# Presentation: 709827

## IMHO...(In Mike’s Humble Opinion)

*Mike Lisa*
*Ohio State University*

- what have we learned (so far)?
- what is exciting (to me)?
- what do I tell my condensed-matter colleagues in the coffee room?

## What have we learned at RHIC?An This experimentalist’s Perspective * 

- Wise “forefathers” designed complex detectors in anticipation of a complex problem
- Tremendous output since late 2000 – ~80 physics papers / 3 years!
- Huge diversity of results
- hard probes (J/, D, jets...)
- momentum-space shapes (spectra, v2, v4...)
- femtoscopy (HBT, non-id correlations, cluster/coalescence...)
- fluctuations (pT, net charge...)
- chemistry (yields, resonances, strangeness...)
- Huge systematics
- particle type (mass, quark content, σ, collision stage)
- rapidity (parton x)
- sNN ()
- centrality (, **shape**)
- system (A-A, p/d-A, p-p) – “clean” (?) references

***** complete with bias/ignorance

**~1 year after**
**Y1 “End of Major Operations”: **
**14 RHIC physics papers**
**To date: ~80 (expt) physics papers**

- ma lisa - QM04

## Sophisticated tools to study a complex system

- A warning from the king of dour...

- “[In a system] where the pieces have different and bizarre motions, with various and variable values, what is only complex is mistaken (a not unusual error) for what is profound.”

- Edgar Allen Poe, in *Murders in the Rue Morgue* (1841)
- discussing chess enthusiasts

- ma lisa - QM04

## PID’d access to range of pT scales

- PID’d access to range of pT scales

- Most compelling observations so far: **[hard]**
- hard probes of bulk medium
- probes “calibrated”/calculable at high pT
- medium decays (99.5%) to low pT particles
- QGP: low-Q phenomenon
- Most frustrating observations so far: **[soft]**
- less clear “new” message from medium *itself*
- dynamic/timescale/chemistry systematics
- importance of understood reference
- Most exciting observations so far: **[“firm”]**
- _particle-identified_ intermediate-pT RAA, v2
*non-trivial* interaction of probe – medium?
- evidence towards partonic medium
- towards a more unified picture?

**?**

- ma lisa - QM04

## [hard] On the right track...

- Singles spectra:
-   clear difference to references
- pp – a medium effect
- dAu – a final state effect
- lower s – a new final state		medium effect
- more differential:  distributions
- “calibrated” probe suppression (jets)
- near-side structure *suggests* parton E (?)

**PRL91 **072304 (2003)

- ma lisa - QM04

## [hard] On the right track...

- Singles spectra &  distributions
- final state medium-induced jet “quenching”
- important: lower pT,assoc
- jets poking through?
- even more differential: jets vs. RP
- expected from above inferences
- “self-referential”
- consistent picture?
- nail down E(L) contribution

- ma lisa - QM04

## [hard] On the right track...

**For now**: limited information content

- Singles spectra &  distributions
- final state medium-induced jet “quenching”
- important: lower pT,assoc
- jets poking through?
- even more differential: jets vs. RP
- jet tomography E(L)
- Could it be (“pre-”)hadronic?
- unscientific to dismiss it outright
- OTOH, my $$: partonic E

- ma lisa - QM04

## [hard]

- Dense
- Compelling!
- Explore further!

- [firm]

- [soft]

- ma lisa - QM04

## With PID - [firm] Definitely on the right track...

- hadronic E?
- lots of theory arguments, but...
- RAA[] > RAA[K]	(E < EK)
- related: “anomolous” B/M
- v2[] > v2[K]    	(E > EK)
- hadron absorption  (almost) “too large” v2

- ma lisa - QM04

## With PID - [firm] Definitely on the right track...

**R****CP**

- hadronic E?
- no
- soft (hydro) + hard (parton E)?
- would imply *mass* systematics
- (better stats on  impt)

- With PID - [firm] Definitely on the right track...

**p****T**** (GeV/c)**

- T. Frawley, QM04

- ma lisa - QM04

## With PID - [firm] Definitely on the right track...

- With PID - [firm] Definitely on the right track...

- hadronic E?
- no
- soft (hydro) + hard (parton E)?
- not only
- In azimuth: v2 “n scaling”
- partonic systematics
- (v2[] will be nice)
-  very suggestive of coalescence scenario
- push down in pT?
- “works” to pTq ~ 500 MeV ~3Tq

- J. Castillo, QM04

- ma lisa - QM04

## [hard]

- Dense, partonic
- Compelling!
- Explore further!

