Search for Q pentaquark at Belle

1
Search for Q pentaquark at Belle
University of Ljubljana
hep-ex/0507014 submitted to PLB
B. Golob University of Ljubljana,
Slovenia Belle Collaboration

• KEKB and Belle detector
• Inclusive production of Q
• Exclusive production of Q

2
KEKB
KEKB asymmetric B factory
U(4s)
p(e-) 8.0 GeV/c
p(e) 3.5 GeV/c
?Ldt 480 fb-1
Lpeak 1.58x1034 s-1 cm-2
Presented analysis ?Ldt 357 fb-1
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Belle detector
Central Drift Chamber
e 3.5 GeV
3(4) layer Si det.
s(pt)/pt 0.3 vpt21
e- 8 GeV
Aerogel Cherenkov (n1.015- 1.030)
m and KL Counter (14/15 layers RPCFe)
Particle ID e(K)85 e(p?K)lt10 _at_ plt3.5
GeV/c
1.5T SC solenoid
EM calorimeter CsI (16X0)
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Measurement method

• kaons produced in ee- annihilation
• as projectiles

p

• search for Q(1540) in
• secondary interactions

CDC
K-,Ks
SVD
N in material
X
K,Ks,KL

• Selection
• identified p, K not from IP (drgt0.1 cm)
• Ks -gt pp-
• detached vtx, not from IP (drgt0.1 cm),
• 3s within m(Ks)
• pK detached vtx (1 cm lt r lt 11 cm)

5
Measurement method
(x,y) coord. of pKs secondary vertices gt
detector tomography
pK pairs arising from interactions with
nucleons in detector material
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Inclusive production of Q
inclusive analysis of m(pK-) and m(pKs) no
suppression of inelastic reactions, no estimate
of charge exchange Kn ? pKs
fit to threshold func. D-wave BW ? resolution
func.
(4.020.08)x104 L(1520) (2.5 G) G and m
consistent with PDG
pK ? L(1520) ? pK formation, p(L) 400 MeV/c
0.5 vtxs with add. K KN ?L(1520) X
?
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Inclusive production of Q
fit m(pKs) to Gaussian 3rd order polinomyal
s2 MeV/c2 from MC small corr. from W- ? L K-
lt 2.5 _at_ 90 C.L.
assuming B(Q?pKs)25 using B(L?pK-) ½
B(L?NK) ½ (451) es from MC
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Exclusive production of Q

• exclusive search for Kn ? Q ? pKs
• motivated by DIANA result
• Phys.Atom.Nucl. 66, 1715 (2003)
• main steps
• suppression of inelastic reactions
• (additional p0 or unrec. p
• major bkg. also contributions from
• Ks,Lp ? pKs)
• normalize to charge exchange Kn ? pKs(Nch)
• Nch indirectly from elastic Kp ? Kp (Nel)
• interpretation NQ/Nch ? GQ
• Cahn, Trilling, PRD69, 11501 (2004)

NQ/Nch 0.66 0.19
GQ 0.9 0.3 MeV
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Exclusive production of Q
number of charge exchange events
MC may not reproduce M and e accurately enough P
and S model dependent
use data and estimate Nch relative to Nel
Kn ? pKs Kp ? Kp
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Exclusive production of Q
process enabling a counting of Kp ? pK
p
D- ? D0p- ? (Kp-)D0 p-
K
ratio Nch/Nel
Material and nuclear effects mostly cancel out
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Exclusive production of Q
reconstruction
p
D- ? D0p- ? (Kp-)D0 p-
K
relations

• EN mN - 2e - pF2/2mN

K projectile
e 7 MeV Sibirtsev et al., EPJ
A23, 491(2005)
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Exclusive production of Q
pF for elastic events (D0), bkg. subtracted
interact- ions on hydrogen
NelD 47026
selected (enhanced elastic reactions)
DmD from secondary pK pairs combined with
additional pions
in bins of m(pK)
NelD 21 7 (Q mass)
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Exclusive production of Q
from 20 of data uniform over running period
from fit to published data typical
single experiment uncertainty
from MC
epKs/epK 0.430.05
sch/sel 0.350.02
FK/FKD 85020
(Q mass)
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Exclusive production of Q
Fit m(pKs) for possible Q signal
yield at various m(pKs) and UL
similar sensitivity as DIANA

• no vtxs with additional tracks
• 50 MeV/c lt pF lt 300 MeV/c
• 3rd order polynom.signal (s2 MeV/c2)

DIANA GQ 0.90.3 MeV
GQ lt 0.64 MeV _at_ 90 C.L.
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Summary

• Q(1540) signal searched for using kaon
• secondary interactions
• similar CM energy as in some positive
• result exps
• inclusive search
• s(KN ? Q(1540)X)/s(KN ? L(1520)X)lt2.5 _at_90
  C.L.
• exclusive search
• K n ? Q(1540) ? p Ks yield normalized to total
  
• charge exchange K n ? p Ks
• similar sensitivity to DIANA exp.
• GQ lt 0.64 MeV _at_90 C.L. for m(Q)1540 MeV/c2
• GQ lt 1 MeV _at_90 C.L. for m(Q)1570 MeV/c2

