Two “particle” correlations at...
Transcript of Two “particle” correlations at...
Two “particle” correlations at RHIC
JET Workshop - LBNLHelen Caines - Yale University
June 18th 2010
Outline:hadron-hadrongamma-hadronjet-hadron
Friday, June 18, 2010
JET Workshop - June 18th 2010Helen Caines
Di-hadron correlations in 1976
2
P. Darriulat et al. NPB107 (1976) 429 ISR √s=53 GeVEvent-by-event analysis of rapidity correlation
Trigger: π0 pT>2 GeV/c
Assoc: Charged particle |180-Φ|<350
px>1.5 GeV/c(px component along π0 axis)
“Structure of Final States with a high pT π0 in p-p collisions”
“..these properties are surprisingly reminiscent of the co-planar two-jet picture first given by Berman, Bjorken & Kogut in the
frame of quark parton models”
Friday, June 18, 2010
JET Workshop - June 18th 2010Helen Caines
Di-hadron correlations in 1982
3
pT,Trig > 4 GeV/ca) pT,Assoc > 0 GeV/cb) pT,Assoc > 1 GeV/cc) pT,Assoc > 2 GeV/c
(note the lack of axis labels)
UA1 PL 118B (1982) 173
“1st observation of correlations between high pT charged particle at the SppS”-
“As at the ISR, hard scattering and fragmentation of partons offers a possible explanation”
Friday, June 18, 2010
JET Workshop - June 18th 2010Helen Caines
Di-hadron correlations in 2003
4
p-p correlations form 3 distinct regions:near-side, away-side, transverse region (underlying event)
Same is true in d-Au
Scattered parton approximated by high pT particle
steeply falling jet spectrum at RHIC behind this assumption
PRL 90, 082302
Di-hadron correlations still used as proxy for jet reconstruction
Friday, June 18, 2010
JET Workshop - June 18th 2010Helen Caines
Di-hadron in A-A - new features
5
After background subtraction:
PRC 78 (2008) 014901
PHENIX
“Mach Cones” “Ridges”
Medium response to hard scattered partons?Results of energy lost by hard scattered partons?
Something else?
PRC 80 (2009) 064912
STAR
Friday, June 18, 2010
Chen HP08
JET Workshop - June 18th 2010Helen Caines
“Ridge” and “Shoulder” properties
6
STAR Preliminary
PHENIX
M. McCumber QM2008 pTassoc (GeV/c)
McCumber QM08
Similar in spectral shape and flavor composition to bulk
Friday, June 18, 2010
Chen HP08
JET Workshop - June 18th 2010Helen Caines
“Ridge” and “Shoulder” properties
6
STAR Preliminary
PHENIX
M. McCumber QM2008 pTassoc (GeV/c)
McCumber QM08
Similar in spectral shape and flavor composition to bulkRidge ∝ Npart independent of system
C.NattrassQM08
Friday, June 18, 2010
Chen HP08
JET Workshop - June 18th 2010Helen Caines
“Ridge” and “Shoulder” properties
6
STAR Preliminary
PHENIX
M. McCumber QM2008 pTassoc (GeV/c)
McCumber QM08
Similar in spectral shape and flavor composition to bulk
Ridge/Jet yield same for √s=62 and 200 GeV
C.NattrassQM08
Ridge ∝ Npart independent of system
C.NattrassQM08
Friday, June 18, 2010
JET Workshop - June 18th 2010Helen Caines
Two component model - ZYAM
7
Analyses assume correlations can be split into two sources the “jet” and the “background”
(rad)!"-1 0 1 2 3 4
!"
/dA
B d
NA
1/N
0.8
1
1.2
1.4
1.6
1.8
2
2.2
Narrow peaks: well-separated
bkg
N.S. + bkg
A.S. + bkg
N.S. + A.S. + bkg
Narrow peaks: well-separated
Simulation A. Adare
(rad)!"-1 0 1 2 3 4
!"
/dA
B d
NA
1/N
0.8
1
1.2
1.4
1.6
1.8
2
2.2
Broad peaks overlap: ZYAM bkg. too high
bkgN.S. + bkg
A.S. + bkg
N.S. + A.S. + bkg 10%)±
2ZYAM bkg (v
Broad peaks overlap: ZYAM bkg. too high
Simulation A. Adare
ZYAM incorrect for broad jet peaksBackground subtraction is non-trivial
PHENIX now use an absolute background normalization A. Sickles et al. PRC 81 014908 (2010)
Friday, June 18, 2010
Bo(1 + 2vAB2 cos2!!)
JET Workshop - June 18th 2010Helen Caines
Two component model - Flow contribution
8
Analyses assume correlations can be split into two sources the “jet” and the “background”
Background approximated via:
DIHADRON AZIMUTHAL CORRELATIONS IN Au+Au . . . PHYSICAL REVIEW C 78, 014901 (2008)
elliptic flow. The pair distribution can be expressed as
N same(!") = #!1 + 2va
2vb2 cos 2!"
"Nmixed(!") + Jet(!")
(10)
Where the Jet(!") represents all pairs from (di)jets. Theintegral of N same can be written as
#d!"N same(!") = Nevts!nanb" +
#d!"Jet(!"). (11)
Comparing to Eq. (9), we obtain
# = !nanb"!na"!nb"
. (12)
Thus, # is simply the ratio of the trigger-partner combinatoricrate in the same event to that in mixed events, which canbe bigger than unity because of centrality smearing (seediscussion in Sec. III E). An alternative approach used to fix #is to assume that the jet function has zero yield at its minimum!"min (ZYAM) [18,52].
Finally, the ratio of jet-induced pairs to combinatoric pairsfrom mixed events, the jet-induced hadron-pair ratio (JPR) isgiven by
JPR(!") # Jet(!")Nmixed(!")
= N same(!")Nmixed (!")
$ #!1 + 2va
2vb2 cos 2!"
". (13)
A representative correlation function is given in Fig. 2 for 0–5% Au+Au collisions and for triggers and partners in 2–3 and1–2 GeV/c, respectively. It shows a peak around !" % 0 and abroad structure around !" % $ . The dashed line indicates theestimated elliptic flow modulated background via the ZYAMmethod. The area between the data points and the dashed linereflects the jet-induced pair ratio. It is only a few percentrelative to the background level.
