Transcript Document

Charm measurements at SPS to RHIC
Y. Akiba (KEK)
March 14, 2003
Strangeness in Quark Matter 2003
Outline
• Physics
– Physics with open charm
• pp, pA, AA
– Physics with charmonium
• pp, pA, AA
• Open charm measurements at fixed target
– Nuclear dependence: cross section, <pt>, A dependence
– Enhancement in Pb+Pb (?) (NA50 IMR)
• Charmonium measurements at SPS and FNAL
– A dependence: normal nuclear absorption, <Pt>
– Anomalous suppression in Pb+Pb (NA50)
• Open Charm measurements at RHIC
– Charm measurement via single lepton
– Run-1 (130 GeV) data (PHENIX)
– Run-2 (200 GeV) prelimnary data (PHENIX)
• Charmonium measurement at RHIC
– First J/Y data at RHIC (PHENIX)
Physics with open charm production
• pp and hadron-hadron collisions
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Comparison with pQCD calculation
Measurement of gluon density G(x)
Intrinstic <kt>
Base line for charm physics in pA and AA
• pA
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Gluon shadowing
Energy loss of gluons in cold nuclear matter
Parton multiple scattering and <kt>
Base line (normal nuclear effect) for charm physics in AA
• AA
– Gluon shadowing
– Energy loss of charm in high density matter
– Thermal production of charm in high temperature QGP
Physics with Charmonium production
• pp : study of production mechanism
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Color evapolation model, Color singlet model, Color Octet model
Production cross section and its pt and s1/2 dependence
Polarization
Production of J/Y, Y(2S), cc, states
Base line for pA and AA
• pA : study of “normal nucleus effect”
– Nuclear dependence of s(J/Y) ….Aa or sabs (nuclear absorption)
– Nuclear dependence of <Pt2> …multiple scattering effect?
– Base line for AA
• AA : study of “medium effect” in high density matter
– J/Y suppression : signature of QGP (Matsui/Satz)
– J/Y formation by c quark coalescence at RHIC/LHC ?
Measurement of charm and lepton/lepton pairs
Charmonium:
lepton pairs
J/Y  e+e-, m+mY(2S)  e+e-, m+mcc  J/Y + g
Open charm:
single lepton and lepton pairs
K


D0
c c
K
D0
Charm signal:
single lepton
lepton pairs
• J/Y has a large branching ratio
(6%) to lepton pairs, and it is
almost exclusively measured by
lepton pair decay.
• Charmed mesons has a large
leptonic branching ratio (D0: 7 %,
D+:17%). Charm production can
be measured indirectly by single
lepton in 0.5< pt<3 GeV/c
(RHIC/PHENIX) and lepton
pairs in 1<M<3 GeV
(SPS/NA50).
– More direct measurement of Dmeson reconstruction is difficult
without a precision vertex
detector
Open charm at fixed target (cross section)
scc in pN,pN
s1/2(GeV)
• Charm cross section by fixed
target experiments are
reasonably reproduced by LO
pQCD event generator
(PYTHIA) with large K-factor,
or by NLO pQCD calculation
(HVQMNR). Note that pQCD
may or may not be applicable to
charm production because
charm mass is small (~1.5GeV)
• In the left figure, world pi+N
data and p+N data are
compared with PYTHIA
calculation. The s1/2 dependence
of the calculation mainly
reflects the underlying PDF.
Open charm at fixed target (<Pt>)
E791 ds/dpT2
WA92 ds/dpT2
pT2 (GeV2/c4)
pT2 (GeV2/c4)
• FNAL E791 and CERN WA92
measured hight statistics Pt
distribution of D-mesons in p+N
collision. (No high statistics data in
p+A is available)
• In the left figure, E791 data and
WA92 data are compared with
PYTHIA calculation with different
<kt> values. <kt> ~ 1.5 GeV/c seems
to be required to reproduces the data.
• Comparison with NLO pQCD
calculation also suggests that
observed pt distribution is harder than
predicted, and large (>1GeV/c)
intrinsic <kt> is needed to reproduce
the data.
• No published data on nuclear
dependence in <pt2> but it can be
similar to that of J/Y
Nuclear dependence of Open charm cross section
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•
Open charm cross section has little or no nuclear
dependence
a = 1.00± 0.05
(E769 250GeV p+A)
a = 0.92 ±0.06
(WA82 340GeV p+A)
a = 1.02 ±0.03 ±0.02
(E789 800GeV p+A)
This is consistent with that there is little nuclear
shadowing at the x region probed by the fixed
target charm experiments.
Significant nuclear suppression is reported by
large xf region (WA78, a=0.81 ± 0.05). This can
be due to nuclear shadowing in small x, but this
is not well understood.
At RHIC, we can prove x region much smaller
than in fixed target. We may observe nuclear
shadowing effect in charm production.