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Selection details, backup

• PID
• p Lp/K gt 0.6, Lp/p gt 0.6
• K LK/p gt 0.6, LK/p gt 0.6
• not identified as e
• L likelihood based on CDC, ACC, TOF
• Ks
• pp- 10 MeV (3s) from m(Ks)
• zdist at vtx lt 1 cm
• dr of daughters gt 0.1 cm
• q(p(Ks), r(vtx,IP)) lt 90o
• pK vtx
• dr(p,K) gt 0.1 cm
• zdist at vtx lt 1 cm
• q(p(pK), r(vtx,IP)) lt 90o
• other

typical resolution on sec. vtx 400 mm (r)
angular cuts (DIANA) do not improve S/N or
sensitivity after the pF selection applied
(suppression of 1.2, e93 ? significance
1.02)
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L projectiles, backup
Formation
Fitted parameters Of L(1520) m1518.50.1
MeV/c2 G13.50.4 MeV PDG m1519.51.0
MeV/c2 G15.61.0 MeV

• possible projectiles to produce L(1520)
• K-, Ks, KL, L (?)
• p(L)1.8 GeV/c (z0.35) to produce L(1520)
• _at_29 GeV fraction L(z0.35) 10
• s(ee-?LX)80 pb
• s(ee-?K0X)470 pb
• N(L)/N(K0) 2
• Tasso, PRD45, 3949 (1992)
• s(K-p?L(1520))3 mb, s(Lp, total)30mb
• assuming equal prod. rate of K0, K-
• Lp?L(1520)X / Kp?L(1520)X 10
• (if s(Lp, total) saturated by L(1520))

L projectiles contribute few to L(1520)
production
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Spectral function, backup
Energy of nucleon within a nuclei Eq vq2mN2
U(q,r) U(q,r) nuclear potential Fermi momentum
300 MeV/c ? Eq mN q2/2mN - U(q,r) if U ?
1/r, virial theorem, U -2 q2/2mN Eq mN -
q2/2mN checks use of Eq mN 2e - q2/2mN,
with fixed e gives - correct mD0 - expected pF
distrib. use of Eq mN ER ER (removal
energy) tuned to reproduce mD0 ? ER26 MeV ER 2e
q2/2mN, nucleons with higher momenta are more
tightly bound

• Sibirtsev et al.
• EPJ A23, 491(2005)
• Z.Phys. A358, 357(1997)

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Q exclusive integrals, backup
all quantities depending only on m(pK) ? factorize

• products Me approx. independent of q ? decoupled
  from F
• fraction of recon. D in pF hydrogen peak w.r.t.
  all
• independent of p(pK) since fraction ? 1/P ? P
  ? F(p(pK))

cancels in the ratio
S(EN,pF) W(pF)d(EN-f(pF)) W(pF) Fermi mom.
distrib. (data) f(pF) defined so that EN
f(pF) ? max. of S(EN,pF)
remaining eff. dependence on p(pK) at given m(pK)
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Q exclusive integrals, backup
ratio Nch/Nel
MC integration pF assumed isotropic w.r.t.
pK e(p(pK)) ? 3 corr. to the ratio uncertainty
dominated by assumed EN, pF relation
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pF distribution, backup
Fit to
(oscillator model)
p01154 MeV/c comparable to other measurements
of pF, e.g. B.M. Abramov et al., JETP Lett. 71,
359(2000)
using ENmN ? hydrogen peak exactly at 0
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additional plots , backup
sch/sel 0.350.02
FK/FKD 85020
NelD47026
from fit to published data typical
single experiment uncertainty
s16 MeV/c2
major uncertainty from EN, pF relation
Fit to m(pKs) sensitivity to GQ 0.42 MeV
epKs/epK 0.430.05
from Geant based MC uncertainties in tracking
and Ks eff., second. vtx eff., material desc.,
reaction kinem., MC stat.
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GQ, backup
R.N. Cahn, G.H. Trilling, PRD69, 11501 (2004)
BW form s(m) BiBfs0G2/4 / (m-m0)2G2/4 s068
mb (J1/2) mass resolution broader than natural
width ? integral I? s(m) dm 107 mb BiBf G
estimate of 26 signal evts in two 5 MeV bins,
bkg. level 22 evts / bin assumed bkg. from
charge exchange, sch4.10.3 mb ? I (26/22) x 5
MeV x 4.1 mb 24 mb MeV BiBf1/2 G0.90.3
MeV
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Ks,KL p ? Q ? p Ks, backup
A. Kaidalov, private comm.
apart from charge exchange reactions also Ks p ?
Ks p and KL p ? Ks p may contribute to signal KL
p ? Q ? p Ks interference between amplitudes for
same final state can lead to hole in s(KL p,
total) due to Q s(KL p, total) 2 mb ?
negative interference lt 1 mb (also depending on
decay angles) s(K n ? Q ? p Ks) 17 mb
(DIANA) hole negligible Ks p ? Q ? p Ks would
also compensate for that
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Other S states, backup
total s(pK-) shows two prominent structures at
1520 MeV/c2 and at 1800 MeV/c2 latter due to
several overllaping L and S states clearly
seen, hard to interpret
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Some additional statistics, backup
95 C.L. limits GQ lt 0.78 MeV (_at_ 1539 MeV/c2)
lt 1.11 MeV (wide range) probability of stat.
fluctuation for the signal of the DIANA size to
the level observed by BELLE 3