А.Б.Курепин, И.А.Пшеничнов ИЯИ РАН, Москва

Physics at NICA, the view fromthe Institute for Nuclear Research,

Moscow

NICA – round table6 ноября 2008 г.

ОИЯИ, Дубна

Outline

IntroductionIntroduction

Problem of anomalous charmonium Problem of anomalous charmonium

suppressionsuppression

Event-by-Event fluctuations Event-by-Event fluctuations

Ultraperipheral interactionsUltraperipheral interactions

ConclusionsConclusions

Charmonium● 33 years ago: discovery of J/ψ, 21 years ago: Matsui & Satz

- colour screening in deconfined matter → J/ψ suppression

- → possible signature of QGP formation● Experimental and theoretical progress since then

→ situation is much more complicated– cold nuclear matter / initial state effects

● “normal” absorption in cold matter● (anti)shadowing● saturation, color glass condensate

– suppression via comovers – feed down from c, ’– sequential screening (first: c, ’, J/ only well above Tc)– regeneration via statistical hadronization or charm coalescence

● important for “large” charm yield, i.e. RHIC and LHC

J/ψ suppression from p-A to Pb-Pb collisions

Projectile

Target

J/

J/ψ production has been extensively studied in p-A, S-U and Pb-Pb collisions by the NA38 and NA50 experiments at the CERN SPS

J/ normal nuclear

absorption curve

• Light systems and peripheral Pb-Pb collisions: J/ψ is absorpted by nuclear matter . The scaling variable - L (length of nuclear matter crossed by the J/ψ) (J/ψ) ~ exp( -abs L)

• Central Pb-Pb collisions: the L scaling is broken - anomalous suppression

4.18 0.35mbJabs

NA60 : is anomalous suppression present also in lighter In-In nuclear systems ? Scaling variable- L, Npart, ε ?

The normal absorption curve is based on NA50 results. Its uncertainty (~ 8%) at 158 GeV is dominated by the (model dependent) extrapolation from the 400 and 450 GeV p-A data. need p-A measurements at 158 GeV

Comparison of NA50 and NA60 results

An “anomalous suppression” is presented already in In-In

Suppression by produced hadrons (“comovers”)

In-In 158 GeV

The model takes into account nuclear absorption and comovers interaction

with σco = 0.65 mb (Capella-Ferreiro) EPJ C42(2005) 419

J/

NC

oll

nuclear absorption

comover + nuclear absorption

Pb-Pb 158 GeV

(E. Ferreiro, private communication)

NA60 In-In 158 GeV

QGP + hadrons + regeneration + in-medium effects

Pb-Pb 158 GeV

B

J/

/D

Y

Nuclear Absorption

Regeneration

QGP+hadronic suppression

Suppression + Regeneration

In-In 158 GeV

Number of participants

fixed thermalization timecentrality dependent thermalization time

The model simultaneously takes into account dissociation and regeneration processes in

both QGP and hadron gas (Grandchamp, Rapp, Brown EPJ C43 (2005) 91)

centrality dependent thermalization time

fixed thermalization time

NA60 In-In 158 GeV

The dashed line includes the smearing due to the resolution

Suppression due to a percolation phase transition

Prediction: sharp onset (due to the disappearance of the c meson) at Npart ~ 125 for Pb-Pb and

~ 140 for In-In

Model based on percolation (Digal-Fortunato-Satz)

Eur.Phys.J.C32 (2004) 547.

Pb-Pb 158 GeV

NA60 In-In 158 GeV

J/ψ suppression (SPS and RHIC)

J/ψ yield vs Npart, normalized on Ncoll.

Unexpected good scaling. Coherent interpretation-problem for theory.

Work start - : Karsch, Kharzeev and Satz., PRL637(2006)75

Invariant mass spectra (Au+Au @ 35 AGeV)

ππ0 0 γγee++ee--

ππ00ee++ee--

ηη γγee++ee--

Identified e+e- After all cuts applied

All eAll e++ee--

Combinatorial bgCombinatorial bg

ρρ ee++ee--

ee++ee--

φφ ee++ee--

Central Au+Au@35AGeV

Simulated statistics: 65k events

Invariant mass spectra Invariant mass spectra J/ψ + J/ψ + ' + ' + combinatorial background combinatorial background superevent 4x10superevent 4x1010 10

central Au+Au@25AGeV UrQMD eventscentral Au+Au@25AGeV UrQMD events with target with target 25mkm25mkm

J/J/ψψ

Ψ’Ψ’

Invariant mass spectra of tracks identified as Invariant mass spectra of tracks identified as

electrons by RICH&TRD with reconstructed electrons by RICH&TRD with reconstructed

Pt>1.2GeV/cPt>1.2GeV/c

Dielectron J/Dielectron J/ΨΨ simulation simulation

27 MeV27 MeV

27 MeV27 MeV

26 MeV26 MeV

mass mass resolutioresolutio

nn

5.95x105.95x10-5-5

1.92x101.92x10-5-5

2.24x102.24x10-6-6

multmult

79790.130.13 121225 AGeV25 AGeV

8383 0.10.1121235 AGeV35 AGeV

1717 0.120.12 7715 AGeV15 AGeV

J/J/ψψ eff effS/BS/Bbeambeam

Table corresponds to 4x10Table corresponds to 4x101010 central collisions central collisions : ~ 55 hours of beam time of full CBM : ~ 55 hours of beam time of full CBM interaction range [1 MHz interation rate, 20% interaction range [1 MHz interation rate, 20% centrality] centrality]

