1
Charmonium, open charm and beauty
production at HERA-B
PIETRO FACCIOLI, for the HERA-B Collaboration
Università di Bologna and INFN
June 14, 2006
Asilomar Conference Grounds,
Pacific Grove, California
2
outline


HERA-B detector and physics topics
results and comparison with previous experiments
 J/ψ production
first data at negative xF
 pT and xF distributions, A-dependence
highest
energy
among
fixed-target
experiments
often unclear
 new: decay angular distributions
experimental
picture,
observation of
low-pT /|xF| especially
 heavier states and feeddown to J/ψ
for p-A
effects
 ψ′/ψ and kinematics
collisions
 fraction of J/ψ’s from χc
largest
test production
χc
 fraction of J/ψ’s from b decays
statistics
models (pQCD
analyzed in
+ initial/final
hadron
state
 charm
collisions
interactions in
 inclusive D0, D+, D*+ and ratios
nuclei)
 A-dependence
3
the HERA-B detector
(top view)
high resolution
large acceptance
(15-220 mrad)
Tracking
Vertex
Detector
920 GeV/c
protons
electrons
20 m
RICH
MUON
ECAL
10 m
good PID
(e±, μ±, π, K,
p)
+ photon reconstruction
Magnet
target wires
(C, Ti, W)
0m
fixed nuclear
target
√s = 41.6 GeV
A = 12 ÷ 184
4
physics at HERA-B
dilepton trigger: ~ 150·106 events
800
ρ/ω
entries (a.u.)
600

J/ψ
104
400
μ+μ-
200
• Do  μ+μ- (FCNC)
10
ψ′
103
• J/ψ, χc, ψ′,
with A-dependence
(1S)
(2-3S)
102
1
e+e-
• inclusive b
production
μ+μ-
two independent
channels (e+e10- + μ+μ-)
10
2
0
0.4
0.6
0.8 1.0
mμμ [GeV/c2]
1.2
-1
2.5
3.0
3.5 4.0
mee [GeV/c2]
4.5
6
7
8
9
10
mμμ [GeV/c2]
11
12
• ,
,
ρ/ω
‘hard photon’ trigger:
~ 35·106 events
~ 210·106 minimum bias events
107
entries (a.u.)
• Ks, K*, Λ, , Ξ+-
3000
• pentaquarks
2000
• Do, D+, D*+, Ds
103
10
10-1
1000
0
• J/ψ
1
1.02
1.04
1.06
mKK [GeV/c2]
1.08
direct
γ, π o, η
production
with four
different
nuclei
MinBias data,
run 20478
HP trigger,
run 20595
105
Ed3σ/dp3 [a.u.]
~50k   KK
4000
pC  γX
10-3
0
1
2
3
4
5
ET [GeV]
6
7
8
5
J/ψ and ψ′ signals
full dilepton data sample (3 target materials)
μ+μ-
e+e104
~ 170 000 J/ψ
~ 3 000 ψ′
σJ/ψ ~ 44 MeV
entries/(25 MeV/c2)
entries/(30 MeV/c2)
~ 120 000 J/ψ
~ 2 200 ψ′
σJ/ψ ~ 64 MeV
104
J/ψ
103
ψ′
2.5
3.0
3.5
4.0
+
2
m(e e ) [GeV/c ]
J/ψ
103
ψ′
2.8
3.2
3.6
+
m(μ μ ) [GeV/c2]
4.0
6
preliminary data (di-electron channel).
Compatible results from the di-muon data,
not shown here.
A
197
<pT> [GeV/c]
J/ψ production kinematics: pT distribution
W
Au
Ti
C
184
Si
48
Be
28
A
12
9
Ti
W
HERA-B
[a. u.]
ds
dpT2
increase
of <pT>
with A
C
pT [GeV/c]
comparison with
p-A results
at similar energy
(√s = 38.8 GeV)
7
xF distribution
Preliminary data (e+e-), compared with p-A results at 38.8 GeV
E771 (Si)
E789 (Au)
HERA-B (C)
E672/706
(Be)
C
E789
(Be, Cu)
Ti
W
first data centred
at negative xF
A-dependence
8
a 1.0
0.9
0.8
0.7
Models (with variants):
- R. Vogt, PRC 61 (2000) 035203, NP A700 (2002) 539
- K.G. Boreskov & A.B. Kaidalov, JETPL 77 (2003) 599
-0.4 -0.3 -0.2 -0.1
0
0.1 0.2 0.3
0.4 0.5 0.6 0.7
0.8
HERA-B preliminary E866 38.8 GeV Be/Fe/W
(di-muon channel,
E789 38.8 GeV Be/C/Cu/W
0.8
carbon+tungsten
E772 38.8 GeV H2/C/Ca/Fe/W
double-wire runs)
NA50 29.1 GeV Be/Al/Cu/Ag/W
errors statistical only
NA3 22.9 GeV H2/Pt
0.7
-0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
0.8
1.0
0.9
xF
decay angular distribution: polarization frames
Il Nuovo Cimento Vol. XXXIII, N. 2 (1964)
Phys. Rev. D16, 2219 (1977)
Gottfried-Jackson (“GJ”)
1) Collins-Soper (“CS”)
target direction in the
J/ψ rest frame = (-)J/ψ
direction in the lab
frame
bisector between beam
and (–)target directions
in the J/ψ rest frame
2) “BEAM”
beam direction in the
J/ψ rest frame
3)
helicity “HCM”
J/ψ direction in the
hadron (p-n) CM frame
9
10
parametrization
2p
j
7p / 4
2l j
dN
µ 1+
dj
3+ l
cos 2j
q
5p / 4
l
3p / 4
qj
=0
example:
l j> 0
p/ 4
0
dN
µ 1+ l
d ( cosq )
q
example:
cos2q
l q< 0
- 1
dN
d ( cosq )dj
µ
1 +
(x axis ^ reaction plane)
l q cos2q
+
l
cosq
qj
- 1/ 2
0
sin 2q sin j
1
1/ 2
+
l
j
sin 2q cos 2j
11
lφ ~ 
CS
lφ
BEAM
HCM
HB 41.6 GeV p-C/Ti/W
NA3 22.9 GeV p-Pt/p-H2
E615 21.8 GeV π±-W
p-W/πW
E537 15.4 GeV p-Be/πBe
p-Cu/πCu
/
/
/
/
12
meaning of lθφ
production
plane
polar
axis
l
l
qj = 0
qj
<0
l q< 0
l j >0
l θφ ≠ 0 means that
the axes of the
current frame are
not principal axes of
symmetry for the
angular distribution.
l
l q> 0
l j >0
qj
=0
l
qj
<0
But it is always
possible to define a
reference frame with
this property: the
angular distribution
can always be
diagonalized to a
form with l θφ = 0
The “natural” polarization frame has l θφ equal to zero: in such frame the
decay distribution is symmetric and is described by only two parameters.
13
lθφ in the three frames
preliminary, m+ m- + e+ eBEAM CS HCM
lθφ
(statistically
~100%
correlated)
<xF>


