# Presentation: 902806

## Recent Results from theHigh-Resolution Fly’s Eye(HiRes) Experiment

- Pierre Sokolsky
***University of Utah***

***PANIC!***
***October, 2005  ***

## Outline

- Introduction of the High-Resolution Fly’s Eye (HiRes) Experiment
- Energy spectrum and features
- Composition and p-air cross-section measurements
- Anisotropy
- The Future: TA and the Low Energy Extension (TALE).

## Introduction to theHigh Resolution Fly’s Eye (HiRes)

**HiRes Collaboration:**
***University of Utah***
***Columbia University***
***Rutgers University***
***University of New Mexico***
***University of Montana***
***Los Alamos National Laboratory (LANL)***
***University of Tokyo***
***IHEP (Beijing, China)***

## HiRes Location

- HiRes is located on the U.S. Army Dugway Proving Ground, ~2 hours from The University of Utah campus.
- The two detector sites are located 12.6 km apart at Little Granite Mountain and Camel’s Back Ridge

## Detector Design

- Each HiRes detector unit (“*mirror*”) consists of:
- spherical mirror w/ ***3.72m******2*** unobstructed collection area
- 16x16 array (hexagonally close-packed) of PMT pixels each viewing*** ******1******° cone*** of sky: giving 5 improvement in S:N over FE (5° pixels)
- UV-transmitting filter to reduce sky+ambient background light
- Steel housing (2 mirrors each) with motorized garage doors

## Typical HiRes Event

- ~21019eV event seen in 1999
- (3× vertical scale)

## Reconstruction of EAS from HiRes Data

- The trajectory of the EAS can be determined in one of two ways:
- Monocular reconstruction using the arrival time of light signal at the detector.
- By intersecting the shower-detector planes (SDP) seen from the two detector sites.

- 2.)

- 1.)

## HiRes Operations

- Continuous operation of HiRes-1 detector since 1997 with 4 major down periods (7 months off after anthrax episode)
- Has been operating at 10% duty cycle since 2001-2002 shutdown

## Physics with HiRes Data

***Stereo data***: best resolution, optimized for ***E>3************10******18******eV***
***HiRes-2 monocular***: can reach down to as low as ***10******17.2******eV***
***HiRes-1 monocular*** data began ~3 years earlier: ***largest statistics***,

**HiRes-2 mono**

**HiRes-1 mono**

**HiRes stereo**

**Tandem Stereo Study**

## Measured shower profile.

***Event by event:***
- Xmax in g/cm2;
- Total energy of the primary particle:
- Arrival direction

*Statistically:*
- composition.
*p*-air inelastic cross-section;

- Measured shower parameters.

## Measurement of UHECR Energy Spectrum

- Combined HiRes-1 and HiRes-2 monocular spectra published:
- 	**Phys. Rev. Lett. 92, 151101 (2004)**** **

## Updated monocular spectrum:Are spectral features seen? 

## 1.	Single power law fit:

- 1.	Single power law fit:

## 2.	Improved fit using two-power laws with a single floating break

- 2.	Improved fit using two-power laws with a single floating break

## 3. Still better fit using three power laws with two floating breaks

- 3. Still better fit using three power laws with two floating breaks

## 
Significance of the deficit at high energy end relative to continuation of power law ?
Extrapolate middle section:
Expect 42.8 events
Observe 15
Poisson
	p= ~10-6

4 is 3 x 10-5
5 is 3 x 10-7

- Significance of the deficit at high energy end relative to continuation of power law ?
- Extrapolate middle section:
- Expect 42.8 events
- Observe 15
- Poisson
- 	*p*= ~10-6
- 4 is 3 x 10-5
- 5 is 3 x 10-7

## Preliminary Stereo Spectrum

- Fit to power law.
- Single index gives poor 2
- Evidence for changing index near ~1019.8 eV

## HiRes Monocular & Prelim Stereo Spectra(Stereo Normalized to Monocular)

**HiRes Monocular & Prelim Stereo Spectra**(Stereo Normalized to Monocular)

## Comparison of HiRes, AGASA and Auger (prelim)

- Spectra

- Blue  triangles
- AGASA
- Circles - HiRes
- Mono
- Purple triangles
- Auger (prelim)

## Interpretation of the UHE Spectrum

- Interaction with the CMBR fractionates the extragalactic flux of protons by red-shift/age
- Observed structures can be attributed to this process
- Pile-up from pion-production causes the bump at 1019.5 eV.
- e+e- pair production excavates the ankle.

