Influence of the πN KΛ -...

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The 2nd PWA Workshop, Zagreb 2005The 2nd PWA Workshop, Zagreb 2005

Influence of the Influence of the ππNN→→KKΛΛchannel to the number and channel to the number and

properties of the P11 properties of the P11 resonancesresonancesBranimir ZaunerBranimir Zauner

Rudjer Boskovic InstituteRudjer Boskovic Institute

•πN→KΛ is a very sensitive process to the number and properties of the P11 resonances in energy range 1.7GeV < W < 1.8 GeV, therefore it is an optimal place to search for the predicted and still missing crypto-exotic pentaquark states

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The 2nd PWA Workshop, Zagreb 2005The 2nd PWA Workshop, Zagreb 2005

ππNN→→KKΛΛ, PWA, resonances, , PWA, resonances, pentaquarks, and do these pentaquarks, and do these terms have something in terms have something in

common?common?

Or, how to get shiny things from Or, how to get shiny things from notnot--soso--shiny raw materials?shiny raw materials?

This is, contrary to the first slide, what this talk will be about.

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Current situation Current situation –– experimental experimental datadata

Experimental data is old. Youngest celebrated Experimental data is old. Youngest celebrated itit’’s 27s 27thth birthday this Maybirthday this May

We are talking about spark chambers We are talking about spark chambers experiments.experiments.

Experiments are all within Experiments are all within ““the experimental the experimental errorerror””....more or less.....more or less.

This is current situation in πN→KΛ channel

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To illustrate:To illustrate:

•Experiments show peaked structure near W=1700 MeV•We want to get that structure and find if there is a way to explain the structure with a resonance

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•However, when we put data sets together, they show inconstistency (in both normalization and energy point where the peak is) and there is not much one can get from them.

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Current situationCurrent situation

Consequence is that theoreticians Consequence is that theoreticians basically ignore these data sets.basically ignore these data sets.

•If one looks in PDG book, one can see that πN→KΛ data is cited only for completeness sake.

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My missionMy mission

Task was Task was simplesimple::

Fit the data to a single channel Fit the data to a single channel -- single single resonance model, and try to get something resonance model, and try to get something

out of it.out of it.

We wanted to show that N(1710) is needed to describe data, and that PW Analises which do not show it, do not show it because they ignore inelastic channels.

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The formalism was extremely simple:The formalism was extremely simple:

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To cut the long story short, I got this:To cut the long story short, I got this:

•Red line comes from PDG resonance parameters•Fitting procedure could not fit data to catch both the peak and tail of the data.•Therefore I fitted data in a way to get peak (green line) and tail (blue line).

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What can we do?What can we do?

We can amalgamate data sets.We can amalgamate data sets.

•Our group had previous experience with inconsistent data, and this step was a logical thing to do.

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Experimental dataExperimental data

•Experimental data has a peak around 1700MeV

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AmalgamationAmalgamation

•We renormalized van Dyck’s and Knasel’s data to get them to the same total cross section•After, we shifted Knasel’s data 9 MeV in W. This step is open to criticism, but all of the shifting was within experimental errors that were stated in their articles.•We wanted to get the structure, not the exact position of the peak, because we wanted a qualitative answer if there is a N(1710) resonance influence in this channel.

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Now what do we get?Now what do we get?

• Extra care was made to fit the peak.• We got the result from differential cross sections and they required no P13

resonance, which was introduced by Knasel et al. and Baker et al in order to describe Knasel’s differential cross sections.

• We beleived Baker’s data more, since it showed two qualities:1. Differential cross sections were continuous (no jumps, just a continuous

line in cos(θ), which was completely different in Knasel’s choice)2. They were linear in contrast with Knasel’s, which were impossible to

classify

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Another resonance?Another resonance?

•We put another resonance in the fit (added through K-matrix formalism), and get a better fit throughout the energy region.The second resonance has parameters M=1780 MeV, Γ=154MeV and a few percent branching fraction into KΛ channel.•With this, we managed to get both peak and the tail of the data.•This all smells of pentaquark. But how can we tell if it’s a pentaquark?

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Pentaquark, or not a pentaquark...Pentaquark, or not a pentaquark......that is a serious question...that is a serious question

KK00 ΛΛ channel has the right channel has the right quark compositionquark compositionIt has a peak in the total It has a peak in the total crosscross--section at the right section at the right placeplaceThe peak is quite narrowThe peak is quite narrow

But that is not enough!But that is not enough!

•As stated before, this smelled of pentaquark, but how can we be sure if the resonance has 3 or 5 quarks?

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So, how can we tell if itSo, how can we tell if it’’s a pentaquark?s a pentaquark?

There are no well defined rules to which we There are no well defined rules to which we could turn to.could turn to.

So, we checked and rechecked quarkSo, we checked and rechecked quark--model model baryon resonance articles and crossbaryon resonance articles and cross--checked checked them with pentaquark articles.them with pentaquark articles.

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And we came to our rules:And we came to our rules:

1.1. The resonance has to be quite narrowThe resonance has to be quite narrow2.2. Branching fractions to elastic and inelastic Branching fractions to elastic and inelastic

channels should be comparable.channels should be comparable.

1.It comes from any article about pentaquarks- Diakonov, Wilczek...2.We (and PDG) get it similar, and all of the three-quark models give disproportion between them

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Is it enough?Is it enough?

NO!NO!

Why not?It’s quite simple. There is a great threat of mistaking the channel opening with a resonance, especially if the channel opening is so near threshold. We need coupled-channel analysis which incorporates not only or channel, but all that have opening in the 1700 MeV region.

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What can we do?What can we do?

There is just one thing to do.There is just one thing to do.

Beg experimentalists to remeasure Beg experimentalists to remeasure ππNN→→KKΛΛ processprocess, but also , but also ππNN→→KKΣΣ

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What else can we do?What else can we do?

We can try to put We can try to put simple Tsimple T--matrix into matrix into the fitting machine as the fitting machine as partial wave data.partial wave data.

However, this step is not without hazard and one should not do it hastily.The danger is that number and distribution of points can jeopradize results, since usually, one will get “artificial” T-matrices.By artificial, it means that T-matrices will be dense in a certain energy region (one where actual measurements were made, and where we did the original fitting) and nonexistant elsewhere.Preliminary results (with such artificial T-matrices) give significant distortion in πN elastic channel, which is opposite

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The EndThe End

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Differential cross sectionsDifferential cross sections

This picture shows agreement between different data sets and different fits. If one looks more closely, one can see that boxes (Baker’s data) shows linearity, while diamonds (Knasel’s) show strange behaviour.

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Does PDoes P1111(1710) exist?(1710) exist?

This is the last published PWA, by Arndt et al., which has no N(1710) in it. Prof. Arndt answered that he does not need the N(1710) to describe the data well.

Influence of the πN KΛ -...

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