W A Horowitz University of Cape Town July 21 2011 1042011 1 MIT CTP Seminar With many thanks to Alessandro Buzzatti Brian Cole Miklos Gyulassy Jiangyong Jia and Yuri ID: 815548
Download The PPT/PDF document "Energy Loss Calculations, RHIC, and Firs..." is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
Energy Loss Calculations, RHIC, and First Results from LHC
W. A. HorowitzUniversity of Cape TownJuly 21, 2011
10/4/2011
1
MIT CTP Seminar
With many thanks to Alessandro
Buzzatti
, Brian Cole,
Miklos
Gyulassy
,
Jiangyong
Jia
, and Yuri
Kovchegov
Slide2Four Fundamental Forces
10/4/2011MIT CTP Seminar
2
Gravity
Electromagnetism
Weak
Strong
John
Maarschalk
, travelblog.portfoliocollection.com
starchild.gsfc.nasa.gov
lhs.lps.org/staff/
sputnam
/
chem_notes
/tritium_decay.gif
Slide3E&M Particle Physics Well Understood
Lagrangian known:QED Vertex:Ex. of Precision QED: g - 2
10/4/2011
MIT CTP Seminar
3
Hanneke
,
Fogwell
, and
Gabrielse
, PRL100 (2008)
Gabrielse
et al., PRL97 (2006)
Slide4E&M and Phase Diagrams
Many body physics less well understood10/4/2011
MIT CTP Seminar
4
www.sv.vt.edu/classes/MSE2094_NoteBook/96ClassProj/examples/triplpt.html
Water
Hydrogen
Calculated,
Burkhard
Militzer
,
Diploma Thesis, Berlin,
2000
Slide5QCD Particle Physics Well Understood
Lagr. known:QCD Vertices:Qual. & Quant. agreement w/ data
10/4/2011
MIT CTP Seminar
5
ALEPH,
PLB284
(1992)
PDG
Slide6What Are We Interested In?
Measure many-body physics of strong forceTest & understand theory of many-body non-Abelian fields
10/4/2011
MIT CTP Seminar
6
Long Range Plan, 2008
Slide7Heavy Ion Collisions
10/4/2011MIT CTP Seminar
7
Collider machines: RHIC, LHC
Relativistic Heavy Ion Collider
Large
Hadron
Collider
Slide8Big Bang vs. Little Bang
10/4/2011MIT CTP Seminar
8
t = -
¥
t = 0
t ~ 1 fm/c
t = +
¥
Initial State
Initial Overlap
Thermalization
QGP
Hadronization
Hadron
Gas
ALICE Collaboration
High Momentum Particle
Slide9QGP Energy Loss
Learn about E-loss mechanismMost direct probe of DOF10/4/2011
MIT CTP Seminar
9
pQCD Picture
AdS/CFT Picture
Slide10pQCD Rad
PictureBremsstrahlung RadiationWeakly-coupled plasmaMedium organizes into Debye-screened centers
T ~ 250 MeV, g ~ 2m
~ gT ~ 0.5 GeV
lmfp ~ 1/g2
T ~ 1 fm
R
Au
~ 6 fm
1/
m
<<
l
mfp << Lmult. coh. em
.10/4/2011
MIT CTP Seminar
10
Bethe-Heitler
dpT/dt
~ -(T3/Mq2)
pT
LPM
dp
T
/
dt
~ -LT
3
log(
p
T
/
M
q
)
Gyulassy
,
Levai
, and
Vitev
, NPB571 (2000)
Slide11MIT CTP Seminar
11High Momentum Particles in AdS/CFT
Model heavy quark jet energy loss by embedding string in AdS space
dpT/dt = -
m pT
m
=
pl
1/2
T
2
/2M
q
J
Friess
, S Gubser
, G Michalogiorgakis, S Pufu, Phys Rev D75
(2007)10/4/2011
Similar to Bethe-
HeitlerdpT/dt
~ -(T3/Mq
2) pT
Very different from
usual
pQCD
and LPM
dp
T
/
dt
~ -LT
3
log(
p
T
/
M
q
)
Slide12Light Quark and Gluon E-Loss
10/4/2011MIT CTP Seminar
12
D
L
q
therm
~ E
1/3
D
L
q
therm
~ (2E)
1/3
See also
Marquet
and
Renk, PLB685 (2010), and
Jia, WAH, and Liao, arXiv:1101.0290, for v2
Gubser et al., JHEP0810 (2008)Chesler et al., PRD79 (2009)Arnold and
Vaman, JHEP 1104 (2011)
SS Gubser, QM08
Chesler
et al., PRD79 (2009)
Light quarks and gluons: generic Bragg peak
Leads to lack of T dependence?