We define %a, %b as the single particle efficiency withinthe PHENIX pseudorapidity acceptance (|&| < 0.35). The truenumbers of triggers and partners are given by
$na
0
%=
$na%&%a;
$nb
0
%=
$nb
%&%b. (14)
(rad)!"0 2 4
)!"C
(
0.99
1
1.01
1.02
1.030-5%
<3 GeV/caT
<2<pbT
1<p
FIG. 2. (Color online) Correlation function for 2 < paT < 3, 1 <
pbT < 2 GeV/c in 0–5% Au+Au collisions. The dashed line represents
the estimated elliptic flow modulated combinatoric background usingzero yield at minimum (ZYAM) method (see Sec. III E).
For uncorrelated sources, the triggers and partners are uniformin azimuth. Thus the true combinatoric pair distribution formixed events is flat with !" with a density of !na
0"!nb0"/(2$ ).
The yield of jet-induced pairs per event (JPY) is given as theproduct of the combinatoric pair rate and the hadron-pair ratio,
JPY(!") =$na
0
%$nb
0
%
2$JPR(!") = !na"!nb"
2$%a%bJPR(!")
='
d!"Nmixed(!")2$Nevts%a%b
(N same(!")Nmixed(!")
$ #!1 + 2va
2vb2 cos 2!"
"). (15)
Thus far, we have made no distinction between triggerand partner hadrons. As discussed earlier in Sec. II, thecorrelation function, hadron-pair ratio, and hadron-pair yieldare symmetric between the trigger and partner pT , i.e.,
C!pa
T , pbT
"= C
!pb
T , paT
",
JPR!pa
T , pbT
"= JPR
!pb
T , paT
", (16)
JPY!pa
T , pbT
"= JPY
!pb
T , paT
".
The associated partner yield per trigger, Yjet ind(!") is ob-tained by dividing the hadron-pair yield per event with thenumber of triggers per event,
Yjet ind(!") = JPY(!")na
0=
'd!"Nmixed(!")
2$Na%b
&(
N same(!")Nmixed(!")
$ #!1 + 2va
2vb2 cos 2!"
").
(17)
Yjet ind is often referred to as the per-trigger yield or conditionalyield. It is clearly not invariant to the exchange of trigger andpartner pT .
The analysis proceeds in the following steps. We firstmeasure the correlation function of Eq. (8). We then obtainthe efficiency for partner hadrons (%b) and the elliptic flowcoefficients for the two hadron categories (va
2 , vb2 ). We then
determine the background level (# ) via the ZYAM backgroundsubtraction method (see Sec. III E), followed by a calculationof the per-trigger yield according to Eq. (17). Subsequently,we obtain the hadron-pair yield by multiplying the per-triggeryield with the inclusive charged hadron yield [6] integrated inthe corresponding trigger pT range.
According to Eq. (6), the hadron-pair yields calculatedfrom the per-trigger yields are independent of which hadron,from the pair, is used as trigger. We used this fact to cross-checkthe efficacy of our analysis. Figure 3 compares the hadron-pairyields obtained when the trigger and partner pT is exchangedin p + p collisions (in pa
T ' pbT ). The open symbols indicate
the results for low-pT trigger hadrons in association withhigh-pT partners. The filled symbols show the converse. Asimilar comparison for 0–20% Au+Au collisions is shownin Fig. 4. Overall good agreement is indicated by thesedistributions. It is important to emphasize here that there isno a priori reason for these distributions to be identical, sincethe cuts on trigger and partner hadrons are a little different(cf. Sec. III B) and therefore could lead to somewhat different
014901-7
PRC 78 014901 (2008)
Higher moments of the expansion ignored
Friday, June 18, 2010
Bo(1 + 2vAB2 cos2!!)
JET Workshop - June 18th 2010Helen Caines
Two component model - Flow contribution
8
Analyses assume correlations can be split into two sources the “jet” and the “background”
Background approximated via:
DIHADRON AZIMUTHAL CORRELATIONS IN Au+Au . . . PHYSICAL REVIEW C 78, 014901 (2008)
elliptic flow. The pair distribution can be expressed as
N same(!") = #!1 + 2va
2vb2 cos 2!"
"Nmixed(!") + Jet(!")
(10)
Where the Jet(!") represents all pairs from (di)jets. Theintegral of N same can be written as
#d!"N same(!") = Nevts!nanb" +
#d!"Jet(!"). (11)
Comparing to Eq. (9), we obtain
# = !nanb"!na"!nb"
. (12)
Thus, # is simply the ratio of the trigger-partner combinatoricrate in the same event to that in mixed events, which canbe bigger than unity because of centrality smearing (seediscussion in Sec. III E). An alternative approach used to fix #is to assume that the jet function has zero yield at its minimum!"min (ZYAM) [18,52].
Finally, the ratio of jet-induced pairs to combinatoric pairsfrom mixed events, the jet-induced hadron-pair ratio (JPR) isgiven by
JPR(!") # Jet(!")Nmixed(!")
= N same(!")Nmixed (!")
$ #!1 + 2va
2vb2 cos 2!"
". (13)
A representative correlation function is given in Fig. 2 for 0–5% Au+Au collisions and for triggers and partners in 2–3 and1–2 GeV/c, respectively. It shows a peak around !" % 0 and abroad structure around !" % $ . The dashed line indicates theestimated elliptic flow modulated background via the ZYAMmethod. The area between the data points and the dashed linereflects the jet-induced pair ratio. It is only a few percentrelative to the background level.
We define %a, %b as the single particle efficiency withinthe PHENIX pseudorapidity acceptance (|&| < 0.35). The truenumbers of triggers and partners are given by
$na
0
%=
$na%&%a;
$nb
0
%=
$nb
%&%b. (14)
(rad)!"0 2 4
)!"C
(
0.99
1
1.01
1.02
1.030-5%
<3 GeV/caT
<2<pbT
1<p
FIG. 2. (Color online) Correlation function for 2 < paT < 3, 1 <
pbT < 2 GeV/c in 0–5% Au+Au collisions. The dashed line represents
the estimated elliptic flow modulated combinatoric background usingzero yield at minimum (ZYAM) method (see Sec. III E).
For uncorrelated sources, the triggers and partners are uniformin azimuth. Thus the true combinatoric pair distribution formixed events is flat with !" with a density of !na
0"!nb0"/(2$ ).
The yield of jet-induced pairs per event (JPY) is given as theproduct of the combinatoric pair rate and the hadron-pair ratio,
JPY(!") =$na
0
%$nb
0
%
2$JPR(!") = !na"!nb"
2$%a%bJPR(!")