- [firm]
- hadronization of
- thermal (?) quarks
- delve into the medium!

- [soft]
- the medium...!

- ma lisa - QM04

## [soft] On the right track to...what?

- Dominant soft sector theme:
- soft sector is flow-dominated [“fact”]
- dN(m)/pT, v2(pT,m), HBT, non-id...
- hydro – works well in p-sector
- probably early thermalization claim is correct [opinion]

- Kolb and U. Heinz (2002)

- ma lisa - QM04

## [soft] On the right track to...what?

- Dominant soft sector theme:
- hydro-like flow describes p-sector
- Bugaboo: space-time (HBT, etc.)
- very difficult to describe simultaneously p- and x-space in “real” models

- D. Teaney, nucl-th/0301099

- ma lisa - QM04

## [soft] On the right track to...what?

- Dominant soft sector theme:
- hydro-like flow describes p-sector
- Bugaboo: space-time (HBT, etc.)
- very difficult to describe simultaneously p- and x-space in “real” models
- to make progress: *parameterize* hydro, twiddle knobs of underlying physics
- short timescales!

**“****BlastWave” fits**

- ma lisa - QM04

## [soft] On the right track to...what?

- Dominant soft sector theme:
- hydro-like flow describes p-sector
- Bugaboo: space-time (HBT, etc.)
- very difficult to describe simultaneously p- and x-space in “real” models
- to make progress: *parameterize* hydro, twiddle knobs of underlying physics
- short timescales!

**“****BlastWave” fits**

- ma lisa - QM04

## [soft] On the right track to...what?

- Dominant soft sector theme:
- hydro-like flow describes p-sector
- Bugaboo: space-time (HBT, etc.)
- very difficult to describe simultaneously p- and x-space in “real” models
- to make progress: *parameterize* hydro, twiddle knobs of underlying physics
- short timescales!

- More hints of short timescales
- azimuthally-sensitive HBT
- source shape!!
**t****K****-t****Ch ** 5 fm/c (entropy, K*/K)
- O. Barannikova, P. Fachini

- ma lisa - QM04

## [soft] On the right track to...what?

- Dominant soft sector theme:
- hydro-like flow describes p-sector
- Bugaboo: space-time (HBT, etc.)
- (admittedly) *simple* estimates indicate shorter timescales than naturally turn up in models
- IMHO, these simple models contain a kernel of truth, and should not be discarded
- certainly, there is no indication for *long* timescales(originally expected / hoped for) in the data

- ma lisa - QM04

## side comment:BlastWave models are useful, but do not abuse

- hydro seems to “work” for multistrange particles as for the rest
- FO hypersurface matters especially for heavy particles [Heinz&Kolb]
- [opinion]: if (!) “real” model (hydro) works for , , why trust instead a parameterization?
- may be early FO, but BW fits are not evidence for it

- Kolb & Rapp, PRC67 044903 (2003)

- ma lisa - QM04

## soft sector– do we have a clean reference?

**T. Gutierrez for STAR Coll, poster**

- HBT R(kT) in AA and pp *presumably* (?) due to different physics
- Flat AA/pp ratio ?!?
- experimentalists hate “coincidences” 

- ma lisa - QM04

## soft sector– do we have a clean reference?

- HBT and soft-sector variables in general:
- relatively featureless terrain *
- usually “explainable”/describable by unremarkable physics (e.g. FO= 1 fm)
- similar for flow, strangeness, dN/dy
- often similar problems at lower s
- where to hang one’s hat?

- * but: horns et al.

- ma lisa - QM04

## soft-sector dreams...

- Harris & Mueller AnnRevNuclPartSci ‘96

- Kolb, Sollfrank, Heinz, PRC62 054909 (2000)

- “we were naïve”

- v2

- dN/dy

- ma lisa - QM04

## Strangeness thermalization/equilibration?

- STAR

- NA57

- Hamieh, Redlich, Tounsi
- PLB486 61 (2000)

- it saturates, but just at the very end
- it equilibrates, but in addition, we have contributions from hard processes?
- Do we understand our reference systematics (centrality)?

- ma lisa - QM04

## [hard]

- Dense, partonic
- Compelling!
- Explore further!

- [firm]
- hadronization of
- thermal (?) quarks
- delve into the medium!

- [soft]
- high 
- high pressure
- short ’s [IMHO]
- no clear indication
- of something really “new”

- cup half full:
*beautiful measurements*
- will be exciting to systematically learn why/how this most important sector hides its secrets

- ma lisa - QM04

## Special thanks to...

- CENSORED TO PROTECT THE INNONCENT...

