А.Б.Курепин, И.А.Пшеничнов ИЯИ РАН, Москва Physics at NICA, the view from the Institute for Nuclear Research, Moscow NICA – round table 6 ноября 2008 г. ОИЯИ, Дубна

Outline Introduction Introduction Problem of anomalous charmonium Problem of anomalous charmonium suppression suppression Event-by-Event fluctuations Event-by-Event fluctuations Ultraperipheral interactions Ultraperipheral interactions Conclusions 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 c, – sequential screening (first: c,, J/ only well above T c ) – 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 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 σ co = 0.65 mb (Capella-Ferreiro) EPJ C42(2005) 419 J/ NColl 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/ / DY Nuclear Absorption Regeneration QGP+hadronic suppression Suppression + Regeneration In-In 158 GeV Number of participants fixed thermalization time centrality 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 N part ~ 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 N part, normalized on N coll. Unexpected good scaling. Coherent interpretation- problem for theory. Work start - : Karsch, Kharzeev and Satz., PRL637(2006)75

Invariant mass spectra 35 AGeV) π 0 γ e + e - π 0 e + e - η γ e + e - Identified e + e - After all cuts applied All e + e - Combinatorial bg ρ e + e - e + e - φ e + e - Central Simulated statistics: 65k events

Invariant mass spectra J/ψ + ' + combinatorial background superevent 4x10 10 central UrQMD eventswith target 25mkm Invariant mass spectra J/ψ + ' + combinatorial background superevent 4x10 10 central UrQMD events with target 25mkm J/ ψ Ψ Invariant mass spectra of tracks identified as electrons by RICH&TRD with reconstructed Pt>1.2GeV/c

Dielectron J/Ψ simulation 27 MeV 26 MeV mass resolution 5.95x x x10 -6 mult AGeV AGeV AGeV J/ψ eff S/Bbeam Table corresponds to 4x10 10 central collisions : ~ 55 hours of beam time of full CBM interaction range [1 MHz interation rate, 20% centrality] Au beam /sec, target 25 μ

35 AGeVCBML= /hour s = 8AGeV MPDL= /hour Counting rate of J/ψ production

Segmented target Target 25 mkm + for J/ Ψ S/B ~12 visible Ψ ' - more time to yield statistic Target 250 mkm for J/ Ψ S/B ~1 Ψ ' are not visible beam 2.5° cm 300μm

Invariant mass distribution of background electrons with Pt>1GeV originated in target Target 250mkm Target 1x50mkm Target 5x50mkm

2. Event-by-event fluctuations Total multiplicity : N s - number of sources, m i - multiplicity from a single source. Geometry 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 m 2 ; Distance from target - 15 m; Number of modules – 107; Module dimensions – 10x10x1600 cm 2

Design and readout Conception Light 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 δ Pb =16 mm and δ Scint =4 mm σ E /E ~ 50%/E.

Measurement of centrality Impact parameter: b~N p, N p is number of interacting (participant) nucleons. N p =A - N spect =A - E s /E A, E s is sum of spectator energies, measured by Zero Degree Calorimeter (ZDC) ; E A 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 0 0 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 r k r k – position vector Q = -----, of the particle k k=1 in perpendicular r k 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 Дальнодействующие электромагнитные силы

Спектр эквивалентных фотонов и сечение фотопоглощения: проинтегрировано по b

Модель RELDIS: Relativistic ELectromagnetic DISsociation (ИЯИ, ,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 ~ b Для коллайдеров: eff = 2 2 beam -1, для LHC – 1.7*10 7

Schematic view of experimental setup for forward neutron emission measurements for 30 A GeV Pb 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 1n1n 2n2n 3n3n

New data: forward neutron emission measurements for 30 A GeV Pb CERN SPS pure EM part ~ Z 2 target /Z 2 target ~ const Phys.Rev. C71(2005)024905

Latest data: forward neutron emission measurements for 158 A GeV In CERN SPS 1n1n 2n2n 3n3n 4n4n

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