Recreating the Birth of the Universe T K

Recreating the Birth of the Universe T. K Hemmick University at Stony Brook 14 -Jan-01 W. A. Zajc 1

The Beginning of Time l Time began with the Big Bang: q l The universe expanded and cooled up to the present day: q q l l All energy (matter) of the universe concentrated at a single point in space and time. ~3 Kelvin is the temperature of most of the universe. Except for a few “hot spots” where the expanding matter has collapsed back in upon itself. How far back into time can we explain the universe based upon our observations in the Lab? What Physics do we use to explain each stage? University at Stony Brook 2 Thomas K Hemmick

Evolution of the Universe Too hot for quarks to bind!!! Quark Plasma…Standard Model Physics Too hot for nuclei to bind Hadronic Gas—Nuclear/Particle Physics Nucleosynthesis builds nuclei up to Li Nuclear Force…Nuclear Physics Universe too hot for electrons to bind E-M…Atomic (Plasma) Physics Universe Expands and Cools Gravity…Newtonian/General Relativity University at Stony Brook 3 Thomas K Hemmick

Standard Model (simplified) l Imagine a college campus on a warm summer day q l University at Stony Brook 4 Students are uniformly distributed in an open field. Now introduce a FRISBEE into the system! Thomas K Hemmick

Standard Model II Students who interact with the FRISBEE form a group. l q Other students don’t interact with the FRISBEE. l q l University at Stony Brook 5 These students are “charged” neutral or “nerds” Now introduce CHESS into the campus! Thomas K Hemmick

Standard Model III l Some charged and some neutral students decide to play chess q q l University at Stony Brook 6 Very short range interaction More than one type of exchange particle Finally, introduce LOVE into the college campus Thomas K Hemmick

Standard Model IV l All the remaining students form into tightly bound pairs q l l University at Stony Brook 7 (and triples) If you break up with one partner, you immediately find another (confinement) Force grows stronger with separation Thomas K Hemmick

Decoding the Analogy Sport Force Exchange Particle Strength Range Calculable? FRISBEE Electro. Magnetic (QED) Photon Moderate Infinite Most accurate theory ever devised CHESS Weak Force (unified w/ EM) W+ , W - , Z 0 Weak Short Perfect LOVE Strong Force (QCD) 8 gluons Strong Infinite Nearly incalculable except for REALLY VIOLENT COLLISIONS! University at Stony Brook 8 Thomas K Hemmick

Electric vs. Color Forces l Electric Force q q l The electric field lines can be thought of as the paths of virtual photons. Because the photon does not carry electric charge, these lines extend out to infinity producing a force which decreases with separation. , l Color Force q q The gluon carries color charge, and so the force lines collapse into a “flux tube”. As you pull apart quarks, the energy in the flux tube becomes sufficient to create new quarks. Trying to isolate a quark is as fruitless as trying to cut a string until it only has one end! CONFINEMENT University at Stony Brook 9 Thomas K Hemmick

What about this Quark Soup? l l If we imagine the early state of the universe, we imagine a situation in which protons and neutrons have separations smaller than their sizes. In this case, the quarks would be expected to lose track of their true partners. They become free of their immediate bonds, but they do not leave the system entirely. They are deconfined, but not isolated q similar to water and ice, water molecules are not fixed in their location, but they also do not leave the glass. University at Stony Brook 10 Thomas K Hemmick

Phase Diagrams Nuclear Matter Water University at Stony Brook 11 Thomas K Hemmick

Making Plasma in the Lab l Extremes of temperature/density are necessary to recreate the Quark-Gluon Plasma, the state of our universe for the first ~10 microseconds. q Density threshold is when protons/neutrons overlap u 4 X nuclear matter density = touching. u 8 X nuclear matter density should be plasma. q Temperature threshold should be located at “runaway” particle production. u The lightest meson is the pion (140 Me. V/c 2). u When the temperature exceeds the mc 2 of the pion, runaway particle production ensues creating plasma. u The necessary temperature is ~1012 Kelvin. l Question: Where do you get the OVEN? q Answer: Heavy Ion Collisions! University at Stony Brook 12 Thomas K Hemmick

RHIC l l RHIC = Relativistic Heavy Ion Collider Located at Brookhaven National Laboratory University at Stony Brook 13 Thomas K Hemmick

