Search for Pentaquarks in 920 GeV Proton-Nucleus Collisions at HERA-B

1
Search for Pentaquarks in 920 GeV Proton-Nucleus
Collisions at HERA-B

• M. Medinnis, DESY
• For the HERA-B Collaboration
• Quark 2004, Tanka Village, Sardinia
• 21 25 September, 2004

2
Experimental situation

• According to a recent count
• 12 reports of a narrow resonance (NR) in nK or
  pK0s near 1530 MeV/c2 (?).
• 8 reports this year of negative results on
  searches for ?.
• H1 reports a NR decaying into Dp (?0c ) but
  Zeus, CDF, FOCUS report non-observation.
• NA49 reports a NR decaying into ?-?- (?--) but
  Zeus, CDF, E690, Babar report non-observation.

The existence of pentaquarks is not
established. If they exist, the production
mechanism is unclear.
J. Pochodzalla, hep-ex/0406077
3
HERA-B contribution

• Search for
• ?(1540) ? p K0s ? p ??-
• ?--(1862) ? ?- ?- ? ?0 ?- ?- ? p ?- ?- ?-
• At mid-rapidity in pA collisions at 920 GeV,
  using a large, clean (pileup ? 10) minimum bias
  sample 200 million interactions
• (A C, Ti, W)

4
HERA-B Detector
920 GeV incident protons
Main tracker
MAGNET
Wire Targets
Vertex Detector
RICH
ECAL
x
z
5
RICH/ECAL Particle ID

• For K0s, ? reconstruction no particle ID
  requirements
• Otherwise (where L ? likelihood)
• Pions (weak) LRICH(e,?,?
  ) gt .01,
  LECAL(e) lt 0.9
• Kaons (strong) LRICH(K) gt
  0.95? mis-id lt 2, p range 12 55 GeV/c
• Protons (strong) LRICH(p) gt
  0.95 ? mis-id lt 1, p range 22 55 GeV/c

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V0 Selection
?
K0s

DCA lt 0.7mm, Mild lifetime cut pt?c? gt .05
GeV/c?cm, K/? ambiguities
are rejected
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?- and ?(1520) Signals
?- recon mp?-m? lt 3?, Cascade topology, ?z gt
2.5cm
8
pK0s mass, Upper Limit
pK0s mass (GeV/c2) for -0.3lt rapidity lt 0.3
event mixing
?mass3.9 MeV _at_ ?
UL(95) Carbon
sensitivity
1.4 1.475 1.55 1.625
1.7
With ?N ? A0.7, UL(95)B?d?/dyy0 3 ?b/N -- 22
?b/N for
1521 MeV lt m(pK0s) lt 1555 MeV
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Excess at 1540 MeV/c2?

• Fit to gaussian with ? exp. resolution fixed
  background in region of highest U.L.
• Result 54 ? 22 evts (2.4 ?)M 1541 ? 1 MeV
• consistent with a fluctuation

counts / 3 MeV/c2
pC
Mass GeV/c2
Nothing seen near 1540 MeV in pW, pTi samples.
pW
pTi
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U.L. vs. Mass, Comparison
? ?nK
Quoted mass Values
? ? pK0s
Q. Zhao F. Close,hep-ph/0404075
HERA-B Upper limit
U.L.(95) ?barns/N
Mass GeV
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?? Mass
HERA-B
(p C)
NA49
--
20
-
10
Counts / 7.5 MeV/c2
-
10
6

1.4 1.8 2.2 2.6 Mass GeV/c2
C. Alt et al. PRL 92, 042003
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?? Combined Plot, UL(95)
HERA-B
Counts / 3 MeV/c2
Rapidity -0.7 lt y lt 0.7 ?mass 6.6 GeV/c2 _at_
1862 MeV/c2
?-?-
B d?/dy ?b/C
Assuming ?N ? A0.7, UL(95) B?d?/dyy0 2.5
?b/N _at_ m(?-?-) 1862 MeV/c2
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Signal Statistics
Signal C Target All targets ? MeV/c2 NA49
K0s 2.2M 4.9M 4.9
? 440k / 210k 1.1M / 520k 1.6
?(1520) 1.3k / 760 3.5k / 2.1k 2.3
?- 4.7k / 3.4k 12k / 8.2k 2.6 1.6k / 550
?(1530)0 610 / 380 1.4k / 940 2.9 (150)
Particle / anti-particle, ? mass
resolution H.G.Fischer, S.Wenig hep-ex0401014
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Summary I ? ? p K0s
See hep-ex/0408048 for more details
UL(95)B?d?/dyy0 3 ?b/N -- 22 ?b/N in
range 1521 MeV lt m(pK0s) lt 1555 MeV
Reaction ?s GeV ?? ? . ?(1520) Source
pA, y?0 42 lt0.92 lt2.7 HERA-B (1530 MeV)
pp, y0 18 2.3 M. Bleicher et al.
pp 20/40 6.3/5.0 F.M. Liu et al.
pp 17 4.7 57 F. Becattini et al.
AA 20 3-10 50-200 J. Letessier et al.
AA 40 3-7 44-140 J. Letessier et al.
()
()
B(? ? p K0s) ? 0.25
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Summary II ?--(1862) ? ?- ?-
See hep-ex/0408048 for more details
UL(95) B?d?/dyy0 2.5 ?b/N
Production ratios and comparison to predictions,
NA49
Reaction ?s GeV ?-- ?- ?-- . ?(1530)0 Source
pA, y?0 42 lt3/B lt4/B HERA-B
pp 20/40 2.5/3.6 F.M. Liu et al.
AA 20 0.4 --1 J. Letessier et al.
AA 40 0.4 -- 1 J. Letessier et al.
pp 17 ?18/B J. Kadija (NA49)
()
()
N(?0) from hep-ex/0401014, ?--/ ?0 eff ratio
HERA-B