- Sorry I couldn’t mention *your* favourite observations...

- ma lisa - QM04

## David Scott 1979

- “In the development of RHI studies, a form of intellectual Ludditism appears to be prevalent.  There is a tendency to assume that no significant progress is being made, when in fact intriguing and unexplainable phenomena exist, the ultimate understanding of which is likely only to come from sustained research”

- ma lisa - QM04

## The End

- ma lisa - QM04

## v2 and HBT from AMPT?

- σ ~ 10 mb

- σ < 6 mb (~ 3 mb?)

- ma lisa - QM04

## [hard] On the right track...

- Singles spectra &  distributions
- final state medium-induced jet “quenching”
- important: lower pT,assoc
- jets poking through?
- low s reference:broadening; no suppression
- jets ?
- new effect at RHIC

- ma lisa - QM04

## horns, steps, kinks

- How could an experimentalist *not* be intrigued by a sharp horn!?
- troubling coincidence of microhorn
- IMHO, I don’t have a well-formed opinion

- A. Rybicki, QM04

- M. Gazdzicki, QM04

- A+A – The Matterhorn

- isospin weighted N+N  p+p :
- the microhorn

- ma lisa - QM04

## horns, steps, kinks

- Unclear to me why exponential fit just to K+ is appropriate
- OTOH, claim is ~2 MeV variation with fit range

- 40 GeV

- 80 GeV

- 160 GeV

- ma lisa - QM04

## horns, steps, kinks

- not connected to old (Bevalac) ideas of EoS, compression, energy conservation  (and N+N+N)?

- LBL Streamer chamber group 1979
- c/o Reinhardt  Stock

- ma lisa - QM04

## scaled pT spectra – c/o Molnar & Voloshin

- 0

- 1

- 2

- 3

- K0S

- 

- 

- ma lisa - QM04

## With PID - [firm] Definitely on the right track...

- With PID - [firm] Definitely on the right track...

- Coalescence models (various flavors)
- promising, distinguishable models
- v2[s] = v2[u,d] ?
- interaction b/t hard/soft quarks?
- dynamics of hadronization!!
- Molnar parton cascade
- σ 3 mb ( 10 mb)
- dN/d  1500-3000 (~ Gyulassy)
- push down in pT?
- “works” to pTq ~ 500 MeV ~3Tq

- P. Sorensen, SQM03

- Fries et al, PRC68 044902 (2003)

- Greco, Ko, Levai PRC68 034904 (2003)

- ma lisa - QM04

## problems at lower s... AGS

**E895 Collab, PRL 84 2798 (2000)**

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## Testing the model at the SPS

- For -...
- Model *under*predicts apparent size below 10 AGeV...
*over*predicts size at 158 AGeV
- Extrapolation to RHIC???

- 	   _NA44_		   _RQMD_
- Rout	4.88  0.21	6.96  0.14
- Rside	4.45  0.32	6.23  0.20
- Rlong	6.03  0.35	7.94  0.21

- I.G. Bearden et al (NA44)
- PRC**58**, 1656 (1998)
- D. Hardtke, Ph.D. thesis (1997)

- ma lisa - QM04

## soft – cont

- equilibration – no saturation of multistrange w/ Npart:
- argument 1:
- it *does* saturate, but only for last 1-2 datapoints
- GCE works (but maybe only for last datapoint)
- if only we had higher Npart points, we’d see it flatten out
- [opinion] strikes me as strange – I hate coincidences
- argument 2:
- it *does* equilibrate, so *would* flatten, but Nbinary contributions are added on top
- but then wouldn’t there be too *much* of strangeness for GCE in central?
- [opinion] reference (low Npart collisions) systematics not understood

- ma lisa - QM04

## soft sector– do we have a clean reference?

- more HBT “puzzles”?
- R(kT) in AuAu attributed to flow – seems reasonable & jibes w/ p-space
- R(kT) in pp *presumably* arises from different physics (tilted strings etc)
- why R(kT)AA / R(kT)pp is flat? – As experimentalist, I hate coincidences!
- not-understood reference 
- strangeness
- steps, kinks, horns – as an experimentalist, I *am* intrigued by the *data*, but
- kink: explainable by “old” concepts of EoS / compressibility energy conservation
- step: I do not find exponential fit to just K+ spectrum “model-independent”
- horn: Rybicki’s isospin arguments ring true: Again, I hate coincidences
- again, reference system (NN) details may not be properly accounted for

- ma lisa - QM04