='
d!"Nmixed(!")2$Nevts%a%b
(N same(!")Nmixed(!")
$ #!1 + 2va
2vb2 cos 2!"
"). (15)
Thus far, we have made no distinction between triggerand partner hadrons. As discussed earlier in Sec. II, thecorrelation function, hadron-pair ratio, and hadron-pair yieldare symmetric between the trigger and partner pT , i.e.,
C!pa
T , pbT
"= C
!pb
T , paT
",
JPR!pa
T , pbT
"= JPR
!pb
T , paT
", (16)
JPY!pa
T , pbT
"= JPY
!pb
T , paT
".
The associated partner yield per trigger, Yjet ind(!") is ob-tained by dividing the hadron-pair yield per event with thenumber of triggers per event,
Yjet ind(!") = JPY(!")na
0=
'd!"Nmixed(!")
2$Na%b
&(
N same(!")Nmixed(!")
$ #!1 + 2va
2vb2 cos 2!"
").
(17)
Yjet ind is often referred to as the per-trigger yield or conditionalyield. It is clearly not invariant to the exchange of trigger andpartner pT .
The analysis proceeds in the following steps. We firstmeasure the correlation function of Eq. (8). We then obtainthe efficiency for partner hadrons (%b) and the elliptic flowcoefficients for the two hadron categories (va
2 , vb2 ). We then
determine the background level (# ) via the ZYAM backgroundsubtraction method (see Sec. III E), followed by a calculationof the per-trigger yield according to Eq. (17). Subsequently,we obtain the hadron-pair yield by multiplying the per-triggeryield with the inclusive charged hadron yield [6] integrated inthe corresponding trigger pT range.
According to Eq. (6), the hadron-pair yields calculatedfrom the per-trigger yields are independent of which hadron,from the pair, is used as trigger. We used this fact to cross-checkthe efficacy of our analysis. Figure 3 compares the hadron-pairyields obtained when the trigger and partner pT is exchangedin p + p collisions (in pa
T ' pbT ). The open symbols indicate
the results for low-pT trigger hadrons in association withhigh-pT partners. The filled symbols show the converse. Asimilar comparison for 0–20% Au+Au collisions is shownin Fig. 4. Overall good agreement is indicated by thesedistributions. It is important to emphasize here that there isno a priori reason for these distributions to be identical, sincethe cuts on trigger and partner hadrons are a little different(cf. Sec. III B) and therefore could lead to somewhat different
014901-7
PRC 78 014901 (2008)
Higher moments of the expansion ignored
Recent work indicates that v3 may be important!
B. Alver & G. Roland PRC 81 (2010) 054905
Friday, June 18, 2010
B. Alver & G. Roland PRC 81 (2010) 054905
dN
d!=
N
2"(1 +
!2vncos(n(!!!n)))
v2 = !cos(2(! " !2))#, v3 = !cos(3(! " !3))#
JET Workshop - June 18th 2010Helen Caines
“Triangular” flow
9
B. Alver & G. Roland PRC 81 (2010) 054905 Triangular anisotropic initial conditions
→ v3 of particles in final state
What’s So Odd About the Ridge and Cone?
15
low pT ridge yield
STAR Preliminary
Mv32
Y. Pandit and P. Sorensen:
Fourier Transform of data from STAR,
Phys. Rev. Lett. 95 (2005) 152301
Large possible <v32> component in intermediate pT data
Centrality dependence is similar to the low pT ridge
P. Sorensen and Y. Pandit SQM2009
Npart
Fourier transform STAR data PRL95 (2005) 152301
v3sizable even in central events
Friday, June 18, 2010
JET Workshop - June 18th 2010Helen Caines
v3 effect on measured correlations
10
After subtracting 1st 3 fourier components: residuals in large Δη almost flat i.e.
the non-triggered ridge appears to have disappeared
B. Alver & G. Roland PRC 81 (2010) 054905
arXiv:0806.0513
Since v3 peaks at 1200 could also explain the “mach cone”Could also explain why ridge and shoulder are so “bulk like”
“simple” explanation - Needs further verification
Friday, June 18, 2010
JET Workshop - June 18th 2010Helen Caines
High pT di-hadron correlations
11
7
!"
dN
/dtr
ig1/N
0
0.5
1
< 3.0 GeV/ctrig
T2.5 < p
< 1.0 GeV/cassoc
T0.5 < p
0
0.2
0.4
< 1.5 GeV/cassoc
T1.0 < p
0
0.2
0.4
< 2.5 GeV/cassoc
T1.5 < p
-1 0 1 2 3 4 5
0
0.1
0.2
< 4.0 GeV/cassoc
T2.5 < p
0
0.5
1
< 4.0 GeV/ctrig
T3.0 < p
0
0.2
0.4
Au+Au 0-12%| < 0.7#"Au+Au |
d+Au
0
0.2
0.4
-1 0 1 2 3 4 5
0
0.1
0.2
0
0.5
1
< 6.0 GeV/ctrig
T4.0 < p
0
0.2
0.4
0
0.2
0.4
-1 0 1 2 3 4 5
0
0.1
0.2
0
0.5
1
< 10.0 GeV/ctrig
T6.0 < p
0
0.2
0.4
0
0.2
0.4
!"-1 0 1 2 3 4 5
0
0.1
0.2
FIG. 3: Background-subtracted azimuthal angle di!erence distributions for di!erent ptrigT (columns) and passocT (rows) in 0-12%central Au+Au collisions (solid circles) and d+Au reference results (open circles). The rapidity range is |!| < 1 and as a resultthe rapidity-di!erence |"!| < 2. Open red squares show results for a restricted acceptance of |"!| < 0.7, using tracks with|!| < 1
. The solid and dashed histograms show the upper and lower range of the systematic uncertainty due to the v2 modulation ofthe subtracted background.
smaller than in d+Au. For 6 < ptrigT < 10 GeV/c (right-most column in Fig. 3), a narrow peak appears at largepassocT in Au+Au, similar to what is seen in d+Au colli-sions and at higher pT in Au+Au collisions [7].
Although the shape of the away-side distributionchanges with ptrigT and passocT , there seems to be no grad-ual broadening as a function of pT : the rising flanks of
the away-side distribution are at similar !! in the entirerange 0.5 < passocT < 2.5 GeV/c and 2.5 < ptrigT < 6. Infact, it could be argued that the away-side distributionis as broad as possible; there is no !! region withoutcorrelation signal.