- see **Phys. Letters B, in press (2005) **(arXiv:astro-ph/0501317) update shown

## DIP as SIGNATURE of PROTONS INTERACTING with CMBFrom V. Berezhinskii

- 			h(E) = Jp(E)/Jpunm (E)            (3)
- 	Jp(E) is calculated with all energy losses included.
- 	Jpunm (E) - only adiabatic energy losses included.

- Dip is stable:
-  to propagation modes (rectilinear or diffusive),
-  to variation of source separation (d=1-60 Mpc),
-  to inhomogeneities in source distribution,
-  to fluctuations in interaction.

- DIP as SIGNATURE of PROTONS INTERACTING with CMBFrom V. Berezhinskii

## Transition energy Ec ≈ 1×1018 eV is a universal value, independent of propagation mode, including different diffusion regimes. 
Prediction of the shape of the dip is robust. It is practically not modified by all known phenomena:

- Prediction of the shape of the dip is robust. It is practically not modified by all known phenomena:

-  propagation modes,
-  inhomogeneities in source distribution,
-  different distances between sources,
-  fluctuations in interaction.

- This makes the dip a more reliable signature of interaction with CMB   than GZK cutoff.  From V. Berezhinskii

## Summary of Spectrum Results

**Monocular Spectrum**
- Using the latest monocular data, HiRes has observed the GZK suppression
- Ankle at ~1018.6eV** **
**Stereo Spectrum**
- Shape consistent with monocular spectrum at 2.5x AGASA statistics
- GZK suppression seen in stereo
- Studies to understand absolute normalization in progress

## HiRes Composition Measurement

**Astrophysical Journal 622 (2005) 910-926**

## Stereo Xmax Measurement

- Two simultaneous measurements of the Xmax allows for ***direct verification*** of the MC resolution

- Data

- MC

## Slide 26

## Measuring Cross-Section: De-convolution Method.

## Test of De-convolution Method

- Correct within
- fitting errors

- Deconvolution is identical for QGSJet
- and SIBYLL. (events through detector
- simulation)

- protons

## Data and Deconvolution Result

- 1348 out of 3346 stereo events pass the quality cuts (data:12/1999-3/2003)

## HiRes Measurement

**HiRes Measurement**

- HiRes:

## Monocular Anisotropy Results
Autocorrelation functions (histogram of cos  between all possible pairs) for HiRes-1 monocular (left)  and AGASA (right)  events above ~4x1019eV Astropart. Phys. 22, 139 (2004)
Search for dipole enhancement in the direction of nearby a-priori sources: null results for the Galactic Center, Centaurs A, and M87  Astropart. Phys. 21, 111 (2004) 
Point source search: null result
	Submitted to Astropart Phys.
Search for cross-correlation with AGASA doublets and triplet:
Observed overlap no greater than that expected by chance from an isotropic
	Submitted to Astropart Phys. 

***Autocorrelation functions*** (histogram of cos**  between all possible pairs) for HiRes-1 monocular (left)  and AGASA (right)  events above ~4x1019eV **Astropart. Phys. 22, 139 (2004)**
- Search for dipole enhancement in the direction of nearby a-priori sources: ***null results*** for the ***Galactic Center, Centaurs A, and M87***  **Astropart. Phys. 21, 111 (2004)**** **
- Point source search: null result
- 	**Submitted to Astropart Phys.**
- Search for cross-correlation with AGASA doublets and triplet:
- Observed overlap no greater than that expected by chance from an isotropic
**	****Submitted to Astropart Phys.**** **

**Stereo Anisotropy Results**
- Stereo angular resolution ***~0.6************ ***
- HiRes stereo data (*E > *1019  eV) is consistent with isotropy at all small angular scales                            **Astrophys. J. Lett. ****610**** (2004) L73**
- Search for Point Sources of Ultra-High Energy Cosmic Rays above 4.0 1019 eV Using a Maximum Likelihood Ratio Test_[ ](http://hires.phys.columbia.edu/papers/apj_623_2005_164.pdf)_**Astrophys. Journal 623 (2005) 164**

**HiRes Anisotropy Results**

- Stereo point spread function

## Correlation with BL Lacertae Objects

- BL Lacertae Object - special type of blazar, active galaxy with jet axis aligned with our line of sight.
- Blazars are established sources of TeV gamma-rays
- Candidates for accelerating cosmic rays to EeV energies

- Somewhat controversial recent history regarding correlations of UHECR with BL Lac objects:
- Tinyakov and Tkachev,   JETP 74 (2001) 445.
- Tinyakov and Tkachev,  Astropart. Phys. 18 (2002) 165.
- Gorbunov et al.,  ApJ 577 (2002) L93.
- Evans, Ferrer, and Sarkar, Phys.Rev. D67 (2003) 103005.
- Torres et al., Astrophys.J. 595 (2003) L13.
- Gorbunov et al.,  JETP Lett. 80 (2004) 145.
- Stern and Poutanen, ApJ 623 (2005) L33.

