Download - p t correlations versus relative azimuth of D-Dbar pairs as a sensitive probe for thermalization
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pt correlations versus relative azimuth of D-Dbar pairs as a
sensitive probe for thermalization
Tsiledakis Georgios
University of Heidelberg
417th WE-Heraeus-Seminar, June 25 - 28 2008, Bad Honnef
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Outline• Introduction
• Primordial c-cbar (D-Dbar) correlations for p-p collisions at 14 TeV
• The Average Momentum Correlator
• Contribution of transverse radial/elliptic flow
• Primordial B-Bbar pt correlations
• Charm Production in ALICE
• D-e pt correlations
• e+ - e- pt correlations from D, B decays
• Conclusions
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Introduction
Total quark mass (MeV)
X. Zhu, M. Bleicher, K.Schweda, H. Stoecker, N. Xu et al., PLB 647 (2007) 366.
1) Higgs mass: electro-weak symmetry breaking. (current quark mass)
2) QCD mass: Chiral symmetry breaking. (constituent quark mass)
Strong interactions do not
affect heavy-quark masses.
Important tool for studying properties of the hot/dense medium at RHIC and LHC.
Test pQCD predictions at RHIC and LHC.
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Low Energy D-Dbar Meson Pair Correlations
(D-Dbar)
= (D) – (Dbar)
• E791 : Eur. Phys. J. direct C1 (1999) 4• WA92 : Phys. Lett. B385 (1996) 487• NA32 : PLB257 (1991) 519 , PLB302 (1993) 112, PLB353 (1995) 547
Correlation variable studied:
103 /
N *
dN
/d(
)
•At low energies, D-Dbar production correlated!
•Pythia describes these correlations!
How about LHC energies?
For many more details, see:
C. Lourenço & H. K. Wöhri,
Phys. Rep. 433 (2006) 127.
D
Dbar
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Charm correlations at LHC In p+p:
c-cbar are correlated
• Flavor creation: back to
back
• Gluon splitting: forward
• Flavor excitation: flat
In Pb+Pb:
Correlations vanish
frequent interactions
among partons !
probe light-quark
thermalization !
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PYTHIA Settings
• PYTHIA (v.6_406)
• 500000 p-p events at √s = 14 TeV
• 1 pair c-cbar/event
• no tracking, 100 % efficiency
• No rapidity cut
• Fragmentation Pv = 0.75 (default)
p
p c
c D
D
ALICE PPR vol. II, J. Phys. G: Nucl. Part. Phys. 32 (2006) 1295-2040
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D+ D*+ D0 D*0 Ds+ D*s+
Primordial D –no decay
Fragmentation of charm quarks into D mesonsC
ou
nts
PID
N(D0) : N(D+) : N(D*0) : N(D*+) = 1 : 1 : 3 : 3
c-cbar D0 + D0bar (61 %)
D+ + D- (19 %)
Ds+ + Ds
- (12 %)
c+ + c
-bar (8 %)
Large fraction of c goes to
D0 mesons
Measure D0-D0bar correlations!
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Primordial D-Dbar angular correlations
FC away side correlation FE + GS flat Rather weak dependence
No pt cut
Enhanced correlations FC back to back GS forward FE flat Strong pt dependence
Correlations sensitive to pt regionStudy pt correlations versus(DDbar)
Azimuthal correlations survive fragmentation
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pt (GeV/c)
0
tt
p
0
tt
t
dpdpdn
dpdpdn
px
t
''
''
x(p
t)
Inclusive pt distribution
D
Cumulant pt variable x
Primordial D-Dbar pt correlations
•Incl. pt-distr. Cumulant x(pt) •2-dim plot (x(pt)1, x(pt)2) for D-Dbar respectively•Is uniform when no correlations are present
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D-Dbar pt correlations – at full
pt correlations are dominated
by large pt effects (along the diagonal
at xx)
Same event
Mixed event
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D-Dbar pt correlations – angular dependence
Gluon Spitting
Flavor Creation
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Measurement of pT Fluctuations using the Average Momentum Correlator
• To quantify dynamical pT fluctuations
– We define the quantity <pt,1pt,2>.