The broad away-side correlation structure in Au+Aucollisions is a truly remarkable observation. Although
At high pT trigger and assoc. particles:
BG small errors in ZYAM, v2, v3,... become negligible
STARarXiV:1004.2377
For higher pT triggers (stronger jet bias)away side “mach cone” no longer visible
Modification/redistribution of jet energy apparent
Friday, June 18, 2010
JET Workshop - June 18th 2010Helen Caines
π0-h correlations
12
PHENIX arXiv:1002.1077v2, Accepted by PRL
0
0.1
0.2
0.3
0
0.1
0.2
0.3 0.5-1 GeV/c!4-5
0
0.2
0.4
0
0.2
0.4 1-2 GeV/c!5-7
0 2 4
0
0.2
0.4
0.6
0 2 4
0
0.2
0.4
0.6 1-2 GeV/c!7-9
2-3 GeV/c!4-5 (x 3.0)
0-20% Au+Aup+p
3-5 GeV/c!5-7 (x 3.0)
2 3 4
0 2 40 2 4
3-5 GeV/c!7-9 (x 2.0)
2 3 4
"#
/d
pair
dN
0 $1/
N
(rad)"#
0
0.1
0.2
0.3
0
0.1
0.2
0.3 0.5-1 GeV/c!4-5
0
0.2
0.4
0
0.2
0.4 1-2 GeV/c!5-7
0 2 4
0
0.2
0.4
0.6
0 2 4
0
0.2
0.4
0.6 1-2 GeV/c!7-9
2-3 GeV/c!4-5 (x 3.0)
0-20% Au+Aup+p
3-5 GeV/c!5-7 (x 3.0)
2 3 4
0 2 40 2 4
3-5 GeV/c!7-9 (x 2.0)
2 3 4
"#
/d
pair
dN
0 $1/
N
(rad)"#
0
0.1
0.2
0.3
0
0.1
0.2
0.3 0.5-1 GeV/c!4-5
0
0.2
0.4
0
0.2
0.4 1-2 GeV/c!5-7
0 2 4
0
0.2
0.4
0.6
0 2 4
0
0.2
0.4
0.6 1-2 GeV/c!7-9
2-3 GeV/c!4-5 (x 3.0)
0-20% Au+Aup+p
3-5 GeV/c!5-7 (x 3.0)
2 3 4
0 2 40 2 4
3-5 GeV/c!7-9 (x 2.0)
2 3 4
"#
/d
pair
dN
0 $1/
N
(rad)"#
π0 correlations same as h± correlations
Friday, June 18, 2010
JET Workshop - June 18th 2010Helen Caines
π0-h correlations
12
At high pT:
Away-side suppressed
PHENIX arXiv:1002.1077v2, Accepted by PRL
0
0.1
0.2
0.3
0
0.1
0.2
0.3 0.5-1 GeV/c!4-5
0
0.2
0.4
0
0.2
0.4 1-2 GeV/c!5-7
0 2 4
0
0.2
0.4
0.6
0 2 4
0
0.2
0.4
0.6 1-2 GeV/c!7-9
2-3 GeV/c!4-5 (x 3.0)
0-20% Au+Aup+p
3-5 GeV/c!5-7 (x 3.0)
2 3 4
0 2 40 2 4
3-5 GeV/c!7-9 (x 2.0)
2 3 4
"#
/d
pair
dN
0 $1/
N
(rad)"#
0
0.1
0.2
0.3
0
0.1
0.2
0.3 0.5-1 GeV/c!4-5
0
0.2
0.4
0
0.2
0.4 1-2 GeV/c!5-7
0 2 4
0
0.2
0.4
0.6
0 2 4
0
0.2
0.4
0.6 1-2 GeV/c!7-9
2-3 GeV/c!4-5 (x 3.0)
0-20% Au+Aup+p
3-5 GeV/c!5-7 (x 3.0)
2 3 4
0 2 40 2 4
3-5 GeV/c!7-9 (x 2.0)
2 3 4
"#
/d
pair
dN
0 $1/
N
(rad)"#
π0 correlations same as h± correlations
Shape the same
Friday, June 18, 2010
JET Workshop - June 18th 2010Helen Caines
away
head
Away-side IAA vs RAA
13
At high pT, IAA > RAA
PHENIX arXiv:1002.1077v2, Accepted by PRL
-110
1
= 4-5 GeV/cT p0!
0-20% Au+Au5-7 GeV/c6% scale uncertainty
/2)!| < ! - "#away (|/6)!| < ! - "#head (|
0 1 2 3 4 5 6 7-110
1
7-9 GeV/c > 5 GeV/c
T p0
!, $ AA R% = 1.68 GeV/fm0&ZOWW,
0.6±ACHNS, K = 4.1
0 1 2 3 4 5 6 7
9-12 GeV/c
(GeV/c)T
partner p
AAII A
A=
(Nta
/Nt )
Au+
Au
(Nta
/Nt )
p+
p
Friday, June 18, 2010
JET Workshop - June 18th 2010Helen Caines
away
head
Away-side IAA vs RAA
13
At high pT, IAA > RAA
PHENIX arXiv:1002.1077v2, Accepted by PRL
-110
1
= 4-5 GeV/cT p0!
0-20% Au+Au5-7 GeV/c6% scale uncertainty
/2)!| < ! - "#away (|/6)!| < ! - "#head (|
0 1 2 3 4 5 6 7-110
1
7-9 GeV/c > 5 GeV/c
T p0
!, $ AA R% = 1.68 GeV/fm0&ZOWW,
0.6±ACHNS, K = 4.1
0 1 2 3 4 5 6 7
9-12 GeV/c
(GeV/c)T
partner p
AAII A
A=
(Nta
/Nt )
Au+
Au
(Nta
/Nt )
p+
p
< 5 GeV/cAT4 < p
partN
< 7 GeV/cBT3 < p
Inclusive
(GeV
/c)’>
T
Head
Reg
ion
<p
0.5
1
1.5
3002001000 400
PHENIX PRC 78 (2008) 014901
Away-side spectrum harder than bulk Same ΔE, IAA > RAA
Friday, June 18, 2010
JET Workshop - June 18th 2010Helen Caines
Theoretical Comparison
14
-110
1
= 4-5 GeV/cT p0!
