# Presentation: 646875

## Rencontres  de Moriond, 
March 8   - March 15

Ralf Seidl (RBRC)
for  the RHIC SPIN collaboration (BRAHMS, STAR, PHENIX) 

- Rencontres  de Moriond,
- March 8   - March 15
- Ralf Seidl (RBRC)
- for  the RHIC SPIN collaboration (BRAHMS, STAR, _PHENIX_)

- La Thuile, March 10th

- R.Seidl: Transverse spin measurements at RHIC

## The RHIC ring(s) with polarized protons

- La Thuile, March 10th

- R.Seidl: Transverse spin measurements at RHIC

**AGS**

**LINAC**

**BOOSTER**

- Spin Rotators

-   200 MeV Polarimeter

-  AGS Internal Polarimeter

-   Rf Dipole

-  RHIC pC Polarimeters

-  Absolute Polarimeter (H jet)

**P****HENIX**

**P****HOBOS**

**B****RAHMS & PP2PP**

**S****TAR**

- AGS pC Polarimeter

- Partial Snake

- Siberian Snakes

- Siberian Snakes

- Helical Partial
-   Snake

- Strong Snake

-  Spin Flipper

- 2  1011 Pol. Protons / Bunch
-  = 20  mm mrad

## Relativistic Heavy Ion Collider

**3**** ****Spin**** Experiments**
-  PHENIX
-  STAR
-  BRAHMS
-  PHOBOS (heavy-ion)

**Characteristics**
- 2 counter-circulating rings
- 3.8 km in circumference
- Top Energies (each beam):
- 100GeV / Au-Au
- 250GeV / p-p
- Mixed Species (d+Au)

- La Thuile, March 10th

- R.Seidl: Transverse spin measurements at RHIC

**Notes:**
The experiment is taking place at Brookhaven National Laboratory at RHIC. RHIC is composed by 2 counter circulating rings - blue and yellow- of 3.8 Km in circumference. RHIC has the ability to accelerate ions at speeds close to the speed of light, and particularly Au Au at 100GeV, pp at 250 Gev or even mixed species, and collide them at 4 different crossing points. STAR is located at 6 o’clock. STAR stands for Solenoidal Tracker at RHIC and it is composed by several detectors that have the ability to track particles produced by collisions and measure their energy.  

## Local polarimetry:Forward Neutron Asymmetries

- Local polarimetry:Forward Neutron Asymmetries

- Zero Degree Calorimeterbehind Dx magnet
- neutron  shower max

**A****N ****= ********0.110±0.015**

- IP12’s first asymmetry

- vertical polarization

- radial polarization

- localasymmetriesat PHENIX

- monitoring of polarization alignment when using spin rotators

- La Thuile, March 10th

- R.Seidl: Transverse spin measurements at RHIC

- PLB650:325-330,2007

## Cross sections in (semi)inclusive DIS and pp, Factorization

- La Thuile, March 10th

- R.Seidl: Transverse spin measurements at RHIC

- fq(x1)  fq(x2) ̃  Dh(z)

- fq(x1)  ̃  Dh(z)

- Hard scales PT and Q2
- Convolution integrals over all involved momenta
- Factorization of involved distribution and fragmentation functions
- (kT)-dependent distribution and fragmentation functions

**k **

**k’**

**Q**

## Cross sections well understood at √s=200 GeV

- 

- La Thuile, March 10th

- R.Seidl: Transverse spin measurements at RHIC

- PHENIX:arXiv:0704.3599 [hep-ex]

- BRAHMS,PRL.98:252001,2007

## Transverse single spin asymmetries AN

- Look at left-right asymmetries relative to one transversely polarized proton beam
- To cancel acceptance effects use square root formula

- La Thuile, March 10th

- R.Seidl: Transverse spin measurements at RHIC

## E704 Asymmetries

- perturbative QCD predicted nearly vanishing  single spin asymmetries
- Huge asymmetries seen in E704 at √s=20 GeV
- Higher twist effect?