<pT> [GeV/c]
The three frames actually see the decay kinematics from different
perspectives
l qj <: l
qj
,l
qj
Ю CS the best frame?
14
lθ and the hierarchy of frames
dN/d(cosθ)  1 + λθ cos2θ
1 dN
Nd(cosθ)
preliminary
HCM
(arb. norm.)
BEAM
(arb. norm.)
m+ mcosθ
lθ
CS
e + e-
preliminary
cosθ
HCM BEAM CS
|lθ|
>
|lθ|
>
mm +e e
+
-
+
-
<xF>
mm +e e
+
-
<pT> [GeV/c]
+
-
|lθ|
15
interpretation
case 1
lθ
HCM
CS
polarization generated
in the CS frame … and translated into
the HCM frame
<pT> [GeV/c]
lθ
case 2
points = data,
lines = Toy MC
<xF>
The data are consistent (for example)
with a polarization
l
q
щ
= - 1 Чexp й
-к pJCM
/ y (2GeV / c)ъ
л
ы
generated in the CS frame
generation in the
HCM frame
CS
<pT> [GeV/c]
No hypothesis of generation in the HCM fr.
can reproduce the data in the CS fr.
The CS frame is the best approximation
of the “natural” polarization frame
 physics: origin of J/ψ polarization
experimental situation: CS frame
16
J/ψ significantly polarized at low momentum (low pT and |xF|)
lθ
E866
E444
NA3
NA3
HB
38.8 GeV
20.6 GeV
22.9 GeV
22.9 GeV
41.6 GeV
p-Cu
π±-C/Cu/W
p-H2
p-Pt
p-C/Ti/W
17
BEAM frame
lθ