0-20% Au+Au5-7 GeV/c6% scale uncertainty
/2)!| < ! - "#away (|/6)!| < ! - "#head (|
0 1 2 3 4 5 6 7-110
1
7-9 GeV/c > 5 GeV/c
T p0
!, $ AA R% = 1.68 GeV/fm0&ZOWW,
0.6±ACHNS, K = 4.1
0 1 2 3 4 5 6 7
9-12 GeV/c
(GeV/c)T
partner p
AAI
ZOWW
Reasonable agreement with data
ACHNS
Consistently falls below data
ASW energy loss + full hydro evolution
Uses a simple hard sphere geometry
Is energy loss mechanism or medium geometry the crucial difference?
PHENIX arXiv:1002.1077v2, Accepted by PRL
Both model calculations fit RAA
Uses simple hard sphere geometry
Friday, June 18, 2010
JET Workshop - June 18th 2010Helen Caines
Npart dependence
15
T*dN/dz
trig
1/N
-110
1
d-AuCu-Cu 0-10%Cu-Cu 20-40%Cu-Cu 40-60%Au-Au 0-12%p-p MFMCu-Cu 0-10% MFMCu-Cu 20-40% MFMCu-Cu 40-60% MFM
Tz0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
) T(z
AAI
0
0.5
1
1.5
Figure 5: Away-side associated particle distribution and IAA for 6 <ptrig
T <10 GeV/c. The error bars represent statistical errors and the boxesrepresent the total systematic errors. The lines represent calculations in MFMmodel.
collisions, indicated by di!erent line styles in the figure.For the lower trigger selection, 4 GeV/c < ptrig
T < 6 GeV/c, the ModifiedFragmentation Model predicts a smaller suppression than observed in the data,whereas PQM cannot explain Cu+Cu or Au+Au results in a consistent fashion.The disagreement between the models and the data suggests that the e!ectof kinematic limits (energy loss cannot be larger than the jet energy) and non-perturbative e!ects, which are not explicitly treated in the model, are significantin this pT -range. For the higher trigger pT range, 6 GeV/c < ptrig
T < 10 GeV/c,a better agreement between the data and MFM is observed. There is an obviousdi!erence between the system size dependence in the two models. While MFMobtains IAA values that are independent on the system at a certain Npart,PQM shows a clear di!erence between the two systems for similar Npart, whenusing a common scaling of the medium density (represented by line styles inthe figure). Further model studies are needed to clarify whether the di!erentscaling behavior in MFM and PQM is mainly a result of the di!erent quenchingformalisms or rather due to di!erences between the medium density models.
In Figs. 2 and 4 we have presented results for a single selection of asso-ciated hadrons, passoc
T > 3 GeV/c. A more di!erential measurement is pre-
10
MFMUses simple hard sphere geometrySeems to get trend of data correct
STAR PLB 683 (2010) 123 6<pTtrig<10 GeV/c
partN0 50 100 150 200 250 300 350
AAI
-110
1Au-Au Cu-Cu
=4qAu-Au PQM =3qCu-Cu PQM
=7qAu-Au PQM q=5.5Cu-Cu PQM
=14qAu-Au PQM =9qCu-Cu PQM
Au-Au MFM Cu-Cu MFM
(a)
partN0 50 100 150 200 250 300 350
AAI
-110
1Au-Au Cu-Cu
=4qAu-Au PQM =3qCu-Cu PQM
=7qAu-Au PQM q=5.5Cu-Cu PQM
=14qAu-Au PQM =9qCu-Cu PQM
Au-Au MFM Cu-Cu MFM
(b)
Figure 4: Npart dependence of the away-side associated-particle yield for
two trigger pT ranges: (a) 4 GeV/c < ptrigT < 6 GeV/c (b) 6 GeV/c <
ptrigT < 10 GeV/c. For both panels 3 GeV/c < passoc
T < ptrigT . The error bars
represent statistical errors and the boxes represent the point-to-point systematicerrors. The gray band represents the correlated error due to the statistical errorin the d+Au data. The lines represent calculations in PQM and MFM models.The values of q̂ are expressed in GeV2/fm.
pression factor IAA = Y awayAA /Y away
dAu , where Y awayAA(dAu) is the away-side di-hadron
correlation strength in heavy-ion and d+Au collisions, respectively. Figure 4shows the results for IAA as a function of number of participants for Cu+Cuand Au+Au collisions. The away-side yield suppression increases with Npart,as expected. The Cu+Cu results show a similar suppression (IAA) at the samenumber of participants as the Au+Au results, despite possible di!erences indensity and path length distributions.
Figure 4 also shows two model calculations implementing the same kine-matic cuts as our analysis.1 One calculation, the Parton Quenching Model(PQM) [5, 26], uses the Salgado-Wiedemann quenching weights [27] with aGlauber-overlap geometry in which the local density scales with the local den-sity of binary collisions !coll. The other model uses a next-to-leading order QCDcalculation with modified fragmentation functions from a higher-twist formal-ism [28] and a hard-sphere geometry where the density scales with the localparticipant density !part [6]. We refer to this model as the Modified Fragmen-tation Model (MFM). The MFM authors used previous data on the suppressionof high-pT away-side yields in central Au+Au collisions [4] to tune their model.The PQM authors present 3 calculations, based on 3 values of q̂ in central
1The model calculations use p+p as the reference, which is expected to be equivalent tothe d+Au measurement used in the data.
9
PQMGlauber overlap geometryMisses Cu-Cu dataNpart scaling of energy loss, frag. as in vacuum for high zT
Friday, June 18, 2010
JET Workshop - June 18th 2010Helen Caines
Path length dependence studies
16
Studying different centralities probes differing path lengthsbut may also vary medium properties
Alternate method:Correlations vs reaction plane
Trigger 12<pT<20 GeV/c
x (fm)
y (fm
)
x (fm)
b=7.5fmb=7.5fm
In-plane Out-of-plane
Trigger Trigger
T.Renk PRC78:034904,2008
b=7.5fmb=7.5fm
In-plane Out-of-plane
Trigger Trigger
y (fm
)
Trigger 12<pT<20, Away 4<pT<6 GeV/c
Calculation indicates there is difference in production points of measured triggers for in- vs out-of-plane
If pTassoc too high production bias
is “lost”
Friday, June 18, 2010
JET Workshop - June 18th 2010Helen Caines
Reaction plane dependence
17
AB!"