E769 250 GeV p± PRL 70,722 (1993)
a = 1.00 ± 0.05
Open Charm enhancement (?) at SPS Pb+Pb
NA50
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•
•
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NA50
NA50 measured di-muon distribution in 1.5<M<2.5 GeV.
The mass distribution is well reproduced by DD pairs + Drell-Yan components in p+A
(@450GeV) with charm cross section scc/A = 36.2±9.1 mb, consistent with charm cross
sections of other experiments
In Pb+Pb, an excess of dimuon signal is observed. The excess can be explained by
enhancement of charm production by factor of ~3 in central Pb+Pb.
The other explanation is possible: e.g. thermal dimuon pair produciton.
J/Y at fixed target and ISR
• Many experimental data in the
last 30 years near threshold to
s1/2 = 63 GeV
• Rapid increase of production
cross section to s1/2 ~ 20 GeV
followed by a gradual increase
in higher energy.
• The s1/2 dependence is similar
to that of charm production
cross section, suggesting that
J/Y and charm ratio is almost
constant with energy
• Detailed, high statistics study of
A dependence by E772/789/866
at 38 GeV and p+A and A+A
measurement by NA38/50
JPSI at fixed target: A dependence
•
•
Significant nuclear dependence of cross section is observed
Power law parameterization s = Aa
a = 0.92
a = 0.919 ± 0.015
a = 0.954 ± 0.003
a = 0.934 ± 0.014
(E772. PRL66(1991) 133) (limited pt acceptance bias?)
(NA38. PLB444(1998)516)
(E866 @ xF=0. PRL84(2000),3258 )
(NA50, QM2001)
•
Absorption model parameterization
•
Small difference in a between J/Y and Y(2S) (E866)
s = 6.2 mb (NA38/50/51) to 4.4 mb (NA50, QM2002)
a(J/Y) – a(Y(2S)) ~ 0.02-0.03 @ xF = 0
JPSI at fixed target: <Pt2>
<pt2>
vs
s1/2
<pt2>
vs L
<pt2> vs A
• <pt2> of J/PSI increases with beam energy
– <kt> increase with energy ?
– Gluon radiation effect? ( pQCD )
• <pt2> of J/Y increases with L (path length in target nuclear matter) or A1/3
– Consistent with multiple scattering of incoming partion ( Cronin effect)
J/Y suppression at SPS
• NA50 observed anomalous
suppression of J/Y in Pb+Pb
collisions at 158 GeV
• Deviation from the nuclear
absorption model (with s~4 to 6
mb) is seen in ET > 40 GeV or e>2.5
GeV/fm3
• If the suppression is due to J/Y
break-up in high energy density
matter, this is a strong evidence for
QGP formation
• If J/Y suppression is due to QGP
formation, almost all of initially
produced J/Y should be suppressed
at RHIC energy
NA50
NA50
Charm and single electron at RHIC
Simulation before RHIC
•
PHENIX data (PRL88)
At RHIC, it is expected that charm decay can be the dominant component of single
electron in pt > 1.5 GeV/c
– Large production cross section of charm ( 300-600 ub)
•
– Production of the high pt pions is strongly suppressed relative to binary scaling
– Production of charm quark roughly scale with binary collisions.
PHENIX observed “excess” in single electron yield over expectation from light
meson decays and photon conversions  Observation of charm signal at RHIC
PHENIX single electron data
PHENIX PRL88 192303
• PHENIX observed excess of
single electron yield over the
contribution from light meson
decays and photon conversoins
• Spectra of single electron signal is
compared with the calculated
charm contribution.
• Charm contribution calculated as
EdNe/dp3 = TAAEds/dp3
– TAA: nuclear overlap integral
– Eds/dp3: electron spectrum from
charm decay calculated using
PYTHIA
• The agreement is reasonably good.
Assuming that all single electron signal is from charm decay and the binary scaling,
charm cross section at 130 GeV is obtained as
010%
scc
 380  60  200mb and
092%
scc
 420  33  250mb
Comparison with other experiments
• PHENIX single electron cross
section is compared with the
ISR data single electron data
• Charm cross section derived
from the electron data is
compared with fixed target
charm data
• Single electron cross sections
and charm cross sections are
compared with
– Solid curves: PYTHIA
– Shaded band: NLO QCD
Assuming binary scaling, PHENIX data are consistent with s systematics o
(within large uncertainties)!
Single electron measurement by PHENIX in RUN2
photon converter method
Single electron spectra :
• data with the converter
• data w/o the converter
Ne
0.8% 1.1%
1.7%
With converter
Conversion in converter
W/O converter
Conversion from pipe and MVD
Dalitz : 0.8% X0 equivalent
Non-photonic
0
0
If all electrons are from photonic source (p0 Dalitz, g conversion, etc), the
ratio is constant. But the data shows that electron yield approach at high
pT each other.
