Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy The STAR experiment at RHIC What are we doing ? Why do we do it ? How do we do it ? What are we doing ? Why do we do it ? How do we do it ?

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy The RHIC Complex 1. Tandem Van de Graaff 2. Heavy Ion Transfer Line 3. Booster 4. Alternating Gradient Synchrotron (AGS) 5. AGS-to-RHIC Transfer Line 6. RHIC ring 1. Tandem Van de Graaff 2. Heavy Ion Transfer Line 3. Booster 4. Alternating Gradient Synchrotron (AGS) 5. AGS-to-RHIC Transfer Line 6. RHIC ring

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy The RHIC Ring Made of two intersecting rings 2.4 miles around Clockwise and counterclockwise Intersect at six locations Close-up of intersection point

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy Inside the RHIC Ring Underground tunnel Super- conducting magnets Cooled by liquid helium Underground tunnel Super- conducting magnets Cooled by liquid helium

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy RHIC’s Ultimate Goal QuarksQuarks Quark-GluonPlasmaQuark-GluonPlasma RHIC Collision KeyKey GluonsGluons

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy RHIC Beam Collisions Approach Collision Particle Shower

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy How many collisions ? when the beams intersect about 1000 central collisions per second occur the detector has to record all the information of all detector components for every event: limited by bandwidth (20 Mb/sec.) -> we can record about 1 event/sec. then we have to analyze about 1 event/sec. to keep up with the recording rate Help: machine duty cycle (50%), we only run 37 weeks/year -> we effectively have 3 seconds per event to analyze (if we only have to do it once) when the beams intersect about 1000 central collisions per second occur the detector has to record all the information of all detector components for every event: limited by bandwidth (20 Mb/sec.) -> we can record about 1 event/sec. then we have to analyze about 1 event/sec. to keep up with the recording rate Help: machine duty cycle (50%), we only run 37 weeks/year -> we effectively have 3 seconds per event to analyze (if we only have to do it once)

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy What is going on ? A Au nucleus consists of 79 protons and 118 neutrons = 197 particles -> 394 particles total p and n consist of u- and d-quarks After the collision we measure about 10,000 particles in the debris! measured particles: p, , K, , d, J/  Y many particles contain s-quarks, some even c-quarks Energy converts to matter, but does the matter go through a phase transition ? A Au nucleus consists of 79 protons and 118 neutrons = 197 particles -> 394 particles total p and n consist of u- and d-quarks After the collision we measure about 10,000 particles in the debris! measured particles: p, , K, , d, J/  Y many particles contain s-quarks, some even c-quarks Energy converts to matter, but does the matter go through a phase transition ?

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy What is a phase transition ? When a system is in equilibrium (all available energy is equally distributed over the constituents) then it can be defined by basic thermodynamic properties (pressure, volume, temperature). A phase transition happens when matter changes its ‘phase’ (e.g. liquid to solid or liquid to gas or gas to plasma). A phase transition can be visualzied by a phase diagram changing two of the three basic thermodynamic properties (e.g. PV-diagram or PT diagram or VT diagram) When a system is in equilibrium (all available energy is equally distributed over the constituents) then it can be defined by basic thermodynamic properties (pressure, volume, temperature). A phase transition happens when matter changes its ‘phase’ (e.g. liquid to solid or liquid to gas or gas to plasma). A phase transition can be visualzied by a phase diagram changing two of the three basic thermodynamic properties (e.g. PV-diagram or PT diagram or VT diagram)

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy How does it look ?

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy What do we have to check ? If there was a transition to a different phase, then this phase could only last very shortly. The only evidence we have to check is the collision debris. Check the make-up of the debris: ◊ which particles have been formed ? ◊ how many of them ? ◊ are they emitted statistically (Boltzmann distribution) ? ◊ what are their kinematics (speed, momentum, angular distributions) ? ◊ are they correlated in coordinate or momentum space ? ◊ do they move collectively ? If there was a transition to a different phase, then this phase could only last very shortly. The only evidence we have to check is the collision debris. Check the make-up of the debris: ◊ which particles have been formed ? ◊ how many of them ? ◊ are they emitted statistically (Boltzmann distribution) ? ◊ what are their kinematics (speed, momentum, angular distributions) ? ◊ are they correlated in coordinate or momentum space ? ◊ do they move collectively ?

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy Signatures of the QGP phase Phase transitions are signaled thermodynamically by a ‘step function’ when plotting temperature vs. entropy. Entropy simply means that different phases are distinguished by having different degrees of freedom. The temperature (or energy) is used to increase the number of degrees of freedom rather than heat the existing form of matter. In the simplest approximation the number of degrees of freedom should scale with the particle multiplicity. Phase transitions are signaled thermodynamically by a ‘step function’ when plotting temperature vs. entropy. Entropy simply means that different phases are distinguished by having different degrees of freedom. The temperature (or energy) is used to increase the number of degrees of freedom rather than heat the existing form of matter. In the simplest approximation the number of degrees of freedom should scale with the particle multiplicity.

