having at least one charged particle in |η| < 1, between √s = 0.9 TeV and 2.36 TeV (open squares) and between √s = 0.9 TeV and 7 TeV (full squares), for various models. Corresponding ALICE measurements are shown with vertical dashed and solid lines; the width of shaded bands correspond to the statistical and systematic uncertainties added in quadrature
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Ongoing analyses : The two-particle azimuthal correlations, higher harmonics and ridges in Pb-Pb at ALICE
40arXiv:1105.3865 ; CERN-PH-EP-2011-073. - 2011
.…the measured anisotropic flow Fourier coefficients give a natural description of these structures……See also numerous QM-2011 - QM-2014 discussions on higher harmonics …the origin of this effect is still a puzzle…
PbPbcentral
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Отбор центральных событий
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Нуклоны-участники, нуклоны-спектаторы
Nspect- число нуклонов-спектаторов
Npart – число нуклонов-участников
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Отбор центральных событий в эксперименте ALICE
43arXiv:1011.3916 [nucl-ex]. Phys. Rev. Lett. 105 (2010) 252301
K. Aamodt et al. (ALICE), JINST, 3 , S08002 (2008)
VZERO: Front view of V0A and V0C arrays
Front view of ZDC ZN and ZP calorimeters
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Centrality dependence of the charged-particle multiplicity densityat mid-rapidity in Pb–Pb collisions at √sNN =2.76 TeV
44arXiv:1012.1657 [nucl-ex], 4 Feb 2011; Phys.Rev.Lett. 106 (2011) 032301
very similar centrality dependence at LHC and RHIC !
(Note 2 scales: “left” (for 2.76 TeV and “right” - for 200 GeV data)
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Charged-particle multiplicity density at mid-rapidity
in central Pb-Pb collisions at √sNN = 2.76 TeV: :
45arXiv:1011.3916 [nucl-ex]. Phys. Rev. Lett. 105 (2010) 252301
ALICE measurement and model predictions
Empirical extrapolation
pQCD-inspired MC
Initial-state gluon density saturation models
Some other approaches
]
46
Multiplicity distributions in pp collisions
Fig. 3 Measured multiplicity distributions in |η| < 1 for the INEL >0|η|<1 event class. The error bars for data points represent statistical uncertainties, the shaded areas represent systematic uncertainties. Left: The data at the three energies are shown with the NBD fits (lines). Note that for the 2.36 and 7 TeV data the distributions have been scaled for clarity by the factors indicated. Right: The data at 7 TeV are compared to models: PHOJET (solid line), PYTHIA tunes D6T (dashed line), ATLAS-CSC (dotted line) and Perugia-0 (dash-dotted line). In the lower part, the ratios between the measured values and model calculations are shown with the same convention. The shaded area represents the combined statistical and systematic uncertainties
Eur. Phys. J. C (2010) 68: 345–354
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Feynman diagrams in the Standard Model for the Higgs decay to two photons in lowest order.
http://www.hep.lu.se/atlas/thesis/egede/thesis-node17.html
Two photon decay – one of the surprises
48CERN, 2 Dec 2010 J. Schukraft 48
Jet Quenching (?) seen via Multiparticle Correlations
• ‘Autocorrelation’: d2Nch/dd (signal)/d2Nch/dd (mixed events)
pp 7 TeV
PbPbperipheral
CMS pp 7 TeV‘near side ridge’
PbPbcentral
PbPbcentral
ppPb
‘near side ridge’:- striking effect, not really understood response of QGP to jet quenching ? initial state gluon radiation ? ???
d2Nch/dd (signal)/d2Nch/dd (mixed events)
49CERN, 2 Dec 2010 J. Schukraft 49
Surprise: High pT Particle Correlations
Δ
Trigger
AssociatedpTt
Trigger Particle
‘away’ side
‘near’ side
UE
Trigger Particle: highest pT particle in event (pTt)Associate Particle: all the others (pTa)
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Кроме того...
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Состав частиц (относительные выходы)
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Ongoing analyses : strange and heavy-flavour particle production
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arXiv:1106.1341v1 [nucl-ex];
Signal of decays selected using displaced decay vertices at central rapidity |y|<0/8 (left) and decays in the forward muon spectrometer 2.5 < y < 4, (right). Pb-Pb collisions,
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Ongoing analyses : Prompt D meson Raa
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RAA (0-20%) shows a suppression of about a factor of 4-5 for pt > 5 GeV/c
Prompt D meson and π+-
RAA are compatible.
Z. Conesa del Valle, report at PANIC, 24 - 29 July 2011, Cambridge, MA, USA
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Подавление J/psi (SPS)
J/Ψ – связанное состояния очарованных кварка и анти кварка
Color Screening
cc
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RHIC AuAu 0.2 nb-1
Lower EnergyCERN-SPS
Подавление J/psi (RHIC)
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Ongoing analyses : J/psi supression (?)in Pb-Pb collisions at √sNN =2.76 TeV (preliminary)
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J/psi production is suppressed (factor ~2) independently on centrality
J/psi behavior is still a puzzle …!?
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