## Gorbunov BL Lac Correlation: New Claim

- The 0.8o angular bin size was optimized by Gorbunov et al.
- It is preferable to perform an ***unbinned**** *maximum likelihood analysis, using the individual errors of each event.
- We performed an analysis similar to that used in the point source search, modified for a multiple-source hypothesis.  We find for E > 10 EeV:
- Estimated number of source events:			ns = 8.0
-       (~ *excess* of events correlating with BL Lacs)
- Fraction *F *of isotropic MC sets with stronger signal: 	*F* = 2×10-4

## Maximum Likelihood Method for Multiple Sources

- We hypothesize that ns events come from a source, and (N-ns) come from background.  For just one source, the partial probability for the ith event is:
- Pi(ns) = nsQ(xi) + (N-ns) B(xi)
- Q(xi) is the probability that the ith event could come from the source, given the angular resolution of the event and the distance to the source.
- B(xi) is the probability that the ith event could come from background, given the HiRes acceptance to the location xi of the event in the sky.
- We let  L(ns) = Product Pi(ns),  and find the value of ns which maximizes the ratio
- R = L(ns) / L(0)
- For the present case with many sources, we adopt the following simple hypothesis: an ensemble of equal luminosity sources, where the jth source is weighted by the HiRes exposure to the source’s location:
- Q(x) = Sum (  Qj(x)  Wj / (Sum W)  )

## Confirmed BL Lacs m>18 (10th  Veron)

- Confirmed BL Lacs m>18 (10th  Veron)

##  + HiRes Events E>1019 eV

-  + HiRes Events E>1019 eV

## BL Lac Correlation: Energy Dependence

- Modify Energy Threshold:
- 1019 eV threshold is due to the fact that HiRes originally published only the arrival directions of events above this energy.
- In the event these particles are neutral, an energy cut doesn’t make sense.
- If we perform the analysis on ALL the events below 1019 eV , there is a weaker correlation: ns = 22  with ln R = 3.10.
- The fraction of isotropic MC sets with stronger signal is            *F* = 6×10-3. This is an independent data set, not used previously.
- For the combined HiRes data set (all energies), the result is:     ns = 31    ,   *F* = 2×10-4

## BL Lac Correlation: Source Sample

- Confirmed BL Lacs in the Veron Catalog are classified as “BL” or “HP” (latter for relatively high degree of polarization).
- So far, only “BL” have been considered. Not clear why.
- If we perform the analysis on the 47 “HP” BL Lacs (using the same m<18 cut as was used for “BL”) and HiRes events above 1019 eV , we find: ns = 3.0,  with *F* = 6×10-3.
- For the complete set of confirmed BL Lacs (i.e. “BL” + “HP”) with m<18, and HiRes events above 1019 eV , we find:             ns = 10.5,  with *F* = 10-5.
- We have performed all of the same tests using BL Lacs with m>18, and no correlation is found.

## TeV BL Lac Correlation

- Six BL Lacs are confirmed sources of TeV g-rays.  Five are in the northern hemisphere and well observed by HiRes.
- We perform the maximum likelihood analysis on each source individually using all HiRes events:

- For the TeV blazars taken as a set, the ML analysis yields:
- 	All energies: 	ns = 5.6  with *F* = 10-3

## Summary of BL Lac Correlation:

- “BL”, m<18, all HiRes events (no E cut): ***F *****= 2×10****-4**
- “BL+HP” with m<18, HiRes E>10 EeV: ***F *****= 10****-5**
- Confirmed TeV blazars, all HiRes events (no E cut): ***F***** = 10****-3**
**These are not independent results: the samples overlap.*****  ***
- Analysis has been *a posteriori*, so above *F* values are not true chance probabilities.
**Correlations must be tested with independent data before any claim can be made.**
- Arrival directions of past year of data have not been analyzed. Data taking through March 2006 will yield an independent data set ~70% of the current sample size: Independent test of BL Lac correlations should be possible

## BL Lac Correlation: Sensitivity of Future Data

- We estimate the sensitivity which future HiRes data will have by resampling the real HiRes events (Bootstrap resampling)
- We simulate 1, 2, 3 years of new data to estimate the distribution of possible signal strengths if the observed correlations are real.
- (Arrival directions of past year of data have not been analyzed.)