RHIC Specifications l l 3. 83 km circumference Two independent rings q q l l 120 bunches/ring 106 ns bunch crossing time Can collide ~any nuclear species on ~any other species 6 1’ Top Center-of-Mass Energy: è 200 Ge. V/nucleon for Au-Au Luminosity q q 5 4 2 è 500 Ge. V for p-p l 3 Au-Au: 2 x 1026 cm-2 s-1 p-p : 2 x 1032 cm-2 s-1 (polarized) 14 1

RHIC’s Experiments STAR University at Stony Brook 15 Thomas K Hemmick

RHIC Video University at Stony Brook 16 Thomas K Hemmick

How is RHIC Different? l It’s dedicated to High Energy Heavy Ion Physics è Heavy ions will run 20 -30 weeks/year l It’s a collider è Detector systematics independent of ECM è (No thick targets!) l It’s high energy è Access to non-perturbative phenomena u Jets (very violent calculable processes in the mix) u Non-linear d. E/dx l Its detectors are comprehensive è ~All final state species measured with a suite of detectors that nonetheless have significant overlap for comparisons University at Stony Brook 17 Thomas K Hemmick

RHIC in Fancy Language l Explore non-perturbative “vacuum” by melting it Temperature scale è Particle production è Our ‘perturbative’ region is filled with q u gluons u quark-antiquark pairs è A Quark-Gluon Plasma (QGP) l Experimental method: Energetic collisions of heavy nuclei l Experimental measurements: Use probes that are q q Auto-generated Sensitive to all time/length scales University at Stony Brook 18 Thomas K Hemmick

RHIC in Simple Language l Suppose… q q q q q l You lived in a frozen world where water existed only as ice and ice comes in only quantized sizes ~ ice cubes and theoretical friends tell you there should be a liquid phase and your only way to heat the ice is by colliding two ice cubes So you form a “bunch” containing a billion ice cubes which you collide with another such bunch 10 million times per second which produces about 1000 Ice. Cube-Ice. Cube collisions per second which you observe from the vicinity of Mars Change the length scale by a factor of ~1013 è You’re doing physics at RHIC! University at Stony Brook 19 Thomas K Hemmick

Nature’s providence How can we hope to study such a complex system? g, e+e-, m+mp, K, h, r, w, p, n, f, L, D, X, W, D, d, J/Y, … PARTICLES! University at Stony Brook 20 Thomas K Hemmick

Deducing Temperature from Particles l Maxwell knew the answer! q Temperature is proportional to mean Kinetic Energy u Particles have an average velocity (or momentum) related to the temperature. u Particles have a known distribution of velocities (momenta) centered around this average. l All the RHIC experiments strive to measure the momentum distributions of particles leaving the collision. q q Magnetic spectrometers measure momentum of charged particles. A variety of methods identify the particle species once the momentum is known: u Time-of-Flight u d. E/dx University at Stony Brook 21 Thomas K Hemmick

Magnetic Spectrometers l Cool Experiment: q q l Hold a magnet near the screen of a B&W TV. The image distorts because the magnet bends the electrons before they hit the screen. Why? : 1 meter of 1 Tesla field deflects p = 1 Ge. V/c by ~17 O a s STAR University at Stony Brook 22 Thomas K Hemmick

Particle Identification by TOF l The most direct way q Measure b by distance/time Typically done via scintillators read-out with photomultiplier tubes Time resolutions ~ 100 ps q Exercise: Show q q l e p K p Performance: dt ~ 100 ps on 5 m flight path è P/K separation to ~ 2 Ge. V/c è K/p separation to at least 4 Ge. V/c q University at Stony Brook 23 Thomas K Hemmick

Particle Identification by d. E/dx l Elementary calculation of energy loss: Charged particles traversing material give impulse to atomic electrons: b Ze l x=bt d. E/dx: STAR The 1/ b 2 survives integration over impact parameters è Measure average energy loss to find b q Used in all four experiments q University at Stony Brook K p p e 24 Thomas K Hemmick

Measuring Sizes l Borrow a technique from Astronomy: q q q Two-Particle Intensity Interferometry Hanbury-Brown Twiss or “HBT” Bosons (integer spin particles like photons, pions, Kaons, …) like each other: u Enhanced 14 -Jan-01 probability of “close-by” emission 25

Measuring Shapes l Momentum difference can be measured in all three directions: q This yields 3 sizes: u “Long” (along beam) u “Out” (toward detector) u “Side” (left over dimension) l Conventional wisdom: q q The “Long” axis includes the memory of the incoming nuclei. The “Out” axis appears longer than the “Side” axis thanks to the emission time: University at Stony Brook 26 Thomas K Hemmick