– It is a covariance and an integral of 2-body correlations.
– It equals zero in the absence of dynamical fluctuations
– Defined to be positive for correlation and negative for anti-correlation.
S. Voloshin. V. Koch. H. Ritter, PRC60 (1999)
/ 2/ 2
Ck pt ,i pt pt , j pt j1,ij
Nk
i1
Nk
and pt pt k
k1
Nevent
/ Nevent and pt k pt ,i
i1
Nk
/ Nk
Nevent = number of events
pt i = average pt for i th event
Nk = number of tracks for k th event
pt ,i = pt for i th track in event
where
pt,i for Dpt,j for DbarNk=1
))((1
,,
111
2,1,
tjttit
N
j
N
i
N
kpairstt pppp
Npp
kkevents
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Average Momentum Correlator - same event analysis
pt (DDbar)~30 GeV/c
At full : <pt,1pt,2> = 0.1995 +/- 0.006 (GeV/c)2
or pt~30 %
Co
un
ts
CERES at SPS has measured ~1% fluctuations for charged particles
<pt,1pt,2> = 22.71+/- 0.32 (MeV/c)2
Ck pt ,i pt pt , j pt j1,ij
Nk
i1
Nk
(GeV/c)2
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Average Momentum Correlator – angular dependence
Enhanced correlations
Only FC produces correlations
at Distinction of the baseline at
middle – flat to 0
Average Momentum Correlator
is a sensitive measure of
back to back correlations
Signal
Background
At full : <pt,1pt,2> ~ 0.20 (GeV/c)2
or pt~30 %
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Transverse radial flow contribution
ptD
ptDbarptD
ptDbar
ptf = m
= 0, 0.3, 0.6, 0.9
E. Cuautle and G. Paic hep-ph/0604246 v2 24 May 2006
Assume a fireball created in a coll. from PYTHIA
Expansion produces additional momentum ptf
Attribute to each pt a randomized position
Add the radial flow component vectorially
pt (GeV/c)
Co
un
ts
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Transverse radial flow contribution on <pt,1pt,2>
Radial flow: = 0, 0.3, 0.6, 0.9
Stronger flow introduces
anti-correlations around = 180o
10000 events for = 0.3, 0.6, 0.9
500k events for = 0
D
Dbar
D
Dbarff
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Elliptic flow contribution
k
k
N
ji
ji
jitjttit
N
jitt
f
fpppp
pp,
,,,
2,1,
))((
)]2cos(21 22
vB
d
dN
We evaluate the elliptic flow expressed in units of (GeV/c)2
•We introduce the measure fi,j
•We calculate the average momentum correlator forDDbar pairs that have flow 10% and 90%
Introduces a cos(2) modulation
|))()(|2cos()()(21 ,2,2, jipvpvf jtitji
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realistic amount of elliptic flow
does not change correlations !
Elliptic flow contribution on <pt,1pt,2>
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Full rapidity (500000 events)
Mid-rapidity (200000 events)
Primordial D-Dbar angular correlationsat mid-rapidity
• NLO dominant at LHC
• Weak D-Dbar correlation in
• Measurement of medium modification of
this correlation in heavy ion collisions is
challenging
FC away side correlation FE flat in GS forward
Use of pt correlator
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Average Momentum Correlator for D-Dbar at mid-rapidity
At full : <pt,1pt,2> = 0.549+/-0.017 (GeV/c)2
or pt~40 %
Stronger signal at mid-rapidity
Full rapidity (500000 events)
Mid-rapidity (200000 events)
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Charm Production in ALICE using D0 K-+
ALICE has a barrel system with high precision
vertexing, PID and electron identification (|| < 0.9)
and a forward muon spectrometer (: 2.5–4.0),
down to low pt.
