Heavy ions at RHIC An experimental point of view PART I : the RHIC PART II : J/  adventure

Bielefeld, sept. 05F. Fleuret - LLR 2 Plan for this lecture RHIC : the machine –Beam, luminosity and species RHIC : the experiments –The four RHIC experiments The PHENIX muon arm –How do we measure dimuons ?

Bielefeld, sept. 05F. Fleuret - LLR 3 Introduction Quark Gluon Plasma : the phase diagram Candidate Quark Star RX J Star collapse High density of matter (5 to 10 times standard nuclear density) Confined matter  plasma high temperature (10 12 K) s. : Plasma  confined matter Big Bang Neutron stars

Bielefeld, sept. 05F. Fleuret - LLR 4 Introduction QGP : experiment history BNL - AGS 4 GeV CERN - SPS 20 GeV BNL - RHIC 200 GeVCERN - LHC 5 TeV Fixed target experiments Collider experiments

Bielefeld, sept. 05F. Fleuret - LLR 5 Introduction QGP : the SPS adventure NA35 NA36 NA49 NA34/2 HELIOS2 NA34/3 HELIOS3 NA44 NA45 CERES NA38 NA50 WA80 WA98 WA85 WA97 NA57 NA52 WA94 SOSO Pb multistrange photons hadrons dimuons dielectrons hadrons strangeletshadrons dimuons : 60 & 200 GeV/nucleon : 200 GeV/nucleon : 158, 40 & 80 GeV/nucleon + pp and pA For reference studies

Bielefeld, sept. 05F. Fleuret - LLR 6 Introduction QGP : the SPS adventure The lead beam programme started in 1994, after the CERN accelerators has been upgraded by a collaboration between CERN and institutes in the Czech Republic, France, India, Italy, Germany, Sweden and Switzerland. A new lead ion source was linked to pre-existing, interconnected accelerators, at CERN, the Proton Synchrotron (PS) and the SPS. The seven large experiments involved measured different aspects of lead-lead and lead-gold collisions. They were named NA44, NA45, NA49, NA50, NA52, WA97 / NA57 and WA98. Some of these experiments use multipurpose detectors to measure and correlate several of the more abundant observable phenomena. Others are dedicated experiments to detect rare signatures with high statistics. This co- ordinated effort using several complementing experiments has proven very successful.NA44NA45NA49NA50NA52WA97NA57WA98 At a special seminar on 10 February, spokespersons from the experiments on CERN* 's Heavy Ion programme presented compelling evidence for the existence of a new state of matter in which quarks, instead of being bound up into more complex particles such as protons and neutrons, are liberated to roam freely.CERN Theory predicts that this state must have existed at about 10 microseconds after the Big Bang, before the formation of matter as we know it today, but until now it had not been confirmed experimentally. Our understanding of how the universe was created, which was previously unverified theory for any point in time before the formation of ordinary atomic nuclei, about three minutes after the Big Bang, has with these results now been experimentally tested back to a point only a few microseconds after the Big Bang.

Bielefeld, sept. 05F. Fleuret - LLR 7 Introduction The SPS adventure : J/  suppression p-AS-UPb-Pb Physics Letters B410 (1997) 337 Hadronic Phase  <  c QGP  >  c NA50

Bielefeld, sept. 05F. Fleuret - LLR 8 Introduction QGP : the SPS adventure The results from CERN present strong incentive for the future planned experiments. While all of the pieces of the puzzle seem to fit with a quark-gluon plasma explanation, it is essential to study this newly produced matter at higher and lower temperature in order to fully characterize its properties and definitively confirm the quark gluon plasma interpretation. The focus of heavy ion research now moves to the Relativistic Heavy Ion Collider (RHIC) at the Brookhaven National Laboratory in the United States, which will start experiments this year. In 2005 CERN's Large Hadron Collider (LHC) experimental programme will include a dedicated heavy ion experiment, ALICE. RHIC time !

Bielefeld, sept. 05F. Fleuret - LLR 9 The experimental challenge –Provide proton and ion beams to study QGP Collision energy : GeV/nucleon Species : from proton (A=1) to Gold (A=197) Number of nucleon collisions : from 1 to ~40 000

Bielefeld, sept. 05F. Fleuret - LLR 10 BNL The Brookhaven National Laboratory Manhattan (New-York) 100 km Long-Island (New-York)

Bielefeld, sept. 05F. Fleuret - LLR 11 BNL The Brookhaven National Laboratory –Generalities Established in scientists, engineers, technicians and support staff 4000 guest researchers annually –Major programs Nuclear and high-energy physics Physics and chemistry of materials Energy research Medical imaging

