forum at shanghai 1 ++ ++ june 28-29, 2005 search for exotic pentaquark and in jefferson lab wangxu...

June 28-29, 2005 Forum at Shanghai 1

++Search for Exotic Pentaquark

and in Jefferson Lab

WangXu

Duke University/MIT

•Motivation

•The Jlab experiments

•Conclusion

+ ++


++The Anti-decuplet predicted by Diakonov et al.

Symmetries give an equal spacingbetween “tiers”

Width < 15 MeV !


++ Summary of ExperimentsWhere Reaction Mass Width ’s*

LEPS C K+K- X 1540 +- 10 < 25 4.6

DIANA K+Xe K0p X 1539 +- 2 < 9 4.4

CLAS d K+K-p(n) 1542 +- 5 < 21 5.2

SAPHIR p K+K0(n) 1540 +- 6 < 25 4.8

ITEP A K0p X 1533 +- 5 < 20 6.7

CLAS p +K-K+(n) 1555 +- 10 < 26 7.8

HERMES e+d K0p X 1526 +- 3 13 +- 9 ~5

ZEUS e+p e’K0p X 1522 +- 3 8 +- 4 ~5

SVD-2 P+N p+-X 1526 +- 3 10 +- 3 5.6

COSY pp K0p+ 1530 +- 5 < 18 4-6

*Gaussian statistical significance: estimated background fluctuation

Negative Results:Not seen by CDF, HyperCP, E690, HERA-B,Aleph, Delphi, Phenix, BaBar, and SPHINX(07/2004)Conflicting results within NA49 ?and CLAS (g11).

+

(1) Summary talk by A. Dzierba at the Quark and Nuclear Physics Conference, May 2004;(2) J. Pochodzalla, hep-ex/0406077


++

- CLAS reported a preliminary hint for a ++ candidate peak in pK+ near 1579 MeV (Pentaquark2004 workshop)

- STAR reported a preliminary hint for possible peaks in pK+ and antip K- near 1530 MeV (J. Ma, APS meeting 05/01/2004)

Width ~ 8.7 MeV , S/sqrt(B) ~ 3.8 15 M events

State content Iz Strong decay model

- dddds -2

0 uddds -1 nK0

+ uudds 0 nK+,pK0

++ uuuds 1 K+p

+++ uuuus 2

• One of several alternative explanation of + Isotensor multiplet (Capstick et al., 2003)

+ Isospin


++CEBAF Electron Accelerator

● Up to 5 pass, .6 to 1.15 GeV per pass.

● Recirculating linac design● 5.75 GeV max beam energy● 100% duty cycle

●2ns microstructure●

E/E < 1∙10-4 (Halls A & C)

● 180 A max current● Beam polarization up to 85%A B C


++

• Pentaquark photoproduction experiments in Hall B (High Statistic)

– g10 deuteron target. E~1 – 3.5 GeV. Verify n(d) +

Data taking complete. Order of magnitude increase in deuteron data.

– g11 proton target. E~1 – 3.5 GeV.

Verify and characterize p +.

Search for p +* .

Search for p .

Data taking complete. Factor of 10 increase in data expected.

• Pentaquark eletroproduction experiment in Hall A (High Resolution) – E04-012/E05-009: proton/deuteron target.Verify n(d)/p + using “quasi real

photo” techinique. Search for and 0 states/Search for state.