Run-2000 l l l First collisions: 15 -Jun-00 Last collisions: 04 -Sep-00 RHIC achieved its First Year Goal (10% of design Luminosity). Most of the data were recorded in the last few weeks of the run. o Recorded ~5 M events The first public presentation of RHIC results took place at the Quark Matter 2001 conference. q q January 15 -20 Held at Stony Brook University at Stony Brook 27 Thomas K Hemmick

Jet Quenching l At RHIC energies, some of the processes are calculable from first principles q q Hard scattering Jets u u l Violent collisions between quarks and gluons. Excess yield at high momentum. One effect of Plasma is the “quenching” of these jets. q q They lose their energy while crossing the plasma. They “cool” down to the soup temperature. University at Stony Brook 28 Thomas K Hemmick

Jet Quenching Observed l Stony Brook Postdoc Federica Messer, presented PHENIX spectra of charged particles. q l (should be dominated by pions). BNL scientist (formed SB student) Gabor David presented measurements of neutral, IDENTIFIED What? ? ? The allpions. charged and neutral pions DIVERGE!! University at Stony Brook 29 Thomas K Hemmick

Identified Particle Spectra l Stony Brook Postdoc Julia Velkovska presented identified charged particle spectra at high momentum q The proton production EXCEEDS the pion production at high momentum u NOONE PREDICTED THAT! u This causes the divergence between “allcharged” and neutral pions. University at Stony Brook 30 Thomas K Hemmick

Where are the Jets? Expectation l l Charged particle production falls below the expectations by about a factor of two despite the proton contamination. Neutral pion production is a factor of 10 below predictions. University at Stony Brook 31 Thomas K Hemmick

Another Surprise! l Rout<Rside!!!!! q q Normal theory cannot account for this Imaginary times of emission!! University at Stony Brook 32 Thomas K Hemmick

Possible Explanation? ? l Stony Brook theory student Derek Teaney (advisor E. Shuryak) calculated an exploding ball of QGP matter. q q q The exploding ball drives an external shell of ordinary matter to high velocities Rout is the shell thickness Rside is the ball size Plasma Shells of ordinary matter University at Stony Brook 33 Thomas K Hemmick

Is it Soup Yet? l RHIC physics in some reminds me of the explorations of Christopher Columbus: q q l He had a strong feeling that the earth was round without having detailed calculations to back him up. He traveled in exactly the wrong direction, as compared to conventional wisdom. He discovered the new world… But he thought it was India! Our status: q q We see jet quenching for the first time. We see results which defy all predictions u Hard proton production exceeds pion production u Imaginary emission time q We could be in India (QGP), the New World, or just a place in Europe where the customs are VERY strange. University at Stony Brook 34 Thomas K Hemmick

Next Steps l Simple Language: q q l After the icecubes collide and melt, fragments leave which are frozen by the time they reach us, masking the true nature of the early state. Lesson: Don’t look at the fragments of frozen water which leave the collision, take a picture using light while the system is melted! Sophisticated Language: q q q Since hadrons are made of quarks, they reform and thereby lose information from the early stage. Photons and leptons leave the plasma directly and give detailed information from the center of the collision! Photons and leptons are rare and require more RHIC running. University at Stony Brook 35 Thomas K Hemmick

Summary l l Extreme Energy Density is a new frontier for explorations of the state of the universe in the earliest times. The RHIC machine has just come on line: q q l The machine works The experiments work The data from signatures of QGP as well as outright surprises… It’s not your Father’s Nuclear Matter anymore! l The real look into the system will come in the next run (May 2001): q l l Electrons, Photons, Muons We dream of India as our glorious destination But maybe…. We’ll find the new world instead. University at Stony Brook 36 Thomas K Hemmick

Electron Identification l l E/p matching for Problem: They’re rare p>0. 5 Ge. V/c tracks Solution: Multiple methods o Cerenkov o E(Calorimeter)/p(tracking) matching University at Stony Brook All tracks Electron enriched sample (using RICH) 37 Thomas K Hemmick

