# Presentation: 853746

## Pentaquark Search at BNL

**I-H.Chiang, M. Diwan, J. Frank, D. Jaffe, S. Kettell, L. Littenberg, P.  Pile, G. Redlinger, M. Sakitt, N. Samios   - BNL**
** **
**A. Artamonov, A. Kozhevnikov, V. Kurshetsov, L. Landsberg, V. Molchanov, V. Mukhin, V. Obraztsov, D. Patalakha, S. Petrenko, D. Vavilov – IHEP-Protvino**
** **
**V. Anisimovsky, A. Khotjantsev, Yu. Kudenko, O. Mineev, N. Yeshov – INR-Moscow**
** **
**T. Komatsubara, S. Sugimoto, T. Yoshioka – IPNS- KEK**
** **
**B. Basselleck – U. of New Mexico**
** **
**N. Muramatsu, T. Nakano – RCNP, Osaka University**

## What are penta-quarks?

- e.g. uuddc, uussd

**What are penta-quarks?**

- Minimum quark content is 5 quarks.
- “Exotic” penta-quarks are those where the antiquark has a different flavor than the other 4 quarks
- Quantum numbers cannot be defined by 3 quarks alone.

- Example: uudds

- Baryon number = 1/3 + 1/3 + 1/3 + 1/3 – 1/3 = 1

- Strangeness = 0 + 0 + 0 + 0 + 1 = 1

## + Baryon

- + Baryon

***M*********1890-180*Y] MeV**

**D. Diakonov, V. Petrov, and M. Polyakov, Z. Phys. A 359 (1997) 305.**

**Exotic: S=+1**
**Low mass: 1530 MeV**
**Narrow width: ~ 15 MeV**
**J****p****=1/2****+**

## Baryon masses 

- Mainly 3 quark baryons:
- M ~ 3Mq + (strangeness)
- 5-quark baryons, naively:
- M ~ 5Mq + (strangeness)
- 1900 MeV for +
- 5-quark baryons, in chiral quark soliton:
- M ~ 3Mq + 1/(baryon size) + (strangeness)
- ~1550 MeV for +

## Theory

**Naïve QM (and many Lattice calc.) gives  M=1700~1900MeV with J****p****=1/2****-****.**
**But the ****negative parity**** state must have very wide width (~1 GeV) due to ****“fall apart”**** decay.**

**For pentaquark**

**Ordinary baryons**

**Positive parity requires P-state**** ****excitation.**
**Expect state to get heavier.**
**Need counter mechanism.**
**diquark-diquark, diquark-triquark, or strong interaction with “pion” cloud?**

**Positive Parity?**

## Why + is so narrow?

**D. Diakonov, Talk at Pentaquak04**

## 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**

## The “noisy” K+n database

**Bugg et al. (1968)**

**Bowen et al. (1973)**

**Bowen et al. (1970)**

**There are **
**clearly some**
**systematic **
**problems in **
**the KN data!**

**Note: errors**
**get larger as**
**momentum **
**goes lower.**

## Previous formation experiment

**hep-ex/0304040**

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

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

**P****K+**** ****<****  ****530 MeV/c**
**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/spill should be easy (AGS ran at 60 times that for E949).**
**LESB3 is a doubly-separated beam that goes up to 800 MeV/c.**
**Can get 80% pure K****+****. **
**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).**

## E949 Solenoidal Detector

- K+ stopping target made of 400 5-mm square scintillating fibers. Can track and measure charged particles therein.
- Low-mass cylindrical drift chamber in 1-T field can measure momenta in this region to < 1%.  In combination with target ~ 1.5%.

## 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.

## 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!

## 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.

## 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**