Current Jlab Program


++ CEBAF Large Acceptance Spectrometer - CLAS

Liquid D2 (H2)target +

start counter; e minitorus

Electromagnetic calorimetersLead/scintillator, 1296 photomultipliers

Drift chambersargon/CO2 gas, 35,000 cells

Time-of-flight countersplastic scintillators, 684 photomultipliers

Gas Cherenkov counterse/ separation648 mirrors, 256 PMTs

Torus magnet6 superconducting coils


++

M(nK+

)

Fitted mass 1.555 GeV

< 28 MeV consistent with detector resolution

Significance 7.8

+ p + K- + + + n + K+

Distribution of (1520) events

M = 1.542 GeV < 21 MeV Stat.sig. = 5.2+

Simulated background

Gaussian background

+ n K- + + + n + K+

Cos*(+) > 0.8

V. Kubarovsky et al., PRL, Jan.‘04

+

CLAS - p /d Results

+ p K0 + + + n + K+

Hep-ph/0505134, No evident of +


++Hall A at Jefferson Lab

Two HRS Spectrometers●0.3 < p < 4.0 GeV/c●-4.5% < Δp/p < 4.5%●6 msr at 12.5° <θ<150°●4.5 msr at θ=6° with septum●-5cm<Δy<5cm

Optics: (FWHM) ●p/p 2∙10-4 (achieved)●0.5 mrad, 1 mrad●δy=1mm

●Can take 1-100 μA ●Luminosity ~ 1038 cm-2s-1

Other devices: •BigBite (~40msr) open geom. spec.,•GeN Neutron Detector: 1.6x4.8 m2


++E04-012 (Pentaquark Partner ++-Search) Layout

%0.1

)1520(

Kp

Kp

Θ++ search:90% CL limit for a Γ=5 MeV state between 1500-1600 MeV is: σγ*p→KΘ++< 3 nb.


++E05-009 (measurement of the + and its width)

Layout• Untagged quasi-

real photons • E ≈ 4 GeV• Septum permits

good coverage of K distribution at low t.

• Forward “tagged” K leads to low momentum +.

• Mass resolution of 2.1 MeV

Clean, direct measurement of Θ+ state. No re-scattering process required.


++ Proposed Experiment I• Photoproduction process:

KpKKp )(

(LH2 Target)SOS K-

HMS P or K+

++e_

Beam Dump

pKKpKpKp ),(/),(


++

Experimental Layout I

• P acceptance : 10%

• ΔP/P: < 0.001

• Solid angle: >7.0 msr

• Flight path: 25 m

• P acceptance : 20%

• ΔP/P: < 0.001

• Solid angle: 9.0 msr

• Flight path: 10 m

SOS

HMS


++ Simulation Results(I)

150 hours Total expected events:23360Sensitivity to ++: <100 pb/srat 3 level

++ mass range from acceptance is 1500 to 1600 MeV

Crosscheck:

pKKp ),(

Crosscheck has a very low background.

++

++

KpKp ),(

srnbdd /0.2/

srnbdd /0.2/


++ Proposed Experiment II• Photoproduction process:

n K (nK )K

(LH2 Target)

SOS K-

HKS K+ Neutron counter

+e_

(out-of-plane)

(K+K-n) √

n K (n )K

Mass calibration

(K+-n) √

Beam Dump


++Experimental SetupExperimental Layout

10 meters from the target

HKS physical angle 32 degree


++ Simulation Results(II)

25 hours Total expected events:5837 (952 with E cut: Ee-125 MeV <E<Ee-25 MeV)

Sensitivity to +: 70 pb/srat 3 level + mass range from acceptanceis 1500 to 1600 MeVImportant for checking twopeaks!

Mass Calibration:

n K (n )K

Mass calibration using particle, better than 0.3 MeV,width better than 1.3 MeV ()

+

Σ-


++Requirements II

• Neutron detector (Hall C/Hall A Gen experiment)• Modification of existing legs for HKS platform• New HKS detector support with local shielding• A downstream iron magnetic shield

– outside the HKS splitter magnet pole and coil

– Beam steering test for SOS done (4.2 GeV beam, -1.74 GeV/c momentum setting at 22 degree), additional shielding around beam pipe helpful.


++Conclusion

• Search for + and ++ is still a challenging and interesting topic.

• This research project may carry on at SSRF in future.

Thank You !

forum at shanghai 1 ++ ++ june 28-29, 2005 search for exotic pentaquark and in jefferson lab wangxu...

Documents