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Physics at NICA, the view from the Institute for Nuclear Research, Moscow. А.Б.Курепин , И.А.Пшеничнов ИЯИ РАН, Москва. NICA – round table 6 ноября 2008 г. ОИЯИ, Дубна. Outline. Introduction Problem of anomalous charmonium suppression Event-by-Event fluctuations

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Physics at NICA, the view from

the Institute for Nuclear Research, Moscow

А.Б.Курепин, И.А.Пшеничнов

ИЯИ РАН, Москва

NICA – round table

6 ноября 2008 г.

ОИЯИ, Дубна


Outline
Outline

Introduction

Problem of anomalous charmonium

suppression

Event-by-Event fluctuations

Ultraperipheral interactions

Conclusions


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 cc, y’

    • sequential screening (first: cc, y’, J/y only well above Tc)

    • regeneration via statistical hadronization or charm coalescence

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


  • 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

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

J/ψ production has been extensively studied inp-A, S-UandPb-Pbcollisions by the NA38 and NA50 experiments at the CERN SPS

Projectile

J/y

Target

J/y normal nuclear absorption curve

NA60 : is anomalous suppression present also in lighter In-In

nuclear systems ?Scaling variable- L, Npart, ε ?


Comparison of NA50 and NA60results

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

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


Suppression by produced hadrons (“comovers”)

The model takes into account nuclear absorption and comovers interaction with σco = 0.65 mb (Capella-Ferreiro) EPJ C42(2005) 419

In-In 158 GeV

J/y / NColl

nuclear absorption

comover + nuclear absorption

(E. Ferreiro, private communication)

Pb-Pb 158 GeV

NA60 In-In 158 GeV


QGP + hadrons + regeneration + in-medium effects

The model simultaneously takes into account dissociation and regeneration processes in both QGP and hadron gas (Grandchamp, Rapp, Brown EPJ C43 (2005) 91)

In-In 158 GeV

fixed thermalization time

centrality dependent thermalization time

BmmsJ/y/sDY

Nuclear Absorption

Suppression + Regeneration

QGP+hadronic suppression

Regeneration

Number of participants

Pb-Pb 158 GeV

centrality dependent thermalization time

fixed thermalization time

NA60 In-In 158 GeV


Suppression due to a percolation phase transition

Model based on percolation (Digal-Fortunato-Satz)

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

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

~ 140 for In-In

Pb-Pb 158 GeV

NA60 In-In 158 GeV

The dashed line includes the smearing due to the resolution


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
Invariant mass spectra (Au+Au @ 35 AGeV)

Identified e+e-

After all cuts applied

All e+e-

Combinatorial bg

ρe+e-  e+e-φe+e-

π0 γe+e-  π0e+e-ηγe+e-

Central [email protected]

Simulated statistics: 65k events


Invariant mass spectra J/ψ + ' + combinatorial background superevent 4x1010 central [email protected] UrQMD eventswith target 25mkm

J/ψ

Ψ’

Invariant mass spectra of tracks identified as electrons by RICH&TRD with reconstructed Pt>1.2GeV/c


Dielectron j simulation

beam

mult

S/B

J/ψ eff

mass resolution

15 AGeV

2.24x10-6

7

0.12

26 MeV

17

25 AGeV

1.92x10-5

12

0.13

27 MeV

79

35 AGeV

5.95x10-5

12

0.1

27 MeV

83

Dielectron J/Ψ simulation

Table corresponds to 4x1010 central collisions : ~ 55 hours of beam time of full CBM interaction range [1 MHz interation rate, 20% centrality]

Au beam 10 9 1/sec, target 25 μ


Counting rate of j production
Counting rate ofJ/ψ production


Segmented target
Segmented target

Target 250 mkm

for J/ΨS/B ~1

Ψ' are not visible

Target 25 mkm

+

for J/Ψ S/B ~12

visible Ψ'

-

more time to yield

statistic

Segmented target 5 x 50mkm

-7 -3.5 0 3.5 7 cm

300μm

beam

2.5°


Invariant mass distribution of background electrons with pt 1gev originated in target
Invariant mass distribution of background electrons with Pt>1GeV originated in target

Target 250mkm

Target 5x50mkm

Target 1x50mkm


2 event by event fluctuations
2. Event-by-event fluctuations Pt>1GeV originated in target

Total multiplicity :Ns- number of sources,

mi- multiplicity from a single source.

Geometry of collision

physics! QGP?

Second component is not interesting and must be removed

Number of interacting nucleons must be known


Beam hole Pt>1GeV originated in target

X

ZDC geometry.

Z

Transverse sizes ~1x1 m2;

Distance from target - 15 m;

Number of modules – 107;

Module dimensions – 10x10x1600 cm2


Design and readout
Design and readout Pt>1GeV originated in target

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 .

Conception

Light readout withWLS-fibersfor 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.


Measurement of centrality
Measurement of centrality Pt>1GeV originated in target

Impact parameter: b~Np,

Npis number of interacting (participant) nucleons.

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

Esis sum of spectator energies, measured by Zero

Degree Calorimeter (ZDC) ;

EAis beam energy.

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


Reconstruction of reaction plane

Reconstruction from centers of modules Pt>1GeV originated in target

MC simulation

Reconstructed angle of reaction plane, deg.

Reconstruction of Reaction Plane

→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

Input UrQMD:reaction plane at 00

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


Z Pt>1GeV originated in target

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

Дальнодействующие

электромагнитные

силы


Спектр эквивалентных фотонов и сечение фотопоглощения: проинтегрировано по b


Reldis relativistic electromagnetic dissociation
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

Разрушается одно из ядер!

Следующий к лидирующему 1-2%

Лидирующий порядок 98-99%

упругий процесс

неупругий процесс


Эмиссия нейтронов в электромагнитной диссоциации ядер свинца и золота

Фиксированные мишени

~10-30 b

Пучки ионов: RHIC& LHC ~100-200 b

Для коллайдеров: geff= 2g2beam-1, для LHC – 1.7*107


Schematic view of experimental setup for электромагнитной диссоциации ядер свинцаforward 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

1n

ADC spectrum for 30 GeV protons

2n

3n


New data forward neutron emission measurements for 30 a gev pb ions @ cern sps

pure EM part ~ Z runs2target

s/Z2target~ const

Phys.Rev.

C71(2005)024905

New data:forward neutron emission measurements for 30 A GeV Pb ions @ CERN SPS


Latest data: runsforward neutron emission measurements for 158 A GeV In ions @ CERN SPS

1n

2n

3n

4n


Conclusions
Conclusions runs

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


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