PP and Charmonium

Ted Barnes Physics Div. ORNL andDept. of Physics, U.Tenn. (and DOE NP) Fermilab 25 Jan 2008

1. What GSI needs to know:

Associated charmonium production cross sections at low to moderate energies

( pp cc + m )

(Will show recent theoretical calculations of these cross sections,Together with all the data in the world.)

2. Why is this intrinsically interesting?

One e.g. NNJ/ or NNJ/ coupling: How does QCD do this?

How do other cc states compare?

1. What GSI (PANDA) is all about:

The search for non-qq mesons.

To most sane theorists this means qq + gluonic excitation,

= “hybrid mesons”.

(Light-q multiquark systems spontaneously dissociate, leaving their advocates behind.)

Smoking gun: hybrids can have all JPC, unlike qq. Just search for a meson with JPC-exotic quantum numbers;

…

Panda logic:Light meson studies (u,d,s) were already well underway (prev. LEAR, BNL, JLAB),How about going to heavy quarks? cc-hybrids? Narrower states, cleaner spectrum.

JPC-Exotic Charmonium hybrids = the ultimate goal of PANDA / GSI.

We already have the LEAR community (ca. 300 people). Let’s use pp.

PANDA at GSI… (ProtonAntiprotonaNnihilationexperimentatDArmstadt)

“m” = light meson(s)

cJ/

X(3872)

cc-H 4.3 [GeV]

pp cc + m, cc-H + m p beam energies…

KEp = 0.8 – 14.5 [GeV]:

Allows access to cc and cc-H mass range.

Kinematics of pp cc + m

s½

Problem:

You can’t make JPC-exotics in s-channel pp annihilation (as in E760/835 here at Fermilab), since pp only accesses conventional meson (qq) quantum numbers. To make J PC- exotic hybrids you have to make something else to recoil against (associated production):

Why associated production? ( pp cc + m, (cc)H

+ m )

p

p

qq quant. nos. only

p

p

All JPC quant. nos.,including cc-hybrids with exotic JPC

something elsee.g. typically

New Problem: Just how big are these cross sections?Let’s look at all the world’s data.

our calc.

Evidently ca. 0.1–0.2 [nb] near threshold for J/ . Other states, other energies??? Nada.

All the world’s (published) data onpp cc + meson (exclusive) processes.

( pp J/ ) E760

pp pp J/ J/ + + 00 from from continuumcontinuum

M. Andreotti et al., PRD 72, 032001(2005)

Expt…

Only 2 E760 points published.

This is E835, c/o D.Bettoni.

Physical cross sec is ca. 100x this.

What PANDA needs to know:

What are the approximate low-E cross sections for pp + meson(s) ?

( is a generic charmonium or charmonium hybrid state.)

Recoil against meson(s) allows access to JPC-exotic .

2. 2. TheoreticalTheoretical estimates of low to moderate energy estimates of low to moderate energy

associated charmonium cross sectionsassociated charmonium cross sections

( ( pppp ccc + m + m ) )

(What you can do in lieu of a direct measurement of these cross sections.

Also includes other possible experiments.)

The actual processes are obscure at the q+g level, so “microscopic” models will be problematic. We just need simple “semiquantitative” estimates.

A quick run through the literature (just 4 references) …

Approximate low to moderate-E cross sections for pp + meson(s) = ?

Four theor. references to date:

1. M.K.Gaillard. L.Maiani and R.Petronzio, PLB110, 489 (1982). PCAC Wpp J )

2. A.Lundborg, T.Barnes and U.Wiedner, PRD73, 096003 (2006). Crossing estimates for ( pp m) from ( p p m) (’ ; m = several)

3. T.Barnes and X.Li, hep-ph/0611340, PRD75, 054018 (2007). PCAC-like model W ( pp ),

c

‘

4. T.Barnes, X.Li and W.Roberts, arXiv:0709.4491v2, PRD to appear soon. [3] model, ee J/ pp (for BES), pp J W and . Dirac and Pauli strong ppJFFs. Polarization.

1. M.K.Gaillard. L.Maiani and R.Petronzio, PLB110, 489 (1982). PCAC-like model Wpp J )

Soft Pion Emission in pp Resonance Formation

Motivated by CERN experimental proposals. Assumes low-E PCAC-like dynamics with the pp system in a definite J,S,L channel. (Hence not immediately useful for total cross section estimates for PANDA.)

Quite numerical, gives W() at a specific E(cm) = 230 MeV as the only example.

Implicit analytic results completed in Ref.2.

Crossing estimates:

We have experimental results for several decays of the type ppm. These have the same amplitude as the desired ( pp m ).Given a sufficiently good understanding of the decay Dalitz plot, we can usefully extrapolate from the decay to the production cross section.

n.b. Also completes the derivation of some implicit results for cross sections in the Gaillard et al. PCAC-like paper.

0th-order estimate: assume a constant amplitude, then ( pp m) is simply proportional to ( ppm ).

