# Presentation: 801464

## Pentaquarks in E949

- Can we settle the issue?
- L. Littenberg                                                                          14 Sept 04

## Sources

- Many of the slides I’m going to show are from Takashi Nakano’s 9 Sept 04 talk to the BNL HENP PAC
- Lots of relevant material on our web site

- http://www.phy.bnl.gov/e949/analysis/pentaquark/

## Pentaquarks – To be or not to be?

**Minimum quark content is 5 quarks.**
**“****Exotic” pentaquarks are those where the antiquark has a different flavor than the other 4 quarks.  **
**Quantum numbers not possible for 3 quarks alone.**
**The ********+****(1540),  an S=+1 exotic pentaquark,  has been seen by  several groups.**
**The quark content would be **
**The width is narrow, below a few MeV**
**It is seen in K****+****N and pK****s **** **
**No signal is seen in pK****+**** so most likely to be I=0**

## Evidence for Penta-Quark States

***Nomad***

**This is a lot**
** ****of evidence.**
**However,...**

## Mass

- Final state:

- Ks  + p

- K+ + n

- (Ks + p )

**A few % difference from zero, but ~20% difference from the KN threshold.**

## Width

**Again, there is inconsistency:**
**Most measurements give upper limits.**
**DIANA has ******** < 9 MeV.   **
**The cross-section implies ********=0.9 MeV.**
**HERMES: ******** = 13 +- 9 stat. (+- 3 sys.) MeV**
**ZEUS: ******** = 8 +- 4 stat. (+- 5 sys.) MeV**
**Arndt *****et al.***** and Cahn *****et al.***** analysis of KN phase shifts suggests that ******** < 1 MeV !!**
**The small width is the hardest feature for theorists to understand...**

## HERA-B (Germany):
reaction: p+A at 920 GeV
measured: K-p and K0p invariant mass
Clear peak for (1520), no peak for +
production rate: +/(1520)<0.027 at 90% C.L.
BES (China):
reaction: e+e-  J/  +-
limit on B.R. of ~10-5

**reaction: p+A at 920 GeV**
**measured: K****-****p and K****0****p invariant mass**
**Clear peak for ********(1520), no peak for ********+**
**production rate: ********+****/********(1520)<0.027 at 90% C.L.**
**BES (China):**
**reaction: e****+****e****-**** ******** J/******** ******** ********+********-**
**limit on B.R. of ~10****-5**

- Null Results

** ****And many unpublished negative results**
**(HyperCP, CDF, E690, BaBar, LEP,,,).**

**    ****If the ********+****  does exist, its production in high energy reactions must be highly suppressed.**
****** ****Model independent experimental search is most desirable.**

## We propose to

- Search for the + in Formation experiment with High intensity kaon beam and Large acceptance detector.

## Cross Section for Formation

- (Courtesy of M. Praszalowicz)

- 1

- 2

- R

## Cross section for “background”

**A. Sibirtsev et al., hep-ph/0405099**

- PK(GeV)

**The background is smooth and well known  (~4 mb).**
**The ********+**** with a narrow width should appear as a bump.**
**If not, a strong limit on the width can be put.**

******=20 MeV**

******=1 MeV**

## Previous formation experiment

**hep-ex/0304040**

******MeV**
******MeV**

**K****+********Xe****→************p X **
**************n ****→************p)**

** ****Xenon bubble chamber**
**P****K+**** ****entered with ****  ****530 MeV/c**
**K****+**** ranged out in the Xenon**
**Require ********K****<100deg.  & ********p****<100 deg.**
**Remove cos ********pK**** <0 ******** back-to-back**

**************n ****→******

- Cahn and Trilling hep-ph/0311245

**************→************n**** **

******MeV**

- consistent with KN phase shift analysis by Arndt et. al.
**Phys. Rev. C68, 042201(R)**

## Kaon supply

**AGS will be running for polarized protons for RHIC.**
**  ****In principle, available between fills (i.e. most of the time).  Flux of 10****12 ****protons per spill should be easy.**
**Can get 2.8 x 10****4  ****475-MeV/c K****+**** per 10****12**** on target.**