Charm production can be studied:
• In the electronic and muonic channels D eX (X) •In several hadronic decay channels: D0 K , D± K D0 K, Ds KK, Ds
D* D0, c pK ALICE PPR II, J. Phys. 32 (2006) 1295
TPC: main tracking device
ITS: high spatial resolution
TRD: good electron PID (high pion rejection)
ToF: extend PID to large pt
109 p-p events
Nccbar/event = 0.16 (PPR2)
c-cbar D0 (61 %)
D0 (4 %)
Eff.(acceptance, reconstruction,
selection eff.) ~ 0.005
S/B ~ 10%
#Events with both D0-D0bar < 10
Looking at semileptonic decays
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Charmed e+/e- correlationsp
t D (
GeV
/c)
pt e- (GeV/c)
De-
•Study e+/e- pt correlations
at the electronic channel D e + X
•BR ~ 15% from D+/-, ~7% from D0
•At low pt the correlation is lost (< 0.5 GeV/c)
•At pt > 1 GeV/c survives
•Need to apply a pt cut:
10% e with pt > 1 GeV/c
1% e with pt > 2 GeV/c
•To account the BG from Dalitz,
conversions, B semileptonic
decays…
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Angular correlation of D-e from D e + X
No pt cut
pt > 1 GeV/c
No pt cut
pt > 1 GeV/c
Semileptonic-decay e are strongly pt
correlated with parent D
e+/e- from D-Dbar decay preserve the
original D-Dbar angular correlation to a
large extent
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D-e pt correlation
K<—D0<—D*—c – c— D*—> D0—>e- + X
Full rapidity
Mid-rapidity
No pt cut
D-e pt correlations survive charm decay
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Charmed e+/e- pt correlations
Full rapidity
Mid-rapidity
Mid-rapidity with pt > 0.5 GeV/c
Mid-rapidity with pt > 1 GeV/c
e+ - e- pt correlations at pt > 1 GeV/c survive charm decay
e+ + X<—D0<—D*—c – c— D*—> D0—>e- + X
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PYTHIA processes for charm/beauty generation
Fra
cti
on
of
each
pro
cess
/All
pro
cess
es
f + f’ f + f’
g + g f + fbar
f + g f + g
g + g g + g
•GS dominant for D-Dbar
•FC dominant for B-Bbar
•FE is flat
D-Dbar
B-Bbar
pt (GeV/c)
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Primordial B-Bbar angular correlations
•At full : <pt,1pt,2> = 2.97 +/- 0.18
(GeV/c)2 or pt~55 %
•GS flat in dN/d but strong in small
using the Average Momentum Correlator
•FC back to back
•The Average Momentum Correlator is
very sensitive to different PYTHIA
processes for beauty generation
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e+/e- correlations from B decays
pt e- (GeV/c)
pt > 1 GeV/c
e+/e- from B decays are strongly pt
correlated at small and large
Need to study background BDe
pt B
(G
eV/c
)
e+ + X<—B0<—B*—c – c— B*—> B0—>e- + X
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Conclusions
In p+p, heavy q-qbar production is correlated
The Average Momentum Correlator is a sensitive measure
Correlations survive hadronization
e+- e- pt correlations at pt > 1GeV/c survive charm/beauty decay
need TRD for electron ID!
need full simulations within ALICE
study changes in correlations and address light quark
thermalization at LHC
e<—D0<—D*—c – c— D*—> D0—>e-
<pt,1pt,2> ~ 0.2 (GeV/c)2 for D-Dbar
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Backup slides
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Measure of mean pT fluctuations
T
dynp
dynpp pT
TT
||sgn
2,2
,
N
pM T
pdynp TT
222
,
• Normalized dynamical fluctuation
222TTT ppp
MpT : variance of MpT dist.
p2T : variance of inclusive pT dist.
