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

2

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

3

A bit of history1998 -- YuV is chairing a ceremony at the SPbSU

of Doctor Honoris Causa for Luciano Maiani

4

Yu.V. Novozhilov, L.Maiani and L.A.Verbitskaya

5

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.

….

6

A bit of history: SPbSU in ALICE at the LHC -- since August 1992

7

Surprise No.1 – HIGGS!

ЦЕРН, 4 июля 2012 !

8

Standard Model Higgs boson decay branching ratios

https://twiki.cern.ch/twiki/bin/view/LHCPhysics/CrossSections#Higgs_cross_sections_and_decay_b

9

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

10

What about other things@LHC?

11

Основные эксперименты на Большом адронном коллайдере

12

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

13

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.

14

CMC: “Unexplained long-range correlations

observed in pPb collisions”

http://cms.web.cern.ch/news/unexplained-long-range-correlations-observed-ppb-collisions

15

Ridge phenomenon in pp and pPb collisions is still unexplained…

16

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)

18

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

19

Pb-Pb collisions at the LHC

20

Charged particle pseudo-rapidity density per participant pair for central nucleus-nucleus and non-single diffractive pp (pp) collisions , as a function of √sNN

20

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!

21

Charged-particle multiplicity density at mid-rapidity

in central Pb-Pb collisions at √sNN = 2.76 TeV

21

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:

22

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

]

23

Centrality dependence of the charged-particle multiplicity densityat mid-rapidity in Pb–Pb collisions at √sNN =2.76 TeV

23

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 …

24

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:

25

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)…”

26

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

27

Surprise: Higher harmonic anisotropic flow measurements

27

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

28

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}

29

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

30

Suppression of charged particle production at large pTin central Pb-Pb collisions at √sNN =2.76 TeV: RAA vs. Pt

30

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

31

Suppression of charged particle production at large pTin central Pb-Pb collisions at √sNN =2.76 TeV:

31

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)

32

Suppression of charged particle production at large pt

in central Pb-Pb collisions at √sNN =2.76 TeV:

32

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

33

Two-pion Bose--Einstein correlations in central Pb-Pb collisions at √sNN =2.76 TeV:

33

Homogeneity-region volume 2 x RHIC (~ dNch/d)

arXiv:1012.4035v2 [nucl-ex]; Phys. Lett. B 696 ( 2011) 328-337

34

Two-pion Bose--Einstein correlationsin central Pb-Pb collisions at √sNN =2.76 TeV:

34

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

35

Ongoing analyses : J/psi supression (?)in Pb-Pb collisions at √sNN =2.76 TeV (preliminary)

35

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)

37

Summary and outlook

37

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!

38

BACK-UP slides:

38

39

“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

40

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

41

Отбор центральных событий

42

Нуклоны-участники, нуклоны-спектаторы

Nspect- число нуклонов-спектаторов

Npart – число нуклонов-участников

43

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

44

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)

45

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

47

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)

50

Кроме того...

51

Состав частиц (относительные выходы)

52

Ongoing analyses : strange and heavy-flavour particle production

52

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,

53

Ongoing analyses : Prompt D meson Raa

53

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

54

Подавление J/psi (SPS)

J/Ψ – связанное состояния очарованных кварка и анти кварка

Color Screening

cc

55

RHIC AuAu 0.2 nb-1

Lower EnergyCERN-SPS

Подавление J/psi (RHIC)

56

Ongoing analyses : J/psi supression (?)in Pb-Pb collisions at √sNN =2.76 TeV (preliminary)

56

J/psi production is suppressed (factor ~2) independently on centrality

J/psi behavior is still a puzzle …!?

57