Why electrons? l One reason: sensitivity to heavy flavor production D 0 D 0 B 0 B 0 D 0 D 0 l Dalitz and conversions K- p+ K- e+ ne K - m+ n m charm e- beauty e. Drell-Yan D- p + D- e + n e D- m+ n m m + m - K + K - n mn m e +e - K + K - n en e m+ e - K + K - n e n m e- e- Study by Mickey Chiu, J. Nagle Other reasons: vector mesons, virtual photons e+e- University at Stony Brook 38 Thomas K Hemmick

p 0 Reconstruction l l l A good example of a “combinatoric” background Reconstruction is not done particle-by-particle Recall: p 0 gg and there are ~200 p 0 ‘s per unit rapidity q So: p 0 1 g 1 A + g 1 B p 0 2 g 2 A + g 2 B p 0 3 g 3 A + g 3 B p 0 q N g. NA + g NB PHENIX p 0 reconstruction p. T > 2 Ge. V/c Asymmetry < 0. 8 . Unfortunately, nature doesn’t use subscripts on photons è N correct combinations: (g 1 A g 1 B), (g 2 A g 2 B), … (g. NA g NB), è N(N-1)/2 – N incorrect combinations (g 1 A g 2 A), (g 1 A g 2 B), … 6 Incorrect combinations ~ N 2 (!) 4 Solution: Restrict N by p. T cuts use high granularity, high resolution detector 39 University at Stony Brook Thomas K Hemmick

BRAHMS An experiment with an emphasis: q q Quality PID spectra over a broad range of rapidity and p. T Special emphasis: u Where do the baryons go? u How is directed energy transferred to the reaction products? q University at Stony Brook Two magnetic dipole spectrometers in “classic” fixed-target configuration 40 Thomas K Hemmick

PHOBOS An experiment with a philosophy: q Global phenomena èlarge spatial sizes èsmall momenta q Minimize the number of technologies: u All Si-strip tracking u Si multiplicity detection u PMT-based TOF q University at Stony Brook 41 Unbiased global look at very large number of collisions (~109) Thomas K Hemmick

PHOBOS Details l Si tracking elements q q l University at Stony Brook 42 15 planes/arm Front: “Pixels” (1 mm x 1 mm) Rear: “Strips” (0. 67 mm x 19 mm) 56 K channels/arm Si multiplicity detector q 22 K channels q |h| < 5. 3 Thomas K Hemmick

PHOBOS Results First results on d. Nch/dh Hits in SPEC Tracks in SPEC Hits in VTX q q for central events At ECM energies of u 56 Gev u 130 Ge. V (per nucleon pair) To appear in PRL 130 AGe. V (hep-ex/0007036) X. N. Wang et al. University at Stony Brook 43 Thomas K Hemmick

STAR l An experiment with a challenge: q Track ~ 2000 charged particles in |h| < 1 Time Projection Chamber Magnet Coils Silicon Vertex Tracker TPC Endcap & MWPC FTPCs ZCal Endcap Calorimeter Vertex Position Detectors Barrel EM Calorimeter Central Trigger Barrel or TOF RICH University at Stony Brook 44 Thomas K Hemmick

STAR Challenge University at Stony Brook 45 Thomas K Hemmick

STAR Event Data Taken June 25, 2000. Pictures from Level 3 online display. University at Stony Brook 46 Thomas K Hemmick

STAR Reality 47

PHENIX l l An experiment with something for everybody A complex apparatus to measure q q q Muon Arms West Arm Hadrons Muons Electrons Photons Executive summary: q Global MVD/BB/ZDC Coverage (N&S) -1. 2< |y| <2. 3 -p < f < p DM(J/y )=105 Me. V DM(g) =180 Me. V 3 station CSC 5 layer Mu. ID (10 X 0) p(m)>3 Ge. V/c South muon Arm High resolution High granularity University at Stony Brook East Arm Central Arms Coverage (E&W) -0. 35< y < 0. 35 30 o <|f |< 120 o DM(J/y )= 20 Me. V DM(g 48 ) =160 Me. V North muon Arm Thomas K Hemmick

PHENIX Design 49

PHENIX Reality 50 January, 1999 W. A. Zajc

PHENIX Results (See nucl-ex/0012008) l Multiplicity grows significantly faster than N-participants l Growth consistent with a term that goes as N-collisions (as expected from hard scattering) University at Stony Brook 51 Thomas K Hemmick

Summary l The RHIC heavy ion community has q q Constructed a set of experiments designed for the first dedicated heavy ion collider Met great challenges in u Segmentation u Dynamic range u Data volumes u Data analysis q l Has begun operations with those same detectors Quark Matter 2001 will q q See the first results of many new analyses See the promise and vitality of the entire RHIC program University at Stony Brook 52 Thomas K Hemmick