E537 p-W/π W /
p -Be/π Be /
15.4 GeV p-Cu/πCu /
WA11 16.8 GeV
31.1 GeV
E672 31.6 GeV
/706
38.8 GeV
E771 38.8 GeV
E615 21.8 GeV
HB
41.6 GeV
π-Be
π-Be
p-Be
p-Be
p-Si
π±-W
p-C/Ti/W
HCM frame
polarization almost completely smeared out, except for pT very close to zero
lθ
E444 20.6 GeV
CDF 1800 GeV
Run II
WA92 25.7 GeV
NA60 17.3A GeV
HB
41.6 GeV
π±-C/Cu/W
p-p
π±-W/Cu/Si
In-In
p-C/Ti/W
18
19
ψ′-to-J/ψ production ratio
Analysis finished. Combined results (e+e- + μ+μ-):
B′σ(ψ′)/Bσ(J/ψ) (%)
+ r ye ў e
1.63±0.08 % (C)
п
By ў® l + l - s y ў м
п
=
=п
н1.99 ±0.26 % (Ti)
BJ/y ® l + l - s J/y п
п
п
о1.62±0.11 % (W)
E705 E288 NA38,
NA38
NA50 &
E444
NA51
184
238
6
12
9
Ry ў= r y ў ґ
BJ/y ®
By
l+ l-
ЧBy
ў®
ў® l + l -
м
п
J/y
п
п
пJ/y
н
J/y
п
п
п
п
оJ/y
p +p p 0p 0
h
p0
= (7.0 ± 0.2 ± 0.4 BRs )%
E789
E771
197
12
9 27
2
64
28
1
108
184
HERA-B
HERA-B
HERA-B
48
12
184
p-A
 p-A results consistent within a 4% variation:
 no apparent dependence on production energy
12
E331
and kinematics (different xF/y, cosθ windows)
 slight dependence on the target nucleus:
NA38/50/51 (+ E866)
s
[GeV]
20
ψ′ kinematics
HERA-B (full stat, e+e-/μ+μ- avg.)
E789 (38.8 GeV)
E771 (38.8 GeV)
NA50 (29.1 GeV)
xF
B′σ(ψ′)/Bσ(J/ψ)
B′σ(ψ′)/Bσ(J/ψ)
measured relative to the J/ψ
distributions: B′σ(ψ′)/Bσ(J/ψ)
as a function of xF. pT , cosθ
cosθ
pT [GeV/c]
l q (y ў) - l q ( J /y ) = 0.23 ± 0.17
21
χc production
selection:
c
J/y g
e+ e m+ m-
{
measurement:
 fraction of J/ψ’s from χc:

s (c c ( i ) ® J/y g )
Rc c = е
s
INCL
(J/y )
kinematical distributions
 A-dependence