Slide13Common variables used are transverse momentum,
pT, and angle with respect to the reaction plane, f
MIT CTP Seminar
13
High-p
T
Observables
Naively
: if medium has no effect, then
R
AA
= 1
Fourier
expand
R
AA
:
10/4/2011
p
T
f
,
g
,
e
-
Slide14MIT CTP Seminar
14pQCD Success at RHIC:
Consistency: R
AA
(
h
)~R
AA
(
p
)
Null Control: R
AA
(
g
)~1
GLV Prediction: Theory~Data
for reasonable fixed L~5 fm and dNg
/dy~dNp/
dy
Y. Akiba for the PHENIX collaboration, hep-ex/0510008
(circa 2005)
10/4/2011
Slide15pQCD Picture Inadequate at RHIC
Lack of simultaneous description of multiple observableseven with inclusion of elastic loss
10/4/2011
MIT CTP Seminar
15
Wicks et al., NPA784, 2007
PHENIX, PRL 105 (2010)
Pert. at LHC energies?
See also J
Jia
from QM09,
J Nagle QM09
Slide16Qualitative Expectations for LHC
For approx. power law production and energy loss probability P(e), e = (E
i - Ef)/E
i
10/4/2011
MIT CTP Seminar
16
Asymptotically, pQCD =>
D
E/E ~
log(E/
m
)/E
~ flat R
AA
(
p
T
)
at RHIC
Rising R
AA
(
p
T
)
at LHC
NB: LHC is a glue machine
Slide17pQCD at LHC?
10/4/2011
MIT CTP Seminar
17
Appelshauser
, ALICE, QM11
p
T
rise in data readily understood from generic perturbative physics!
Slide18Rise in RAA a Final State Effect?
Is rise really due to pQCD?Or other quench (flat?) + initial state CNM effects a la CGC?
10/4/2011
MIT CTP Seminar
18
Albacete and
Marquet
, PLB687 (2010)
PHENIX PRL98, 2007
Y-J Lee, QM11
Require p + A and/or direct
g
Slide19Qual Norm of RAA
From RHIC to LHC10/4/2011MIT CTP Seminar
19
WAH and M
Gyulassy
, arXiv:1104.4958
Suppression from RHIC to LHC
generically
increases
Assume QGP density scales with observed particle multiplicity: ~2.5x more dense than RHIC
ALICE, PRL105, 2010
Slide20Quant. (Qual?) Conclusions Require...
Further experimental resultsTheoretically, investigation of the effects ofhigher orders in
as (large)
kT/xE (large
)MQ/E (large?)
opacity (large?)
geometry
uncertainty in IC (small)
coupling to flow (large?)
Eloss
geom. approx. (?)
t
<
t
0 (large: see Buzzatti
and Gyulassy)dyn. vs. static centers (see Buzzatti
and Gyulassy)hydro background (see Renk, Majumder)
better treatment ofCoh. vs. decoh.
multigluons (see Mehtar-Tani)elastic E-lossE-loss in confined matter
10/4/2011MIT CTP Seminar
20
Slide21Varying a
s has huge effect<e
>rad,pQCD ~ as
3; <e>
el,pQCD ~ as
2
Role of running coupling, irreducible uncertainty from non-pert. physics?