Bielefeld, sept. 05F. Fleuret - LLR 12 BNL The Brookhaven National Laboratory –Facilities : AGS and RHIC AGS : fixed target experiments RHIC (3.9 km) : colliding beams A G S S P S R H I C

Bielefeld, sept. 05F. Fleuret - LLR 13 RHIC at BNL The RHIC project history – 1983 : the project conceived as part of US NSAC (National Science Advisory Committee) Long Range Plan – 1986 : CDR submitted to DOE and collider R&D began – 1989 : detector R&D initiated – 1991 : construction began – : four detectors approved, one-by-one – 1999 : construction completed – 2000 : Relativistic Heavy Ion Collisions Physics Program began 17 Years after the Idea was Conceived

Bielefeld, sept. 05F. Fleuret - LLR 14 Delivering protons –The injector : the LINAC Extract the protons –Booster (200 m) Accelerate to 1.5 GeV –AGS (800 m) Accelerate to 24.6 GeV Deliver the RHIC 24.6 GeV 1.5 GeV RHIC : the machine 200 MeV

Bielefeld, sept. 05F. Fleuret - LLR 15 Delivering ions –The injector : the Tandem Extract the Au ions –HITL : Heavy Ion Transfer Line Stripping –Booster Accelerate to 500 MeV –AGS Accelerate to 10 GeV Deliver the RHIC Au 14+, 1 MeVAu 79+, 10 GeV Au 77+, 500 MeV Au 32+, 1 MeV RHIC : the machine

Bielefeld, sept. 05F. Fleuret - LLR 16 RHIC : the machine The injectors –The tandem (van de Graff) for ions –The LINAC for protons Tandem Van De Graaff, since 1970, accelerates 40 species, from hydrogen to gold LINAC, since late 60s, accelerates (polarized) protons up to 200 MeV TANDEM LINAC

Bielefeld, sept. 05F. Fleuret - LLR 17 RHIC : the machine The pre-accelerators –The booster –The AGS Booster, since 1991, accelerates up to 2 GeV, ¼ of AGS size Alternating Gradient Synchrotron ( AGS ) since 1960, 240 magnets, accelerates up to 10 (23) GeV AGS Booster

Bielefeld, sept. 05F. Fleuret - LLR 18 RHIC : the machine The accelerator Blue Ring Yellow Ring (Clockwise) (Counter- Clockwise) Arc RHIC 9 GeV/u Q = +79 Beam Energy = 100 GeV/u

Bielefeld, sept. 05F. Fleuret - LLR 19 RHIC : the beam The beam Blue beam  clockwise Yellow beam  counter clockwise –Structure 55 bunches (packets) per beam ~10 9 Au ions per bunch 12.8  s per revolution

Bielefeld, sept. 05F. Fleuret - LLR 20 RHIC : the beam Beam injection and acceleration Acceleration BLUE Fill 55 bunches YELLOW Fill 55 bunches Storage energy Total Yellow current Bunched Yellow current Total Blue current Injection energy

Bielefeld, sept. 05F. Fleuret - LLR 21 RHIC : the beam performances

Bielefeld, sept. 05F. Fleuret - LLR 22 RHIC : the beam Monitoring luminosity N = L x  –Example : PHENIX AuAu 2004  N = L AuAu x  AuAu ~ 241  b -1 x 6.9 barn ~ 1.6 giga events PHENIX pp 2003  N = L pp x  pp ~ 0.35 pb -1 x 23 mb ~ 8 giga events  N J/  = L pp x  J/  ~ 0.35 pb -1 x 2.6  b ~ events  N J/    ~6% x events ~ events Zero-Degree Calorimeters

Bielefeld, sept. 05F. Fleuret - LLR 23 RHIC : performances RHIC delivered Au-Au luminosity

Bielefeld, sept. 05F. Fleuret - LLR 24 RHIC : performances RHIC delivered Cu-Cu luminosity

Bielefeld, sept. 05F. Fleuret - LLR 25 RHIC : performances Aronson

Bielefeld, sept. 05F. Fleuret - LLR 26 PHENIX DATA TAKEN RunYearSpeciess1/2 [GeV ]  Ldt NTotData Size Au+Au130 1  b M3 TB 0201/02 Au+Au p+p  b pb M 3.7 G 10 TB 20 TB 0302/03 d+Au p+p nb pb G 6.6 G 46 TB 35 TB 0403/04 Au+Au  b -1 9  b G 58 M 270 TB 10 TB 0504/05 Cu+Cu p+p nb nb  b pb G 0.4 G 9 M 85 G 173 TB 48 TB 1 TB 262 TB Physical process Writing on filesHadronisation, decays Interaction with the detector Response of the detector