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy The STAR Experiment Conceptual Overview

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy Simulated Collision in STAR Number of tracks in STAR according to a simulation of a central Au-Au Collision = 2000 Central = Head-on Peripheral = Glancing Number of tracks in STAR according to a simulation of a central Au-Au Collision = 2000 Central = Head-on Peripheral = Glancing

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy Simulation Close-Up Solution for the high particle density problem: build a high resolution detector (zoom in on the problem)

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy Actual Collision in STAR (1) Actual STAR data for a peripheral collision Actual STAR data for a peripheral collision

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy Actual Collision in STAR (2) Actual STAR data for a central collision

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy The STAR Experiment (cut) STAR from the inside-out

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy How Do We Measure Things ? particles go from the inside-out they have to traverse certain detectors they should stop in the outermost detector the particle should not change its properties when traversing the inner detector DETECT but don’t DEFLECT !!! inner detectors have to be very thin (low radiation length): easy with gas, challenge with solid state materials (Silicon). particles go from the inside-out they have to traverse certain detectors they should stop in the outermost detector the particle should not change its properties when traversing the inner detector DETECT but don’t DEFLECT !!! inner detectors have to be very thin (low radiation length): easy with gas, challenge with solid state materials (Silicon).

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy Different Techniques of Detection Tracking and Vertexing ◊ gas or Silicon detectors Measure Time Of Flight ◊ scintillators with phototubes Measure Energy ◊ calorimeters Tracking and Vertexing ◊ gas or Silicon detectors Measure Time Of Flight ◊ scintillators with phototubes Measure Energy ◊ calorimeters

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy Calorimetry and Time of Flight Calorimetry ◊ build a device that surrounds all other detectors made of many layers of very dense material (e.g. Pb) in which the particles stop and deposit all their energy. Measure energy by interspersing scintillator layers. Time Of Flight ◊ build a detector layer sufficiently far away (radially) from the intersection point to measure the flight time for each charged particle. The start time is the time of interaction the stop time is the impact time of the particle on the time of flight layer (made of scintillators). Different particle species have different time of flight for the same momentum due to their difference in mass. Calorimetry ◊ build a device that surrounds all other detectors made of many layers of very dense material (e.g. Pb) in which the particles stop and deposit all their energy. Measure energy by interspersing scintillator layers. Time Of Flight ◊ build a detector layer sufficiently far away (radially) from the intersection point to measure the flight time for each charged particle. The start time is the time of interaction the stop time is the impact time of the particle on the time of flight layer (made of scintillators). Different particle species have different time of flight for the same momentum due to their difference in mass.

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy Tracking detector principle charged particle (ion) traverses the active volume and liberates electrons from the active material (silicon or gas) by applying a voltage gradient to the active volume the generated electron cloud is steered towards a detector edge there the electrons are collected and counted measurements:a.) position of cloud impact = position of particle impact 1 b.) time for cloud to reach edge = position of particle impact 2 c.) number of electrons in cloud = ion energy loss in active material charged particle (ion) traverses the active volume and liberates electrons from the active material (silicon or gas) by applying a voltage gradient to the active volume the generated electron cloud is steered towards a detector edge there the electrons are collected and counted measurements:a.) position of cloud impact = position of particle impact 1 b.) time for cloud to reach edge = position of particle impact 2 c.) number of electrons in cloud = ion energy loss in active material

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy Tracking/Vertexing Detectors STAR has three tracking detectors ◊ Silicon Vertex Tracker (SVT) ◊ Time Projection Chamber (TPC) ◊ Forward Time Projection Chamber (FTPC) TPC’s are gas detectors SVT is a solid state detector STAR has three tracking detectors ◊ Silicon Vertex Tracker (SVT) ◊ Time Projection Chamber (TPC) ◊ Forward Time Projection Chamber (FTPC) TPC’s are gas detectors SVT is a solid state detector

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy Tracking Detector Schematic 1.) generate e-cloud 2.) drift e-cloud 3.) focus e-cloud 4.) record e-cloud (position and time) 1.) generate e-cloud 2.) drift e-cloud 3.) focus e-cloud 4.) record e-cloud (position and time)

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy How Do We Measure Things ? measure a track by connecting points in different radial planes (SVT has three planes, TPC has 45 planes) put the tracking detectors in a magnetic field -> the charged particle track will be curved ( r = mv/qB -> r = p/qB) the radius is proportional to the particles momentum curvature direction tells us particle charge measure a track by connecting points in different radial planes (SVT has three planes, TPC has 45 planes) put the tracking detectors in a magnetic field -> the charged particle track will be curved ( r = mv/qB -> r = p/qB) the radius is proportional to the particles momentum curvature direction tells us particle charge

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy How Do We Measure Things ? in inner detectors (SVT and TPC) the particles lose only a tiny bit of energy and are not or very little deflected the tiny bit of energy is sufficient for an energy loss measurement. in outer detector (EMC) the particles are stopped and all their remaining energy is measured. in inner detectors (SVT and TPC) the particles lose only a tiny bit of energy and are not or very little deflected the tiny bit of energy is sufficient for an energy loss measurement. in outer detector (EMC) the particles are stopped and all their remaining energy is measured.