Nontrivial changes from better elastic treatment
10/4/2011
MIT CTP Seminar
21
S Wicks, PhD Thesis
Slide22Quantifying Sensitivity to Geometry IC
KLN CGC vs. WS Glaub. and rotating RP
Effect not large enough for pQCD
10/4/2011MIT CTP Seminar
22
Effects of geom. on, e.g. v
2
, might be quite large
Possibly truly extreme
initial geometry?
See also
Renk
et al., PRC83 (2011),
Jia
, WH, Liao, 1101.0290
Betz,
Gyulassy
, and
Torrieri
, arXiv:1102.5416 [
nucl-th
]
Slide23Aside: pQCD and Jet Measurements
CMS sees redistribution of lost energy at large anglesNaive pQCD expectation: collinear radiation10/4/2011
MIT CTP Seminar
23
Wyslouch
, CMS, QM11
Slide24pQCD and Wide Angle Radiation
Naively, pQCD => xtypical, q
typical ~ m/E;
m ~ 0.5 GeVAll
current Eloss calculations assume small angle emission (
k
T
<<
xE
)
Collinear approximation is (maximally) violated;
x
typ
~
m/EpQCD not obviously inconsistent
10/4/2011MIT CTP Seminar
24
WAH and B Cole, PRC81, 2010
C Roland, CMS, QM11
B Cole, ATLAS, QM11
z
Slide25Quantification of Collinear Uncertainty
Factor ~ 3 uncertainty in extracted medium density!“qhat
” values from different formalisms consistent w/
i unc.
10/4/2011
MIT CTP Seminar
25
WAH and B Cole, PRC81, 2010
Slide26Coll. Approx. and Constrained v2
Fix dNg/dy from R
AA, calculate v2Expect: larger v
2 for smaller opening anglet
coh = xE/k
T
2
larger for smaller
q
max
more paths in deep LPM (
D
E ~ L
2
) region
Not large sensitivity
10/4/2011
MIT CTP Seminar
26
Rad
Only
Rad
+ El
WAH,
in preparation
v
2
p
T
20-30%
p
0
20-30%
p
0
v
2
p
T
Slide27Geometry, Early Time Investigation
Significant progress madeFull geometry integration, dynamical scattering centersRHIC suppression with dNg
/dy = 1000Large uncertainty due to unconstrained, non-equilibrium
t < t0
physicsFuture work: higher orders in opacity
10/4/2011
MIT CTP Seminar
27
Buzzatti
and
Gyulassy
, 1106.3061
Slide28With Caveats in Mind...
Quantitatively compare a parameter free “prediction” from WHDG for LHC, rigorously constrained by RHIC
Increase density at LHC by observed increase in particle multiplicity
10/4/2011
MIT CTP Seminar
28
PHENIX PRC77, 2008
Slide29WHDG band from 1-
s
RHIC
dN
g
/
dy
extraction
Note that
constrained predictions have small uncertainty from collinear approx
WHDG
p
0
R
AA
at LHC: First Results
Constrain WHDG at RHIC
Make LHC predictions assuming
dN
g
/dy ~ dN
ch/dh=> dNg
LHC/dy = 2.4 dNgRHIC
/dy
10/4/2011
MIT CTP Seminar
29
WAH and M
Gyulassy
, arXiv:1104.4958
Data shown at Kruger2010
Slide30ALICE Published Results
NB: ALICE unmeasured p + p interpolation > LO pQCDAlso, small reported unc. in Nbin
Fluctuations important at large centralities
10/4/2011
MIT CTP Seminar
30
WAH and M
Gyulassy
,
arXiv:1104.4958
Slide31WHDG Compared to RCP
Examine RCP, ratio of central to peripheral RAA
10/4/2011
MIT CTP Seminar
31
p + p
unc
ertainty
cancels
0-5% R
AA
to
70-80% R
AA
Validity of E-loss in very peripheral collisions?
WAH and M
Gyulassy
, arXiv:1104.4958
Slide32WHDG Describes RAA
and v2?
Fixed by RHIC data, parameter-free WHDG describes preliminary R
AA and v2 quite wellv
2 at very high pT
?