Bielefeld, sept. 05F. Fleuret - LLR 27 RHIC : computing The RHIC Computing Farm (RCF) –Data storage –Computing farm ~20 computers for PHOBOS ~60 computers for BRAHMS ~250 computers for PHENIX ~380 computers for STAR RCF Intel Linux Processor Farm 1276 CPU

Bielefeld, sept. 05F. Fleuret - LLR 28 RHIC : research The RHIC research community ~1000 people from ~100 Institutions - Worldwide Brazil, Canada, China, Croatia, Denmark, France, Germany, India, Israel, Japan, Korea, Norway, Poland, Russia, Sweden, Taiwan, UK, US

Bielefeld, sept. 05F. Fleuret - LLR 29 Outline RHIC : the machine –Beam, luminosity and species RHIC : the experiments –The four RHIC experiments THE PHENIX muon arm –How do we measure dimuons ?

Bielefeld, sept. 05F. Fleuret - LLR 30 RHIC : the experiments Physics goal and experimental design –How to proceed with experimental design (partial answers) ? The QGP phase transition will not be « seen » at RHIC  Instead, it will emerge as a consistent framework for describing the observed phenomena  avoid single-signal detectors There are « no » cross sections at RHIC except   GEOM ~ few barns   CENTRAL ~ (1-10)%  GEOM  But  QGP ~  CENTRAL ?  preserve high-rate and triggering capabilities Expect the unexpected  maintain flexibility as long as €’s allow

Bielefeld, sept. 05F. Fleuret - LLR 31 The four RHIC experiments Two small experiments – BRAHMS B road RA nge H adron M agnetic S pectrometers – PHOBOS Phobos is the name for a moon of Mars, and the detector at one point was supposed to be called MARS -- Modular Array for RHIC Spectra. Phobos is a scaled- down version of MARS; hence the name. Two large experiments – STAR S olenoidal T racker A t R HIC – PHENIX P ioneering H igh E nergy N uclear I nteraction e X periment

Bielefeld, sept. 05F. Fleuret - LLR 32 The four RHIC experiments Comparing coverage Example : N J/    = L pp x  J/    x A ~ 0.35 pb -1 x (2.6  b x 6%) x 25% ~ events N = L x  x A

Bielefeld, sept. 05F. Fleuret - LLR 33 BRAHMS –Broad Range Hadron Magnetic Spectrometer The collaboration –~50 participants –14 institutions –8 countries The detector –At the 2 o’clock –1 mid-rapidity spectrometer –1 forward rapidity spectrometer –Measures charged hadrons –Very large rapidity range BRAHMS PHOBOS STAR PHENIX

Bielefeld, sept. 05F. Fleuret - LLR 34 BRAHMS reality

Bielefeld, sept. 05F. Fleuret - LLR 35 PHOBOS The collaboration –~50 participants –8 institutions –3 countries The detector –At the 10 o’clock –2 arm spectrometer magnets –Si  -strip detector –Time Of Flight –Count the total number of produced particles –Measures low P T charged particles PHOBOS BRAHMS STAR PHENIX

Bielefeld, sept. 05F. Fleuret - LLR 36 PHOBOS reality

Bielefeld, sept. 05F. Fleuret - LLR 37 STAR The collaboration –~ 600 participants –52 institutions –12 countries The detector –At the 6 o’clock –Large TPC –Silicon vertex tracker –EM calorimeter –Time of flight –Track ~2000 charged particles in |  |<1 STAR BRAHMS PHOBOS PHENIX

Bielefeld, sept. 05F. Fleuret - LLR 38 STAR reality

Bielefeld, sept. 05F. Fleuret - LLR 39 PHENIX The collaboration –~450 participants –51 institutions –11 countries The detector –Tracking (DC, PC) –Beam counters –EM calorimeter –TOF –RICH –Muon spectrometers –Measures everything PHENIX BRAHMS PHOBOS STAR

Bielefeld, sept. 05F. Fleuret - LLR 40 PHENIX reality d+Au Au+Au

Bielefeld, sept. 05F. Fleuret - LLR 41 The four RHIC experiments Many results 361 pages Very high energy density Parton energy loss (jet quenching) Collective motion (flow) Consistent with a strongly coupled QGP PHENIX : 40 publications STAR : 48 publications BRAHMS : 14 publications PHOBOS : 26 publications

Bielefeld, sept. 05F. Fleuret - LLR 42 Very high energy density AGS (AuAu)   Bj = 1.5 GeV/fm 3 SPS (PbPb)   Bj = 2.9 GeV/fm 3 RHIC (AuAu)   Bj = 5.4 GeV/fm 3