Specific example, (pp J ):

2. A.Lundborg, T.Barnes and U.Wiedner, hep-ph/0507166, PRD73, 096003 (2006). “summer in Uppsala, c/o U.Wiedner”

Charmonium Production in pp Annihilation:Estimating cross sections from decay widths.

These processes are actually not widely separated kinematically:

p

we know … we want …

J/

p

p

A

p

A

J/

dt

For a 0th-order (constant A) cross section estimate we can just swap 2-body and 3-body phase space to relate a generic cc

( pp ) to ( pp

Result:

where AD is the area of the decay Dalitz plot:

Next, an example of the numerical cross sections predicted by this simple estimate, compared to the only (published) data on this type of reaction…

( pp J/ ) from ( J/ pp

compared to the E760 data points:

our calc.

Not bad for a first rough “phase space” estimate. Improved cross section estimates require a model of the reaction dynamics (next).

const. amp. model

all the world’s published data (E760)

Other channels may be larger,however the constant Amp approxis very suspect. N* resonances?

Calculates the differential and total cross sections for pp

using the same PCAC type model assumed earlier by Gaillard et al.,but for incident pp plane waves, and several choices for

c

‘

The a priori unknown pp couplings are taken from the (now known)pp widths.

3. T.Barnes and Xiaoguang Li, hep-ph/0611340; PRD75, 054018 (2007). “summer in Darmstadt, c/o K.Peters”

Associated Charmonium Production in Low Energy pp Annihilation

Assume simple pointlike hadron vertices;

g

5 for the NN vertex,

= g

(

5, -i

, -i, -i

5) for

cJ/and’

Use the 2 tree-level Feynman diagrams to evaluate d/dt and .

g

5

PCAC model of pp + 0: T.Barnes and X.Li, hep-ph/0611340; PRD75, 054018 (2007).

+

m = 0 limit, fairly simple analytic results…

unpolarized differential cross sections:

(in the analytic formulas)

simplifications

M = m

m = mp

x = (t - m2) / m2

y = (u - m2) / m2

f = -(x+y) = (s - m

2 - M 2) / m2

also, in both d</dt and <,

r i = m

i / m

(analytic formulas)

m = 0 limit, fairly simply analytic results…

unpolarized total cross sections:

However we would really prefer to give results for physicalmasses and thresholds. So, we have also derived the morecomplicated m

.ne. 0 formulas analytically.

e.g. of the pp J/ 0 unpolarized total cross section:

Values of the {pp

} coupling constants?

This is where it gets really interesting.

To predict numerical pp + 0 production cross sections in this model, we know g

pp = 13.5 but not the { g

pp }. Fortunately we can get these new

coupling constants from the known pp partial widths:

Freshly derived formulas for ( pp ):

Resulting numerical values for the { gpp

} coupling constants:

(Uses PDG2004 total widths and pp BFs.)

g

5

!!

!

Now we can calculate NUMERICAL total and differential cross sections for pp any of these cc states + .

We can also answer the big question,

Are any cc states more produced more easily in pp than J/?

(i.e. with significantly larger cross sections than ( pp J/) )

( pp J/ ), PCAC-like model versus “phase space” model:

(J/ pp) input “phase space”

(J/ pp) and g

NN=13.5

Input“real dynamics”

And the big question…

Are any other cc states more easily produced than J/? ANS: Yes, by 1-2 orders of magnitude!

Final result for cross sections. (All on 1 plot.)

Have also added two E835 points (open) from a PhD thesis.

An interesting observation:

The differential cross sections have nontrivial angular dependence.e.g. This is the c.m. frame (and m

=0) angular distribution for

pp c at E

cm = 3.5 GeV:

Note the (state-dependent) node, at t = u.

Clearly this and the results for other quantum numbers may have implications for PANDA detector design.

beam axis

Predicted c.m. frame angular distribution for pp c

normalized to the forward intensity, for Ecm

= 3.2 to 5.0 GeV by 0.2.

spiderman plot

Predicted

c pp

Dalitz plot.

(c/o Xiaoguang Li)

The t=u node in pp

c maps

into a diagonal DP node.

Mp

2

[GeV2 ]

Mp

2 [GeV2 ]

Predicted c.m. frame angular distribution for pp J normalized to the forward intensity, for E

cm = 3.4 to 5.0 GeV.

Predicted J/ pp Dalitz plot.

(c/o Xiaoguang Li)

No t=u node, just a local minmum.

Mp

2

[GeV2 ]

Mp

2 [GeV2 ]

Summary:

1. Re GSI:

For studies of JPC-exotics in pp collisions you need to use associated production.

In the charmonium system even basic benchmark reactions like

pp J/ 0

are very poorly constrained experimentally . Measuring this and related s for various cc + light meson(s) m would be very useful. We have predictions.

2. Re direct s-channel: pp

Measurement of pp couplings of known cc states and new cc-ish candidates like X(3872) is very important, both to see if they are evident, fix widths and BFs, and to quantify their pp couplings.

END