- La Thuile, March 10th

- R.Seidl: Transverse spin measurements at RHIC

- Adams et al. (E704), PLB 264, 462 (1991).
- Adams et al. (E704), PRD 53, 4747 (1996).

**BNL-AGS  √s = 6.6 GeV 0.6 < p****T**** < 1.2**

## Single spin asymmetries also at higher scales: Confirmed at  RHIC at √s=200 GeV

- La Thuile, March 10th

- R.Seidl: Transverse spin measurements at RHIC

**STAR: PRL.92:171801,2004**

**STAR:arXiv:0801.2990v1 [hep-ex]**

## Recently also PT dependence

- higher twist  1/PT dependence
- Not really seen in lower PT data,
- maybe at higher PT though

- La Thuile, March 10th

- R.Seidl: Transverse spin measurements at RHIC

**Prediction by:**
** ****(Sivers): **D’Alesio and F. Murgia, *PRD ****70, 074009 (2004)***
***and (twist-3): *** C. Kouvaris, J. Qiu, W. Vogelsang, F. Yuan, PRD*** ****74, 114013 (2006).*

**STAR:arXiv:0801.2990v1 [hep-ex]**

## Single Spin Asymmetries at mid rapidity

******0**** (2001/02)**

- pt (GeV/c)

- pt (GeV/c)

- PHENIX, PRL.** 95, **202001 (2005)

- P=15% in 2002, P=47% in 2005
- polarization scaling uncertainty: 30%(2002), ≈ 20%(2005)
- residual polarization in *unpolarized* beam:	< 10% and small AN

- May provide information on gluon-Sivers effect
- gg and qg processes are dominant
- Transversity+ Collins is suppressed

- La Thuile, March 10th

- R.Seidl: Transverse spin measurements at RHIC

## Brahms asymmetries at √s=200 GeV

- La Thuile, March 10th

- R.Seidl: Transverse spin measurements at RHIC

- p

- J. H. Lee and F. Videbaek (BRAHMS), AIP Conf. Proc. 915, 533 (2007)

- 4 degrees

- 2.3 degrees

- 2.3 degrees

- 2.3 degrees

- K- and p asymmetries puzzling

## Asymmetries also seen at √s=62 GeV

- La Thuile, March 10th

- R.Seidl: Transverse spin measurements at RHIC

**PHENIX, Chiu et al., nucl-ex/0701031**

## Brahms asymmetries at √s=62 GeV

- La Thuile, March 10th

- R.Seidl: Transverse spin measurements at RHIC

- p

**BRAHMS, arXiv:0801.1078** [nucl-ex]

## What creates these single spin asymmetries?

- Transverse  momentum dependent  distribution function: Sivers effect
- Transversity with transverse momentum dependent fragmenation function: Collins effect
- Higher twist effect on the distribution function or fragmentation function side : Description found to be equivalent to TMDs at intermediate PT

- La Thuile, March 10th

- R.Seidl: Transverse spin measurements at RHIC

- Sivers function

- unpol FF

- Collins  function

- Transversity

## Naïve Sivers interpretation

- La Thuile, March 10th

- Taken from H. Tanaka in Trento’04

- Attractive rescattering of hit quark by gluon creates transverse momentum
- M.Burkardt [hep-ph0309269] – impact parameter formalism
- Orbital angular momentum at finite impact parameter
- observed and true x differ
- Observable left/right asymmetry

- >

## Recent theoretical progress in understanding the ANs 

- Fitting HERMES and COMPASS Sivers  data,
- Take Collins contribution into account and
- Calculate phases to describe RHIC AN results

- Boglione, D’Alesia, Murgia
- e-Print: **arXiv:0712.4240** [hep-ph]

- La Thuile, March 10th

- R.Seidl: Transverse spin measurements at RHIC

- Reasonable well agreement vs  xF
- Not so well agreement at lower PT

- STAR asymmetries:

## Brahms asymmetries

- Pion asymmetries fairly well described
- At least same sign for both K asymmetries  as in data

- La Thuile, March 10th

- R.Seidl: Transverse spin measurements at RHIC

- J. H. Lee and F. Videbaek (BRAHMS), AIP Conf. Proc. 915, 533 (2007)