entries/(10 MeV/c2)
c
preliminary
2002/2003 data
(di-muon sample)
background: mixed events
after background subtraction
m(μ+μ-γ)-m(μ+μ-) [GeV/c2]
from the 2000 data, with
370 ± 74 χc’s (μ+μ- + e+e-):
R(c) = 0.32 ± 0.06 ± 0.04
[Phys. Lett. B 561, 61 (2003)]
new data: 40 bigger χc statistics
(the largest analyzed in a hadronic experiment)
22
R(χc)
preliminary evaluation
(2002/2003 data):
(21 ± 5)% of the produced
J/ψ’s come from χc decays
based on 1300 χc’s
reconstructed in the di-muon channel
(less than 10% of the total statistics)
R(c c )
E771
(p-Si)
(%)
E369/
610/
673
(p-Be)
π-A
2000
E705
(p-Li)
expected
final
precision
2002/3
prelim.
ISR
(p-p)
CDF
(p-p)
HERA-B
s
[GeV]
23
J/ψ’s from b decays
detached J/ψ’s
pA  bb X
b  J/ψ Y  e+e-/+- Y
Rb =
46.2 ± 8.2
36.9 ± 8.1
m+ m-
e + e-
N ( J/y ¬ b)
N TOT (J/y )
= (0.065 ± 0.011)%
- normalization by total J/ψ cross sect.
- correction by BR of b  J/ψ
σ(bb) = 14.9 ± 2.2stat±2.4syst nb/nucleon
[Phys. Rev. D 73, 052005]
σ(bb) (nb/nucleon)
- extrapolation to full xF range
mee
m
102
HERA-B N. Kidonakis et al.
E789
E771
10
1
R. Bonciani et al.
400
500
600
700
800
900
1000
proton energy (GeV)
24
indirect and direct J/ψ production
Using partial/preliminary HERA-B results:
(7.0±0.4)%
(to be (21 ± 5)%
improved!)
s
J/y
DIR
s
= s
J/y
pN
J/y
INCL
й
к1 - R
кл
χc
J/ψ
- R
(0.065±0.011)%
ψ′
J/ψ
- R
b
J/ψ
[41.6 GeV ] = (663 ± 74stat ± 46syst ) nb/nucl
щ
- Kъ
ъ
ы
ISR
extracted from MB data
E331 E705
E444 UA6
(72 ± 5)% of the J/ψ’s
are produced directly
NA3
E672/706
NA50
E595 E288
curve: NLO NRQCD fit of all data
(Maltoni et al., hep-ph/0601203)
E331
NA3
p-p
p-A
E771
E789
25
open charm: reconstructed signals
p+
N
N
preliminary
D0+D0
194 ± 20
entries/(10 MeV/c2)
entries/(10 MeV/c2)
D
+
p D *+ 0
D
K-
p+
D±
92 ± 11
p+
p+
N
preliminary
0
preliminary
D
p
entries/(0.5 MeV/c2)
K-
p
K-
p+
D*±
49 ± 10
| m( K p ) - m( D0 )|< 50MeV
| m( K p ) - m( D0 )|> 50MeV
Kπ inv. mass [GeV/c2]
Kππ inv. mass [GeV/c2]
m(Kππ)-m(Kπ) [GeV/c2]
D cross sections
26
comparison with p-p/p-A results
D0+D0
D±
HERA-B prel.
HERA-B
prel.
without E789:
with E789:
√
D*±
HERA-B
prel.
√

D0: unclear situation at high √s


E789 result clearly disfavoured
energy dependence well described
in each case by the function
s D µ [1 - 1.2/( s )0.35 ]12

√
reflecting the behaviour of proton
PDFs (Lourenço & Wöhri)
isospin symmetry
cross section ratios: experiments vs. isospin symmetry
ud
3 polar. states
s DIR ( D0 ) = s DIR ( D+ ) =
1
s ( D* )
3
PDG averages for
D*0, D*±  D0, D±
feeddown BRs
s INCL ( D± )/ s INCL ( D0 )
s INCL ( D*± )/ s INCL ( D0 )
= 0.326 ± 0.003
= 0.497 ± 0.001
violated
by a factor of
1.87 ± 0.25
experiments
avg. = 0.61 ± 0.08
D±/D0
avg. = 0.43 ± 0.09
D*±/D0
HERA-B
prel.
HERA-B prel.
ud
ud
√
√
27
28
mass spectra
by target material
(e.g. for D0):
entries/(10 MeV/c2)
A-dependence
C
70 ± 11
Ti
W
19 ± 6
103 ± 14
α(D0)= 0.92±0.08
Kπ inv. mass (GeV/c2)
α(D±)= 1.02±0.09
experimental situation (p-A):
α(D*±)= 1.05±0.14
αAVG.(xF~0) = 1.01 ± 0.03
W
Ti
C
curves: σpA = σpN·Aα
(prel.
D-meson
average)
consistent with
no suppression
summary
J/ψ production in p-A collisions at √s = 41.6 GeV …
 high statistics, clean signals, two decay channels
 wide kinematical coverage
 pT up to 5.5 GeV/c
 negative xF
 A-dependence:
 flat suppression
 down to xF ~ -0.35
… and its components:
 ψ′-to-J/ψ ratio
 fraction of J/ψ’s from χc
 fraction of J/ψ’s from b
J/ψ decay angular distributions
 longitudinal polarization rapidly increasing in magnitude with
decreasing pT and |xF|
 strong hierarchy of frames: the direction of the original interaction
(CS frame) is better than the J/ψ “flight” direction (HCM) as a
reference for the observation of the “true” decay distribution
open charm
 D0, D±, D*± inclusive production cross sections and ratios
 A-dependence consistent with α = 1
29