10/4/2011
MIT CTP Seminar
32
Y-J Lee, QM11 and
cdsweb.cern.ch/record/1352777
WAH and M
Gyulassy
,
arXiv:1107.2136
Slide33NB: R
AA requires production, E-loss, FFDoes not immediately follow that R
pAA << RDAA
<< RBAA
And D RAA
at LHC?
10/4/2011
MIT CTP Seminar
33
WAH and M
Gyulassy
, arXiv:1107.2136
Slide34MIT CTP Seminar
34AdS/CFT at RHIC
String drag: qualitative agreement in heavy flavor sector
WAH
,
PhD Thesis
10/4/2011
Akamatsu
,
Hatsuda
, and Hirano, PRC79, 2009
Slide35AdS/CFT Energy Loss and Distribution
10/4/2011MIT CTP Seminar
35
2.76
TeV
In AdS/CFT, heavy quarks: wide angle energy loss
Jo Noronha, M
Gyulassy
, and G
Torrieri
, PRL102 (2009)
WAH,
in preparation
0.2
TeV
Simple Bragg peak model
Slide36MIT CTP Seminar
36
LHC R
cAA(pT)/R
bAA(pT) Prediction
(with speed limits)
T(
t
0
):
“(”,
corrections
likely small for
smaller
momenta
T
c
: “]”, corrections likely large for
higher momenta
WAH, M. Gyulassy, PLB666 (2008)
10/4/2011Qualitatively, corrections to
AdS/CFT result will drive double ratio to unity
Slide37Measuring the Initial Gluon State
What is the spatial distribution of gluons in a highly boosted nucleus?What are the initial conditions fed into hydro in HIC?10/4/2011
MIT CTP Seminar
37
T Hirano, et al.,
Phys.Lett.B636, 2006
Slide38h/s Extraction
Factor at least 2 uncertainty in h/s from ICNaive pQCD => h/s ~ 1
Naive AdS/CFT => h/s ~ 1/4
p
10/4/2011
MIT CTP Seminar
38
Teaney
, Users’ Meeting 2011
Slide39IC from Higher Harmonics
10/4/2011MIT CTP Seminar
39
Chen et al., arXiv:1106.6350
Slide40Measuring the IC
eRHIC could give experimental handle on initial geometryRecall e + A diffraction exps. on A at rest
10/4/2011
MIT CTP Seminar
40
Hahn, Ravenhall, and Hofstadter, Phys Rev 101 (1956)
Slide41Gluon Distribution of A at x ~ 10-3
10/4/2011MIT CTP Seminar
41
Coherent vector meson production in e + A
e
J/
y
A
e
A
g
*
Must reject incoherent
collisions at ~100%
WAH, arXiv:1102.5058
Slide42Conclusions (1 of 2)
Does rise in RAA(pT) imply perturbative E-loss dominant at LHC?To make a qualitative statement need:
Experimental control over production effectsReduced exp. uncertainties at large (~100 GeV/c)
pTConsistency check btwn
pQCD and multiple observables at large (~100 GeV/c) p
T
, especially v
2
Recent LHC Results:
Published ALICE R
AA
suppression generically difficult to understand in typical
dE
/
dx picture (both pQCD and AdS/CFT)E-loss in (currently) uncontrolled pre-thermalization dynamics?Possibly signal of AdS/CFT Bragg peak physics
Soft particle energy loss at very wide anglesNot inconsistent with pQCD or AdS/CFT pictures
10/4/2011MIT CTP Seminar
42
Slide43Conclusions (2 of 2)
WHDG zero parameter LHC predictions constrained by RHIC appear to:(Possibly) systematically oversuppress light hadron R
AADescribe light hadron v2
at “intermediate” pT ~ 20 GeV
/cDescribe D meson suppressionCAUTION: many important effects not currently under theoretical control
HOWEVER: qualitative agreement suggests continued effort interesting and worthwhile
AdS
Eloss
: consistent with RHIC and LHC within large theoretical uncertainties
Looking forward to exciting future distinguishing measurements, esp. heavy quark suppression separation
Exciting prospects for measuring initial spatial distribution of gluons in a highly relativistic nucleus at an EIC
10/4/2011
MIT CTP Seminar
43