Au beam 10Au beam 10 9 9 1/sec, target 25 1/sec, target 25 μμ

BS

S

35 AGeV

CBM L=1029 640 1/hour

√ s = 8AGeV

MPD L=1027 30 1/hour

Counting rate of J/ψ production

Segmented targetSegmented target

Target 25 mkm Target 25 mkm

++for J/for J/ΨΨ S/B ~12 S/B ~12

visible visible ΨΨ ''

--more time to yield more time to yield

statisticstatistic

Target 250 mkm Target 250 mkm

for J/for J/ΨΨ S/B ~1 S/B ~1

ΨΨ' are not visible' are not visible

beam

2.5°

-7 -3.5 0 3.5 7 cm-7 -3.5 0 3.5 7 cm300μm

Invariant mass distribution of Invariant mass distribution of background electrons with Pt>1GeV background electrons with Pt>1GeV

originated in targetoriginated in target

Target 250mkmTarget 250mkm

Target 1x50mkmTarget 1x50mkm

Target 5x50mkmTarget 5x50mkm

2. Event-by-event fluctuations

Total multiplicity : Ns- number of sources,

mi- multiplicity from a single source.

i

Ns

i

mN

1

s

NmN

Nm

mNs

222

mNN sGeometry of

collision

Second component is not interesting and must

be removed

physics! QGP?

Number of interacting nucleons must be known

ZDC geometry.

Beam hole

X

Z

Transverse sizes ~1x1 m2;

Distance from target - 15 m;

Number of modules – 107;

Module dimensions – 10x10x1600 cm2

Design and readout

ConceptionLight readout with WLS-fibers for reliable and uniform light collection.

Signal readout with Micropixel APD (MAPD) to avoid nuclear counter

effect, detection of a few photons signal, compactness, low cost. Longitudinal segmentation – for permanent calibration of scintillators in radiation hard conditions, rejection of secondary particles. Modular design – transverse uniformity of resolution, good reconstruction of reaction plane, flexible geometry, simplicity.

Modular Lead/Scintillator sandwich compensating calorimeter. Sampling ratio Pb:Scint=4:1.

Expectation: For thickness δPb=16 mm and δScint=4 mm σE/E ~ 50%/√E .

Measurement of centrality Impact parameter: b~Np ,

Np is number of interacting (participant) nucleons.

Np=A - Nspect=A - Es/EA ,

Es is sum of spectator energies, measured by Zero

Degree Calorimeter (ZDC) ;

EA is beam energy.

This technique is used in most heavy ion experiments at CERN (WA80, NA49, NA50, ALICE…) and RHIC.

Reconstruction of Reaction Plane

Input UrQMD: reaction plane at 00

MC simulation

Reconstruction from centers of modules

Reconstructed angle of reaction plane, deg.

Good accuracy is due to fine transverse ZDC granulation. To be improved by taking deposited energy weights.

→ → M rk rk – position vector

Q = ∑ ----- , of the particle k k=1 → in perpendicular │rk│ to the beam axis

plane M – particles in the event used for reconstruction

Электромагнитные взаимодействия в столкновениях релятивистских ядер

● Ультрапериферические взаимодействия: нет перекрытия ядерных плотностей

● Воздействие Лорентц-сжатых кулоновских полей может быть представлено как поглощение эквивалентных фотонов (Weizacker-Williams method)

● Фотоядерные реакции: электромагнитная диссоциация и рождение адронов

● Реакции фотон-фотон: рождение экзотических частиц

Z

Дальнодействующиеэлектромагнитные силы

Спектр эквивалентных фотонов и сечение фотопоглощения: проинтегрировано по b

Модель RELDIS: Relativistic ELectromagnetic DISsociation

(ИЯИ,1995-2008,А.Ильинов,И.Пшеничнов ) ● Поглощение фотонов ядрами – многостадийный

процесс: – поглощение фотона на внутриядерном нуклоне или

на квазидейтонной паре (учитывается свыше 100 каналов при энергиях фотонов несколько ГэВ)

– внутриядерный каскад образовавшихся адронов – статистический распад возбужденного остаточного

ядра – модель SMM: конкуренция испарения нуклонов и кластеров - деление - мультифрагментация

Поглощение одного или двух фотонов приводящее к одиночной диссоциации

Следующий к лидирующему 1-2%Лидирующий порядок 98-99%

упругий процесс

неупругий процесс

Разрушается одно из ядер!

Эмиссия нейтронов в электромагнитной диссоциации ядер свинца и золота

Фиксированные мишени ~10-30 b

Пучки ионов: RHIC& LHC ~100-200 b

Для коллайдеров:eff

= 22beam

-1, для LHC – 1.7*107

Schematic view of experimental setup for forward neutron emission measurements for

30 A GeV Pb ions @ CERN SPS

S0, S1, SS – plastic scintillator detectors.

MBPL and MBPL - Magnets

Energy spectra of the neutron calorimeter in proton and Pb runs

ADC spectrum for 30 GeV protons

1n

2n

3n

New data:forward neutron emission measurements for

30 A GeV Pb ions @ CERN SPS

pure EM part ~ Z2target

/Z2target

~ const

Phys.Rev.C71(2005)024905

Latest data:forward neutron emission measurements for

158 A GeV In ions @ CERN SPS

1n

2n

3n 4n

Conclusions

1. Measurement of charmonium production

at MPD NICA is possible

2. For event-by-event physics the development of

ZDC is indispensable

3. Electromagnetic interactions at NICA energies

will provide new insight to nuclear structure