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy Energy Loss Measurements use the tiny bit of energy loss in the tracking detectors plus the track momentum information for particle identification

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy Energy Loss Measurements 2 for faster particles (higher momentum) we have to use the time- of-flight method

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy What can we measure ? momentum, energy and abundance of charged particles particle species decaying particles momentum, energy and abundance of charged particles particle species decaying particles

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy What can we measure ? Global Observables ◊ multiplicity (= number of charged particles) ◊ energy (= energy deposited in calorimeter) Specific Observables ◊ particle specific yields ◊ particle specific kinematic spectra ◊ correlation between particles ◊ fluctuations of any observable Global Observables ◊ multiplicity (= number of charged particles) ◊ energy (= energy deposited in calorimeter) Specific Observables ◊ particle specific yields ◊ particle specific kinematic spectra ◊ correlation between particles ◊ fluctuations of any observable

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy What can we measure (cont.) if we have enough particles then we can measure observables event-by- event ! 80% of all emitted particles are pions observables based on pions can be measured event-by-event if we have enough particles then we can measure observables event-by- event ! 80% of all emitted particles are pions observables based on pions can be measured event-by-event

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy The STAR Experiment Conceptual Overview

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy The STAR Experiment (TPC) Construction in progress Connecting components

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy The STAR Experiment (TPC) Overview while under construction

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy The STAR Experiment (SVT) The final device…. … and all its connections … and all its connections

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy The STAR Experiment (SVT) Overview while under construction

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy Specific Topic: decaying particles a neutral particle decays into two charged particles inside the active tracking volume e.g.  -> p  - (ct = 7.89 cm)

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy Why measure decaying particles ? Our nature is made of elementary particles that contain only light quarks (u,d) and that are stable (protons, electrons) Elementary particles with heavy quark content (s,c,b,t) are not stable and rare but they can be produced in the laboratory. We suspect that a lot of these particles were produced during the Big Bang and subsequently decayed. Of these, particles with strange quark are most abundant and have the longest lifetime. Let’s look at some of these particles. Our nature is made of elementary particles that contain only light quarks (u,d) and that are stable (protons, electrons) Elementary particles with heavy quark content (s,c,b,t) are not stable and rare but they can be produced in the laboratory. We suspect that a lot of these particles were produced during the Big Bang and subsequently decayed. Of these, particles with strange quark are most abundant and have the longest lifetime. Let’s look at some of these particles.

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy How do we measure ‘strange’ particles ? If we assume that the particles generated in a heavy ion collision are moving with close to the speed of light we can measure their decay distance by multiplying their lifetime with the speed of light (c  ) particleQuark content massLifetime (ct) Proton (p)uud938 MeVstable Lambda  uds1115 MeV7.89 cm Xi (  ) uss1321 MeV4.91 cm Omega (  ) sss1672 MeV2.46 cm

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy Why measure strangeness ? We reconstruct the masses out of the momenta of the decay products (daughters) We cut on the proper masses and measure the yield to determine possible enhancement factors. Strange particles are definitely produced ! We measure the kinematics (momentum distributions) to learn about production mechanisms and thermodynamical properties of the system (volume, pressure, temperature) to check whether a phase transition was possible We reconstruct the masses out of the momenta of the decay products (daughters) We cut on the proper masses and measure the yield to determine possible enhancement factors. Strange particles are definitely produced ! We measure the kinematics (momentum distributions) to learn about production mechanisms and thermodynamical properties of the system (volume, pressure, temperature) to check whether a phase transition was possible

Relativistic Heavy Ion Collider Brookhaven NatIonal Laboratory Brookhaven ScIence AssocIates U.S. Department of Energy Summary and Conclusion STAR is a state-of-the-art high energy collider detector. It took eight years and about $40 Million to complete this project. STAR’s complete 2  coverage allows us to measure thousands of particles in a single collision. Both, accelerator and detector are full operational The challenge to detect interesting physics now lies with the software analysis programs and the ingenuity of young scientist like you. STAR is a state-of-the-art high energy collider detector. It took eight years and about $40 Million to complete this project. STAR’s complete 2  coverage allows us to measure thousands of particles in a single collision. Both, accelerator and detector are full operational The challenge to detect interesting physics now lies with the software analysis programs and the ingenuity of young scientist like you.