<N> : mean multiplicity
pT : inclusive (event-averaged) mean pT
= 0 for purely statistical fluctuation > 0(< 0) with positive/negative two-
particle correlation or dynamical EbyE fluctuation
pT
Dimensionless measure
TTT ppp FΣN 2
Proportional to mean covarianceof all particle pairs / eventRobust under change of multiplicity due to changes in beam energy and acceptance
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c-cbar angular correlations
PYTHIA production
No pt cut
Away side correlation
= (c) – (cbar)
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D-Dbar pt correlations - Mixed event analysis
Full
Uniform populated – no correlations
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Gluon splitting
Full
D-Dbar pt correlations - Same event analysis
High pT correlations at small
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Flavor excitation
Full
D-Dbar pt correlations - Same event analysis
Rather flat
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Pair creation
Full
D-Dbar pt correlations - Same event analysis
High pT correlations at big
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Average Momentum Correlator for same/mixed events
Ck pt ,i pt pt , j pt j1,ij
Nk
i1
Nk
Ck pt ,i pt pt , j pt j1,ij
Nk
i1
Nk
Mixed events
Same events
GeV2
GeV2
Co
un
ts
Co
un
ts
Ck pt ,i pt pt , j pt j1,ij
Nk
i1
Nk
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Correlation strength for primordial D0 and D0 from D*
Generate D0, D+/-, Ds (no resonances)
with Pv=1 (0.75 default)
Generate D* (only resonances) with
Pv=0 and decay them…
correlations survive resonance decay
50000
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No flow10% elliptic flow90% elliptic flow
Elliptic flow contribution on dN/d
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Radial flow contribution on dN/d
= 0, 0.3, 0.6, 0.8, 0.9
With increasing near-side/away-side peaks are enhanced
10000
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Charm Production in ALICEALICE has a barrel system with high precision
vertexing, PID and electron identification (|| < 0.9)
and a forward muon spectrometer (: 2.5–4.0),
down to low pT.
Charm production can be studied:
• In the electronic and muonic channels D eX (X) •In several hadronic decay channels: D0 K , D± K D0 K, Ds KK, Ds
D* D0, c pK
ALICE PPR II, J. Phys. 32 (2006) 1295
D0 K-+ the cleanest channel
• pair of opposite-charge tracks with large impact parameters• good pointing of reconstructed D0 momentum to the primary vertex
TPC: main tracking device
ITS: high spatial resolution
TRD: good electron PID (high pion rejection)
ToF: extend PID to large pT
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Full rapidity (500000 events)
Mid-rapidity (200000 events)
pt for D-Dbar at full and mid-rapidity
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43Mid-rapidity (200000 events)
Full rapidity (100000 events)
Fra
ctio
n o
f ea
ch p
roce
ss/A
ll p
roce
sses
pt (GeV/c)
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Number of charmed electrons 109 p-p events
Nccbar/event = 0.16 (PPR2)
c-cbar D0 (61%)
c-cbar D+/- (20%)
D e + X (15% from D+/-, 7% from D0)
10% e with pt > 1 GeV/c
#events with e+/e- from D0 = 0.16*0.612*0.072*109 ~ 300000At pt > 1 GeV = 3000
#events with e+/e- from D+/- = 0.16*0.202*0.152*109 ~ 144000At pt > 1 GeV = 1440
~ 4500 clean e+/e- pairs with pt > 1 GeV at full rapidity
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e+ - e-
D-e
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D-Dbar
B-Bbar
At full : <pt,1pt,2> = 2.97 +/- 0.18 (GeV/c)2
or pt~55 %
At full : <pt,1pt,2> = 0.2 +/- 0.006 (GeV/c)2
or pt~30 %
Co
un
tsC
ou
nts
Ck pt ,i pt pt , j pt j1,ij
Nk
i1
Nk
Ck pt ,i pt pt , j pt j1,ij
Nk
i1
Nk
(GeV/c)2
(GeV/c)2