longitudinal spin transfer of in polarized pp collisions at 200 gev n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Longitudinal Spin Transfer of in Polarized pp Collisions at 200 GeV PowerPoint Presentation
Download Presentation
Longitudinal Spin Transfer of in Polarized pp Collisions at 200 GeV

Loading in 2 Seconds...

play fullscreen
1 / 20

Longitudinal Spin Transfer of in Polarized pp Collisions at 200 GeV - PowerPoint PPT Presentation


  • 66 Views
  • Uploaded on

Longitudinal Spin Transfer of in Polarized pp Collisions at 200 GeV. Qinghua Xu, LBNL for the STAR Collaboration SPIN 2006, Oct 6, 2006. Motivation Proof-of-principle analysis at low p T with STAR Preliminary results for D LL in inclusive production

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Longitudinal Spin Transfer of in Polarized pp Collisions at 200 GeV' - nitesh


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
longitudinal spin transfer of in polarized pp collisions at 200 gev
Longitudinal Spin Transfer of in Polarized pp Collisions at 200 GeV

Qinghua Xu, LBNL

for the STAR Collaboration

SPIN 2006, Oct 6, 2006

  • Motivation
  • Proof-of-principle analysis at low pT with STAR
  • Preliminary results for DLL in inclusive production
  • Summary and outlook

Qinghua Xu, LBNL

why study
Why study ?
  • Due to its self-analyzing weak decay,  polarization
  • has been widely studied in different processes with
  • many interesting results (following talks).

Unit vector along proton momentum in rest frame.

polarization vector

decay parameter 0.642 0.013

  • What can we learn from polarization with
  • polarized pp collider at RHIC?

Qinghua Xu, LBNL

slide3

What can we learn with in polarized pp collisions ?

  • Longitudinal spin transfer in
  • polarized proton-proton collisions:

measures the transfer of beam

polarization to hyperon.

  • contains a strange quark, can it
  • provide sensitivity to

 production is expected to be

dominated by u quark, while s_bar plays a dominate role for production at large pT!

How sensitive is anti-Lambda DLL to

Qinghua Xu, LBNL

slide4

Spin transfer of in pp collision

Q. X, E. Sichtermann, Z. Liang, PRD 73,2006

Q2=5 GeV

Pol. frag. func. model

-0.090.02 (Inclusive DIS)

0.010.03 (Semi-inclusive

DIS-HERMES)

  • Anti-Lambda DLL may give new insights into at high pT!

Qinghua Xu, LBNL

slide5

Spin transfer versus double spin asymmetry

0<<1 for DLL

-1<<1 for ALL

[GeV]

  • DLL is ~ 4X more sensitive to than ALL.
  • ~0.01 measurement will distinguish parameterizations.

Qinghua Xu, LBNL

slide6

RHIC- the first polarized pp collider

Stable polarization direction - transverse

Longitudinal polarization at STAR/Phenix

4 spin orientations:

++,+-,-+,--

AGS Heclical Partial Snake

Qinghua Xu, LBNL

slide7

STAR Detector

TPC

(-1.6<<1.6)

p

  • is reconstructed by combining
  • TPC tracks with opposite charges after
  • particle identification from energy
  • loss and applying topological cuts.

V0_vertex

V0_DCA

  • primary vertex

Qinghua Xu, LBNL

slide8

2005 data: ~3 pb-1, ~50% beam polarization

  • ~3X106 minimum bias events,
  • ~30X103 (24X103) analyzed.
  • Invariant mass & kinematics

<pT>~1.3 GeV

<|xF|>~0.0075

M=1.1157 GeV(PDG)

  • Cross section of reasonably described by pQCD.

nucl-ex/0607033, submitted to PRC

Qinghua Xu, LBNL

slide9

Method to extract DLL

  •  polarization is usually extracted from the momentum distribution of its
  • weak decay ( ):

: angle between the momentum of decay proton in ’s rest frame and ’s momentum at the lab frame

: decay parameter: 0.642

A(cos): detector acceptanceafter integrating over momentum space

  • P() in inclusive pp reaction change its sign when flipping beam helicity,
  • due to parity conservation:
  • Asymmetry between  counts with opposite polarization within : [1,2]:
  • Equation to extract DLL:

Qinghua Xu, LBNL

slide10

Signal and Background

  • Background from K0s:
  • --- a cut of cos<-0.2 applied.
  • Subtracting bg. contribution to DLL

r: fraction of background under the peak

Qinghua Xu, LBNL

slide11

Comparison of DLL with two methods:

  • Time stability of DLL:

# fill

Qinghua Xu, LBNL

slide12

Results of DLL :

<pT>~1.3 GeV

<|xF|>~0.0075

Systematic error

---scale uncertainty from beam polarization measurement not included.

  • Positive is along the polarized beam direction.
  • Statistical uncertainty is ~0.05, systematic < 0.01.

Qinghua Xu, LBNL

slide13

Systematics:

  • 4X10-3from relative luminosity measurement.
  • 2% from decay-parameter (0.6420.013).
  • 2% from transverse beam polarization components at STAR.
  • +17% scale uncertainty from RHIC beam polarization measurement.

Cross check with K0s:

LL/Pbeam

K0s: 0.010.01

# fill

  • K0s are spin-0 meson -> null  measurement.
  • reconstruction/analysis similar to (anti)Lambda.
  • Statistical error is ~1/5 of (anti)Lambda’s DLL.

Qinghua Xu, LBNL

slide14

Summary

  • Spin transfer DLL for anti-Lambda in proton collisions is sensitive to at large pT (pT > ~6 GeV/c)
  • Proof of principle analysis from 2005 minimum bias data

<pT>~1.3 GeV

<|xF|>~0.0075

Systematic error

---scale uncertainty from beam polarization measurement not included.

Qinghua Xu, LBNL

outlook
Outlook
  • Triggering is needed to efficiently reach high pT.
  • In 2005, we collected most of the data with a jet-patch
  • trigger and the projected precision is:
  • Considering dedicated trigger development, andlooking
  • forward to high-luminosity running periods.

1.6 pb-1 of BJP2

0<<1

Qinghua Xu, LBNL

slide16

Backup slides

  • Possible dedicated trigger for high pT anti-Lambda:
  • Different pre-shower response to anti-proton in
  • electromagnetic calorimeter than photon
  • Triggering on high pT pion with muon trigger
  • Higher level trigger on distribution of invariant mass
  • versus momentum ratio of proton and pion

Qinghua Xu, LBNL