Quarkonia
production with the
HERA-B
experiment
J. Spengler, MPI Heidelberg
The Hera-B Detector
• Fixed target detector at e-p ring HERA, Desy
• High rate forward spectrometer (< 40MHz)
• Wire targets (different materials) in proton halo
• Proton beam at 920 GeV/c (√s = 41.6 GeV)
184W
• High resolution vertexing
• Very good particle ID for (e, , , K, p)
• Hardware track trigger for lepton pairs
• Multiple trigger level
12C
48Ti
z [cm]
• On-line event reconstruction
2
The Hera-B Detector
Angular coverage in bending plane:
15 - 220 mrad
3
Data Sample
Data taking: 30. Oct 2002 - 3. Mar 2003
•
150 · 106 dilepton triggered events with
~300,000 J/
see posters of
W. Gradl (Q21)
and M. Villa (Q20)
achieved J/ rates: 1200 - 1400 / hour
in 2000: 30 - 40 / hour
•
210 · 106 minimum bias events
achieved logging rates: 1000 Hz (1.7 TB/d)
•
90 · 106 hard photon + Glueball trigger
see talk of A.
Gorisek;
posters of
T. Knöpfle (S10),
C. van Eldik (S8)
and T. Zivko (S9)
see poster of
M. Bruschi (Q22)
4
Topics
1) pt distribution
xF distribution
J/
A-dependence
Decay angle distribution
2) (2s) production
(2s)
3) c/J/ production ratio
c
4) bb cross section
bb
5)  production
e + e+ -
(1-3s)
Disclaimer: All results are preliminary
5
J/ production; e+ e80% of statistics
≈101,000 J/
width: 64 MeV/c2
J/


(2S)
Dilepton mass accessible from 0 - 11 GeV/c2
6
J/ production; +J/
Approx. 177,000 events
Mass: 3095 MeV/c2
Width: 44 MeV/c2
Approx. 3,000 events
Mass: 3674 MeV/c2
Width: 53 MeV/c2
(2S)
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pT distribution of J/
80% of e+esample
Parameterization:
2 6
 


d
35    pT 

   1 

2
dpT

 256  pT  


Results
for <pT>:
Target Exp.
C 920
W 920
Range
< 4.8
< 4.8
Au 800 E789
Si 800 E771
< 2.6
< 3.5
e
1.22
1.29

1.22
1.30
error
0.01
0.01
1.29
1.20
0.009
0.01
stat.
only
8
xF distribution of J/
Parameterization:
10% of e+esample
d
   (1 x F )c
dx F
Is it adequate to describe the
exp. data ??

Target
Exp.
C, W 920
Si 800 E771
Au 800
Cu 800
E789
E789
Negative xF range
accessible for the time
Range
-0.35 <xF<0.15
-0.05 <xF<0.25
c
(5-6.5)0.3
6.540.23
-0.03<xF<0.13
0.30<xF<0.95
4.910.18
5.210.04
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A-dependence of J/

Parameterization of cross section:  pA   pN  A ;   N/(  L)
Determine  from two different targets:
NW L C C 
1

 log  

log( AW / AC )
NC L W W 
stat. errors only
• C (A=12.0) and W
(A=183.8) target
• 25% of full e+esample
• Ratio of efficiencies
includes full detector
+ trigger simulation
• Ratio of luminosities
under investigation 
norm. to E866 result
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A-dependence of J/
NRQCD pred.:
R. Vogt
Expected stat.
error for full
data sample:
Nucl. Phys. A700
(2002) 539
HERA-B range
BCKT pred.:
K.G. Boreskov,
A.B. Kaidalov
JETP. Lett. 77
(2003) 599
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cos distribution of J/
80% of e+esample
Parameterization:
dN
   (1   cos2  )
d cos
J/ polarization described by
parameter :
 = (0,1,-1)  (no, trans., long.)
polarization

Target
Exp.
C, W 920

(-0.5;+0.1)0.1
Be 530
E672/706
0.010.15
Be 800
E672/706
-0.110.15
Si 800
E771
-0.090.12
Cu 800
E866
0.0690.08
Expected error of  vs. pT
(Muon channel):
Important
tests of
models
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(2S) to J/ ratio
• Measure (2S)e+e- relative
to J/  to reduce systematic
uncertainties
• Carbon target
• 30% of e+e- statistics used
• nJ/ = 30k
• n(2S) = 650
 (2S ) n(2S ) Br(J /  e e ) J / 
R(2S ) 



 
J /
nJ /  Br((2S)  e e ) (2S )
13
(2S) to J/ ratio
• J/ /  (2S) = 0.720.01
• Stat. errors only;
• Use (J/) = 357±8±27 nb/N based on E771
and E789 results
R(2S) = 0.13 ± 0.02
(2S) = 46 ± 12 nb/N
Systematic studies
ongoing
Muon channel gives
compatible result
14

c to J/ production ratio
2
R c 
 ( 
i1
ci)
 Br(  ci  J / )
 (J /)
N(  c ) J / 


N(J /)   
• ECAL resolution does not allow to separate c1 and c2
states (m = 46MeV). c0 neglected due to small Br.
•  ≈ 0.4
Results of 2000 (Phys.Lett. B561(2003) 61:
N(c) = 37074 (both +-, e+e-)
R(c) = 0.320.060.04
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c to J/ production ratio
Analysis of 2002/03 data:
• Comb. background by event
mixing
• Carbon target
• In 15% of +- statistics we find
about 1300 c
•Expect N(c) ~ 15k for full sample
R(c) = 0.21±0.05
Systematic studies ongoing
Electron channel gives
compatible result
m (GeV/c2)
16
pA bb+ X, bJ/+Y
Method:
Detached vertex analysis to
separate B signal (decay length ~7
mm) from direct J/
 bb
nB
1
 J / 

nJ /  R  Bz  Br(bb  J /)
Results of 2000:
Eur. Phys.J. C26(2003) 345:
2.2
3.9
e+e- = 8.63.2 ; +-= 1.91.5
146
 bb 32127
nb /N
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pA bb+ X, bJ/+Y
Analysis of 2002/03 data:
• 35% of e+e- and +- statistics
• Expect NB ~ 100 for full sample
• Carbon + Tungsten target
• J/ acceptance: -0.35<xF<0.15
(90% of bb cross section)
• Preliminary results of both
channels compatible
• 1.5  lower than 2000
measurement
 bb12.3
3.5
3.2
nb /N
18
pN  + X, +-, e+en  Br(J /  l  l )  J / 
  J / 

 
 
n J /  Br(  l l )

Drell-Yan
Drell-Yan
Comb. BG
Comb. BG
M(+-) (GeV/c2)
M(e+e-) (GeV/c2)
Drell-Yan contribution compatible with E866
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pN  + X, +-, e+e• All C and W data used
• Relative production of
(1S)/(2S)/(3S) fixed on
E605 data
Events
Br• d/dyy=0
+-
33±7
3.9±1.1 pb/N
e+e-
31±10
2.9±1.2 pb/N
both
3.4±0.8 pb/N
•  shapes taken from MC
• Modified Craigie applied
to allow for nuclear
suppression: =0.990.05
Br 
d 
dy
Not used
in fit
 m 
( s )   o exp   o   A 1
s

y 0
√s (GeV)
20
Summary
o
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HERA-B has finished data taking.
Large dilepton sample (both +-, e+e-) allows for
detailed study of J/ (300k), (2S),  and bbproduction
Quality of data is very good
HERA-B has large acceptance (negative xF) and good
particle identification
Analysis of 2002/03 data in progress
First preliminary results presented
New collaborators welcome to contribute to analysis
of this rich data sample
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