status of j-parc k1.8 beam line

Status of J-PARC K1.8 Beam Line

Kiyoshi TanidaDepartment of Physics and Astronomy,

Seoul National UniversityHNP2011, POSTECH

Feb. 24, 2011

J-PARC: Where is it?

J-PARC (Japan Proton Accelerator Research Complex)

Tokai, Japan

50 GeV Synchrotron (15 mA)

400 MeV Linac (350m)

3 GeV Synchrotron (333 mA)

Material and Biological Science Facility

World-highest beam intensity : ~1 MW x10 of BNL-AGS, x100 of KEK-PS

Neutrino Facility

Nuclear & Hadron Physics in J-PARC

J-PARC Hadron Hall

Handron Hall

Beam Dump

K1.8

K1.8BR

K1.1

K1.1BR 30~50 GeV primary beam

Productiontarget (T1)

Strangeness nuclear physics at K1.8BR and K1.8

g spectroscopy of L hypernuclein-rich L hypernucleiX hypernucleiLL hypernucleiX-atomic X raysQ+ searchWeak decays of L hypernucleiK- nucleus bound statesPion double charge exchangew nucleusYN scattering

K- nucleus bound statesK- atomic X raysh nucleusf nucleusHyperon resonances

approved / proposed (incl. LOI)

High Mom. Line

Q+ studyg spectroscopy of L hyp.S hypernucleiQ+ hypernuclei

KLHadron mass in nucleiNucleon quark structuremeson structure

June, 2007

June, 2007

Dec, 2008

K1.8 beamline

Design of K1.8 beam line

Double stage E.S. Separators

MS2(V)

MS1(Vertical Slit)

Mom(Horizontal slit)

IFV(V)IFV(H)

Beam analyzer(dp/p~10-4)

Primary proton beam (protons/spill)

30 GeV-9mA2.0E+14

Length (m) 45.853Acceptance (msr.%) 1.4K-(p) intensity (ppp) @1.8 GeV/c 1.4E+06 @1.5 GeV/c 0.54E+06 @1.1 GeV/c 0.08E+06Electrostatic separators 750kV/10cm, 6m×2Single rate @ MS2 @ 1.8 GeV/c ＞ 8E+06K-/(p-+m- ) @ FF @ 1.8 GeV/c 3.5X/Y(rms) size @ FF (mm) 19.8/3.2

Apr, 2010K1.8 beamline

SKS Spectrometer• High resolution:

– dp/p ~0.1%– Mass resolution:

~ 2 MeV (FWHM)• Large acceptance

– 100 msr, up to ~1GeV/c

• Variations for high mom.– SKS-Plus Keeping resolution

– SKS-Minus Keeping acceptance

2.7T(395A)

~1.5T

Brief History & Status• Construction completed in July 2009• First beam in September

– Beam Line commissioning with intermittent beam time– Concurrent with accelerator commissioning

• All components were found to work well• Beam intensity and structure is the current issue

• First Physics beam time in Nov. 2010– E19 experiment (Q+ search)

Beam Conditions• Beam intensity: ～ 3.5 x 1012 protons per 6 second cycle

– ~1% of the design. Still, higher than KEK-PS– x3 intensity demonstrated– Pion intensity: > 107/s possible. Limited by detectors.

• Kaon is clearlyseen– Purity is to be

improved(low sep.voltage)

• # of K-

~25 k/cycle consistent

K-/π- ratio ~ 0.14

π-

K-

Preliminary

Beam microstructure

• Instantaneous intensity >> average intensity– Limiting the available intensity due to detector pileup– We ran at 1.1 Mp/spill (2.2s) Instantaneous rate: ~10 MHz

– Gradually improving

E19 ExperimentMysteries about Pentaquark, Q+

• Does it really exist?– Confirmation with good sensitivity is crucial

• Width? Why so narrow?– Certainly < 1MeV– No bump in K+n K+n, K0p

• Spin & parity?– 1/2+? 3/2+? 1/2-? ...

• Its nature?– KN? KpN? ...

High resolution search. Why?• For good S/N ratio

– Q+ is above KN threshold, and is NEVER BG free– High resolution really helps to achieve good S/N ratio crucial for good sensitivity

• Width measurement– Almost certainly, < 1 MeV– Similar or better resolution necessary!

• Typical resolution so far ~ 10 MeV– No high resolution search– There is a good chance for high resolution experiments.

Missing mass spectroscopy

p(p-,K-)Q reaction: KEK-PS E522Miwa et al.PLB635 (2006) 72.

• Poor resolution ~13 MeV (FWHM)• Low statistics: < 1010 p- on target

• Still, there was a hint of peak: 1.9 mb/sr 2.5s significance

Statistics: x100 Resolution: x1/5

Actual Run in Oct./Nov.• Beam time: 156 hours

– +116 hours for commissioning and calibration• Total statistics: 7.8 x 1010 pions on target

– ~5% of the proposal

Test data: p(p-,K+)S-

• Good mass resolution: 1.9 MeV (FWHM) achieved

• Cross section OK

• Good performanceconfirmed

Preliminary result

• No peak• Upper limit for a peak ~0.4 mb/sr (very preliminary)

c.f. 3.9 mb/sr in E522 “hint” ruled out

Summary• Physics experiment in K1.8 beam line has just

started!• All detectors are working very well.• Beam intensity & structure is the current issue

– Intensity: ~1% of design, still enough for pions– Structure limits the available intensity to ~1 MHz– Improving with efforts of accelerator group

• E19: Q+ search in p(p-,K-) reaction– Detector performances are very good– No peak observed– Upper limit ~0.4 mb/sr Ruled out the “hint” in previous KEK-PS E522 spectrum

– We will take more data in the coming runs

Future prospects• The next beam time is scheduled in Apr. 2011

– We will continue to run E19 and E27– Improvement of beam structure expected

• Another beam time expected in autumn 2011– Beam intensity: 1 x 1013/cycle (3% of design) expected– E10, E13 (E19) will run, and E05 will take pilot data.

• More exciting experiments are waiting!