- √s=200 GeV

## Heavy flavor related single spin asymmetries

- Open charm single spin
- 	asymmetrie s most sensitive to gluon Sivers function (d’Alesio et al,....)
- J/ slightly more involved due to questions concerning production
- new calculations for charmonium from F.Yuan, arXiv:0801.4357 [hep-ph]

- La Thuile, March 10th

- R.Seidl: Transverse spin measurements at RHIC

## Sivers Back-to-back jets

- Idea: Jets should be sensitive to initial kt of quarks and gluons
- No sensitivity to final kt of hadrons
- Possibility to pin down   Sivers effect in pp collisions
-  Measure spin depentent deviation of  dijets

- La Thuile, March 10th

- R.Seidl: Transverse spin measurements at RHIC

- D. Boer and W. Vogelsang, Phys. Rev. D **69**, 094025 (2004)

## Sivers back-to-back jet measurements 

- La Thuile, March 10th

- R.Seidl: Transverse spin measurements at RHIC

**STAR,PRL,99(2007)142003**

##   Experiment SIDIS vs Drell Yan:  

- La Thuile, March 10th

-   ***0.1        0.2        0.3   x***

-   ***Sivers Amplitude***

**0**

-   **Experiment SIDIS vs Drell Yan:  **
**Sivers|****DIS****= − Sivers|****DY**
** ******* Test**** ****QCD Prediction of Non-Universality *****

- HERMES Sivers Results

- Markus Diefenthaler
- DIS Workshop
- Műnchen, April 2007

**0**

- RHIC II  Drell Yan Projections

- Feng Yuan
- Werner Vogelsang

## Other future measurements

- Direct access to transversity via Interference Fragmentation function
- No Sivers –like contributions
- kT integrated, evolution understood
- Open charm single spin asymmetries
- Direct photon – jet Sivers asymmetries
- Drell Yan for Sivers function and
- 	Boer-Mulders function

- La Thuile, March 10th

- R.Seidl: Transverse spin measurements at RHIC

## Summary	

- Single spin asymmetries confirmed at higher √s
- Increasing with xF for pions and kaons
- Compatible to zero for small and negative xF
- PT dependence only falling for higher PT ,lower not well understood
- First heavy quark single spin asymmetries compatible with zero
- Sivers Back-to-back measurements compatible with zero due to partial cancellations of  DY type and SIDIS type contributions
- More exciting results in the future

- La Thuile, March 10th

- R.Seidl: Transverse spin measurements at RHIC

## La Thuile, March 10th 

- La Thuile, March 10th

- R.Seidl: Transverse spin measurements at RHIC

## Transversity

- La Thuile, March 10th

- In helicity basis: helicity distribution and momentum difference and sum of diagonal amplitudes
- Transversity contains helicity flip and is not diagonal
- Helicity is conserved quantity for (nearly) massless quarks
- All interactions conserve helicity/chirality
- 	Transversity cannot be observed in DIS

## 	Sum of quarks with parallel and antiparallel polarization relative to proton  spin
	(well known from Collider DIS experiments) 

- La Thuile, March 10th

- q(x), G(x)

- 	Difference of quarks with parallel and antiparallel polarization relative to longitudinally polarized proton
- 	(known from fixed target (SI)DIS experiments)

- q(x),G(x)

- 	Sum of quarks with parallel and antiparallel polarization relative to proton  spin
- 	(well known from Collider DIS experiments)

- q(x)

- Quark distributions in spin bases

- 	Difference of quarks with parallel and antiparallel polarization relative to transversely polarized proton
- 	(first results from HERMES and COMPASS – with the help of Belle)

- Unpolarized distribution function q(x)

- Helicity distribution function q(x)

- Transversity distribution function q(x)

## Transversity and friends

**Unpolarized DF**
**helicity DF**
**Transversity DF**

**Sivers function**

**Boer-Mulders function**

**q(x)**

******q(x)**

******q(x)**

- La Thuile, March 10th

- R.Seidl: Transverse spin measurements at RHIC