Possibility for hypernuclei including pentaquark, Q

1
Possibility for hypernuclei including pentaquark,
Q
High resolution search for Q

• Kiyoshi Tanida (Seoul National Univ.)
• 19 Sep 2009
• PUHF_at_J-PARC

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Part I.High resolution search of Q by (p-,K-)
reaction possible width measurement
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Mysteries about pentaquark Q

• Does it really exist?
• Confirmation with good sensitivity is crucial
• Lets assume the answer is yes.
• Width? Why so narrow?
• Certainly lt 1MeV
• No bump in Kn? Kn, K0p
• Spin parity?
• 1/2? 3/2? 1/2-? ...
• Its nature?
• KN? KpN? ...

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Why high resolution?

• For good S/N ratio
• Q is above KN threshold, and is NEVER BG free
• High resolution really helps to achieve good S/N
  ratio? crucial for good sensitivity
• Width measurement
• Almost certainly, lt 1 MeV
• Similar or better resolution necessary!
• Typical resolution so far 10 MeV
• No high resolution search
• There is a good chance

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J-PARC E19

• The first exp. _at_K1.8(Spokesperson M. Naruki)
• p(p-,K-)Q reaction
• A good resolution2 MeV (FWHM)expected thanks
  toK1.8 beamline and SKS
• Sensitivity 100 nb/sr
• Stage 2 approved Day-1

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p(p-,K-)Q reaction KEK-PS E522

• Poor resolution 13 MeV (FWHM)
• Low statistics lt 1010 p- on target
• Still, there was a hint of peak 1.9
  mb/sr 2.5s significance
• ? Statistics x100 Resolution x1/5

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Expected spectrum
1.9?b/sr G 0
Width measurable down to G 1MeV
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Toward even higher resolution?

• Most likely, GQ lt 1MeV ? E19 is not enough
• How can we go higher resolution?
• Use of dispersion matched beamline/spectrometer(H
  . Noumi, talk available later)
• Latest design is suitable for p(p-,K-)Q reaction
• Excellent resolution down to 0.1 MeV (FWHM) is
  possible
• No tracking detectors for beam particles.
• High beam intensity (up to 109/spill) possible
• Similar statistics as E19
• Higher beam intensity x100
• Thinner target x1/10
• Smaller spectrometer acceptance x1/10

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An example of floor layout (by Noumi)
A23 Magnet from Saclay
Exp. T
...connected to K1.8BR. It can also be designed
to be connected to T2
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Layout Plan in Extended HD-Hall
T2
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Part II.Possibility for hypernuclei including Q
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Motivation

• Extend Baryon-Baryon interaction to include
  anti-decuplets
• May give a hint about the nature of Q
• For example, D. Cabrera et al., nucl-th/0407007
  calculated self-energy of Q-KN channel (i.e.,
  K-exchange)? weak, not enough to give bound
  states
• If Q-KpN channel is taken into account, strong
  binding can be obtained (cf. N(1710) strongly
  couples to Npp)
• There are many other scenarios...
• Well, its interesting in itself, isnt it?

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3D nuclear chart
?
S1
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How can we produce?

• 3 important factors to be considered
• s sele x Neff x f
• Large elementary cross section
• Small momentum transfer
• Mass resolution
• Missing mass spectroscopy with 2-body reaction
  (with only charged particles involved) is
  preferable.
• Background
• Should be small or strong reduction methods
  should exist

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Possible Production Methods

• (K,p) reaction Proposed by Nagahiro et
  al.PLB 620 (2005) 125
• Momentum transfer 500 MeV/c
• Elementary cross section lt 3.5 mb/sr (KEK-PS
  E559)Miwa et al., PRC
• (p-,K-) Momentum transfer 1 GeV/c small cross
  section (lt a few mb/sr E522)
• d(g,L(1520)) small momentum transfer, suffers
  from poor resolution

We propose (K,p) reaction K. Tanida and M.
Yosoi, J-PARC LOIhttp//j-parc.jp/NuclPart/pac_08
01/pdf/LOI_Tanida_pentahyper.pdf
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The (K,p) reaction