## Slide 42

## Slide 43

## Future Prospects

- HiRes will cease operation at the end of March 2006
- Analysis of major topics to be completed by summer of 2007 (30th ICRC)
- Subgroups of HiRes have joined the Telescope Array (Delta, UT, USA)
- Grond array of 576 (1.2km spacing) scintillation counters
- Three fluorescence sites looking inward
- US contribution: low-energy extension down to 1016.5 eV
- TALE will also make TA into a fully stereo-hybrid detector

## Apertures of TA nested detectors

## Slide 46

## Physics Goals of TA

- Understand the AGASA/HiRes discrepancy above 10 EeV with hybrid array
- Study the ankle region in Stereo with slowly changing aperture. 1 - 10 EeV
- Study second knee region with tower detector and infill array .03 - 1 EeV
- Study composition with same methodology from .03 to 100 EeV.
- Definitive result on BL-Lac correlations and other anisotropies.

## Updated Atmospherics

- The atmosphere over Utah appears stable and in good agreement with seasonal “Standard atmosphere” Models
- Residuals between measurements and model are typically less than ~10 mBar in the troposphere.

- Summer

- Winter

- Spring

## How much does the reconstructed shower Xmax shift using Radiosonde data (SLC) vs. using the US standard atmosphere model?

- Xmax  (gm/cm2)

## Systematic Errors

- All three experiments quote systematic errors ~ 25 gm/cm2.
- Dominant contributions
- `Mirror survey
-  Cherenkov subtraction
-  Atmospheric profile
-  Aerosol corrections

## Composition Comparison

- Fly’s Eye Stereo - Xmax resolution ~45 gm/cm2   measured resolution function
- HiRes/MIA - hybrid experiment. Resolution function estimated from simulations ~ 45 gm/cm2 .
- HiRes stereo - Xmax resolution measured, 30 gm/cm2 .

## Estimating Systematics

- Highest energy data is best measurements
- 		- most complete profile
- 		- minimum Cherenkov subtraction
- 	Energy scale for all three experiments is consistent (location of ankle and second knee).
- 	Use HiRes stereo average Xmax and Fly’s Eye stereo average Xmax above 1018 eV.
- 	Require a 13 gm/cm2 upward shift for Fly’s Eye to bring means into agreement
- 	Shift all Fly’s eye Xmax data points by the same amount.

## Slide 53

## Slide 54

## Filled circles, HiRes; Triangles,

- HiRes/MIA, Open circles, Fly’s Eye
- (shifted).

## Elongation Rate

- Simple shift of Fly’s Eye data brings all date into reasonable agreement.
- Fly’s Eye and HiRes data are in excellent agreement above 1018 eV.
- HiRes/MIA shows earlier transition to “protons”, but point by point discrepancy is small.
- HiRes/MIA systematics are better understood, however.

## What about Xmax distributions?

- Are Xmax distribution widths consistent?
- Two overlap regions
-  - Fly’s Eye and Hires/MIA in 3x1017 to 5 x 1017 eV bin.
- Fly’s Eye and HiRes stereo in > 1018  eV bin.
-     No evidence of discrepancy in distribution widths.

## Fly’s Ey vs HiRes/MIA 3-5 x 1017 eV

- Fly’s Ey vs HiRes/MIA 3-5 x 1017 eV

## Fly’s Ey vs HiRes > 1018 eV

- Fly’s Ey vs HiRes > 1018 eV

## Normalized Xmax distributions for

-  3-5 x 1017, 5-10 x 1017 and > 1018 eV.

## Conclusions

- A simple Xmax shift brings all three experiments into reasonable agreement.
- Widths of Xmax distributions are in agreement.
- Normalized Xmax distribution show jump to wider distribution above 1018, consistent with change to protons.
- Interpretation of elongation rate over limited energy range is problematic - Need large dynamic range in a single experiment!

## Systematic Uncertainty in Xmax

- Effect of pointing accuracy – 15 gm/cm2
- Effect of atmospheric variation – 10 gm/cm2
- Effect of using Std Atmosphere –10 gm/cm2
- Reconstruction bias – 5 gm/cm2
- Sum in quadrature – 21.2 gm/cm2
- 3-season model shifts published Xmax vs E results 10 gm/cm2 larger/deeper
- Will use 3-season-model in future work with composition:

## BL Lac Correlation: Previous Claims

**BL Lac Correlation: Previous Claims**

- Tinyakov & Tkachev,   JETP 74 (2001) 445.
- Tinyakov and Tkachev,  Astropart. Phys. 18 (2002) 165.
- Gorbunov et al.,  ApJ 577 (2002) L93.

## BL Lac Correlation: New Claim

**BL Lac Correlation: New Claim**

- Gorbunov et al.,  JETP Lett. 80 (2004) 145.

- Most recent claim by Gorbunov is based on published HiRes data. It uses a 10 EeV threshold, so it is a new claim.