It is an evidence for non-photonic electrons (i.e. charm/bottom decay)
RUN2 single electron result
•
•
•
The yield of non-photonic electron at 200 GeV is higher than 130 GeV
The increase is consistent with PYTHIA charm calculation
(scc(130GeV)=330 mb  scc(200GeV)=650 mb)
Large systematic uncertainty due to material thickness without converter. The error will be
reduced in the final result.
Centrality Dependence
PHENIX data is consistent with the PYTHIA charm spectrum scaled by number of
binary collisions in all centrality bins!
Observation from PHENIX single electron data
• NA50 has inferred a factor of ~3 charm enhancement at SPS. PHENIX does not
see such a large effect at RHIC.
• PHENIX observes a factor of ~3-5 suppression in high pT p0 relative to binary
scaling. PHENIX does not see such a large suppression in the single electrons.
• Initial state high pt suppression excluded? ( CGC, strong shadowing)
• smaller energy loss for heavy quark ? (dead cone effect)
NA50 - Eur. Phys. Jour. C14, 443 (2000).
Binary Scaling
PHENIX Preliminary
N part
J/Y at RHIC
• J/Y production in N+N
– J/Y production mechanism
– Spin dependence (gluon polarization DG(x))
• J/Y production in Au+Au
– Suppression by QGP formation?
– Enhancement by recombination of charm and anti-charm in QGP?
• PHENIX can measure J/Yee in |y|<0.35 and J/PSImm
in 1.2<|y|<2.4
– Wide kinematics coverage
– Independent measurement in two channels
• PHENIX can measure of both open charm and J/Y
– VERY strong constraint on the models of J/Y production
J/Yee and J/Y mm in pp @ 200 GeV
e+e- |y|<0.35
mm- 1.2 < y < 2.2
|y| <0.35
NJ/Y = 24 + 6 + 4 (sys) Bds/dy = 52 + 13 (stat) + 18 (sys) nb
1.2 < y < 1.7 NJ/Y = 26 + 6 + 2.6 (sys) B ds/dy = 49 + 22% + 29% (sys) nb
1.7 < y < 2.2 NJ/Y = 10 + 4 + 1.0 (sys) B ds/dy = 23 + 37% + 29% (sys) nb
pp  J/Y at RHIC (<Pt>)
1.2<y<2.2
• shape of pT distribution is consistent with a PYTHIA calculation
• average pT
– <pT>y=1.7 = 1.66 ± 0.18 (stat.) ± 0.09 (syst.) GeV/c
– slightly larger than measured at lower energies
– consistent with a PYTHIA extrapolation to RHIC energy
ppJ/Y at RHIC
e+ eµ+µ-
Br (J/l+l-) s (p+pJ/X)
= 226  36 (stat.)  79 (sys.) nb
s (p+pJ/X)
= 3.8  0.6 (stat.)  1.3 (sys.) µb
•
PHENIX data agrees with the
color evaporation model
prediction at s=200 GeV
J/Y  e+e- in Au+Au collisions at sNN = 200 GeV
• e+e- invariant mass analysis
• very limited statistics
N=10.8  3.2 (stat)  3.8 (sys)
• split minimum bias sample into 3
centrality classes
Centrality dependence of J/Y yield
•
J/Y B-dN/dy per binary collision compared to different models for J/Y absorption
patterns
– J/Y scale with the number of binary collisions
– J/Y follow normal nuclear absorption with given absorption cross sections
– J/Y follows same absorption pattern as observed by NA50 (Phys. Lett. B521(2002)195)
Attention:
all curves are normalized
to the p+p data point!
<Nbc>=45
present accuracy
p+p
<Nbc>=297
<Nbc>=791
NO discrimination
power between
different scenarios
Much more statistics is needed!
Coming soon --- J/Y measurement in d-Au at RHIC
J.C.Peng
Nuclear shadowing
effects in J/Y production
soon will be studied by
PHENIX.
PHENIX μ
PHENIX e
E866 (mid-rapidity)
NA50
Observed signal online
Crude calibration
Comparison of J/Y yield
in central arm and two
muon arm is useful to
distinguish different
shadowing models
PHENIX has seen J/ signal in
d-Au collisions and expects to
get a few thousands J/ at the
end of the run.
Summary and outlook
• SPS and fixed target
– Open charm production
• Charm production scale with A in p+A collision (no nuclear effect)
• NA50 IMR data can be interpreted as a large enhancement of charm in Pb+Pb
– J/Y production
• Extensive data on normal nuclear effect in J/Y production in p+A by E866 and
NA38/50
• Suppression of J/Y production in Pb+Pb beyond normal nuclear absorption is
observed by NA50
• RHIC
– Charm production measured by single electron is consistent with the
binary scaling (with relatively large error).
• Little gluon shadowing at RHIC?
• Little energy loss effect in charm quark?
– The first J/Y data in pp and AuAu at RHIC is obtained
• Much more statistics is needed to measure J/Y suppression at RHIC