0 0.5 1 1.5 2 2.5 3
) (ar
b. u
nits
)AB!
"J(
-0.2
0
0.2
0.4
0.6
0.8
1
1.20# [4.0,7.0] GeV $
TAp
± [3.0,4.0] GeV h$ TBp
= 200 GeV - Cent 20-60%NNsAu+Au
= 0.66(3)"
]°,15° [0$| A!-%|
]°,90° [75$| A!-%|In-plane
Out-of-plane
4<pTTrig <7, 3<pTAssoc<4 GeV/c
M.McCumber RHIC/AGS Users 2010
Friday, June 18, 2010
JET Workshop - June 18th 2010Helen Caines
Reaction plane dependence
17
AB!"
0 0.5 1 1.5 2 2.5 3
) (ar
b. u
nits
)AB!
"J(
-0.2
0
0.2
0.4
0.6
0.8
1
1.20# [4.0,7.0] GeV $
TAp
± [3.0,4.0] GeV h$ TBp
= 200 GeV - Cent 20-60%NNsAu+Au
= 0.66(3)"
]°,15° [0$| A!-%|
]°,90° [75$| A!-%|In-plane
Out-of-plane
(rad)s!0 0.2 0.4 0.6 0.8 1 1.2 1.4
Near
PTY
(arb
. uni
ts)
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
]"183 [0,# !$
0.06 (stat+sys)± = 0.94 in/PTYoutPTY
-correctedrp%
0" [4.0,7.0] GeV # TAp
± [3.0,4.0] GeV h# TBp
= 200 GeV - Cent 20-60%NNsAu+Au
in-plane out-plane
(rad)s!0 0.2 0.4 0.6 0.8 1 1.2 1.4
Away
PTY
(arb
. uni
ts)
-0.05
0
0.05
0.1
0.15
Renk - Phys.Rev.C78:034904,2008Pantuev - private communication
]","97 [# !$
0.25 (stat+sys)± = 0.60 in/PTYoutPTY
-correctedrp%
0" [4.0,7.0] GeV # TAp
± [3.0,4.0] GeV h# TBp
= 200 GeV - Cent 20-60%NNsAu+Au
in-plane out-plane
20-60% Away-side yield out-of-plane< in-planeAway-side yield out-of-plane ~ in-plane0-20%Away-side yield out-of-plane ~ in-plane
Only weak path length dependence
4<pTTrig <7, 3<pTAssoc<4 GeV/c
M.McCumber RHIC/AGS Users 2010
Friday, June 18, 2010
JET Workshop - June 18th 2010Helen Caines
More direct access to partonic energy
18
γdir → partonic energy
S/B low due to large π0 backgroundγfrag/γdir ~30-40% at pTγ> 8 GeV
Need high pT for clean sample Statistical sample
W.Vogelsang
Au
Au
γ h±
Friday, June 18, 2010
JET Workshop - June 18th 2010Helen Caines
More direct access to partonic energy
18
γdir → partonic energy
S/B low due to large π0 backgroundγfrag/γdir ~30-40% at pTγ> 8 GeV
Need high pT for clean sample Statistical sample
W.Vogelsang
Au
Au
γ h±PRC 80 024908 (2009)
arXiv:0912.1871
γdir near-side peak non-zero - remaining contamination
- fragmentation photons
Away-side peak - clear suppression
Friday, June 18, 2010
JET Workshop - June 18th 2010Helen Caines
IAA of away-side γ-hadron correlation
19
π0-h and γ-h display comparable suppressionNo large path length effects in range/accuracy of measurementData disfavors model where energy distributed to low pT at large
angles (Renk-YaJEM)
zT=pTh/pTγ…notethatz≈1forγs,whilez<1forπ0s.
Need more accurate data over wider range to make firm statements
arXiv:0912.1871
M.Connors QM09
Friday, June 18, 2010
JET Workshop - June 18th 2010Helen Caines
Higher-statistics: Jet-hadron correlations
20
Reconstruct jet:Anti-kT, R=0.4, pt,cut>2 GeV and pt,rec(jet)>20 GeVCorrelate jet direction with hadrons in event Δϕ=ϕJet − ϕassoc., ϕJet = jet-axis found Jet trigger creates large bias - surface?
Δϕ1
Recoiljet
Triggerjet
Δϕ2
Friday, June 18, 2010
JET Workshop - June 18th 2010Helen Caines
Higher-statistics: Jet-hadron correlations
20
Reconstruct jet:Anti-kT, R=0.4, pt,cut>2 GeV and pt,rec(jet)>20 GeVCorrelate jet direction with hadrons in event Δϕ=ϕJet − ϕassoc., ϕJet = jet-axis found Jet trigger creates large bias - surface?
Increases S/BDecreases background correlations
Δϕ1
Recoiljet
Triggerjet
Δϕ2
Friday, June 18, 2010
0.2<pt,assoc<1.0 GeV 1.0<pt,assoc<2.5 GeV
pt,assoc>2.5 GeV
Open symbols p+p
STAR Preliminary0-20% Au+Au
STAR Preliminary0-20% Au+Au
STAR Preliminary0-20% Au+Au
J.Putschke RHIC/AGS 2009
JET Workshop - June 18th 2010Helen Caines
Jet-hadron correlations Au-Au vs. p-p
21
High Tower Trigger (HT): tower 0.05x0.05 (ηxϕ) with Et> 5.4 GeV
Open symbols p+p
Open symbols p+p
J.Putschke RHIC/AGS Users 2009
Friday, June 18, 2010
0.2<pt,assoc<1.0 GeV 1.0<pt,assoc<2.5 GeV
pt,assoc>2.5 GeV
Open symbols p+p
STAR Preliminary0-20% Au+Au
STAR Preliminary0-20% Au+Au
STAR Preliminary0-20% Au+Au
J.Putschke RHIC/AGS 2009
JET Workshop - June 18th 2010Helen Caines
Jet-hadron correlations Au-Au vs. p-p
21
High Tower Trigger (HT): tower 0.05x0.05 (ηxϕ) with Et> 5.4 GeV
Broadening - recoil-side
Softening - recoil-side
Caveat: “Jet v2” effects still under investigation
Direct measurement of
modified fragmentation
Open symbols p+p
Open symbols p+p
J.Putschke RHIC/AGS Users 2009
Friday, June 18, 2010
!"#$%&'&(("($#)$*%$
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$!"#$%"'+",-./0(&'$#)$*%$
1234$%'"(.5.,&'6$
JET Workshop - June 18th 2010Helen Caines
Preliminary look at jet v2
22
Path length dependence of energy loss?Jet influencing event plane?