Bielefeld, sept. 05F. Fleuret - LLR 43 Jet quenching away sidenear side hadrons q q leading particle leading particle hadrons q q leading particle leading particle p-p A-A

Bielefeld, sept. 05F. Fleuret - LLR 44 Jet quenching Non central collisions y x

Bielefeld, sept. 05F. Fleuret - LLR 45 Flow Flow at the partonic level x y z  solid: STAR open: PHENIX PRL91(03)

Bielefeld, sept. 05F. Fleuret - LLR 46 outline RHIC : the machine –Beam, luminosity and species RHIC : the experiments –The four RHIC experiments THE PHENIX muon arm –How do we measure dimuons ?

Bielefeld, sept. 05F. Fleuret - LLR 47 Why dimuons ? Muons are insensitive to strong interaction A lot of physics within reach –Meson dimuon decays , , , , J/ ,  ’, ,… –Open charm muon pairs Through semi-leptonic decays –Drell-Yan dimuons

Bielefeld, sept. 05F. Fleuret - LLR 48 Measuring dimuons Measuring J/       –Invariant mass spectrum –We don’t measure muon mass  need to identify muons –Need to know muon momenta

Bielefeld, sept. 05F. Fleuret - LLR 49 Detector Design Overview

Bielefeld, sept. 05F. Fleuret - LLR 50 –(Muon are less energetic in collision mode)  must have small absorber. Measuring muons beam other muon absorber MuID MuTr absorber

Bielefeld, sept. 05F. Fleuret - LLR 51 Detector design Overall view 10° 35° MuID MuTr

Bielefeld, sept. 05F. Fleuret - LLR 52 Detector reality

Bielefeld, sept. 05F. Fleuret - LLR 53 The muon identifier Goal –Identify muons –Making a preselection of the tracks

Bielefeld, sept. 05F. Fleuret - LLR 54 The muon Identifier Concept and design –6 panels per gap (5 gaps) Small panel Large panel The South Muon Identifier

Bielefeld, sept. 05F. Fleuret - LLR 55 The muon Identifier Detector segmentation

Bielefeld, sept. 05F. Fleuret - LLR 56 The muon Identifier Making a road - clusters - roads

Bielefeld, sept. 05F. Fleuret - LLR 57 The muon tracker Goal –Making a precise measurement of the tracks

Bielefeld, sept. 05F. Fleuret - LLR 58 The muon tracker Detector design channels/arm

Bielefeld, sept. 05F. Fleuret - LLR 59 The muon tracker 3.2 mm - Ionization in the gas - Strips collect induced signal Measuring the signal

Bielefeld, sept. 05F. Fleuret - LLR 60 The muon tracker => strip number (1 dim) Using 2 planes (stereo angle) => (x,y,z)  ~ 90  m with cosmic studies 3.2 mm Measuring hits

Bielefeld, sept. 05F. Fleuret - LLR 61 The muon tracker Making a stub Gap 1 Gap 2 Gap 3 Stub

Bielefeld, sept. 05F. Fleuret - LLR 62 muon ID + muon tracker Making a track - stubs - coordinates - tracks

Bielefeld, sept. 05F. Fleuret - LLR 63 Measuring momentum Measuring momentum  magnetic field –Charged particle tracks bend :   P  &  => particle momentum  

Bielefeld, sept. 05F. Fleuret - LLR 64 Invariant mass spectrum What we get What we want Need to remove combinatorial background

Bielefeld, sept. 05F. Fleuret - LLR 65 Combinatorial background What is it ? –In standard dimuon experiments, the main sources of background are the (uncorrelated) decays of  and K mesons. –Can be minimized by having the hadron absorber as close to the collision point as possible. –Combinatorial background sources also give  +  + and  -  - pairs, which can be used to estimate the corresponding  +  - contribution   absorber

Bielefeld, sept. 05F. Fleuret - LLR 66 Get rid of the background –Background estimation For a given event :N + (N - ) = nb of  + (  - ) For a large number of event (on average) Simplification : 2 hypothesis  N+ and N- are uncorrelated

Bielefeld, sept. 05F. Fleuret - LLR 67 Getting the signal The simplest method

Bielefeld, sept. 05F. Fleuret - LLR 68 Computing cross sections Efficiencies –Many sources of inefficiencies Example : N J/    = L pp x  J/    x A x  ~ 0.35 pb -1 x (2.6  b x 6%) x 25% x 50% ~ 6825 events

Bielefeld, sept. 05F. Fleuret - LLR 69 Unique facility (so far) to do nucleus-nucleus collisions from 20 to 200 GeV/nucleon STAR