• Elementary process d(K,p)Q
• Small momentum transfer
• High resolution missing massspectroscopypossibl
  e

n
T
p
K
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Elementary cross section (1)

• Calculation by Nagahiro and Hosaka using on-shell
  approximation
• Total cross section is proportional by GQ
• ds/dW 1 mb/srfor GQ 1 MeV

GQ 1 MeV
ds/dW2p(mb/sr)
peak at finite angles (q 420 MeV/c)
cosq(in CM)
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Elementary cross section (2)

• Phenomenology by Friedman and GalPRL94 (2005)
  072301 Phys. Rep. 452 (2007) 89
• They suggested 0.1-0.5 mb
• based on kaon absorption data
• tr potential fails to fit
• trDVopt is good
• DVopt could be attributed to Q production due
  to KnN ? QN

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Background process

• Kaon decay is not a background
• Preferable compared to the (K,p) reaction
• Main backgrounds
• Kp quasi elastic scattering and Kn charge
  exchange reaction
• Can be estimated from old experimental data5
  mb/sr and 1.5 mb/sr for pK1 GeV/c and qplab 0
  deg.
• Proton momentum is mostly around 1.2 GeV/c, while
  pp1.1 GeV/c for Q production events? needs
  Fermi momentum of 200 MeV/c actual BG would
  be small ( 1 mb/sr/MeV)

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Reduction of BG
Quasi-elastic scattering
n
p
K
Q production
n
T
p
K0
p
K
Detect K0 and/or proton in sideway counters(Q
decay momentum is 270 MeV/c)
Ultimately, 2-step BG limits (S/N1 in on-shell
approximation)
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Yield estimation (1) at K1.8

• K1.8SksPlus
• pK 1.1 GeV/c
• Intensity 3 x 105/spill
• 30 msr, efficiency 0.5
• Resolution 3 MeV FWHM
• Target liq. d 1.6 g/cm2
• Yield 1.1 event/hour/(mb/sr)
• Feasible from a few mb/sr
• Easy, if cross section is as large as 0.1 mb, as
  estimated Friedman
• We dont need K0/p tagging for good S/N ratio
• Background study is possible, at least

beam K
scattered proton
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Yield estimation (2) at K1.1

• gt 10 times higher beam intensity
• gt11 event/hour/(mb/sr)
• Feasible even for on-shell approximation
• E.g., assuming 0.1 for K0/p tagging efficiency,
  0.5 mb/sr would be enough
• Note T? pK0 1/2, K0 ? K0s 1/2, and K0s ? pp-
  2/3so that K0s ? pp- tagging is not efficient.
  Proton/K tag is preferred.
• To be studied...
• How to achieve high tagging efficiency?
• How far BG can be reduced?
• 0 deg. vs finite angle. Which is better?
• Need detailed MC simulation and careful design.

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Experimental Setup (1)
Sks-Plus spectrometer

• 95total bend
• 7m flight path
• Dx0.3 mm (RMS)
• High resolution
• DE 3 MeV FWHM

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Experimental setup (2)

• Sideway counters
• High resolution is not necessary. Simple setup
  may be OK.
• Need to detect low energy protons

toSKS
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Toward Hypernuclei

• Naively, s increases with A(A-1)
• Efficient recoilless production for s-shell
  target (4He) ? Similar statistics as d target
  (or even larger).
• Fermi momentum is larger need to be cautious
• Heavier hypernuclei may be difficult
• Increase of background.
• FSI for decay particles.
• Still possible if KnN ? QN is dominant
• How about the width?
• Reduction is expected due to Pauli blocking and
  smaller decay energy.
• QN ? KNN process may increase it.

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Summary

• Part I. High resolution search of Q
• Missing mass spectroscopy with (p-,K-) reaction
• Width measurable to 1 MeV in E19, and to 0.1 MeV
  with high-resolution beam line.
• Part II. Search for Q-hypernuclei
• (K,p) reaction recoilless production of Q
  possible
• We would like to start with d(K,p)Q
• Detection of p/K0 in sideway counters reduce BG
• Feasible at K1.8 or K1.1 beamline.
• If d(K,p)Q is successfully measured, we will
  search for 3QHe.