A.Ohlson Jet Summer School
Jet appears to be correlated with the event plane
Friday, June 18, 2010
STAR Preliminary !"##!$%&'(#)*!+*),!-.!/%#(0#%-)!1$!
!2)-!/.3)!4)5.6),!
!4%3,.5!2)-!/.3)!4)5.6),!
!78)(9:(!2)-!/.3)!4)5.6),!
!2)-!/.3)!%-!;9<)&)3-!=!4)5.6),!
JET Workshop - June 18th 2010Helen Caines
Preliminary look at jet v2
22
Jet presence modifies the event planeNeed to calc. event plane using forward detectors
Path length dependence of energy loss?Jet influencing event plane?
A.Ohlson Jet Summer School
Jet appears to be correlated with the event plane
Friday, June 18, 2010
STAR Preliminary !"##!$%&'(#)*!+*),!-.!/%#(0#%-)!1$!
!2)-!/.3)!4)5.6),!
!4%3,.5!2)-!/.3)!4)5.6),!
!78)(9:(!2)-!/.3)!4)5.6),!
!2)-!/.3)!%-!;9<)&)3-!=!4)5.6),!
JET Workshop - June 18th 2010Helen Caines
Preliminary look at jet v2
22
Jet presence modifies the event planeNeed to calc. event plane using forward detectors
Path length dependence of energy loss?Jet influencing event plane?
A.Ohlson Jet Summer School
Jet appears to be correlated with the event plane pT (GeV/c)
π0 v
2
PHENIX PRC80:054907 (2009)
Friday, June 18, 2010
JET Workshop - June 18th 2010Helen Caines
Modification of recoil jet
23
Out-of-cone energy R>0.4:10<pt,jet trig <15 GeV/c = 2.47 GeV15<pt,jet trig <20 GeV/c = 2.98 GeV20<pt,jet trig <50 GeV/c = 2.99 GeV
low pTassoc : azimuthal width: Au-Au > p-p
high pTassoc : azimuthal width: Au-Au ~ p-p
J.Putschke RHIC/AGS Users 2009
Friday, June 18, 2010
JET Workshop - June 18th 2010Helen Caines
Modification of recoil jet
23
Out-of-cone energy R>0.4:10<pt,jet trig <15 GeV/c = 2.47 GeV15<pt,jet trig <20 GeV/c = 2.98 GeV20<pt,jet trig <50 GeV/c = 2.99 GeV
low pTassoc : azimuthal width: Au-Au > p-p
high pTassoc : azimuthal width: Au-Au ~ p-p
low pTassoc : assoc. yield Au-Au > assoc. yield p-p
high pTassoc : assoc. yield Au-Au < assoc. yield p-p
J.Putschke RHIC/AGS Users 2009
Friday, June 18, 2010
JET Workshop - June 18th 2010Helen Caines
Modification of recoil jet
23
Out-of-cone energy R>0.4:10<pt,jet trig <15 GeV/c = 2.47 GeV15<pt,jet trig <20 GeV/c = 2.98 GeV20<pt,jet trig <50 GeV/c = 2.99 GeV
low pTassoc : azimuthal width: Au-Au > p-p
high pTassoc : azimuthal width: Au-Au ~ p-p
Energy outside R=0.4 ~ accounts for di-jet suppressionEnergy gained at low pT ~ that lost at high pT
low pTassoc : assoc. yield Au-Au > assoc. yield p-p
high pTassoc : assoc. yield Au-Au < assoc. yield p-p
J.Putschke RHIC/AGS Users 2009
Friday, June 18, 2010
(rad)!"-1 0 1 2 3 4
!"
/dA
B d
NA
1/N
40
41
42
43
44
2.5-3.0 GeV/cA
Tp
0.5-1.0 GeV/cB
Tp
(rad)!"-1 0 1 2 3 4
su
btr
acte
d)
2 (
v!
"/d
AB
dN
A1/N
0
1
2
3
4
R < 0.4"0-10% HT Au+Au:
R cut"0-10% HT Au+Au: no
R < 0.4"HT p+p:
R cut"HT p+p: no
STAR preliminary
v2 = STAR event-plane, v2{4} average
JET Workshop - June 18th 2010Helen Caines
Hybrid-approach: hjet-h
24
Blue: All htrig-hassoc pairs in event Red: htrig-hassoc pairs in event with htrig within ΔR=<0.4 of jet
Same v2 used for both as initial estimationZYAM applied
How to interpret enhanced correlation?- sampling higher Q2 events- removing non-jet background?
Select only events with jet>10GeV, R=0.4, pTpart>2GeV/cLook at h-h correlations
A.Adare RHIC/AGS Users meeting 2010
Au-Au yields larger than p-p at low pTB...qualitatively consistent with
measured h-h IAA.
Friday, June 18, 2010
(rad)!"-1 0 1 2 3 4
!"
/dA
B d
NA
1/N
40
41
42
43
44
2.5-3.0 GeV/cA
Tp
0.5-1.0 GeV/cB
Tp
(rad)!"-1 0 1 2 3 4
su
btr
acte
d)
2 (
v!
"/d
AB
dN
A1/N
0
1
2
3
4
R < 0.4"0-10% HT Au+Au:
R cut"0-10% HT Au+Au: no
R < 0.4"HT p+p:
R cut"HT p+p: no
(rad)!"-1 0 1 2 3 4
!"
/dA
B d
NA
1/N
40
41
42
43
44 3.0-4.0 GeV/cA
Tp
0.5-1.0 GeV/cB
Tp
(rad)!"-1 0 1 2 3 4
su
btr
acte
d)
2 (
v!
"/d
AB
dN
A1/N
0
0.5
1
1.5
2
2.5
3
3.5
4R < 0.4"0-10% HT Au+Au:
R cut"0-10% HT Au+Au: no
R < 0.4"HT p+p:
R cut"HT p+p: no
STAR preliminary
v2 = STAR event-plane, v2{4} average
JET Workshop - June 18th 2010Helen Caines
Hybrid-approach: hjet-h
24
Blue: All htrig-hassoc pairs in event Red: htrig-hassoc pairs in event with htrig within ΔR=<0.4 of jet
Same v2 used for both as initial estimationZYAM applied
How to interpret enhanced correlation?- sampling higher Q2 events- removing non-jet background?