## Technique

**Trigger on K****S ******** ********+****,********-****, measure in drift chamber + tgt.**
**dE/dx across 20cm width of tgt spans 40 MeV range in CM energy.**
**Reconstruct proton in target (& sometimes in chamber).  Can get momentum except for sign of P****L ****(but usually is +) from transverse range + energy.**
**From K****S**** + p reconstruct center of mass - remove Fermi momentum.**
**Multiple cross-checks:**
**Excitation curve (already limits width to 1-2 MeV).**
**K****S**** missing mass technique**
**Some p's seen in the chamber.**
**Run at different momenta to cover wide range, decouple geometry from kinematics.**
**Run K- and study ********(1520).**

## M distribution from E949 showing KS +- 

## KS candidate in the E949 target

- Beam’s-eye view of event in E949 target.  Kaon enters at ~300 MeV/c.  At this low momentum proton doesn’t get very far

## KS candidate in the E949 detector

- End and side views of event in E949 detector.   Green rectangles outside of drift chamber are range stack scintillators with in-time energy.  Purple drift chamber track is out-of-time random.

## 2nd KS candidate in the E949 target

- 2nd KS candidate in the E949 target

- Incoming K+

- ’s

- Beam’s-eye view of 2nd event in E949 target.  This time the recoil proton either overlaps the incoming K or is absent

## 2nd KS candidate in the E949 detector

- End and side views of event in E949 detector.

## Spin Considerations

- The+ spin can be determined by the decay angular distribution
- For K+n  +  Ko p, spins of the K’s are 0 and of the nucleons are 1⁄2.
- Can define z-axis as the direction of the incoming K+ in the + CoM.
- Follows that the z component of the + spin, JZ must have the values of 1⁄2.
- Can then calculate the Ko angular distribution in the + CoM system for various values of its spin J:

**J****P****	****	****I(********) **
**1/2********	****	****1**
**3/2********	****	****1+3 cos****2******
**5/2********	****	****1-2 cos****2******** +5 cos****4******

-   One notes that I() is the same for both parities of a given spin.
-   To unravel the parity, look for interference with background waves since    such effects give rise to odd powers of cos.
-   There’s a significant S wave amplitude in the + region and the flat JP = 1⁄2+ distribution converted by interference to asymmetric cos form.

## Monte Carlo of CM angle acceptance

- Distribution generated isotropic in CM

- If the decay angle of the is measured , its spin and parity may be determined through interference with BG.

## Reconstructing the CoM K scattering angle

## Rates

**"Background" rate ~800 K****s****/pulse.**
**For ********+**** width 1MeV, integrated cross-section is 26.4mb-MeV, which would give about 1/6 as many events, 1/10 with K****S ****into********+****,********-****.**
**AGS spill to be optimized, assume e.g. 1.3sec/3.6sec, gives 10****5**** spill per 100 hours or 8M produced ********+**** per 10****12  ****POT for 1-MeV width.**
**Acceptance for K****S**** ~ 10%, so 800,000 ********+****/week in which we see K****S****. Proton acceptance not yet known, but geometrical acceptance high. Overall shouldn't be <10%, so at least 80,000 ********+****/week, going in.**

- Running requests : ~ 1012 POT for 5 weeks
-  - need to get detector on air, vary momenta, do K- runs.

## Things to do-before deciding if a proposal is warranted.

**Detailed Monte Carlo & studies of E949 data to get resolutions and acceptances.  Requires mods to E949 software.**
** ****Studies of pattern recognition in target**
**Fine tuning of strategy**

## Background + resonance

## Interference

- Sibirtsev et al. in  nuc-th/0407011 claim very strong interference. Also v. large rescattering in Xenon. Note that we’re working in C-12 vs Xe-131.  Still need to worry about resolution!

## Closeup

- Need to distinguish this from this with resolution of ~10MeV want to be sensitive to effect 10x smaller than on left!

## What if you don’t reconstruct?

- K stops

## Possible modified geometry

- Move tgt DS.  Use present B4 hodoscope as tgt.  Many more protons get to DC.  Energy measured in tgt and CsI endcap.  Lower evt rate, but more would be fully reconstructed.