Select only events with jet>10GeV, R=0.4, pTpart>2GeV/cLook at h-h correlations
A.Adare RHIC/AGS Users meeting 2010
Au-Au yields larger than p-p at low pTB...qualitatively consistent with
measured h-h IAA.
Friday, June 18, 2010
(rad)!"-1 0 1 2 3 4
!"
/dA
B d
NA
1/N
40
41
42
43
44
2.5-3.0 GeV/cA
Tp
0.5-1.0 GeV/cB
Tp
(rad)!"-1 0 1 2 3 4
su
btr
acte
d)
2 (
v!
"/d
AB
dN
A1/N
0
1
2
3
4
R < 0.4"0-10% HT Au+Au:
R cut"0-10% HT Au+Au: no
R < 0.4"HT p+p:
R cut"HT p+p: no
(rad)!"-1 0 1 2 3 4
!"
/dA
B d
NA
1/N
40
41
42
43
44 3.0-4.0 GeV/cA
Tp
0.5-1.0 GeV/cB
Tp
(rad)!"-1 0 1 2 3 4
su
btr
acte
d)
2 (
v!
"/d
AB
dN
A1/N
0
0.5
1
1.5
2
2.5
3
3.5
4R < 0.4"0-10% HT Au+Au:
R cut"0-10% HT Au+Au: no
R < 0.4"HT p+p:
R cut"HT p+p: no
(rad)!"-1 0 1 2 3 4
!"
/dA
B d
NA
1/N
39.5
40
40.5
41
41.5
42
42.5 4.0-6.0 GeV/cA
Tp
0.5-1.0 GeV/cB
Tp
(rad)!"-1 0 1 2 3 4
su
btr
acte
d)
2 (
v!
"/d
AB
dN
A1/N
0
0.5
1
1.5
2
2.5
3
R < 0.4"0-10% HT Au+Au:
R cut"0-10% HT Au+Au: no
R < 0.4"HT p+p:
R cut"HT p+p: no
STAR preliminary
v2 = STAR event-plane, v2{4} average
JET Workshop - June 18th 2010Helen Caines
Hybrid-approach: hjet-h
24
Blue: All htrig-hassoc pairs in event Red: htrig-hassoc pairs in event with htrig within ΔR=<0.4 of jet
Same v2 used for both as initial estimationZYAM applied
How to interpret enhanced correlation?- sampling higher Q2 events- removing non-jet background?
Select only events with jet>10GeV, R=0.4, pTpart>2GeV/cLook at h-h correlations
A.Adare RHIC/AGS Users meeting 2010
Au-Au yields larger than p-p at low pTB...qualitatively consistent with
measured h-h IAA.
Friday, June 18, 2010
(rad)!"-1 0 1 2 3 4
!"
/dA
B d
NA
1/N
40
41
42
43
44
2.5-3.0 GeV/cA
Tp
0.5-1.0 GeV/cB
Tp
(rad)!"-1 0 1 2 3 4
su
btr
acte
d)
2 (
v!
"/d
AB
dN
A1/N
0
1
2
3
4
R < 0.4"0-10% HT Au+Au:
R cut"0-10% HT Au+Au: no
R < 0.4"HT p+p:
R cut"HT p+p: no
(rad)!"-1 0 1 2 3 4
!"
/dA
B d
NA
1/N
40
41
42
43
44 3.0-4.0 GeV/cA
Tp
0.5-1.0 GeV/cB
Tp
(rad)!"-1 0 1 2 3 4
su
btr
acte
d)
2 (
v!
"/d
AB
dN
A1/N
0
0.5
1
1.5
2
2.5
3
3.5
4R < 0.4"0-10% HT Au+Au:
R cut"0-10% HT Au+Au: no
R < 0.4"HT p+p:
R cut"HT p+p: no
(rad)!"-1 0 1 2 3 4
!"
/dA
B d
NA
1/N
39.5
40
40.5
41
41.5
42
42.5 4.0-6.0 GeV/cA
Tp
0.5-1.0 GeV/cB
Tp
(rad)!"-1 0 1 2 3 4
su
btr
acte
d)
2 (
v!
"/d
AB
dN
A1/N
0
0.5
1
1.5
2
2.5
3
R < 0.4"0-10% HT Au+Au:
R cut"0-10% HT Au+Au: no
R < 0.4"HT p+p:
R cut"HT p+p: no
(rad)!"-1 0 1 2 3 4
!"
/dA
B d
NA
1/N
39.2
39.4
39.6
39.8
40
40.2
40.4
40.6
40.8
41
41.2
41.4 6.0-10.0 GeV/cA
Tp
0.5-1.0 GeV/cB
Tp
(rad)!"-1 0 1 2 3 4
su
btr
acte
d)
2 (
v!
"/d
AB
dN
A1/N
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8R < 0.4"0-10% HT Au+Au:
R cut"0-10% HT Au+Au: no
R < 0.4"HT p+p:
R cut"HT p+p: no
STAR preliminary
v2 = STAR event-plane, v2{4} average
JET Workshop - June 18th 2010Helen Caines
Hybrid-approach: hjet-h
24
Blue: All htrig-hassoc pairs in event Red: htrig-hassoc pairs in event with htrig within ΔR=<0.4 of jet
Same v2 used for both as initial estimationZYAM applied
How to interpret enhanced correlation?- sampling higher Q2 events- removing non-jet background?
Select only events with jet>10GeV, R=0.4, pTpart>2GeV/cLook at h-h correlations
A.Adare RHIC/AGS Users meeting 2010
Au-Au yields larger than p-p at low pTB...qualitatively consistent with
measured h-h IAA.
Friday, June 18, 2010
JET Workshop - June 18th 2010Helen Caines
Summary
25
Two particle correlations have long given access to jet physics “Triangular” flow could explain “Ridge” and “Mach-cone”
similarity with the bulk matter propertiesfurther study needed
At high pT ridge and mach cone disappearaway-side jet reduced but shape similar to p-p energy redistributed to to low pT
Modeling RAA doesn’t guarantee prediction of IAAGeometry or energy loss mechanisms more important?
Reaction plane analysis hints at path length energy lossJet may show v2
path length dependent energy loss or biased event-plane?γ-h suppression like h-h in pT range exploredJet-h indicate away-side energy broadened and softenedhjet-h although biased give cleaner correlations
Friday, June 18, 2010